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January 21

Surface roughness

if two tubes one of steel and other of Zr-4 is coswaged is it possible to get 0.1 microns gap cosidering there suface roughness also?203.199.205.25 (talk) 03:52, 21 January 2009 (UTC)

I don't know what Zr-4 is (do you mean Zircaloy-4 (Zry-4)?) or exactly how you plan to swage the two, but this link may help you. It discusses the surface roughness height for steel produced by different methods. [1] Since 4 microinches is about .1 micron you are going to need to get a very very very smooth set of tubing. If you are talking about Zircaloy-4 when you mean ZR-4, I stumbled across some micrographs from an electrode corrosion test. In the tests, it was found that Zircaloy-4 is susceptible to forming corrosion films which have surface irregularities which eyeballing the pictures appear to be on the order of a micron or so in height. That could be a problem depending on what exactly you are using the tubing for. From experience, stainless steel hypodermic tubing with a net diameter difference of 25.4 microns threads cleanly and slides easily but definitely not frictionlessly. I am going to guess that on the level of .1 micron the surface irregularities are going to be significant. I am no expert on this so I would suggest asking someone who has done this sort of thing or simply trying it out if it isn't difficult and you have materials and methods on hand. 152.16.15.23 (talk) 05:31, 21 January 2009 (UTC)

BATTERY

BATTERY THAT CAN BE CHARGED WITHIN 30 SECONDS FOR 2 HOURS WITH 5000V OR MORE VOLTAGE SUPPLY. —Preceding unsigned comment added by 117.99.4.227 (talk) 05:29, 21 January 2009 (UTC)

Apparently that battery is MAKING YOU SHOUT. Now, do you have a question, or did you merely want to scream at us about your battery? --Jayron32.talk.contribs 05:36, 21 January 2009 (UTC)

I would suggest you start with Rechargeable battery and Battery charger. I am not sure what your question is because you seem to have omitted the first word. If your question is, "Can a battery be charged within 30 seconds for 2 hours with 5000V or more?" the answer is no. Attempting to recharge many types of rechargeable batteries with a voltage of that magnitude is likely to irreparably damage the battery via excessive heating. Additionally, the battery could also explode. According to rechargeable battery, Duracell and Rayovac now sell chargers that can charge AA- and AAA-size NiMH batteries in just 15 minutes. It is good online etiquette to not use all-capital letters when writing because it is interpreted as yelling. 152.16.15.23 (talk) 05:58, 21 January 2009 (UTC)

(following EC) ::Sounds like an awful lot of juice and a very short time. Couldn't you charge a capacitor first and then design your circuit to take your merry time to charge the battery?? I'm also not quite sure If I understand your question correctly: You are trying to find out whether there's a rechargeable battery that will supply in excess of 5kV for 2 hrs. That would most likely be a (huge) battery array, but with that many you are likely to run in to all sorts of strange effects because of internal resistance. Electrolysis of water and Fuel cell might help. 76.97.245.5 (talk) 06:15, 21 January 2009 (UTC)

You don't say how much current you need this thing to source or at what voltage...that's a crucial question! It certainly sounds like you need a supercapacitor rather than a battery. If you need to source a lot of current then putting that much energy in one place so quickly means that any inefficiency within the battery/capacitor is going to get turned into heat. So if the charging process is even a tiny bit inefficient (say it's 80% efficient - so 20% of the energy gets turned into heat) - then the battery is going to get insanely hot - and presumably destroy itself. When you charge more slowly, the battery has time to radiate that heat naturally and it's not much of a problem...but even batteries that recharge over hours do get noticably hot during the process. If you shorten that time to 30 seconds then all of that heat is still created - but all at the same time! This will get the thing so hot that it'll literally melt (that's if the liquids inside don't boil or otherwise explode). So you need to find a supremely efficient solution that'll keep the heat down - or you'll need to consider some kind of active cooling approach. You could also consider other means to store the energy. For example, you would wind up a spring in a clockwork motor or pump water to the top of a tower and let it flow back through a turbine. My long-case clock can be wound up in 30 seconds and runs the clock for a month - that (technically) meets your requirements - but without knowing how much current & voltage it has to generate, there is no way to know whether that would work for you. More information needed please! SteveBaker (talk) 14:12, 21 January 2009 (UTC)

Any device which stores large amounts of energy is inherently dangerous. Things fall, explode, react chemically, cause electrocution, etc. High voltages are easy to get from batteres, by connecting lots of cells in series. Humphry Davy built a primary (non-rechargeable) battery of 2000 cells of zinc and copper way back in 1808, which likely produced 2000 volts or so and could supply it for an extended time if the current draw was small. It could supply about 3 kilowatts[2]. Lead-acid batteries provide about 2.1 volts per cell, so 2500 cells would suffice. It would be pretty dangerous and there would be a great danger of death or injury from electric shock. The 30 second recharge demand is unrealistic. You could use other forms of energy storage, such as putting current into a Superconducting magnetic energy storage, charging a capacitor, spinning up a flywheel, winding a spring, compressing air, lifting a weight, heating up a thermal storage mass, or adding chemical fuel to a device. Edison (talk) 19:30, 21 January 2009 (UTC)

Plastic In Bandy Balls

What kind of plastic makes up Bandy balls? Are they hollow? Please look at the description here:

To the rightmost a modern, plastic bandy ball.

96.53.149.117 (talk) 05:47, 21 January 2009 (UTC)

Some more info from our Swedish page: The thing is 60 mm in diameter and weighs 60g. Maybe OP could find s.o. who speaks Russian and see what the Russian page / googling in Russian will give him. If you trust this article [3] new balls in Sweden are 2.4 mm thick, it doesn't say whether that's just a coating or whether they're hollow. That's barely a tenth of an inch. They're also a tad bigger at 62.4 mm76.97.245.5 (talk) 06:25, 21 January 2009 (UTC)

Bandy balls are not hollow, the inside is cork. Usually, I should add, since the official rules only require that the ball shall be made of an "approved material". Here is an article, in Swedish but with pictures, about bandy balls being made in Sweden out of cork and PVC plastic. --Rallette (talk) 07:51, 21 January 2009 (UTC)

And as to that Aftonbladet article, it is actually about a dispute in the Swedish bandy league over the size of the ball. The ball used to be 60 mm in diameter, but this was increased in 2001 to 62,4 mm for better audience and television visibility. One team refused to use the new ball, but the bigger size is now official. So the 2.4 mm is just that increase in diameter, not the thickness of the plastic.--Rallette (talk) 08:03, 21 January 2009 (UTC)

We had this question just the other day - but I'll repeat the answer (and repost the photo at right showing the stages of construction): They are made of cork, covered with a "knitted" material that looks like some sort of knotted rope and then painted with a thick coat of red paint. As far as I can tell from our article - they are not made of plastic at all - although there may be unofficial practice balls or something that aren't made "properly". SteveBaker (talk) 14:01, 21 January 2009 (UTC)

The description on that picture's page says the ball on the far right is a modern, plastic bandy ball. -- Mad031683 (talk) 17:25, 21 January 2009 (UTC)

It may well be they're made or have been made in a number of different ways; my answer was mainly based on that newspaper article about the major Swedish manufacturer (Jofa), who make them by spraying a shell of PVC onto the cork core. This also squares with my personal experience with bandy balls: the ones I've seen and handled (and even played with, this all brings back some awkward schoolday memories) have been of the plastic coated kind. I imagine the process described by SteveBaker is the original or old-fashioned way, and the knobbly surface of today's balls is an imitation of the result.--Rallette (talk) 09:16, 22 January 2009 (UTC)

penicillin test

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Milkbreath (talk) 20:17, 21 January 2009 (UTC)

Whether this is a medical advice request is being debated here: [4]. StuRat (talk) 13:38, 22 January 2009 (UTC)

747-400 seat cushion dimensions

What is the depth of a Thai Airways Boeing 747-400 ecomony class aircraft cushion? I need the measurement from the front of the seatback to the front of the seat cushion, NOT the pitch.Sarahonthemove (talk) 08:03, 21 January 2009 (UTC)

There are different seat dimensions for different airlines, unfortunatley. Each airline has the 747-400 constructed to their specs. American Airlinesloves to boast of their extra leg room in economy class. I, personally, have struggled to locate these mysterious few extra inches. :-) Operator873 (talk) 09:00, 21 January 2009 (UTC)

Depleted uranium

Is ever used for the core of bowling balls? Thankyou. --90.240.55.65 (talk) 10:08, 21 January 2009 (UTC)

I personally doubt it. Bowling balls simply don't require the density. Even making the ball's core from mostly iron would be enough Nil Einne (talk) 11:22, 21 January 2009 (UTC)

(EC)For example Bowling ball says they're 21.6cm. Even assuming the inner core is only 16cm that would give a volume of 4/3 pi 8 cm^3 i.e. 2.14466058 liters. Taking the density of iron at RT from our article that is, 7.874 g/cubic centimetre we end up with nearly 17 kg. That is already a lot heavier then "Regulation ten-pin bowling balls must weigh no more than 16 pounds (7.2 kg)". While I appreciate some are constructed in somewhat different fashion then just having a solid core of weight, clearly you don't need the density given by depleted uranium. Nil Einne (talk) 11:41, 21 January 2009 (UTC)

Ok I know what he was thinking, cuz I was thinking it too... no way right? Then I got to looking and searching... And then I nearly puked. Are You Kidding Me? (Click Here). Yes, Virginia, there is a Santa Clause... and an "Enriched Uranium Bowling Ball" with a core made of U235. Wow... I'm left speechless by this... Upon further mental reasoning... U235 Uranium core has got to be a marketing gimic. U235 is radioactive with a halflife of 700 million years. Nevermind, I feel better now. Operator873 (talk) 11:25, 21 January 2009 (UTC)

I beg forgiveness from all Wikipedians out there. I don't know what to say to explain my lack of mathmatical and realistic reasoning. In a famous word, "oooopsieee." Operator873 (talk) 11:44, 21 January 2009 (UTC)

The benefit to using depleted uranium (or any other denser material) would be a reduction in the moment of inertia of the ball whilst remaining in the legal range of ball weights. As Nil Einne points out, you can easily reach the maximum allowed weight with very conventional materials - but if you used something with greater density, you could concentrate that mass in the center of the ball rather than distributing it through a larger part of the volume of the ball. The result would be a ball that ought to be much more responsive to spin - it would change direction more easily as friction 'grabs' it and it would be easier to impart more spin onto the ball when you start it rolling. So I can definitely see an advantage for better players to have a denser center even if the ball remains at the legal maximum.

Sadly, our article on bowling balls doesn't say what their centers are currently made from. If they are already using (say) lead - then the benefits of switching to depleted uranium would perhaps be quite significant in allowing more spin to be applied. If you are riding the competitive edge, it might make the difference. Lead has a density of 11gcm^-3 and uranium is up at 19gcm^-3 (about the same as gold)...we should probably calculate how much that would help the "spinability" of a 16lb ball...but I'm not going to because I'm feeling lazy today! Osmium would be the most dense "practical" choice - at 22gcm^-3 it's even denser than gold...sadly, if you buy Osmium from these guys it's going to cost you $880,000 to get 16lbs of Osmium oxide...which you'd have to refine...so you might want to stick with the Uranium! The ultimate would be a Hassium-centered ball. Hassium is more than twice as dense as uranium or gold...of course it's not going to be cheap since it has to be made atom by atom in a nuclear reactor...and it's radioactive as all hell...and it's going to turn back into lead within an hour or two...unless 16lbs is more than it's critical mass - in which case what you have is more of an atom bomb than a bowling ball(!)...but for that championship game where the slightest edge matters, nothing else can beat it.

SteveBaker (talk) 13:54, 21 January 2009 (UTC)

Does blowing up the bowling alley (and most of the surrounding city) count as a strike? --Tango (talk) 14:00, 21 January 2009 (UTC)

Yes. You're certainly unlikely to risk a 7-10 split - but sadly it risks a counter-strike. SteveBaker (talk) 20:53, 21 January 2009 (UTC)

Years of researching this matter by watching the Loony Toons has taught me that no matter how badly the bowling ally is demolished, in the middle of the rubble, at least one pin will still be standing. It may be badly scorched. It may be wobbling. But it will not fall. APL (talk) 14:29, 21 January 2009 (UTC)

I see you're familiar with my bowling style! SteveBaker (talk) 20:53, 21 January 2009 (UTC)

Natural Polymers

I need a conclusion on the topic Natural Polymers. —Preceding unsigned comment added by 59.93.15.143 (talk) 12:40, 21 January 2009 (UTC)

Without seeing your essay it's impossible to give a conclusion 78.146.113.20 (talk) —Preceding undated comment was added at 13:02, 21 January 2009 (UTC).

We don't have an article on natural polymers - but if you do a search on the term, you'll find that there is a lot of material on the topic scattered throughout the encyclopedia.

Natural rubber might be a good place to start, but perhaps not the best place to conclude. StuRat (talk) 13:42, 21 January 2009 (UTC)

There's also the ubiquitous carbohydrate and protein, the two types of polymers used by organisms to fill structural (and a myriad of other) roles. If you're not just looking for structural functions, I would be remiss if I neglected to mention the nucleic acid polymers, RNA and DNA. – ClockworkSoul 18:14, 21 January 2009 (UTC)

I just noticed these, which may be helpful: biopolymer and bioplastic. They need some love, but you may find them helpful. – ClockworkSoul 18:18, 21 January 2009 (UTC)

I have almost completed my project on Natural Polymers, I just need a conclusion. The sub-topics were Nucleic acids, natural rubber, protein, cellulose and chitin. It mainly contains structure, characteristics and their uses. All I need is a conclusion. Any ideas?59.93.1.19 (talk) 14:28, 22 January 2009 (UTC)

There's the old standby "life itself would be impossible without X". Of course, there are a huge number of things which can be argued to fall under category X. (And, of course, natural rubbers may have also prevented quite a few lives. :-) ) StuRat (talk) 17:08, 26 January 2009 (UTC)

Iris Depigmentation

Is there a disease or condition in which the iris in the eye will slowly depigmentate (years), especially in teens or young adults? I am aware of what glaucoma can do to the elderly..... --Emyn ned (talk) 14:09, 21 January 2009 (UTC)

Perhaps a nutritional deficiency could also cause this. Also, glaucoma doesn't always just affect the elderly. StuRat (talk) 15:31, 21 January 2009 (UTC)

--Emyn ned (talk) 17:45, 21 January 2009 (UTC)

Lingual Frenectomy in Adults?

I have asked this question recently but was never answered. I am asking what are the medical benefits, if any, for adult lingual frenectomy? Are there any sound medical reasons an adult would need this, not want this? --Emyn ned (talk) 14:11, 21 January 2009 (UTC)

Have you read Lingual frenectomy? --Tango (talk) 14:39, 21 January 2009 (UTC)

Better question, have you? --Emyn ned (talk) 14:40, 21 January 2009 (UTC)

The one benefit they listed which might apply to adults is to "help improve speech". However, this, and any other benefits, would only apply if there's some abnormality to begin with. StuRat (talk) 15:27, 21 January 2009 (UTC)

I thought the article in Wiki only refers to children or infants. Did I misread it? It is possible...--Emyn ned (talk) 15:29, 21 January 2009 (UTC)

It doesn't specify that the speech improvement only applies to children. --Tango (talk) 15:40, 21 January 2009 (UTC)

The article in Wiki says:

This is used to treat a tongue tied patient. Immediately after this minor oral surgery, the tongue can often dramatically extend out of the mouth which it could not do before. This can help reduce breastfeeding complications, help improve speech and promote proper tooth arch development.

The last sentence implies that everything else stated was referring to infants. I realize that adults can be tongue tied, but the article does not imply that at all. If the Ref Desk doesn't know the answer to my question, that's all right. No need to conjecture. It is possible that adult Lingual Frenectomy is only done for aesthetic reasons. --Emyn ned (talk) 15:50, 21 January 2009 (UTC)

While breastfeeding complications and tooth arch development would seem to refer to children, that doesn't mean the speech improvement does (although, in most cases it will do - why wait until adulthood to fix a speech impediment?). --Tango (talk) 17:01, 21 January 2009 (UTC)

I am only referring to reading comprehension here. The article clearly implies children only despite your opinion that the article references adult speech impediment. All in all, the article ONLY refers this procedure as performed on children. Please let's not fight about what you think the article should state. Besides Tango, do you have a direct answer to my original direct question? Do you have any knowledge or expertise in oral surgery in general? --Emyn ned (talk) 17:45, 21 January 2009 (UTC)

BTW Tango, don't confuse my bluntness for rudeness. I do actually want to know if you have any knowledge or expertise in oral surgery in general. I would like to know which volunteer takes the most medical/biological questions on this board. --Emyn ned (talk) 21:48, 21 January 2009 (UTC)

Woah - slow down here. We're all just volunteers - we're not REQUIRED to answer your question. If you need an answer from an expert in oral surgery then this is a question of a medical nature that we are emphatically NOT allowed to answer. If it's just general curiosity then please listen to the volunteers because they are amongst the smartest people you'll ever meet AND they have this incredible encyclopedia at their fingertips which they know how to use effectively. There is also an element of common sense here. So chill out - stop arguing with the very people you're asking to help - listen to what they have to say and take away whatever nuggets of truth you wish. If you don't want to do that - then please feel free to head over to Yahoo Answers] and seek the truth there. Thanks. SteveBaker (talk) 20:48, 21 January 2009 (UTC)

SteveBaker, in that case, Tango and the rest of the Ref Desk volunteers should state "we're not REQUIRED to answer your question". I can't listen to the volunteers because they are not speaking. However, I can READ their responses. And in response to your comment "they are amongst the smartest people you'll ever meet AND they have this incredible encyclopedia at their fingertips which they know how to use effectively", why does my original question remain unanswered? Any reason will suffice. BTW - I was already chilled. I wanted to point out to Tango that reading comprehension should be required when responding to questions.

In the meantime, do you have an answer to my question or did you just want to bite OP's? --Emyn ned (talk) 21:37, 21 January 2009 (UTC

I couldn't find any relevant Pubmed or Google references for this in adults. Axl ¤ [Talk] 21:54, 21 January 2009 (UTC)

The reason for the focus on treatment of children in the phrase you quoted might be because that's the most common application of the procedure. Medicine is compartmentalized into pediatrics, geriatrics and the like to allow practitioners and researchers to focus on the most relevant factors. The medical professions try to prevent or counteract an impairment as close to it's onset as possible. The more is known about a condition and the longer treatments have been around the closer to early intervention you get. That means that if the known onset is in childhood or prenatal there are fewer adult sufferers who remained untreated and treatment and new developments are going to be focused on young patients and treatment in the womb. Information on such conditions will reflect that. An article on Alzheimer's disease on the other hand will rarely contain information on treatment in children. OR When the Allergy wave hit I used to be frustrated by having to wade through tons of information on treatment of children and babies. So I sympathize if you find the sentence you quoted frustrating. Information on application of the procedure in adults may be hard to come by. If you do find something you could add a paragraph to the article. If it is indeed rarely done, be sure to identify that by adding something line "In rare cases..." 76.97.245.5 (talk) 23:01, 21 January 2009 (UTC)

Emyn ned, my impression is that you don't realize that some of your responses are very off-putting. Not sure whether this is helpful, but please realize that folks on the RefDesk are well-intentioned and well-informed as a rule. This is not a medical advice forum, it is a Reference Desk for Science questions. People have tried to be helpful within the guidelines we have, so if you're not satisfied with the answer please don't criticize. Please assume good faith. --Scray (talk) 02:14, 22 January 2009 (UTC)

Emyn ned another thing you don't seem to appreciate is that the RD isn't like some single entity. It's possible someone could give a better answer but hasn't yet seen your question, or perhaps has but can't be bothered replying after seeing the way you responded. If you really need an answer so desperately, I believe there are one or two doctors around, I don't know if there are any whose expertise is in this area but if you offer to pay them I'm sure they could research the matter better. For that matter, even no experts could as well. Nil Einne (talk) 11:45, 22 January 2009 (UTC)

P.S. This article [5] while not a reliable source, suggests speech improvement is actually a common reason for adults seeking the surgery, contrary to your beliefs to the contrary. The good thing is, again despite your claims to the contrary, nothing in our article suggests it is the speech thing is for adult only. It also gives other reasons. Having said that, there's no evidence any of the reasons, even in children are really a case of need. Actually that applies to a lot of surgeries we're it comes down to a balance of the advantages and potential complications. If the advantages are overwhelming (e.g. a significant improvement of the quality of life) and the complications/disadvantages few for most people the choice is clear but unless your going to die without the surgery, it's difficult to say you need the surgery. Perhaps you're thinking of the definitions used, particularly by government funded health services and I guess insurance companies for elective surgery but even these are rather complicated Nil Einne (talk) 11:49, 22 January 2009 (UTC)

The history of Medicine is littered with cases where surgeons have jumped in to "correct" things in children that seem abnormal - only to later discover that they weren't abnormal at all - or that fixing them wasn't necessary because the child would "grow out of it" later - or that the risk of the procedure exceeds the actual benefits. Hence (no doubt) there is extreme caution involved in leaping into something like this. This may explain why the procedure isn't common in kids. I would assume (without evidence) that the issue of whether to perform this surgery on kids or not would hinge on whether there were collateral developmental issues with not treating it early. Does a child with this condition actually fail to learn intelligable speech such that when treated for it as an adult, the impairment continues after surgery corrects the anatomical problem? If so then you'd expect there to be more research into treating children. If the surgery is effective even when delayed into adulthood - then probably doctors will advise a 'wait and see' approach simply because adults survive surgery at better rates than little kids do.

