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June 6

Jellyfish as pets.

An IP recently asked me if Jellyfish could be kept in a houshold aquarium. I told him/her basically that I didn't know for sure. I offered some in depth, but basic, guidance on how to do it, while reinforcing that I think it is a very bad idea to try. The whole reply can be seen at my talk page. After replying, I realised that while I may not have the answers, someone else might. Basically I have to questions:

• Can jellyfish be kept in a household aquarium?

• Was my reply right, wrong, or a little of both?

Thanks for any guidance on this.Drew Smith What I've done 05:58, 6 June 2009 (UTC)

Perhaps this web site can help.--Lenticel ^(talk) 06:13, 6 June 2009 (UTC)

I recently was at an event where someone was selling jellyfish kits for several hundred dollars each. I'll offer some observations from what I saw. This doesn't mean that his "kit" was actually a good idea or the optimal solution. He also seemed to be offering only one species of jelly, so these observations may not apply generally.

1. The largest tank on display was not huge, perhaps only 80 gallons and held three large jellies and basically nothing else. No scenery, no reefs, no other fish, nada. Maybe this was an open water species and preferred that; I don't know.
2. The smallest tank was perhaps 15 gallons and held one small jelly, and nothing else.
3. The "ground" in his tanks seemed to be made of rounded plastic stones roughly the size of a thumb but somewhat fatter.
4. Most of his tanks were vertically oriented, i.e. they were taller than they were wide. At the largest scale this was perhaps 3:1. All of the tanks were rounded and had no sharp corners on their vertical face.
5. All of his tanks had heavy duty aerators. Noticeably stronger than I have ever seen on aquariums of similar size. These were mostly enclosed, presumably to prevent the jelly from swimming over the air flow.
6. The type of jelly in question had very short tentacles.

I wasn't interested enough to ask about care and feeding, so I don't know anything about the water quality or nutritional requirements. I did see some sort of food packs though, so presumably they can eat things other than live/recently caught food. Hope this helps. Dragons flight (talk) 06:47, 6 June 2009 (UTC)

This helps, in that keeping jellies as pets is more common than I thought. On the other hand I have never seen a "kit" that actually keeps its intended inhabitants alive for even a fraction of its lifespan. Goldfish can live up to forty years in the wild, and seldom live more than a few months in "kits".Drew Smith What I've done 09:21, 6 June 2009 (UTC)

Physical strength requirements of Formula 1

Not sure if this is more suited to the Entertainment or Science section, so please feel free to move it

During today's qualifying for the Turkish GP a commentator stated that 10kg of weight would add 0.3 seconds per lap. Obviously that is quite a lot of time (adding about 21 seconds in a 70 lap race). This has made be wonder about the impact of keeping down a driver's weight and the trade offs that might entail. As an example, according to this page Jenson button weighs about 68kg, whereas I weigh about 95kg (I shouldn't, but I do!). At 0.3 seconds per 10kg per lap, I would, with the same driving skill, be 0.81 seconds slower per lap, or 56.7 seconds slower for a 70 lap race. So it would seem that, no matter how skillful, somebody weighing 95kg could never be successful in F1. This makes me wonder why successful F1 drivers do not tend to weigh even less. The jockey Willie Carson, seems to have weighed about 49kg, which would give him roughly a 0.6 second per lap advantage, or 42 seconds per race - presumably a woman would have even greater potential weight wise. Obviously skill is the overriding factor, but I cannot see why a woman, or a much lighter male would not be capabale of the same level of skill. So, I wonder if it is about the physical demands of F1. Is it that a degree of strength is required, that would override the weight advantage of a woman or a lighter male? I would have thought that riding a horse required greater strength than driving a Formula 1 car, and that jockeys must have a very good strength to weight ratio, but obviously there are other factors at play here, because Formula 1 is not full of drivers with the stature of jockeys. I would appreciate any thoughts on this. Thanks Chuny Beetroot (talk) 12:30, 6 June 2009 (UTC)

You do need to be very physically fit to withstand the g-forces. I'm not sure how strong jockeys need to be, but probably not as strong as a F1 driver - I can't see why they would need much strength. --Tango (talk) 13:08, 6 June 2009 (UTC)

Formula1.com says "cars must weigh at least 605kg (including the driver), but traditionally teams build the car to be considerably lighter and then use up 70 kg of ballast to bring it up to weight." So that means the weight of the driver is mostly irrelevant (all it does is given the team less ballast to move around to change the balance of the car for specific tracks). This reply (I don't know how reliable it is) claims quite a diversity in F1 driver heights (and surely weights, as the tall ones listed aren't beanpoles and the shorter ones noticeably chunky). That said, this article claims KERS promotes smaller drivers. 87.112.85.8 (talk) 13:59, 6 June 2009 (UTC)

On the official Formula 1 site the Toyota team doctor says, among other things, There is no other sport in the world which compares to the demands Formula One puts on the heart. SpinningSpark 14:07, 6 June 2009 (UTC)

Higgs boson

Might one find one or more Higgs bosons at the center of a Black Hole? ---- Taxa (talk) 12:52, 6 June 2009 (UTC)

If our theories are correct, there are Higgs bosons everywhere, they are just difficult to see. We can't say what is at the centre of a black hole, it is a singularity, which is scientist-speak for "we haven't got a clue". --Tango (talk) 13:12, 6 June 2009 (UTC)

My thinking is somewhat askew from the thinking of others. I was trained specifically to think outside the box. I have no problem, for instance, with 10/zero(0)=10. Its logical to me that when you divide by zero nothing happens. I apply the same logic to the center of a Black Hole and to a Higgs boson . It may not be possible for anyone other than myself to consider that not having a clue is not an acceptable answer unless you explain why you do not have a clue. ---- Taxa (talk) 13:42, 6 June 2009 (UTC)

I'm afraid that isn't "thinking outside the box", that is just being wrong. If 10/0=10 then we can multiply both sides by zero and get 10=10*0, but anything times zero is zero, so you have 10=0, a contradiction. Thinking which is unconventional can be a good thing, but it still has to be logically consistent. We don't have a clue about what happens at the centre of a black hole because the mathematical model we use to describe black holes breaks down at the centre and gives a result that doesn't make sense (ie. various infinite physical values, which aren't consistent with how those values are defined). Hopefully someone will come up with a theory that can explain the centre of a black hole, but they haven't yet. If you have a theory which explains black holes in terms of Higgs bosons, feel free to write it up and submit it to a peer reviewed journal, but I doubt it will be accepted because I suspect you don't actually understand what a Higgs boson is (I'm not clear on the details myself, but I fail to see any way that their presence in black holes could resolve the singularity, if they exist they will be there because they are everywhere, that doesn't help anything). --Tango (talk) 14:17, 6 June 2009 (UTC)

Not quite. The problem is that you are still thinking inside the box. You still see the division sign (/) as operational. By outside the box I no longer see the division sign as operational when a zero value is below it. What you see is that 10 is the result of an arithmetic operation. What I see is that no arithmetic can or has taken place. Its as if I were screening the values with an "if, then" statement and if the value under the division sign is zero then no arithmetical operation can take place. You see the division sign instead as an arithmetical operator that is turned on not matter what the values are because you are still thinking inside the box. You are unable to recognize that the division sign itself, its use or operation is not always valid, that there is a chink in the division sign. -- Taxa (talk) 19:23, 6 June 2009 (UTC)

If you open your mind to much... [1]. What you do by "thinking outside the box" is redefining the / sign to mean something different from what it usually means. I can just as well claim that 2+2 = 5 (by redefining "=" to mean "bigger than" and "+" to mean concatenation of the decimal representations of the arguments. --Stephan Schulz (talk) 19:36, 6 June 2009 (UTC)

Taxa, you said "Its logical to me that when you divide by zero nothing happens." so don't come now with "By outside the box I no longer see the division sign as operational when a zero value is below it." Divide by zero means divide by zero. It is by definition operational. you cannot arbitrarily redefine the meaning of words like division and call if "thinking outside of the box". That's no different than saying that instead of deviding by rezo I will replace it with my favorite color, 10/0=blue=humpty dumpty=dejavu. Even when thinking outside of the box things still must make sense, otherwise it's just plain rubish. Dauto (talk) 19:49, 6 June 2009 (UTC)

Have you observed that 2+2=5? My observation of the function of the division sign is based upon empirical evidence that the division sign is not operational dependent upon the value which is below the division sign or in other words that the division sign is turned off or no longer functional dependent entirely upon the value of the divisor. -- Taxa (talk) 19:58, 6 June 2009 (UTC)

Mathematics is not an empirical subject. You can't "observe" 2, it is an abstract concept. You can define the "/" symbol in a different way to me if you like, but don't expect anyone else to use your definition because it isn't useful. Division is useful because it obeys certain rules (like a/b=c => a=bc) that let us work with it in useful ways, if you redefine it in a way that means those rules no longer hold, then it isn't useful any more. This isn't about being open minded, it is about pragmatism. There are all kinds of mathematical objects that can be defined (infinitely many, in fact, but don't ask me which infinity), some of them are useful, so get used, most aren't useful, though, so, for the most part, get ignored (pure mathematicians play around with things that aren't necessarily useful to the real world (until a scientist comes along and finds a use for them - scientists are amazingly good at that), but they are generally useful to something, even if they are just ascetically pleasing for are useful for making mathematicians happy). --Tango (talk) 20:12, 6 June 2009 (UTC)

My great great grandfather found that he could use a simple pan to fry fish, pan for gold, keep the rain off his head. Unfortunately he learned the hard way that his pan could not stop a bullet. Thanks to empirical evidence that his most valued multipurpose tool could not serve to save his life in the capacity of armor I now know that it is a function the pan is incapable of performing and not one which I would want to try. The division sign is merely a tool and its inability to function when the divisor is equal to zero is quite enough for me to reach the conclusion the division sign is not capable of this function. -- Taxa (talk) 21:08, 6 June 2009 (UTC)

Hmmm... there are some things best not tested by direct empirical observation! I don't see the relevance of that anecdote, though... We know the division operator isn't capable of functioning when the second parameter is zero, that's why we just say you can't do that. You're saying that it can function and functions as the identity, which isn't consistent with the rest of its behaviour. --Tango (talk) 22:07, 6 June 2009 (UTC)

No you have it right now. "...the division operator isn't capable of functioning when the second parameter is zero..." What many people do not realize is that it is the function of the division sign that is the problem rather than the value of zero. -- Taxa (talk) 22:47, 6 June 2009 (UTC)

When did I have it wrong? Could you give an example of someone that doesn't realise that? I'm not sure it is appropriate to distinguish between a problem with one or the other, rather than saying it a problem with how they interact, but if you had to choose one or the other then the problem would be with division, simply because you define zero first. --Tango (talk) 23:12, 6 June 2009 (UTC)

By accepting that the function of division breaks down when zero is the divisor then you can accept 10/0=10. If you insist that the function of division does not break down then you will argue that 10 divided by zero can not equal 10 because 10 times zero does not equal 10. -- Taxa (talk) 23:31, 6 June 2009 (UTC)

When you accept that you can't use the regular definition of division to handle division by zero you have a choice. You can leave it undefined, or you can arbitrarily define it to equal something. Either gives you a valid mathematical function, but the former turns out to be more useful. You can define 10/0=10 if you want to, but there is just no reason to do so. It doesn't help you in solving any problems, which is what maths is all about. --Tango (talk) 01:04, 7 June 2009 (UTC)

When I am writing a workaround to deal with some practical division by zero problem in C, I find that MAX_INT (or something similar, the largest allowable value) is more commonly a useful answer than "nothing happens". Sometimes MAX_INT but keeping the sign of the number being divided. Sometimes applying a sign to the number from some other variable. Other times "nothing happens" might suit me, or zero. So if you're going to argue from practicality, there isn't a definite answer to be found there either. 81.131.14.50 (talk) 00:53, 7 June 2009 (UTC)

Taxa, I think that rather than thinking outside a box, you may be still trapped inside one. When we learn mathematics, it is usually as an "operation" - an action. You start with two apples, you add three apples, and the result is five apples. That's the thought process you're applying when you state 10/0 = 10. "You start with 10, you divide by 0, which doesn't change anything, so you're left with what you started with, which is 10." When you really get into mathematics, however, you need to break out of this action-oriented box, and view mathematics as relationships, rather than actions. It's no longer "10 divided by 5 is 2", but also "5, when divided into 10 is 2", and "2 is related to 10 by the division with 5". It's this relationship view which fuels Tango's assertion that 10/0 = 10 implies 10 = 10*0. The relationship of 10, 5, and 2 in "10/5 = 2" is the same as the relationship of 10, 5 and 2 in "10 = 2*5", because of the relationship between division and multiplication. You could break that relationship, but then it's no longer multiplication and division, and furthermore, as Dauto mentions, you could just as easily say that "10/0 = blue" or "10/0 = a cup of weak tea" as "10/0 = 10", because the power, nay, the whole point of division as a concept is its relationship to multiplication and other mathematical constructs. Part of that relationship is that "X/Y = Z" implies that "X = Z*Y". You certainly are free to come up with a mathematical operation where "10 op 5 = 2" and "10 op 0 = 10". It wouldn't be division, though. (Mathematicians make up new mathematical operations all the time, though they usually call them functions. And again, although functions are usually taught as actions, they're more appropriately viewed as a relationship, as a mapping of a set of numbers onto another set of numbers.) -- 128.104.112.106 (talk) 00:27, 7 June 2009 (UTC)

I don't think using the apple analogy is fair when dividing by zero, as even dividing by fractions is counter-intuitive (10 apples divided by 0.5 people leads to 20 apples each). However, I would like to ask how this would apply to molecules, i.e. with the law of mass action, specifically chemical equilibria? For example, let's say we have HCl + H₂O → H₃O⁺ + Cl^-, the HCl has fully dissociated (in this case there is one of each molecule, not one mole of each molecule). Thus the acid dissociation constant would be: K_A = [H₃O⁺][Cl^-]⁄[H₂O][HCl], which leads to 1*1 / 0*0. How is this solved? (Sorry if this is too off-topic and should be a new thread). --Mark PEA (talk) 16:46, 7 June 2009 (UTC)

The raction can temporarily reverse itself. [H₂O] and [HCl] should be seen as the (non-zero) probabilities that at any given time there will be a H₂O and/or a HCl present. Dauto (talk) 22:37, 7 June 2009 (UTC)

Okay so I should have stated that I'm assuming that after the reaction, the two products will never collide again (I tried to state it by saying there was only one of each molecule). I guess you will argue that on the reactants side there was only two molecules, so if they are capable of colliding why not the products, let's assume there is something surrounding the molecules which will attract their charge (effectively "solvate" but in a heterogeneous situation, maybe some complex situation à la Maxwell's demon). Anyway 128.104's response below answers my question. --Mark PEA (talk) 23:09, 7 June 2009 (UTC)

I used the operation on apples not to show intuitiveness, but to demonstrate how mathematics is usually taught. Your example of 10/0.5 = 20 uses the same "action oriented" viewpoint, illogical as the situation may be. "You start with 10 apples, divide them between 0.5 people, which results in 20 apples per person." The illogicality only points further to the fact that division has a broader life as a relational statement, rather than a procedural one. It's illogical because "dividing between 0.5 people" makes no physical sense. On the other hand, with division as a relationship, sense is restored "if there are 10 apples for every 0.5 people, then there is 20 apples for every 1 person." For your second point, you can only calculate equilibrium constants if the system is in equilibrium - you can't say that one hydronium and one chloride ion are "in equilibrium" with HCl and water. This is a similar situation to the original question! The fact that you are dividing by zero indicates that you've extended the mathematical models further than they are valid. If you just have two molecules, you can't derive an equilibrium constant, because it is not in equilibrium. Likewise, we can't say what happens at the singularity in the middle of a black hole, because our current models all break down. On the other hand, if we're happy saying (1*1)/(0*0) = 1, then we get a K_A = 1 for HCl, which will result in no end of trouble when you're back to dealing with liter solutions of HCl, as the true value is closer to 10 ^-7. -- 128.104.112.106 (talk) 22:31, 7 June 2009 (UTC)

Yes, sorry, my question really was... If we discover an acid that fully dissociates, what is its K_A value? (because you can't divide by zero) I guess you just don't give it one, or I am effectively asking what the K_A of a proton is. I completely agree on your final point that 1/0 doesn't = 1, or any x/0=x, it was the reason why I brought up equilibrium constants. --Mark PEA (talk) 23:09, 7 June 2009 (UTC)

I think you (Tango) must have meant gravitational singularity but you linked to the dab page by mistake. As a mathematician, do you also think that mathematicians speaking of a mathematical singularity is also to be interpreted as "haven't got a clue"? SpinningSpark 13:57, 6 June 2009 (UTC)

Not by mistake, just by laziness! In mathematics, singularities are well defined places where something goes wrong and are well understood. In physics, a singularity is somewhere where our mathematical model indicates there is a mathematical singularity, which generally means our model is flawed. --Tango (talk) 14:17, 6 June 2009 (UTC)

The mathspeak for "haven't a clue" is indeterminate. Dmcq (talk) 14:36, 6 June 2009 (UTC)

Not really, an indeterminate isn't something we don't know the value of, it's something that doesn't have a well defined value. I think "conjecture" would be the closest mathematicians have (basically it means "guess"). --Tango (talk) 15:07, 6 June 2009 (UTC)

See also independence (mathematical logic). A conjecture at least might be provable from existing axioms if someone clever enough comes along. Something independent can't be proved without new axioms. The continuum hypothesis was a conjecture for a long time, but proved independent in the 1960's, putting it closer to "haven't a clue" (or maybe "meaningless") territory. 67.122.209.126 (talk) 18:12, 6 June 2009 (UTC)

Something which has been proven independent of an axiom system isn't something we don't know about. We know everything there is know, the result is just neither "true" or "false". I think conjecture is the better analogy. Conjectures could, in time, but proven or disproven (or proven independent), just as gaps in scientific theories could, in time, be filled. --Tango (talk) 18:29, 6 June 2009 (UTC)

I was thinking of imdeterminate as in indeterminate form. the limit of x/sin(x) as x goes to zero gives the indeterminate form 0/0. In this case one can find the value 1 by other means but anything is possible. But yes conjecture is very good. And independent and undecidable and uncomputable and incomplete too... I think maths is well on the way in developing a theory of types of "haven't the foggiest". Soon we'll have terms like meta-controversial for instance and know exactly what they mean. :) Dmcq (talk) 20:12, 6 June 2009 (UTC)

0/0 is indeterminate, which doesn't mean we don't know what it equals, it means it doesn't equal anything. $\lim _{x\to 0}{\frac {x}{\sin(x)}}$ isn't indeterminate, it is simply "1". If you solve it and get an indeterminate form as the answer that just means you've done it wrong and need to find a method which actually works. --Tango (talk) 20:16, 6 June 2009 (UTC)

Pssst, you mean as it goes to 0. Dragons flight (talk) 20:52, 6 June 2009 (UTC)

I was just testing to see if you were paying attention! (Fixed now.) --Tango (talk) 21:08, 6 June 2009 (UTC)

Hi there, I plugged $x/sin(x)$ into Wolfram|Alpha and got a nice graphical result. So 0/0 sorta converges to 1 with that equation but it doesn't equal 1. How weird. ~~ Ropata (talk) 07:18, 11 June 2009 (UTC)

Electrical arc

Is an Electric arc related to electrical ionisation as described here [2]. Thank you. Clover345 (talk) 17:16, 6 June 2009 (UTC)

Yes. --Dr Dima (talk) 21:17, 6 June 2009 (UTC)

Unknown garden plants for identification

Can anyone help me identify these please, all found in an english garden? This rather elegant garden plant http://i599.photobucket.com/albums/tt74/liverpoollarry/unknownplant1.jpg also had a more or less flat group of flowers above the frame. Photo taken a few weeks ago.

The small plant above the ruler in this scan http://i599.photobucket.com/albums/tt74/liverpoollarry/unknownplants2.jpg is part of a rockery-type plant, probably perennial, that I saw growing in low spreading mats with numerous flowers, and also growing out of cracks in the side of walls. When fresh the ends of the petals on the flower bend out more. It may be a Camanula or Bellflower, but they differ considerably in appearance and I want to try to identify its species or variety.

The plant beneath the ruler may be just a weed - but lots of them have suddenly appeared grouped together. Thanks. 84.13.50.195 (talk) 18:32, 6 June 2009 (UTC)

The first plant is an Aquilegia. --TammyMoet (talk) 19:38, 6 June 2009 (UTC)

The second plants: Campanula is latin for Bellflower. I'd say it's one of the Campanula family. The plant below the ruler is one of the Vetches, hard to say which - could be a Black Medick or a Hop Trefoil. It's a weed! --TammyMoet (talk) 19:43, 6 June 2009 (UTC)

Thanks. After searching around some more I think the middle one is probably Campanula portenschlagiana, variety Hoffman’s Blue, common name Dalmation bellflower. The final one seems to be, as you say, Hop Trefoil, Trifolium campestre. Edit: now I think the middle one is more likely to be Campanula muralis. The c. port... seems to be a much bigger plant - difficult to tell the size in photos. 78.149.117.117 (talk) 20:06, 6 June 2009 (UTC)

what kinds of companies use corporate astrologers?

Googling "corporate astrologer" (in quotes) shows some 22,000 results. So my question is about what kinds of companies use these servicse? Do any very large companies (market cap in the billions) use services like this? 94.27.141.190 (talk) 18:50, 6 June 2009 (UTC)

If they do, I doubt they would admit to it! --Tango (talk) 18:59, 6 June 2009 (UTC)

While only superficially comparable with astrology the article on Feng_shui cites sources that mention Donald Trump, Walt Disney, Singapore Polytechnic and the New York College of Health Professions inter alia as taking the subject seriously. Cuddlyable3 (talk) 19:06, 6 June 2009 (UTC)

Feng shui — as a decorating style — will generally produce an appealing aesthetic though, so even if you don't care for the mystical underpinnings, you might still choose to consult a feng shui designer. Dragons flight (talk) 19:59, 6 June 2009 (UTC)

I'm kind of skeptical about this, if only because if you ask ten feng shui "experts", you're likely to get ten different aesthetics. (Bullshit!, as I recall, demonstrated this rather well.) I'd say the appeal of the final aesthetic depends more on the decoration sense of the individuals in question than the principles of feng shui. -- Captain Disdain (talk) 07:34, 7 June 2009 (UTC)

This is more trivia than an answer to this question, but I'm sure I read somewhere about Microsoft and Apple competing in who had "the best" corporate astrologer. Tbh I think its no more than a psycological effect, but no one asked for my opinion.Alaphent (talk) 19:50, 6 June 2009 (UTC)

Microsoft and Apple! Couldn't have asked for a better response. Cite, please! 94.27.141.190 (talk) 19:52, 6 June 2009 (UTC)

Like I say, trivia only. It was read in on an online economics magazine, I've forgotten which, but it may have even been tongue in cheek. Sorry.... Alaphent (talk) 20:53, 6 June 2009 (UTC)

My guess is that only companies that sell horoscopes, or have some motive for promoting astrology, would pay for astrology services, since there's no credible scientific basis for the "predictive" results generated. Perhaps it's useful public relations in some segments, but that's marketing and not Science. --Scray (talk) 20:58, 6 June 2009 (UTC)

It is always good to cite sources on the refdesk. The above answer thinks too highly of people using logic, as can be illustrated by feng shui and Nancy Reagan#Influence in the White House. I have no sources to cite on corporate astrologers, but I am not going to sit and speculate on the refdesk that corporations make decisions based on "Science". Tempshill (talk) 23:44, 6 June 2009 (UTC)

There's also a huge gap between corporate decisions and individual decisions made by people on corporate boards. It's possible that someone is able to make his/her way into a position of power and decision-making - such as a CEO or president - and once there, make decisions based on astrology or coin-toss or any other technique. However, I suspect that such decisions would be worse than informed, scientific decisions, and would thus yield in undesired results. The corporation would quickly decide to remove such an individual, who is free to believe what they want as long as they don't do it with shareholders' money. Nimur (talk) 04:46, 7 June 2009 (UTC)

I notice that all the corporate astrologers on the first page are based in India. This seems excessive, even considering the possibility that India is renowned in corporate circles the world over for producing the best astrologers. So perhaps the answer is Indian ones. 81.131.14.50 (talk) 00:03, 7 June 2009 (UTC)

I'm from India, and yes, you'll stumble upon an astrologer here whenever you trip. But most of these men like to advertise themselves as corporate astrologers. True, no company is started here without a bhoomi pooja under some astrologers and swamis, and yes, there are a couple of high profile people who give their ""expert guidance" to companies for large sums, but nevertheless, you don't see many companies recruiting astrologers for their services. Say if they're going to start a new business, they might consult a family astrologer, or when they are about to open a new building, they might ask when is the "good time". But i'm very doubtful about corporate astrologers. Rkr1991 (talk) 04:02, 7 June 2009 (UTC)

The Mouse vs. Elephant Effect

I was watching a nature show, and a cheetah cub—the fearsome little devil—made a playful charge at a herd of wildebeest—which resulted in all of these 300+ pound animals fitted with horns making a run for it. I see this kind of embarrassing herd behavior all the time on nature shows. Obviously in some instances herd behavior has evolutionary advantages. But, when legions of gargantuan animals flee from some dogs—is this an example of a maladaptive behavior resulting from individuals evolving at the cost of the herd? i.e. it seems like it would make more sense for the prey to band together and confront the outmatched predator.

Alfonse Stompanato (talk) 21:54, 6 June 2009 (UTC)

Running away is generally the best way to avoid coming off worse in a fight. Is there any real disadvantage to running away? --Tango (talk) 22:03, 6 June 2009 (UTC)

Yes, there is, but it's a small disadvantage really. You can't feed when you are running away, and you spend some energy on running away, too. You are right, it is still much better than to risk injury or death. That is actually the reason why mammalian sensory system is "tuned" to make much more False Positives than False Negatives on identification of predators or of threats in general. If you make a False Positive, you stop grazing for five minutes, and then resume. If you make a False Negative, your brain stem is in someone else's stomach. --Dr Dima (talk) 22:36, 6 June 2009 (UTC)

But wouldn't a cooperative defense be so effective as to both conserve energy and prevent one of the herd from being picked off? The herd runs—and the young ones get taken out. I have actually seen some footage of aggressive behavior coming from water buffalo—they encircled their young, stood their ground, and actually gored some lion cubs that the pride hid in the tall grass (the herd stumbled upon the pride in this case). But, I guess my problem is that flight seems over represented in situations where the prey is greater than the predator in both size and number. Alfonse Stompanato (talk) 01:01, 7 June 2009 (UTC)

Yes Alfonse, you are right. Cooperation works better than "every one save yourself", but cooperation requires coordenated actions which require comunication. That's alot to ask from volution. Meanwhile the one wilderbeast that thinks twice before running is the one that ends up eaten. Just because a behaviour is more eficient doesn't mean that evolution will find its way there. Nevertheless some species do evolve cooperation as a defense. Dauto (talk) 03:36, 7 June 2009 (UTC)

It is faster to run, without thinking, than to take the time necessary to evaluate the situation, and perhaps conclude that flight is not necessary. There also may be advantages to running, such as exercise, and being physically prepared for the next time -- when flight may actually be very necessary. Also, the animals fleeing may be doing more than meets the eye. It may be akin to a training exercise, in which they practice their scattering techniques, and develop group dynamics that will be protective of the youngest or even the weakest. Bus stop (talk) 03:47, 7 June 2009 (UTC)

I'm pretty sure cheetahs raise their young as with most mammals. I'm guessing then if there was a cheetah cub, there would normally be cheetah parent/s close by. I don't know the details of what you were watching, perhaps the cheetah cub was being raised by humans or whatever but clearly it's unresonable to expect wildebeast to be able to appreciate such differences when such a thing is extremely abnormal. In other words, while it may seem odd for wildebeast to run away from a cheetah cub because of the risks from the cub, running away from a cheetah cub because cheetah cub usually means cheetah parent/s are close by makes far more sense Nil Einne (talk) 07:24, 7 June 2009 (UTC)

The cheetah can outrun the wildebeest but must select a young or ill animal for attack and is quickly exhausted. The defensive strategy of the wildebeest includes stampeding as a herd. This puts a predator in danger of being trampled and keeps young animals inaccessible, and it is a well adapted behaviour. It makes better sense than banding together against predator(s) that could then gather and harry the herd indefinitely. What the OP calls a playful charge by a cheetah cub is a serious activity by which it learns how to get close to a herd and how the herd reacts when spooked. A cub is likely to get closer to the herd than an adult so the alarm to the herd is correspondingly greater. BTW Mice do not prey on elephants and a mouse vs. elephant effect is unsourced. Cuddlyable3 (talk) 09:17, 7 June 2009 (UTC)

It's a matter of evolution: Suppose you are one of the Wildebeast - and suppose that the herd's instinctive strategy is to stand their ground and try to defeat the cheetah. By standing your ground - you run a small risk that the cheetah will kill you before the rest of the herd manage to bring it down. So a slightly better strategy for you, personally - would be to run away while the rest of the herd deals with the cheetah. This produces a small evolutionary benefit for those who possess the "run away" gene. Over hundreds or thousands of generations, evolution would ensure that sooner or later, the gene for the instinct to stand-your-ground would be out-evolved by the gene for running-away. Hence, Wildebeast evolve to run away. More notably, consider the opposite position: Suppose the whole herd has the gene for running-away (as real Wildebeast do)...what happens to the individual who gets the mutated "stand-your-ground" gene? Sadly, he dies the very first time a cheetah feels hungry. There is no way for that gene to get passed on. SteveBaker (talk) 01:26, 8 June 2009 (UTC)

See African Buffalo for an example of an animal that (sometimes) doesn't run. They aren't built for speed as wildebeest are. You can now argue whether wildebeest evolved to outrun cheetah or whether they survived because they could outrun them. Animals that flee from predators in a herd or flock have a higher survival rate than those that don't all act together, because most predators track motion and when there's too much going on they can get confused and become unable to track one individual. (Imagine you're in a crowd of waiters carrying trays of food and just when you've made up your mind to try some chocolate cake there's a juicy steak coming past. :-) Deciding "why" in animal behavior can usually be argued with some clever reason, but the likelihood of that being the actual cause is rather dubious. 71.236.26.74 (talk) 14:27, 8 June 2009 (UTC)

what would convince you of my ability to remote view?

I'm reading this article on "remote viewing" and I just wonder based on it why research universities the world over didn't either refute or verify the "paranormal" effect beyond a shadow of a doubt as soon as they learned Stanford was doing it? It is so easy to verify, isn't it? I mean, what would convince you of my ability to remote view? Isn't it enough if we pick a dictionary of ten thousand objects that are easy to draw (different colors, etc, to bring it up to 10k), you roll some dice and draw the one that comes up, while I tune into what you're drawing from thousands of miles away? I should get it right one time in ten thousand, getting it right 20% of the time should cinch the thing, shouldn't it? If not, what would convince you of my ability to remote view? —Preceding unsigned comment added by 94.27.141.190 (talk) 22:54, 6 June 2009 (UTC)

"Research universities" typically have serious research to do. But the James Randi Educational Foundation has debunked claims of PSI powers for ages - in fact, they will pay you ONE MILLION DOLLAR if you can prove, under reasonable experimental conditions, that you have any kind of paranormal abilities. --Stephan Schulz (talk) 23:06, 6 June 2009 (UTC)

Stanford is a very serious research University! My quesiton is why don't Princeton, Harvard, Yale, MIT, Columbia, and Brown -- the other research Universities of the same calibre...there aren't that many of them! -- try to either definitively verify or refute the claims?