Examples that I can think of are with cross-eyed babies...about 15 to 20 years ago, it was discovered that if that's not corrected within just a few months of birth, the child will never form the brain "circuitry" to perform adequate depth-perception - and even if the eyes straighten themselves out by (say) two years of age as they typically do. Just three or four years ago, the impairment was considered permenant and untreatable. Hence, early correction of cross-eyes in tiny babies is currently seen to be essential. However, in just the last couple of years there have been a few cases of successful adult treatment - where certain exercises can allow someone with no effective depth perception to see in perfect 3D - research into brain plasticity tends to back this up. It should now be expected that early intervention for cross-eyed babies would be regarded as a bad idea - it being better to let them un-cross naturally and to treat the resulting brain underdevelopment later. In that case, we're right on the nexus of "OMFG! They treated all of those poor babies unnecessarily!"...having only recently gone through "OMFG! We didn't treat this baby and now it's permenantly impaired!"...it's a tough business!

So - expect caution, and a firm adherence to the "First, Do No Harm" oath that doctors are (mythically, I think) supposed to swear to. SteveBaker (talk) 15:19, 22 January 2009 (UTC)

While not your fault given the way the discussion has progressed, I think you may have gotten confused. As far as I'm aware, the claim made by the OP, semi supported by the refs that the surgery is usually performed on children and the OP was demanding to know if there was any reason why an adult would need the surgery and if there was, why our article didn't say there was (even though our article didn't really comment on the age the surgery is performed). I don't know if I got this through or not but my point was the 1) It appears the surgery is performed on adults for at least one of the same reasons it is performed in children 2) Whether you can say they 'need' the surgery as opposed to 'want' the surgery is an extremely complicated issue since it's a continuum, there's no line between need and want and depends on how you classify each. On your point, from my brief look through the refs and wikipedia articles, it looks like there is some controversy of how often this surgery should be performed (and although I never saw any, I'm guessing there is also some discussion over whether it should be delayed to adulthood) which while an interesting ethical issue, not really one for the RD and AFAIK is not what the OP was asking. Nil Einne (talk) 16:34, 22 January 2009 (UTC)

All, found more info at this article ankyloglossia. Pretty much mirrors what Nil Einne wrote. Can we now end this discussion. I am tired of discussing and wasting space on how Steve Baker's feelings were so hurt. If you bite OP's, expect, once in a while, someone might bite back. --Emyn ned (talk) 17:05, 22 January 2009 (UTC)

This snipping of the membrane under the tongue, if done badly, can result in a tongue which can be thrust out of the mouth to an unseemly extent, as in the case of am individual I know. Edison (talk) 05:35, 23 January 2009 (UTC)

Total size of all Wikipedia articles

Please see Wikipedia:Reference desk/Computing#Total_size of all Wikipedia articles for duplicate question. Cycle~ (talk) 14:49, 21 January 2009 (UTC)

This page seems to imply there are only 4330 people with >100 total edits? This seems really low to me, am I reading it right? Thanks Anythingapplied (talk) 21:34, 22 January 2009 (UTC)

That page, which is 2+ years out of date, is referring to >100 edits per month in the column you are reading. Dragons flight (talk) 21:41, 22 January 2009 (UTC)

Submarine motion

hai i am doing aeronautical engineering i suppose to do a working model of submarine is it possible to get the up and down motion of the submarine by using a elevator as in a aircraft? —Preceding unsigned comment added by Veeraraghavan.D (talk • contribs) 15:00, 21 January 2009 (UTC)

(I added a header for your question.) I don't understand what you mean. Is it possible to have an elevator inside a submarine? Sure it is. But the "up and down motion" part is confusing -- an elevator isn't going to make the submarine rise or descend. (It doesn't do that in an aircraft, either.) -- Captain Disdain (talk) 15:09, 21 January 2009 (UTC)

Are you talking about a passenger elevator ? I'm sure they meant elevator (aircraft). StuRat (talk) 15:15, 21 January 2009 (UTC)

Oh... yeah. Never mind. Ahem. (Geez, it's not often that my English vocabulary fails me, but what the hell, here's something to file away for future reference...) -- Captain Disdain (talk) 15:48, 21 January 2009 (UTC)

Consider yourself lucky, you managed to improve your vocab today. We should all strive for that every day. :-) StuRat (talk) 03:47, 22 January 2009 (UTC)

Ironically, if there was a passenger elevator on a sub, which lacked a counterbalance but relied exclusively on motors to raise it, moving it up and down would slightly change the depth of the sub, based on "every action causes an equal and opposite reaction". StuRat (talk) 03:54, 22 January 2009 (UTC)

Are you sure? I think it would push you one way when the elevator accelerated and then push you the other when the elevator stopped- zero net force. You'd need a mile high elevator that you could keep going and going so you can stay deep for awhile and then you stop the elevator to go back to where you were. 72.236.192.238 (talk) 18:43, 22 January 2009 (UTC)

You're correct that there would be no net, long term change in the depth of the submarine, but it would cause small, temporary changes in depth, that's all I'm saying. StuRat (talk) 18:52, 22 January 2009 (UTC)

(I improved the header.) In the short term, yes, but to maintain a certain depth you will need to alter the buoyancy of the submarine. This is typically done by filling and emptying ballast tanks. You might wonder why this is different from aircraft. Well, (heavier-than-air) aircraft must always be moving forward to stay aloft, and you can therefore use an elevator to adjust the altitude, but submarines are often still, or moving too slowly for the elevator to be used in this way. StuRat (talk) 15:13, 21 January 2009 (UTC)

I have definitely seen pictures of Personal submarines that use control surfaces exclusively to control their depth. The obvious problem of this is that you need constant forward motion to fight the craft's normal buoyancy. (Compare to an airplane.)

This isn't practical for large navel submarines need to be able to control their depth independently of their forward speed. APL (talk) 15:25, 21 January 2009 (UTC)

The best depth control makes use of a ballast tank which can be variably filled with water or gas (usually from a compressed gas tank). There are other submarine depth control techniques such as elevators (which are used on large navy submarines in conjunction with ballast tanks). ROVs are often designed to be neutrally buoyant (a difficult challenge, sensitive to tiny variations), the idea being that the ROV will float at whatever depth it is currently at - and then a vertical motor or propulsion system is used to set that depth. You can fight buoyancy with such a method but it will impact your energy budget, controllability, and reliability. Nimur (talk) 15:37, 21 January 2009 (UTC)

(ec) You're probably looking for our article on dive planes. A surfaced submarine with its ballast tanks 'blown' (empty) has a substantial amount of positive buoyancy; it would be difficult or impossible to force it beneath the surface using its dive planes alone, and the submarine would have to be under constant thrust.

A large military submarine beneath the surface and with ballast tanks 'trimmed' (adjusted) to neutral buoyancy will tend to hold a constant depth — the average density of the submarine matches the surrounding water. Since both submarine and surrounding water are poorly compressible – and consequently, have nearly constant density even through large changes in depth – it is very difficult to select a depth using ballast adjustments alone. (It would also take a long time for the submarine to change depth, as very small changes in buoyancy would be used.)

Instead, a very small amount of forward thrust combined with elevation changes of the dive planes allows a submarine commander to change depths without requiring further adjustment of ballast tanks. Unlike elevators on aircraft, submarines fit dive planes in up to three locations: bow, stern, and sail/conning tower (these last are sometimes called 'fairwater planes'). Since water is much, much, much denser than air, the control surfaces on a submarine are smaller and work at much lower speeds than comparable equipment on an aircraft. TenOfAllTrades(talk) 15:46, 21 January 2009 (UTC)

A very detailed guide to building a model submarine with an electric motor and a ballast tank which has a compresssed air supply to make it resurface after it dives is found in "The boy's book of submarines" by A. Frederick Collins, pages 21-48. Although the book was written in 1917, you could alter the shape to match that of modern submarines. Although Collins discussed diving planes elsewhere in the book, his model omitted them. Edison (talk) 18:54, 21 January 2009 (UTC)

It's possible to get downthrust with an 'elevator' - and indeed, real submarines do have such things for subtle depth and attitude adjustment (those are the "Bow planes"). However, they only work when you're moving through the water - and only when the elevator is submerged...both of which might be a problem. Real submarines sink because they pump water into and out of ballast tanks - compressing the air inside...but that's a pain to deal with in a model. The model submarine we have at home for messing around in our swimming pool uses a propeller encased in a vertical tube as a 'down-thruster' to drive it underwater - and before you play with the submarine, you have to adjust the bouyancy with little metal disks to get the submarine to very slowly rise by itself when the motor shuts off. That's for the vital reason that you want to be able to get the submarine back when it goes too deep for the radio signal to reach it anymore - or if the batteries die on you. With ALMOST neutral bouyancy, the thruster controls both up and down motion while the propeller and rudder deal with turning and forward or reverse motion. If you drive the submarine too deep and the radio stops working, the electronics inside simply stop all of the motors so the submarine can gently rise until radio contact is re-established. This works amazingly well - much better than I thought it would. When you drive the submarine too deep, all you really notice is that it refuses to go any deeper - but if you look closely, you see that it's actally drifting up and down over a period of a half second or so as the vertical thruster motor cuts in and out - but that gives you enough control that you can still steer at maximum depth. The trouble with an 'elevator/bow-planes' is that once the submarine goes too deep for you to control, you really want it to come back up automatically. Theoretically, turning off the thrust motor will stop the boat from moving forwards - then the bow planes can't drive it down anymore - so it'll float back up into radio range. That's a difficult approach because even when you shut off the thrust motor, the sub will still slide through the water for quite a distance before water resistance slows it down enough for the bow planes to stop working. For all of that time, you have no radio control because the sub is still too deep. So now you need to alter the bow plane angle to push the sub upwards when it loses radio contact. Ikky. That's why I like the vertical thruster concept. SteveBaker (talk) 20:33, 21 January 2009 (UTC)

Wouldn't a balloon work for a model? You put a balloon inside the hull, with the hull open to the water. You then attach a tube to the neck of the balloon (making sure it's airtight) and take the tube up to the surface. You then blow the balloon up to make the submarine surface and let the air out to make it sink (after adding the appropriate amount of weights, anyway). --Tango (talk) 20:59, 21 January 2009 (UTC)

steel

what is the weight of 10mm mild steel plate per square meter as per indian standards —Preceding unsigned comment added by 122.167.114.29 (talk) 16:58, 21 January 2009 (UTC)

You can find the density of mild steel in our article. For Indian standards, you would need to check the website of a steel service centre in India to see what actual thickness they roll "10mm" steel to. Franamax (talk) 17:07, 21 January 2009 (UTC)

According to our article, the density of mild steel is: 7,861.093 kg/m³. If it truly is 10mm thick then the weight is 78.611kg/m² regardless of where you happen to be! However, (as Franamax alludes) some materials are quoted a being some thickness "before polishing" or they might include some kind of protective coating or whatever. So I suppose it's possible that 10mm steel plate isn't exactly 10mm thick in India. (Just like a '2x4' piece of timber is really only 1+1⁄2" × 3+1⁄2" in reality because the 2"x4" refers to the dimensions before planing). SteveBaker (talk) 19:22, 21 January 2009 (UTC)

concrete specimen

when we subject aconcrete cube 15*15*15 cm to acompressive strength , the regular result will start from 150 kg\cm2 to 500 kg\cm2 in ordinary structures , and as we know cement is the material which provide cohesive bond between concrete components , so why is that the compressive strength of a cement cube will be much less than aconcrete one , since that the essintisl bond is been provided by cement... the answer must have scientific base.., thank you...? —Preceding unsigned comment added by 79.173.224.133 (talk) 20:28, 21 January 2009 (UTC)

The little rocks and other 'aggregate' carry most of the compressive loads in concrete. Cement lacks that. SteveBaker (talk) 20:35, 21 January 2009 (UTC)

You may be interested in our articles on Cement and Concrete. Your engineereing teacher likely also talked about this in class, so if you re-read your notes from that day, teh information is likely there. Also, if your teacher gave you a textbook, it is likely in there as well. --Jayron32.talk.contribs 20:49, 21 January 2009 (UTC)

Let's assume good faith, shall we? While the OP may have been learning about this in class recently, the question could well be something they've thought of for themselves rather than homework. --Tango (talk) 20:53, 21 January 2009 (UTC)

I assumed no bad faith at all. The reference desk is designed to help people find answers to questions. Lecture notes from ones own classes and textbooks given out in those classes are likely going to contain lots of good information for answering this question. If you have a place better than his own textbook to look this information up in, please feel free to add it. But please, the assumption of the assumption of bad faith is an assumption of bad faith in itself. --Jayron32.talk.contribs 22:20, 21 January 2009 (UTC)

i had reed about it ... the explanation presented that alot of cement will release alot of heat from the reaction and so ... larg volume changs will occure producing dangrous hairy cracks within the mass of concrete which cause the low compressive strength ... but if we manage to avoide the heat effect could the compressive strength come larger or it will remain the same...? --Mjaafreh2008 (talk) 09:49, 22 January 2009 (UTC)

Well, it would seem to me that the methods of avoiding the heat effects all involve adding something to the cement in some way. I suppose you could add a network of pipes through the cement through which we could pump water to keep the cement cool; however in order to have enough pipes to be effective, you'd have created what would essentially be reinforced concrete; the pipes would act like rebar and would at that point be serving exactly as the aggregate stone does in concrete. I'm not sure we have any reliable method of cooling the drying cement in a manner that does not end up creating what would functionally be concrete anyway. Plus, I am pretty sure that the aggregate itself provides considerable strength, even assuming that the cement could be cooled and dried under ideal conditions. --Jayron32.talk.contribs 13:08, 22 January 2009 (UTC)

Obviously concrete with no cracks is stronger than concrete with cracks! It is indeed a standard practice to try to abate the heat when that's an issue. See Hoover Dam#Concrete_pouring for an example. --Sean 14:10, 22 January 2009 (UTC)

Except the question was not about "cracked concrete" vs. "uncracked concrete". The question was about "cement" vs. "cement with stuff in it" (otherwise known by the name "concrete"). The question was about why concrete was stronger than an otherwise idenitcal amount of pure cement. The OP then noted that in his reading, he came accross the explanation that the aggregate (the stuff in the cement that makes it concrete) had a dampening effect on heat generation, and that was what resulted in a stronger product. He then asked about other ways to dissipate the heat in such a way as to retain the purity of the cement; however I noted that I doubted that any system which could be used to dissipate the heat of the drying cement would not in itself produce a product which was essentially concrete. In other words, it would be impossible to actually effectively cool a block of pure cement without in some way introducing foreign materials or objects; which would then make it concrete. --Jayron32.talk.contribs 18:14, 22 January 2009 (UTC)

The ways they have to control heat build up when making large concrete structures (like dams for example) is to pour in thin layers - let each layer cool - then pour another layer. But I saw a Discovery channel thing about making large concrete structures in the middle east where they mixed ice and in some cases even dry ice into the cement along with the aggregate. So there certainly are ways to do that without pipes and such. SteveBaker (talk) 21:18, 22 January 2009 (UTC)

Regarding sight

Why do objects farther away appear smaller? And is there a way to mathematically find the relationship bewteen apparent size and distance (i.e. inverse relationship)? —Preceding unsigned comment added by 65.92.7.221 (talk) 21:58, 21 January 2009 (UTC)

Articles such as Perspective (visual) and Visual angle may be of use to you. --Jayron32.talk.contribs 22:17, 21 January 2009 (UTC)

(EC)See Perspective (visual). For a mathematical calculation of image size versus distance, see Visual angle. For an excruciatingly mathematical treatment of the subject, see "Teaching Leonardo" by Rick Faloon. You might also find Vanishing point useful. Edison (talk) 22:20, 21 January 2009 (UTC)

I poked around and couldn't find a reference in Wikipedia, but it's a simple ratio. An object one meter away will look ten times bigger than the same object ten meters away. This is for apparent size in inches or centimeters, not degrees or radians. --Milkbreath (talk) 22:31, 21 January 2009 (UTC)

What does "apparent size in inches/centimeters" mean? Axl ¤ [Talk] 23:15, 21 January 2009 (UTC)

I was afraid somebody would ask that. Say you're on the International Space Station, and the Space Shuttle is approaching head-on. If you know the Shuttle's wingspan, you can determine how far away it is by holding a meter stick out and noting its apparent wingspan on the stick. If you then measure from your eyes to the stick, you can calculate the distance by the ratio eye-to-stick/eye-to-shuttle = apparent wingspan/true wingspan. --Milkbreath (talk) 23:43, 21 January 2009 (UTC)

Imagine you are looking through a window that's 'Z_W' meters in front of your eyes. Some object is X_O meters across and Z_O meters from your eyes. The size of the object as it appears to be on the glass of your window is: X_W = X_O x Z_W / Z_O Hence, when the object is twice as far away, it's appears to be half the size. The reason is a matter of similar triangles. If you draw a line that's the same size and distance as the object and then form a triangle from the ends of that line back to your eyes...then draw another triangle using the width and distance of the image of the object that you see on your window - then the ANGLES inside those triangles has to be the same...right? Geometry 101 says that two triangles with the same interior angles are SIMILAR and the ratio of their sides is the same. Hence, the ratio X_W / X_O equals Z_W/Z_O -- which you can rearrange into my equation above. That is also the "why" of why things get smaller as they get further away. If the angles stay the same (which is also implied by the object retaining the same general shape) as it gets further away - then in order to keep that true - the size has to change in the same exact proportion. SteveBaker (talk) 00:04, 22 January 2009 (UTC)

Have you tried trigonometry? ~AH1^(TCU) 03:36, 24 January 2009 (UTC)

Titan vs. Europa over 5-7 billion year sun

Isn't it possible when sun swells up in 5 to 6 billion years, Europa's ice can melt into oceans, and Titan I thouhgt will keep some atmosphere. It is ultraviolet light and solar winds which kill atmopshere. Europa's surface is made of frozen oxygen and methane, when sun heats up I thouht it will sublime into atmosphere. This all deepnds on sun's expansion. Maybe for a certain amount of time, Europa can harbor life, eventually Titan will drain probably about 90% of atmosphere, but it will keep some at least, I thought.--69.226.46.118 (talk) 23:40, 21 January 2009 (UTC)

Both those moons are very small, so if they heated up the Earth-like temperatures (and they could well end up much hotter or much colder, it would be a pretty big coincidence if they were just right) they would lose (most of) their atmospheres very quickly. It would probably take some effort to make them breathable anyway, so it would probably be better just to build domes or similar on them and just worry about a little bit of atmosphere. However, the Sun will only remain a red giant for a very short period of time on astronomic scales (millions of years, maybe). If the human race survives the next 5 billion years, I hope it is thinking more long term than the next few million (especially since Earth will be uninhabitable in about 1 billion years, so they'll have already had 4 billion years of living with a dead planet, so they ought to be prepared to live with a dead star!). --Tango (talk) 23:56, 21 January 2009 (UTC)

Europa may harbor life now. The oceans on Europa are among the best candidates for harboring life in our solar system outside the Earth. Dragons flight (talk) 00:02, 22 January 2009 (UTC)

• What about Mars. The academic paper said when the sun heats up in aobut one billion year, frozen carbon dioxiode and wapour can gradually sublimes, creating a greenhouse effect and more substantial atmosphere, may make Mars blue again. Anyways, I saw one source said the sun's expansion could be up too 400 R (up to 1.6 AU or so), will it expand enough to penetrate Mars' orbit. Mars may be swallow up as well, but unlikely-but no guarentee to survinve. Europa's ice layers is made up of oxygen and methane, it is possible that it may create an atmosphere for short time. Do Tango mean if they create an atmopshere for short of tme, it will go away quickly. The thing is ultraviolet, and solar winds wipes out atmospheres. —Preceding unsigned comment added by 69.226.46.118 (talk) 00:12, 22 January 2009 (UTC)

No, no, no! We have to put an end to this "after the sun turns into a red giant" crap. Step 1: The sun's intensity grows by 10% per billion years - this is quite enough to boil away our oceans long before the sun does the red giant thing. Step 2: Before it blows up - it first collapses and becomes (for a while) 1,000 to 10,000 times brighter. That's quite enough to boil all of the oceans on Europa and sterilise life there. Step 3: There is a "Helium pulse" - for a very brief time, the sun gets 100,000,000 times brighter. This ensures that all hope of anything at all surviving or having an atmosphere is gone. Step 4: It gently expands and swallows some of the toasted wrecks of molten lava that might be close enough - tearing more apart due to bizarre tidal effects.