Sometimes they do. There isn't much point, though. The people making the claims never accept the results and people that would accept the results don't believe the claims in the first place. Unless there is some evidence to support the claims, there is no reason to refute them - you can't spend limited research funding refuting every random thing somebody claims. There have been studies done on various types of ESP, etc., and the results have always been the same. There is no reason to suspect the results of a new study would be any different and there are better things to spend the time and money on. --

Tango (talk) 01:12, 7 June 2009 (UTC) The onus is on the OP to define in advance what remote viewing ability s/he claims to have. After that we would need to agree on a test that A) the parties are willing and able (practically and economically) to carry out, B) can give a result with high statistical confidence and C) includes precautions to eliminate unintended influences. "Beyond a shadow of a doubt" is a subjective not an objective measure, and it may reflect ignorance as readily as evidence. If I roll ordinary 6-sided dice the OP should be able to guess the result 16-2/3% of the time. Getting that right 20% of the time doesn't cinch anything. Cuddlyable3 (talk) 08:36, 7 June 2009 (UTC)

What am I currently consuming? I'll give you a hint: it's not a crustacean. -- Consumed Crustacean (talk) 23:11, 6 June 2009 (UTC)

Very funny. I'm no medium. 94.27.141.190 (talk) 23:54, 6 June 2009 (UTC)

By the way if I told you "a starbucks coffee" with lots of whipped cream and chocolate shavings and other assorted crap, and it turned out to be wrong, that would not be very good evidence that against "remote viewing". I want to know why research universities don't refute or verify the claims of Stanford (isn't it an ivy leage school?) in a scientifically conclusive way? —Preceding unsigned comment added by 94.27.141.190 (talk) 23:57, 6 June 2009 (UTC)

Actually, we're quite proud of the fact that Stanford is NOT an Ivy League school. We're a bunch of west-coast types - we're much too scruffy to fit in at a place like Harvard. (I have personally been told that I was not permitted to enter the Harvard library!) Though we don't have four hundred years of legacy, our fine institution is perfectly content to have a particle accelerator, a functioning radar telescope, and a Republican Think Tank six blocks away from an enchanted broccoli forest commune. Take that, east-coast intellectual types! And yes, it is very important to point out that our sister institution, SRI International, was responsible for the research into parapsychology; this research took place after the two institutions diverged. Nimur (talk) 01:11, 7 June 2009 (UTC)

The assertion that it hasn't been refuted is most likely wrong. This kind of crap has been proven to be exactly that over and over again, and yet people either come up with excuses that conveniently explain why it didn't work or simply ignore it. I mean, take homeopathy, for example -- there's no shortage of research that clearly shows it doesn't work, but that doesn't keep people from insisting that it does. The problem here is that people who want to believe in this kind of stuff really aren't swayed by reasonable arguments or scientific proof. One reason why universities don't waste time on researching this stuff is that there's no reason to assume it works, and plenty of evidence to indicate that it doesn't. If a really, really convincing remote viewer suddenly popped up, I'm sure that would be a different story. As it is, though, most scientists prefer to work on things that aren't completely ridiculous. (Or which, at least, are of interest to them, which may not be the same thing...) -- Captain Disdain (talk) 00:23, 7 June 2009 (UTC)

Stanford Research Institute is not Stanford University It is an independent research group. As for the 1970's work on ESP, methodological failures can produce amazing results. There is a long and well documented history of poor methodology at various labs producing amazing ESP results. The article SRI International says "A lengthy exchange ensued, with the external researchers finally concluding that the failure of Puthoff and Targ to address their concerns meant that the claim of remote viewing "can no longer be regarded as falling within the scientific domain." Edison (talk) 01:02, 7 June 2009 (UTC)

Stargate Project appears to have some related information, too. Tempshill (talk) 01:04, 7 June 2009 (UTC)

Edison is right on on this. SRI is a well-known case of physicists being hood-winked, and is not really part of Stanford University. Randi got involved with SRI started appering to be taken in by people like Uri Geller if I recall. --98.217.14.211 (talk) 02:21, 7 June 2009 (UTC)

Here is their paper, Information transmission under conditions of sensory shielding, published in the journal Nature in 1974. Nimur (talk) 03:43, 7 June 2009 (UTC)

I can recall a story in Snake Oil Science about the SRI. The anecdote was something about how the fellow in charge of some line of research (on remote viewing IIRC) presented that he had higher-than-chance results. When pressed, he admitted that there were some trials that didn't have that result, but because the people involved must have been intentionally screwing up the test, he stashed the data away and didn't count it. -- Consumed Crustacean (talk) 04:28, 7 June 2009 (UTC)

In direct response to the original question, "what would convince...", I think the starting point is to define remote viewing. In the paper I linked above, it was not really clear what "counted" as a successful remote viewing. For example, although I'm located in California, I can close my eyes and visualize a major landmark, say Eiffel Tower, in my mind. I can describe a lot of things about it. Because I'm pretty good with time-zones, I can guess the time of day, and because I check the international weather forecasts reasonably often, I can even tell you what kind of day it is in Paris. Have I "remotely viewed" anything? What level of correct information is necessary to count as a remote view? What level of incorrect information is necessary to throw out the "viewing" as unsuccessful? What information is necessarily provided or withheld? If you can develop a systematic framework for these questions, then you can run a double-blind experiment to test whether or not you have satisfied those criteria. What is fundamentally the limiting case is that you will not succeed at any such experiment if the criteria are sufficiently well defined. That is why the 1974 Uri Gellar research is discredited. The experimenters jumped right in and started counting P-norms, decibels of EEG attenuation, and so forth - without even defining what counted as a successful "view"! They did go to great lengths to preclude the possibility of Mr. Gellar knowing what the drawing should have been. But they forgot to define a valid judging criteria for the post-experiment comparison. So, they ended up with a bunch of line drawings, and they had some that really do look stunningly similar to the "target" image - but they never really stated "how similar" is an acceptable drawing. Even worse are the "descriptions of remote places" trials. In these experiments, the subject describes a remote place. Later, judges decide if the description matched the remote place. But the judgement criteria is not spelled out in gory scientific detail. If these details were present and explained in the experimental setup, the experiments would be repeatable and could be subject to scientific testing. As they stand right now, the experiments are subjective and not scientific. Nimur (talk) 05:41, 7 June 2009 (UTC)

The onus is on the OP to define in advance what remote viewing ability s/he claims to have. After that we would need to agree on a test that A) the parties are willing and able (practically and economically) to carry out, B) can give a result with high statistical confidence and C) includes precautions to eliminate unintended influences. "Beyond a shadow of a doubt" is a subjective not an objective measure of confidence, and it may reflect ignorance as readily as evidence. If I roll ordinary 6-sided dice the OP should be able to guess the result 16-2/3% of the time. Getting that right 20% of the time doesn't cinch anything. Cuddlyable3 (talk) 08:36, 7 June 2009 (UTC)

There are several things that have to be nailed down - but I think the OP's original statement would work pretty well. We have two identical books of (say) one hundred very diverse pictures, which are numbered - we agree that someone a suitable distance away uses a random number generator to pick a picture from the book and at 12 noon, GMT concentrates on it or stares at it or whatever the remote viewer claims is necessary. Meanwhile, the viewer has been kept alone in a windowless room with a clock from before the time that the random numbers were generated until they asserts that they have 'picked up the image', sketched what they saw and (since interpretation of that image is iffy) - we'll stipulate that the viewer must then look through their copy of the book and nominate between one and three photos that match what they saw. Once they have listed between one and three numbers, these will be communicated to the experimenters and that round of the experiment is over. The experiment will be repeated ten times. The results are then assessed with standard statistical tools to determine the probability of this happening by chance - and only if the result is that there is a less than 0.1% percent chance of this happening by chance alone do we give this effect any credance. I'm pretty sure that if someone were to agree to terms like this then the Randi institute folks would be happy to test that person and award them a million dollars for passing the test. SteveBaker (talk) 17:40, 7 June 2009 (UTC)

Incidentally, that would require them to get at least 4 out of 10 correct (assuming I can do basic probability, which is a big assumption... it took me two attempts!). --Tango (talk) 18:26, 7 June 2009 (UTC)

Actually, I'm not much of a statistician, but I'm not sure one set of 10 would be enough (unless they are claiming 100% reliability, which they rarely do, they just claim to be better than random chance). I think you need to do several sets of 10 and then do some fancy statistical analysis. Do we have a statistician in the room? --Tango (talk) 18:30, 7 June 2009 (UTC)

Imagine if Maxwell's Equations only worked "better than random chance." You'd pick up your mobile telephone, and 3 out of 10 times, its batteries would undergo the statistical thermodynamic processes necessary for chemically induced voltage. Electrons would statistically drift down the conductors with a 1 in 5 outcome; and they would flow into a transistor amplifier and 1 out of 6 times, amplification would occur... more electrons would flow into an antenna and induce an electromagnetic perturbation on the surrounding air... depending on convection patterns, the air near the antenna would perturb the dielectric constant 1 in 2 times, allowing effective coupling between the antenna and the radio channel... oh wait, these things are already statistical. Using statistics is perfectly fine to describe physical laws, if there is a physical law to describe. We're able to build machines and cope with statistical chances because when we scale up the size, the law of large numbers kicks in and we have a nearly deterministic system. Scientists are perfectly happy to use statistics, but we don't like making crap up. That's why we don't believe in psychokinesis or remote viewing. Nimur (talk) 19:09, 7 June 2009 (UTC)

It's perfectly legit to be impressed by a result that's consistently "better than random chance". Even if Remote Viewing does not work with 100% reliability (there are human factors involved.), or even if it doesn't work by the same mechanism that its proponents put forth (Extraordinarily likely, even if RV is real!) it would still be an exciting discovery, well worth The Amazing Randi's million bucks.

If I could predict lotto numbers "better than random chance" the Lottery Commission would absolutely be interested in finding out how I was doing it, they wouldn't wait until I'd revised my method to 100% reliability. APL (talk) 16:27, 9 June 2009 (UTC)

I agree with APL and indeed I would be disturbed if any scientist completely ignored something that was statiscally shown to be not due to random chance simply because the result wasn't impressive enough. Generally speaking, in most science anything which is not due to random chance is usually considered worthy of further analysis (i.e. it is often the null hypothesis that a difference is simply due to random chance and it is only when it is not that the result is worth further investigation). I'm pretty sure that the JREF for example only requires someone to be able to do something good enough that it is not due to random chance. And I suspect many sceptics likewise. Of course, it's not possible to prove something wasn't due to random chance, you can just say it is highly unlikely so if the difference is minor, the result may be mostly ignored for reasons of timing, funding etc (and for something like the JREF they'd likely need many trials before they're convinced you are really capable of predicting something better then random chance if the percentage is small to avoid the risk you just got luck) but it doesn't mean the result isn't of potential significance. A good real example of course is with drugs. No drug testing agency I know of requires a drug to be 100% effective. Nor does any company not release a drug simply because it is not 100% effective. The primary thing they require/expect is that the drug must be better then a no drug or perhaps an existing drug. And indeed many patients are perfectly happy with drugs that are not even close to 100% effective when the alternative is worse. (Of course this depends on the condition and side effects, a drug which reduces chance of pregnancy by 10% and has serious common side effects like death will be of little interest, a drug which reduces chance of cancer metasasing by 10% and has few side effects is likely to be of great interest.) Nil Einne (talk) 19:50, 9 June 2009 (UTC)

1 in 2 times allowing effective coupling between the antenna and the radio channel...:: You just described AT&T cell service! —Preceding unsigned comment added by 94.27.225.206 (talk) 20:48, 7 June 2009 (UTC)

June 7

bound photons

Spontaneous emission of bound photons from relativistic free electrons. What is a "bound photon"? Please provide an answer that can be understood by a biologist. --JWSchmidt (talk) 01:57, 7 June 2009 (UTC)

From a really quick glance at the referenced paper it looks like the "bound photon" is a photon in one of the cavity modes, that is, a photon emitted in a discrete rather than a continuous spectrum. Cavity modes must obey the boundary conditions imposed by the cavity walls, and therefore may not, generally speaking, have just any wavelength (and any energy), but only one of the discrete -- but infinite -- list of allowed wavelengths (and thus allowed energies). Generally, a particle is said to be bound when it cannot escape to infinity in any direction. An energy spectrum of such particle is discrete, at least as long as the potential it is bound in is not changing too fast or the lifetime of the particle is not too short. --Dr Dima (talk) 02:25, 7 June 2009 (UTC)

Thanks. Cavity quantum electrodynamics talks about cavity photons functioning as part of a quantum computer. Would such photons be "bound photons"? --JWSchmidt (talk) 02:45, 7 June 2009 (UTC)

Yes, I think they would be. --Dr Dima (talk) 03:56, 8 June 2009 (UTC)

Many-worlds Question

Is it possible that beings from another universe can come into ours and interact with us? Or if quantum immortality is true, then won't a person visit us, or has already visited us (even me personally)? —Preceding unsigned comment added by 66.66.149.43 (talk) 04:41, 7 June 2009 (UTC)

No. Nimur (talk) 05:00, 7 June 2009 (UTC)

There is nothing in physics which would prevent this from happening, because what you are describing is beyond the purview of physics (which only deals with our universe, even if other universes exist). It is on the same level as asking "is it possible that God exists?" Of course it's possible, but physics has nothing to say on the matter.-RunningOnBrains^{(talk page)} 05:07, 7 June 2009 (UTC)

Mind me asking what the heck is quntum imortality? Dauto (talk) 06:19, 7 June 2009 (UTC)

Why not read our article Quantum immortality? Nil Einne (talk) 08:36, 7 June 2009 (UTC)

"Quantum immortality" is an incorrect and backwards reading of the anthropic principle. Its premise is something like this - "if a being is conscious, then all previous incidents which might have rendered it no longer conscious did not occur." For some reason, which is the really illogical part, it then concludes, "no future event will occur that will render this being unconscious (dead)." Somehow, this is linked into the idea of a quantum non-deterministic universe, by way of superposition of all possible outcomes of every possible event - and self-selection (by anthropic principle) of only those events which maintain the being as conscious (living). This doesn't really have anything to do with "quantum" anything. I'm not even really sure why this theory gets propagated - it's sort of a half-baked, nonsensical idea. But, like perpetual motion, immortality seems to spark some kind of fury in non-scientists, who hope to cherry-pick the parts of science that will somehow support their wishful thinking. Nimur (talk) 14:41, 7 June 2009 (UTC)

I think you are the one misreading it. The theory is more like: If the "many worlds" interpretation of quantum mechanics is true - then every quantum-mechanical event that can turn out in more than one way results in multiple universes in each of which the event happens differently. Since all events are ultimately quantum mechanical in nature - there is a universe in which you personally died because you were killed in a car wreck that you narrowly avoided in this universe. There is another in which you died due to a childhood disease. There are in fact an infinite number of universes in which every possible fate that could befall you has indeed befallen you.

Now - marry that (highly theoretical, and possibly dubious) hypothesis with the "anthropic principle". The 'strong' anthropic principle says that the universe is conducive to your existance BECAUSE if it was not, you would not be here to observe it. So, (for instance) it has been remarked that if the earth did not have a large moon - or if the charge on the electron differed by 1% or if water didn't expand a little as it froze - then life on Earth would be impossible. Why are we so amazingly lucky in all these respects? Well, the anthropic principle points out that in all existances in which there is intelligent life that is able to observe these conditions - the conditions must be conducive to that life.

OK - so put the many worlds and anthropic principles together - and you say that since (by definition) the only universes in this infinite number of universes in which you are able to note that you are still alive are the ones where you happened (by sheer chance) to have had all of the prior quantum events come out in favor of you living. Taken to an extreme - you cannot die because there will always be a universe in which by an AMAZING sequence of lucky breaks and one in a quadrillion chances - you happen to survive. Hence, you PERSONALLY will be immortal - although those around you will not (although they'll all be immortal in some other universe).

However, those who think this is "wishful thinking" need to carefully consider what this really implies. Suppose you are really sick - something painful and incurable. With this combination of hypotheses, you can't die. No matter what - you'll be in a universe where (though in continuous and nearly unbearable pain) - you can't commit suicide. You put a gun to your head and pull the trigger to try to end your misery...the gun will jam - or a freak gust of wind will blow the gun out of your hand. No matter what you do, there is no way out. Given you'll live forever - it's certain that you'll lose limbs, become blind and deaf - be in continuous anguish...for all eternity. If ever there was something close to old-testament hell - then Quantum Immortality is it.

(Going off-topic here.) Steve, I thought you said you worked your way through the whole Bible once? Where exactly did you find this "old-testament Hell"? There are a few lines in the Book of Daniel, but other than that Hell seems to be almost entirely a new-testament concept, as far as I can tell. The OT God might have done a bit of smiting, but once the smitten were dead, the narrative appeared to stop. --Trovatore (talk) 21:11, 7 June 2009 (UTC)

I don't remember much of whatever I read of the bible but based on the behaviour of God in the OT I would be just as worried about the OT heaven as I would be the (largely undisscussed?) hell. Let's face it, that God was psychotic.Nil Einne (talk) 19:55, 9 June 2009 (UTC)

I sure hope there is an error in the theory somewhere!

SteveBaker (talk) 17:10, 7 June 2009 (UTC)

Also, not every divergence into "many worlds" will result in an explicit separation between "living" and "dead" - there are hundreds of trillions of quantum "decision points" which occur all the time, and most of them have no impact on whether or not you will be conscious and alive at the next "time step." (Think about every photon of sunlight colliding with every molecule of nitrogen on its way down to earth - most of the time, whichever way the stuff scatters out, you live anyway). But, the many-worlds interpretation suggests that the universe necessarily schisms at each of those. So, there should be exponentially increasing numbers of universes, most of them pretty similar, with an exponentially schisming "thread" of consciousness. Which one is the "real" you? This whole infinite-universe-schisming methodology is sort of silly, especially since it yields absolutely nothing predictive or otherwise scientifically helpful in understanding our universe. Nimur (talk) 18:30, 7 June 2009 (UTC)

And it also does not follow from logic or basic understanding of quantum mechanics. Quantum mechanics describes statistical probabilities for certain state transitions, rather than deterministic behavior. However, the common interpretation that there is a "small but nonzero chance" that anything can happen is simply incorrect. There is a probability density function for any physical observable, and that probability can and is often zero for certain outcomes. So, "immortality" implies that at no time will you ever encounter any situation which has a "dead-end" on the constantly schisming set of outcomes - which is sort of silly also, given that we observe living creatures dying all the time. Changing the quantum state of a bunch of atoms must still follow rules. Nimur (talk) 18:36, 7 June 2009 (UTC)

I think you really need to start by defining "universe". I would (roughly) define "universe" to mean a collection of causally connected things (you may not have everything causally connected to everything else, but there needs to be at least a connection via other things). By that definition, any being that can enter our universe is part of our universe. So, by definition, the answer to your question is "no". --Tango (talk) 16:17, 7 June 2009 (UTC)

Thanks for the explanations. I can't help but think that calling that wishful thinking is too generous. Hogwash comes to my mind. Dauto (talk) 22:29, 7 June 2009 (UTC)

OK, great points all around first of all. To me, quantum immortality makes sense. But because I can personally theoretically live forever, then that means that everything works like that, right? Since everything is made up of quantum particles then everything should have "quantum immortality" in the sense that anything can happen to it, it's just that in this universe we're observing it doesn't. But wouldn't it follow that if anything is possible then wouldn't someone from another universe be able to travel to this universe and say "hey! I'm from another universe!"? Because it's a possibility. So if the theory is true, then how come this hasn't happened OR is it completely probable that it can happen, it just hasn't happened yet? —Preceding unsigned comment added by 66.66.149.43 (talk) 00:22, 8 June 2009 (UTC)

A possible answer is that it is physically impossible to travel between universes. Everything which can physically happen, in some universe somewhere, does; but not anything else. A more gratifying answer is that it is physically impossible unless a time machine exists at the destination. (That is to say an inter-universe travel machine, universes and moments in time being the same thing.) 213.122.32.39 (talk) 03:52, 8 June 2009 (UTC)

Another thought which just occurred to me is that the emergence of a traveler into just one universe, and not any of the very similar alternate versions of that universe, is by definition an extremely unlikely event. ("The same across universes" is the definition of likely.) So if time machines have perfect accuracy, then you'd pretty much never see anybody arrive, just because of probability. Then again I suppose you have to multiply that tiny probability by the number of possible visitors, which is very large since it includes everybody in all possible futures (even though most of them wouldn't want to come here), so in conclusion, meh. 213.122.32.39 (talk) 04:22, 8 June 2009 (UTC)

Speeding up formal education

What research has been done into increasing the rate at which students can complete their formal education (e.g. decreasing sleep and leisure requirements to allow a greater course load, increasing retention from lectures, increasing comprehension-adjusted reading speed, increasing learning ROI on practical exercises)? Is this likely to become more of a priority if the demand for highly skilled workers continues to increase? NeonMerlin 04:42, 7 June 2009 (UTC)

I think a lot of research has been done on time-to-productivity. In my fields, there is an always-raging debate between the need for advanced degrees versus simple bachelors' degrees - in other words, which is more productive, two years of on-the-job training, or two years of post-graduate study towards a Master's Degree ( ... or six years of post-graduate training for a Ph.D.)? There's a lot of academic debate about this as well. Most academic research into education is not about "speedup" as much as it is about improved retention and comprehension. There's a lot of research on "force-multipliers" - such as using technology to allow one teacher to impact more students. I think this is the most practical framework you will find for "speeding up" formal education. Also, the military has developed a huge body of rapid training - take a look at AKO or NKO. I hear that the language courses for many overseas deployments claim to teach "basic fluency" from zero prior knowledge in the span of six or eight weeks (though this may be a dubious claim). Nimur (talk) 04:59, 7 June 2009 (UTC)

The question that comes to mind is "..and then what?" Formal education should not be a goal to be completed in and of itself. Used to be a time where it was thought to prepare you for a career in your later life. Standard testing (which works for some) has created a slew of students who are not prepared for anything but solving standard tests. There are "robot hack" jobs that require nothing else. The worrysome thing is that ingenious and creative minds that industry would need fall through the hiring cracks. As a consequence technological advances and inventions needed to stay ahead of the curve aren't happening. (And we'll all go wondering why the next economic crash happened.) If you don't spend time-off from studying for "leisure requirements" how do you ever build up a social network. Your course results will only get your resume past the software keyword engine in hiring. If you don't show sufficient social skills during the interview you won't get hired. (OR: Just last week my hubby's group turned down the more qualified applicant because they all agreed he appeared to be hard to work with.) Word of mouth is a far more effective tool for getting contracts or getting hired than any other I know of. Most (better) universities check applications for extracurricular activities. 71.236.26.74 (talk) 19:26, 8 June 2009 (UTC)

Magnetic force based "black holes"

Is there a "Black hole" based on the force of magnetism rather than gravity? -- Taxa (talk) 04:58, 7 June 2009 (UTC)

No. Nimur (talk) 04:59, 7 June 2009 (UTC)

Black holes form by a runaway collapse of matter, i.e. increasing density causes further increase in density ad infinitum. Since there is no phenomenon in physics by which a magnetic field could intensify itself, a "magentic hole" is impossible. -RunningOnBrains^{(talk page)} 05:03, 7 June 2009 (UTC)

but the magnetic force is much stronger than the gravitational force (brian greene: "a puny magnet can pick up a paper clip, overcoming all of the massive Earth's gravity" [paraphrased]. In fact gravity is some e-42 as strong as magnetic force!).

So it is a valid question, could we collapse a black hole by magnetic compression? 79.122.74.190 (talk) 07:35, 7 June 2009 (UTC)

No, as Runningforbrains said, the issue is not the strength of the force, but the feedback loop that is set up. Gravity results in an increase in density, causing increase in gravity. There is no mechanism by which the magnetic force could alter its magnetic domain and cause an increase in force, without the external application of energy.YobMod 08:16, 7 June 2009 (UTC)

My question is whether a traditional, gravity-based black hole, could be created through the initial compression of the proper mass down to the proper size not due to Gravity, but through a magnetic force? The point is that without the magnetic compression, the mass would not be critical enough (small enough volume) to turn into a black hole, but with the magnetic compression, the mass becomes small enough to pass the critical point and become a blcak hole. Would this be possible? 79.122.44.114 (talk) 10:23, 7 June 2009 (UTC)

Sure. It doesn't matter how the necessary density is achieved, just that you get enough mass into a sufficiently small volume. Some physics models predict the possibility that we will even be able to create micro black holes using the Large Hadron Collider. (In the LHC, very large amounts of energy – effectively mass, by E=mc² – get packed into a very tiny space when highly energetic particles collide. There's an outside chance that sufficient density can be achieved to make tiny, temporary black holes in this way.) TenOfAllTrades(talk) 15:38, 7 June 2009 (UTC)

Why would the black holes from the LHC be temporary? Once they are formed, doesn't anything that come within their event horizon just increase their mass (remaining in a point volume), making them ever bigger and bigger black holes? If not, then what's to stop whatever process would end these black holes from ending (on a larger scale) normal black holes? Thanks! 94.27.225.206 (talk) 15:53, 7 June 2009 (UTC)

See Hawking radiation. In theory, the smaller the black hole, the shorter its lifespan. A black hole created by the LHC would likely evaporate before it even gobbled up a single atom. This is why actual physicists are not concerned by the possibility of mini-black holes, even if a few botanists and biochemists are. -RunningOnBrains^{(talk page)} 16:29, 7 June 2009 (UTC)

The magnetic force is not stronger than the gravitational force. They have different units. It's like saying a pound is heavier than a foot is long. The closest you could get is using Planck units, in which case the gravity and the electromagnetic force both have a strength of one. — DanielLC 15:29, 7 June 2009 (UTC)

Daniel, you should be more careful with what you say. I can't think of a single way in which your statement that the electromagnetic force may have a strength of one would make any sense. The most natural way to measure the strength of the electromagnetic force is through its coupling constant which is adimensional. Dauto (talk) 17:53, 7 June 2009 (UTC)

Muscles + Oxygen = Energy

Would any of you know of an exercise or a few types of exercises to make your muscles require less oxygen?

Sleep. Cuddlyable3 (talk) 09:58, 7 June 2009 (UTC)

I don't think there's anything that makes them require less oxygen, but I know anaerobic exercise makes it so you can get oxygen there faster. — DanielLC 15:24, 7 June 2009 (UTC)

Intelligence as absence of stupidity

It is often said that "intelligence has its limits, but stupidity knows no bounds." This suggests that intelligence is merely the absence of stupidity, just as cold and darkness are the absence of light and heat (hence there is a minimum possible temperature but no maximum possible temperature), and that as a perfect vacuum would be perfectly dark, so too would it be perfectly intelligent. Is there a theoretical elementary particle that carries stupidity? Is it possible that some or all Standard Model particles carry it? NeonMerlin 07:07, 7 June 2009 (UTC)

Um what? Particles carrying stupidity??? Intelligence is present in a vacuum??? How do you even define intelligence and stupidity let alone carry them in particles or observe them in vacuum? I think your confusing a cute, quaint or fun comment with some sort of deep scientific statement. I doubt even many philosophers will make such a suggestion Nil Einne (talk) 07:14, 7 June 2009 (UTC)

It's also said, among other things, that a stich in time saves nine, but to hear that and start wondering what kind of a garment the stitches are on is to miss the point of the proverb. These aren't some kind of universal and literal hard facts, you know. -- Captain Disdain (talk) 07:28, 7 June 2009 (UTC)

Sayings do hold deep truths but may have to be slightly adjusted to be exactly right. For instance one can't have one's cake and eat it, unless one does them in that order (and I'm not going to think of the other alternative). A bird in the hand is worth two in the bush, unless you're talking about women. If pigs could fly a lot of biology and physics would have to be rethought but I'm sure we'll manage it one day with genetic engineering. I think in this case the saying is referring to the fact that for instance an intelligent person would say something intelligent and then stop whereas an idiot could go on wittering for ever. And furthermore.... :) Dmcq (talk) 07:49, 7 June 2009 (UTC)

It simply means that stupidity is not a conserved quantity. SpinningSpark 09:26, 7 June 2009 (UTC)

Intelligence is an attribute that can be defined and tested in various ways. There is no consensus on its limits. The word stupidity is not as suggested the opposite of intelligence but a disparaging term for negligent thinking. Persons that have high intelligence by some criteria, e.g. IQ score, are not immune to stupid actions. The OP offers hypotheses about a particle nature of stupidity that fail the scientific method because they lack falsifiability or a useful prediction. Cuddlyable3 (talk) 09:53, 7 June 2009 (UTC)

I'm sure I saw an advertisement that said there was a clever-dumb balance so it must be a conserved quantity. Advertisements are covered by the advertising standards agency and must be truthful. Dmcq (talk) 14:23, 7 June 2009 (UTC)

I presume you are referring to the toothless Advertising Standards Authority (United Kingdom) created by the advertising industry themselves whose idea of "self-regulation" is the occasional meaningless ticking off. If you believe anything they say . . . Stupidity behaves rather more like the (unconserved) entropy equation;

$\Delta S=\int {\frac {-dQ}{T}}$

Where Q is intelligent actions and T is the "intelligence temperature" - average intelligence per individual. SpinningSpark 13:18, 8 June 2009 (UTC)

Does anyone else see how ironic this question is? --Shaggorama (talk) 22:52, 7 June 2009 (UTC)

I do. There's even a related old saying, "It is better to remain silent and be thought a fool, than to open your mouth and remove all doubt". I think next week I'll post a topic here that says that I heard that all people who post here are actually dimwits who are in denial. We'll count how many responses come back as verbose versions of "No we're not!". They probably won't 'get' that either.

Heat death, temperature and entropy

The article about Heat death says "The heat death is a possible final state of the universe", and that is a state in which "it has reached maximum entropy" and 'In a "heat death", the temperature of the entire universe would be very close to absolute zero'. The article about entropy says "When heat is added to a system at high temperature, the increase in entropy is small. When heat is added to a system at low temperature, the increase in entropy is great". So In heat death, the entropy becomes maximum and temperature is the lowest, but if heat is added to a system (I think that means a rise in temperature), the entropy increases. Then what is the high entropy in the heat death comprised of? I have been guessing that high entropy usually means high temperture. Like sushi (talk) 10:37, 7 June 2009 (UTC)

You can think of it this way: when you transfer some heat from a high-temperature system to a low-temperature system, the high-temperature system loses a relatively small amount of entropy while the low-temperature system gains a relatively large amount, so overall entropy increases. The entropy is (locally) maximum when the temperatures are equal. Adding heat would increase the entropy, but the heat has to come from somewhere (first law). If the whole universe is at the same temperature then the loss in entropy where the heat was removed would exceed the gain in entropy where it was added, which is forbidden by the second law. -- BenRG (talk) 14:20, 7 June 2009 (UTC)

Wet matches

I left a box of matches outside last night and they got soaked in the rain. When I try to strike them, the head of the match just crumbles into a wet mush. If I leave them and the box out in the sun today, might they dry out and be useable again? Frank Bruno's Laugh (talk) 11:18, 7 June 2009 (UTC)

Sure, why not. Try it and let us know tomorrow. Avoid the temptation of putting them in the oven on a low setting though (for obvious reasons!) 94.27.225.206 (talk) 12:41, 7 June 2009 (UTC)

Yep, that worked fine. The charcoal that go wet is still a bit mushy! :) I did consider putting the matches in the electric oven on a low setting (starting with one), thinking that it wouldn't have been hot enough to ignite them, but I guess that wouldn't have been a good idea? Might it work with the charcoal? Frank Bruno's Laugh (talk) 15:01, 7 June 2009 (UTC)

I'd be surprised if they still worked. In my experience regular matches don't have a lot of tolerance for weird environments (and degrade rather quickly with age or humidity). That being said, matches are pretty cheap, so it's not exactly the end of the world. --98.217.14.211 (talk) 14:59, 7 June 2009 (UTC)

They actually seem in pretty good shape, so I guess I got lucky (they did get a real soaking) Frank Bruno's Laugh (talk) 15:05, 7 June 2009 (UTC)

If you're taking some matches somewhere they run the risk of getting wet (e.g. a camping trip), a tip I once read is to dip them in melted candle wax. I can't say I've ever tried it, and I imagine a cheap lighter would be a better bet. 87.81.230.195 (talk) 23:58, 7 June 2009 (UTC)

Yes, yes. Before use, just melt the wax off with a lighter. 79.122.119.18 (talk) 06:21, 8 June 2009 (UTC)

I see what you did there. Tempshill (talk) 17:41, 8 June 2009 (UTC)

I have dipped old-style kitchen matches (the old-fashioned strike-anywhere kind) into wax and that made them completely waterproof and they would still light just fine without having to melt the wax away or anything. I haven't tried it with safety matches. 207.241.239.70 (talk) 19:12, 8 June 2009 (UTC)

Human blood

What are the risks with drinking (fresh) human blood? Vimescarrot (talk) 14:01, 7 June 2009 (UTC)

Oh, and the possible (dietary) health benefits? Vimescarrot (talk) 14:07, 7 June 2009 (UTC)

Maybe I'm stating the obvious but a dietary benefit would be increased iron intake. I'm guessing that there are no immunoreactive issues as the antigens should be metabolized and/or not absorbed by the gastrointestinal tract. --Mark PEA (talk) 15:32, 7 June 2009 (UTC)

It might be worth pointing out here that increased iron intake is not always a benefit. Iron is a necessary nutrient, but it's also somewhat toxic, and there is apparently no dedicated mechanism for getting rid of the excess. There is some information at our articles on human iron metabolism and iron overload.

A few years ago there was a minor splash made by the observation that many of the risk factors for heart disease have in common that they are associated with higher levels of iron in the body, and it was hypothesized that iron was a contributing cause to heart disease. I can't find an article about that in WP, and I don't really know how the idea has fared, though I imagine we'd have heard more about it if there were good evidence for it. --Trovatore (talk) 20:01, 8 June 2009 (UTC)

There are obvious risks of the transmission of disease. I think that's probably about it. You could overdose on iron (and maybe other constituents) if you drank too much of it, but that basic principle applies to anything. --Tango (talk) 16:35, 7 June 2009 (UTC)

There's also likely a risk of criminal charges, depending on who's blood it was and how you acquired it :-D -RunningOnBrains^{(talk page)} 17:03, 7 June 2009 (UTC)

You're not planning to eat your bone tumor, are you? Nimur (talk) 18:20, 7 June 2009 (UTC)

Sorry, but I must note that this line made me laugh for no less than 20 seconds. Tempshill (talk) 04:29, 8 June 2009 (UTC)

Bone tumours aren't made of blood. On a slightly related note...What about the, uhh...various components of what comes out of a female during menstruation? (I'm given to understand that it isn't just blood...) Is that any more risky? Also, what about eating a tumourous bone? That last one is just for laughs, really. The first one, I'm specifically thinking of oral sex. Vimescarrot (talk) 19:16, 7 June 2009 (UTC)

What are you, 12? Menstrual fluid doesn't get ingested during oral sex, mmmmkay? 94.27.225.206 (talk) 20:12, 7 June 2009 (UTC)

I see no reason why that isn't possible. Vimescarrot (talk) 20:33, 7 June 2009 (UTC)

If you give oral sex to a woman that is menstruating, I would expect some of the menstrual fluid to be ingested. --Tango (talk) 21:04, 7 June 2009 (UTC)

The amount would be so small though, would it really matter? —Preceding unsigned comment added by 82.43.88.87 (talk) 22:26, 7 June 2009 (UTC)

That's exactly what I'm asking. Vimescarrot (talk) 22:34, 7 June 2009 (UTC)

According to a (purportedly non-fiction) book I read some years ago, committing cunnilingus on a menstruating woman (with or without her consent) was an act for which US Hell's Angels could earn a Red Wings badge, or Black Wings if she were black. I mention this purely in the spirit of encyclopaedic completeness, not because I endorse the custom or attitudes involved in any way. 87.81.230.195 (talk) 23:55, 7 June 2009 (UTC)

This is a reference desk. Is it too much to ask for a few references, especially when dealing with matters of health? According to Aidsmap, a project of NAM (National AIDS Manual, UK registered charity, founded 1987):

The levels of HIV in vaginal fluid vary. They are likely to be highest around the time of menstruation (having your period), when HIV-bearing cells shed from the cervix are most likely to be found in vaginal fluid, along with blood. Oral sex will therefore be more risky around the time of menstruation. Factsheet here

According to The Body, a service of Body Health Resources Corporation:

It is important that you do not perform unprotected oral sex on a woman when she is menstruating (blood has a much higher concentration of HIV), and if you are experiencing any problems with your oral health (sores, abrasions, inflammation). If you would like to decrease the risk of transmission even further, you can use a latex barrier--like a dental dam or a condom cut into a square--between your partner's vagina and your mouth. Explanation here

Sources please! BrainyBabe (talk) 12:06, 8 June 2009 (UTC)

vampirism? —Preceding unsigned comment added by 82.43.88.87 (talk) 19:59, 7 June 2009 (UTC)

Not exactly human blood but animal blood (eg. pig blood) is a delicacy in Southern China; very smooth and tender, with a jello-like texture and a bit of iron after-taste. --antilived^{T | C | G} 23:06, 7 June 2009 (UTC)

I believe there is less risk from animal blood than human blood, since the diseases present in animal blood are less likely to be infectious to humans. --Tango (talk) 00:45, 8 June 2009 (UTC)

I seem to remember reading of a nomad culture where cattle are regularly bled for drinking; but maybe that was fictional. —Tamfang (talk) 04:43, 8 June 2009 (UTC)

The Maasai of East Africa certainly do that - they mix cow urine into a mixture of cow blood and milk to make it clot. According to our article, these days they only do this on ceremonial occasions or when someone is sick. When we lived in Kenya in the early 1970's, my parents bought a rather beautiful beaded gourd from a Maasai tribesman - sadly, they assumed it was a tourist trinket when in fact it was all-too authentic and still contained the guy's lunch! Despite a lot of cleaning, and soaking the insides with bleach, the...erm..."distinctive" odor of the thing never quite went away! SteveBaker (talk) 10:53, 8 June 2009 (UTC)

Well, since we are digressing, see Blood as food (alas, not a great article). Note that the consumption of raw duck and chicken blood in dishes that are delicacies in Vietnam is one of the few ways in which humans can catch so-called "bird flu" (H5N1) from birds, see BBC article. BrainyBabe (talk) 08:11, 8 June 2009 (UTC)

I believe there is less risk from animal blood than human blood, since the diseases present in animal blood are less likely to be infectious to humans. That is a rather risky belief given the number of counterexamples of diseases transferred from animals. BTW. Off hand I could probably come up with a shorter list that can not be transferred than ones that can. Just for tip of the iceberg examples see Rabies, Trichinella, Apicomplexa, vCJD, Cryptosporidiosis. Some of these get most commonly transferred by other means than consumption of blood, but that doesn't mean it can't be transmitted that way. Even intestinal parasites are often present in an infected individual's blood. Some allergologists think that humans need a certain exposure to parasites and infectious agents to prevent allergies. If only 1 in X gets infected it that figure won't make you happy if you turn out to be the one. 71.236.26.74 (talk) 15:59, 8 June 2009 (UTC)

See selection bias. Most diseases cannot be transferred from one species to another. The only animal diseases you have probably heard of (unless you are a vet) are ones that can be transferred to humans since those are the ones that make the news (or ones your pets have caught, I suppose). There is certainly some risk, but it is far lower than the risk of drinking human blood. Pretty much any human disease can be transferred by drinking human blood (the risk is rather low for some since stomach acid, etc., are quite good at killing ingested contagions, but there is still a significant risk). --Tango (talk) 16:54, 8 June 2009 (UTC)

We have an article, Zoonosis, but it doesn't seem to make comparisons to human-to-human infections. --Tango (talk) 16:58, 8 June 2009 (UTC)

Interesting discussion is interesting! I love digression - it's a great way to learn. Vimescarrot (talk) 17:14, 8 June 2009 (UTC)

You might e right about selection bias (although I do know plenty of diseased that affect only non-humans - and I'm still not a vet). There is however the factor of immunity that makes diseases that "jump species" worse than those within the same. Trusting expert opinion reported in the media in this matter our immune system is just having a lot harder time dealing with pathogens introduced via animal vectors than human to human. So, you could catch the flu by drinking human blood, but would your immune system be more likely to deal with that than a bird flue virus you ingested with chicken blood? 71.236.26.74 (talk) 19:48, 8 June 2009 (UTC)