So - no life left ANYWHERE within a few lightyears. Game over. SteveBaker (talk) 00:15, 22 January 2009 (UTC)

Incidentally, if it is only ~1000 then Triton and Pluto would see flux like the modern day Earth and could be quite livable for a while. Dragons flight (talk) 01:57, 22 January 2009 (UTC)

Yea right, Triton have been slowly diminishing it's orbit, and somewhere between 1.4 and 3.6 billion years, Triton will most likely get torn apart by tidal force, most likely form a ring. Few billion years, Neptune's rings like Saturn's now will go away too. About pluto, why you think pluto will get benefit, it's so faraway from sun.--69.226.46.118 (talk) 02:46, 22 January 2009 (UTC)

Was I unclear? At ~1600 times modern luminosity, Pluto would get the same amount of light as the Earth does now. Hence, when the sun is a red giant, Pluto would be expected to have roughly the same temperature as the Earth does now. Pluto is not so far away that one can ignore it when you start throwing around factors of 1000. Dragons flight (talk) 03:31, 22 January 2009 (UTC)

Life couldn't survive the helium pulse even at that distance. And once the sun actually reaches the red giant stage - the energy it pushes out to a lower level than it does now. So Pluto's fate as the Sun ages is that it slowly gets nice and warm and for a short time (well, assuming it's orbit doesn't expand too much due to the reduction in mass of the sun) life could even survive there - then it's bombarded by the planetary nebula - then it's irradiated to hell, sterilizing anything that might have survived - then it's back to being an even colder ice-ball than it is now. It's hard to imagine any kind of life that would survive that kind of mistreatment...and that's what it takes to still be there when the sun becomes a red giant. SteveBaker (talk) 03:56, 22 January 2009 (UTC)

• • First, does planetary nebula even swallow and destroy planets. I originally thought Pluto's orbit might almost double by then.--69.226.46.118 (talk) 04:16, 22 January 2009 (UTC)

That's after sun's giant stage, when sun forms a planetary nebulae and disintegrates it's outer laers. Between sun's maximum extent and white dwarf stage, there is something call "planetary nebulae". Planetary nebulae big enough (trillions of mile across), it glows white but don't swallow planets. At step two Titan is further from sun, it's atmosphere might just be half gone. At that time, Titan probably heats up to Mars' surface temperature, then when Titan heats up to around Earth's temperature, then the atmosphere is probably down to 0.02.--69.226.46.118 (talk) 00:31, 22 January 2009 (UTC)

Atmospheres bleed away over time even without UV and solar wind (although, there will be plenty of both anyway), warm air molecules move around a lot, at any given time a certain proportion will be moving around enough to escape and will do so. I guess it's possible that Mars will become close to habitable for a short period as the Sun brightens, before it gets bright enough to scorch the planet (probably only a span of a few million, or tens of million years), but it would probably be some time after the Earth was rendered dead, so the human race would have to survive elsewhere for a few million years anyway... --Tango (talk) 00:44, 22 January 2009 (UTC)

When the sun "explodes", it's quite possible that the gas planets (and other bodies with atmospheres) will be reduced to their core. So even if the inner oceans of Europa survive, they will probably freeze over since there will be no tidal action from Jupiter. ~AH1^(TCU) 03:33, 24 January 2009 (UTC)

I can't see the sun exploding with enough energy to strip a large portion of Jupiter's atmosphere away, some sure, but not much. (This is just intuition, I haven't looked it up or done any calculations, so I could be wrong - if you have a reference, please say.) --Tango (talk) 21:03, 24 January 2009 (UTC)

January 22

Aerated autoclaved concrete

Does anyone know how to make Aerated autoclaved concrete? —Preceding unsigned comment added by Elatanatari (talk • contribs) 05:24, 22 January 2009 (UTC)

The "Raw materials" section of its article explains it. DMacks (talk) 06:03, 22 January 2009 (UTC)

I meant more like the exact ratio of ingredients and the chemical processes that take place. --Elatanatari (talk) 01:28, 25 January 2009 (UTC)

Neat search tip: when you're looking for "how to make" something, try adding the word "patent" to your search terms. I did that and was able to find this. 152.16.16.75 (talk) 11:04, 25 January 2009 (UTC)

How to have a nightmare

Is there any way I can arrange to have a nightmare shortly before I need to get up in the morning, sufficiently intense that I'll rapidly become wide awake and fully alert, won't have to drag myself out of bed, and will be relieved to have returned to the real world, rather than disappointed as after a pleasant dream? NeonMerlin 06:01, 22 January 2009 (UTC)

I suppose a cassette player on an appliance timer, set to go off an hour before you wake up, with sufficiently spooky sounds on it, might work. StuRat (talk) 06:08, 22 January 2009 (UTC)

That's not really going to be reliable, because even if the tape could trigger nightmares, which is dubious, you've still got to synchronize it to your REM sleep cycles. If I recall correctly, REM sleep is the minority of your actual sleeping time. So that would very rarely work, if at all. APL (talk) 06:14, 22 January 2009 (UTC)

Our article on lucid dreaming may be of interest. --Jayron32.talk.contribs 06:18, 22 January 2009 (UTC)

(lyrics of Lucid Dreams by Franz Ferdinand removed) --Scray (talk) 12:22, 22 January 2009 (UTC)

When I was very young I convinced myself, in that way of children, that if I crossed my hands over my chest like a mummy while I slept then I'd have nightmares. And you know what? It worked very well—I had fantastical, nightmarish dreams whenever I set upon doing it. Later I tried to figure out why that might be, as it was obvious that any connections with mummies were only in my head, but that, of course, is quite a lot. I think the act of convincing myself that what I did would produce nightmares did, in fact, produce nightmares in some strange and subliminal way. I haven't tried it again for a long time, but it seemed to work even when I knew that it was just in my head—maybe something about the contrivance of it? I don't know. But hey, it's worth a shot—no harm if it doesn't work. --98.217.14.211 (talk) 15:42, 22 January 2009 (UTC)

Self-hypnosis it is, then. Julia Rossi (talk) 20:52, 22 January 2009 (UTC)

But with self-hypnosis, there's nobody there to stop you from clucking like a chicken. :-) StuRat (talk) 02:07, 26 January 2009 (UTC)

If you want to wake up at the best possible time then there are a few options available:

• http://www.happywakeup.com/en/index.htm
• http://www.sleeptracker.de/
• http://www.axbo.com
• http://www.reuters.com/article/technologyNews/idUSL0878172320070829

Isaac Asimov years ago noted the amazing ability of the brain to wake one up shortly before an alarm is to go off. He speculated that maybe (mechanical) alarm clocks made some small sound, or there was some alteration in their ticking shortly befre the alarm sounded. Without ruling out that hypothesis, I note that I have many times woken up a minute before a purely electronic alarm sounded at odd hours of the night, when I had to get up for some reason or other. I assert that it is possible to program the brain to wake you up at a particular time when there is something to be done. Edison (talk) 05:32, 23 January 2009 (UTC)

There is a much better modern explanation for Asimov's observation - which is that our conscious mind doesn't operate in "realtime" as we think it does. We are consciously registering events at least seconds (and possibly more) behind "realtime" and we're getting a highly edited version of events because the conscious brain simply doesn't have the bandwidth to handle all of that data. Our subconscious mind is doing ALL of the work and making our consciousness merely think that it's in charge. The subconscious edits the timeline to make all of this seem self-consistant and that means that since subconsciously we are collecting data BEFORE the alarm goes off - and long before the conscious mind needs to know about it - there is no problem with collecting some of the memory of events just beforehand and inserting those into the stream of events going to the conscious part. Like so many things in our world - the mind doesn't work the way common sense says it does and life is MUCH weirder than you'd think. SteveBaker (talk) 14:42, 23 January 2009 (UTC)

Asimov's explanation was exactly right for me, as I regularly woke up one minute before my alarm was set. It was a mechanical alarm clock with flipping cards containing the digits, and it did make a noticeably different click one minute before the alarm went off. The cat would also hear this, apparently, and pester me for breakfast. StuRat (talk) 15:50, 23 January 2009 (UTC)

Kramer: Alarm clocks? I never use 'em. Don't trust 'em.
Jerry: What do you do?
Kramer: I have a uh...mental alarm. I set my head for... quarter to seven and... (makes sound with the lips - "pop!") ...I get up!
Jerry: Always works?
Kramer: It never fails. .froth. (talk) 18:26, 23 January 2009 (UTC)

NeonMerlin, the answer is yes, and there are many ways to do it. One of the easiest ways to do it is to ingest the appropriate dosage of an OTC drug (but only under your doctor's supervision) that contains diphenhydramine (such as Benadryl) at least two hours before you go to sleep. An added bonus is to set the alarm for about 4am, wake up immediately, then go back to sleep. This will work if the dosage and alarm is set accordingly. Don't ask me why it induces nightmares, but it does. Although I don't have experience with it, another drug, Varenicline (Chantix), is said to have the same nightmarish effects, although this is by prescription only and should only be taken under the supervision of a physician. Eschewing this route, another thing that seems to cause nightmares in some people (although this is purely anecdotal) is pizza. I'm not entirely sure what the ingredient is, but it is apparently something in the tomato sauce, and probably can be traced to an herb or spice. You might try ordering a late-night pizza with extra sauce before you go to bed, as this also seems to be effective, but only causes nightmares in some people. Viriditas (talk) 08:14, 26 January 2009 (UTC)

Creation of unfeasably large nuclei through the quantum zeno effect

A question arose in freenode ##physics, where a fellow wondered if it would be possible to create through nucleosynthesis elements heavier than would normally be possible due to high decay frequency by forestalling decay with the quantum zeno effect: sampling (measuring) the state of the nucleus at a frequency high enough that the probability of decay is vanishing.

A precursory search reveals nothing relating to the application of the quantum zeno effect to heavy atomic nuclei. Theoretically, one would suppose, there is a limit for frequency of measurement at some function of the planck time, and thus at some point the probability of a quantum vacuum fluctuation somewhere within the nucleus occuring between measurements will break even. However, I am not mathematically-conversant enough to be able to calculate even roughly this limit.

Any thoughts? 86.157.24.150 (talk) 12:45, 22 January 2009 (UTC)

Except that functionally, rapid "sampling" is functionally equivalent to bombarding the nucleus with particles; there is no such thing as "passive observation" in the quantum world, which is why observation always effects the properties of what you are looking at; you can only observe BY altering the properties of the subject. So while you may think that you are delaying decay by simply watching the particle to make sure it doesn't decay, what you are really doing is delaying decay by adding lots of energy to the system in such a way as to cause the decay to take longer. Paradoxes in the quantum world only appear to be paradoxes if you make incorrect assumptions about the ability to make passive observations. Once you realize that ALL observation occurs only by changing the target subject, then the apparent paradoxes disappear. SteveBaker is much more conversant in these matters than I, so I am sure he will be able to direct you to a more quantitative explanation. --Jayron32.talk.contribs 18:05, 22 January 2009 (UTC)

A few comments. First, to 86.157: if it was a simple quantum tunneling (think Gamow model) then, yes, a measurement that localizes the tunneling particle to the volume inside the potential well (rather than outside) reduces the amplitudes of the continuum (outgoing wave) components of the wavefunction and thus hinders tunneling for a short while. That is the essence of the quantum Zeno effect. However, for superheavy nuclei there are many decay modes to be expected, and I don't think it is even remotely possible, with present-day technology, to measure the location of all the possible "fragments" of the superheavy nucleus. And you need to do this more than once, and without destroying the nucleus in the process... So, in brief, it does not look like a feasible experiment to me at present, although it may, in principle, become feasible at some point in future. And a side note: our article on quantum tunneling is quite incomplete, and does not nearly give a proper insight in terms of scattering theory or energy spectra. I won't have time to fix it anytime soon, but I probably will fix it eventually. Now, to Jayron: I'm not sure what you mean by "passive observation", but a concept of "null measurement" is well established in quantum mechanics. Think of lack-of-interaction as a measurement: a photon passed through the system without scattering; nothing happened to the system, but some information about it has been gained. --Dr Dima (talk) 19:45, 22 January 2009 (UTC)

That;s true, however such null measurements do not actually cause "spooky action at a distance", or quantum paradox, or the "quantum zeno effect" that the OP is refering to. After-the-fact information gathering is NOT the same as live sampling, which is what the OP is asking about. Think to the classic double slit experiment. Measuring the location at which the electrons hit the target is a "null measurement" and does not effect the behavior of the electrons as they pass through the slit; knowing where the last electron hit does not effect where the next one will hit (it is still random) any more than not knowing would. However, live sampling of the slits themselves, where you "watch" which slit the electrons go through DOES effect the electrons flight path, and thus affects the outcome of the experiment. What the OP is asking about is whether some sort of rapidly repeated sampling could some how affect the decay rate of the particles. If you only count the particles after they have decayed, then no it won't. If you set up a device to observe the particles as they decay, then yes it very likely CAN effect the decay rate; however its not the fact that information is obtained that matters. You could set up your obeservation equipment and then not collect the data; and the decay rate would be effected by the same as if you tabulated the data. Its not information collection that matters; its observation in this case. --Jayron32.talk.contribs 02:54, 23 January 2009 (UTC)

Your understanding of the term "null measurement" is incorrect. A null measurement is a measurement (i.e. something causing the measurement effect) that isn't associated with any (ordinary causal) interaction between the system of interest and your lab equipment. Measuring the location at which the electrons hit the target is not a null measurement, since the electrons do interact with the target. The classification has nothing to do with the time at which the measurement takes place. That really has no relevance in quantum mechanics. All that matters is what you learn about the system. The reason measuring the electrons at the target shows an interference pattern in the double-slit experiment is because that particular measurement doesn't tell you which slit the electrons went through. It's pointedly not because the measurement takes place after the electrons have already gone through the slits. There's no theoretical reason why a null (i.e. interaction-free) measurement can't cause the quantum Zeno effect just like any other measurement. -- BenRG (talk) 14:15, 23 January 2009 (UTC)

Effect of Sildenafil (Viagra)

I read the subject published on Wikipedia concerning Sildenafil,but I have a quistion which is: we know that Sildenafil is not recommended for the patient with cardiac problems, althought sometimes it's given as antihypertensive drug? Can you give me a simple explanation on how it can be use for this case.

Thank you —Preceding unsigned comment added by Ghost whispers (talk • contribs) 16:36, 22 January 2009 (UTC)

Sildenafil is well-known to reduce blood pressure. However Pfizer noticed an unusual side-effect when their male volunteers took the drug. ;-) Hence it subsequently became marketed for erectile dysfunction. Sildenafil is also used to treat pulmonary arterial hypertension. Axl ¤ [Talk] 17:38, 22 January 2009 (UTC)

Expanding universe

If the expanding universe is stretching space and, I presume time, and we and our measuring instruments are an inevitable part of this expansion, then how do we determine that it is expanding and the rate at which it expands? 196.2.124.251 (talk) 17:19, 22 January 2009 (UTC)

The size of a ruler (and other material objects) is not affected by the expansion of space. Dragons flight (talk) 17:29, 22 January 2009 (UTC)

Why are rulers not part of the expansion? 196.2.124.251 (talk) 17:36, 22 January 2009 (UTC)

Because the chemical bonds holding them together are stronger than the expansion. --Tango (talk) 17:44, 22 January 2009 (UTC)

That's not quite right. The expansion of the universe is not a force. When you think of something like a balloon expanding, the force (pressure) causes it to happen, and that force puts a strain on the chemical bonds holding the balloon together, actually altering the properties (like size and shape of the balloon). The expansion of the universe is a different sort of event entirely; what is expanding is the actual space between objects. Its not that the objects are being pushed away from each other by some unknown force; its that the space between the objects is actually ITSELF getting bigger. This expansion does not affect other forces except where those forces are themselves dependant on distance (i.e. inverse square law forces like gravity. For example, the force of gravity between two objects will decrease due to the increasing distance between them, but it is not counteracted by any applied "force"; if it were, you would see decreasing gravity effects to be GREATER than the increasing distance due to cosmological expansion, and you do not. --Jayron32.talk.contribs 17:57, 22 January 2009 (UTC)

While the expansion is not a force, it does require a force to overcome it. If that force isn't strong enough, the objects get further apart, if it is strong enough, they don't. --Tango (talk) 18:50, 22 January 2009 (UTC)

If the actual space between objects increases, then surely that would include the space between molecules and the space between atoms? Would the dimensions of the nucleus itself not also be affected? 196.2.124.251 (talk) 18:02, 22 January 2009 (UTC)

The size of objects is determined by chemical bonding. These bonds have a characteristic length and resist efforts to stretch or compress them. You can't use your hands to appreciably stretch a ruler, and for the same reason the expansion of the universe doesn't change the length of a ruler. The bonds simply return to their natural size after being perturbed. Dragons flight (talk) 18:11, 22 January 2009 (UTC)

(EC) No. As Jayron32 says, the expansion does not constitute a force, hence it does not enter into the equations governing stable structures held together by electromagnetic or gravitational forces. These forces keep the physical distances (that's the distances that enter e.g. Newton's and Coulomb's laws) between, say, the nucleus and the electron in a hydrogen atom or between the Sun and Earth, constant (I'm using simplified pictures of these things, of course). To describe the situation, you could say that these forces cause Earth to move through an expanding space, that motion balancing the expansion. Or you could say, equally appropriately and much simpler, that the space in the solar system or the hydrogen atom is, in fact, not expanding at all. What it boils down to is that the phrase "Space is expanding" is an imperfect rendition in plain language of what the mathematical equations of general relativity imply (in pretty much the same way as the expanding balloon is an imperfect model for the universe), and is indeed to some extent a coordinate-dependent concept. --Wrongfilter (talk) 18:18, 22 January 2009 (UTC)

Going back to the trusty balloon model, if the universe is like the surface of an expanding balloon, does that mean that objects on the surface, like a ladybug, will also expand when the balloon is blown up ? No. StuRat (talk) 18:46, 22 January 2009 (UTC)

The idea of only select portions of space being affected by expansion sits rather awkwardly. If the space between atoms, and in fact the dimensions of atoms themselves, had to change in step with universal expansion, then surely the changes would not be detectable by any measurement one could carry out? 196.2.124.251 (talk) 20:49, 22 January 2009 (UTC)

Yes, you are correct. If absolutely everything changes then it would be indistinguishable from a situation in which absolutely nothing changed. Please note though that changing "everything" would also requiring changing the force laws that depend on distance by a comparable amount. The idea that physical matter stays the same size is comparable to saying that the strength of the forces holding matter together are unaffected by the expansion. Dragons flight (talk) 20:57, 22 January 2009 (UTC)

Things changing by just the right amount so that everything still appears the same, is a notion that happened once before, isn't it? Michelson and Morley. 196.2.124.251 (talk) 21:28, 22 January 2009 (UTC)

More specifically, Lorentz's interpretation of Michelson and Morley (and the source of the Lorentz contraction that we still use today). --98.217.14.211 (talk) 23:25, 22 January 2009 (UTC)

The expansion of the universe is sort of like gravity—it is very weak over short distances, powerful over long distances. Compare that with, say, electromagnetism. You can observe that a tiny, tiny magnet easily contains more strength over a short distance than the gravity of the entire Earth. However the strength of the magnetic force quickly diminishes as you get away from the source. The expansion of the universe isn't going to affect things at scales that are governed by chemical bonds, electromagnetism, etc. But it'll affect things at big, big scales—entire galaxies moving apart from one another, staying internally ordered by the powerful shorter range forces. --98.217.14.211 (talk) 23:25, 22 January 2009 (UTC)

The idea of an expanding universe selectively affecting the spaces that make up its structure, doesn't fly well. The "internal ordering" at chemical, and for that matter quantum scales, is simply another way of saying that things don't seem to change at that scale, and what I'm saying is that is to be expected if everything changed proportionately, when we wouldn't be able to tell if there were a change, would we? 196.2.124.251 (talk) 04:50, 23 January 2009 (UTC)

See, that's the thing. The expansion of the universe is a measureable effect, so any conclusion that would lead us to not notice it (if, for example, our "rulers" were growing at the same rate as the expansion) is a faulty conclusion at the a priori level. It must be a bad understanding because it does not explain observation. So we need to come up with conclusions about what is happening that fit the observations... --Jayron32.talk.contribs 04:57, 23 January 2009 (UTC)

Well, strictly speaking, what has been measured is redshift, the rest is surmise 196.2.124.251 (talk) 05:15, 23 January 2009 (UTC)

"selectively affecting the spaces that make up its structure, doesn't fly well"—why not? All of the forces have limited ranges on which they act. I don't see why the expansion of space would be different. The expansion force (though I am aware it is not technically a "force") is so small and so slight on the micro level that it can't compete with the strong localized forces like the nuclear force or the electromagnetic force. Think about how powerful expansion of space would have to be to have any affect on the nuclear force—it just isn't going to happen. One way to think about it is as particles in a giant grid. Let's say the grid spaces double slowly and weakly over time. On the whole of the grid, the grid space increases. But localized groups of particles, tightly bound to each other, are going to stay together. The net result is that the spaces between the clumps of particles will change but the particles themselves will stay internally ordered, not because the doubling is "selective" but because it is far too weak to affect the powerful forces that maintain their internal organization. You don't have to postulate any selective or intelligent force here—just one that is weak on small scales. Again, consider the example of gravity and electromagnetism. A tiny magnet easily defies the entire gravitational force of the earth. But as a whole, on the aggregate, gravity is powerful enough to organize the entire solar system. Different scales do get affects by forces differently. --98.217.14.211 (talk) 11:27, 23 January 2009 (UTC)

The expansion is not just "not technically a force" it is quite simply not a force. Therefore it is not a small effect on small scales, it is no effect. --Wrongfilter (talk) 11:46, 23 January 2009 (UTC)

Quite so! The assumption that in some way forces (or some of them) would be immune to such an expansion, is bizarre. In dimensional analysis a force would be (mass x length)/(time x time). At its most basic level time could be measured by the orbital period of an electron around a proton. If the mass and the scale of an atom's components were to change as a result of universal expansion, then the forces in such a system - be they gravitational, electromagnetic or nuclear - would all seem to remain constant. Since we and our instruments are of the very same stuff we are examining, it is impossible to gain an outside perspective. 196.2.124.251 (talk) 12:23, 23 January 2009 (UTC)

But our instruments do detect the expansion. Your theory doesn't match observation, so it must be wrong. --Tango (talk) 12:30, 23 January 2009 (UTC)

It has an effect, that effect is just easily compensated for by other effects (due to actual forces). --Tango (talk) 12:18, 23 January 2009 (UTC)

Let's try again. Why does the Universe expand? We do not know. It expands because we observe it to expand. Peacock ("Cosmological Physics") expresses it as follows: "The Universe expands today because it expanded yesterday." When we solve Einstein's field equation to build a model of the Universe, we put the expansion in as an initial condition. The field equation admits solutions that are not expanding, solutions that are for instance contracting. But that doesn't conform to our initial conditions, hence we throw these solutions out and only keep those that are expanding at the present time. Expansion is not a dynamical effect, it is not part of the dynamical equations, and there is no necessity for space to expand everywhere and at all times. Whatever caused the Universe to expand initially is not known, and it is not relevant for this discussion. Now, consider for example a cluster of galaxies (whose structure is unaffected by anything except gravity): At some point in the past, the region occupied by the galaxies that now belong to the cluster was expanding, the distances between the galaxies increased, and the whole thing was well described by a Robertson-Walker metric. But because the matter density in that region was higher than the average, the expansion was reversed, so the region collapsed. As the local density increases due to the collapse, the Robertson-Walker approximation to the true local metric breaks down, and in fact the cluster virializes. Today, the metric in a cluster is anything but Robertson-Walker. Clusters form stable objects and space in clusters has forgotten that it once expanded a long time ago. --Wrongfilter (talk) 13:04, 23 January 2009 (UTC)

OK Let me try again too. Does the Universe expand? We do not know. Why do we think it expands? Basically because of our interpretation of redshift. Do we get redshift if and only if it is caused by recession? No, there are a number of redshift causes we know and doubtless many that we as yet don't know. Then why does the mainstream of astrophysicists and cosmogonists believe in an interpretation based on expansion? Largely because it is the flavour of the month and because of something called Cosmic Microwave Background Radiation which is considered the best argument ever in favour of a Big Bang and a consequent expansion. Does this mean there are dissenting opinions on expansion? Certainly! There are some great minds in the fields of cosmogony and theoretical physics who are not at all convinced by the circumstantial evidence supposedly supporting the Big Bang. Does this mean the jury is still out in this case? It most certainly does! 196.2.124.251 (talk) 13:40, 23 January 2009 (UTC)

There are many more phenomena than just redshift that are consistently described by relativistic cosmology (and the big bang, incidentally, is not part of the theory). Alternative models are welcome if they're sufficiently sensible. --Wrongfilter (talk) 13:55, 23 January 2009 (UTC)

Alright, name 4 great minds in physics or scientific cosmogony that don't believe in the expansion of the universe? Some people argue about the details, or dark energy, but I can't think of any that dispute the entire idea of expansion. Dragons flight (talk) 14:15, 23 January 2009 (UTC)

I've said it before and I'll say it again: the expansion of the universe is just objects moving apart. Forget general relativity and spacetime curvature, it's just plain old Galilean inertia. There's nothing mysterious about "the space between objects increasing". That's what happens when things move apart. There's nothing mysterious about the expansion applying to some things and not others. Just because some things are moving away from each other doesn't mean others can't be moving towards each other or maintaining a constant distance. There's nothing deep here except for the Galilean principle that objects don't need to be pushed to keep moving, and the cosmic inflation (or whatever) that gave them the initial separating velocity. When Peacock says "the Universe expands today because it expanded yesterday", he's expressing Galileo's principle.

The only exception to the above is a cosmological constant (if it's real, which isn't clear yet). It does behave like a force: like a centrifugal (not centripetal) force, in fact, but directed in all three dimensions instead of only in a plane perpendicular to a rotational axis. But this force is utterly negligible in ordinary situations compared to another force that people routinely neglect: the self-gravitation of your lab equipment. For a meterstick weighing one kg, the ΛCDM cosmological constant is trying to pull the ends apart with a relative acceleration of about 10⁻³⁵ m/s², while self-gravitation (Gm/r²) is trying to push the ends together with a relative acceleration of about 10⁻⁹ m/s². We don't have the technology to measure the self-gravitation of a meterstick to one part in 10²⁶. The cosmological constant is noticeable at large scales only because the overall density of matter in the universe is so low, about 10²⁷ times smaller than the density of air. -- BenRG (talk) 13:19, 23 January 2009 (UTC)

Viewing it as just standard Galilean inertia (incidentally, wasn't it Newton that talked about inertia? At least he's the one the law is named after, although that doesn't usually mean much.) only works for an infinite universe. If the universe is finite (a 3-sphere, say), it would be impossible for everything (on a large enough scale) to move away from everything else, there would have to be things moving together on a large scale, but we don't see that (we see Hubble's law instead). Now, it could just be our bit of the universe (ie. the 46 billion light year radius ball around Earth, or whatever the number is) where everything is moving outwards, but that would violate the Copernican principle. If what you're saying was the mainstream understanding, then people wouldn't still be wondering what shape the universe is (well, there are still plenty of options, but it narrows it down a lot). --Tango (talk) 14:29, 23 January 2009 (UTC)

Hubble flow is simply the inertia of galaxies and other matter evolving under general relativity following an explosive initial condition. The global curvature and/or closure of the universe requires general relativity to understand, but Galileo (or is it Newton?) provides a perfectly functional local understanding of Hubble flow as purely a manifestation of inertia. Incidentally, Hubble flow does not violate the Copernican principle. If you sit at any point defined to be (0,0,0) in space and observe that all matter is moving radially away from you with a velocity proportional to its distance, then one can rigorously show (after a change of coordinates) that an observer at any other point in space reaches exactly the same conclusion. Dragons flight (talk) 15:09, 23 January 2009 (UTC)

If you view it as space expanding, everyone sees the same, if you view it as objects moving through space, you don't. There is no way all objects can move apart when they are restricted to a finite and constant volume of space. --Tango (talk) 15:17, 23 January 2009 (UTC)

So why restrict them to a finite and constant volume? You need GR to get the time evolution and global properties right, but there is no local difference between saying "space is expanding" and "objects are moving apart". Dragons flight (talk) 15:40, 23 January 2009 (UTC)

Except that if the expansion were simply objects moving away from a big explosive force, then over time they would continuously decelerate due to gravitational effects. However, most measurements now show that the expansion is not decelerating, but actually speeding up! Its got to be something more than "moving apart because the big bang pushed everything out into empty space". It didn't push stuff into empty space, it CREATED that space, and is indeed still creating that space. The Big Bang was not an instantaneous event, it is a process which is still occuring. --Jayron32.talk.contribs 17:37, 23 January 2009 (UTC)

That's because of the cosmological constant, which adds an extra factor to the equations. That doesn't really effect what we're talking about. --Tango (talk) 17:42, 23 January 2009 (UTC)

Because, for all we know, the universe is finite. The global shape and compactness of the universe is an open question. --Tango (talk) 17:42, 23 January 2009 (UTC)

But at a sufficiently small scale those questions are irrelevant, because even if the universe is globally curved, it must still be locally flat. As it happens, to within our measurement ability, the entire visible universe seems to be "small" since we haven't been able to definitely identify any large scale curvature (or the universe may simply be globally flat and infinite). Also, the global issues don't change the observation that Hubble flow is locally equivalent to the inertial evolution of mass moving apart following an initial explostion. Dragons flight (talk) 21:47, 23 January 2009 (UTC)

The two theories are mutually exclusive, either space is expanding, or it isn't. Yes, they are indistinguishable on small scales, but we can distinguish them on larger scales and our observations (together with the Copernican principle) say it is space that's expanding. The mechanism is the same on whatever scale you are considering. --Tango (talk) 00:06, 24 January 2009 (UTC)

No, our observations say things are flying apart due to interia, embedding in and evolving under a framework of general relativity. That is what "the expansion of space" means physically. Such motion is perfectly consistent with the Copernican principle as mentioned above. I think you may have listened to one too many balloon analogies. The balloon analogy creates the impression the distances between all objects are being driven apart by some dynamical property of the universe. This is false. It is an incorrect understanding of Hubble flow, which is a fundamentally and observably an inertial process. Dragons flight (talk) 00:36, 24 January 2009 (UTC)

If the universe is a 3-sphere (which is one possibility that hasn't been ruled out, although observations put a lower bound on its radius), how can everything be getting further away from everything else unless more space is being created inbetween them? There is a maximum distance anything can be away from anything else, so once you reach that distance you have to stop moving apart, or you'll just start moving back together again from the other direction. --Tango (talk) 01:25, 24 January 2009 (UTC)

The size of a closed universe in GR is a manifestation of its curvature. Curvature in turn is locally a manifestation of mass density. The inertial tendancy of mass in our universe to be flying apart (due to the big bang) causes local curvature to decrease (assuming a closed universe) and this in turn would causes the global volume of the universe to increase. You have causation backwards I think. It is not that the universe gets larger and this forces things to fly apart, but rather it is because things are flying apart that we say the universe is getting bigger. The key point here isn't to fret about the impact of closure on the universe's evolution, but rather to realize that Hubble flow is a perfectly sensible classical and inertial solution once one starts with a Big Bang initial condition. Hence, even though GR does add wrinkles to the problem, it isn't necessary to invoke GR to broadly explain how or why things are flying apart. The answer to why we observe Hubble flow is simply because the universe is carrying forward its inertia following the Big Bang. Dragons flight (talk) 01:24, 25 January 2009 (UTC)

Dragons Flight, you are wrong. In fact, the expanding baloon analogy is quite good and the idea that the distances between objects is expanding due to a dynamic property of space (governed by GR) is the right one. The catch is the fact that the uniformly expanding universe is a solution to the GR equations obtained by assuming uniformily distributed mass and negligible proper velocities. Those assumptions are valid only for scales larger then galaxy clusters. Within galaxys due to virialization of the matter the correct solution (locally) is no expanssion at all Dauto (talk) 00:31, 25 January 2009 (UTC).

Thank you for your opinion Dauto, but I am not wrong. The easiest way to see this is by realizing that Hubble flow is a solution to the classical dynamics of a uniform and isotropic universe given the Big Bang initial condition. You lose the pressure term and the curvature term, but Newtonian gravity will otherwise given an identical expression for the evolution of the Hubble flow. General relativity adds corrections, but Hubble flow is at its heart a manifestation of classical inertia. There is no bogeyman somewhere blowing on the universe's balloon to make things move apart. Things move apart because they are carried by the inertia they recieved in the big bang. Dragons flight (talk) 01:24, 25 January 2009 (UTC)

Hubble flow as classical inertia gives results that match our observations in an infinite Newtonian universe, that doesn't mean it is correct. Consider a 3-sphere universe at a particular instant in time, what directions are all the bits of matter moving? There is no solution in which they are all moving apart, some of them have to be moving towards each other. That matter density decreasing would cause the universe to expand doesn't help if you can't get matter density to decrease in the first place. --Tango (talk) 16:29, 25 January 2009 (UTC)

If every local observer witnesses inertial Hubble flow in their neighborhood, then the space is expanding (inertially). The global observer might say that is impossible, as you do, by arguing that space is finite. The only way to reconcile this is to say that space is expanding. But don't you see the tautology, space is expanding (inertially) everywhere if and only if everyone witnesses inertial Hubble flow? (I have to be a little careful here because processes like dark energy lead to non-interial expansion, and in particular the local observer would then observe non-inertial flow.) The assumption of a Big Bang initial condition in a closed universe implies space is expanding in exactly the same way as it does in infinite Euclidean universe, since ultimately the shape of space is a composite of infinitely many local patches. The more interesting question is what happens in a portion of the universe where gravity has overcome Hubble flow and locally matter is collapsing? Is that part of the universe experiencing any expansion? No, that piece is collapsing. Again the evolution of the local shape of space is a reflection of the local mass dynamics. The (inertial) expansion of space is not merely opposed by gravity it is actually stopped in the local patch. Dragons flight (talk) 20:01, 25 January 2009 (UTC)

What is this space expanding stuff? (see Space/matter further down). That galaxies might be moving apart, one could understand even though the circumstantial evidence is highly suspect, but how does that make "space" expand? 196.2.124.248 (talk) 15:09, 27 January 2009 (UTC)

Highly suspect? Do you have a better explanation for cosmological redshift? --Tango (talk) 20:23, 27 January 2009 (UTC)

Foucault pendulum in Lost

I guess he was trying to find out where in the world he is with a foucault pendulum. Longitude is impossible to determine with it of course, but it got me thinking about latitude. The article says that the pendulum appears to take different amounts of time to return to its original floor-relative position depending on your latitude, so by measuring that time you can determine your latitude. But this is very confusing to me. Isn't the whole idea of a Foucault pendulum that the ball swings back and forth with no external forces except the top of the string getting pulled along with the rotation of the Earth (and gravity of course)? Doesn't that mean that when the rotation of the Earth brings it round 360 degrees back to its starting point that the swing of the pendulum should be the same as when it started? In other words, shouldn't the pendulum take the same amount of time on every latitude: 360 degrees in 1 day? 72.236.192.238 (talk) 18:37, 22 January 2009 (UTC)

Do yourself a favor, as I did: Stop trying to make scientific interpretations of events in LOST. It's all Hurley's dream anyhow :-D -RunningOnBrains 19:52, 22 January 2009 (UTC)

Yes yes lost is a bit out there (There are rules! Principally that time travel is impossible; second, that you can't change the past.. unless you say "please let this work" 3 times.) but I'm mostly asking about the pendulum. Hours of swinging my cell phone back and forth around my fist have only made me more confused. I really think that the pendulum should be "back where it started" relative to the ground at the end of the day, regardless of latitude, although I admit it must move at the poles and not move at the equator and don't understand what happens in between. It can't possibly have anything to do with Solar time can it? 72.236.192.238 (talk) 20:12, 22 January 2009 (UTC)

Latitude is easy to measure though. What's wrong with measuring the angle to which either Polaris or the Sun or any of the planets rises above the horizon? All of those things lie in the plane of the ecliptic - so you know the angle of your local horizon to that. You need to take account of the tilt in the earth's axis - and I suppose if you don't know what time of year it is, you might need to take both a daytime and a nighttime reading to get that. But that's WAY simpler than messing around with the pendulum. (And I agree that I don't see how it actually works) The trick is in figuring out longitude...but I don't see how the pendulum helps there. Unless you've got a pretty well detailed almanac or a perfectly synchronised clock - you're basically doomed. SteveBaker (talk) 19:54, 22 January 2009 (UTC)

It works because the precession of the plane of the pendulum in 24 hours is not 360 degrees, it is $360\cdot \sin \phi$, with $\phi \,\!$ being the latitude. The calculation is in the article, but to accept this result consider that the plane does not rotate at all at the equator, and there must be a smooth transition between that value and the 360° at the poles. Geometrically, if you're familiar with vectors, the rotation about the vertical that we're looking at here, is only a part of the angular velocity vector of the Earth (of magnitude 360°/24\,h), a projection of the latter onto the local vertical, which of course has a smaller magnitude, implying a slower rotation. And yes, I also find it difficult to actually picture what's going on here. --Wrongfilter (talk) 20:08, 22 January 2009 (UTC)

Hmmmm with your velocity vector analogy I just thought of sort of a way to picture it:

Forget the rotating frame of reference and the markings on the floor, and think of the pendulum as being fixed in space above the earth as the earth rotates below it. On the equator the pendulum just swings back and forth like the article says; the earth rotates below it but it doesn't affect the pendulum. But once you move north of the equator and become slightly more aligned with the axis of rotation, you can imagine the pendulum experiencing torque and starting to turn slowly. As you get to the pole, the pendulum's spin catches up with the speed of the earth until when the axis of rotation and the pendulum are perfectly aligned they're in sync. Now that's very easy to picture, and the jump to the torque being a fictitious force is almost as easy to accept, though not really to picture. 72.236.192.238 (talk) 20:31, 22 January 2009 (UTC)

Another thing just occurred to me to explain why the pendulum doesn't turn over the equator. Imagine a low pressure zone in the northern hemisphere, and air is rushing north to fill it. It moves in a straight line but the earth rotates under it, seeming to a ground-based observer that it's deflected it to the right. No matter which way you approach from it will deflect clockwise. But if there's a low pressure zone right on the equator, the earth isn't rotating under it! There's no coriolis effect at all because it's completely orthogonal to the only axis of rotation. 72.236.192.238 (talk) 20:54, 22 January 2009 (UTC)

I don't think that was a foucault pendulum on the show, since the pendulum wasn't on the island it was in Los Angeles I don't see the point of using it when GPS is available. That was some instrument they used to find the island so they could go back. Unless I missed some other pendulum on the show... -- Mad031683 (talk) 21:49, 22 January 2009 (UTC)

That it doesn't rotate at the equator can perhaps be seen best from that it will rotate in opposite directions at the two poles. Dmcq (talk) 23:25, 22 January 2009 (UTC)

Two quick points. Wrongfilter is right that a Foucault pendulum will tell you your latitude, but Steve is right that observing the sky is a much easier way to do it. As for what was shown on the show, I have no comment.

And one slower point. We usually think of the Coriolis effect as a fictitious force that appears to deflect an object's motion sideways on the Earth's surface. That's true as far as it goes, but there is also a vertical component. Because the effect is generated by the Earth's rotation, the "force" is necessarily felt in a plane parallel to the equator. There is a Coriolis effect at the equator -- but it's entirely vertical. (Imagine moving rapidly east along the equator so that your speed was added to the Earth's rotational speed. You would get slightly lighter. That is an upward Coriolis effect.) As your latitude increases, the Earth's surface comes nearer to being parallel to the plane of the equator. Therefore the horizontal component of the Coriolis effect increases and the vertical component decreases, becoming zero at the poles. This is also why the Foucault pendulum reveals your latitude: as seen from the Earth's rotating surface, it is the Coriolis force pushing it sideways with each swing the causes its plane to rotate, and at higher latitudes, the (horizontal part of the) force is greater. The vertical part, of course, has no effect on its plane.