Yes, I think that is true. Most human-to-human diseases are fairly minor (like the common cold), whereas animal-to-human diseases, while very rare, are often quite a lot worse. That isn't just due to immunity, it is due to evolution of the disease as well. Killing your host is not generally a good way to reproduce, so serious diseases in humans tend to die out in time, but if they were less serious in a given animal they could live on in that animal and only be serious when they get transmitted to humans (usually it would stay in the original human, diseases of animal origin that can be transmitted from human to human are very rare indeed - that's the big fear about bird flu, that it could mutate into a form that can be transmitted between humans, at the moment it can't so just kills a handful of people that have close contact with birds). --Tango (talk) 17:05, 9 June 2009 (UTC)

Surgical memento

If surgeons are removing something from you, are you allowed to keep it? Vimescarrot (talk) 14:03, 7 June 2009 (UTC)

Let me guess. No? Bus stop (talk) 14:06, 7 June 2009 (UTC)

Why not? And if that's a guess, why would you think that? Vimescarrot (talk) 14:08, 7 June 2009 (UTC)

I don't know. I'm just joking. I really don't know. But since intuitively I would assume one should have the right to take possession of a part of one's body that has been surgically removed from one's body, it probably is the case that it is the opposite. There is probably some reason why removed body parts become the property of the medical facility in which the surgery took place. But I really don't know. Bus stop (talk) 14:51, 7 June 2009 (UTC)

Human tissue is generally classified as biohazardous material, and has to be properly disposed of in a high temperature medical incinerator. So the hospital isn't allowed just to give you a decaying necrotic kidney home in a plastic bag. They'll give you an inanimate calculus like a gallstone, because there's no risk of disease. In theory they could preserve stuff in formaldehyde, but there are considerable additional compliance costs to do with human anatomy regulations and biomedical waste; it's not the hospital's core business, so they're unlikely to want to do all that stuff. Hopper Mine (talk) 15:45, 7 June 2009 (UTC)

Is bone an "inanimate calculus"? Vimescarrot (talk) 15:57, 7 June 2009 (UTC)

Very much not; it's a complex matrix full of living cells (it couldn't very well get cancer if it was inanimate). It is possible for a lab to sterilise bone (this is done to cadaverous bone allowing it to be safe for transplant), leaving only the inorganic hydroxylapatite matrix, but this is an involved and expensive process - it's not something they'd do for souvenirs. Hopper Mine (talk) 17:57, 7 June 2009 (UTC)

I guess it depends on what they are removing. My friend kept his gall bladder stones, but some things might be toxic?91.111.74.247 (talk) 14:55, 7 June 2009 (UTC)

A bone tumour. Vimescarrot (talk) 15:01, 7 June 2009 (UTC)

note that this is by the OP. So, OP, why would you want to keep a bone tumor??? 94.27.225.206 (talk) 15:47, 7 June 2009 (UTC)

Well, why do people keep teeth? Vimescarrot (talk) 15:55, 7 June 2009 (UTC)

To get money from the tooth fairies, obviously. Now, everyone knows that the bone cancer fairies are just a myth. Frank Bruno's Laugh (talk) 18:51, 7 June 2009 (UTC)

Good thing I don't have bone cancer, then...Vimescarrot (talk) 19:13, 7 June 2009 (UTC)

This may be of some help to you. Frank Bruno's Laugh (talk) 15:10, 7 June 2009 (UTC)

Maybe the OP was talking about surgeons removing a foreign object. If it's not dangerous, I see no reason why you couldn't have it. Of course, if it was a bullet, knife, or some other weapon, they might be obliged by law to hand it over to the police for forensic investigation. Astronaut (talk) 17:35, 7 June 2009 (UTC)

-just re-read that ... a bone tumour? Are you serious? Astronaut (talk) 17:36, 7 June 2009 (UTC)

Why would I not be serious? Vimescarrot (talk) 17:47, 7 June 2009 (UTC)

A cancer is no more hazardous to others than regular tissue of the same type (barring use in transplants, obviously, and maybe cancers associated with viruses). It's just a minor programming error, not some primal nuncio of feculence; it's not contagious. That said, all living human tissue is thick with a wide range of pathogens, and it's all considered hazardous for good reason. Hopper Mine (talk) 18:05, 7 June 2009 (UTC)

If you're just thinking "ew gross", it's surprisingly common for people to feel sentimentally attached to what is, after all, part of themselves. This is true even for tumours; some people seem to think "that's the little bastard that caused me so much trouble", and want to keep it as a trophy. Hopper Mine (talk) 18:14, 7 June 2009 (UTC)

It sounds like Hopper and Frank answered my question, although if anyone disagree they're welcome to say so. Thanks. Vimescarrot (talk) 19:13, 7 June 2009 (UTC)

Famous persons could sell their excised body parts for considerable sums. These would pass from hand to hand as collector's items or investments. Soft tissue would be in a sealed glass tube. There would be a registry of ownership to ensure against fraud. If authenticity is still questioned, DNA tests could be made. – GlowWorm. —Preceding unsigned comment added by 98.21.108.254 (talk) 03:39, 8 June 2009 (UTC)

In some cases where something is removed the surgeon may actually be required by the insurance company to keep what was removed or even send it (preserved) to the insurance company as proof the surgery was actually conducted. I don't know how common that requirement is. Someguy1221 (talk) 03:47, 8 June 2009 (UTC)

— all due respect, but I think you must have just made that up. I imagine an insurance adjuster in his cubicle taking 50 FedEx shipments per day that are all dripping pus and blood. Tempshill (talk) 04:27, 8 June 2009 (UTC)

Or rather, I said that because a close relative was unable to keep a bone that was removed for precisely that reason. I do think your image is pretty amusing, and is why I mentioned I don't know how common that is. The incident I mention was the first time I'd ever heard of it being a practice. Someguy1221 (talk) 02:33, 9 June 2009 (UTC)

Just last week, my wife came home from the hospital with two screws that were removed from her leg. (They had, of course, been installed in a previous surgery.) The screws were clean and shiny, and had been autoclaved after removal. -- Coneslayer (talk) 16:23, 8 June 2009 (UTC)

Not supposed to give legal opinion, but I've heard that in Australia you retain ownership of removed body parts, but not your dead body. Polypipe Wrangler (talk) 05:31, 12 June 2009 (UTC)

Inertia on the bus(non-technical explanation preferred)

When riding the bus, passengers experience inertia when it accelerates(they move backwards relative to the bus) and when it decelerates(they keep moving forwards). However, why does there seem to be less inertia(and consequently less risk of getting tossed around and crashing into things/people) when you're seated than when you're standing? I don't have much background in physics, so I'd like a non-technical answer. 69.224.113.202 (talk) 18:15, 7 June 2009 (UTC)

You have exactly the same inertia, whether you are seated or standing, because inertia only depends on your mass. While standing, though, your center of mass is higher, and you are generally in a less stable position, so you might feel the sways and even stumble around a bit as the bus accelerates. This is strictly due to how stable your stance is, not how much inertia you have. Nimur (talk) 18:18, 7 June 2009 (UTC)

To expand a little on what Nimur said: when you're sitting down and typically leaning back against the seat, that's a very stable position. Not only are you braced against the seat, your butt and the backs of your thighs against the seat afford you plenty of friction that tends to hold you on the seat, especially if the seat is made of something relatively coarse, like fabric, instead of a more slippery material. If I tried to yank you away from the seat, I'd probably have to use quite a bit of force. But if I wanted to do the same to you when you're standing, it'd be a lot easier, because not only would your center of mass be higher so it'd be much easier to tip you over, there wouldn't be a lot of friction to hold you in place. Unless you were prepared for me and had strongly braced yourself, I could probably yank you off your feet without any real trouble. Another way to look at this might be to imagine a rolled-up carpet in a bus. If you stand it up, it tips over very easily, but if you lay it down, it'll most likely pretty much stay put. If the roll starts to tip over, you're going to have to use quite a bit of strength to get it back upright, because at that point you'll be working against its own mass. That's what happens when you stand up and have to work to stay on your feet: once your balance starts to go, it's your own mass that's making you fall down, more than anything else. You need to work to re-balance the load that consists of your body. -- Captain Disdain (talk) 23:33, 7 June 2009 (UTC)

Similarly, notice that when you're standing, you get thrown around most if you don't use a handhold, less if you hold on with one hand, still less if you hold on with two. The force on you is the same, but the more you're braced, the more easily you can resist it. Sitting down braces you even more, and sitting down with a hand against the seat in front (if possible) does still better. --Anonymous, 3:55 UTC, June 8, 2009.

When a person is standing in a bus, the body's center of mass is at the end of a longer leverage arm than when the person is seated. Specifically, the axis of turning is at the feet rather than the buttocks. Thus when seated, the center of mass is only slightly above the center of turning.
Also, when a bus is decelerating, the abdominal muscles of a seated person resist the inertial effect rather than the weaker ankle muscles of a standing person. Specifically, when a person is seated, holding the abdominal muscles and knees rigid and bracing the feet on the floor opposes the turning inertia of the upper part of the body. When the bus is accelerating, the person is simply pressed back in his seat. Furthermore, the mass of the legs of a seated person is below the axis of turning, reducing the body mass above that point.
All this assumes there is no slippage on the seat or floor. Inertia thus results in a turning effect. - GloWorm. —Preceding unsigned comment added by 98.21.108.254 (talk) 03:59, 8 June 2009 (UTC)

Twins conceived on successive months

Further to the excellent sourced answer above, about the time between the delivery of twins (or other multiple births), I remembered a friend-of-a-friend story. It seemed improbable, but then, so did the idea of delivering one baby and then keeping the other in utero for more than a few minutes. Here is the idea -- twins are born: one is substantially bigger than the other, and hits all the developmental milestones a full month or more before the tinier sibling. What is the probability of the bigger being conceived one month, and the smaller the next, because ovulation for some strange reason was not suppressed? In other words, not "can you get pregnant if you do it standing up?" but "can you get pregnant if you are already pregnant?". BrainyBabe (talk) 20:19, 7 June 2009 (UTC)

I don't know the answer, but I think it is quite unlikely to happen - you don't just need ovulation to take place, but the embryo to successfully implant in the uterus lining. I know some contraceptive pills don't reliably prevent ovulation, but do prevent implantation, so I would imagine pregnancy could be similar (although ovulation is even more unlikely when pregnant than when on the mini-pill). --Tango (talk) 21:02, 7 June 2009 (UTC)

This being an encyclopedia, we have an article on this rare phenomenon: see superfetation. --Cookatoo.ergo.ZooM (talk) 21:03, 7 June 2009 (UTC)

Well, I knew it was quite unlikely to happen; I wanted to know if it was impossible. I am grateful for the pointer to the article, which I never would have found on my own! BrainyBabe (talk) 08:17, 8 June 2009 (UTC)

Submersed in Water

Is there a length of time after which it would become dangerous for a person to remain in water? Assuming access to a toilet and the water is freshly running would a person eventually get sick? I'm thinking there is some sort of limit as your fingers prune after too long. The Aquatic ape hypothesis, which albeit mostly unsupported, provides some possible insight, but I can't seem to find conclusive proof of a danger from extended exposure. TheFutureAwaits (talk) 21:15, 7 June 2009 (UTC)

Incidentally, why do fingers prune? And why don't toes prune? Does pruning take place in other land-dwelling animals after prolonged water exposure? —Preceding unsigned comment added by 98.21.108.254 (talk) 02:42, 8 June 2009 (UTC)

Toes do prune. Try it and see. As for the causes there is a section dedicated to this. Sifaka ^talk 03:13, 8 June 2009 (UTC)

OK. Toes prune too. It's been a long time since I took a bag lunch and spent the whole day at the swimming pool with my pals. (What fun we had !) - GlowWorm.

You might like to look at David Blaine - see Drowned Alive. DJ Clayworth (talk) 16:58, 9 June 2009 (UTC)

Or you might realise that David Blaine is a magician and is therefore irrelevant to this discussion. SteveBaker (talk) 03:27, 10 June 2009 (UTC)

Interesting, I'm sure I've ever heard anyone allege that the "Drowned Alive" stunt was an illusion. What would be the point? It seems like it would be entirely possible to do it straight, and rather difficult to fake? APL (talk) 04:07, 10 June 2009 (UTC)

Oh, or did you simply mean that the accounts of his injuries may be exaggerated (or censored) for dramatic publicity reasons, and therefore unreliable? APL (talk) 04:09, 10 June 2009 (UTC)

Most people spend 9 months fully immersed in an aquatic environment! The main risks with extended water immersion are hypothermia or salt exposure. Rob Hewitt spent 4 days lost at sea with only his wetsuit. Other people have swum the Atlantic or the Mississippi taking several months, at 8 hours per day in the water. ~~ Ropata (talk) 09:03, 12 June 2009 (UTC)

The need to urinate

Why is it that if I already need to urinate, the closer i get to a toilet the worse it gets? Like, for instance, if I'm driving home I may notice that I need to urinate, but have no trouble getting it, but once I get to the door of my house I start dancing around, and then it rapidly accelerates into a mad dash to the bathroom! Is it psychological? positional? --96.231.171.95 (talk) 22:46, 7 June 2009 (UTC)

If it's any comfort, I experience the very same thing. I've always assumed that it's an example of Pavlovian conditioning, and it's interesting that this still works even when one is consciously aware of it. 87.81.230.195 (talk) 23:42, 7 June 2009 (UTC)

Yep, it happens frequently enough to wonder just how Pablovian could it be if we are so concious of it happening and still can't control it? hydnjo (talk) 00:47, 8 June 2009 (UTC)

If this were an instance of conditioning, then we would expect the urge to pee to arise whenever a suitably coniditioned individual was near a bathroom, but this is clearly not the case. --Shaggorama (talk) 04:06, 8 June 2009 (UTC)

I disagree. I've gone into a bathroom to wash my hands or do something else that is only going to the bathroom in the literal sense, and felt the need to do it in the figurative sense. 67.182.169.172 (talk) —Preceding undated comment added 23:06, 9 June 2009 (UTC).

Something autonomic, I bet. Getting out of the car means you relax, relaxation makes you liable to pee. Once you've actually released the flood gates it's difficult to stop mid-flow, so I guess there's some kind of preparatory stage, a pre-pee process if you will, which is likewise difficult to stop. 213.122.32.39 (talk) 05:08, 8 June 2009 (UTC)

I suspect it's just that you have mentally 'released', you've made it to your goal (home) and then like 213.122 says once you've released it becomes much harder to stop so makes it more rushed to get there. I know that's how I explain it to myself. 194.221.133.226 (talk) 07:44, 8 June 2009 (UTC)

I think it's definitely psychological. If you suddenly get distracted by something that's important enough, the sensation will cease -- or at least that's how it goes for me. Sure, it takes a moment, but I've had a phone call knock me out of that "I gotta go right now" mode, for example. -- Captain Disdain (talk) 08:39, 8 June 2009 (UTC)

Pareto principle definitely. Jay (talk) 18:01, 9 June 2009 (UTC)

electrical generator

How does a generator work?

In particularly, I'm wondering how a wind turbine generates electricity? —Preceding unsigned comment added by 69.144.23.204 (talk) 23:23, 7 June 2009 (UTC)

See Electrical generator or more specifically, Electromagnetic induction. In short, voltage is produced across a conductor situated in a changing magnetic field or a conductor moving through a stationary magnetic field. -- Tcncv (talk) 00:00, 8 June 2009 (UTC)

As for wind turbine specifics, you may find the Wind turbine design article worth reading as well and many of the other articles linked from the "Wind Power" navigation box at the botton of that page. The conversion of wind energy to rotating mechanical energy and the conversion of rotating mechanical energy to electrical energy are best though of as two separate processes. -- Tcncv (talk) 00:15, 8 June 2009 (UTC)

In brief - when a magnetic field is moved past a wire, it generates a tiny amount of electricity. Spinning a magnet inside coils of wire (or spinning coils of wire inside some magnets) makes the magnetic field move past LOTS of wires - which makes a useful amount of electricity. The wind spins a shaft which spins the magnet (or the coil). It's basically an electric motor working 'backwards' - instead of putting electricity in and getting mechanical rotation out - you put mechanical rotation in and get electricity out. You can prove this yourself: If you take a small battery-operated electric motor (eg from a kid's toy) and connect a flashlight bulb across its terminals - you can spin the motor with your fingers and light the bulb. If you connect some fan blades to your motor and let the wind make it spin - then you've made your own personal wind turbine! SteveBaker (talk) 01:08, 8 June 2009 (UTC)

Are you sure that's true - I though they were wired in a different way. If it is true, then it would be easy to make a home wind turbine using an old washing-machine motor, although the electricity out of it would fluctuate greatly in its voltage, current, and Hz. 78.149.238.54 (talk) 19:38, 8 June 2009 (UTC)

It really has to be a DC motor. Washing machine motors run on alternating current - so probably this trick won't work (it depends on the design). But a direct current (DC) motor - pretty much any kids' toy or battery operated electric drill motor - will work wonderfully. And yes - of course you can make your own home wind turbine from bits and pieces you have lying around someplace...you can make nearly anything if you put your mind to it! A few years ago I made a computer controlled milling machine from an old router and some rollerskate bearings (and my current project is to re-make it with more power and precision). However - whether your home wind turbine would be efficient enough to be "useful" - is one of those devils that will be hiding in the details. SteveBaker (talk) 12:33, 9 June 2009 (UTC)

Ah ha! Now you are saying it won't work. "this trick won't work (it depends on the design)" - in other words the wiring is different as I wrote earlier. 78.147.57.78 (talk) 20:41, 9 June 2009 (UTC)

No - I'm saying that you have to read what I actually wrote:

"If you take a small battery-operated electric motor (eg from a kid's toy)..."

At no point did I say "It would be easy to make a home wind turbine using an old washing-machine motor"...those were your words. DC motors are NOT wired differently from DC generators - do the experiment it works just fine. AC motors may or may not be - it depends on the design...there are synchronous motors, squirrel-cage motors, induction motors, DC motors with AC rectification...some designs could work as generators - but others do not. It's the design of the motor that matters - not that "they were wired in a different way" as you said. AC motors are totally different beasts from DC motors. So I'm not changing my story - and I'm certainly not agreeing that you're right - I'm telling you to read what I wrote - which was correct. SteveBaker (talk) 03:25, 10 June 2009 (UTC)

It's absolutely true. A fun thing to do is to wire two small electrical motors to each other and turn the shaft on motor A and watch the shaft of motor B move. (Or maybe I'm just easily amused.) APL (talk) 00:41, 9 June 2009 (UTC)

Would that work? If you had two toy electric motors for example, I presume the output of one would be AC, yet the required input of the other would be DC. I'm still sceptical that electric motors would work in reverse as a dynamo without changing the wiring. Are there any YouTube videos of this? 89.242.125.32 (talk) 11:04, 9 June 2009 (UTC)

Yes - it works - providing you have two DC motors of similar size/voltage/etc. You can do it easily - just connect the wires from one motor onto the back of the other - turn one motor and the other one will turn as well. I've done this a gazillion times to demonstrate the effect - mostly using Lego Technic's motors (because you can connect them back-to-back very easily using the standard Lego connectors). Obviously there are losses in the system - so the second motor turns a bit more slowly than the first. But "Proof by YouTube" is a really REALLY bad idea because a solid 90% of the "science" videos on YouTube are faked. SteveBaker (talk) 12:33, 9 June 2009 (UTC)

Like SteveBaker said, A YouTube proof is worse than no proof at all. But this is a trick you can try yourself really easily. Get yourself two of these and wire them together. You don't even need to solder them, get some wires with alligator clips on them. I've done this many times, (Like I said, I'm easily amused), I promise that it works. APL (talk) 04:23, 10 June 2009 (UTC)

Yes, it really works. BTW it works for both AC and DC motors. They will give you respectively AC and DC currents. Dauto (talk) 18:28, 10 June 2009 (UTC)

A toy DC motor has to spinn pretty fast to make enough voltage to light a bulb or to spin another motor. A drill atttached to the shaft of one motor will spin it fast enough to power another motor. A DC motor is easier to use as a generator than an AC motor, where you will likely have to control the excitation voltage and strictly control the speed. There are mechanical variable speed drives which have been used in AC home hydro plants of 10 kilowatt output. Edison (talk) 21:33, 10 June 2009 (UTC)

"A toy DC motor has to spinn pretty fast to make enough voltage...to spin another motor." Did you TRY it?

Ok, you want a video? Here you go!.

I can't believe I spent time on this, but any excuse to get out my Legos is a good excuse. (Sorry the video isn't that great. I really need to get a tripod.) APL (talk) 01:07, 11 June 2009 (UTC)

June 8

Plant without soil

I have this plant in my garden which grows on a rock. It does not touch any soil which I can see and I can move the whole rock (about 1 metre wide and long) with the plant on it anywhere. The plant grows on one face of the rock, about 1 metre long and has big leaves about 30 cm long. What kind of plant is this and how does it live without soil?

Thanks in advance, 220.244.76.121 (talk) 02:40, 8 June 2009 (UTC)

Some species of air plant maybe? SpinningSpark 03:12, 8 June 2009 (UTC)

Plants living on a rock or rocks are called lithophytes. Lithophytic plants are way too numerous to list. Can you post a picture of the plant somewhere? That would be the best. Telling us what part of the world you are living in would also help. --Dr Dima (talk) 03:38, 8 June 2009 (UTC)

Having said what I said, it may actually be a good idea if we at least start a list of lithophytic plants. The problem is, there are plants like Capparis sp. or Hyoscyamus sp. that thrive in cracks of a rock or in a crevice of a stone wall, but are far more often found in regular soil; and there are plants like some species of Laelia that are almost obligate lithophytes. Should we come up with a criterion, or just bundle them and let the reader read? --Dr Dima (talk) 03:48, 8 June 2009 (UTC)

Even trees can grow without soil. Here is one I photographed in Scotland. Plants only need air, water, and a tiny amount of nutrient. See hydroponics.--Shantavira|^{feed me}

Alternative earphones with remote and microphone for iPod touch

moved to WP:RD/C#Alternative earphones with remote and microphone for iPod touch Nil Einne (talk) 17:01, 8 June 2009 (UTC)

Which vegetable oil is most healthy for vegetarians?

I'm looking for answers based on scientific evidence rather than something resulting from opinions formed from advertising or habitual use (eg olive oil). These two tables http://www.vaughns-1-pagers.com/food/vegetable-oils.htm http://www.annecollins.com/dietary-fat/omega-3-efa-6-chart.htm give lists of consituents of the oil, since I could not find a similar table on Wikipedia.

Canola oil is another name for rapeseed oil. I see that the amount of Omega3 in Canola oil differs considerably between the two tables - the small print in one of them says the amount listed is reduced during processing. I'm also wondering how much Omega3 there is in supermarket-bought 100% walnut oil, probably formed from hot-pressing, since neither of the labels on bottles from two different supermarkets mention it - yet I would have thought this would be a selling-point.

Fat summary: saturated fats - bad, should be avoided as far as possible. Transfats - very bad but not found in *liquid" vegetable oils. Monounsaturated - good, reduce bad cholesterol. Polyunsaturates - not so good as they reduce good cholesterol. But Omega3, which is a kind of polyunstaturated fat, is on the other hand good for you and said to be insufficient in peoples diets.

So given the above, which vegetable oil is best? Expense is not an issue. It may be that a blend of oils, determined by linear programming might be optimal. 78.149.143.187 (talk) 11:54, 8 June 2009 (UTC)

The question is clearly expressed, but I am not sure if the title is supposed to add an element to the mix. Is there a reason to believe that the healthiest oil for vegetarians would not also be the healthiest for omnivores? Also, the healthiest oil on strictly nutritional grounds may not be commercially available. Are you looking for something you can purchase and consume now, or a project to research? For example, argan oil and babassu oil are cultivated, and acorn oil to a lesser extent. You may care to investigate Sclerocarya birrea (S. caffra), aka the marula. BrainyBabe (talk) 12:21, 8 June 2009 (UTC)

We even have an article: Marula oil. BrainyBabe (talk) 12:28, 8 June 2009 (UTC)

I am looking for something available from supermarkets or health food shops. I do not know if the best oil for vegetarians would be the same as that for omnivores. Marula oil, at least, seems to have a lot of saturated fat in it. 89.242.81.255 (talk) 14:41, 8 June 2009 (UTC)

I don't think you can come up with a clear answer to this, since as with so many things when it comes to diet, there is still a fair amount of dispute. How can you come up with a 'best' when you aren't sure what's better? For example there is some evidence olive oil is good for you olive oil#nutrition but how good and why? As the phenolic compounds (and vitamins), which may be partially the cause of olive oil's alleged healthy properties, break down significantly in 12 months [3] the oil may be good in 2-3 months, not so good or at least no different if it's 12 months old. How significant the omega 3 to omega 6 ratio is another thing that remains unclear [4]. Another issue particularly since you talked about unusual oils. If these are organic or other speciality products, they may lack added antioxidants etc which despite the beliefs of those who think everything should be natural could be beneficial. Also, virgin olive oil and other oils with a low smoke point may not actually be a good oil for high temperature cooking (particularly anything over 200 degrees C) such as deep frying or perhaps traditional Asian style stir frying and high temperature roasting/baking due to the low smoke point [5]. Indeed this very high temperature cooking particularly deep frying is one area (IMHO) where the science is particularly unclear due to the complexity of what is formed, what breaks down, oxidises, etc [6] [7] [8]. Some of the beneficial compounds in olive oil may also decrease relatively rapidly for example [9]. And oils high in polyunsaturated fatty acids are prone to oxidation [10] [11] so it's possible an oil high in saturated fats may in fact be better then an oil high in PUFA for high temperature deep frying perhaps even if you only use the oil once. Remember that even if if the quantities formed are small, depending on how bad these are it could still be worse. This may be more of an issue in a restaurant etc but it does depend how often you reuse the oil (if at all), how long you deep fry for and temperatures. Home cooking is more likely to lack a temperature controlled deep fryer, filtering to remove crumbs and the deep fryer may be uncovered all of which are likely to be bad. And interesting enough, repeated heating and cooling of the oil may make things worse since the lower temperatures are apparently quite bad when it comes to oxidation [12]. Another factor, if you are referring to deep frying or any other case where you reuse the oil because of the oxidation, formation of potential carcinogens and other issues associated with repeated use, while you've said expense is not an issue, if using a more expensive oil means you will re-use it (more?), then it's potentially better for you to use the cheaper oil but refresh your oil more often. Of course since deep frying is not particularly healthy, it may just not do it, and things may not be so complicated. But then again, a perhaps interesting issue is the answer may even depend on the person. If you have a family background with a lot cases of cancer then you potentially should be more worried about carcinogens then if you have a family background with a lot of cases of coronary heart diease. One final thing that's worth remembering is where the money is coming from for research etc. Ge

You may wish to tryhempseed oil, which according to our article is extremely high in EFA's. However it is not suitable for high temperature frying. --TammyMoet (talk) 18:09, 8 June 2009 (UTC)

Sorry I should have added that I never fry food, except very ocasionaly vegetable stir-fry. The great majority of the oil would be eaten by drizzeling over pasta, salads, etc. And it was "BrainyBabe" who mentioned the exotic oils, not me. The choices I have in practice are between things like canola, olive, flax, or walnut oils, or combinations thereof. 78.149.238.54 (talk) 19:15, 8 June 2009 (UTC)

In that case, hempseed oil is the best bet. It tastes good too! --TammyMoet (talk) 08:15, 9 June 2009 (UTC)

I think your best bet is simply to vary your cooking oil. Butter, canola, olive, peanut are four common ones that spring to mind. Vranak (talk) 02:28, 11 June 2009 (UTC)

Does cooking linseed make its oil accessable?

The Omega3 oil found in linseed, also called flax seeds, is believed to be beneficial. While flax oil is available it is expensive and tastes bitter in my experience. Flaxseed is much cheaper and tastes OK. But I understand that if you eat it raw it just goes straight through you without any of the oils inside the seed being digested, due to the seed-coat protecting them. To be digested it should be ground before eating - which is inconvenient to do.

My question is, does boiling linseed for 15 or 20 minutes (by adding to pasta or rice etc) rupture the seed coat and make the oils inside available to be digested? 78.149.143.187 (talk) 12:08, 8 June 2009 (UTC)

Yes it ruptures the seed coat. Whether it affects the quality of the oil is another question, as something boiled is not coldpressed. One simple way of ingesting raw linseed oil is to take a spoonful of linseed and chew it for 30 seconds, then swallow with a little water. I do not find the taste bitter. No need for coffee or spice grinders, etc. BrainyBabe (talk) 12:24, 8 June 2009 (UTC)

How do you know it ruptures the seed-coat please? 89.242.81.255 (talk) 14:51, 8 June 2009 (UTC)

Because if you chew with normal vigour for 30 seconds, not bite and gulp in two seconds but masticate with your molars for half a minute, the linseed becomes a paste. Try it yourself. Spit it out and look. Poke it with your finger. Can you see any intact seeds? Some might call that original research, frowned on here, but I would call it the empirical method. "Suck it and see", as they say, or in this case, spit it and see. This method is simple, free, requires no equipment, and does not depend on another level of processing (to gelcap form) with its own issues of stability, etc. Also, he enzymes in saliva help the process of digestion begin correctly; see that article. BrainyBabe (talk) 18:00, 8 June 2009 (UTC)

Sorry, what I meant was, how do you know it ruptures the seed-coat after being boiled for 15-20 minutes? 78.149.238.54 (talk) 19:23, 8 June 2009 (UTC)

Ah, the problem of the unclear referent! Again, perform the experiment. Boil a handful of linseed in a pot of water. (Leave out the additional ingredients such as rice, so that you are observing a single variable.) After 20 minutes' boil, turn off the heat. Look at it. Let it cool down. Poke it with your finger. Do you see any intact seed hulls? You can perform the same experiment with a grinder (electric or manual) or a mortar and pestle, for comparative purposes. BrainyBabe (talk) 06:33, 9 June 2009 (UTC)

FWIW, you can also get cold-pressed lin/flaxseed oil in gelcap form. No taste at all there. --Kurt Shaped Box (talk) 12:31, 8 June 2009 (UTC)

What you want out of your linseed oil (most likely) are polyunsaturated fatty acids. Heating oil will turn those into ordinary fatty acids at temperatures ard. 195 F- 265 F. In addition flaxseed oil also has it's Smoke point at the upper end of that range. Labels like "cold extracted" or "cold-pressed" make a lot of sense for your salad oil. For cooking oil it's less useful and can even be bad. For frying you have to keep and eye on the smoke point and Trans fat. (P.S.: For more info see Nil's detailed post above.) 71.236.26.74 (talk) 16:52, 8 June 2009 (UTC)

"Heating oil will turn those into ordinary fatty acids at temperatures ard. 195 F- 265 F." That's very interesting - do you think that is the reason why the supermarket walnut oil does not mention Omega3 on the label, despite giving the % composition of other fat types, because its likely to have been obtained by hot-pressing and thus the Omega3 has been turned into a more ordinary fat?? And, by the way, I almost never fry food. 78.149.238.54 (talk) 19:29, 8 June 2009 (UTC)

More likely because it isn't a mandatory part of Nutrition facts labels. The second reason is that "high in omega 3" is just as efficient for marketing and they can't be sued if some curious consumer group does some testing and finds there's not as much as they thought. Then there is the fact that omega3s are mot all that stable and do deteriorate after a while. With walnut oil you also don't get mega market manufacturers who can shell out money for testing that isn't requited by law. With all types of oil there's things they don't test for like Benzopyrene, Benzyl butyl phthalate or Bis(2-ethylhexyl) phthalate. Cyanide is another ref-desk favorite. Then there's Tannin which is good or bad for you depending on how much (total) you consume and whom you ask. Buying organic or at health food stores won't make a difference there, because their products are just as likely to contain the above as the stuff off the supermarket shelf. In short not everything is all that healthy as the media would make it seem once you start looking under the hood. And there is such a thing as way too much information. Use what you think tastes good and try to eat a varied and mixed diet. (If you have to be a vegetarian remember to take B12 supplement. You won't get that from any plants and your body will run out of it at some point. 71.236.26.74 (talk) 22:34, 8 June 2009 (UTC)

You are confusing vegetarians with vegans. 89.240.49.146 (talk) 22:48, 8 June 2009 (UTC)

By heating these polyunsaturated fats, you can polymerize them and make a skin. This is how oil paint works, although that may use oxygen as well. The branched chain fatty acid is very hard for humans to metabolise. (we need an article on these) Graeme Bartlett (talk) 22:04, 8 June 2009 (UTC)

Death by hypodermic to the heart?