--Anonymous, 05:47 UTC, January 23, 2009.

Incidentally, the vertical Coriolis effect is illustrated in Ringworld by a permanent sideways hurricane above a puncture. —Tamfang (talk) 18:47, 24 January 2009 (UTC)

Actually, they were trying to determine the location of something else. Remember that was Ben and that woman who had the pendulum and they weren't on the island. But who knows, maybe they have some sort of secret back door way of getting on the island where this room is located. But if you had a secret back door way of getting on the island, why would you need to know where it is located? A Quest For Knowledge (talk) 14:59, 27 January 2009 (UTC)

:: in gene notation

What does the notation something::something mean in regards to genes? E.g. spt10::KanMX6 ? ----Seans Potato Business 20:24, 22 January 2009 (UTC)

Googling for "double colon" genetics tells me that A::B designates a particular insertion of the B transposon within the gene A. --Sean's Utter Lack of a Potato Business 20:49, 22 January 2009 (UTC)

Its perhaps more typical in today's usage, that the double colon is used to denote a fusion gene has been engineered by inserting a sequence in frame behind, or in front of, a coding gene. So MC1R::GFP would indicate that you have a gene construct that has the Melanocortin 1 receptor gene sequence followed by the sequence for green fluorescent protein. The result, when the construct is expressed is a fusion protein. Rockpocket 06:44, 23 January 2009 (UTC)

January 23

air compressor

I want to know that what is two-stage air copressor? and how i done it's intercooling and thermal analysis? —Preceding unsigned comment added by Munish malik (talk • contribs) 00:24, 23 January 2009 (UTC)

See our article titled Gas compressor, expecially the section with the name Staged compression. Cheers! --Jayron32.talk.contribs 02:42, 23 January 2009 (UTC)

how do explosions destroy things

will ... i looked about the meaning of explosions , and it was a rapid chang in volume , but i need to understand whats the mechanisem of destruction effect ... how did it destroy objects within the range . —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 01:28, 23 January 2009 (UTC)

Shock wave? Also, even a simple "rapid change in volume" means there's a lot of force pushing out in all directions...push against "something" hard enough and it will break. DMacks (talk) 01:48, 23 January 2009 (UTC)

Overpressure says that (for example) C4 explosive produces 10 psi (pounds per square inch) of "overpressure" (although it doesn't say how much C4 or in how much volume?!?) - but let's run with that number. Suppose you have a brick wall that's 20' long by 10' high. That's around 30,000 square inches - and at 10psi of pressure, the explosion would exert a third of a million pounds of pressure onto the wall! It's really not hard to imagine why that would destroy the wall! SteveBaker (talk) 03:03, 23 January 2009 (UTC)

Another way to look at it: The forces exerted by the explosion are not applied equally for all parts of the exposed object – typically having the greatest effect on the near exposed surface of the object. That causes internal stresses (compression, tensile, sheer, or torque) within the object which may exceed its strength. The result is that the object distorts or breaks up. Those same forces may then accelerate different parts to different velocities resulting in a scattering of the remains.

In contrast, if the forces were applied equally to the entire object, down to the atomic level inside and out, the object would remain intact because there would be no internal stresses. Theoretically, the object could survive near-infinite acceleration in such cases. Examples would include gravitational and possibly electrical and magnetically induced acceleration. For example, the earth's gravity exerts an enormous amount of force on the ISS, but the station remains intact because the force is applied uniformly. If an equal force were applied using a thruster pack connected to one module of the station, the resulting stresses would likely cause structural failure. -- Tcncv (talk) 05:15, 23 January 2009 (UTC)

And note that if it is easier for the object in question to maintain its structure and to just move, it'll do that rather than be destroyed, even if the explosive force is huge. (See, for example, Project Orion (nuclear propulsion)) --98.217.14.211 (talk) 11:18, 23 January 2009 (UTC)

Viewing memories from a cat's brain?

Did I dream this? I remember reading, a few years ago, an article about a scientific study that was able to somehow find images from the memory of the cat, somehow encoded into its brain cells. It was accompanied by a few blurry pictures of a man that were said to be from the cat's brain. Knowing what I know now about how memory works, this seems somewhat unlikely, but I'd like to find the article again. Does anyone know about it? Was it a hoax? 99.245.92.47 (talk) 01:52, 23 January 2009 (UTC)

This is the closest I could find on a quick search. I'm pretty sure it's not the article you were after, but will (purr-haps) jog your memory? Cycle~ (talk) 02:36, 23 January 2009 (UTC)

That's by measuring the neural activity in realtime - that can only work at the instant the cat sees the image. There is no way we know enough to extract a memory of an image - that would require decoding the entire storage mechanism - and we are a tremendous way away from being able to do that. It was either a hoax or you are remembering the research on seeing the images in realtime. SteveBaker (talk) 02:55, 23 January 2009 (UTC)

I would not be surprised if something like this were possible far in the future, but it seems beyond the capabilities of today's technology. I note that there was a recent report of a brain scan technique which could brain imaging to accurately detect which letter of the alphabet a person was looking at, and iirc they hypothesized that the technique might also allow determining which letter the subject was thinking of. Edison (talk) 05:25, 23 January 2009 (UTC)

Yes - but that's still "What you are thinking about right now" - and that's a VERY different matter than "Extracting images from memories". It's pretty clear that our memories of scenes from the past do not consist of a bunch of pixels stored away like a photo in your computer. Instead we have a bunch of associations. We have a picture on the wall at home that I "remember" - there is a river with some canal boats and a pub in the background. I can "picture" that painting clearly in my mind - but I can't tell you the colors of the boats or the number of windows on the front of the pub. That's because I'm only remembering the concept of "classic village pub", "river" and "canal boats" - I don't have anywhere in my brain the actual image stored. Hence, in order to reconstruct that image, the computer would have to be able to extract from my memory not just the memory of the painting - but also my general concept of what a village pub typically looks like. That would require decoding more or less the whole of the brain function - and THEN being able to reconstruct the pathways by which we remember things. Worse still - if the person remembering that photo was an expert on 18th century architecture - he wouldn't be remembering a "village pub" - he'd be remembering a particular style of architecture and construction. An expert on canal boats would be remember a particular boat manufacturer and a specific model number they produced. A horticulturalist might remember the species of tree off to the left of the pub. Someone who's been there will also remember the flavor of the beer they serve there and details of the pub interior that aren't even IN the painting. No two people will remember that picture in the same way. We know that memories are stored in a diffuse 'holistic' manner so nothing short of scanning the connections between every neuron in the brain would enable us to do this. So this is AMAZINGLY beyond our current understanding - let alone the technology to measure what we'd need. Worse still - the number of neural connections in even a cat's brain are vastly too great to store in the available RAM + disk space of even a pretty large super-computer. So even if we knew what to do - we don't have the storage space to process it. It's going to be 30 to 40 years of "Moores law" improvements before we have a computer that has the power to do this - I'm betting a hundred years before we know enough about brain organisation to do it. This is science-fiction technology. So our OP is DEFINITELY mistaken. The only question is how/why. SteveBaker (talk) 14:21, 23 January 2009 (UTC)

Here's the story Edison's referring to — Matt Eason ^{(Talk • Contribs)} 01:35, 25 January 2009 (UTC)

It was more recent than 1999, and definitely talked about memories, but thanks. 99.245.92.47 (talk) 05:51, 23 January 2009 (UTC)

Your are either mistaken - or you've been hoaxed. It's not remotely possible with todays technology. SteveBaker (talk) 14:21, 23 January 2009 (UTC)

They did a study on cats dreaming where they removed the block that keeps cats (and us) from moving their muscles in response to the dreamed reality. They found cats dream about hunting and stalking. But that's not memories either, they might have mentioned those in the report, though. 76.97.245.5 (talk) 09:18, 23 January 2009 (UTC)

Hmmm - if they'd used dogs they could have saved themselves a lot of trouble! I've owned many dogs over the years and you can EASILY tell that this is what they are dreaming about because that suppression of muscle action during REM sleep isn't as complete as it is with humans (and perhaps cats). Dogs sleep a lot - so you have plenty of chance to watch! When you see their eyes start to move under their eyelids - you know they are entering REM sleep. Then within seconds you can see the tips of their paws twitching as they walk in their dreams - you see the feet first twitch in a 1-2-3-4 pattern like they are walking - then you see them start to twitch in pairs like they are running - you can see their bodies heaving like they are breathing fast (but they really aren't) - then you will see the jaws moving and the cheeks puffing slightly in and out and you may even hear very soft barking (more like little 'yip' sounds). On some occasions, I've seen the dog's running pattern stop and chewing actions happen in the jaw. It's totally compelling - my dog dreams of running and chasing things - sometimes of catching and eating them. No question about it. Cats on the other hand...who knows? SteveBaker (talk) 14:18, 23 January 2009 (UTC)

Yeah, cats do that too. I don't know why they felt the need to operate on some cats' brains to see this when I've had countless cats go through the same thing curled up on my lap. They run, they creep, they pounce, they bat prey, they eat it. All in twitching paws and jaw, sometimes with little smackings of the mouth. 79.66.105.133 (talk) 12:53, 25 January 2009 (UTC)

Do female athletes and sportswomen, especially in 'masculine' sports, have more testosterone than average women?

I would expect so but is there any good scientific work on the subject? Just seeing today's featured article made me think about it.--Ib.nib op.cit. (talk) 06:31, 23 January 2009 (UTC)

Because they say (citation needed) that oestrogen is produced by fat, and that testosterno is produced by muscle. Is this true?--Ib.nib op.cit. (talk) 06:34, 23 January 2009 (UTC)

Here is a nice review of the scientific literature: Athletes’ Testosterone Levels by Sports Team: An Exploratory Analysis. Note also that during the Cold War, East Germany decided to administer about 60 times the natural level of testosterone per day to their female athletes (under the direction of Manfred Ewald). The result was striking. Although a relatively small country, the GDR excelled in the Olympic medal tables during the late 70s and 80s. Their female athletes and swimmers did particularly well. Rockpocket 07:09, 23 January 2009 (UTC)

It's important to distinguish between the questions, "do women who have more testosterone tend to end up in 'masculine' sports?", and "do women in masculine sports tend to end up with more testosterone?". --Sean 12:46, 23 January 2009 (UTC)

One of the problems that the sports officials have had is determining whether some of their "female" competitors are truly female (See: Santhi Soundarajan)- to that end they have defined limits to the amount of testosterone that they consider normally "female" and a few women have been outraged to discover that they are excluded from female sports because the officials consider them to be "men" by virtue of their body chemistry [6]. So I think the answer is likely to be a cautious "yes". Cautious because of the definition of a "masculine" sport...weight lifting? shot putt?...yeah - sure. Is rifle shooting "masculine"?...if so then I need to change my answer and say "no". SteveBaker (talk) 13:48, 23 January 2009 (UTC)

In the Physical exercise article you see that one of the consequences of exercise is increased testosterone production. So yes, female athletes will have more testosterone than other females, but male athletes also have more testosterone than other males due to the amount of exercise they do. Anythingapplied (talk) 15:00, 23 January 2009 (UTC)

Neanderthal cranial size

What is the current consensus concerning the cranial capacity of H. neanderthalensis? Was it smaller, about the same, or larger than H. s. sapiens? Viriditas (talk) 09:27, 23 January 2009 (UTC)

Human on the left - Neanderthal on the right

We have an article: Cranial capacity which contains a table of cranial capacities:

• Orangutans: 275–500 cc
• Chimpanzees: 275–500 cc
• Gorillas: 340–752 cc
• Humans: 1100–1700 cc
• Neanderthals: 1200–1700 cc

So more or less the same. Of course we have FAR more human skulls to measure - so we know where the outliers are in the data set (ie we've seen incredibly small and incredibly large skulls) - but the relatively limited number of Neanderthal skulls that we've found could easily mean that we simply have not yet found any of the larger or smaller-brained individuals yet. That suggests to me that the 1200 to 1700 range is probably narrower than it really was. That's why I'd tend to say "larger".

We should be careful about what we take away from those numbers though. Larger skull capacity doesn't necessarily equate to greater intelligence. Neanderthals also had much larger nasal cavities than modern humans - so they may have had a very acute sense of smell - that being the case, they may have devoted more of their brain to processing, analysing and remembering olfactory sensations. So even with a larger brain than us - they may not have been as smart. Also, while Neanderthals were typically shorter than modern humans - they would have been taller than the humans that were when Neanderthals were common - and their body's were generally chunkier. (Our Neanderthal article somewhat scathingly compares them to modern Americans & Canadians!) But our Brain to body mass ratio and Encephalization articles point out that a rough measure of intelligence can be obtained by comparing the ratio of body mass to brain size between species. So even with slightly bigger brains, if their bodies were significantly larger than the humans of their era then perhaps we have to assume that they were not quite so smart. (Did I just imply that Americans and Canadians are stupid?)

But whatever the difference - it would probably be fairly small and there would certainly have been some Neanderthals who were smarter than some Humans - and vice-versa.

SteveBaker (talk) 13:39, 23 January 2009 (UTC)

That last bit is an easy claim to make. Clarityfiend (talk) 00:13, 24 January 2009 (UTC)

Neanderthals (who should probably be considered to be human, but a different subspecies from modern humans) survived under harsh conditions for hundreds of thousands of years. Their tenure might even surpass that of mmodern humans, when all results are in. Not really so stupid as some modern humans like to think. Much of the criticism of Neanderthals sounds like early 20th century "racial superiority" screed of eugenicists about the supposed superiority of some groups of humans over others. Edison (talk) 00:00, 24 January 2009 (UTC)

The problem is - if they were smarter and stronger - how come they were out-performed by the cromagnons? It's not a matter of 'racism' - it's a matter of scientific enquiry. In the changing environment of that era - they must have had some flaw (compared to modern humans) - it's just a question of what that flaw was. SteveBaker (talk) 00:17, 24 January 2009 (UTC)

It's possible that their flaw was just a lack of luck, of course. Algebraist 00:20, 24 January 2009 (UTC)

One theory suggests that the cro-magnons (modern humans) may have out competed the Neanderthals because the environment changed in Paleolithic Europe from dense forests to wide grasslands due to the change in climate.[7] The modern humans were pre adapted to a grassland environment because they migrated to Europe from Africa. The Neanderthals hunting strategies, tools and physical characteristics were better suited to a dense forest habitat. The Neanderthals were ambush hunters while as modern humans were better suited for perusing game across long distances which may have given modern humans a tremendous advantage over the Neanderthals (moderen human's physical build made them better runners[8] and their weapons and hunting stratiges were better adapted to a grassland enviorment). Neanderthals presumably used heavy spears to stab prey while as modern humans used lighter spears to throw at animals from a distance which also was more useful in a grass land environment. Also because of their large stocky builds Neanderthals may have required more calories than modern humans (Neanderthals may have required as much as 5,000 calories a day while as modern humans only require 2,000 or 3,000 calories a day)[9] and because their hunting methods became inefficient with the changed landscape they probably did not get the energy they needed and starved to death.--Apollonius 1236 (talk) 13:39, 24 January 2009 (UTC)

Thanks. Can anyone recommend the most recent articles or research on the subject? I added this statement to the Neanderthal article: "Neanderthal cranial capacity is thought to have been as large or larger than modern humans, indicating that their brain size may have been the same or greater." Is this accurate? Based on what I've read, I think it is. Recently, User:Tibbets74 added this statement: "however, a 1993 analysis of 118 hominid crania concluded that the cranial capacity of H.s. neandertal averaged 1412cc while that of fossil modern H.s. sapiens averaged 1487cc."[10] I temporarily moved it to a footnote because referring to a study from 1993 raised a red flag for me. Obviously, there's been new research since then and I found it strange to refer to a single paper (from 16 years ago) in the lead section. Any ideas? Or is this discussion best suited for the article talk page? Viriditas (talk) 04:02, 24 January 2009 (UTC)

OK - we've switched from a RefDesk question to a question about what Wikipedia should or should not state...those are not the same thing! No - a 1993 peer-reviewed paper trumps what we said here. The article should contain Tibbet74's comment and not yours because you have no references. Measurement of skull volumes is not likely to have changed over 16 years so his/her reference is an excellent one despite it's age. (The RefDesk uses references - it doesn't create them!). But (a) a sample of only 118 skulls is not many and (b) it's NOT true to say that brain size matches cranial capacity and (c) a difference of 75cc in a skull of around 1400cc is likely to be close to the limits of experimental error and (d) the range of sizes in one species is something like 1200 to 1700 - so while a 75cc increase might indicate an average brain size - it tells you nothing about one individual Neanderthal versus one individual human. However, a fact is a fact - and Tibbet74's fact is a good one. If you need to dispute it then you need references of your own...and this debate belongs on the Talk: page of the article...not here. SteveBaker (talk) 14:52, 24 January 2009 (UTC)

Thanks, but I think you misunderstood (and assumed too much from) what I wrote. I know how the RefDesk works, and my edit to the Wikipedia article was made 23 minutes before I asked my question, not after. I never said I didn't have references (I do and I still need to add them) and Tibbet's material is still in the article as a note. What I did request was a) a summary of the current consensus on the matter, and b) any recent, important articles on the subject. As for facts, depending on the field or subject, they tend to change over time, as I'm sure you are aware, so citing a paper from 1993 when there are more recent papers on the subject is a red flag. Also, the lead section isn't the best place to introduce new information, which is why I moved it to a note and made a minor change to what was previously in the lead. Viriditas (talk) 08:33, 25 January 2009 (UTC)

Brain size does not nessecarily correspond to intelligence. ~AH1^(TCU) 18:08, 25 January 2009 (UTC)

spiral bevel gears

Can the teeth of spiral bevl gears can be forged directly without any machining? —Preceding unsigned comment added by 203.90.64.100 (talk) 10:57, 23 January 2009 (UTC)

First, what size? Microscopic gears can be produced by building them up layer by layer or laser cutting. Small ceramic gears can be baked from powdered metal. As for larger metal gears the question would come to: Would that be feasible and what properties would you gain in the process? AFAIK machining is a cost efficient way to produce the desired precision of pitch and regularity. 76.97.245.5 (talk) 16:06, 23 January 2009 (UTC)

Electronics

I'm having trouble trying to understand something to do with electricity/electronics. In a circuit current is said to take the path of least resistance. So what I don't understand is why parallel circuits work: wouldn't the current just flow through the path which has the least resistance? --212.120.247.244 (talk) 14:07, 23 January 2009 (UTC)

Everything that moves is said to take that path. The "resistance" in "path of least resistance" is the general word meaning opposition to movement. The "resistance" in electronics is a special case of the word, borrowed rather than make up a new one, a well-defined term meaning something like "opposition to the gross movement of electrons in non-reactive media". There is another, more specific term, "impedance", that actually applies more accurately to electronics and is the word best thought of when thinking about these things. Bottom line, electrons do not take the path of least resistance, they take all paths available in inverse proportion to the impedance of those paths. --Milkbreath (talk) 14:42, 23 January 2009 (UTC)

See also path of least resistance and parallel circuits.