My roommate and I noticed that "The Rock" was showing again yesterday. This inspired the conversation that led to me posting the following. Towards the end of the movie Nicolas Cage's character injects an antidote he desperately needs directly into his heart. One of us believes that this scene is realistic, at least in principle, believing that if the antidote had the proper effect quickly enough and if he had a high enough pain threshold, then the character should be ambulatory rather soon and functioning at nearly his normal level. The other of us believes that the process of injecting anything directly into the heart would lead to death rather quickly, given the required injury to the heart itself. I tried Googling this issue without much luck. Any thoughts, anyone? —Preceding unsigned comment added by 68.37.188.33 (talk) 15:01, 8 June 2009 (UTC)

Hopefully someone with more medical knowledge will reply in detail. but intracardiac injections are real. I think they're only used in extreme emergencies because of the obvious danger to the heart itself and the coronary artery. APL (talk) 15:10, 8 June 2009 (UTC)

Am personally skeptical that it would work like that, but its a great movie anyway. 65.121.141.34 (talk) 16:37, 8 June 2009 (UTC)

As APL said, intracardiac injection is real, but it is only done by professionals. Nicholas cage was not paying much attention to where he jabbed that needle, and wasn't working to hard to keep it still while it was in. It seems to me that he would have microscopically shredded the tissues in his heart, and would have died. Plus, with that quick jab, he could be injecting the antidote into the muscle instead of he blood stream, which would kill him.Drew Smith What I've done 21:23, 8 June 2009 (UTC)

In old murder mysteries, people were killed by a hatpin jab to the heart. There are also medical reports of a hatpin thrust into the heart causing death. Seems much like a hypodermic jab. Edison (talk) 17:06, 9 June 2009 (UTC)

FYI nerve gas antidotes in autoinjectors are not injected in the heart. AFAIK they're always injected in a muscle (e.g. on the outside of the thigh). It's doesn't make for such a dramatic scene, though.Sjö (talk) 19:24, 9 June 2009 (UTC)

Pulp Fiction also had a scene with an intracardiac injection. Ugh!!!! 67.122.209.126 (talk) 13:28, 10 June 2009 (UTC)

Wikipedia's article is incorrect. Intracardiac injections are not "often used" in emergencies. Streptokinase is never given by this route. Axl ¤ [Talk] 18:37, 10 June 2009 (UTC)

This letter in The Lancet describes several case series. However the technique is not recommended by any resuscitation council, nor is it widely practiced. Axl ¤ [Talk] 18:46, 10 June 2009 (UTC)

I have fixed the article now. Axl ¤ [Talk] 18:54, 10 June 2009 (UTC)

To address the original question, it's been about 10 years since I saw the movie so I reviewed our article. The injection of atropine might work. Nerve agent antidotes usually contain pralidoxime as well as atropine. However I am unconvinced that intracardiac injection would have any benefit over intravenous injection, particularly in someone who is conscious (and therefore has circulating blood). Axl ¤ [Talk] 19:06, 10 June 2009 (UTC)

Before doctors were trained in CPR, and before electric defibrillators were common, doctors would inject adrenaline directly into the heart with a large bore needle several inches long. This was common from the 1920's to the 1960's. See this publication from thee 1920's. Note that they even mention cardiac massage(probably internal via incision) and artificial breathing. They do not claim the technique had a high success rate. [13] . See also [14]. Edison (talk) 21:19, 10 June 2009 (UTC)

heat into electricity

is there something maybe like a solar panel which can convert relatively large amounts of heat say a 10000 joules possessed by its surrounding air at a 1000 kelvin within a few seconds or even a few milliseconds? --harish (talk) 15:04, 8 June 2009 (UTC)

In principle this is just a heat engine - you pump a working fluid through a heat exchanger so it absorbs heat and maybe undergoes a phase change as well. Then you pass the hot fluid through a turbine which extracts work from it. While driving the turbine, the fluid expands and cools, so you pump it round again. In practice, 1000K is a high working temperature - for comparison, the superheated steam in a fossil fuel power plant has a maximum temperature of about 800K. So you probably need to borrow technology from the nuclear industry which is designed for higher working temperatures - maybe advanced gas-cooled reactor or very high temperature reactor technology. If you want to increase the power of your heat engine then you increase the surface area of your heat exchanger and pump fluid through at a faster rate. Gandalf61 (talk) 15:56, 8 June 2009 (UTC)

There is also the thermoelectric effect, which has some similarities to the photoelectric effect, but it is even less efficient in practice. Nimur (talk) 17:00, 8 June 2009 (UTC)

You really need a temperature DIFFERENCE in order to extract some energy. So if all of the machine's surrounding air is at 1000K, you've got to find a way of connecting the thing to something at much lower temperature. If you can do that then using some substance that is a gas at 1000K but a liquid at the lower temperature (water might be a reasonable choice) then water is flashed into steam by your 1000K heat source - is used to drive a turbine - the outlet from which is passed through cooling coils in the cold part of the system to condense back into water and continue around to the hot side again. A steam engine would work - so would a stirling engine...there are many possibilities...although it's hard to imagine anything that could do that within seconds. But if the entire machine is immersed in 1000K temperatures - there is nothing you can do to extract energy because that would violate the laws of thermodynamics. SteveBaker (talk) 18:40, 8 June 2009 (UTC)

It depends on exactly how you interpret the question - if it is one batch of hot stuff containing 10kJ being converted at once, then a few seconds is probably unrealistic, if it is a continuous process converting 10kJ per second, that is perfectly achievable. A typical fossil fuel power plant generates far more than 10kW. --Tango (talk) 18:56, 8 June 2009 (UTC)

The archetypal device that does this conversion is a Stirling engine. The max possible efficiency is determined by the Carnot cycle. 207.241.239.70 (talk) 19:25, 8 June 2009 (UTC)

How far do iron ore Lake Freighters travel from Minnesota or Northern Michigan, through the Soo Locks & past

the Mackinac Bridge then south on Lake Michigan to the steel mills in Gary, Indiana? —Preceding unsigned comment added by 72.204.36.33 (talk) 15:52, 8 June 2009 (UTC)

You should be able to figure this out yourself, I would think, by looking at a map and using its scale. You might use our articles about Duluth, Minnesota, Soo Locks, and Gary, Indiana to get an idea of where these places are. —Bkell (talk) 00:48, 9 June 2009 (UTC)

Using Google Earth, I get between 850 and 900 miles from Duluth to Gary. I tried to keep a short path but actual lake freighters have to stay in separated upbound and downbound shipping lanes so the the actual mileage may vary a little depending on the direction of travel. Rmhermen (talk) 02:58, 9 June 2009 (UTC)

porcupines

Are porcupine quills coated with venom or bacteria to cause infection? The article did not seem ot mention this one way or another. 65.121.141.34 (talk) 18:57, 8 June 2009 (UTC)

No, they are not. They are modified hairs - nothing more. The keratin makes them stiff. You may be thinking of hedgehogs. Many breeds of hedgehogs perform a ritual commonly called "anointing". They spread various chemicals (which may contain poisons) on their quills. Some people think that they do it increase the odds of infection in a predator. Others think it is just for camouflage. -- kainaw™ 19:03, 8 June 2009 (UTC)

I read in The Book of General Ignorance that the hedgehogs specifically chew poisonous frogs and suchlike and spread the resultant juice over their spines. Vimescarrot (talk) 21:37, 8 June 2009 (UTC)

Page 93. It also mentions the smells of many things can cause this behaviour, including shoes, cigar butts, furniture polish, creosote, coffee, boiled fish, face cream and distilled water. The animal world is a funny thing. Vimescarrot (talk) 21:39, 8 June 2009 (UTC)

Distilled water has a smell? (I mean, to any creature other than Shai-Hulud?) Tempshill (talk) 23:59, 8 June 2009 (UTC)

There are creatures far smaller than the mighty Sandworm that can nevertheless smell pure water quite well. Try "insect water receptors" in Google Scholar, and you will not lack the stuff to read for the evening :) --Dr Dima (talk) 01:13, 9 June 2009 (UTC)

I'd say The Book of General Ignorance is well titled. Richard Avery (talk) 06:56, 9 June 2009 (UTC)

While it true that porkies don't purposefully coat themselves in biological agents, they are not particularly "clean" animals. Part of thier mating ritual involves the male urinating on his partner. Yes a "natural" Golden Shower. They also "Den" for the winter and live with thier own faeces. Thier meat is parasite free and you can eat them raw (tastes awful though) but I wouldn't suggest licking one. 67.193.179.241 (talk) 10:35, 9 June 2009 (UTC) Rana sylvatica

Urine is not "dirty", and faeces (from a healthy animal) are not infectious (how would the porcupine survive the winter while "incubating" with it, if it were "dangerous"?). You may find this behaviour disgusting, but this does not make the animal unclean in any objective way. --TheMaster17 (talk) 12:40, 9 June 2009 (UTC)

Feces from healthy animal may still contain pathogens dangerous to other animals. APL (talk) 12:52, 9 June 2009 (UTC)

I read in The Book of General Ignorance that the hedgehogs specifically chew poisonous frogs.. Since Hedgehogs are not found in South America which is AFAIK the only place that has poison frogs: How the blazes can they chew them? (Help remedy my general ignorance:-)71.236.26.74 (talk) 18:13, 9 June 2009 (UTC)

They probably get them in pet stores.

Seriously, though. Poison Dart Frogs are not the only frogs that contain poisons. A bunch of them contain skin irritants that might be sufficient for the hedgehogs' purpose.

Or the book could have been completely wrong. Very possible. APL (talk) 18:34, 9 June 2009 (UTC)

If hedgehogs were to buy poison dart frogs in a pet store, they'd be in for a very bad surprise: captivity-bred poison dart frogs do not contain batrachotoxin! The poison dart frogs don't produce it, they get it from the beetles they eat; see the ref in batrachotoxin#Source. On the other hand, toad posion bufotenin is probably produced by the toad itself. --Dr Dima (talk) 20:50, 9 June 2009 (UTC)

Thought they might have mistaken a toad for a frog. Mistaking a frog for a toad isn't that unusual, but the other way round? Maybe the "General Ignorance" people should wait for the next edition of their own book ;-)71.236.26.74 (talk) 04:08, 10 June 2009 (UTC)

Poisonous frogs do not only occur in South America. Poison dart frogs are just one familly of frogs: their fame does not precude the existance of poisonous frogs on other continents, eg. Wikipedia has at least 15 articles on African poison frog species (see Mantella), so hedgehogs could indeed have population overlaps with poison frogs.YobMod 15:36, 10 June 2009 (UTC)

The book says toads, not frogs, although I was given to believe that there is no scientifically concrete definition distinguishing the two, so I call them all frogs. Does that help? Vimescarrot (talk) 18:07, 10 June 2009 (UTC)

Name of those polystyrene packing forms?

Hi - I need a generic name for those shaped polystyrene blocks you find in boxes of new equipment. Is there one, can anyone help?

Thanks,

Adambrowne666 (talk) 20:20, 8 June 2009 (UTC)

Do you mean Foam peanuts? Or do you mean Expanded polystyrene shaped blocks like the ones used to protect electronic equipment in its shipping box? --Dr Dima (talk) 20:33, 8 June 2009 (UTC)

The latter, please, if there is a simple name for them. Adambrowne666 (talk) 20:43, 8 June 2009 (UTC)

They are called "molded expanded polystyrene" or "foam shipping blocks". --Dr Dima (talk) 20:48, 8 June 2009 (UTC)

Foam shipping blocks - perfect! - thanks for the prompt replies, Dr Dima Adambrowne666 (talk) 20:51, 8 June 2009 (UTC)

"Rigid plastic foam blocks" is another term used. —Preceding unsigned comment added by 98.17.43.186 (talk) 11:33, 9 June 2009 (UTC)

Styrofoam Cuddlyable3 (talk) 19:57, 9 June 2009 (UTC)

No, not Styrofoam. That is a common mistake. Styrofoam is a patented brand of polystyrene foam, and can come in any shape (e.g. sheets or disposable coffee cups), and not necessarily as shipping blocks. In other words, not all styrofoam is molded into shipping blocks, and not all shipping blocks are made of styrofoam. --Dr Dima (talk) 20:30, 9 June 2009 (UTC)

All matter Black hole

If all of the matter in the Universe fell into a Black hole how big would the Black hole be? -- Taxa (talk) 20:45, 8 June 2009 (UTC)

As big as the whole universe. --Jayron32.talk.contribs 21:02, 8 June 2009 (UTC)

That depends on the size and density of the universe. The entire universe is probably infinite, so that would result in an infinitely big black whole. If you mean just the observable universe, then it still depends on the density. I believe if the density were exactly equal to the critical density, then the Schwarzschild radius of the black hole would be equal to the current radius of the observable universe (the event horizon would essentially be the cosmological horizon). This isn't a coincidence and, in that situation, you could sort of think of the universe as being inside a black hole (emphasis on "sort of"). I believe current estimates put the density quite a bit lower than that, though, so the black hole would be smaller than the current observable universe. --Tango (talk) 21:09, 8 June 2009 (UTC)

BenRg seems to think that the statement above is not quite correct as you can see here. Dauto (talk) 02:49, 9 June 2009 (UTC)

I've done the maths, BenRG is correct (well, I get 390 billion light years, rather than 250 billion, but close enough). I've done some further calculations and it isn't the volume of the observable universe that corresponds to a black hole of critical density, it's the Hubble volume (which is often mistaken for the volume of the observable universe, which probably explains my mistake - either I, or whoever wrote wherever I read it, got them mixed up). (Actually, my calculations came out with it being about 10% off the Hubble volume, I'm not sure where the discrepancy came from - different sources for the various constants, probably.) --Tango (talk) 03:15, 9 June 2009 (UTC)

Could what we consider the universe be inside a black hole, without us being aware of it? 89.242.125.32 (talk) 10:32, 9 June 2009 (UTC)

If we are not aware, how should we answer your question? ;-) Scientific answer: As no theory at the moment is able to describe the central singularity of a black hole (where the mass is located), there is no way we could answer this. But you are free to speculate that these "coincidences" have a deeper meaning, it is just not proveable at the moment. --TheMaster17 (talk) 12:45, 9 June 2009 (UTC)

A black hole doesn't necessarily have all the mass at the centre. It takes time for the mass entering the black hole to get to the centre. General relativity tells us it will always get there in finite (proper) time, but it will spend some time not being there. If the universe was going to undergo a big crunch, that might be consistent with it being in a black hole (that isn't expected to happen, though, the expansion is measured to be accelerating, not slowing). There is a multiverse theory that involves universes in black holes, see Lee_Smolin#Fecund_universes. --Tango (talk) 16:58, 9 June 2009 (UTC)

June 9

Strange photometer problems

I was doing an experiment on Malus' law using a photometer, which was basically a light detector hooked up to a power supply unit and an ammeter. I turned up the sensitivity using a knob on the power supply, and starting measuring light intensity for different angles between the polarizers. For every angle that's not 85-95 degrees, I measured a current of 65.0-65.2 mA. The light falling on the photometer was obviously changing in brightness, but the ammeter reading was not! So I had to repeat the whole experiment using the lowest possible sensitivity, which gave better results.

Then, out of curiosity, I turned off my optical bench's light source. There was still a reading on the ammeter. I covered the photometer with my thumb, and the reading did not change AT ALL! I would attribute that to electronic noise, except I walked over to somebody else's photometer, which was EXACTLY THE SAME, and the ammeter read 0.0 when I covered it.

What's the explanation for my strange observations? Why didn't the ammeter readings change when I turned up the sensitivity? Why the reading when I covered the photometer? --99.237.234.104 (talk) 00:28, 9 June 2009 (UTC)

Your photometer is broken. SpinningSpark 15:56, 9 June 2009 (UTC)

Good--I wanted to make sure I wasn't missing something obvious about the operation of photometers. --99.237.234.104 (talk) 18:57, 9 June 2009 (UTC)

Plant species identification??

Could anyone help in identifying the plants in these photos. Here is the first entire plant [15] and here is a closeup of the flowers [16], the second entire plant is here [17] with a closeup of the flowers [18] The plants are growing in New Hampshire. Thanks --Captain-tucker (talk) 00:51, 9 June 2009 (UTC)

Some species of Lilac maybe? Not sure. We had lilacs in our yard growing up in New Hampshire, so I know they grow there. --Jayron32.talk.contribs 03:53, 9 June 2009 (UTC)

I'd say they are both members os the genus Weigela. The first possibly being weigela florida , the second I cannot determine. Originally from Asia but now common garden shrubs widely grown in temperate regions. Richard Avery (talk) 06:49, 9 June 2009 (UTC)

I concur but it is most likely a cultivar, bred for colour, flower size, duration of bloom and shrub size.67.193.179.241 (talk) 10:44, 9 June 2009 (UTC) Rana sylvatica

dynamics

plane kinetics of rigid body —Preceding unsigned comment added by Msohaibg (talk • contribs) 01:19, 9 June 2009 (UTC)

Do you have a question? The reference desk is not a search-engine, it is staffed by human volunteers, and we can best help you if you phrase your question in full sentences rather than keyword queries. Nimur (talk) 01:49, 9 June 2009 (UTC)

Surprising BBC statement about type 2 diabetes

This article http://news.bbc.co.uk/1/hi/health/8085762.stm says (in the info box on the right) that type 2 diabetes is a "Long-term condition caused by too much glucose in the blood". The first impression this gave me was that they are saying that eating sugary foods will give you diabetes, but that's a myth, isn't it? My understanding is that 1) being obese may aggravate a genetic predisposition to get diabetes, and 2) we don't really know what causes it.

Perhaps they mean something else, such as "characterized by" or "aggravated by" rather than "caused by"?

I am thin, with a sweet tooth, a state of affairs I enjoy, hence my interest. 213.122.54.27 (talk) 01:51, 9 June 2009 (UTC)

As I understand it, diabetes causes too much glucose in the blood, not the other way around. That seems like a mistake by the BBC - their science reporting is better than many news sources, but it still leaves a lot to be desired. --Tango (talk) 03:17, 9 June 2009 (UTC)

Actually, Diabetes mellitus type 2 IS caused by extended periods of elevated blood glucose. It is called "insulin resistant diabetes" also; and is a very different disease than Diabetes mellitus type 1. Type 1 Diabetes is basically a disease where your pancreas shut down and stops making insulin at all. No insulin means that your body stops processing glucose correctly. Type 2 Diabetes means that your body makes insulin just fine, but that your metabolism is out-of-whack and your body "resists" the insulin, and your glucose remains elevated at unsafe levels. Basically, with Type 2 Diabetes, if you constantly maintain a high blood-glucose level, your body gets used to that, and stops trying to lower it using insulin. It is caused mainly by eating too much high-glycemic index foods. Unlike Type 1 diabetes, much Type 2 Diabetes is mostly behavioral disease (except in the elderly and in a few other cases) and in the early stages is reversable with lifestyle changes. The BBC report is 100% accurate in the statement about what causes Type 2 Diabetes. --Jayron32.talk.contribs 03:49, 9 June 2009 (UTC)

I'd disagree slightly about this description of Type 2 Diabetes... While it is generally true that the pancreas "makes insulin just fine" the problem is that the pancreas eventually can't make enough insulin to overcome the peripheral insulin resistance. The problem develops slowly and insidiously, probably as a result of BOTH environmental/behavioral (poor diet, lack of exercise) and genetic components leading to impaired glucose (blood sugar) homeostasis. I agree with Tango that the high blood sugar is really an end result of a system that's out of whack. In the very early stages of the disease (what some would call "pre-diabetes" but which is really just part of the ongoing process), you might not have abnormally elevated blood sugar but rather abnormally elevated insulin levels, as the body struggles to keep the blood sugar in the normal range. Eventually, the peripheral resistance to the action of insulin becomes so great that even with maximal insulin production the body doesn't respond enough to keep the blood sugar level normal. Elevated blood sugar is what the diagnosis of "diabetes" is based on. This is why, as Jayron says, the early stages of the disease are reversible, since if you can fix the diet and increase exercise you can reduce the resistance of the peripheral tissues (mostly adipose tissue) so that they respond to insulin normally. What the BBC might have meant is that type 2 diabetes is characterized by high blood sugar, which then has a whole host of secondary effects (peripheral neuropathy, renal failure, coronary artery disease) that collectively make up the major morbidity of the condition. --- Medical geneticist (talk) 13:44, 9 June 2009 (UTC)

Sorry 213 but BBC is right, as Jayron pointed out. You should watch your sugar intake even if you are thin as a broom. Dauto (talk) 04:18, 9 June 2009 (UTC)

You need to be more specific. What exactly do you mean by "watch your sugar intake"? How much is too much? It would be a bit reactionary to tell someone that they can't enjoy a bite of chocolate or a cookie every so often. That is most certainly NOT going to "cause" diabetes. --- Medical geneticist (talk) 13:57, 9 June 2009 (UTC)

I think watch you sugar intake, while not that specific, is good enough in simple terms. If the OP wants to know more, they can ask or research themselves. I don't think it's misleading as it's not as if Dauto said you should never intake sugar or should cut your sugar intake down to zero. You can 'watch' you sugar intake fine even if you enjoy a bite of chocolate or cookie every so often. Similarly, it is fine general advice to watch you sodium intake or watch you intake of fats and oils. It doesn't mean you need to cut them completely out of your diet or that you can never eat a Pavlova or bag of chips Nil Einne (talk) 19:11, 9 June 2009 (UTC)

It IS misleading. Everyone has a different basal metabolic rate and different levels of physical activity. Some will do better with a low-fat diet, others should follow a low-carb diet. There isn't really a one-size-fits-all recommendation other than to maintain a healthy body weight and try to exercise regularly. The OP may be perfectly fine with whatever "sugar intake" s/he maintains. It isn't our place to give advice or opinions, just references. If the OP wants advice s/he should go to a nutritionist. (I'm not trying to invoke the medical advice restriction here, just pointing out that advice is complicated and "watch your sugar intake" is too vague and may not apply to everyone.) --- Medical geneticist (talk)

Calm down there. My statement was indeed prety vague, but not by accident. I gave a vague statement because I didn't know all the necessary information in order to give a less vague statement but I still wanted to convey the idea that just because someone is thin doesn't necessarily mean they can eat whatever amount of sugar they fill like without any health consequences. I think my statement was the best possible under the circunstances. I stand by what I said enougth to say it again. People should watch their sugar intake even if they are thin as a broom. Dauto (talk) 03:51, 10 June 2009 (UTC)

I'm not trying to have a cow, just asking for references... enough said. --- Medical geneticist (talk) 23:40, 10 June 2009 (UTC)

The high blood sugar in Type 2 diabetes is a symptom or result rather than a cause. The BBC is misleading. If a non-diabetic, who does not have impaired glucose tolerance eats some big sugar laden treat, it does not result in prolonged high blood sugar, thanks to the adequate release of insulin and the normal tissue response to it. See Glucose tolerance test. In a normal patient, even 75 g of sugar does not produce high blood sugar(over 7.8mmol or 140 mg/dl) 2 hours later. Edison (talk) 17:02, 9 June 2009 (UTC)

However, people who maintain high blood sugar levels over long periods of time, for example, have demonstrably higher incidences of Type 2 Diabetes. There is a correlation between the onset of Type 2 Diabetes and lifestyle... --Jayron32.talk.contribs 02:50, 10 June 2009 (UTC)

Thunder does not cause lightning. Correlation is not causation. Edison (talk) 05:22, 10 June 2009 (UTC)

The BBC soundbites are misleading at best. Medical geneticist and Edison give good answers. Dauto's comments are less helpful. Axl ¤ [Talk] 19:25, 10 June 2009 (UTC)

Reduction Potential in Pourbaix Diagrams

Hello. I am wondering how to calculate the reduction potential in Porubaix Diagrams. For example, the reduction potential between Fe3+ and FeO4 -2 in thisdiagram? Please! I have looked in my textbook, lecture notes, and online and I find nothing, and my exam is tomorrow! Thanks =) P.S The answer is NOT 0.4. P.PS Link to the diagram http:/upwiki/wikipedia/commons/thumb/8/85/Pourbaix_Diagram_of_Iron.svg/605px-Pourbaix_Diagram_of_Iron.svg.png Cuban Cigar (talk) 10:10, 9 June 2009 (UTC)

It's not that hard. You don't give enough information to find the answer; but you also need to know the pH of the solution. At a given pH, draw a vertical line on the graph. The cell potential needed to make the transition between two states is where this vertical line crosses a region border on the graph. For example, at pH=2, the cell potential of the Fe²⁺ -> Fe reduction is E0 = ~-0.6 while the Fe³⁺ -> Fe²⁺ has E0 = ~0.79 and the FeO4^2- -> Fe³⁺ has E0 = ~1.75. The other forms in the chart are not stable at pH = 2 and could not exist. At other pH levels, there would be different values. --Jayron32.talk.contribs 12:13, 9 June 2009 (UTC)

Oh yes I forgot to include: the ph is 0. I'm still a bit confused though...is there a diagram that would explain it? I think a diagram would make it much more clear =)114.77.68.9 (talk) 12:51, 9 June 2009 (UTC)

OK, so if the pH=0 then use the vertical line at pH equals 0, and the reduction potential of each of the transitions is listed on the vertical axis. --Jayron32.talk.contribs 02:47, 10 June 2009 (UTC)

Ah ok thanks heaps =)114.77.68.9 (talk) 07:41, 11 June 2009 (UTC)

Look-and-say sequence (now asked at WP:RDMA)

This is maybe rather a question concerning language than science: When Conway introduced this sequence in his 1986 article, he directly explained the rule and stated: "I note that more usually one is given a sequence such as [example] and asked to guess the generating rule or next term." Can we conclude from that whether he invented the system himself or not? If not - is there a way to ask him (there is no public contact address)? --KnightMove (talk) 11:33, 9 June 2009 (UTC)

Are you asking whether or not Conway invented the "Look and say sequence" (which is a specific sequence of numbers that obeys certain rules) OR are you asking if Conway invented the "Here's a series of numbers, identify the next number in the series" type of question? Because the former may be true, but the latter is definately not; it has been part of IQ tests such as WAIS since well before Conway was a working as a mathematician and likely before he was born. See Integer sequence for some examples. --Jayron32.talk.contribs 12:04, 9 June 2009 (UTC)

Also, you are likely to find better answers at the Mathematics Ref Desk. --Jayron32.talk.contribs 12:06, 9 June 2009 (UTC)

Thx for the hint. I was asking for the former, but you may start with any other sequence; Conway himself gave the example 55555 ; 55 ; 25 ; 1215 ; 11121115. --KnightMove (talk) 12:23, 9 June 2009 (UTC)

In that case, if you have access to the Journal he published the original 1986 paper in you should read that paper. I would guess that if he were basing his research on earlier work, he would clearly have listed his references which contained the more seminal work. The other option is that the concept of a "Look and say" sequence is old enough to have been lost in the mists of time; and as such does not have an original discoverer. But either way your best chance is to find his original paper and look there. --Jayron32.talk.contribs 12:32, 9 June 2009 (UTC)

These sorts of tests always infuriated me. As anyone who has ever studied polynomial interpolation can attest to, providing a subsequence of n numbers defines a countably infinite number of valid polynomials - so asking "what is the next number in this sequence" is making a huge number of unstated assumptions about the behavior of the overall sequence. Most commonly, a requirement is that all members of the sequence must be integers; but even then, with sufficient mathematical maneuvering, a countably infinite number of valid polynomials will still always fit. And if you're willing to use any other method of sequence generation (besides integer-sampled polynomials), you have an uncountably infinite set of sequences. Bluntly put, the people who ask these sorts of questions profess little to no knowledge of higher mathematics - and they intend to test somebody else's "IQ" ? Nimur (talk) 17:05, 9 June 2009 (UTC)

I've heard this sentiment before, but it seems tantamount to saying that science is impossible. The sequence is raw data and the answer you give is a theory, and some theories are better than others. I think almost anyone would agree that the sequence 55555, 55, 25, 1215, 11121115 is better explained by the look-and-say rule than by 5/6 (66666 − 3473104x + 6210289x² − 3362372x³ + 558587x⁴). The latter is clearly not an explanation at all since it's longer than the data. The look-and-say rule I think is shorter than this data in whatever encoding system people use when judging the value of scientific theories. -- BenRG (talk) 18:55, 9 June 2009 (UTC)

There is another factor in science, though - the mechanism. A simple law is of limited use if you don't have a sensible theory regarding the mechanism behind that law. You can use the law to make predictions about precisely what the law is about, but nothing else, to come up with predictions about new things requires a mechanism. With these kinds of number sequences there is never any kind of mechanism, it is all completely arbitrary. --Tango (talk) 18:59, 9 June 2009 (UTC)

What do you mean by mechanism? Is that just another word for a model? Is that extra step always necessary or even useful? What is the mechanism behind quantum mechanics? Does that last question even make sense? Dauto (talk) 21:24, 9 June 2009 (UTC)

The mechanism behind something is what makes it happen. A scientific law is just a formula, for example Ohm's law is V=IR, the mechanism has to do with electrons bouncing around. Kepler's laws of planetary motion are just simple rules with no explanation, the mechanism behind them is the inverse square law of (Newtonian) gravity (Kepler didn't know that, he derived the laws empirically, and they were still useful before Newton explained them, but once you understand the mechanism behind them you can improve upon them - for example, you can introduce new factors to get more precise results). These examples aren't very good... The concept is easier to understand in something like biology. We may have results that say a particular drug increases someone's chances of surviving a disease by 10%, which is all well and good, but if we want to improve on that it is useful to know the mechanism by which the drug works - for example, it might inhibit a particular enzyme. If somebody makes a scientific claim without giving a plausible mechanism, you would be more sceptical of their results. So, if the sequence above arose in nature and someone wanted to predict what would come next, they would probably go with the polynomial extrapolation, rather than the look-and-say rule, since it is easier to think of a plausible mechanism for it. I can't think of any way natural could follow the look-and-say rule, but polynomials come up in all sorts of ways. --Tango (talk) 23:15, 9 June 2009 (UTC)

I thought the Kepler's laws vs the inverse square law was a good choice for what you are saying. Kepler's laws can only be used to describe the very planetary motions that Kepler used to obtain the laws to begin with. But once you understand that they are a consequence of Newton's gravitation you can than use that to describe other motions such as precessions and all sorts of wobbles, etc. The problem with that is that Newton's inverse square law isn't a mechanism at all. It's just another simple law described by a simple mathematical formula and would therefore need its own explanatory mechanism according to your statement. I think your statement was too general. Sometimes a working model is better than a mechanism. Coming back to the original question, clearly, as BenRG said, the look and say is a better model than the polynomial extrapolation (which doesn't explain anything). I would be very wary of any model rooted on a polynomial of fourth degree extrapolation unless, as you said, there was a good mechanism behind that polynomial. Dauto (talk) 05:03, 10 June 2009 (UTC)

The fact that gravity isn't really a mechanism is why it was a bad example - I think most examples in physics end up being long chains of theories upon theories. Biology is the same, of course, but people are more willing to stop at a reasonable point and just accept it as fact. Mechanisms certainly aren't always required - Kepler didn't have one but that didn't make him doubt his results. They are nice to have, though, and give us a good idea of how much confidence to have in a claim for which we don't have particularly good empirical evidence (and a sequence of 5 numbers isn't very good empirical evidence for anything). --Tango (talk) 05:18, 10 June 2009 (UTC)

Dead arm while sleeping

I'm not sure where to find info on this, and in fact, I'm not even sure how to really look for it (is there no different term for limb numbness [i.e. that which isn't caused by some sort of condition] than parasthesia?), but I've always been rather prone to sleeping on my arm and then waking up finding it numb; as far as I can remember it would happen every few weeks or so, definitely nothing of concern. Lately it's been interrupting my sleep more though, yesterday I woke up three times! I sleep on my front (I can't sleep on my back -- so much so that I often turn on my back in the morning to prevent myself from falling back asleep!) and I'm pretty tall and skinny, which I think might make it easier for me to get caught up in my arms while I'm asleep, but I was wondering if anybody had any suggestions for how I stop my arm from getting squashed so much? I alternate between sides (front-ish orientation) and sleeping on my front, but my arm always seems to be able to find a position to get caught in! Thanks! 210.254.117.186 (talk) 12:17, 9 June 2009 (UTC)

Not that I have any recommendations, but the medical term for "limbs falling asleep", or rather going numb due to laying on them is called Paresthesia and is usually caused by compressing a nerve in the limb. The compressed nerve stops sending signals to the Central Nervous System, so your brain basically changes the way it interprets the signals from that limb. When the compression stops, the nerve begins to transmit signals to the CNS normally, but the CNS takes some time to "catch up" and re-adjust its processing to correctly interpret the signal. This "readjustment" period is what causes the numbness and "Pins and needles" feeling as the limb comes "back on line". Its exactly like walking from a dark room to a light room; your body does not adjust instantly so there is temporary (but harmless) discomfort during the adjustment phase. --Jayron32.talk.contribs 12:28, 9 June 2009 (UTC)

Anything that is an ongoing problem with sleeping is worth talking to a doctor about. I don't mean to sound alarmist, but there is always a chance that what's changed is something you aren't thinking of. Of course the Reference Desk does not allow medical advice, let alone speculation. --Anonymous, 12:47 UTC, June 9, 2009.

Assuming it is just a quirk of your nature and nothing medical a body pillow or memory foam mattress topper might be worth considering. But do check with your doc. 71.236.26.74 (talk) 14:33, 9 June 2009 (UTC)

Perhaps sleep with your arm under the pillow? ~AH1^(TCU) 01:40, 11 June 2009 (UTC)

Logic Gate Amplifiers.

File:DigitalInverterVTC.png

I built that on silicon in 2005, measured it, and it's one of my first contributions to Wikipedia! Nimur (talk) 17:08, 9 June 2009 (UTC)

1. Where can I find articles and analysis on using NOT gates in their linear region as amplifiers?(TTL, CMOS, LS TTL, high speed CMOS)
2. Also, up to what frequency can they be used?
3. I want to see if I can use them to amplify signals in 10-50MHz range. —Preceding unsigned comment added by 59.93.15.239 (talk) 15:03, 9 June 2009 (UTC)

That's a blast from the past, haven't seen that trick used in a long while. Not sure where to find articles, don't think I've seen one since the internet started. Basically you need lots of negative feedback to keep it in the linear region. Probably won't work with most modern gates because they are heavily buffered to keep the device out of the linear region. It worked with older unbuffered CMOS because basically, you only had one transistor stage in there and it was an amplifier, just not being used as one. The frequency bandwidth it will work on depends on the speed of the device, rough rule of thumb, halve the maximum bit rate and call it Hz. SpinningSpark 15:23, 9 June 2009 (UTC)

You can check the Inverter (logic gate) article - and take a look at that fine image of a voltage transfer curve for a NOT gate operating in its linear region! (Un)fortunately, most commercial inverters designed for CMOS or TTL logic have much much higher gain, so you'll have to carefully select your operating point. Why wouldn't you just use a high-gain amplifier, which is designed for tunable bias points? Take a look at the datasheet of any amplifier you are interested in using. 50MHz is not at all unreasonable, but you're really going to have to watch your operating point, because unless you are right on the dead-center of the linear region, you'll likely trip the circuit to high- or low- output only, (after all, they are intended for digital circuits). Nimur (talk) 17:08, 9 June 2009 (UTC)

Also, read through the Application Notes for the 7404 inverter at Texas Instruments, especially Designing with Logic and Input and Output Characteristics of Digital Integrated Circuits (data). You may find the App Notes discussions a bit more high-level than the data-sheet (which is, of course, just the specifications). Nimur (talk) 17:48, 9 June 2009 (UTC)

A resistor connected from output to input of the NOT gate (inverter) suffices to bias it in its linear region. If the resistance is low enough for the voltage drop due to gate input current to be insignificant, the working point can be found simply by drawing a line from origin (0,0) to (2,2) on the transfer curve shown. The working point is where the line crosses the curve. Connect the input signal to the gate input via a capacitor (ac-only amplifier) or a resistor (dc and ac amplifier). The inverter shown has only about 2x voltage gain which limits its usefulness as an amplifier. Actual high gain CMOS and TTL inverters are easy to use this self-biased way and can provide the bandwidth you want. However you cannot use Schmitt trigger inverters that have no linear region. A useful application is to amplify a weak ac signal to a full logic swing. A clock oscillator can be constructed from one or two inverters. Cuddlyable3 (talk) 19:46, 9 June 2009 (UTC)

The reason I asked is that on micro chip's site, in one of the app notes on power line communication, there is a 2stage amp using not gates. and my friend who is building that schematic for his project wanted to know how they designed values of those biasing resistors. 59.93.26.185 (talk) 08:23, 10 June 2009 (UTC)

Biased in its linear region the NOT gate is like an operational amplifier that has only its - input accessible. The same rules apply for defining gain by external components as for an opamp e.g. A 1k ohm feedback resistor and a 330 ohm input resistor define an amplifier of gain -3. Higher resistor values can be used with CMOS inverters that have small input current. Cuddlyable3 (talk) 19:12, 12 June 2009 (UTC)

I read the links @ the bottom. One reason I don't want to use rf amp chip is that most are surface mount and I cant solder them for my home projects and that they are harder to obtain in nearby shops. Thanks for the links. 59.93.26.185 (talk) 08:23, 10 June 2009 (UTC)

How about a simple operational amplifier? 741 amp chips still come in DIP package. When you do you search, most manufacturers and distributors allow you to restrict to a particular package type - you probably want DIP for basic hobbyist stuff (it will fit into perforated board and prototyping kits, etc). Nimur (talk) 14:04, 10 June 2009 (UTC)

Help Me Preparing My Work

There is going to be held a competition in our medical school in which students have been asked to present their research works about any scientific topic. I am going to present my work about the relation that exists between structure of an object and the function realized by it, especially focused on human body going from atomic level to organism as a whole. I need answers of the questions like , if the protons are inside the nucleus then what importance it may have on the functioning of an atom and its role in biological systems, if glycogen has a cyclic structure then how it is important in its role in human body, if renal cortex has a vertical arterial system then why it is so, the functional importance of the cells participating in the structure of brain. Can someone guide me knowing answers of such questions and getting interesting information , Something precise PLZ. I searched on Pub Med but there is cluster of scattered things. Some web addresses, some opinions, some guidelines. Thanks —Preceding unsigned comment added by 200.55.135.211 (talk) 16:35, 9 June 2009 (UTC)

The topic "structure and function" sounds far too general for a presentation of less than encyclopedic length. For a med school presentation, your idea on the structure of glycogen, or the value of the arrangement of arterial structure of the kidneys are possibilities, but the function of the proton in the atom or the "function of cells in the brain" sound far too general. Maybe start with an interesting new development in one of these areas and make that the conclusion of your presentation. Edison (talk) 16:55, 9 June 2009 (UTC)

Are you looking to do a "report" on a topic (i.e. summarize a body of work) or are you really planning to prepare an independent "research project" where you identify a question and study it in a laboratory setting? It sounds like what you want to do is summarize what others have discovered about "structure and function" which, as pointed out by Edison, is far too broad-reaching a question to be summarized in a precise fashion. Perhaps you should pick an area to focus on. It doesn't matter what RefDesk contributors think is interesting, you should pick something that is deeply interesting to YOU so that you'll be motivated to do the best job. There are so many possible examples that it doesn't even make sense for us to suggest articles or books for you to start from. I'm sure you'll get better answers here (not to mention a better final result) if you focus your question first. By the way, glycogen is a branched polymer (of glucose molecules), not a cyclic structure. Glucose is cyclic. --- Medical geneticist (talk) 17:29, 9 June 2009 (UTC)

Careful with micro- vs macromolecular description: flycogen's structure discussion says it's a branched structure of glucose units, each of which is cyclic. DMacks (talk) 17:43, 9 June 2009 (UTC)

Isn't that what I said? Clarification added. BTW, I'd like to see what "flycogen looks like!  ;-) --- Medical geneticist (talk) 17:51, 9 June 2009 (UTC)

d'oh. google/googlescholar find a bunch of that typo in the literature too:) DMacks (talk) 18:04, 9 June 2009 (UTC)

Internet over radio (not internet radio)

Is it possible to connect everything through radio? Would it be much slower than fiber optic? Is it in use somewhere in the world? --Mr.K. (talk) 16:52, 9 June 2009 (UTC)

Many people access the internet via a wireless (radio) connection. At what point do you contemplate having it work by radio? There might be bandwidth problems if every home communicated with every other home at will by radio connected internet. It could be done via cellphone-like technology, but the charges might be extremely high. Edison (talk) 16:58, 9 June 2009 (UTC)

Take a look at packet radio, which was a precursor to the modern 802.11 family of wireless protocalls. It is indeed possible to connect things by radio, but open air is a shared-channel by "unknown number" of users (unlike a wire, which is shared by N users, a maximum number pre-determined by the engineering specifications of the protocol). As per my earlier discussion about air-to-ground radio, available bandwidth is proportional to operating frequency (by physical limitation); and unfortunately, on earth (with atmosphere), higher frequencies have limited range. This means you need a hierarchical, hub-based "repeater" system - with all of the associated troubles of an untrusted network and a peer-to-peer network routing protocol (at the network switching level, not at the software-level as a modern file-sharing program uses "p2p"). In short, if you could control every radio in the world, and force it to comply with your protocol, then "wireless-only" internet would probably be a very efficient, low-infrastructure-cost alternative, and it would certainly solve the "last mile problem" that plagues wire-based network infrastructures. But, radio is a shared channel, and despite government regulations, you can't assure that your signals won't be interfered with by other users - so it's best to keep wireless transmissions short-range, high-bandwidth, and use lots of error-checking along the way. Nimur (talk) 17:23, 9 June 2009 (UTC)

endangered animals

OK, I have a question on how the endangered labels work. An example using data from our articles shows that the black rhino is critically endangered (the highest level of scarcity) with 3,600 animals left. The White Rhino is only near threatened (1 level lower then common) and it has 17,500 animals left. That does not seem like a very big difference. Can someone explain how this works? 65.121.141.34 (talk) 19:11, 9 June 2009 (UTC)

It may be worth reading IUCN_Red_List#Categories and look into the rules. I think this is the standard framework used for grouping species in terms of their endangered. ny156uk (talk) 20:57, 9 June 2009 (UTC)

It doesn't really explain why two very similar animals would have such a different label for a relatively small difference in numbers. 65.121.141.34 (talk) 18:47, 10 June 2009 (UTC)

There isn't a relatively small difference in numbers....there are nearly 5 times as many of one as there are of the other. Alaphent (talk) 10:44, 11 June 2009 (UTC)

If you look at the links from there Near Threatened (white rhino) and Critically endangered species (black rhino) you'll see that to be considered critically endangered it needs to be "species numbers have decreased, or will decrease, by 80% within three generations." From here it is logically quite easy to see that one species is considered in greater danger because of either it's fast-reduction in numbers, or an anticipated fast reduction in numbers. Near threatened is not quite as 'bad' a scenario. Volumes alone is not really a good comparison factor since the 'normal' population of animal will be very different depending on its size, location and habitat. ny156uk (talk) 21:19, 10 June 2009 (UTC)

Speed of light...

I was under the impression that it is impossible for anything with mass to move at the speed of light. Yet earlier when I asked about an object falling for infinity long (imagine it falling in a vacuum or something close to a vacuum such that its terminal velocity is greater then c), someone told me the relativistic mass would increase. Shouldn't the relativistic mass go to zero as v goes to c? —Preceding unsigned comment added by 24.171.145.63 (talk) 21:44, 9 June 2009 (UTC)

The rest mass of something traveling at c must be zero. The relativistic mass of something traveling at c need not be zero. However, to examine the condition you ask about, the mass (rest or relativistic) of something approaching c can be anything. — Lomn 22:02, 9 June 2009 (UTC)

(edit conflict) Interesting question. As I understand it, no object with mass can go faster than the speed of light, even if it is falling (and therefore accelerating) an infinitely long ways. Your friend is right that the object's mass would increase—as the object's velocity approaches c, some of the energy that is added to it with the intent of speeding it up is instead converted into mass through E=mc². Interestingly enough, this would only increase the gravitational pull in your scenario, compounding the effect...I'm no physicist, but I imagine this scenario would violate a law of thermodynamics because energy is being constantly created. Also, gravitational pull decreases exponentially as you move farther out, so there would theoretically be no gravitational force making the object fall if the larger object is infinitely far away. Just tossing ideas out there—hopefully I'm correct.  :) —Pie4all88 ^{T C} 22:06, 9 June 2009 (UTC)

Definitely not. As an object speeds up, its relativistic mass increases, making it harder for it to go faster and impossible for it to reach the speed of light. You may be thinking along the lines that as matter approaches c, it becomes more like light, but that's not the case. Clarityfiend (talk) 22:26, 9 June 2009 (UTC)

It's an odd thing. The relativistic mass increase is a factor that gets larger and larger as you approach the speed of light - and AT the speed of light, it's infinite. So an object that has any mass at all at 'normal' speeds would have infinite mass at the speed of light. That's why things with mass can't go that fast - to give it infinite mass requires infinite energy. But for photons - which conveniently have a zero rest-mass - their mass at the speed of light is (in a sense) zero times infinity...which could be any number you could imagine. Hence they can have non-zero relativistic mass - but if they were to slow down by even the tiniest amount - their mass would drop to zero. SteveBaker (talk) 03:10, 10 June 2009 (UTC)

Say a photon is traveling away from a black hole that it neared. The light is moving slower than c, correct? Does this mean, then, that there is a fundemental difference between light that is traveling in a vacuum without gravitational interference and light that is still in a vacuum but not moving at its maximum speed? Would the photoelectric effect still work if light slowed down at all? Or do I have this all wrong? —Pie4all88 ^{T C} 16:58, 10 June 2009 (UTC)

No, light always travels at c. Light moving away from a black hole is redshifted, so it loses energy but due to having a lower frequency, rather than a lower speed. --Tango (talk) 17:26, 10 June 2009 (UTC)

Ah, thanks for the link! I was under the impression that redshift only occurred with acceleration or the expansion of the universe...but I suppose that an object escaping a large gravitational field is decelerating, so this would make sense. One more thing, though—say a friend of yours falls into a black hole. I remember being told that an outside observer would never actually see him reach the event horizon; he would seem to get closer and closer while gradually fading away (I imagine he would also get blueshifted). Why would he fade away if light always travels at c? I assumed that the light reflecting off of him and barely escaping from falling into the event horizon would be moving exponentially more slowly toward the observer, which is why you would see him fade away rather than fall in. Can someone please enlighten me as to where I am going wrong? —Pie4all88 ^{T C} 18:35, 10 June 2009 (UTC)

You're going wrong at the same point you went wrong before. the light doesn't move more slowly toward the observer. It redshifts, and that's what's meant by fading away. Dauto (talk) 18:42, 10 June 2009 (UTC)

Ah, I may understand what you guys are saying now. So the person wouldn't "fade away", per se; they would seem more and more redshifted as they fell in and sometime before entering the event horizon, the light would stop being in the visible spectrum. This would happen in real time, then (er, as instantaneous as it can be given c), right, rather than residual light slowly fading away? —Pie4all88 ^{T C} 20:04, 10 June 2009 (UTC)

Getting closer, but still not quite there yet. As the person approaches the black hole's horizon any light being emitted would suffer an ever increasing redshift that would tend to infinite. That has two important consequences. First, the light would not only shift until it was no longer visible, but would actually shift until its frequency would go to zero and therefore become unobservable, hence we say the person would fade away. Second, redshift means a decrease in frequency which is the same as a increase in time periods. So if the person is sending a beep every second (as measured by their watch) the interval between subsequent beeps would appear to get bigger and bigger (as measured by the outside observer) due to redshift. If the last beep happens just as the in-falling person crosses the horizon that last interval would suffer an infinite redshift which means that the outside observer would have to wait an infinite amount of time before he could observe that last beep. In other words, the in-falling person would appear to slow down as they approached the horizon. Dauto (talk) 03:35, 11 June 2009 (UTC)

Limit to Acceleration?

Is there a limit to how fast something can accelerate? I imagine there would be, based on the inertia of an electron. —Pie4all88 ^{T C} 22:16, 9 June 2009 (UTC)

Do you mean a theoretical limit like the fact that speed is limited to the speed of light? I don't believe so. If you apply an arbitrarily large force, you'll get an arbitrarily large acceleration (it isn't proportional once you take relativity into account, of course). --Tango (talk) 22:31, 9 June 2009 (UTC)

The limits are essentially the amount of energy you can apply (which in theory is something like the mass of the visible universe times the speed of light squared!) and the structural limits of whatever it is that you're accelerating. Of course this insane acceleration could not be sustained for very long because relativistic effects will increase the effective mass of the thing you're accelerating...and thereby reduce the acceleration that your energy budget allows you to apply. But I can't think of any 'hard' limits. SteveBaker (talk) 03:01, 10 June 2009 (UTC)

(Really? Two comments: First, I think that's a hand-wavey and probably totally incorrect estimate of the total energy in the universe. Second, energy is not related to acceleration - it is related to velocity. In the same way that you need a time-derivative of velocity to get an acceleration, you need a time-derivative of energy to get the power necessary for that acceleration. When's the last time you measured your Mini Cooper's "number of joules consumed for 0 to 60 in 2.8 seconds"? You need a horsepower and a torque and a mass to estimate the acceleration. Hypothetically, if you could harness the entire energy of the universe, there's still not any necessary inherent constraint on how quickly you can transfer that into a billiard-ball. I'm thinking that maybe a better estimate of maximum acceleration is something like, Speed of Light over Planck Time (asymptotic limit), but I'm just pulling this out of my own head. I've never heard of a maximum acceleration limit in any physics class I ever took.) Nimur (talk) 14:11, 10 June 2009 (UTC)

Following is a statement from the book "Motion Mountain" (The Adventure of Physics) by Christoph Schiller

We will discover that, just as special relativity is based on a maximum speed c,

general relativity is based on a maximum force (c**4)/4G or on a maximum power (c**5)/4G.

121.242.23.197 (talk) 07:05, 10 June 2009 (UTC)Vineet Chaitanya

That's his own work, rather than an accepted scientific result. I'm just reading his paper on the subject now, but it is very recent (2003) so I'm not sure the scientific community has had sufficient time to review it. --Tango (talk) 16:59, 10 June 2009 (UTC)

Upon further investigation, that paper doesn't even seem to have been published in a peer-review journal. That is a red flag to me... --Tango (talk) 17:10, 10 June 2009 (UTC)

Yes, that's very suspecious. Interestingly my estimate below gives a result in the same ball park of that paper, but I see that more as a practical limit than as a hard limit. Dauto (talk) 17:41, 10 June 2009 (UTC)

I never heard of such a limit. I'm inclined to agree with Nimur. Another interesting point of view is that the maximum acceleration is the one imposed on a couple of eletrons placed at a planck distance from each other $a={\frac {e^{2}}{4\pi \epsilon _{0}l_{P}^{2}m_{e}}}$ Both of these estimates (Nimur's and mine) give absurdly high accelerations. Dauto (talk) 17:00, 10 June 2009 (UTC)

Very interesting discussion, guys! Thanks for all the responses so far. And yep, Tango, that was my line of thinking. I suppose there's no theoretically "largest" position, though, so you can't say that since velocity has a maximum value, acceleration does as well. At least, not without a major development in physics.  :) —Pie4all88 ^{T C} 17:15, 10 June 2009 (UTC)

Well, I partially take that back. I suppose you could consider the edge of the observable universe to be the "maximum" distance away from a central point. So it's be more like a radius. It doesn't seem like the universe itself has edges, so you can't use that value. Hmm. —Pie4all88 ^{T C} 17:20, 10 June 2009 (UTC)

Special relativity does put a limit on acceleration of an extended object (something with a size). If you pull on one end of an object of length L with a constant acceleration exceeding c²/L, it will break no matter what its composition. The reason is that uniform acceleration describes a hyperbola in spacetime (see hyperbolic motion), and anything beyond the asymptotes (which cross at a distance of c²/a) can't possibly catch up with you without exceeding c.

There is a Planck acceleration of c/t_P ≈ 10⁵² m/s² at which one might expect classical ideas about acceleration to break down. The Planck force c⁴/G and the Planck power c⁵/G are unusual in that they don't depend on h, so you might expect them to have a meaning in non-quantum general relativity. Whether they're maximums (as Motion Mountain claims) I don't know, but they might be. Acceleration is inversely proportional to radius of curvature in spacetime, and odd things might happen when your radius of curvature becomes smaller than your Schwarzschild radius, that is, when c²/a < 2Gm/c², that is, when ma > c⁴/2G. That's only off by a factor of two from Schiller's value. -- BenRG (talk) 21:43, 10 June 2009 (UTC)

How to safely hang a suspended sign like this one

Hello, thanks for taking a look at my question. I have been doing a lot of searching and I can't find a suitable answer to this.
I have seen a few instances of a sign being suspended over a roadway, often as sort of an "entryway" into a city or neighborhood. An example is this one hanging over Highway US 199 in Grants Pass, Oregon.
My questions are:

1. Assuming the sign is held up by cable(s) hung between 2 vertical poles (one on either side of the road) with no other stays or trusses or guy wires, how would one calculate the needed materials for structural integrity? In other words, if the sign has a mass of X, and the distance between the poles is Y, then how would I find out how strong/thick the cables and poles must be? (We can assume the poles and cable are steel)
2. Within the United States, is there any national building code or regulation that would cover a sign such as this, or is it up to local building codes in each jurisdiction? (We can assume the sign is hanging over a local street, and not over a state or national highway)

Thanks for your help! John —Preceding unsigned comment added by JohnMGarrison (talk • contribs) 22:22, 9 June 2009 (UTC)

See this e.g.[19]. Remember you can't just rigidly hang something with cables at full tension. You have to allow for wind, heat expansion/contraction of the material and the like. One of those engineering headaches where you get something like the Tacoma Narrows Bridge if you overlook something or underestimate some effect. 71.236.26.74 (talk) 23:21, 9 June 2009 (UTC)

Thanks for the link to the Interstate sign guidelines. For my question, I am just wondering about suspending over a local city street - would that be a matter of local codes? As for the structure, I am mainly interested in just supporting the weight. We can assume for now that the cables will allow for heat expansion, etc. JohnMGarrison (talk) 23:31, 9 June 2009 (UTC)

Check what DOT is in charge for your area. They also have lower level county/city ones. I don't know who does what, but I know you can't just hang as sign by yourself. You have to get them to do it for you (For the above reasons). Unless we are talking private road. They'd probably be able to help you with that, too. 71.236.26.74 (talk) 23:56, 9 June 2009 (UTC) P.S. in my experience when calculating suspending things like signs, weight is the least worry when calculating cable gauge and tension. I've long since forgotten most of what I knew. I just work with the guys who do stuff like that somewhere down the line. Even they now just type their numbers into the software. :-) 71.236.26.74 (talk) 00:12, 10 June 2009 (UTC)

Two comments. First, you are asking a legal question, not a science question. We are prohibited from giving legal advice. You should contact the local government or a lawyer. Second, you cannot ignore wind. Even a "small" sign over a street will have a fairly large sail area, probably larger than the mainsail on a small sailboat. Look at the masts and rigging on even a small sailboat to see the effect. -Arch dude (talk) 14:00, 10 June 2009 (UTC)

I don't mean to be asking a legal question at all. I am really interested in the physics of how to support the weight of the sign. The second part of my question was more to see if anyone knows how the government handles this type of building project. Let's forget the second part of my question and just focus on the first. Where can I find an equation to tell me how strong the poles and cables must be in order to support the sign? Thanks, JohnMGarrison (talk) 17:10, 10 June 2009 (UTC)

I simplified this question and asked it again below. Please see below. JohnMGarrison (talk) 17:48, 10 June 2009 (UTC)

June 10

Long term stability

From this site they said about :"long term stability time, what's the collisison of mercury, Earth, and Mars even mean, and what is the eccentricity of inner planets, and what the section mean about Pluto's eccentricity?--69.226.38.106 (talk) 01:01, 10 June 2009 (UTC)

The orbits of the planets (see orbital eccentricity) could change enough after billions of years for some of them to smack into each other (i.e. collide). Clarityfiend (talk) 02:29, 10 June 2009 (UTC)

In physics, there is a concept known as the n-body problem which basically states that for any value of n>2, the reliability of predicting the long-term motion of interacting bodies quickly drops to zero. In other words, where you have any group of objects which are all interacting with each other, if there are more than 2 objects in the group, their behavior is chaotic and their motion cannot be reliably predicted in the long term. In the short term, planets in our solar system behave like a 2-body problem (i.e. the planet itself and the Sun) since the gravitational effects of each planet on other planets is small, so on the order of, say, a few decades or a few hundred years, we can fairly accurately predict the motion of each planet by ignoring interplanetary gravitational effects. However, over time the system becomes less and less predictable because, over time, the planets gravitational effects on each other will sort of "add up" resulting in a system which diverges greatly from our predictions after several millions of years. What this all means for that article is that, while it looks like now the planets are in stable orbits, in 10-20 million years there is no way to predict how they will behave. We can be pretty sure the planets are not going to smash into each other simply by the fact that they have SO much space to move around in that even if their behavior becomes entirely unpredictable, it still only results in an infinitessimally small chance of collision between two of the major planets. However, what the chaotic behavior of the solar system means is that while we can be fairly certain the planets won't smash into each other, we can make no reliable predictions about exactly WHERE they will be in say another 50 million years. --Jayron32.talk.contribs 02:41, 10 June 2009 (UTC)

What I think they are saying is that while the average distance of these planets from the Sun may not change by much - the orbits may become more oval...less circular. If that's enough to make the orbit of one planet cross the orbit of another - then KAPOWW!!! - a very big mess! However, the timescale for these events is in the billions of years - more than you, I or humanity in general need worry about. Many of the events described are not due to happen for 5 billion years - and that's about as long as the Sun will last. So it's really kinda unimportant in the grand scheme of things. SteveBaker (talk) 02:54, 10 June 2009 (UTC)

Surely you aren't insinuating that five billion years and the ultimate fate of the sun and earth are unimportant in the grand "scheme of things", just because it's so much longer than a human lifespan timescale? I had no idea the grand scheme was so human-centric! Nimur (talk) 15:05, 10 June 2009 (UTC)

The long term stability of planetary orbits over a time period longer than the star they are orbiting will survive in its present form is pretty unimportant. When the sun throws off its outer layers and becomes a red giant the orbits will drastically change anyway, so stability is hardly an issue. --Tango (talk) 17:13, 10 June 2009 (UTC)

Here is a recent article from Space.com detailing the possibility of future collisions of inner planets as the Sun changes in size, with even the possibility of destabilizing the entire inner solar system. ~AH1^(TCU) 20:27, 10 June 2009 (UTC)

This site say possible collision between Mercury and Earth, or Venus and Mars with Earth. Since Mercury is the smallest, then when it collides with Earth or Venus, then Mercury might be torn apart. If Mars collides with Earth or Venus, then Mars could be torn apart too. When collision comes, usually small one is gone, the big ones survvies.--69.226.38.106 (talk) 23:31, 10 June 2009 (UTC)

For the possible effects of a planet colliding with Earth, see this calculator. For other solar system objects, here is a less accurate and more informal calculation. Assuming the present average orbital speed of the planet, and neglecting that of the Earth's, as well as both planets' escape velocities, and assuming a 20-degree angle at collision, Mercury melts all of Earth and changes its rotation period/axial tilt, Venus destroys the Earth, and Mars melts just over half of Earth, disturbing it rotation and tilt. It appears the higher result for Mercury is caused by its density and speed. ~AH1^(TCU) 01:30, 11 June 2009 (UTC)

They said in this article about Pluto and neptune orbital can change in 10-20 million years nobody will know what will happen to Pluto, but I don't think Pluto will ever crash into Neptune, that's Triton. It said Pluto and Neptune is 3:2 ratio, then Pluto might just get closer to Eris or I don't know. Since Moon and Earth is tidally lock, Galilean moons of Jupiter is also tidally lock, does that mean Galilean Moons is moving further away from Jupiter, sometime, Galilean moon will just eject from Jupiter. Is Titan also moving away from Saturn.--69.226.38.106 (talk) 02:06, 11 June 2009 (UTC)

• I honestly don't know anything about Long term stability of outer planets. I have absolutely no ides what they talking about Galilean moon vs. Jupiter. This is about the most clean I can ask question. I need some answers.--69.226.38.106 (talk) 23:03, 11 June 2009 (UTC)

Quantum physics paradox

Where's the mistake in this formula?

$i\hbar =i\hbar {\frac {dp}{dp}}=i\hbar {\frac {d}{dp}}p=xp=x(-i\hbar {\frac {d}{dx}})=-i\hbar (x{\frac {d}{dx}})=-i\hbar ({\frac {d}{dx}}x-1)=-i\hbar (1-1)=0$

70.26.154.226 (talk) 04:48, 10 June 2009 (UTC)

Is dx/dx the first derivative of x with respect to x? It looks like you are confusing differentiation with multiplication in some places. --Jayron32.talk.contribs 05:49, 10 June 2009 (UTC)

If you make the substitution $x\rightarrow i\hbar {\frac {d}{dp}}$ you tacitly assuming to be working in the momentum space. Notice that here $x\,$ is an operator which therefore requires an state function $\psi \,$ to operate on. That factor is conventionally left out but you must keep in mind that it really is there. So, by ${\frac {dp}{dp}}$ we actually mean

${\frac {d(p\psi )}{dp}}=({\frac {dp}{dp}})\psi +p{\frac {d\psi }{dp}}=\psi +p{\frac {d}{dp}}\psi$

Or, after droping the $\psi \,$ according to convention

${\frac {dp}{dp}}=1+p{\frac {d}{dp}}$, and similarly we have

${\frac {dx}{dx}}=1+x{\frac {d}{dx}}$.

You used that last one correctly in your sixth step but than forgot about it in your seventh step. The right sequence is

$i\hbar =i\hbar 1=i\hbar ({\frac {dp}{dp}}-p{\frac {d}{dp}})=xp-px=x(-i\hbar {\frac {d}{dx}})-(-i\hbar {\frac {d}{dx}})x=-i\hbar (x{\frac {d}{dx}}-{\frac {dx}{dx}})=-i\hbar (-1)=i\hbar$

Dauto (talk) 05:52, 10 June 2009 (UTC)

Oh, that makes sense. 70.27.198.174 (talk) 17:25, 10 June 2009 (UTC)

Telecommunication in ships

Where can i get info about Telecommunication in ships?? i.ve already seen the wikipedia page.. Shraktu (talk) 04:55, 10 June 2009 (UTC)

Admiralty List of Radio Signals is a book from the HMSO which may be of use. Inmarsat could also be relevant. I will look for some more great sources later! Graeme Bartlett (talk) 07:17, 10 June 2009 (UTC)

What Wikipedia page did you go through? Here are some I found in Category:Maritime communication - Marine and mobile radio telephony, Maritime Mobile Service Identity, Vessel traffic service, Ship Security Alert System, Automatic Identification System, Global Maritime Distress Safety System, Long Range Identification and Tracking. Jay (talk) 07:21, 10 June 2009 (UTC)

Head on crash?

Is a head on crash, at say 70 km/h, between 2 cars the same as one car hitting a solid stationary object at 140 km/h? I can't seem to get a definitive answer from myself. My preferred opinion is that it's not, because the change in momentum of the first situation car is half that of the second car, is it not? 124.169.131.68 (talk) 05:14, 10 June 2009 (UTC)

OK, I'll kick off the discussion. Yes, it is the same, if the 2 cars have the same speed and mass. Edison (talk) 05:31, 10 June 2009 (UTC)

If the collisions are perfectly elastic they are the same. In reality, car crashes, whether with other cars or stationary objects, are inelastic - lots of the energy goes into crumpling, heat, and other forms of energy loss. I think the essential question here though is: which scenario is more dangerous to the people in the car? Dcoetzee 05:43, 10 June 2009 (UTC)

(EC)Probably not; but the "solid stationary object" is vague. If a car at 140 km/h hits a parked car it would have roughly the same effect as two cars hitting head on at 70 km/h, asuming the parked car was immobilized, such as resting against a wall. However, if the car is hitting a wall directly at 140, the wall will deform less than a car would, so the car in this case would suffer more damage than hitting the parked car, since the deformation of the parked car would absorb some of the momentum of the collision; the wall will not. --Jayron32.talk.contribs 05:46, 10 June 2009 (UTC)

In fact, for either the head-on crash or the crash into a strong and solid wall, a totally inelastic collision is a much more realistic approximation than a totally elastic one. Which means that all the kinetic energy is converted to other forms, and a lot of it will go into damaging the car. Well, a car at 140 km/h has four times the kinetic energy of one at 70 km/h, so the 140 km/h crash releases twice as much energy as the head-on.

As Jayron says, a crash into a similar but parked car at 140 km/h is different -- that car will be put into motion by the collision, so it's not totally inelastic. --Anonymous, 05:55 UTC, June 10, 2009.

Thats not quite correct, assuming that the two collisions involve the same bodies then they will be the same. In accordance with galilean relativity, which is still accurate for small speed approximations such as this, all that matters is the two vehicles speed with respect to their centre of mass, which is the same in both cases. If however one car is held stationary (such as resting against a wall), then that will cause the collision to be different. This misunderstanding relates to the fact that the elasticity of a collision is not defined by the bodies final speed, or kinetic energy, in an arbitrarily chosen lab frame, but their seperation speed. Elocute (talk) 10:06, 10 June 2009 (UTC)

Another in the "no" category. Assuming that the two cars in the 70 kph head-on collision are the same (important for simplification as discussed above), let's consider what happens to car A: it's traveling 70 kph when its bumper hits car B, and at that point the bumper stops moving -- the crash occurs at that point where momentum cancels out. The equivalent single-car system is for car A to hit an ideal non-moving concrete wall at... 70 kph. The energy of car B in the original system can be safely and entirely ignored. If you're not persuaded by this, consider the original system but place an ultra-thin ideal concrete wall between the two cars -- the collision will be the same as if no wall existed. If you can place that ideal wall, though, then you can ignore what happens on the other side of the wall. — Lomn 11:27, 10 June 2009 (UTC)

It is not true to say that these situations are different, it is an extremely outdated idea to prescribe any significance to particular reference frames. Any apparent extra energy that you have in one frame cannot be used as it is recquired to keep the centre of mass of the system in constant motion. The laws of physics are the same for all reference frames and that is a tenet of modern science that is applicable to all situations. As long as the car approach speeds are the a constant the same collision will occur, regardless of the distribution of this approach speed between the car. Elocute (talk) 12:36, 10 June 2009 (UTC)

Er, what? You may want to clarify by tying your comments to a particular portion of mine. — Lomn 12:56, 10 June 2009 (UTC)

I'm just saying the two situations are the same. And then justifying that. I interpreted you post to say the situations were different, and so believed it recquired refuatation. Elocute (talk) 10:02, 11 June 2009 (UTC)

This is an old question - and we've discussed it here at least once before. The kinetic energy of the crash between two identical cars, hitting head on is twice that of one car hitting a brick wall. However, that energy is absorbed by crushing and crumpling the metal of the car(s) and with two cars, you have twice as much 'crumple zone' to absorb that energy - so we'd expect the damage to each car and the forces applied to the drivers to be exactly the same as with one car hitting a wall. That, however, assumes a totally solid wall which takes no damage whatever in the impact. That's really impossible - there are no infinitely rigid objects - so in practice, because the wall absorbs some of the energy in the single-car case, you're likely to be slightly better off hitting the wall than hitting another car. If the stationary obstacle is something that deforms or can be pushed out of the way (like a stationary car, for example) then the benefits of hitting the stationary object just get better still. SteveBaker (talk) 12:35, 10 June 2009 (UTC)

Note: the above is for a wall collision at 70 kph. Hitting a wall at 140 kph, for any substantially recognizable definition of "wall" (that is, not "a wall made of marshmallow creme"), is going to be worse. — Lomn 12:56, 10 June 2009 (UTC)

Steve hit my point. If the passengers were in perfectly rigid billiard balls with no way of seeing out, in a collision they would have no way of telling whether they hit a wall at 70 km/h or another ball going the other direction at 70 km/h, yes?124.169.131.68 (talk) 13:42, 10 June 2009 (UTC)

Yes, agreed, but in the original question that started this thread, they hit the wall at 140 km/h, which is very different from a 70 km/h head-on collision, even though relative velocities before the collision are the same in the two scenarios. Gandalf61 (talk) 13:47, 10 June 2009 (UTC)

Yes, but the difference is solely due to the difference between a car and a wall, not differences in velocities. A head on collision between a car at 70km/h and a wall (somehow) moving at 70km/h would be the same as a car hitting a stationary wall at 140km/h. --Tango (talk) 17:16, 10 June 2009 (UTC)

Gandalf, if the same objects have the same closing speed, the collision is the same. Elocute (talk) 10:00, 11 June 2009 (UTC)

Nonsense. True but only relevant if you assume the "solid stationary object" in the original question is another identical car, which isn't stated. See my response below. Gandalf61 (talk) 22:23, 11 June 2009 (UTC)

Clarification

The appropriate scenarios for comparison are:-

• A: Two cars approaching each other on a straight line, each travelling at 70 kph.
• B: One car travelling at 140 kph directly towards the front end of a stationary car.

The damage taken by the cars depends on the impulse (change in momentum) applied to the cars. (Technically, the maximum force applied is probably more relevant, but this will be proportional to the impulse).

In scenario A, car 1 has momentum +70m (where m is the car's mass), and car 2 has momentum -70m (let's assume that our base unit for speed is kph). Due to crumpling of the cars, the collision is likely to have a low coefficient of restitution, leading to a (relatively) inelastic collision. Momentum must be conserved. The momentum from the two will tend to cancel each other out, causing them to come (approximately) to rest together. The impulse applied to car 1 is -70m. The impulse applied to car 2 is +70m.

In scenario B, car 1 has momentum +140m. Car 2 has momentum 0. Again, let's assume an inelastic collision. The combined mass of the two cars is 2m. Momentum must be conserved. Therefore the velocity of the combined cars is +140m divided by 2m, which is +70 kph. The impulse applied to car 1 is +140m - (70m), which is -70m. The impulse applied to car 2 is 0 + (70m), which is +70m.

In both scenarios, the impulses received by the cars are the same. Therefore the damage sustained should be the same.

In the third scenario, where a car travelling at 140 kph hits a stationary wall, we haven't defined the mass of the wall (and ground to which it is immovably attached). Let's assume that the wall's effective mass is a lot higher than that of the car (otherwise it wouldn't be an effective wall). The initial momentum of the car is +140m. The initial momentum of the wall is 0. Again, momentum is conserved. The final momentum of the combined car/wall is +140m. The velocity of the combined car/wall is +140m divided by a very high mass, which is close to zero. Therefore the change in velocity of the car is nearly -140 kph. Therefore the change in the momentum is nearly -140m, nearly twice as much damage as the collision in scenario A.

Kinetic energy is not a helpful concept in this problem because the amount of energy described varies according to the frame of reference. Axl ¤ [Talk] 20:51, 10 June 2009 (UTC)

I'll disagree on a couple of counts. First, the impulse is not the only relevant factor; the crushability (is there a proper term for this?) of both bodies matters significantly. Consider the difference between hitting a stationary wall at 70 kph versus hitting a mountain of marshmallow creme: in both cases, the car receives the same impulse, but with the marshmallow mountain it is spread over a much longer time, making for a much more gentle impact. Similarly, being in a car with larger (softer) crumple zones would spread out the impact, making for less damage to the occupants. Also, note that the relative crushability of the two bodies matters as to which one gets damaged more: if you hit a wall, the car is much softer, so it absorbs all of the energy of deformation; with the marshmallow mountain, it's much softer and hence takes almost all of the energy of deformation, leaving the car gooey but otherwise intact.

Speaking of energy of deformation, kinetic energy does matter ('cause it's what causes all that deformation), and it is helpful provided you do the math all the way through. In scenario A, each car has initial kinetic energy 2450m (that's .5*m*v^2), for a total of 4900m; their final KE is 0, so the whole 4900m goes into deforming the cars (and flinging bits off at high speed, etc). In scenario B, car 1 has initial KE of 9800m and car 2 zero, for a total initial KE of 9800m. This is twice the initial KE of scenario A, but watch where it goes: after the totally inelastic collision, both ex-cars are sliding along the roadway at 70 kph, giving each 2450m of KE, for a total final KE of 4900m. The difference, 4900m, goes to energy of deformation, part-flinging, etc, and it's exactly the same as in scenario A.

Finally, I'd like to quibble about one difference between the scenarios that everyone's been ignoring: what happens after the initial impact. In scenario A, there are two ex-cars at rest in the road. In scenario B, there are two ex-cars sliding down the road at 70 kph, maybe recieving additional damage as they come to a halt. Remember, they've still got 4900m of KE available to do further damage (e.g. if one of the ex-cars starts rolling over). -- Speaker to Lampposts (talk) 07:20, 11 June 2009 (UTC)

The two situations are exactly the same. Any increment in total kinetic energy is unusable as the Centre of Mass of the system must maintain a constant velocity. Changing reference frames (which is essentially what this problem is) will never cause the dynamics of the situation to be different. Both situations are exactly the same apart from the frame in which they are viewed. Elocute (talk) 09:58, 11 June 2009 (UTC)

Elocute, the two scenario are not identical apart from a change of reference frame. In the "head on" scenario, we are assuming that the second car has the same mass as the first. In the "wall" scenario we are assuming that the wall is immovable, so it must have a very large mass compared to the car (an "ideal" wall has an infinite mass). That is the key difference. The two scenarios have different outcomes (and the "stationary car" is a third scenario, which is different again if the stationary car has its hand brake on). Look at the motion of the centre of mass immediately after the collision in each case. Is the wall moving at 70 km/h immediately after the collision ? No it isn't.Gandalf61 (talk) 12:34, 11 June 2009 (UTC)

Who has claimed that hitting a wall is the same as hitting another car? The situation being discussed is two cars crashing into each other, either both moving or one moving and one stationary. The situation with a wall isn't interesting and was covered very quickly. --Tango (talk) 17:21, 11 June 2009 (UTC)

The original questioner said "a solid stationary object" which to me (and, clearly, to several other editors) means an immovable object such as a solidly built wall with foundations. If they had meant a stationary car I imagine they would have said so, and they would not have said "the change in momentum of the first situation car is half that of the second car", which is obviously not true for the stationary car scenario. Gandalf61 (talk) 22:23, 11 June 2009 (UTC)

"Consider the difference between hitting a stationary wall at 70 kph versus hitting a mountain of marshmallow creme: in both cases, the car receives the same impulse, but with the marshmallow mountain it is spread over a much longer time, making for a much more gentle impact."

— Speaker to Lampposts

I agree, which is why I included the caveat "Technically, the maximum force applied is probably more relevant, but this will be proportional to the impulse". Axl ¤ [Talk] 14:12, 11 June 2009 (UTC)

Bcf v Bcfe

Could some please provide an explanation of the differences betweeb Bcf and Bcfe?203.100.252.138 (talk) 05:29, 10 June 2009 (UTC)

Some context would help. See [20]. Billion cubic feet? Bioconcentration factor? For the energy field, see [21]. Edison (talk) 05:34, 10 June 2009 (UTC)

Some gas exploration and production companies report their reserves using BCF, Billions Cubic Feet for the gas and BCFE, Billions Cubic Feet Equivalent for any oil. Conversely, some oil companies do the reverse and quote their gas reserves as BBOE or billions of barrels oil equivalent, in fact I think that this is more common than using BCFE for oil (strictly that should be liquids as much of their non gas reserves may be condensate). Mikenorton (talk) 08:31, 10 June 2009 (UTC)

The companies do this so that they can discuss their performance using a single measure. There is a standard calculation to convert between them, approximately 1 barrel of oil = 6,000 cubic feet of gas, based on the amount of energy produced on burning. Mikenorton (talk) 09:14, 10 June 2009 (UTC)

An added benefit is that these conversions do not fluctuate with relative price changes. A barrel of oil equivalent is a specific quantity of natural gas, irrespective of the market price of gas or oil on any particular day. This makes it easier to compare quantities of gas production to oil production over a whole company - instead of specifying in dollars, which adds a whole economic variable into the comparison. Nimur (talk) 15:53, 10 June 2009 (UTC)

geographical location 0°,0°

Which place on earth has a geographical location 0°,0°???Shraktu (talk) 10:01, 10 June 2009 (UTC)

A piece of ocean floor lying 614 km south of Accra, Ghana and 977 km west of Port Gentil, Gabon. Mikenorton (talk) 10:12, 10 June 2009 (UTC)

... which is in the Gulf of Guinea. It's where the middle red horizontal and vertical lines cross in this map projection. Gandalf61 (talk) 10:15, 10 June 2009 (UTC)

Why should it be the ocean floor and not the ocean surface? The "riddle" that I once read was "Where does 0 latitude meet 0 longitude at 0 altitude?"! Jay (talk) 11:40, 10 June 2009 (UTC)

Well, yes indeed - because otherwise I could perhaps answer our OP by saying "the center of the earth". However, Shraktu did say "What place on earth"...so even the most ridiculous nit-pick should allow Mikenorton's answer to be the correct one.