How about if you connect a superconductor and a non-superconducting wire in parallel? Will the non-superconductor get truly no current whatsoever? Not even due to some quantum mechanical random process thingamagic? 88.114.222.252 (talk) 14:50, 23 January 2009 (UTC)

Let's do the math. Ohm's law says I=E/R. We can't use that, because division by 0 is undefined (boy, am I glad this isn't the math desk—they'd eat me alive). So let's look for the voltage drop across the superconducting leg: E=IR, the voltage drop equals the current through the leg times zero, zero. With zero voltage drop across the parallel array, there can be no current through any resistive leg, because current through that leg would cause voltage drop, and there has to be a potential difference for there to be current. So, right, no current. I'll hand this off now to anybody who feels qualified to do that voodoo that the quantum guys do so well. --Milkbreath (talk) 15:23, 23 January 2009 (UTC)

It's like a traffic jam. There are two routes from A to B. Route #1 is slightly shorter (less 'resistance') than route #2. So all of the cars start heading down route #1...but this causes a traffic jam - so now, smart motorists will take route #2 because even though it's a bit longer, it'll get them from A to B faster because there is no traffic jam...this relieves the traffic on route #1 - so now people go that way because it's faster. In a perfect world where everyone behaved rationally and everyone had 'perfect information' - the two routes would carry traffic in inverse proportion to their 'resistances' so that everyone gets there in the best possible time. That's what happens with electrical resistance - which is why the current splits in inverse proportion to the resistances of the two paths. The "path of least resistance" thing is a kind of rule of thumb - it's not physically what happens. MOST of the electrons take the easy route - and if there is a significant disparity then it'll SEEM like they all took the path of least resistance. So if you wire up a short length of copper wire (with a resistance of say 0.001 ohms) in parallel with a ten megaohm resistor - then almost all of the current flows down the wire (1/0.001 versus 1/10000000 - so a billionth of the electricity struggles through the resistor and all of the rest takes the copper and your science teacher can boldly tell you that the electricity took the path of least resistance). If you take a 100" length of copper wire and a 101" length of copper wire and put those in parallel - then their resistance is so similar that the voltage will travel down both at almost exactly the same rates. SteveBaker (talk) 14:56, 23 January 2009 (UTC)

I like to think of it as pipes (conductors) and water (electrons), where a small diameter pipe is like a wire with more resistance. So, if you have two ways for water to drain out of a lake, one being a large pipe and one being a small pipe, water will drain down both pipes, but more will go down the large pipe (which is like the wire with least resistance). StuRat (talk) 15:39, 23 January 2009 (UTC)

The "path of least resistance" thing is a rule of thumb; but in order to be true it would imply that, ahead of time, each electron knows before it enters a wire which wire it should go down to travel down the "path of least resistance". In reality, the first electrons through will go down both wires at exactly the same probability, until the electrons start to "back up" to the junction, at which point further electrons will still choose their path randomly, but will now not choose 50/50 but will choose by the ratio of the resistance between the wires. --Jayron32.talk.contribs 17:30, 23 January 2009 (UTC)

I think a philosophical approach must be taken here. In the superconductive branch R is not zero. It simply does not exist. It cannot exist in a superconductor. Since R does not exist, the formula I=E/R cannot be applied - one of the terms is missing. – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 22:14, 23 January 2009 (UTC)

IR=E looks less mathematically impossible: Ix0=0 is true for any I. And that's correct...you can load an essentially arbitrary amount of current into a superconductor. An algebraist would say "dividing both sides of IR=E by R is not appropriate if R could be zero" precisely because it would lead to a limitation not present in the original equation...if you're gonna do that, you have to keep separate track of that side-effect of the manipulation. DMacks (talk) 23:19, 23 January 2009 (UTC)

If someone tells you that - you simply have to point out that the "original" form of the equation could have been IR=E and transforming it into I=E/R could have been the mathematically invalid step. So which form of the equation is the 'real' one? I'm going with the convenient one! SteveBaker (talk) 01:50, 24 January 2009 (UTC)

Superconductors have no resistance, but there appears to be a limit to how much current they can carry. If one exceeds its critical current, at a given temperature and magnetic field "quench." This quenching property can be used as a fault current limiter [11]. Are there superconductors immune to this limit, or are there ways of operating them (extremely low temperature?) that avoid quenching? Seems doubtful. Maybe someone has studied the phenomenon. It is a real problem in superconduction magnet windings, where quenching results in the stored energy becoming heat and often destroying the winding. Edison (talk) 23:55, 23 January 2009 (UTC)

Another thing to keep in mind (though I now see it's already been mentioned) is that superconductors have zero resistance, not necessarily zero impedance. That is, current flowing through a superconductor does not lose any energy to dissipation. It can still lose energy to, for example, radiation, and it should be possible for there to be a transient potential difference across it. So to answer 88.114.222.252 is that sure, the non-superconductor can get some (transient) current. --Trovatore (talk) 03:31, 24 January 2009 (UTC)

What Trovatore says makes sense; the impossibility of perpetual motion and the inviobility of the second law of thermodynamics pretty much guarantees that all systems will "bleed" energy in some form. While a superconductor may lack resistance in the traditional sense, what it does not lack is the fact that there is some friction-analog in the system. If nothing else, electrons in motion generate a magnetic field, and this magnetic field will interact with other availible magnetic fields (even, like, the earth's own magnetic field) such that over time, the magnetic fields in the super conductor will interact these other magnetic fields, gradually slowing down the flow of electricity. It may well be a VERY gradual slow down, but its still real, and it still allows the system to obey the laws of physics. --Jayron32.talk.contribs 04:47, 24 January 2009 (UTC)

Well, it's not going to slow down because of a static magnetic field. You have to have a changing field to change the current in a superconducting loop. I don't offhand see any reason it wouldn't be as likely to increase the current as to decrease it.

Perpetual motion machines "of the first kind" "of the third kind", the ones that just keep moving but you can't extract any useful work from them, are not a priori impossible -- consider an electron orbiting an atom (assuming there's no such thing as proton decay). --Trovatore (talk) 04:52, 24 January 2009 (UTC)

Think about it this way. In a circuit, the conducting wires' resistance is so low that there's barely any difference in the different paths of a parallel circuit. Assume that the resistance is zero (which of course isn't the case), and you'll see why 2 x 0 and 4 x 0 both = 0. That little bit of extra distance really doesn't make much of a difference. Unless, of course, there's a resistor lined onto the conducting wire for every centimetre of wire, then there'd be a difference. ~AH1^(TCU) 16:03, 24 January 2009 (UTC)

I'm not sure what you're responding to here. In a superconductor, according to currently accepted theory, the resistance really is exactly zero.

But, if I've analyzed this correctly, that doesn't mean that if you put a superconductor parallel to a normal conductor and then apply voltage, you'll get zero current in the normal conductor. The reason is that the DC laws do not apply perfectly except to entirely unchanging systems (of which there aren't any).

When you turn on the voltage, a current starts to flow in the superconductor, which generates a magnetic field, which stores energy. That means you have to supply the energy to create the magnetic field. Therefore it doesn't happen instantly. In the mean time there is a potential difference across the normal conductor, and therefore also some current. --Trovatore (talk) 22:55, 24 January 2009 (UTC)

Just in case no one has mentioned it above (I cant be bothered to read it all) I should mention the Current splitting rule--GreenSpigot (talk) 04:14, 25 January 2009 (UTC)

OOoh look we have an article on this. Its called Current divider--GreenSpigot (talk) 04:17, 25 January 2009 (UTC)

microbiology

what i meant by streptolysin test,where is it applied and which is the procedure of carrying it out? —Preceding unsigned comment added by 196.202.206.37 (talk) 14:48, 23 January 2009 (UTC)

Do you mean Antistreptolysin O titre? If so, follow the references at the bottom of that article. SteveBaker (talk) 14:59, 23 January 2009 (UTC)

Question about the hologram universe article in New Scientist issue 2691

I love this article - fantastic stuff [[12]]

But it made me wonder: if 'the amount of information papering the outside must match the number of bits contained inside the volume of the universe', do the theorists believe that includes all the information implicit in everything we do? - do the bits include changes across time in our physical universe? if so, are the bits also changing across time, or are the changes themselves also encoded in the bits?

Thanks Adambrowne666 (talk) 21:21, 23 January 2009 (UTC)

I'm not sure I understand your question. I've read the article, and it's rather vague, and seems to try to explain everything in layman terms, which probably add more confusion than it resolves. I'm sure the original authors have a solid mathematical description of their theory. Our article about the Holographic principle has some more information about this topic. baszoetekouw (talk) 21:53, 23 January 2009 (UTC)

In "holographic" theories, there is generally a one-to-one correspondence between states on the boundary and states on the inside. In other words, things on the inside change if and only if things on the boundary also change. Dragons flight (talk) 22:10, 23 January 2009 (UTC)

Thanks, Dragons - sorry for not explaining myself, Baszoetekouw; will check out the article. Adambrowne666 (talk) 03:55, 25 January 2009 (UTC)

What does "space is a vacuum" mean?

Does space have atoms? Or just nothingness? It sure would be fun to capture a jar of that! When space bends from nearby mass, what exactly is it that's bending!? This has always confused me. Why does your blood boil in space? --THE WORLD'S MOST CURIOUS MAN (talk) 23:16, 23 January 2009 (UTC)

We have a detailed Outer space article, which includes a whole section about the environment (i.e., "what is in there?"). Outer space is a definite and fairly simple thing--be careful not to confuse it with the more advanced idea of spacetime. DMacks (talk) 23:26, 23 January 2009 (UTC)

Every atom has a gravitational field that extends to infinity. Therefore a light beam cannot be outside gravitational fields. In the case posited, the atoms of the glass jar will affect the light except where two atoms cancel each other's gravitational field because they are equidistant on each side of a point position in the light. More distant atoms will augment the gravitional field of the jar atoms. – GlowWom. —Preceding unsigned comment added by 98.17.34.148 (talk) 23:44, 23 January 2009 (UTC)

So many questions! Fortunately - for today only - the RefDesk has a five-for-the-price-of-one deal!

1. Does space have atoms? Or just nothingness? - yes, there are atoms - but a LOT less than here on the surface of the earth. As you move out deeper and deeper into space - the number of atoms in every cubic meter gets less and less. In orbit, near the earth, there are still quite a lot of atoms - enought to gradually slow satellites down so that they have to be boosted into higher orbits once in a while. Out near Pluto - there is a lot less. Halfway between our star and the next one - there is almost nothing - but still there will be the odd atom here and there. In the deep voids between galaxies - less even than that.
2. It sure would be fun to capture a jar of that! - not really. You can get the same effect (a totally empty jar) with a decent vacuum pump down here on earth. But it would have to be quite a sturdy jar not to collapse from the pressure of the earth's atmosphere pushing in on it without any air inside pushing back the other way.
3. When space bends from nearby mass, what exactly is it that's bending!? - space ITSELF is bending...the actual nothingness bends...
4. This has always confused me. - you and just about everyone else! The things that go on in the universe frequently only make sense when you look at the mathematics. Most of the time, you have to simply turn off your common sense and trust to the numbers.
5. Why does your blood boil in space? - it's not exactly true that it does. Liquids behave strangely - they both freeze AND boil at the same time. Water left alone in the vacuum freezes AND evaporates from the surface. It freezes because it's cold - it boils because there is no air pressure to oppose the molecules flying off the surface. When a human is exposed to space, the fluids take a while to cool down to freeze - and your skin applies some tension to prevent it from immediately boiling. It's generally believed that humans could survive a brief exposure to the vacuum. We have an article about that Vacuum#Effects_on_humans_and_animals and Human adaptation to space.

SteveBaker (talk) 00:04, 24 January 2009 (UTC)

It doesn't freeze because it's 'cold' exactly; it freezes because it is evaporating. Space isn't exactly cold in any meaningful sense. 79.66.105.133 (talk) 12:48, 25 January 2009 (UTC)

Good answers, but your answer to #2 is not quite right...interstellar space is much emptier than any vacuum achievable at the earth's surface(according to this Tufts page). It would certainly be interesting to some scientists to study the "nothingness" out there in more detail.-RunningOnBrains 01:54, 24 January 2009 (UTC)

That's an interesting page and it accords well with our Vacuum#Quality article. However, us humans can employ more ingenious tricks than nature itself, things like getters, and can make an ultra high vacuum that's pretty competitive with most regions of space. Maybe you're thinking of intergalactic space being much emptier, as Steve noted. Franamax (talk) 02:37, 24 January 2009 (UTC)

Well, yes - indeed. Worse still - even if you got a super-hard vacuum, a few microseconds later, some silicon and oxygen atoms shed from the glass jar itself would contaminate your pure vacuum. Yeah - indeed - you don't get a pure vacuum here on earth.

The actual numbers are rather revealing:

• Best artificial vacuum: 10⁹-10⁴ molecules per cm³
• On the Moon: 4x10⁵ molecules per cm³
• Interplanetary space 10 molecules per cm³
• Interstellar space 1 molecule per cm³
• Intergalactic space 10^-6 molecules per cm³ (1 molecule per cubic meter!)

So we can maybe get down to ten thousand molecules per cm³ - which is a better vacuum than the surface of the moon...but nowhere near as good as in the space between planets, between stars or between galaxies. SteveBaker (talk) 03:30, 24 January 2009 (UTC)

What about vacuum energy? ~AH1^(TCU) 03:22, 24 January 2009 (UTC)

The source to a lot of these facts are from the book Modern Vacuum Physics by Austin Chambers which is can be read online at google books here —Preceding unsigned comment added by Anythingapplied (talk • contribs) 07:08, 24 January 2009 (UTC)

Your blood doesn't boil in outer space. At least, not unless you get a cut. It won't freeze unless it boils, as the boiling is what causes it to cool enough to do so. See freeze drying for why this would happen. It would make you saliva and the water on your eyes boil. — DanielLC 22:49, 25 January 2009 (UTC)

You don't need a particularly sturdy container to contain ultra high vacuum. Most any walled glass vessel will do. The pressure difference across the wall is almost the same whether the vessel contains rough- or ultrahigh- vacuum. ike9898 (talk) 20:33, 26 January 2009 (UTC)

Energy stored in air, compressed by supersonic object

There is an object, say a flat square, that is accelerated to supersonic speeds. This will create a shock wave behind the object. But also, many waves will all crunch together directly in front of the object and build up an area with high pressure. What is the energy of these waves in front of the object?

This might be hard to figure out without any specific numbers, but you can just assume whatever is reasonable, because I was just wondering whether the energy is enough to knock over a person. --Yanwen (talk) 23:55, 23 January 2009 (UTC)

That energy is what creates a sonic boom. Where is this person standing? If they are directly in front of the object, then the object itself will knock them over... --Tango (talk) 00:03, 24 January 2009 (UTC)

Right, the plane or whatever will probably run into the person and kill him because he is in the direct path of the shockwave (and supersonic airplane). But I just need a rough approximation of the energy of the shockwave in Joules or something.--Yanwen (talk) 22:08, 25 January 2009 (UTC)

Also, as an analogue, I've heard that an unsuitable plane flying into a sonic boom (passing the sound barrier) would be like passing into a brick wall. ~AH1^(TCU) 03:19, 24 January 2009 (UTC)

There must be some factors which limit the energy in a sonic boom, or else a plane traveling at the speed of sound would have a wave in front that would build up without end. StuRat (talk) 06:41, 24 January 2009 (UTC)

Well, the wave spreads out, that's why you can hear it. --Tango (talk) 22:10, 24 January 2009 (UTC)

Most of the sound waves aren't aimed straight forward, so those you can hear. But, the portion of the waves headed straight forward should theoretically "collect" at the leading tip of an aircraft going exactly mach 1. StuRat (talk) 15:11, 25 January 2009 (UTC)

Conveniently that portion is 0, since "straight forward" is zero solid angle. Moreover, any air that is being carried with the plane (as would have to happen if there was any collection going on) can now carry energy away and dissipate it, because its bulk speed is that of the plane and it can propagate sound relative to the plane at its sound speed. As you get farther in front of the plane, the bulk speed drops (toward the ambient air's speed) — and the sound speed changes in some more complicated way — until a point is reached where the sum falls to the plane's speed and the disturbance can just keep its lead. The energy added to that disturbance by the oncoming air is dissipated around the aircraft by the intermediate zone which is capable of doing so. --Tardis (talk) 16:58, 26 January 2009 (UTC)

So you're saying there's a dead spot, straight in front of a plane, where it's absolutely silent ? I find that difficult to believe. StuRat (talk) 21:20, 27 January 2009 (UTC)

Well, at any non-trivial distance in front it will be silent, because the plane is supersonic. Otherwise, I'm not sure what you mean — are you talking about the leading edge of the disturbance? There's a shock wave there which is (effectively) discontinuous, and there is presumably noise behind it (because information can propagate up to it from behind) and no noise in front of it (where nothing has happened yet). In the shock itself (which is actually at least a few atoms wide) concepts like "sound" don't really apply because the gas does not act like a fluid on that length scale. There will probably be vibrations of some sort in it that decay as you move forward through the shock. --Tardis (talk) 04:54, 28 January 2009 (UTC)

Chaos Theory. Is this a croc, or what?

There is essentially no randomness. Everything unfolds in a certain order, or else it wouldn't have happened that way. Every single thing is the absolute result of an absolute action. Correct?--Sunburned Baby (talk) 23:46, 23 January 2009 (UTC)

Moved this question here from the Misc. desk. -- Captain Disdain (talk) 00:21, 24 January 2009 (UTC)

Sorry, there is randomness. See determinism and quantum indeterminacy. Chaos theory is a little different: it's the idea that even if there *wasn't* any randomness, a complex system is so sensitive to its starting conditions that you can't predict the outcome anyway. --Sean 00:38, 24 January 2009 (UTC)

No - Sunburned Baby is not correct. If anything, the complete opposite is the case! True, fundamental randomness is everywhere.

• Heisenberg's uncertainty principle guarantees that you can't know exactly where a particle is and what speed it's going at - hence randomness at the lowest levels of existence.
• Schrodinger's equation is the fundamental description of a particle - it says that (for example) an electron is essentially a "probability cloud" a fuzzy blob of uncertainty.
• Quantum theory - particles and antiparticle popping into existence from literally nowhere - more randomness.
• At the level of atoms - an atom of uranium 232 has a half-life of around 70 years. This means that if you have a big pile of the stuff - half of it will have decayed down to something else after 70 years. But if you have just one atom - there is a 50/50 chance of it breaking down before 70 years are up. But you don't know when it'll do that. The event of the atom emitting a neutron is completely and utterly random.
• Even at the 'macro' level Chaos theory says that no matter how precisely you measure some kinds of events - you can't do so precisely enough to predict what comes next. Take my favorite example. Place a large sheet of paper on a table. Put two magnets a few inches apart onto the paper - mark their positions - call one of them "RED" and the other "BLUE". On some kind of very rigid stand, tie a pendulum with a magnetic 'bob' on the end so it hangs somewhere between the two magnets. You'll need two pencils - one red, the other blue. Now - hold the pendulum over the paper and note the point beneath it. Let the pendulum swing around - it's swing will be disturbed by the two magnets - but eventually - the bob will come to rest hovering over one or other of them. Mark the point where you released the pendulum from with either a red or a blue dot depending on where it ended up. Do this a LOT of times. What you find is that there are some 'release points' where the pendulum always ends up over the red magnet - and others where it ends up over the blue. If you do the experiment enough times - you'll see there are large, solid areas of red marks and large solid areas of blue marks. But there are some areas that are striped or checkered alternately red/blue/red/blue. There are areas where those regions get very small and it becomes impossible to start the pendulum from the EXACT position where you released it before so the red and blue gets all mixed up. But the equation for the motion of the pendulum is well known - it's very simple physics - so we can program a computer to simulate the pendulum's motion. But even when you calculate where the regions of red and blue are in the simplest system with no air resistance and no friction and a perfectly flexible bit of string and idealised perfect magnets - the 'map' of red and blue starting points is a fractal...like the mandelbrot set. So the closer you look at the picture, the more detail it reveals. In some areas of your table - moving the starting point of the pendulum by even a millionth of the width of an atom is enough to change the outcome. Since quantum theory and the uncertainty principle apply to the pendulum bob - this experiment "amplifies" quantum uncertainty to the point where it matters.
• It goes on...Hawking radiation from black holes is random. Catastrophy theory induces fundamental randomness. Godel's theorem says there are fundamental pieces of mathematics that can neither be proven true or false.
• There are 'for real' infinities and zeroes in the universe - and when you plug those into sane, normal equations - the answer often comes out "undefined" - so some things are fundamentally unpredictable.

The universe is a total mess! Your idea of the clockwork universe is about as far from the truth as it's possible to be. This upsets a lot of people - Einstein spent almost all of his productive life trying to 'fix' this. But sadly - the computer you're sitting in front of right now wouldn't work if the universe worked 'mechanically' without randomness.

SteveBaker (talk) 01:36, 24 January 2009 (UTC)

Your examples are somewhat incomplete. Schrodinger and Heisenberg don't, by themselves, introduce randomness. They replace our concepts of deterministic point masses, with wave functions that still obey deterministic rules. Rather it is the process of measurement that introduces randomness by forcing the wave function to choose amongst multiple states in a probabilistic manner. It is only that process of wavefunction collapse that is random. The rest of the time, wave functions evolve according to rules that are just as deterministic as the rest of physics (even though the objects they describe act in ways that are hard to understand). In fact, wavefunction collapse might also be just an illusion, in which case, all of quantum mechanics is deterministic, albeit in a way that does not correspond to the classical notions of how matter should behave. Dragons flight (talk) 02:19, 24 January 2009 (UTC)

On another note, this is one of the areas where I have problems. You say that the randomness becomes apparent when a measurement is made, and looking at that article (through the forest of tags), it mentions "observers" and "measuring apparatus". This implies that physicists have wisely confined themselves to describing only their particular experiment and acknowledged that if they hadn't written down the results, the results might not have actually happened. But that plus a dollar buys me a cup of coffee. If a bird flies through the photon stream, is it an observer? Is its feather a measuring apparatus? What about a rock? What if the cat was late-period pregnant when it went into the box? Does it have a born/unborn kitten? We have pretty solid evidence that kittens are not quantum states, so when that kitten gets born, does it become a measuring apparatus? I can follow the line of reasoning, but it does seem to me that it leads pretty quickly to "stop asking" as the next response. Either that or "many worlds" which to me is mis-stated, it should be "incredibly huge number of worlds within the first two nanoseconds". This stuff has bothered me for a long time. :) Franamax (talk) 03:01, 24 January 2009 (UTC)

It's worth reading Neal Stephenson's latest book (it's fiction - and oddly compelling) - his idea of 'state space' is another interesting take on many worlds - it takes things yet one step further than classic many-worlds. SteveBaker (talk) 03:36, 24 January 2009 (UTC)

(ec) I see nothing "sad" about this. I'm kind of mystified why people would want the world to be deterministic. What would be the point of anything, then?