On a more useful note, one of my favorite sites on the Internet is the Degree Confluence Project which aims to have a photograph and description for every integer latitude/longitude intersection - and they are probably have about half of them done. Hence, if you head over to http://confluence.org/confluence.php?lat=0&lon=0 - you can see a photograph of 0°,0°. Predictably - it's a remarkably unremarkable piece of ocean - no visitors' center, no gift shop selling "I'm a zero!" t-shirts! The story behind the photograph is actually rather interesting - this particular group of visitors took with them a hollow steel sphere containing a hard vacuum to symbolize zero-ness and dropped it onto the ocean bed at (0,0). The ocean there is about 5,000m deep! SteveBaker (talk) 12:22, 10 June 2009 (UTC)

Water is part of Earth, so if he asked what point on Earth, you'd say on the water. Technically, he said on earth. Water isn't earth, dirt is. Even more nit-picky, he never said it couldn't be under any earth, and anywhere but the center of the Earth is going to be on some of it. — DanielLC 21:23, 10 June 2009 (UTC)

Haha, based on that site, the meaning of life is located here! Outlook doesn't look good...Drew Smith What I've done 09:12, 11 June 2009 (UTC)

The OP asked "on earth", and not "on land". Even otherwise, it may take a billion years for the ocean floor to become land. Jay (talk) 09:37, 11 June 2009 (UTC)

This particular bit of ocean floor is highly unlikely ever to become land, its likely fate is to be subducted back into the mantle along a destructive boundary at a location that we can only guess at. This will happen within the next couple of hundred million years for sure, possibly a lot sooner than that. Mikenorton (talk) 13:16, 11 June 2009 (UTC)

Melting point of granite and silica

Granite, a rock composed largely of silica, has a fairly low melting point (for rocks); between 700 and 900 celsius, typically. However, silica has a melting point considerably higher; closer to 1650 C, according to silica. What is bringing the temperature down so much? I initially thought it might be because granite melting is measured at depth, not STP, but if it were to be melted at STP I'd expecting the melting point to be lower. —Preceding unsigned comment added by 157.203.42.175 (talk) 12:23, 10 June 2009 (UTC)

Eutectic point describes mineral eutectic mixtures - that is, certain combinations of minerals that may have a cumulative melting point lower than any of the constituent elements. The material properties of liquid-to-solid phase transitions, especially in the presence of crystal structure formation, is extraordinarily complex and is an active area of scientific research. Briefly summarized, it is quite possible that the presence of other molecules in the liquid mixture prevents crystallization until a much lower temperature (consider it like a "dopant" impurity). Even a small impurity in an otherwise crystalline structure can cause huge changes in macro-material properties. Nimur (talk) 14:26, 10 June 2009 (UTC)

For crustal materials, granite has the composition of the eutectic mixture, which is why it's so common. The precise composition and the melting temperature depend on the amount of water in the system; the more water, the lower the temperature at which it melts. Pressure (i.e. depth) also has an effect, but it's of less importance. Mikenorton (talk) 15:10, 10 June 2009 (UTC)

DivX, avi, mp4, Xvid

Hi I put this on Divx but I should put it here:-

Divx, mp4 and avi are all over the internet from game trailers to home made camcorder stuff, iPod, keep going... Okay. When you read about them they are often grouped together, DivX and avi in particular. Anyways what this is all about is.. computers run avi. I have a load of avi and mp4 short films. I want to buy a dvd player capable of putting those on my bigger screen without turning my noisy computers on. Mp4 is easy to find. So, I am fairly convinced that a dvd player saying DivX will play avi because I check online and the talk is about compatibility but it's not clear. I just can't convince myself one way or another. Even here (DivX) it says "Partial backwards compatibility with AVI" but if there is a solid connection between DivX and avi, such as "As standard DivX compliant software/firmware can decode the infinitely popular en mass use avi format" or "DivX compliant has been known to be programmed with avi capabilities" or "DivX software has been produced with the capability of decoding it's strongest relative, avi, but as yet, avi decoding is rare in DivX compliant dvd machines." I will go ring a shop now about it but as for reading online ebay, wikipedia, none of those I couldn't satisfy myself if avi decoding was or not coming standard run in DivX. I was always sort of semi-convinced that DivX and avi were basically the same line but it's not written down like that. It's always in there but never exactly explained. Even avi provides us a sort of vague but un-solid connection between these two I would like to distinguish them properly if anyone can help at that pls. ~ R.T.G 13:04, 10 June 2009 (UTC)

AVI is a container format, which is a specified packing order for the bytes that describe the video, audio, and any other multimedia (like subtitles, metadata about the media clip, etc.) You can put almost any type of compressed multimedia (any codec) inside an AVI file. To make it worse, many encoders will put non-standard codecs into AVI formats anyway (like variable-bit-rate-audio), and because of sloppy software, these files "work" in many media players, so nobody complains. MP4 is an approximate name for a container format, designed only for use with a specific family of codecs. It has also come to refer to that family of codecs as well. Codecs are rules for compressing and expanding streams of bytes into full images to reconstruct a movie. Codecs do not specify a file-format or a specific byte order. DivX is a brand-name for a commercial version of several different codecs, including an implementation of H.264, (roughly speaking, a type of MP4). If a device claims it can play DivX files, it probably implements the DivX decoder, and probably expects the file to be in an AVI container. This does not mean that it can play all MP4 files, which might be encoded with any of a wide number of other standard codecs. To play a file, a player must understand the container format and have a compatible decoder for any given file. Nimur (talk) 14:33, 10 June 2009 (UTC)

Aaah you are right. In the 'Properties->Summary' there is info on wether the files are Xvid or what. I does seem that most of the files are DivX or Xvid so I am just taking the word now that these formats would accept the avi container naturally, once they are Xvid and DviX. tnks! ~ R.T.G 15:00, 10 June 2009 (UTC)

Note that the H.264 version of DivX (DivX 7) was only released in January 2009 and the H.264 DivX codec is called DivX Plus HD. While it's possible some files marked DivX are encoded with the H.264 codec, I've never come across any personally. Generally speaking, the vast majority of DivX files, and DivX players are MPEG-4 ASP compatible only. XviD is also an MPEG-4 ASP codec although the features enabled by default may vary from that supported by DivX. Generally speaking though, most DivX players will be able to play a XviD encoded file fine, at worst perhaps requiring a difference fourCC (once you started talking HD things may start to get more problematic). In any case, this isn't really a science desk question. Note that as DivX and XviD are MPEG-4 ASP, it's possible to store them in the MP4 container, as well as ogm and Matroska. Nil Einne (talk) 07:21, 11 June 2009 (UTC)

I guess the thing is to buy the one that takes the firmware upgrades and to check in the shop that it plays most of your stuff. It's a bit like when they raed the cpu's to 1gz, a new one every few weeks. ~ R.T.G 13:22, 12 June 2009 (UTC)

Explosive friction

There are "weak" elements to such a degree that on a mathematical symetrical chart the there is a space where in all probability the very weakest are there but too weak to detect (I saw a TED talks about it very good). There are detectable wavelengths that just cut through our little crust like rain and we never even notice them. According to our science they are a kind of light and therefor a kind of mass. So, what I am saying is there is a grain to the fabric that is infinitely fine to our perception. So, when an explosion goes off a rapid expansion occurs. Let's say you are watching a movie and the guys put some C4 plastic around a door. Enough force is produced to break steel as big as you like. The only opposing friction is in the air. Now I know little about it but it seemed to me that the force against the door would be represnted opposingly as compressed air with a mass and velocity enough to break the door open. i.e. not only to move the air as fast as a truck heavy enough to break the door but to instantly cause compression in the air the mass-size of that truck. But, the amount of air in the mass of a truck is enormous, is there really enough friction in free floating air alone to produce that kind of opposing force? Wouldn't the same charge work in space? If any charge worked in space like that (and would it?), where would the opposing friction come from then? Is it possible that large friction is produced against radiated cosmic mass whose natural home/origin is right in the middle of explosive (star) forces? If you were feet first on a steel plate (in space) and an explosion occured beneath the plate, apparently you would fly in the opposite direction but there must be friction right? If there was no opposing friction a space-walker could happily sleep through a huge explosion right beside him and just be pushed off at speed, right? It must grip something and in an area of open space the largest mass is the radiation? Also, if you can answer some of that, what effect, with a view to friction, do explosions have on magnetism? ~ R.T.G 14:16, 10 June 2009 (UTC)

It's not friction, RTG, it's momentum. In your steel plate example, gases are forced away from the plate by the explosion. This gives them momentum, which is equal to mass times velocity. In order to balance that momentum so that the universe doesn't fall over, they need to push the plate in the opposite direction. That is why the plate experience a force. The law of conservation of momentum means that the momentum of the gases is equal and opposite to the momentum of the plate (plus you standing on it). As an equation: (mass of gases) x (speed of gases) = (mass of plate etc.) x (speed of plate etc.). The gases might not appear to have enough mass to produce much of a force on the plate, but when you multiply their small mass by their huge speed, you get a large momentum. --Heron (talk) 16:23, 10 June 2009 (UTC)

Well I didn't think that explosives produced a signifigant amount of gases. Maybe I should read up a bit about C4 and TNT. ~ R.T.G 17:19, 10 June 2009 (UTC)

No it is absolutely the function of explosives to produce as much gas as possible - with as much velocity as possible. SteveBaker (talk) 18:18, 10 June 2009 (UTC)

This is a bit off the wall but friction on stellar scales can be quite impressive. But in such cases it is not explosive force but massive, massive gravitational forces at play. --98.217.14.211 (talk) 17:21, 10 June 2009 (UTC)

What would be the blast effect at normal atmospheric pressure versus the blast effect in space, of the same explosive set off at the same distance from the same surface? Gas effects only, neglecting bomb casing fragments. Edison (talk) 21:07, 10 June 2009 (UTC)

The explosion pushing against the plate is effectively a very short-lived rocket. The thrust equation for a rocket includes a term for the reduction in thrust due to ambient pressure, but in an explosion the exhaust pressure ought to be vastly greater than atmospheric pressure, so I doubt that atmospheric pressure would make much difference to the thrust. --Heron (talk) 09:52, 11 June 2009 (UTC)

The explosion which cuts steel is also quite different to the stick of dynamite used for mining, for example. To cut steel or blow a doorway into a wall one would use a shaped charge which uses the explosionto force a material (typically copper) through the thing to be cut, so you have high velocity gasses in one direction, and a high velocity "blade" of lining material going in the other direction. For the explosion+plate in space, see also Project Orion --Polysylabic Pseudonym (talk) 05:20, 12 June 2009 (UTC)

Thats a good article "Even compared to today's best chemical rockets or even other nuclear designs, Orion's potential performance was stunning." ~ R.T.G 13:43, 12 June 2009 (UTC)

A problem of Doppler effect

The article about emission theory points out an odd result as a problem, that, 'a radiant star moves across our field of vision, light given off by differently-moving atoms in its atmosphere should take different amounts of time to reach us. Since the retreating atoms would have a "red" Doppler shift, and the approaching ones a "blue" Doppler shift, the passing star might be expected to appear as a "rainbow streak".' If Doppler effect (relativistic or non-relativistic) does occur, similar problems seems inevitable. If "rainbow streak" is unobservable, why is it? Doppler effect surely occurs, doesn't it? Like sushi (talk) 15:55, 10 June 2009 (UTC)

Yes, relativistic doppler effect does occur but the conclusion that light given off by different atom should take different amounts of time to reach us is faulty. They don't. Dauto (talk) 16:46, 10 June 2009 (UTC)

IF emission theory was true - then we might expect some of these strange things...but it's not true - so we don't see them.

Out in the real universe (the one in which relativity won this argument) atoms moving through the atmosphere at different speeds and directions would indeed be producing doppler-shifted light. That has nothing to do with travel time though because the speed of light is constant no matter the relative speed of source and . But the speed that atoms move relative to one-another is so tiny that it's negligable compared to the motion of the star relative to us...and in any case there are insanely large numbers of atoms and the various colors are going to average out. SteveBaker (talk) 18:52, 10 June 2009 (UTC)

Putting aside the travel time of light and motion of atoms, just assuming that Doppler effect occurs still seems to cause "rainbow streak" if "a radiant star moves across our field of vision". I thought the motion of the star causes "rainbow streak".

I may have been misunderstanding what is written. It says 'when a "star moves across"' and "the passing star...", so I thought motion of the star was included in the cause. Is the motion of the star not taken into account here? Does it cause Doppler effect but it's not what is called "rainbow streak" here?

Like sushi (talk) 01:06, 11 June 2009 (UTC)

Perhaps you don't understand how the doppler effect works: The amount of color shift depends on the speed of the light source relative to us. If the star is moving in more or less a straight line at more or less constant speed over the period we're watching it for - then the redshift will be constant. The light would look a little reddish - or a little blueish - but it can't VARY in color unless it's accelerating...and accelerating pretty rapidly too! I guess you might see a rainbow redshift as a star fell into a black hole or something. SteveBaker (talk) 03:09, 11 June 2009 (UTC)

I thought of a star moving side to side, initially from a relatively far point, through a nearest point, then to a relatively far point. But thinking about it, the effect may be far too small. Do you think so?

Like sushi (talk) 09:28, 11 June 2009 (UTC)

And if the speed of the star does not change much, and if the prediction of shift by emission theory is also dependent on the speed of the source, does it not turn out that "rainbow streak" does not practically occur by emission theory either?

Like sushi (talk) 09:50, 11 June 2009 (UTC)

That's true. But stars are so far away - and move so amazingly slowly - that it would take hundreds of human generations for the star to go from rushing more or less towards us to rushing more or less away. So in the case you describe, the color of the star would indeed change from a blueish tint to a reddish tint as it went past - just as the sound of a car engine goes "wiiiiiiiooooooo" as it goes past you. But the star takes so long to do that and the speed is so slow that the color shift is fairly small and the time it takes to change from blueish to reddish is measured in thousands to millions of years (at best). So I suppose technically there could be a 'rainbow streak' - but you'd have to be watching a star that's doing this specific manouver for millions of years in order to see it. SteveBaker (talk) 14:26, 11 June 2009 (UTC)

calculating gas viscosity

I have 89% H2, 8% CH4 1% C2H6, and 1% N2 with a remainder in higher MW gasses. Is there a formula I would use to calculate the gas viscosity? 65.121.141.34 (talk) 16:02, 10 June 2009 (UTC)

The constant of viscosity of a gas can be calculated as follows. Just realised I have no idea how to write a formula in here, I'll try the cumbersome method of trying to write it in words.

The constant of viscosity of a perfect gas is equal to one third of the mean free path multiplied by the mean speed and the gas's molar mass and concentration. These could all be worked out from the information you are given and a periodic table.

The other method you could use is to conduct a Pouiseuille flow experiment, which will also allow to you work out the viscosity.

Hope this helps a little bit Alaphent (talk) 16:23, 10 June 2009 (UTC)

Suspend a weight between two poles - how strong must the cable and poles be?

Hello, I asked a question above and I think I confused the issue by including too much information. What I am looking for is information on a physics question. Suppose I have two steel poles set vertically into the ground. The distance between the two poles is Y. Between the two poles is stretched a steel cable. I want to hang weight X in the middle of that cable. There are no other supports or guy wires involved. How do I calculate the needed size/strength of the cable and poles? Thanks! JohnMGarrison (talk) 17:14, 10 June 2009 (UTC)

Can we assume X is significantly greater than the weight of the cable itself? --Tango (talk) 17:24, 10 June 2009 (UTC)

Yes, we can assume that. I want to treat this as a very simple problem - no wind, no weight of materials, etc. Any ideas? JohnMGarrison (talk) 17:38, 10 June 2009 (UTC)

We need to know the length of the cable - is it taut - or does it sag in the middle? In your previous question you talked about a sign as your weight 'X' - be aware that if you treat the weight as a 'point mass' then the answer will be radically different if the weight were suspended at a couple of points along the wire instead of just one. These cases are all different (even if the poles are the same distance apart and the mass of 'X' is the same in each case):

    |\       /|        |\        /|      |_____________|
    | \     / |        | \      / |      |      |      |
    |  \   /  |        |  \____/  |      |      X      |
    |   \ /   |        |  |XXXX|  |      |             |
    |    X    |        |          |      |             |
    |         |        |          |      |             |

SteveBaker (talk) 18:14, 10 June 2009 (UTC)

However, if the distance between the poles is much greater than the size of the sign, we can reasonably approximate it as a point mass. --Tango (talk) 18:47, 10 June 2009 (UTC)

That's certainly true - but our OP was originally talking about hanging some kind of banner across the street - so the span of the sign could easily be 80% of the distance between the poles. Depending on the stiffness of the sign - that could make a massive difference. When the wires a loose, (as in my left-hand diagram) more of the weight is acting downwards on the poles. Most poles are extremely strong in compression - so that would be a good thing. However, if the wire is more or less straight (as in the right-hand diagram) - then all of the force would be applied to bending the poles inwards - which would be very likely to bend, snap or uproot them. The difference between the middle diagram and the left-hand one is that the diagonal parts of the cable are at an even steeper slope than in the left-most case. SteveBaker (talk) 18:59, 10 June 2009 (UTC)

Photo 1

• Great ASCII art Steve - thank you. I see what you mean about compression vs bending. You are right that what I really have in mind is not a point mass, but something that spans a significant fraction of the distance. I am thinking about a neighborhood sign such as in the photo to the right:

The poles don't show in that picture but my guess is that the sign spans about 60% of the distance between the signs. The cables supporting the sign are angled like in your first 2 drawings. I think your middle drawing is closest to this actual case, except that in the actual case the sign is suspended by 4 cables: 2 attach to the center, while 2 attach near either end. (and then 2 more cables below the sign for stabilization).

This is a sign hanging over a street in San Diego, California. I'd like to understand how to size the cables and poles so that they safely support a sign like this. Again, we need to assume no additional guy wires are possible, just the poles. JohnMGarrison (talk) 19:42, 10 June 2009 (UTC)

Update: In Photo 2 and Photo 3 you can see the supporting poles. JohnMGarrison (talk) 19:46, 10 June 2009 (UTC)

If you don't have guy wires you'll need to either have wide bases on the poles or have them sunk a significant distance into the ground. Is one of those an option? --Tango (talk) 19:49, 10 June 2009 (UTC)

Hmm at a guess I'd say the sign was designed so that the middle wires (the ones that meet at a point) and the tops of the poles corresponding to them can support all the weight of the sign. That would seem to be the conservative way to calculate it. The other wires seem to be there just to keep the sign stable and provide a little more peace of mind for people standing under it (also a redundancy if one of the middle cables fails due to corrosion or whatever). It looks from the pictures that the poles are much bigger than they "need" to be and metal cables like that can hold much more weight than that sign. Checking to make sure would involve making a free body diagram of the sign, using it to make sure the tension on the cables is less than what they're rated at, checking to see that the bending of the poles is not beyond their strength (you could do that from fundamentals or you can likely find a rating for it being bent like that) and check that the pole is buried deep enough in concrete at the base to support the moment without moving. At least that's what I think :) TastyCakes (talk) 20:01, 10 June 2009 (UTC)

• Tango: Yes, the poles could be sunk very deep into the ground if required. Thickening the base is also a possibility but the desire would be to not take up too much of the sidewalk as shown in photo 2.
• TastyCakes: I think you are right that the middle cables probably support all the weight. In that case, can we treat this like a point mass? In the case of this sign, the poles do bend in slightly. I don't think they were built that way so that must have happened over time.

1. Suppose for a moment that someone was worried that the poles lean in a little, and they want to calculate if the sign was safe. Is there a simple formula they could use to get at least a rough idea?
2. If this design were to be strengthened while keeping the same basic design (in other words, not added bars, trusses, cables), what would be the simplest way to do that? Bigger cable? Thicker post? Bury the post more deeply? Taller post (to ensure more compresion and less sideways force)?

Thanks very much! JohnMGarrison (talk) 20:15, 10 June 2009 (UTC)

Yes, I think you can treat it as a point mass. As for the poles being strong enough, this appears to be a fairly straight forward Bending question. An engineering book on statics or mechanics of materials should have the necessary formulas. To make the structure overall stronger, you'd have to figure out the weakest part of it now - that is what part of it is closest to its failure point. I don't know if it would be the poles or the cables in this case, you'd have to get at least a rough estimate of the numbers. If the cables are the weaker link, put bigger ones in, if the pole is the weakest link, put a bigger one in or support it somehow (with guide wires or something). TastyCakes (talk) 20:42, 10 June 2009 (UTC)

Also note that the fastener that the two middle cables are attached to could be the weakest point and should be analysed to check. TastyCakes (talk) 20:46, 10 June 2009 (UTC)

I've got a whole bunch of stuff here on Wire Rope Safe Working Load Table. Sling Angle SWL, Wire Rope Clips/Number and Spacing but no way am I going to disclose that here, nor am I going to check my Machinery Handbook for column loading. JMG, you blew your cover long ago - you seem to be asking about how to suspend an actual sign on an actual rope above actual human beings. There's only one answer - consult a licensed professional engineer. It's a simple enough problem, maybe $400 to find the solution, max.

It's nice that you try to devolve this to a simple physics problem, but you still aren't phrasing it right. You should be asking for a formula to calculate the stress in the various components. Instead you ask for the "needed size". This is a no-no. We have no way of knowing the needed factors for wind-loading, ice-loading, nor any other safety factors in your jurisdiction. You need to specify the precise design case and ask an engineer to work it out. You're playing with fire if you really want to hang a sign. No-one here carries liability insurance. Franamax (talk) 21:42, 10 June 2009 (UTC)

• Franamax. thanks for the input but you really assume too much. I am not about to hang a sign like this myself. I'm just trying to learn more about it to satisfy my curiosity. That isn't worth a $400 consultation. Also, as I said more than 1 time, I'm not interested at this point in all the intricacies such as wind (we have some in San Diego) or ice (which we rarely have). I'm just trying to learn the basics right now. I'll follow TastyCakes suggestion and read up on bending. Thanks, TastyCakes. If anyone else knows a simple formula I could use to get the approximate stress, I would be grateful. JohnMGarrison (talk) 22:09, 10 June 2009 (UTC)

JMG have you contacted your local DOT yet?71.236.26.74 (talk) 22:03, 10 June 2009 (UTC)

With regards to the sign shown here in Photo 1, the City of San Diego says the sign meets code and is safe. I have heard a local resident say that "national building codes have been revised since Hurricane Katrina and that signs can no longer be suspended by cables." I don't think building codes are set at a *national* level. That is why I asked at one point about building codes. I emphasize again I am not looking for legal advice and I am not looking for a structural engineer to give me a hard and fast answer. I'm just looking to learn a bit about the issues involved, particularly the physics. JohnMGarrison (talk) 22:17, 10 June 2009 (UTC)

Update: I think my neighbor was thinking of International Building Code, which does attempt to bring some standardization across the United States. It seems, however, that local jurisdictions may adopt it completely or with changes or not at all. JohnMGarrison (talk) 23:38, 10 June 2009 (UTC)

In that case (and sorry if my alarm bells started ringing), the critical factors seem to be stress in the cable, stress at the connectors, and side-loading stress on the vertical column. Stress in the wire is dependent on the angle between the support and the load (see SB's ASCII diagrams, the lesser the angle between load and support, the greater the stress in the wire). My handbook for SWL for a Two Part Bridle Sling with a 120-degree included-angle (roughly analogous if you draw the sling upside down) is 920 lbs for 1/4" wire rope - but note that the stress rises rapidly as the included angle approaches 180-degrees, and lift figures are based on still air, since no crane operator fires up on a windy day. The side-loading on the column is basically one-half of the suspended weight acting horizontally, figure out the cosines for yourself but these are dwarfed by the safety factors. Machinery Handbook or Mark's Engineering will give you those calculations, be aware though that column calculations are subject to dispute. That's why a guy wire is so often used on the other side, then the column strength can be calculated as a simple compression/buckling problem, you can use Euler's formula or the AISC standard for that. The notable item in all this is safety-factor x safety-factor x safety-factor. You're asking a question which science doesn't necessarily answer, but engineering does - the difference being that engineering is concerned with which choices result in the least number of people dying as a result of the "oopsies". Franamax (talk) 22:56, 10 June 2009 (UTC)

1. From the geometry of the cable length, pole separation Y and the way the weight is attached, calculate the angle w by which each cable deviates from horizontal.

2. When the tension in a cable is T the upward component of the force is T.sine(w)

3. When there are two cable spans as in SteveBaker's sketches we have X = 2.T.sine(w) where X and T are in the same units such as pounds or kilograms. Then by manipulating: T = X/(2.sine(w)) gives the tension T in the cables.

4. When there are more than two cable spans at different angles from horizontal it is not obvious how the weight X is shared among them. It would be safer to allow for a cable to break, i.e. the possibility of each cable bearing the whole weight X as calculated above.

5. The pole tops are pulled horizontally by a force T.cos(w) tending to bend them inwards. The downward force on the poles is simply X/2.

6. The sign in the photographs has additional cables holding the bottom corners down. Any tension in those cables adds to the effective weight X of the sign and to the horizontal force on the poles. Without wind there is no need for those cables, but their presence implies that there can be wind. The calculations in 2. to 5. above take no account of wind. Cuddlyable3 (talk) 23:01, 10 June 2009 (UTC)

• Dear Franamax, Cuddlyable3, thank you very much. This is exactly the kind of info I was looking for. I originally knew enough to realize I had to care about both downwards force and sideways force, but I didn't know exactly how to start. This will get me started in the right direction. Thanks again, JohnMGarrison (talk) 23:13, 10 June 2009 (UTC)

The thing is that hanging a sign is an engineering problem. That is only partly physics. A large part in engineering is (still) trial and error. So you get people in labs that pull cables till they break. You get guys in another lab that dangle weights from cables and kick the weight with various speeds and frequencies till the cable breaks. Next door they're doing the same thing, but they're freezing or heating the cable, too. The results end up in materials data sheets and engineering handbooks or software. Just for starters I don't think your calculations include the elasticity of your cables yet. Even without wind your cables are going to stretch when you apply tension. Wire rope is also going to twist, so you are getting an elastic spring effect and some torsion. All without wind and still not even thinking of California's earth quaking. The reason the person mentioned the revised building codes is that when there's a notable incident engineers go and do forensics afterward. So you find that the signs with the X gauge cable hung by N number of wires got blown off by Andrew and after Katrina they found that only the signs on cross beams survived. They write a report that gets reviewed by lots of committees dealing with standards. If enough committee members agree the standard gets changed. 71.236.26.74 (talk) 23:47, 10 June 2009 (UTC)

Thank you, anon. I know about these issues in a general sense. I have relatives who are engineers. I know that they do a lot of testing, and I know that there is *always* a large safety factor applied to whatever they *think* is a sufficient solution. I also know that our understanding of these things evolves with experience. Thanks for your help. JohnMGarrison (talk) 23:52, 10 June 2009 (UTC)

Matter and antimatter would be a subset of what?

In other words, France and China are both countries. Matter and antimatter are both... what? (as in a term that exclusively englobes only those two terms -not something too vast as universe, which also includes "energy and momentum, and the physical laws and constants that govern them"-) Not sure if such a term exists, but worth a try, I guess. Thanks, ♠TomasBat 17:38, 10 June 2009 (UTC)

I just checked the Wiktionary definitions for matter and antimatter. The defs "(physics) Matter made up of normal particles, not antiparticles. (Non-antimatter matter)" and "(physics) Matter that is composed of the antiparticles of those that constitute normal matter" imply that matter is both a general term, referring to compositions of particles and compositions of anti-particles, as well as a term referring specefically to that composed of particles. Thus matter would be the term I would be looking for, right?

---

Matter: (physics) The basic structural component of the universe. Matter usually has mass and volume.

• Matter: (physics) Matter made up of normal particles, not antiparticles. (Non-antimatter matter).
• Antimatter: (physics) Matter that is composed of the antiparticles of those that constitute normal matter.

♠TomasBat 17:46, 10 June 2009 (UTC)

Sounds good to me. Just keep in mind you shouldn't take any of the above definitions very seriously. There is no scientifically based definition of what should be considered a particle and what should be considered an anti-particle. We chose to define an electron as a particle and a positron as an antiparticle simply because ordinary matter is composed of lots of electrons (among other particles) but no positrons. But that's just a convention. the oposite convention would work just fine. Dauto (talk) 18:03, 10 June 2009 (UTC)

Our matter article says, "in discussions of matter and antimatter, normal matter has been referred to by Alfvén as koinomatter", which implies that what you say above is correct: normal matter and antimatter are both a kind of matter, and you have to distinguish from context which "matter" you mean. --Sean 18:14, 10 June 2009 (UTC)

The word you are all looking for is Substance. --Shaggorama (talk) 05:26, 13 June 2009 (UTC)

Relativity, exponential curves, infinity of time(ish)

All natural things outside of pure mathematics would seem to have a solid portion of infinite exponential curvature in their structure. Apparently instruments were available at one time with the sensitivity to record and calculate the Einstein theory of time dilation on a supersonic craft and found dilation theory to be bang on, definite fluctuations in time/motion in the supposed direction. Einsteins theories also, if I am quoting correctly, viewed the uppermost light wave we can detect to be more or less the uppermost and fastest matter there is. So, given that the exponential curve of improbability is part of the fabric of everything off paper, would it be delicate to assume that further up the ladder of detection, as is the nature of light, a certain amount of exponentiality occurs in the dilation curve so as light would not only be younger than any other entombed and ageing matter, but so little aged that in our perception hasn't even aged at all? What is the likelyhood, as with quark and quantum theory, that light goes far beyond our scales in terms of substance? ~ R.T.G 18:06, 10 June 2009 (UTC)

Could you say that again but using phrases that make sense so normal people will understand it? Dauto (talk) 18:35, 10 June 2009 (UTC)

I don't really understand what you are saying, but I can tell you that time dilation has been measured using atomic clocks on aeroplanes and spacecraft. I can also tell you that light, in a sense, experiences infinite time dilation, so experiences no time passing at all. Proper time for a photon is not well defined, but can be thought of as not progressing at all. So, all light has zero age from its own point of view. Light is not generally considered to be matter, although it can be thought of as being made up of particles, photons. There is a very big difference between matter travelling close to the speed of light and light itself, due to the matter having non-zero rest mass. Does any of that help? --Tango (talk) 18:45, 10 June 2009 (UTC)

Hmmm... I said most stuff seems to be what you would call an expression of a 3 dimensional fractal:- a ratio with a mathematical formula appied that goes on forever (1 + 1 = 2 + 1 = 3 + 1 = 4.... 1 atom + 2 atom = 3 + 2 atom = 5 + 2 atom = 7 atom... 1 X mass + 2 X speed = 3 X time + 1 mass + 2 speed = 6 time + 1 and 2 = 9 x time...) Apparently travelling at the speed of light can alter time to a ratio of 8:1 (an object at the speed of light ages 1 year for every 8 of our normal years, time dilation). Physical evidence has been shown of time dilation. If light has mass then would it be possible that light itself is an object affected by time dilation and if so, as they smashed the atom and found smaller peices called quarks and smashed them and found smaller peices again, could there be light in the upper range beyond our detection, and, if there is light going faster than we can comprehend, could the ratio of time dilation be infinite (could a beam of light we haven't detected be going so fast that for every 1 year that passes at speed much more than 8 years passes in normal time, even hundreds, thousands of years until there was a mass or energy to which the concept of time passing was minor or immeasurable?). Surely, if all forms of light are structures with different mass or with different wavelengths they travel a different speeds. For instance, what is the speed of a quark or a Preon in relation to visible light? What is the speed and mass of electricity? I don't know how to simplify or which terms are wrong. If it is possible to move time dilation from a ratio of 1:1 to 2:1, 3:1 up to 8:1... is it not natural to assume ratios of 10:1, 100:1, 1000:1 and so on? If it is conceivable, what are the hypothesis? Is it fair to say that the 8:1 dilation ratio and the speed of light as we know it may be like a 'hard limit' to us in all practicality, but, more reasonable to assume the possibility of an infinite and possibly exponential curve on the acceptable values of light speed and time dilation? If that is reasonable, is there even some failed experiments in studying it? I'm sure the like of Einstein or those he inspires must have worked extensively at it, no? ~ R.T.G 20:25, 10 June 2009 (UTC)

I've already told you, time dilation at the speed of light in infinite. An object travelling at the speed of light doesn't age at all. I have no idea where you got the figure of 8 from, but it is completely wrong. --Tango (talk) 21:06, 10 June 2009 (UTC)

I got 8:1 off a movie or something to be honest but the idea that light speed was finite I find in general ("nothing faster than light : The speed of light = x") I guess I am driving at a sort of flat light (light diamond?) which would probably possess that immunity to time. It does help. Perhaps light is invisibly balanced with a dark-matter anti-light and finite speed would make sense. Flat light could be a balancing point between that (something is bound to be stationary or it really does go bang!). OK, thanks tango :D ~ R.T.G 23:42, 10 June 2009 (UTC)

The speed of light is finite, it's about 300,000,000 m/s, but the time dilation at the speed of light is infinite. The factor is ${\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}$. If v=c you end up dividing by zero, which (in this context, where we are only interested in v approaching c from below) gives us zeroinfinity. I really have no idea what you are talking about with flat light and anti-light, you seem to be just making up words. --Tango (talk) 23:52, 10 June 2009 (UTC)

You seem to have a lot of technical terms mixed up and confused. I suggest you might try reading over our article on special relativity a bit more carefully. Time dilation is relatively straightforward and contains the actual equations and derivations for coming up with it. It is not as complicated as you seem to think it is—it is wonderfully, elegantly simple if you just reason through it. --98.217.14.211 (talk) 23:53, 10 June 2009 (UTC)

I'm sorry, variance in light speed is a possibility. Even here on Wikipedia (Speed of light) it says, "...observations show the variation of the speed of light as the universe ages is less than two parts in 10 to the power of 16 per year, for both microwaves and visible light." As for saying anti-light... in a universe of dark-matter and anti-matter on faith, words like anti-light and dark-light are as 1 is to 2, a to b etc. Light is in waves, if it was flatter/less wavy/more streamlined, would it not go faster (obviously that will get me a "no it doesn't change speed")? According to Tango, dilation is considered infinite as things stand but I've never heard it described as infinite and we are bombarded with titbits about dilation sometimes. In our perception light is a force comparable to gravity and magnetism. All natural things we know are rough around the edges with potential spikes not smooth and constant (maybe that is just what light is, the only smooth and constant matter there is but who knows, just as likely not, isn't it?). ~ R.T.G 15:16, 12 June 2009 (UTC)

You need to read more basic science before you can seriously think about such things. I'll try parsing your last paragraph and I hope that will help you understand why.

You said: I'm sorry, variance in light speed is a possibility. Even here on Wikipedia (Speed of light) it says, "...observations show the variation of the speed of light as the universe ages is less than two parts in 10 to the power of 16 per year, for both microwaves and visible light."