On the other hand, QM's challenge to realism (see for example Aspect experiment) is rather more disturbing. I just recently saw in the article on hidden variable theories that Edward Nelson has a hidden variable interpretation that is still indeterministic, but saves realism (though not, I guess, locality).

On a side note, chaos theory is definitely not a croc. Whether (at least as espoused by some of its exponents) it is a crock is a subtler question. --Trovatore (talk) 02:24, 24 January 2009 (UTC)

I think OP just had it the wrong way around Crock is chaos. Everything unfolds in a certain order and you still end up with a perfectly chaotic mess in the kitchen. :-) 76.97.245.5 (talk) 03:11, 24 January 2009 (UTC)

Observer bias? ~AH1^(TCU) 03:16, 24 January 2009 (UTC)

(after ec)The OP might like to consider Richard Feynman's theory of sum over histories as an explanation of what is perceived to be "the way things happen". —Preceding unsigned comment added by TammyMoet (talk • contribs) 15:25, 24 January 2009 (UTC)

will mabye the world is big and complex for us ... will not evry thing could be rulled by mathmatical formula , but i belive that even a particle of sand flaying in the desert is going to some where for a reason ...no thing is happining as a coincidence ... if you read the quraan (islam book) you will find articles about earth ... sky ... oceans ... moon ... sun ... it talked about moon been split in half ... about univers explosion in the future ... about stage of human growing in the mother billy ... about sun and moon is moving ... about that the earth is loosing an amount from its mass with time ... it talked about evry thing ... evry thing will happen for areason ... evry single tiny small thing . —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 21:43, 24 January 2009 (UTC)

Well - sadly, it doesn't matter that you feel like that - or that some book of religious mythology says otherwise - but the science and the mathematics is VERY clear. Quantum theory is all about fundamental randomness - and quantum theory is ESSENTIAL for things like flash memory chips. Chaos theory is right there in the Mandelbrot set.

To deny fundamental randomness is to deny that the very computer that you are reading this post on can work. So - if the Qur'an says that there is no randomness in the universe then you have to face up to this question: EITHER:

1. The Qur'an is correct and the computer you are using can't possibly work. ...OR...
2. The Qur'an is in error and the computer you are using works just fine.

Since you are still reading this post - you should probably assume (2). Failing that - you need to take the question off to some bunch of religious nutjobs because science is VERY clear on this point.

There is no fundamental "reason" why a particular atom of uranium should choose some exact moment to spit out a neutron and decay. That's a fundamental scientific truth that you can't dodge. Nuclear power stations and atom bombs wouldn't work the way they evidently do if there was a 'reason' why the neutron picks a particular moment to do it's thing.

It's arguable that the entire universe couldn't exist if there wasn't some kind of fundamental randomness. When the big bang happened, the universe was PERFECTLY symmetrical because it was a zero sized dot. As it expanded, all forces would be pulling precisely equally in all directions - all energy and mass would have to be completely uniformly distributed. You need the tiniest wiggle in there somewhere - the tiniest disparity from mathematically perfect symmetry - or else there is no way for large scale features to ever appear. So if there was no randomness - there would be no way for anything other than a perfectly smooth uniform universe to come from that. Randomness makes atoms and everything else up to and including galaxies.

I know that giving up on the idea of a clockwork universe is tough - great scientists have fought to find other explanations for almost 100 years now...and as yet, there is no alternative theory that really explains what Quantum theory explains.

Now - having said that - the randomness averages out once there are more than a few bazillion atoms so at the 'macro' scale where humans experience life, things do seem to be completely regular and predictable - but we can provoke that fundamental randomness and with the right situation (the two-magnets-and-a-pendulum experiment - or the "butterfly effect" in weather prediction - or with a geiger counter) you can make those microscopic randomnesses become very evident. That's how we know it's true.

SteveBaker (talk) 01:43, 25 January 2009 (UTC)

Schroedinger's cat and Quantum theory--GreenSpigot (talk) 04:21, 25 January 2009 (UTC)

Many things we see in the quantum world seems random. Electrons not being where they're supposed to be (Heisenberg's uncertainty principle), nuclei decaying for no apparent reason, and chaos theory etc. But what if it's just our observations that are uncertain, but the universe itself is completely deterministic. This "perceived" randomness is not actually there. Just because we can never determine both the exact position of an electron and it's momentum at the same time doesn't mean that it doesn't have an exact position or momentum. Even when the decay of a nucleus is apparently random, there has to be a reason that it decayed at that specific point in time, we just don't know the reason. As for the magnetic pendulum, the only thing preventing us from determining the outcome is the precision and accuracy (or lack thereof) of our measurements. The angle of release is an exact number; but our perception of the angle of release, however, is not exact and cannot be exact. If you release the pendulum from exactly the same spot every time, you will get the same result every time. If you don't, then that means your measurements are not accurate, not because the universe is random. (I think I might be talking about Hidden variable theory, which has been disproved by Bell's theorem, but I think there is a difference.)--Yanwen (talk) 21:30, 26 January 2009 (UTC)

January 24

Non-teratogenic mutagens

Are there any human mutagens which are not human teratogens? NeonMerlin 02:38, 24 January 2009 (UTC)

Look at Mutagen and Teratology. Human cells contain DNA. A substance or process that will alter the DNA is called mutagen. It can, e.g. lead to cancer. If the DNA that gets damaged is in an cell that will develop into a baby's cell then a birth defect may result. 76.97.245.5 (talk) 02:56, 24 January 2009 (UTC)

How about UV light? lots of skin cancer but no birth defects.--Digrpat (talk) 14:39, 24 January 2009 (UTC)

Thats only because embryos tend to be protected from UV exposure during development. If you expose embryos to UV light, you see teratogenic effects [13]. Rockpocket 19:05, 24 January 2009 (UTC)

Space tube: Sucking or Blowing?

If I created a hollow tube to space, like a giant earth straw, would it have any movement of air at the bottom? If I covered the bottom with my hand, would I feel a slight sucking or blowing? Would there be any forces at play that might suck air constantly through it like a siphon? (such as air pressure differences, time dilation, movement of the end of the straw through space). Or might it blow out air? ever so slowly? Would the answer changed if the tube was slowly getting narrower as it went up or wider? I know it wouldn't act as a straw in the same sense because the vacuum of space should be almost exactly countered by the weight of the air, but is this changed at all by putting a tube around it? Thanks. Anythingapplied (talk) 07:12, 24 January 2009 (UTC)

No, I really don't think so. Assuming that such a tube could really exist, the reason the atmosphere (mostly) stays where it is is that gravity keeps it where it is, just like it keeps us from flying off. Some of that gas would be inside the tube, but I don't see what difference that would make: gravity would still hold it down. I guess if the tube conducted heat really ridiculously well, it might cool way down in the vacuum when it was in the dark and heat up when it was in direct sunlight, and that might have some small effect on some of the gas inside... but, really, no. (And if for some reason I'm wrong, that's great, because in that case the real answer can only be interesting as hell... but I'd be very surprised to hear that.) -- Captain Disdain (talk) 09:00, 24 January 2009 (UTC)

If the air was moving one would able to extract energy from it; which would break conservation of energy. So one can assume that there would be no air flow in the tube. —Preceding unsigned comment added by 129.67.37.225 (talk) 13:44, 24 January 2009 (UTC)

I agree - nothing special happens unkess the tube itself is doing something (which, in this kind of thought experiment, it doesn't!) SteveBaker (talk) 14:30, 24 January 2009 (UTC)

I have a way to convince the OP. Consider a straw in a glass of water. The pressure at the bottom of the glass is higher than the pressure at the surface - just as the pressure at the top of your giant atmosphere straw is greater at the bottom of the atmosphere than at the top. The liquid level in the straw stays level with the top of the liquid in the glass...same deal with the atmosphere. QED. (Oh - if you try to do the experiment with a real straw in a real glass of water - the level in the straw will actually be a millimeter or two higher than in the glass - but that's because of surface tension...if you used a glass of mercury (please don't!) then the level in the straw would be lower than in the glass.) SteveBaker (talk) 15:00, 24 January 2009 (UTC)

You wouldn't get any net movement of air, but you would get temporary winds blowing in or out when the barometric pressure of the atmosphere changed. Specifically, when the barometric pressure goes up, wind would blow into the straw, and when it went down (which usually means bad weather is on the way), wind would blow out of the straw. This assumes that the straw is perfectly rigid, so it's sides can't expand or contract to compensate for the pressure. Note that this air-blowing-in-or-out-to-equalize-pressure effect doesn't have to do with the straw being vertical, or extending into space, but applies to any large volume of air with a narrow opening to the atmosphere, such as certain caves. StuRat (talk) 15:23, 24 January 2009 (UTC)

Space/matter

In what sense does matter "create" space? Does it mean that without matter there is no space? Is the quality of space somehow dependent on the amount and distribution of matter? 196.2.124.248 (talk) 08:02, 24 January 2009 (UTC)

As far as I'm aware, there is no sense in which matter creates space. Where have you encountered the idea? Algebraist 13:36, 24 January 2009 (UTC)

This might be a reference to the metric expansion of space which is affected by the amount of mass in the universe. Spacetime could exist wothout matter and in that case would be perfectly euclidean. SpinningSpark 13:55, 24 January 2009 (UTC)

There is unfortunately some religious arguments from some fairly ignorant people on how the universe was clearly created by a deistic entity. They refer to space as 'the distance between obejcts' as one of their steps in the argument. But on the flip side space is to an extent defined by objects; as with a zero or one object universe, space does not exist. —Preceding unsigned comment added by 129.67.37.225 (talk) 13:50, 24 January 2009 (UTC)

Now now, let's not go ripping on religious people here. You can't disprove God scientifically.-RunningOnBrains 20:28, 24 January 2009 (UTC)

That's one of those "If a tree falls in a forest and there is no-one there to hear it - does it make a sound?" questions - to which the answer is an unambiguous "Well, DUH!". If there are no particles around for the space to be measured against then does it exist? This is the kind of thing that gets philosophers very excited. But in truth it's a rather bogus argument because we have virtual particles causing quantum foam - so if there is space-time then there is matter (at least briefly) - and it is sometimes argued that the existence of that foam is what causes space-time to exist. Which means that even in a universe that's completely devoid of galaxies, gas clouds, stars, planets, grand pianos and pink aardvarqs - there would still be virtual particles and hence matter. I don't think we know the answer to our OP's question at the quantum level. At the macro level, it's hard to argue that without at least one object there could be no space - we don't know that and because a universe with no matter in it could not be measured or probed in any way - we can't tell for sure. If you can't put a tape-recorder into the forest then it's hard to demonstrate that the falling tree makes a sound...although all that we know says that theoretically, it must. SteveBaker (talk) 14:26, 24 January 2009 (UTC)

If matter then has very little to do with space, what is meant by a "finite" universe - is it the matter which is finite (which one can understand even if it is unlikely) or is it the space which is finite (difficult to understand and even more unlikely) or is it both (extremely unlikely and impossible to understand)? 196.2.124.248 (talk) 22:24, 24 January 2009 (UTC)

I think it usually refers to space, ie. the volume of the universe is finite. I don't see anything particularly difficult to understand about that - it's just like saying the surface area of Earth is finite. --Tango (talk) 22:46, 24 January 2009 (UTC)

Well now, I think one immediately gets into deep water there. If the volume is finite then what would the bounding surface consist of? Obviously not a rigid structure and also not open space, since that would just be more space - space would have to extend infinitely in all directions holding an infinite amount of matter - see Cosmological principle. 196.2.124.248 (talk) 07:47, 25 January 2009 (UTC)

You don't need a boundary. Go down a dimension and think of the surface of the Earth. The Earth's surface area is definitely finite, but there is no edge. --Tango (talk) 03:40, 26 January 2009 (UTC)

No - that argument is totally specious. You wrote "the volume of the universe is finite" which directly implies that it is bounded. There is no need to "go down a dimension". Speak to a mathematician. 196.2.124.248 (talk) 18:59, 26 January 2009 (UTC)

Compressible liquids

its afact that liquid get heavier as its gets colder , which means that liquid mass increase as the temperature decrease . and recalling that mass dont change , so to have the same mass the volume must get smaller . which lead to the idea that liquid could be compressed . and as you know liquid couldnt be compressed. —Preceding unsigned comment added by 86.108.61.209 (talk) 15:21, 24 January 2009 (UTC)

It's almost a fact that liquids get 'denser' (not 'heavier') as they get colder. It's not true of water close to freezing point. So a plastic bucket of water won't get any heavier as it cools (it's mass won't change either) - the level of the liquid in the bucket will get lower as the water shrinks (until close to freezing - when it'll get a little bigger). It's almost a fact that liquids are incompressible. But they aren't UTTERLY incompressible. Our article on water explains that water at the bottom of the deep oceans is compressed by about 1.8% compared to water on the surface at the same temperature...not much - but it IS compressible. So, sorry but you're, wrong! SteveBaker (talk)

Many of the "rules of thumb", like that liquids are incompressible, are only convenient approximations. The reality is that they are, but for most casual computations, the amount of compression is low enough so that it may be ignored. StuRat (talk) 20:18, 24 January 2009 (UTC)

Second moment of area

what is the second moment of area ... i need a text meaning , please no math expressions. thank you ...? —Preceding unsigned comment added by 86.108.61.209 (talk) 15:30, 24 January 2009 (UTC)

Sadly - there are some things for which you really NEED math - and this is one of them. This is a means to calculate the likely stiffness of a beam by reference to the cross-sectional shape. It's sometimes called "The area moment of inertia". But the property depends on where the beam is being bent so it's not as simple as a number that tells you how stiff something is. You need the math...sorry! SteveBaker (talk) 16:52, 24 January 2009 (UTC)

Second moment of area will tell you a lot, but again it is a bit math-heavy (calculus included). The lead paragraph of that article gives a pretty good description of "what it is", but there is no way to find its numerical value aside from the math on the page.-RunningOnBrains 17:53, 24 January 2009 (UTC)

treeful of goats??

despite the protestions of this article, it's a hoax, right? —Preceding unsigned comment added by 82.120.227.136 (talk) 15:42, 24 January 2009 (UTC)

We have a picture of goats in an Argan tree at our article. DuncanHill (talk) 15:53, 24 January 2009 (UTC)

I thought encyclopedia dramatica links were forbidden on Wikipedia?? —Preceding unsigned comment added by 82.120.227.136 (talk) 16:09, 24 January 2009 (UTC)

The photo in our article really doesn't look like a photoshop job (although it has been processed by the Mac version of photoshop in some way - that's probably just a color tweak and crop). The lighting is perfect and the interaction of the fluffy fur and the complicated leaves doesn't have the signs of the more common tweaks people do when faking photos. The picture in the OP's article is pretty low-rez so it's hard to tell. So no - I think it's real. Mountain goats are insanely nimble - and those trees are pretty gnarled and have plenty of footholds. Our article makes it clear that there is fruit on the trees - and in that barren landscape, the goats would have plenty of incentive to try. SteveBaker (talk) 16:43, 24 January 2009 (UTC)

There is (or was recently) an advert on British TV which included a treeful of goats - I forget what the advert was for (trees, possibly) but you saw the goats in the tree and their owners saying something about what trees meant to them. DuncanHill (talk) 16:50, 24 January 2009 (UTC)

Wasn't it one of the HSBC's "we're the world's local bank" adverts? --Tango (talk) 20:33, 24 January 2009 (UTC)

Could have been - I must admit that trees (and goats) are rarely advertised on British television. DuncanHill (talk) 20:40, 24 January 2009 (UTC)

See lots more goats in trees, and a video, at [14]. DuncanHill (talk) 16:53, 24 January 2009 (UTC)

Some of my extended family have goats, and I've seen them climb trees, on top of sheds, even on top of other animals (the stupid sheep, usually). They're pretty nimble, and these are just the domesticated goats. -- JSBillings 17:41, 24 January 2009 (UTC)

All sorts of kids apparently like to climb trees.Edison (talk) 20:40, 24 January 2009 (UTC)

There's a picture very similar to this one (7 goats in an argan tree) in the Photo Journal section of the Feb 2009 issue of National Geographic. Seems legit there. --Scray (talk) 22:34, 24 January 2009 (UTC)

Both the Argan and Argan oil mention goats climb the trees. While the supporting refs I've seen aren't great (one is dead, the other one is not necessarily a reliable source) the argan tree and oil definitely exists as supported by multiple refs and I suspect a number of the refs in the argan article probably mention the goats Nil Einne (talk) 06:34, 25 January 2009 (UTC)

What kind of bacterium does this?

Okay, so this might sound like a medical question, which of course is not allowed, but before you delete it, please read the following. The object of my question happened over a decade ago, I am completely healthy and I am not asking for medical advice. It's only for curiosity.

When I was two years old, I was operated of a hernia in the groin. It seems the doctors forgot a couple of sutures inside, which became infected. For eight years, this infection gave no symptoms, until one day I felt a hard thing in my groin, went to the doctor and was operated straight away. It seems a bag of pus had been growing in my groin for eight years, and it was about to burst (and maybe cause sepsis). The operation and subsequent course of antibiotics eliminated all bacteria, so I recovered pretty quickly.

So, I have two questions which, as I said above, are just for curiosity and are in no way a request for medical advice:

1. How come it took eight full years for the bag of pus to develop? Don't most infections spread quickly?
2. What kinds of bacterium create bags of pus within the body? I read Staphylococcus aureus does, but surely there must be others?