Yes, that is a possibility but it is considered a highly speculative possibility. There no evidence that it actually has happened and your quote of less than two parts in 10 to the power of 16 means that if there is any variation, it is so small to the point of being unobservable with current technology. That does not mean that it is impossible but it does mean that all observations are consistent with the current scientific consensus that there is no variation. We should stick to scientific consensus unless there is some strong reason to do otherwise.

You said: As for saying anti-light... in a universe of dark-matter and anti-matter on faith, words like anti-light and dark-light are as 1 is to 2, a to b etc.

unlike anti-matter and dark-matter, anti-light and dark-light aren't standard terms within science jargon. If you're going to introduce new terms, you need to be very specific about what you mean by those terms, otherwise they become meaningless pseudo-scientific babble. Your attempt at an explanation was words like anti-light and dark-light are as 1 is to 2, a to b etc. Sorry but that is woefully inadequate definition. Anti-matter and Dark-matter have very specific definitions that do not lend themselves to such analogies. You most definitely can (and should) do better than that. By the Way, Anti-matter and Dark-matter are not based on faith. Anti-matter has been produced and observed in labs and cosmic rays for more than 70 years now and its existence is a very well stablished fact of nature. Dark-matter existence has also become stablished on very strong observational grouds throughout the last decades. I can go into more detail about their eperimental evidence later if you desire.

You said Light is in waves, if it was flatter/less wavy/more streamlined, would it not go faster (obviously that will get me a "no it doesn't change speed")?

You missunderstand the statement that light is a wave. That does not mean that light follows a wavy path down the road. In fact light follows a staight path. By wave it is meant that something is oscillating and that oscillation propagates. In the case of light the electric field and the magnetic field are both oscillating and propagating and that's what's meant by light is a wave. That clearly underscores your lack of basic understanding about the things you are talking about.

You said According to Tango, dilation is considered infinite as things stand but I've never heard it described as infinite and we are bombarded with titbits about dilation sometimes.

Tango is right. You're also right to complain about being bombard by titbits of disconnect information that is often misleading or even downright wrong. That's why my advice is to stop paying attention to all that misinformation and to read a good book about the subject form your local library.

You said In our perception light is a force comparable to gravity and magnetism.

Your perception is misleading. light is definitaly related to magnetism (As I said, it is the oscillation of the electric and magnetic fields) but it is not a force properly speaking.

You said All natural things we know are rough around the edges with potential spikes not smooth and constant (maybe that is just what light is, the only smooth and constant matter there is but who knows, just as likely not, isn't it?).

I don't know what to make of that. I think you have expressed yourself extremely poorly here. Dauto (talk) 17:34, 12 June 2009 (UTC)

That is all I am looking for:- what is that speculation, even if highly unlikely, with some variance there must have been speculation. If I am correct dark-matter is matter of enormous mass beyond that we can even analyse and anti-matter is a speculation, with some proof, that matter as we know it could exist as an anti-matter that would be destructive to it's counter parts. Perhaps a light we have not detected exists with zero oscillation at an even greater speed (flat-light?/dark-matter). Perhaps an anti-light exists similar to how anti-matter exists but how would you define that? I don't know. Don't even have any ideas about it beyond the relationship between matter and anti-matter. "All natural things we know..." - Even light is various. Absolute exactness is only true on paper/mathematics. Obviously it is outside my sphere but at any rate it is hard to beleive that radio waves do not have a standard difference in speed to gamma radiation even if that is so minute that we never detected it (although of course not much good if never detected). Is there truly nothing in a possible upper spectrum to gamma radiation even if undetected or inconclusive? Hardly out of the realm. ~ R.T.G 20:51, 12 June 2009 (UTC)

Antimatter in action!

RTG: Please - stop talking...just stop. These words that you are typing are all just nonsense - babble - any old scientific-sounding words strung together at random. Dauto did a masterful job of trying to dissect your stream-of-consciousness BS - and I agree - you have absolutely not the first clue about what you're talking about - it's not that you are a little bit wrong - you aren't even using words that make sense in a scientific context! Go and read some text books...heck just tune into the science channel once in a while!

You say things like "If I am correct dark-matter is matter of enormous mass beyond that we can even analyse and anti-matter is a speculation". What kind of arrogance makes you think you have a snowball's chance in hell of being right? The odds of your (frankly) wild-assed guess about dark matter being within a million miles of being right are very, very close to zero. Antimatter is certainly not "speculation". Let me just give you a clue about how inane that statement is. Positrons are anti-electrons...genuine, honest-to-goodness anti-matter. They were discovered in 1932 for chrissakes - this isn't something new and revolutionary. People actually USE anti-electrons all the time in their day-to-day lives. If you get cancer and have a "PET" scan at your local hospital they are using Positron emission tomography to look at your tissues. Yeah - positrons...antimatter...the stuff you think is "speculative". We use antimatter every day in thousands of hospitals around the world! The pretty spinning image at right was taken using antimatter in a PET scanner. Speculation!?! Have any clue how dumb that statement sounds?

So - please - your rambling statements are useless. It's fine that you don't know much science - we're here to help you with that. But if you ask a question of our knowledgeable experts, have the politeness to either accept the answer - or go elsewhere to express your random opinions. I've heard that homeopathers, perpetual motion machine designers and believers in the Time cube will be happy to listen to what you have to say - and probably incorporate it into their own wild-assed theories. But if you want to know how the universe REALLY works - shut up and listen - read some introductory text books - heck even try reading some Wikipedia articles - we have fine writing on antimatter, dark matter and all of those other interesting subjects. But please, hold off making ANY theories of your own until you've studied the wise words of people who've spent a lifetime studying, calculating and experimenting before coming to their conclusions. With the facts at your fingertips - you'll be able to ask questions that actually mean something - and get answers that help you to understand more.

If you keep up this kind of behavior, everyone here on the science desk is going to write you off as a crank or a troll - we'll start to ignore your questions - and if you keep it up, we'll probably start deleting them on sight. SteveBaker (talk) 23:02, 12 June 2009 (UTC)

SteveBaker has already hit all the points here. BTW steve, nice picture. I just want to reinforce the point that there is no royal road to science, which is another way of saying that you will never achieve true understanding of those things you're talking about unless you sit down and do the hard work of studying science. It is a long road, but every step of it is worth the effort. The first thing you must do is to stop doubting (for the now at least) what scientists are telling you. Believe me, the speed of light really is constant. Dauto (talk) 04:32, 13 June 2009 (UTC)

Although the term isn’t one that would be used by scientists, you could say that “anti-light” does indeed exist. However, “anti-light” is the exact same thing as “light”. Light consists of elementary particles called photons. You can annihilate a photon with the photon’s antiparticle. However, the photon’s antiparticle is just another photon. The situation is different with, say, electrons, because an electron has a nonzero charge, namely, –e. The charge of a particle and its antiparticle must sum to zero, so the antiparticle of an electron, the positron, must have a charge of +e, which is different from the –e charge of an electron. So the positron is a different kind of particle from an electron (unless you start talking about time reversal) . But the charge of a photon is 0, the negative of which is still zero, so you can’t distinguish between a photon and its antiparticle based on charge. There don’t exist “antiphotons” which are distinguishable from photons.

“Flat light” is another phrase that a scientist wouldn’t use, but the concept can be viewed as fitting in with current scientific theory, at least as a limit. The photons that light consists of come in various wavelengths. A photon with a longer wavelength can sort of be thought of as being “flatter” than a photon with a shorter wavelength, although “flatness” brings to mind a kind of transverse “thickness” to a photon that isn’t really accurate. But as pointed out by others, in any experiment ever performed, “flatter” light (i.e., photons with a longer wavelength) has the exact same speed as “wavier” light (i.e., photons with a shorter wavelength). Even the tiniest difference in speed between the two would result in a violation of special relativity, among other things.

The statement “If I am correct dark-matter is matter of enormous mass beyond that we can even analyse” may be a perfectly reasonable guess, depending on how you interpret the phrase “beyond that we can even analyse”. The most widely discussed models of nonbaryonic dark matter are based on the cold dark matter hypothesis. One of the two proposed categories of what cold dark matter consists of is weakly interacting massive particles, of which the leading candidate is the neutralino. The proposed neutralinos do indeed have an enormous mass, compared to other elementary particles. Red Act (talk) 09:50, 13 June 2009 (UTC)

Top Speed

Basically, if I know the power and torque of my engine at a specific rpm. As well as the mass and drag coefficient of the car/bike, is it possible to work out a theoretical top speed? Alaphent (talk) 18:43, 10 June 2009 (UTC)

No, that is insufficient. You also need details about the transmission and the wheels - basically, which engine RPM corresponds to which speed of the outer rim of the tire. It is rarely the case that the engine provides maximal shaft power at the highest attainable speed. And even then you will only get an approximation. --Stephan Schulz (talk) 20:52, 10 June 2009 (UTC)

No - you don't need that. But you DO need to know the rolling resistance. If you have all of the numbers you can get a pretty close approximation that way. If you know the peak power output - it's pretty safe to assume that the car will be producing that amount of power at it's top speed. Then you can compute the drag force in Newtons and the know that:

 Power = ( Drag + RollingResistance ) x Speed

Of course drag is proportional to speed squared - so you wind up with a quadratic equation for the maximum speed. The only other things you need to know is the peak power of the motor in Watts, the coefficient of drag, the density of the air and the frontal area of the vehicle.

If you don't know the rolling resistance or the drag coefficient - you can do it experimentally. Get a friend to sit in the car with you with a stopwatch. Find a long, straight, level, empty, stretch of typical road on a windless day - get the car up to (say) 70mph - then put the car in neutral and without touching the brakes - let it coast until it stops. (Please be VERY careful doing this!) Have your copilot note the times at which you reach 65mph, 60mph, 55mph...all the way down to 5mph. Armed with those times & speeds - you can calculate the acceleration (well, 'deceleration') every 5mph from 70mph to zero. Knowing the mass of the car (and that Force = Mass x Acceleration) - you can calculate the force due to a combination of drag and rolling resistance that caused that deceleration - and you can do that for every 5mph of speed. Multiplying each number by that speed gives you the amount of power the engine would have to provide in order to counteract the combined drag/friction forces (Power = Force x Velocity). Get some graph paper and plot that graph. Now you have a graph of engine power needed to maintain a constant speed versus speed. Since drag is proportional to the speed squared and rolling resistance is proportional the speed you should get a curve that indicates a steeply increasing power demand at higher speeds. Now - all you have to do is extrapolate that curve until the amount of power required equals the power that the engine can produce at the wheels. That's your top speed!

SteveBaker (talk) 23:52, 10 June 2009 (UTC)

Bacterial Infections

Why are Gram Negative infections supposed to be so much worse for the human body than Gram Positive ones? Is this actually true? 87.115.3.165 (talk) 22:02, 10 June 2009 (UTC)

Have you read our pages yet? Gram-negative bacteria, Gram-positive bacteria "worse for the human body" isn't a very qualifying term. More drug resistant, higher number of infectious species, shorter incubation time, higher reproduction rate, primarily targets essential organs, etc.? The Immune system has a lot to do with it. 71.236.26.74 (talk) 22:19, 10 June 2009 (UTC)

See Endotoxin. --NorwegianBlue ^talk 00:15, 11 June 2009 (UTC)

Grandma's cold treatment

I got a cold, and a friend advised me to put salted water into my nose. Question: has anybody heard about this remedy? I am not necessarily asking for a medical advice about its validity, I just would like to make sure it's not another :-( practical joke on me, before trying out --pma (talk) 22:42, 10 June 2009 (UTC)

It's not new, see [22] [23] [24] and also nasal irrigation. Nanonic (talk) 22:48, 10 June 2009 (UTC)

It may or may not help - but it's not a practical joke - my wife also swears by it. However - we're not allowed to offer medical advice here - so we can't tell you whether it works or not - or whether to try it or not. SteveBaker (talk) 02:47, 11 June 2009 (UTC)

I can say from firsthand experience that it feels weirder than shit the first time you try it. --jpgordon^{::==( o )} 15:52, 11 June 2009 (UTC)

Why did you try stuffing shit up your nose? O_o Vimescarrot (talk) 18:26, 11 June 2009 (UTC)

June 11

Balloon on bus accelerating forward.

This was a problem from a physics book I vaguely remember; I never quite figured it out and someone else's question reminded me. A bus is accelerating forward. A balloon is tied to a string attached to a chair. Why does the balloon go forward as well. If I remember correctly it was from one of the Feynman lectures on physics book so I doubt the question is wrong. But to me it would seem the balloon should go backwards, not forwards. Any possible explanations that involve simple Newtonian mechanics (nothing about fluids or pressure; I don't think it said WHAT the balloon was filled with but I'm assuming standard balloon with helium.24.171.145.63 (talk) 03:16, 11 June 2009 (UTC)

:By who's perspective? To a person on the bus, the balloon will drift backwards, until the string stops it, and then it will go forwards with the bus. However, to a person standing on the street, the balloon will drift forwards but at a rate slower than the bus does, since the air in the bus generates a small amount of friction on the balloon, and will push if forward slightly. --Jayron32.talk.contribs 03:28, 11 June 2009 (UTC)

No Jayron, the balloon actually moves foward (even from the perspective of the person inside the bus) because the air around the balloon is heavier than the balloon and moves backward forcing the balloon forward (just as it falls downward, forcing the balloon upward). Dauto (talk) 03:48, 11 June 2009 (UTC)

Ah yes, of course. That makes sense. Scratch my earlier reply. --Jayron32.talk.contribs 03:56, 11 June 2009 (UTC)

Actually ... when the bus accelerates several forces will affect the ballon's motion:

• the motion of the bus, pulling the string -- the most significant force, causing the balloon to move forwards with the bus
• the balloon's inertial mass -- causing it to drift backwards relative to the passengers
• assuming calm atmospheric conditions (no wind), air pressure or friction would be a small factor opposing the balloon's drifting motion —Preceding unsigned comment added by Ropata (talk • contribs) 09:35, 11 June 2009 (UTC)

You forgot its bouyancy, which is the one which causes it to drift forwards relative to the bus. Elocute (talk) 10:14, 11 June 2009 (UTC)

Also, the bus will pull the string in the opposite direction the balloon is being pushed. If it is indeed moving forward, the bus will pull the balloon back. — DanielLC 14:10, 11 June 2009 (UTC)

Yes bouyancy is the key here. The gas in the balloon is lighter than air (which is why it's floating). Imagine a cork floating in a glass of water in the bus. As the bus accelerates forwards - the water in the glass sloshes towards the back of the bus - which forces the lighter cork to move forwards. That's very easy to visualize because you can see the water. However, the same thing is happening with the balloon which is floating in the air. When the bus accelerates, the air sloshes towards the back of the bus - forcing the balloon to move forwards...it seems counter-intuitive - but that's because we're not used to seeing things that are lighter than air. SteveBaker (talk) 12:06, 11 June 2009 (UTC)

We need to state that we are referring to a balloon that has positive buoyancy--it would rise toward the ceiling if untied. My daughter's physics class was given this problem, and the debate was so fierce that she drove to a store, purchased a balloon, and verified by experiment that the balloon goes forward. I pointed out to her that one result of general relativity is that accelerated frames of reference are indistinguishable, if the buoyant force opposes gravity, it must also oppose any other acceleration. on the bus, if you tie a plumb bob and a balloon to the same pivot point, the two strings will form a straight line in steady state tilt or steady state acceleration. -Arch dude (talk) 13:03, 11 June 2009 (UTC)

Yes, the equivalence principle is the easy way to see this. A bus accelerating forward is equivalent to a bus tilted backward (in both cases you're pressed into your seat). A helium balloon has to behave the same relative to the frame of the bus in both cases, and that means moving diagonally in the front-ceiling direction. -- BenRG (talk) 16:17, 11 June 2009 (UTC)

Why would the balloon move forward? I don't understand the part about the air inside the bus "sloshing" backwards. Yes, there will be "sloshing," but will it be only backwards? I think such "sloshing" will be complex, going around the seats and any other complexity to what otherwise might be a simple geometric volume. Supposing instead of a bus, we were considering a hollow cylinder. And instead of windows, which might be opened or closed, we considered the cylinder totally closed. Would the balloon still move forward? If so, that would be assuming that the air at the back of the cylinder became more dense, or compressed, than the air at the front of the cylinder. But is this really the case, to any appreciable degree, at acceleration rates concerning busses? I have my doubts about that. In theory that sort of reasoning might apply. But I am not so sure it applies in a bus accelerating from a standstill, no matter how fast the driver attempted to accelerate the bus. I think a more likely explanation for the balloon moving forward might be complex air currents resulting especially from open windows. But I am not sure. Bus stop (talk) 16:37, 11 June 2009 (UTC)

Yes, even in your cylinder example, it would happen. Yes, the acceleration causes an increase in density at the rear of the bus. If the bus starts turning left, the density will increase on the right and the balloon wil move to the left.--Sphilbrick (talk) 16:42, 11 June 2009 (UTC)

Yes, that's exactly what happens. The air at the back of the balloon becomes more dense than the air at the front of it creating a pressure gradient force on the balloon that's enought to push it forwards. This is entirely equivalent to the vertical pressure gradient that makes the balloon float. Dauto (talk) 18:24, 11 June 2009 (UTC)

Do you understand why the balloon floats in the first place? The reason it moves forward under acceleration is exactly the same as the reason it floats. In a completely sealed cylinder in steady-state 1G forward acceleration, the balloon will be at an angle of 45 degrees even though there is no air movement whatsoever. You really need to purchase a balloon and get someone else to drive you and accelerate. The effect is dramatic, not subtle at all. -Arch dude (talk) 19:55, 11 June 2009 (UTC)

Interesting. Thank you. Bus stop (talk) 18:28, 11 June 2009 (UTC)

Aight thanks guys 24.171.145.63 (talk) 19:25, 11 June 2009 (UTC)

Y Chromosome

If I understand genetics correctly (hopefully I do) then everything that makes a person male comes from their father via the Y chromosome, whereas what makes a person female comes from one X chromosome of the mother and father respectively.

Therefore does this fact of nature indicate that generally men (or male animals even, if this helps rule out the cultural and psychology influences) would prefer the birth of a son?

In other words, a father completely influences the male characteristics of his sons but only half the female characteristics of his daughters. So in the interest of passing on one's genes (which according to The Selfish Gene and natural selection indicates is the main reason for competition for mates and for having children) wouldn't men prefer sons while women would be indifferent? Perhaps this also explains why inheritance laws have typically favored sons in most cultures? TheFutureAwaits (talk) 09:54, 11 June 2009 (UTC)

It seems to me that since males have no female parts, they wouldn't influence a female offspring at all. Rather, the fathers female ancestors gens, plus the mothers genes, would control the female parts.

As for whether this affects favoritism or not, is beyond me.Drew Smith What I've done 10:31, 11 June 2009 (UTC)

My apologies if I'm stating the obvious, but men are XY and women are XX. Therefore men do influence half of what makes their daughters female (in terms of sex chromosomes; female being the "default" sex is an issue beyond the scope of this question). You know:

Xm1Ym1 (father) + Xf1Xf2 (mother)

could result in Xm1Xf1 (female) , Xm1Xf2 (female), Ym1Xf1 (male) or Ym1Xf2 (male).

Of course the man's X chromosome came from their own mother but the man's Y came from his father; we could got back generation after generation but I don't see how this impacts the original question: Do men favor son's because they completely contribute what makes their sons male but only contribute half of what makes their daughters female. TheFutureAwaits (talk) 10:53, 11 June 2009 (UTC)

The XY chromosome system is the sex-determination system in most mammals, but not in all animals - birds have an entirely different genetic system (see ZW sex-determination system); some reptiles have a non-genetic temperature-dependent sex determination; some fish and molluscs can even change sex. So in evolutionary terms the Y chromsome is a fairly recent arrival. Even if we stick to mammals, a father contributes more genetic material to his daughters than to his sons (the X chromosome is 153 million base pairs long; the Y chromosome only 60 million base pairs) so an evolutionary argument could predict favouring daughters over sons. OTOH, if there are fewer males than females in the adult population, then a son will produce more grandchildren, on average, than a daughter ... Gandalf61 (talk) 11:02, 11 June 2009 (UTC)

There are ~25,000 genes that affect a person's physical characteristics, most of which are NOT on the X or Y chromosome. Early in embryogenesis, the gender is completely indeterminate -- males and females all have the same embryonic tissues (Mullerian ducts and Wolffian ducts) that will go on to form the basic internal genital structures through the process of sex determination and sex differentiation. The embryonic genital tubercle and genital folds will develop into the external genital structures. Therefore, you should think of the Y chromosome as having a "switch" (the SRY gene) that turns on a complex genetic program that results in the embryonic gonads becoming testes in a male, whereas the absence of the SRY gene (which is true in XX females but also in Turner syndrome and Swyer syndrome) the default is to form ovaries. Everything follows from that point in development -- testes produce antimullerian hormone that causes regression of the female internal structures, and testosterone that promotes development of characteristic male external genitalia. In the absence of these signals (and probably in the presence of some X-linked gene signals), the system defaults to a female phenotype. Most of the genes that are involved in this process are actually NOT on the sex chromosomes, so would allow contributions from both parents, even though the switch that starts off the process is on the Y. Why would it make sense for the small number of genes on the Y chromosome to be more "selfish" than all the others? There are far more genes on the autosomes. --- Medical geneticist (talk) 11:41, 11 June 2009 (UTC)

Aren't you overlooking the importance of the SRY "switch"? It seems rather easy to argue gender has a profound effect on many other genes. My hypothesis is that men would favor sons as they are genetically and ultimately phenotypically more related to their fathers versus daughters. The gene/chromosome is exclusive to one parent and has a massive influence on the development of the individual. TheFutureAwaits (talk) 12:05, 11 June 2009 (UTC)

OK - these explanations have gone WAY off the rails. It's not complicated:

Women have two X chromosomes - men have one X and one Y. The child gets one of the mother's sex chromosomes and one of the father's - but it's random which one. So if the baby is a girl, she got one of her mother's X chromosomes (it's random which one) and the X chromosome from her father. If the baby is a boy - he gets one of his mother's X chromosomes (again, at random) and the Y chromosome from the father. Either way - the kid got one of the two genes from the mother and one from the father so that is no reason to prefer to have a boy child.

Where the confusion lies is that someone here thinks that a girl baby could get both of her X chromosomes from the mother and a baby boy could get both the X and the Y from the father. That's NOT what happens! But if that were the case then in the case of a girl, it would be true to say that there are two possibilities: Both X's from mommy or one X from mommy and one from daddy. There would therefore hypothetically be (on average) 75% of the genetic material in girls coming from the mother and 25% from the father. In the case of a boy - there would certainly have to have gotten the Y from the father but the X could come from either parent - so on average, 75% of the genetic material in boys would come from the father and 25% from the mother. It would then make evolutionary sense for the father to 'prefer' boys to girls because on average they'd contain more of his genetic material. I think that's what the OP imagines. But that's not what happens.

If fathers prefer their boy offspring to their girls (and I'm not convinced of that) - it's more likely to be that it is the traditional role of the father to pass on male-dominated skills (hunting, tracking, boat-building, beer-drinking, whatever) to their sons and for women to pass on traditionally female-oriented skills (nagging, shopping, etc??<shrug>) to their daughters - so it would perhaps make evolutionary sense for the males to preferentially bond with their sons and the females to bond with their daughters. SteveBaker (talk) 12:26, 11 June 2009 (UTC)

Basically what I said, except alot clearer and alot more complicated...Meh, whatever.Drew Smith What I've done 12:40, 11 June 2009 (UTC)

As to whether fathers prefer boy offspring, depressingly it seems to be so. Here is a little evidence on the subject. "...if the first child is a boy, the probability of his father leaving the household is 25 percent less than if the first child is a girl." "We find that the birth of a son speeds the transition into marriage when the child is born before the mother's first marriage." However, there are many complicating factors. Interestingly, it seems that the preference-behaviour is shown by people who would say, and probably believe, that they have no such preference. 80.41.126.158 (talk) 19:59, 11 June 2009 (UTC)

I don't disagree with any of the above but I just want to point out that, unless I'm missing something, evolutionary arguments regarding sex-preference don't add up. The only way a gene causing men to prefer sons would be selected for is if it caused such a strong preference that it made men kill their daughters (or render them infertile somehow). Can such a gene be selected otherwise? Zain Ebrahim (talk) 13:13, 11 June 2009 (UTC)

Okay, this is getting silly. No one here (at least that I'm aware of) thinks both X's come from the mother. See what I posted above in response to Drew...

Xm1Ym1 (father) + Xf1Xf2 (mother) could result in Xm1Xf1 (female) , Xm1Xf2 (female), Ym1Xf1 (male) or Ym1Xf2 (male).

It seems like a simple misunderstanding but Steve, I would appreciate if you would cross out that section of your discussion since no one is advocating that point of view.

Anyway, what I AM saying is the Y chromosome is ultimately responsible for the creation of a male child. The father is the only one with a Y chromosome and thus 100% responsible for the gender characteristics of a male (XY) child (X from the mother, Y from the father). In the case of a daughter both parents contribute equally to the gender characteristics as one X comes from the mother and one from the father.

Therefore as a father is wholly responsible for the male characteristics of the son but only 50% responsible for the gender characteristics of a daughter it follows that men would prefer sons. TheFutureAwaits (talk) 13:40, 11 June 2009 (UTC)

The gender is decided by the Y chromosome, but the characteristics are decided by the combination. Let me pose a hypothetical question that may make things a little clearer. What would happen if someone where born with two Y chromosomes?Drew Smith What I've done 14:02, 11 June 2009 (UTC)

That's not possible, the embryo would fail to develop. XYY can occur but YY can not as there are many genes on X which people require to live. However I am not sure this hypothetical applies to the question... I think the terminology may be throwing people off. Also Drew, can you provide a citation or example for confirmation of your statement "The gender is decided by the Y chromosome, but the characteristics are decided by the combination."?

The male gender characteristics are the result of the activation of a male phenotype by the SRY gene. Therefore what makes a person male and all the male characteristics (not ALL characteristics but those which are unique to males) are caused by the Y chromosome which comes from the father. Does this clear up any confusion on the point I am trying to make? TheFutureAwaits (talk) 14:44, 11 June 2009 (UTC)

According to The XYY Man he'd be some kind of a super-hero. In reality, he'd have XYY syndrome which I suggest you read. Note that there are also XXX girls...(which, strangely, seem to be advertised a helluva lot in certain parts of downtown Dallas). If you're suggesting someone with two Y chromosomes and no X - they'd certainly never get as far as being born because there are a shit-load of genes on the X chromosome that you can't survive without - so the question is moot. SteveBaker (talk) 14:41, 11 June 2009 (UTC)

That point of view makes no sense to me. An X chromosome has more genes than a Y chromosome which means that a man actually passes more of his genes to his dauthers than to his sons so, if anything, that naive application of the selfish gene principle would lead to men prefering their dauthers. Dauto (talk) 14:37, 11 June 2009 (UTC)

Except I'm not refering to the number of genes, but rather to the impact the SRY gene has on the resulting phenotype caused by all the other genes. The Selfish Gene was an earlier work of Dawkins which he expanded on in The Extended Phenotype which may explain a bit more the theory behind my reasoning. Essentially the father has a much greater impact on the phenotype of a son versus a daugther as everything which makes that son male comes from the father. For daughters the contribution is shared equally. TheFutureAwaits (talk) 14:50, 11 June 2009 (UTC)

"Everything which makes that son male comes from the father" is a trick of language. It has no scientific meaning. The father's genetic material determines the sex of the child, whether male or female. The father supplies 50% of the genetic material whether the child is male or female (slightly less than 50% for a male). That includes 50% of the genes that are preferentially expressed in males and 50% of the genes that are preferentially expressed in females. The mother and father contribute equally to the phenotype of a male child and they contribute equally to the phenotype of a female child. -- BenRG (talk) 15:24, 11 June 2009 (UTC)

It's about activation, not just numbers. See my responses to Daruto and Looie below. TheFutureAwaits (talk) 16:44, 11 June 2009 (UTC)

This reminds me of the work by David Haig on Parent–offspring conflict which is related to genomic imprinting and Intragenomic conflict. David D. (Talk) 15:03, 11 June 2009 (UTC)

Halleujah! This is what I've been getting at the whole time. I can't claim expertise in this stuff though and the articles actually seem a bit sparse, so can anybody explain whether any evidence confirm or contradicts my hypothesis that the father has a much greater impact on the phenotype of a son versus a daugther as everything which makes that son male comes from the father and thus men would prefer sons? TheFutureAwaits (talk) 15:43, 11 June 2009 (UTC)

Your hypothesis is false. As MedicalGeneticist explained (but maybe in too complicated a way), the things that make a man male are scattered all over the genome. The Y chromosome is tiny, and the main thing it contains is a set of "switches" whose function is to activate the male-related genes on other chromosomes. In females, these genes are present but they don't get activated. The contents of the Y chromosome differ very little across people. Therefore, the mother and father both have essentially equal impacts on the phenotype of a son. Looie496 (talk) 16:16, 11 June 2009 (UTC)

Yet the switch makes all the difference. When the other genes are not activated then they do not impact the phenotype so ultimately the father DOES make a larger determination. TheFutureAwaits (talk) 16:28, 11 June 2009 (UTC)

Clearly you're not refering to the number of genes. My point is that you probabily should be refering to the number of genes, unless you can show us that the inheritance of that single gene present in the Y chromosome is more relevant than the inheritance of all the genes present in the X chromosome which you haven't done so far, as far as I can see. Just saying that you are not talking about my point doesn't make it go away, mind you. Dauto (talk) 16:21, 11 June 2009 (UTC)

See above, it's more important because this gene controls the activation of the other genes you are refering to. If they aren't activated the phenotype doesn't change so ultimately the fact that it controls the activation makes it more important than the pure number of inactive genes. TheFutureAwaits (talk) 16:28, 11 June 2009 (UTC)

I desagree. I think the fact that it is a simple switch makes it even less important. Prove wrong if you can. Dauto (talk) 16:46, 11 June 2009 (UTC)

I think it's rather obvious if something has control over a process then it is rather important. Not necessarily more important than the process but in this case it influences the outcome of gender, something the other genes don't do. I would also argue the fact that it alone determines gender makes it extremely important. The differences that result biologically because of gender are very far reaching. TheFutureAwaits (talk) 18:52, 11 June 2009 (UTC)

Well, I would argue that since all that gene does is determine gender that makes it extremely unimportant as far as it concerns the matter of wheather a father would prefer a son or a dauther. You've simply asserted the oposite point of view but without giving any real reasons for us to accept it. On the other hand I know for a fact that fathers love their dauthers. Dauto (talk) 19:06, 11 June 2009 (UTC)

Getting back to the original question about "selfish genes" and wanting to pass on one's genes, the idea that a male should prefer sons based on wanting to pass on his genes has been adequately refuted. A male actually passes on slightly more genes to his daughters since the X chromosome carries more genes. Look at the Y chromosome article -- in some species, there are only 4 genes on the Y chromosome. Your argument attaches too much importance to the SRY gene. What if I "hypothesized" that people with orange eyes would rather have children with orange eyes because the "orange eye gene" is selfish? It just doesn't make sense. There are enough social/cultural reasons given for sex preference in offspring that your theory about a genetic basis just doesn't add anything useful. --- Medical geneticist (talk) 17:19, 11 June 2009 (UTC)

If the SRY gene determines gender then it influences a person's morphology more than pretty much any other gene (yes there are HOX genes but these don't get passed on only half the time). So what I'm saying is it is reasonable the "selfishness" of this gene would be extremely influencial. As a consequence of a gene contributed by only one parent the child's morphology is vastly changed.

If a father has a son everything that makes that son male comes from the father. If a father has a daughter the gender characteristics are cause by both the mother and father. Therefore, a father wishing to pass on his genes would prefer sons as the sons will pass on his male characteristics to their children, daughters will not. TheFutureAwaits (talk) 19:01, 11 June 2009 (UTC)

A father wishing to pass on his genes would prefer a daughter as the daughter will have more of his genes than a son. Being a male is not that important, really. Dauto (talk) 19:13, 11 June 2009 (UTC)

This is becoming a circular argument, as I said earlier it's not about the number of genes it's about the end result. Let's try this: do you agree that the gender of a child is determined by the genetic contribution of only the father? TheFutureAwaits (talk) 20:23, 11 June 2009 (UTC)

No one is arguing that the contribution of the SRY gene is unimportant in determining the gender. It is a critical switch between a male and female phenotype. However, you are incorrect in your assertion that "everything that makes that son male comes from the father". Have a look at the androgen receptor and androgen insensitivity syndrome articles and then tell me whether you still think that the mother does not contribute to the male phenotype in her sons. --- Medical geneticist (talk) 20:48, 11 June 2009 (UTC)

Androgen receptors are present in men and women; the information is interesting but it doesn't refute the fact that only the contributions of the father determine whether a male is born. The father is solely responsible for whether the switch is triggered and child becomes a boy or a girl. That's where the importance lies; all the genes that interact as a result of this trigger are still dependent on SRY in the first place. TheFutureAwaits (talk) 21:12, 11 June 2009 (UTC)

I don't think anyone has denied this last statement of yours. What is your point? Tempshill (talk) 22:38, 11 June 2009 (UTC)

Besides, the genes themselves don't care about the phenotypical outcome as long as they get to be inthe next generation. That's what's meant by selfish gene. And all those genes on the X chromosome are selfish and want to be in the next generation and don't care that much wheather it is a male or a female. The SRY gene is outnumbered and, despite of what you said, I think that does matter. Dauto (talk) 21:30, 11 June 2009 (UTC)

Going back to the first principles of evolution, suppose a mutation occurs on the Y chromosome being passed on to a son. The son with the mutated Y chromosome has a 50% chance of passing it on to a child; he'll definitely pass it to sons and definitely not pass it to daughters.

Now suppose a mutation occurs on the X chromosome being passed on to a daughter. That daughter has a 50% chance of passing it on to a child; all her children receive an X from her, but only half will receive the mutated X. So both sons and daughters have a 50% chance of giving the mutation to their children. Being on the Y chromosome offers no advantage. --Bowlhover (talk) 03:22, 12 June 2009 (UTC)

How can you make black through mixing colors?

Hi all,

If you had only primary colors available, would it be possible to mix them together in such a way to make perfect black? (We can assume hypothetically perfect primary colors.) If not, what colors are needed in order to produce perfect black?

Thanks! --Sam —Preceding unsigned comment added by 146.115.120.108 (talk) 13:17, 11 June 2009 (UTC)

It depends. Are we talking about Addition of Colors? (Like mixing colored light) Or are we talking about Subtraction of Colors? (Like mixing paint). Check out Color mixing to learn the difference. But briefly, if you're subtracting colors, then yes, you can mix red, blue and greenYellow, Magenta and Cyan, to form black. But if you're adding colors, then mixing red,blue and green will form white. APL (talk) 13:28, 11 June 2009 (UTC)

The three primary colors in subtractive mixing are yellow, magenta, and cyan, not red, blue and green. Cuddlyable3 (talk) 20:32, 11 June 2009 (UTC)

Of course! I knew that. I was ... just testing. APL (talk) 23:43, 11 June 2009 (UTC)

(ec) In theory, yes, see color mixing#subtractive mixing. In reality, you end up with some kind of dark mud colour because some light is still being reflected. This is the reason printers always use three colours plus black in full colour printing - the "mixed black" is just not good enough for quality documents. SpinningSpark 13:30, 11 June 2009 (UTC)

Our article is also a little misleading, you might get a nice dark black as shown with subtractive mixing using filters but it won't happen with pigments as the article claims. I might just go edit that. SpinningSpark 13:37, 11 June 2009 (UTC)

Some inkjet printers can produce a perfectly usable black with only the CMY pigments. APL (talk) 14:03, 11 June 2009 (UTC)

For additive mixing - mixing light - such as you do on a computer screen - then using zero amounts of the three primary colors gets you black. For subtractive mixing - paint, dyes, etc - you'd theoretically use the maximum amount of all of the primary colors. The problem with subtractive mixing is that firstly, the three primary colors that you'd ideally want are not perfectly manufacturable with available chemicals - and secondly that the means by which dyes, inks and paint pigments work means that they really cannot do a perfect job. SteveBaker (talk) 14:32, 11 June 2009 (UTC)

I can mix a good subtractive black with clear pigments in acrylic paints. I seldom want flat black because it rarely occurs in nature, but I can mix it. I spent an hour learning how. Most of the time, however, I want black with an edge, a punch, and that means a red-black, a blue-black or whatever suits the painting. // BL \\ (talk) 03:31, 12 June 2009 (UTC)

Is this person mentally challenged?

Someone online told me a few days ago that the solution to the world's problems was to "have a party for everyone." Now, obviously if you can't diagnosed OPs, you can't diagnose people. :-) But, is this a normal thing for an adult to think? (Okay, I'll admit they may just be saying they're an adult - but you'd think someone pretending to be an adult wouldn't be talking about magically bringing Mideast peace by having a party for everyone.)

What psychological reason would a person have for believing that by jsut throwing a party and inviting everyone, that: A. the people will come; and, B. that they'll put aside so much hatred? I know that in some cases, ordinary citizens have come together peacefully, but that's not the same thing as everyone stopping it.209.244.30.221 (talk) 15:00, 11 June 2009 (UTC)

Well it worked in south park with Timmy and the bloods and the crips. It would have to be one bitchin' party though. TastyCakes (talk) 15:06, 11 June 2009 (UTC)

Perhaps he was referring to a party in his mouth in which obviously everyone is invited. It's actual not a horrible idea; a world peace day celebration couldn't cause much harm. TheFutureAwaits (talk) 15:11, 11 June 2009 (UTC)

Unless someone used it to cover their sneak attack. Then it would just make things worse. I think people make the mistake that all of the world leaders are rational, which may or may not be the case. 65.121.141.34 (talk) —Preceding undated comment added 15:36, 11 June 2009 (UTC).

This sentiment also embodies the naive assumption that all wars, violence, and feuds are fundamentally "bad" for everybody, and that if we just agreed to stop having wars, violence, and feuds, everyone would be happier. Unfortunately, human history has shown us many times that wars are often beneficial to one or more responsible players. These players have no incentive to stop the war/violence/feud. Most often, they are able to separate themselves from the negative repercussions of conflict, either via force projection, effective defense, or some other method. They can then reap all the benefits while subjected to minimal harm, and are inclined to perpetuate the conflict indefinitely (until some strategic situational change). Nimur (talk) 16:04, 11 June 2009 (UTC)

Attempting a serious response: People mature psychologically in different ways. Some people may have difficulty formulating a realistic Theory of mind and fail to appreciate the potential threat of coercing various hostile tribes to attend a mass "social" gathering. However, people who voluntarily attend such a gathering would presumably share your friend's hope that we can all get along.

Several political movements have attempted to overcome the inherent fractiousness of human nature, by setting a singular purpose for their followers. Marxism teaches that religion, culture, and ethnicity are secondary to the great historical class struggle for economic justice. Christianity teaches that money, sex and power are secondary to the holy injunction to live a life worthy of Heaven. Secular humanism teaches that autonomy and freedom of thought are among the highest virtues, and the individual actualizes their dreams by hard work and merit. Dictatorships (benevolent or otherwise) demand that the subject peoples submit to the will of the sovereign. All these systems have inherent flaws because humans exhibit behaviour spanning from wonderful atruism to despicable evil.

The only way we can all "just get along" is if/when a large enough proportion of the population decides themselves to do so, through their shared belief and values. Otherwise humanity is always going to be a troublesome collection of competing tribes. ~~ Ropata (talk) 17:50, 11 June 2009 (UTC)

The OP friend's call to "have a party for everyone" has been interpreted as "throw a party for everyone" which is difficult to do. However if the caller meant "have a political party for everyone" they may be postulating that democracy would solve the world's problems better without political parties. Far from implying mental disease, that is a critical viewpoint that merits consideration. It supports the idea of Direct democracy whereby citizens vote on issues directly without intermediate representatives or parties. Examples of direct democracies are seen in Landsgemeinde in some Swiss cantons and in many countries an occasional referendum (plebiscite) that is held to resolve a specific issue. There are obvious practical difficulties with controlling government this way. However the speaker may have had a more ominous idea that only one political party should be permitted for everyone i.e. a single-party state such as a communist state or a form of fascism. All these are political standpoints that should be open to debate, though inapropriate for this Science desk, but there is a bad precedent for equating dissident political opinion with mental disease. Cuddlyable3 (talk) 20:26, 11 June 2009 (UTC)

I think the one that works is not "have a party for everyone" but is "everyone has a party together and likes it" but that won't feed people who are hungry :( ~ R.T.G 20:28, 11 June 2009 (UTC)

Well I would assume this party has snacks and drinks, but yeah long term, they still have no food. And on a more serious note, you would have a very difficult time hosting a party for everyone on earth not only logistically, but also without gravely insulting at least one group. That means, your catering can have no alchohol or you will insult the Muslims, no pork products for the same reason. No beef because of Hindus. In fact, better go no meat at all for the vegans. Now you upset just about everyone else who was hoping for some beer and pizza. My point is that if you can't even get the catering to work out for all these groups, how do you expect them to work more serious issues out? I do not know this person and can not tell if they were serious, but they appear to be hopelessly idealistic. 65.121.141.34 (talk) 20:50, 11 June 2009 (UTC)

The best part about throwing an everybody-in-the-world party is that there are no neighbors to complain about the noise. APL (talk) 21:02, 11 June 2009 (UTC)

A fair amount of the world doesn't drink, would this be a dry party? TheFutureAwaits (talk) 21:17, 11 June 2009 (UTC)

Back to te original question. I doubt the person was serious. However, taking the question at face value, and assuming they were serious, I would have to say that, yes, this person is perfectly sane, but most likely wrong. There are many mature, rationale, successful (have an apartment and car) adults who would do nothing but party if given the chance. Now how many of those people are in politics? :)

On a side note, war is not a bad thing. War distracts countries from developing dangerous technologies. War boosts the economy. War keeps the population under control. War is an outlet for aggression. Without war, society would collapse. Now bring on the insults and rebuttals, because I know they are coming.Drew Smith What I've done 03:44, 12 June 2009 (UTC)

Rebuttal... Wars are excellent routes for technological advances. No one cares about the money you are spending on it, and you have a very strong motivation to develop new stuff to get the bad guys. 65.121.141.34 (talk) 13:19, 12 June 2009 (UTC)

God forgive me but you pluck ones out to represent all of the differing opinions/religions etc. but you make sure 100% they will not kill or even badly injure each other ever. You put them all on a spacecraft like the Arthur C Clarke Rama with all they need to sustain themselves or party and tell them they are going to a far away star. Then just throw them into orbit and watch them like Big Brother. You have picked them all out correctly so none dominates, none suffers too severe depressions, competitiveness is mild and the environment gets adequate care (which means excellent care really). You sit back and watch them all and they instinctively produce the solution to human differences. Maybe thats what the Earth is already. ~ R.T.G 15:33, 12 June 2009 (UTC)

How do you select them so that you know that they will never kill or intentionally injure each other? I suspect even the Amish (about as pacifist a group I have ever seen) probably have the rare murder. 65.121.141.34 (talk) 16:37, 12 June 2009 (UTC)

WW2 was a good motivator for scientific progress, but is that typical of all wars? WW2 was a special case in many ways. For example, what technological advances has the civil war in Darfur produced? APL (talk) 18:46, 12 June 2009 (UTC)

You mean Darfur Sudan??? Probably because everyone else did the technological advances that they are using in their war 20+ years ago. 65.121.141.34 (talk) 19:53, 12 June 2009 (UTC)

Ah! selecting them is the trick, I couldn't let you in on that. ~ R.T.G 20:52, 12 June 2009 (UTC)

June 12

Cancer in Whales

I was wondering why whales don't die early from cancer but in fact can be very long lived and as usual have found it is a question other people have asked before and actually it's called Peto's Paradox. I haven't seen any statistics on it though. Do people study of whales that are caught to determine if they have tumours?

Can you explain why would you expect them do die early from cancer? Dauto (talk) 01:26, 12 June 2009 (UTC)

This recent article from LiveScience may be relavent. ~AH1^(TCU) 01:38, 12 June 2009 (UTC)

And silly me. I was thinking with all the coal mining going on there, there was bound to be higher rates of lung cancer. OK, that was the worst joke EVER. I didn't even laugh at that.--Jayron32.talk.contribs 03:22, 12 June 2009 (UTC)

It took me a while to get it, but when I did I thought it was pretty good...Drew Smith What I've done 03:46, 12 June 2009 (UTC)

As to the why, I was reading about Bowhead Whales and how they can live over 200 years and are 50 tons in weight. If one in eight of people die of cancer then even if we ignore the extra time a cancer has to grow but each person weight bit of the whale has that chance of a malignant cancer then overall their chance of escaping it would be something like (1 - 1/8) to the power of (50*2000/200) which google calculator tells me is about 10^-29, i.e. they should all die of cancer and it's a wonder they live so long. By the way that's very interesting about chimps having a much lower rate. Dmcq (talk) 08:36, 12 June 2009 (UTC)

I guess, more properly stated, my question really is why would anybody expect the whale cancer rate per cell to be the same as a human cancer rate per cell? I don't see why it should be. In fact I think it should be expected to be a much slower rate given that a huge animal like that is necessarily going to have a much slower methabolic rate per cell. Dauto (talk) 13:10, 12 June 2009 (UTC)

Per Dauto's remark, the assumption of a uniform risk of malignant transformation per unit body weight does not bear scrutiny. Even within the human body, different tissues (and, for that matter, different cell types within those tissues) have vastly different probabilities of becoming cancers. Malignant tumours derived from fat cells (liposarcomas and their ilk) are exceedingly rare, whereas cancers of the mucosal lining of the colon and rectum (colorectal cancer) are depressingly common. While one should be cautious about carrying these assumptions across species, it is likely that all that whale blubber – accounting for up to half the mass of the bowhead whale – is resistant to malignant transformation. TenOfAllTrades(talk) 14:12, 12 June 2009 (UTC)

As to the rate per cell the whale lives far longer so that should offset its slower metabolic rate, thats why I didn't put in a factor for their longer life. Also since the cells divide many more times there's more opportunity for them to go wrong I'd have thought even in normal growth. As to the different tissues the whales have the same tissues so corresponding organs can be compared, they have colons and rectums too only far far larger. Dmcq (talk) 14:45, 12 June 2009 (UTC)

Speculation: high metabolic rate + relatively low volume of cells = high possibility that for humans, cancer is going to kill you. Whales are low rate and high volume, even if one had cancer, would it become large enough to kill it? More interesting as Dmcq points are are high rate, low-volume animals that don't have cancer problems. --98.217.14.211 (talk) 15:40, 12 June 2009 (UTC)

I don't see that the size makes much difference once a cancer has gone malignant. It'll spread and multiply and the only difference the victim's size makes is that it'll take a little bit longer to kill a bigger one.

Going backwards from whales to humans I get that if humans had an equivalent rate then death from cancer would have to be about 0.2% or less - which sounds much more reasonable and attainable by evolution than the 10^-29 chance of surviving for whales I got the other way round. It still means whales must have some very good anti-cancer protection. I would have thought also it implies any evolutionary clock for whales would run much slower than expected for smaller mammals which mightn't be too hard to check. Dmcq (talk) 17:52, 12 June 2009 (UTC)

Well, Bovines are very resistant to all kinds of cancer. Whales are much closer to cattle (both are Ferungulata) than to humans. This does not mean that they have the same defenses, but it does make it at least plausible that whales have good cancer resistance. --Stephan Schulz (talk) 22:25, 12 June 2009 (UTC)

Where did you get that cows were resistant to cancer? I didn't find statistics but a web search seemed to show that cancer in cows was quite common and it having gone malignant was a common cause for condemning meat. And it's not as though they have long lives. Dmcq (talk) 09:43, 13 June 2009 (UTC)

I got it from the Science Magazine Podcast from April 24th (first interview, on the sequencing of the cattle genome - "cattle rarely develop spontaneous cancers [...] and almost never auto-immune diseases") - about 7'47" into the program. Archive,mp3. Sorry, not much more there, and I cannot make out the name of the researcher. --Stephan Schulz (talk) 10:16, 13 June 2009 (UTC)

Tidally lock

Formation and evolution of the solar system#Moon-ring system said Europa, Io is tidally lock from Jupiter. is Titan tidally lock from Saturn? Does that mean Europa is moving further away from Jupiter? Is Titan moving away from Saturn? Pluto is also tidally lock with Charon. Does that mean eventually their moon will escape away from planet, until the moon escapes and become a own planet. Even the source isn't too clear.--69.226.38.106 (talk) 04:01, 12 June 2009 (UTC)

See Tidal locking. We do have an article on this... --Jayron32.talk.contribs 04:19, 12 June 2009 (UTC)

On List of known tidally locked bodies they only gave lists of planet/moon in locking. But they didn't say if moon is moving away or closer to planet. Which ratio means moon s moving closer to planet is 3:2 or 2:3?--69.226.38.106 (talk) 04:30, 12 June 2009 (UTC)

The ratios have nothing to do with the movement closer to and farther from the respective planets; the ratios have to do with the nature of the tidal lock. The ratio 3:2 means that the object makes three rotations per two orbits; 2:3 would mean two rotations per three orbits. As far as moving away from or towards the planet, you would have to know whether or not the moon's rotational speed is getting faster or slower as a result of the tidal lock. If the moon had to slow down to become locked, then, by conservation of angular momentum, it will be move FASTER in its orbit, thus drifting away from its planet. If it had to speed up its rotation, then it will have to slow down its orbit, and will drift towards its planet. This is all explained in the article. --Jayron32.talk.contribs 05:28, 12 June 2009 (UTC)

The article Tidal acceleration explains in more detail about the drifting away from a planet by a moon as the result of Tidal locking. --Jayron32.talk.contribs 05:31, 12 June 2009 (UTC)

Jayron's answer is slightly imprecise but he pointed to the article (Tidal acceleration) that explains all that in detail. To answer the OP's questions: Yes, Europa is moving away from Jupiter but not because it is tidally locked. It does so because it's orbit around Jupiter is prograde with a period longer than Jupiter's rotational period. samething is true for Titan. Triton, on the other hand has a retrograde orbit and is therefore moving closer to Neptune. Charon's orbit is stable because Pluto itself is also tidally locked. Dauto (talk) 06:01, 12 June 2009 (UTC)

Question about polish people

Do Poles have yellow skin like that of a chinaman? They appear to, despite being otherwise 'white' in appearance.--Kempist (talk) 10:50, 12 June 2009 (UTC)

There's a picture of some at the start of the Poles article. I don't see what you're seeing. Perhaps you have an old picture that has gone a bit yellow? Dmcq (talk) 12:49, 12 June 2009 (UTC)

No, I saw a guy today who was obviously Polish/Slavic and he looked almost exactly the same as white British except with a yellow tone to his skin that white British people generally lack.--Kempist (talk) 13:11, 12 June 2009 (UTC)

No, I don't. In fact, people frequently remark about how tan I am, but maybe I'm the exception to the rule. A Quest For Knowledge (talk) 13:14, 12 June 2009 (UTC)

Not sure what you are referring to. Most Poles are Slavs, and so share similar characteristics to other Slavs, such as Russians or Ukranians. However, Poland is surround by nations of different ethnicities, so there is bound to be a wide variation in appearances as people intermarry. Consider that the Magyars of Hungary and the Estonians are both Uralic peoples originally from Central Asia, while the Germans likely originated on the Baltic shores of Scandanavia. The fact is there is far more variance than assumed in an "ethnic" group, and such definitions are fluid and hard to nail down. What makes Nicholas Sarkozy French and Alberto Fujimori Peruvian and Linda Ronstadt Mexican-American is not just genetic lineage, but also environment. A person is Polish because they live in Poland, even if all eight of their great grandparents came from other countries... --Jayron32.talk.contribs 13:25, 12 June 2009 (UTC)

Discussing peoples in Europe is particularly dicey because they don't seem to have stayed put for any considerable length of time. IMHO quite a few Polish people have a pasty to rosy complexion. Compare Images Voelkerwanderungkarte.png, Karte völkerwanderung.jpg, Invasions of the Roman Empire 1.png71.236.26.74 (talk) 15:42, 12 June 2009 (UTC)

I just had a look at the corresponding pictures in the British people and Poles articles. Comparing them against each other there is an overall slight difference in the shape of the heads I think but otherwise nothing at all obvious I think. Have you seen a lot of people from Poland? it doesn't sound like it if you're talking about one person, and you sure they were from Poland rather than it being obvious somehow? After all it's quite possible for individuals to have a yellower skin either from ancestry or kidney disease or a tan or there's just a great variation amongst people. Some of those British or Polish people in the pictures could be interchanged quite easily without anyone noticing I think. Dmcq (talk) 14:30, 12 June 2009 (UTC)

Troll. Tempshill (talk) 15:27, 12 June 2009 (UTC)

If you are referring to my blunder a minute ago: Nope just dusty old idiot nor knowing how to use a gallery. :-(71.236.26.74 (talk) 15:50, 12 June 2009 (UTC)

I've seen plenty of yellow looking British and I didn't think they were Chinese. Heavy drinkers. The Poles come over here and bang they are drinking around the clock (sometimes) you too would be gone yellow. Some of that yellow is natural anyway even if you were pure black. You think this is a yellow colour but you also think that the best way to pronounce Belgique is Belgi-um. If you look at those and still see yellow, go to the fourth row down, compare the elderly orient-asian man with the elderly caucasian man. There is plenty of yellow in the skin colour but it is typical. Yellow/brown/pink (white man). You are just a bit of a snob, sorry. Don't worry about it it's good for you. ~ R.T.G 15:56, 12 June 2009 (UTC)

Since nobody has yet openly stated it, the original poster should be aware of a few things:

• This sort of comparative racial ethnography is widely discredited by modern scientific analysis. (As mentioned above, mass migrations and population diffusion are so prevalent that they render the 19th-century ethnic archetypes wholly inaccurate).
• Cultural definitions are more relevant than biological distinctions. Take a look at Polish people and Chinese people. Most anthropologists do not use skin pigment as a primary indicator of cultural identity.
• The use of the term Chinaman may be construed as pejorative (offensive) in most contexts. Our article discusses the debate surrounding use of this term.
• The lumping of skin-color and a generally offensive term suggest that the question is not asked in good faith.

Our general policy is to assume good faith on your part - possibly, this original poster is not aware of the implications of such a question - and in deference to the possibility that English is not your first language, or you are unfamiliar with cultural norms, I have posted this response as such. However, racially offensive questions are not very well received. While we don't censor such questions, because we value free speech, I think this question is inappropriate and unscientific. If you have a specific scientific question about ethnic or cultural identity; or if you have a specific question about human skin pigments, you should rephrase your question. Nimur (talk) 18:00, 12 June 2009 (UTC)

That is correct; the OP is a troll, and everyone who has responded, including myself, has been successfully trolled. Tempshill (talk) 22:00, 12 June 2009 (UTC)

Out of curiousity, are there visible differences between Koreans, Chinese and Japanese? IOW, if you see an Asian person, can you tell which country they are from? For example, can you tell that Jin from Lost really is Korean? A Quest For Knowledge (talk) 18:18, 12 June 2009 (UTC)

I see nothing racially offensive about the content of the question though I know some people treat people of other races badly for no other good reason than their color. Personally I'm prejudiced in that I have liked both the Poles and Chinese I have come across, it's my negative prejudices I have to be a bit more careful about. And by the way yes I can tell Koreans Chinese and Japanese apart quite easily normally. Dmcq (talk) 18:32, 12 June 2009 (UTC)

Well, Jin's name is very Korean, that kind of gives it away. Like guessing the nationality of man named Sean O'Grady. Livewireo (talk) 19:02, 12 June 2009 (UTC)

really? I have asked this question of numerous japanese and Chinese people (and one mongolian) and they all said they could not tell the difference between Chinese and Japanese people until they heard a person speak (or only based on cues such as clothing). Don't many people depend on this fact? Spies, Korean-born-Japanese-pop-stars etc - if there are obvious visible differences, then the vast majority of people seem to be missing them. But then i am pretty sure that no English person could really identify a Pole under controlled conditions - people think they can because of subconcious social cues.YobMod 19:07, 12 June 2009 (UTC)

Well there are lots of different types of Chinese people so you get all sorts but I must admit I'm very surprised. My first language was Chinese though I'm not Chinese myself so that probably helps with seeing them as different. Dmcq (talk) 19:22, 12 June 2009 (UTC)

There's a test at [25]. I didn't do as well as I though I would and seemingly lots of nationals from those countries do worse. Dmcq (talk) 20:44, 12 June 2009 (UTC)

I've read that carotene-based tanning products are popular in parts of Europe. That can give an unusual cast to someone's skin color. APL (talk) 18:40, 12 June 2009 (UTC)

A bit late for WP:DENY but OP blocked. See talk. hydnjo (talk) 22:26, 12 June 2009 (UTC)

tennis

What is a "winner" in a tennis game?utkarsh (talk) 11:04, 12 June 2009 (UTC)

This was answered on the Miscellaneous desk. Please don't post the same question on multiple desks. AndrewWTaylor (talk) 11:20, 12 June 2009 (UTC)

Adolescent development

http://aces.nmsu.edu/pubs/_f/f-122.pdf Reading this it seems that late adolescents (17-19) are pretty much adults, they have empathy for others, have a clear identity and are able to think logically etc. So what factors still make them adolescents from a scientific point of view. 81.154.253.59 (talk) 11:43, 12 June 2009 (UTC)

From a biological point of view, you are adult since puberty. Thinking logically, having an identity or empathy are not signs that you are an adult, not matter how desirable these characteristics are.--Mr.K. (talk) 12:42, 12 June 2009 (UTC)

Psychologically, such character traits may be used to distinguish adolescents and adults (depending on which theories are believed), which is called "psychological age". Cf. "chronological age", "biological age" and "social age". Chronological age is the most simple to detirmine, as one just counts from birth, but may not always be the most useful. Biological age has useful developmental markers such as puberty, but these may not correspond to social age - is a sexually functional 12 year old an adult? The answer is always culturally dependant. A 25 year old man could have the psychologically adaptive capabilities of a child, and his adult status may depend upon situations (eg. he is adult enough for sex, but all his money is stored in a trust fund controlled by others). So the scientific answer is "it depends on which science, and why the age is needed".YobMod 13:15, 12 June 2009 (UTC)

(EC with yobmod)However, from a sociological point of view, what makes one person capable of taking on adult responsibilities varies greatly from society to society, and people will tend to act as they are expected; thus when a society expects a 14-year old to be an adult, one will often find a 16-year old having adult-like psychology. When another society places the age at 18, they will find most 16-year olds to have child-like psychology. And the biological definition of adulthood is not a bright-line. Puberty is a process, and I would venture that it is the end of puberty, and not the start, that is a better definition of full adulthood, but reasonable people may disagree on when that occurs. --Jayron32.talk.contribs 13:17, 12 June 2009 (UTC)

Jepp - i didn't go into social age, but the textbook i am getting this from distinguishes that from psychological age. Social age means taking on responsibilites associated with a certain age, whereas psychological age is detirmined by "adaptive behavioural strategies". I don't think changing the social role necessarily changes the psychological age - teenage mother's need extra support as their social age is far advanced while their pschological age is not (and to some extent is dependant on biological age).YobMod 13:29, 12 June 2009 (UTC)

(outdent)One hugely influential psych theory that differentiates between adolescenthood, young adulthood, middle adulthood etc is Erikson's stages of psychosocial development. And biological changes associated with growth continue much past puberty - chest hair growth for example may not have even started by age 19.YobMod 13:29, 12 June 2009 (UTC)

There is a lot of evidence that brain development is not complete at age 18 - particularly the areas relating to self-restraint and risk-taking. Some studies show that full maturity does not arrive until perhaps age 25:

• http://www.dartmouth.edu/~news/releases/2006/02/06.html
• http://www.washingtonpost.com/wp-dyn/articles/A52687-2005Jan31.html
• http://www.youthadvocacyproject.org/pdfs/Brain%20Annotated%20Bibliography.pdf (Loads more links in here)

But we start to get into a fuzzy argument here - after all, people even later in life (in their 40's and 50's) start to change mental recall strategies from raw memory (which begins to fade) to using intelligence/logic-based strategies (which continues to strengthen). Should we argue that "brain development" continues into your 40's and 50's and declare all 30 to 40 year olds "under age" for some activities demanding cold, hard logic? Surely not?! But it's also arguable that humans evolved in a situation where they'd mostly be dead by age 25 (average longevity in the bronze age was 18 years!) - and even in ancient Rome, Greece and medieval europe 25 was about the average life-expectancy, so if brain development is still happening at age 25 - should we not consider 18 year-olds to be the "normal adults" (with their high risk-taking and poor self-restraint being considered "normal") and the 30+ year olds to be "post-adult" and incapable of considering "normal" degrees of risk? It's just a matter of terminology in the end. What we should perhaps be asking is whether it makes sense to impose limits on 17 to 19 year-olds because of this risk-taking difference. Limiting alcohol use and access to fast, dangerous machines might make sense even if we decided they were to be called "adult" because a "normal" level of risk-taking is still too risky when the stakes are that high. SteveBaker (talk) 16:20, 12 June 2009 (UTC)

Steve, although the average life expectancy in those times was 25 years or less, this was mostly a result of the large numbers of children born who did not make it to adulthood. A lot of times, if a person got past that first part, they would often live 50+ years. 65.121.141.34 (talk) 16:33, 12 June 2009 (UTC)

As mentioned, life expectancy is a terribly misleading statistic, especially if the distribution of age at death is heavily bifurcated (as is the case when infant mortality is statistically significant). Nimur (talk) 17:31, 12 June 2009 (UTC)

Cutting Limes

Why is it when I cut limes, my hands are never sticky? Actually, when I cut limes sometimes I don't wash my hands because they smell nice afterwards? Is it the low sugar content? If so, what type of sugar? --Reticuli88 (talk) 18:59, 12 June 2009 (UTC)

See Limonene the solvent action is mentioned in Orange oil. 71.236.26.74 (talk) 20:49, 12 June 2009 (UTC)

• To answer your question, when you cut out limes, oranges or lemons your knife and your hands will never be sitcky, because it is not made of oils such as meat, chickens, or barbeques. When you wash dishes or hands with citrus fruits, watermelons, apples, or grapes all you have to do is rinse with water, but you don't have to clean it with your soap.--69.226.38.106 (talk) 22:20, 12 June 2009 (UTC)

May I ask a follow-up question, regarding the washing of fruit? It's common knowledge that one should wash, say an apple or grapefruit before eating, even though you don't necessarily eat the skin of the grapefruit - but my girlfriend has a tendency to wash an apple with washing-up liquid before eating it - a little drop on the sponge, wipe fruit, rinse fruit thoroughly. I find it awful. Is this practiced/common/uncommon/unspeakable? --Ouro (blah blah) 06:40, 13 June 2009 (UTC)

Fruit gets washed mostly to get pesticide residues and waxes (the "make the fruit look pretty on display at the store stuff"). Dishwashing liquid can contain lots of chemicals and you can't know how they might react with those you wish to get rid of. In addition those chemicals only get tested for irritating skin, not for what they do if the get ingested. In case your friend doesn't like the results she gets with plain water and a brush she might try adding a bit of baking soda. It's safe to eat (for all but a very few people with certain medical problems) and if nothing else has a slight Abrasive effect. A study (sorry can't get at it) has found that vegetable washes they advertise aren't any more effective than plain water and a brush. 71.236.26.74 (talk) 07:09, 13 June 2009 (UTC)

warm "blooded" plants

In his speculations about the possibility of the most ultimate spread of life into space in Infinite in All Directions, Freeman Dyson discussed the advantages of warmbloodedness and mused on the fact that plants have never evolved this trait. What conceivable advantages for plants could such a trait have? --Halcatalyst (talk) 22:46, 12 June 2009 (UTC)

Plants have evolved other safeguards against temperature changes besides "warmbloodedness". The ability to maintain a constant temperature, aka basal metabolism is a fantastically wasteful process. You basically are eating all day just to keep your temperature up. There are certainly advantages to it, but seeing as plants evolved other systems to deal with the ups and downs of the external temperature, it doesn't seem like there was much need for them to evolve this trait, given the obvious disadvantages that come along with it. --Jayron32.talk.contribs 23:12, 12 June 2009 (UTC)

I do believe it is lotus plants that elevate their temperature above the night-time surroundings. That to me would qualify as "warm-blooded" and it does convey an evolutionary advantage. I may need a few minutes to get the links though. (Especially since the 7th game of the Stanley Cup final series starts in a half-hour) Franamax (talk) 23:24, 12 June 2009 (UTC)

Whew, just in time. It is "Thermoregulating lotus flowers", R. Seymour & P. Schultze-Motel, Nature 383, 305 (26 September 1996) doi:10.1038/383305a0 My Nature subscription only lets me access fulltext back to '97, but as I remember the content, the plant upregulates to 2-3 degrees above ambient temperature. Anthems are starting, the game is on, must go now. :) Franamax (talk) 00:08, 13 June 2009 (UTC)

Warm bloodedness makes a more active life possible. You have to eat more, but you also have the energy to find the food. Plants, however, are rooted in the earth, which seriously limits their mobility and makes such a lifestyle unlikely. Unless they uproot themselves, like the Triffids. So it would make most sense if that trait evolved first. But I don't know of any real plants that can do this. The best chance of this happening seems to me to be in the water, where plants can float around and then still get their nutrients the plant way. Once they do that, the ability to swim may become an advantage, in which case warm bloodedness starts to make sense.

But then there is the necessity for muscles, which will be needed to use this energy. One way for plants to move is by growing. But then they would have to do that at an incredible pace and most of their energy would have to go into growing (and then splitting off in several plants, I imagine, something that plants are good at). The only other way that plants can move that I can think of is the way certain carnivorous plants do it. The descriptions sounds a bit like the way muscles work (note that I'm not a biologist). And the way the signal is passed on even sounds a bit like a nervous system, which seems to me to be another necessity, for rapid response to the environment. Give these plants another million years of evolution, and who knows..... DirkvdM (talk) 07:32, 13 June 2009 (UTC)

June 13

What is this bug?

In the past two days, I've seen two of these little guys crawling around. Because I was too terrified to get a picture, I've done this awful MSPaint approximation. They're about 3/4 of a cm long, and the spots look like little fuzzy bits, and are arranged in a rectangle, with the darker orange on the outside and the beige on the inside. There is no shell or wings or anything, and they're not shiny. I'm in Toronto, Canada. I've never seen anything like it in my life -- what are they? And should I be worried? --✶♏‭ݣ 01:23, 13 June 2009 (UTC)

I don't know, but that's a great drawing, maybe you could sell it for $10 000 on eBay! ~~ Ropata (talk) 03:36, 13 June 2009 (UTC)

Oh, Ropata, that one made me laugh! Thanks, Ouro (blah blah) 06:44, 13 June 2009 (UTC)

That drawing and your description makes me think these might be ladybird(ladybug)larvae. There are many species of which the Harlequin ladybird is causing a little concern in the UK following its invasion from mainland Europe over the last few years. Here[26]is an image of a Harlequin Ladybird larva. What I don't know is how common these beetles are in Canada. You have little need to be worried on a personal level as they eat aphids and other small creatures, unfortunately including the larvae of other ladybird species. Richard Avery (talk) 07:18, 13 June 2009 (UTC)

Coccinella septempunctata is Canadian and has a pic of the larva in the article.71.236.26.74 (talk) 07:28, 13 June 2009 (UTC)

Carnivoran trait

Why do dogs, cats and bears have ridges on the roofs of their mouths? --Lazar Taxon (talk) 01:43, 13 June 2009 (UTC)

According to Answers.com,

Those ridges are called rugae. They are meant to help break down the food you are chewing, as food is pressed up against them during mastication. —Preceding unsigned comment added by Ropata (talk • contribs) 06:20, 13 June 2009 (UTC)

Walking dinosaurs

When I naively looked at pictures of dinosaurs , I think I see a pattern. There seems to be two types of dinosaurs.

1. Dinosaurs that walk/move on two legs

2. Dinosaurs the walk/move on fours legs.

It seems to me untrained mind that all the herbivore dinosaurs walk on four legs while all the carnivore dinosaurs walk on two legs.

This to me seems really really odd, if you are a carnivore then you need all the speed in the world to catch your prey. Therefore you must run faster by using all four of your legs, running on two legs is really stupid.

No carnivores today would run on two legs because your prey would run away faster than you can chase them.

I approach this question and I came up with 3 ideas. I want everyone to criticize me ideas and suggest new ones.

Three Basic Ideas.

1. Carnivore dinosaurs run on two legs because they have a long thick tail. Because they evolve into having long thick tails, they are unable to run on four legs therefore they must run on two legs to balance their tails.

2. Carnivore dinosaurs are blind, therefore they run on four legs. As they are blind they must hunt with their nose (sense of smell) therefore their front legs must be short as they move around with their noses to the ground.

3. Carnivore dinosaurs only hunt in shallow streams, as they must move in shallow streams, the fastest way to move around is on two legs rather than on four legs. So they hide underwater and slowly move closer to their prey and pop up in the last minute to run on two legs towards their prey. This makes a lot of sense to me as I practice running on four legs on a shallow stream and it is very difficult.

122.107.207.98 (talk) 08:39, 13 June 2009 (UTC)

First, I doubt that your hypothesis is right. Many birds (cladistically two-legged dinos) are herbivores. And why would you assume that a 4-legged animal is necessarily faster than a 2-legged on? Humans are excellent long-distance runners (well, trained humans ;-), Ostriches can run at over 70km/h. Take a look at some kangaroos occasionally. Not all carnivores run their pry down in a sprint - there are endurance hunters, scavengers, and lurkers as well. And of course, to catch prey it is enough to be faster than the slowest prey - in fact, if anything the prey would have an incentive to evolve for speed ("The fox is running for its next meal, but the hare..."). --Stephan Schulz (talk) 09:19, 13 June 2009 (UTC)

Running on two legs does not make sense because it actually increases the amount of air friction as the dinosaur chases it's prey. If it had run on four legs, it will minimize the air friction and have a streamline aerodynamic form and get a better grip on the ground. 122.107.207.98 (talk) 11:23, 13 June 2009 (UTC)

How hot is boiling water?

I was watching QI last night when Hugh Fearnley-Whittingstall mentioned that water on a "rolling-bowl" was much hotter than water that was simmering. I have never really understood the difference between boiling and simmering, because in both cases the water is turning into vapour and therefore presumably reaching 100C, and I would not have expected that it would go over 100C (at least not by very much). Now I am wondering whether, on a rolling boil, whether so much heat is being put into the bottom of the pan that the water actually is getting much hotter (as HFW states) than 100C, before it gets a chance to vapourise. I read Boiling_water#Boiling_in_cookery but it does not seem to give a definite answer. Can anyway help clarify what actually happens please? Frank Bruno's Laugh (talk) 09:21, 13 June 2009 (UTC)

Pressure at the bottom of an open saucepan of water is higher than atmospheric due to the weight of water above. This raises the boiling temperature slightly. With heat applied from below there is continual vaporisation of water at the base from which bubbles of vapour rise and are replaced by new water. This process absorbs considerable heat energy due to the latent heat of vapourisation that water requires. Superheated steam could be generated only by such a huge inflow of heat that vapour is generated faster than can be replaced by liquid. Cuddlyable3 (talk) 11:14, 13 June 2009 (UTC)

Suicide Question

Hello,Im not seeking medical advice, just a curiosity, whats the best method of commiting suicide if you are locked in a room whit absolutely no tools (only your body)? (Not my case , if im writing this I have electricity and I can finish myself of this way. DST

It's good that you don't seek medical advice because Wikipedia won't give it. The best method is not to entertain a morbid curiosity. Cuddlyable3 (talk) 11:20, 13 June 2009 (UTC)

Its a scientific question, no morbid curiosity i stated it before.

Cancer rates in mammal species including humans

Are the rates across different species similar, or do they differ? 89.243.85.18 (talk) 11:16, 13 June 2009 (UTC)

See the section on whale cancer above. They seem to differ, and differ significantly. --Stephan Schulz (talk) 11:23, 13 June 2009 (UTC)