Thanks for your help! —Preceding unsigned comment added by 83.34.49.91 (talk) 16:23, 24 January 2009 (UTC)

I'd say there are at least a couple of scenarios to explain the late appearance of the abscess. First it is possible that the infecting organism had been there all along but something changed after 8 years, like an alteration in you immune system, that caused it to suddenly reproduce itself in greater quantity and cause the sign you mention. The other possibility is that the suture caused some minor damage to your internal tissues at some point which was then infected by a passing organism. I guess it is possible that the abscess slowly developed over 8 years but I think you might have discovered it before. Not all infections spread quickly. The tubercle bacillus is an increasingly common example of an organism that can live within the body for months or years not showing signs and undetected. There are a number of bacteria that might cause this type of abscess and with out culturing a swab from the site we can only guess. Richard Avery (talk) 16:55, 24 January 2009 (UTC)

1. It most likely didn't take eight years to develop, rather, the suture that was left in place became a focus of infection years later. It was "seeded" by a transient bacteremia, say from a dental procedure or other instrumentation, or from local infection.
2. Staph is the most likely candidate. Though other organisms cause abscesses, Staph is the most common cause, and is ubiquitous. Tubercular groin abscess would be distinctly unusual - the microbiology of abscesses vary with setting and location. In one study of cutaneous abscesses, 66% of all positive cultures were staph. Streptococcus comes in second; this is what you'd expect, as they're skin organisms. Some abscesses are polymicrobial; others are sterile; almost every organism has been reported to cause abscesses somewhere. You don't mention the size of the abscess, but obviously to acquire an impressive size, the abscess must occur in a place where a small abscess will not cause pain, and where there is sufficient leeway to grow - thus some places are more common than others. - Nunh-huh 03:00, 25 January 2009 (UTC)

This certainly may have taken years to develop. Small colony variant staphylococci are one example of organisms that can cause occult infections that, even without treatment, can lay dormant for decades.[15] If this was a staph infection, and I agree that's likely, then hematogenous seeding from a dental procedure is exceedingly unlikely since staph are a tiny proportion of dental bacteria. Another explanation that has not been discussed is that the suture may have been infected but walled off in fibrous tissue that was not conducive for bacterial growth; then, some sort of local trauma (stretching/tearing of the tissue surrounding the suture) resulted in disruption of that microenvironment, perhaps a little serum or blood got to the suture, and this provided the right environment for the bacteria to resume growth. Just conjecture. --Scray (talk) 03:33, 25 January 2009 (UTC)

This paper[16] reports multiple small-colony variant (SCV) staphylococcal infections, some indolent for decades. This paper[17] reviews much of the literature on SCV organisms, noting that SCV strains have been described for a wide variety of Gram-positive and Gram-negative species. Some, including SCV staph, can live dormant for long periods of time intracellularly. --Scray (talk) 04:26, 25 January 2009 (UTC)

Equations of motion

I've seen the equations of motion for constant acceleration derived using both definite and indefinite integration. Which one is the better approach? —Preceding unsigned comment added by 65.92.228.224 (talk) 19:25, 24 January 2009 (UTC)

I think it's just personal preference. It just depends on whether you like to work with constants of integration or limits of integration, they end up being equivalent. --Tango (talk) 20:31, 24 January 2009 (UTC)

Kids holding books upside down

My mother just told me that when I was one or two years old, I held picture books upside down. She was naturally concerned about that, but the pediatrician told her that that was normal and I'd turn out all right, which I think I can confirm. At least I'm not holding the monitor upside down as I'm reading Wikipedia. ;-) But the explanation the doctor gave, or at least what my mother remembers, doesn't make sense to me: It had something to do with the image is projected upside down in the retina. This is true, of course, but it is equally true for the book as for anything else I see. Unless I had been first walking on my hands (which my mother said I didn't), I must have seen the world in the same way I saw any book. So I'm wondering if there is any explantion for this? Do other kids turn their books, too? (My mother didn't remember what my younger siblings did.) — Sebastian 22:43, 24 January 2009 (UTC)

It seems very possible that it's normal to hold a book upside down as a kid. Think about it: You're new to the world, and don't know what everything is supposed to look like. So you look at it one way and say to yourself, "Hey, that's a picture of something, but I don't know which way it goes, so I'll guess this way." Analogy to an older person: If you find a book of alien texts (which you have never seen before), and you try to read it, there's a good chance that you'd read it upside down, because you had no idea which way it should go. flaminglawyer 22:58, 24 January 2009 (UTC)

Yes, but that would result in you holding books upside down at most 50% of the time (probably less since you'll usually recognise something in the picture). Is there any explanation for holding them upside down almost all the time (which is what the OP seems to mean)? --Tango (talk) 23:05, 24 January 2009 (UTC)

Yes, that's what I meant. Of course, I can't be sure about the percentage; it is well possible that my mother selectively noticed the unusual cases. — Sebastian 00:21, 25 January 2009 (UTC)

The argument the doctor gave is hogwash though. Sure, the lens in your eye does result in the image on the retina coming out upside down and flipped left-to-right. When the doctor was pinned to the wall by an anxious parent and needing to produce a passable answer RIGHT NOW, that's what he pulled out of his memory from Med School. But as an explanation, it simply doesn't hold water. You see all of the world that way up all the time - that's "normal". That IS the right way up. Holding the picture of the moo-cow in the book the opposite way around from moo-cows in the real world isn't explicable in that way. I don't know what the explanation is...but that's CERTAINLY not it. SteveBaker (talk) 01:14, 25 January 2009 (UTC)

You are right, the image is indeed projected on the retina upside-down; and you are right again, this has nothing to do with how we perceive the "up" and "down" directions in the world. In human infants the connections in the visual cortex, as well as between the visual cortex and other areas of the brain, form largely under the influence of sensory stimuli. AFAIK, we are not born with visual concept of "up" and "down", even though our heads are quite different from our bottoms. The visual sense of "up" and "down", as well as "left" and "right", forms through visual stimulation, and it would have formed largely the same way if the image on the retina was not flipped. Humans learn very fast to use mirrors, so flipping the world around any axis is not a huge problem for our brain; not even for an adult brain. In fact, there are experiments in which adult humans are fitted with prism glasses that flip the visual world by 180 degrees; humans adapt to the flip and function more-or-less normally after a few hours or days. So no, you don't tend to hold the book upside-down because the image on the retina is flipped. Neither do you flip the trees and houses upside-down when you go for a walk (or at least so I hope). Two-year-olds do turn the books upside-down, but I always thought it is just out of curiosity; or more often they would just pretend to be reading, without actually realizing the book is upside-down. That is probably the explanation you are looking for. Now, if you have older siblings, it's a different story entirely. When an older kid learns to read, younger siblings tend to watch. The book can not be easily seen or read from behind the older kid's back; so the younger kids approach from the other side, and end up facing the book from the wrong direction. I heard stories about younger kids in large families who actually started reading upside-down, and had to relearn in school to read the "proper" way. That may also be the case. Hope this helps. --Dr Dima (talk) 02:14, 25 January 2009 (UTC)

I think you got it. Since I don't have older siblings, I go with the curiosity explanation. If I were a cat, I'd be dead now, despite the bonus lives. — Sebastian 02:46, 25 January 2009 (UTC)

I can still read anything upside down. It's a handy kind of obscure skill that I'm guessing many people have. Julia Rossi (talk) 05:58, 25 January 2009 (UTC)

Are you Gemma Williams? [18] Rockpocket 07:00, 25 January 2009 (UTC)

No, the usual way is fine as well, no colour filters required.  :) Julia Rossi (talk) 07:17, 25 January 2009 (UTC)

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ףסש ¡әәӋ 07:49, 25 January 2009 (UTC)

Reading upside down is a useful skill when reading a book to children. You can hold the book facing them so they can see the pictures and then lean over the top to read it. --Tango (talk) 17:13, 25 January 2009 (UTC)

January 25

Burying charcoal to mitigate global warming

James Lovelock recommends burying charcoal in a non-biodegradable fashion. What are the advantages and disadvantages of this form of mitigation?

Note: I originally asked this question at Talk:Mitigation_of_global_warming#Burying_charcoal before it occurred to me that this reference desk might be a better place to ask. Would you please answer at that talk page instead of here? 69.228.235.107 (talk) 02:55, 25 January 2009 (UTC)

The talk page of articles isn't really the place to ask such questions as they are solely for discussions about improving the article. Technically your question could be removed although I'm not suggesting anyone does so. Since no one has answered there I would suggest you simply direct people here. Nil Einne (talk) 06:17, 25 January 2009 (UTC)

The reason I asked was because I had hoped to improve the article. 69.228.235.107 (talk) 07:42, 25 January 2009 (UTC)

I understand that, but most of what's being discussed here has nothing to do with improving the article, as with most RD questions particularly those of this sort which are likely to result in a far amount of discussion which isn't directly sourced. It possible you may eventually get something here which could be added to the article but that's not really the purpose of article talk pages. In talk pages like that, no one tends to mind but in extremely active ones any sort of OT talk such as a question like this will often be deleted or archived or at least you may get people telling you to ask it somewhere else. So it's a good idea to get into the habit of asking questions like that here, your far more likely (in general) to get an answer and it's also easier for someone to find the discussion in future Nil Einne (talk) 08:18, 25 January 2009 (UTC)

He talks about plowing it into farmer's fields, but then plant roots would get at the carbon, pull it into the plant, and make it part of the carbon cycle again. Carbon sequestering requires putting the carbon somewhere that life can't get to it. StuRat (talk) 06:16, 25 January 2009 (UTC)

Note that the OP (and the linked article) said non-biodegradable charcoal. I'm not aware there is any form of charcoal that isn't relatively biodegradable although I guess you could make some sort of plastic with it. There's also the question of whether having all this non-degradable material is going to eventually prevent plants from growing when you end up with too much of it. Nil Einne (talk) 06:21, 25 January 2009 (UTC)

Why charcoal? To make charcoal, you take a lump of wood - and heat it to drive out the water...why bother? The production of that heat uses energy - and that almost certainly produces CO2 which diminishes or even eliminates the benefits of burying the charcoal. Why not just bury the wood? The actual business of burying in farmland seems difficult too - dumping it in old coalmines or worked out open-cast mine pits (and then covering with dirt) would be better. SteveBaker (talk) 06:25, 25 January 2009 (UTC)

Why charcoal? Because you just want to make sure that the carbon stored in the plant growth doesn't get released as carbon dioxide. If you bury wood, it quickly gets broken down and the carbon is released as carbon dioxide. If you can convert it to nonbiodegradable charcoal (and I don't know how feasible the methods given really are; I agree with the potential effect on farmland) the carbon won't get released as carbon dioxide unless someone burns it. Sure, a little carbon dioxide is produced in making the charcoal, but not nearly as much as would have been produced if the whole thing was broken down as happens when you bury wood or plough your stubble back into a field. 79.66.105.133 (talk) 12:34, 25 January 2009 (UTC)

Here is an idea. Why don't we just grow trees, cut them down and turn them into furniture. Won't this be just another form of carbon capturing technology? We will make a law that says it is illegal to burn furnitures. 122.107.203.230 (talk) 06:55, 25 January 2009 (UTC)

@StuRat plant roots don't usually process/transport carbon in plants AFAIK. They draw CO2 from the air for photosynthesis and minerals and water from the ground. But there are a lot of chemical processes going on in soil. As soon as the carbon has reacted and been bound into something that a fungus can use it's back in circulation. These guys also seem to find it palatable [19]. Plowing under the charcoal doesn't sound like a good idea [20]. The article doesn't concern wood specifically grown for carbon sequestering, but farm waste like straw. If you'd compare firing your hearth with straw to using charcoal you might come out ahead, but most of the biofuel from farm waste processes have so far proved to be uneconomical or coming with a negative energy balance. That's one reason why we now make ethanol from sugar rather than straw. (Also see wood gas.) Transporting the charcoal made from straw to a coalmine and sinking it into the pit would also consume energy. Digging up coal and then sinking charcoal in it's place sounds a bit odd anyway. The BTUs you get out of charcoal don't differ that much from what you get from coal (Can't link it, but it's ard. 9,000 BTU for charcoal and 6,000 - 14,000 for coal. The numbers for charcoal from straw would come out somewhat different, though.) That method would also be chucking a lot of nutrients plants need into the hole. You'd either have to separate those out or wait till they concentrated at the bottom and dig them up again after a considerable period. I guess they stumbled over that argument and then refined their original idea to "plowing it under". You'd have to move it to the processing plant and then move it back and spread it onto the field, that would consume energy. If you converted it into charcoal on the field you'd lose the "biofuel" advantage they touted and I guess then their calculations would not come out ahead. Reminds me of the saying, "It's the technology of the future - and always will be." 76.97.245.5 (talk) 10:40, 25 January 2009 (UTC)

Surely this entire discussion is based on a misunderstanding. It isn't Carbon we want to sequester, but CO2. Surely charcoal is essentially carbon. Planting trees is good because it takes CO2 and breathes out O2 whilst making the C into "tree". -- SGBailey (talk) 11:34, 25 January 2009 (UTC)

I believe that the idea is that excess carbon in the biosphere will readily be combined with oxygen from the air to form carbon dioxide. StuRat (talk) 14:55, 25 January 2009 (UTC)

Thus far it (mostly) works. The problem arises when you then burn or decompose the tree. That creates greenhouse gases (CO2). Which is why the guy in the linked article came up with his idea. Charcoal can be created in an anaerobic process (see Pyrolysis). That way less CO2 would be released into the atmosphere. The question is whether the big picture will come out as producing CO2 as a consequence of any component necessary to get from tree (or straw) to charcoal in the ground and whether the charcoal stays in the ground or is used up to make CO2 down the line. There are many examples of seemingly good ideas that turned out to be huge mistakes once all the consequences became obvious. 76.97.245.5 (talk) 13:11, 25 January 2009 (UTC)

Also, won't burning massive amounts of organic material in a low oxygen environment to produce charcoal also produce carbon monoxide ? StuRat (talk) 15:02, 25 January 2009 (UTC)

It looks like Biochar is a fairly well-developed article on the topic. 69.228.235.107 (talk) 16:42, 25 January 2009 (UTC)

Rope bridges over big gaps

[Posting here because it's the closest to engineering] Before modern technology (i.e. helicopters), how were big rope bridges built over gorges? I'm guessing that a small bridge, maybe even something like the Carrick-a-Rede of 20 metres, could be begun by someone strong throwing a rope all the way across the gap, but Inca rope bridge discusses one of 67 metres. I could understand if these were low bridges over rivers, but seeing that these connect cliffs dozens of metres high, I'm assuming that it's not possible simply to carry the rope over. Nyttend (talk) 04:28, 25 January 2009 (UTC)

You do need someone at each end of where your bridge will be, and you do need to get the rope across - the trick is, you don't try to throw a big heavy rope. You throw a thin, light rope, and use that to haul thicker ones across. Tying a monkey's fist, or a stone, in the end of the light rope makes it easier to throw accurately, and by swinging it around before releasing it will go further. If the chasm is too wide to throw even a light rope across, then you throw it across at the bottom and then climb the sides, paying out as you go. DuncanHill (talk) 04:57, 25 January 2009 (UTC)

If you can't climb the sides of the gorge at the point you want the bridge, then climb down where you can, and walk along to a point below the bridge site. Your colleagues at the top of the gorge lower a line to you (the same being done on the other side), and you attach this line to your heaving line. The heaving line is then pulled up to the top of the gorge. DuncanHill (talk) 05:01, 25 January 2009 (UTC)

It would be a lot easier to explain with a) some rope, b) a suitable gorge, and c) a plentiful supply of Scouts to run around carrying things. DuncanHill (talk) 05:16, 25 January 2009 (UTC)

"Plentiful" gave me another clue: If you have at least three people, you can have one on each side throw down a line to a third one at the bottom. The third person just ties the two lines together, and voilà! — Sebastian 05:23, 25 January 2009 (UTC)

Now that's good! I must remember that :) DuncanHill (talk) 05:28, 25 January 2009 (UTC)

The idea of pulling a very fine thread across - and then using that to pull a thicker rope - and that up to the full-sized rope makes sense. But if a fine thread is all you have to get across there then a bow and arrow would get it over there. Perhaps even a trained bird of prey could carry enough fine thread across the gap. Modern archers using 'traditional' bows shoot at targets at 50 yards (and 90 yards is common with modern bows) - it's clear that the best archer the bridge constructors could find could make an arrow go 67 meters...given that accuracy and penetration of the target are irrelevent. However, the Inca's didn't use bows - they used slings...but (amazingly) our sling (weapon) article says that a slinger could fling a rock 600 meters(!) - ten times more than is needed here! So IMHO, it's overwhelmingly likely that this is what they would do. SteveBaker (talk) 06:35, 25 January 2009 (UTC)

The slings and arrows of outrageous bridge-building... DuncanHill (talk) 16:55, 25 January 2009 (UTC)

A kite with a following wind could carry a cord for miles...... 196.2.124.248 (talk) 07:40, 25 January 2009 (UTC)

In fact, a kite is exactly what they used in 1848 to begin the construction of the first bridge over the gorge at Niagara Falls. A prize was offered to the first boy to perform the task. --Anonymous, 04:53 UTC, January 26, 2009.

That reminds me when I was wondering how spiders do it. I know they can drift in the air, but I've seen a web anchored at two branches from different trees, with the upper anchoring points about 8 m apart and about at the same height. Since the spider's body was about 1 cm long, and it was in a dense forest where you wouldn't expect strong winds, I can hardly imagine that the spider drifted horizontally for 8 m. — Sebastian 05:19, 25 January 2009 (UTC)

@Sebastian There are several ways that spiders get that gap bridged. As described in Spider web some dangle a sticky thread to float in the winds till it gets caught somewhere. Sometimes they also use rappelling, swinging themselves to and fro till they get to a good spot. They lengthen or shorten the thread they are hanging on as needed. Then there's Ballooning (spider) although that's more commonly used to get away from close relatives. [21] (Know thy enemy. Arachnophobia is less productive than informed avoidance.:-) Did Incas use Blowguns? Our article doesn't say, but it isn't a new weapon and is widely used throughout the Americas. I'm not sure you could tie a thread to a dart, though. The slingshot method looks like the most likely scenario. 76.97.245.5 (talk) 08:51, 25 January 2009 (UTC)

You're right, they just use the threads alone, so the weight of the spider does not play a role. Still, it is amazing that they manage to bridge 8 m that way, even in a calm forest! — Sebastian 23:12, 25 January 2009 (UTC)

It seems amazing to us chunky humans - but remember that air resistance is proportional to cross-section which is proportional to the square of the size of the animal - but weight is proportional to the cube of the size of the animal - so at the scale of a spider, wind is a force that's VASTLY more powerful than at our scale of experience. A 1cm spider experiences 200 times the amount of wind force (pound-for-pound) than a 2m human does. So we might consider 40cm to be bridgeable with a human-scale parachute in a modest breeze...8m is a snap for a spider. SteveBaker (talk) 02:03, 26 January 2009 (UTC)

Circuit schematics: are these good?

I've designed the circuits [22] and [23], based on [24] and [25], respectively, and I was wondering if someone could audit the designs for me. I'm planning to build them both and I want to make everything is correct before I order my parts and/or start soldering. I don't things to blow up or to have to spend a lot of money on more parts and/or shipping.

So would these circuits work, theoretically? If there's anything even remotely wrong, please let me know so I can fix it before buying parts. --Link ^(t•c•m) 10:22, 25 January 2009 (UTC)

I haven't looked at them but the usual thing to do is run them through a simulator, for instance a version of SPICE for analogue circuits, and see what happens. Dmcq (talk) 11:32, 25 January 2009 (UTC)

There are a number of diy electronic forums on the net which are probably a lot more suitable for this. On a quick look though you're not going to lose a lot of money so why not just go for it? You can always socket something expensive and it's unusual to destroy things if you get the power the right way round and ground yourself. Dmcq (talk) 11:57, 25 January 2009 (UTC)

Your first two links are PostScript files, which I can print, but can't view (there are PS viewers, but I don't have one). You might want to provide them in another format. StuRat (talk) 14:38, 25 January 2009 (UTC)

Death by toaster?

I have a habit of fishing bagels, muffins etc out of my toaster with a knife, without switching off the power. People are always telling me that this is dangerous because I risk getting a shock. I have always assumed that touching the elements would be no more dangerous that touching the elements on an electric grill or hob. Am I dicing with death everytime I have a crumpet? ToastShock (talk) 10:38, 25 January 2009 (UTC)

It depends upon what country you are in. In the UK, the two ends of the toaster element are neutral and live. Iff your socket and toaster are wired correctly then when it has "popped up", one end of the element will be disconnected from the live supply. If the wiring is wrong, it could be the neutral that is disconnected, in which case you stand a chance of connecting to live. I suggest you use a wooden kebab skewer in future or better yet unplug the toaster. -- SGBailey (talk) 11:13, 25 January 2009 (UTC)

On my toaster (made in China for Philips, sold in Canada), when it has popped up, the element is disconnected from both sides of the plug: in other words, the switch is a double-pole one. I noticed this feature when looking at the wiring of a previous toaster and have just verified it for my present one by using an ohmmeter while it was unplugged. But, of course, even if your toaster has this safety feature, you should not count on it! --Anonymous, 05:16 UTC, January 26, 2009.

Yes, and it isn't even spectacular enough for the Darwin Awards Dmcq (talk) 11:45, 25 January 2009 (UTC)

Following EC: I'd definitely say you are tempting fate. There are safeguards like fuses, circuit breakers and improved Toaster designs [26] that should take effect in case of an accident. But you are basically relying on those working properly and you not accidentally switching the toaster on or creating a contact. I don't know your grill, but the heating element wires in a toaster are live when the toaster is on [27]. If you damage the insulation you may also create a short to the case and then get shocked when you touch it the next time you make toast. There are a couple of people each year who win the "shouldn't have done that" lottery. The saying goes: "Engineers try to make things fool-proof but fools always prove to be ingenious." Unplug the toaster and use a basting brush or rubber dough scraper if something got stuck. 76.97.245.5 (talk) 11:50, 25 January 2009 (UTC)

I'd change that last sentence to "or", as you don't need to take any other precautions besides unplugging the toaster, since they don't contain capacitors or batteries (which store electricity). So, once it's unplugged, it's perfectly safe. Also note that if we are including everything that can possibly go wrong, then those toasters with metal housings can also be charged electrically, if a live wire is in contact with the exterior. This could be true when the toaster is on, or off, or both. This, in conjunction with you having wet hands and standing barefoot in a puddle of water connected to ground, and touching the outside of the toaster could cause you to become, well, toast. StuRat (talk) 14:32, 25 January 2009 (UTC)

I mentioned the soft implements because people have managed to create a short by poking a fork or knife into their toaster and then got zapped when they touched it later, or it started a fire. (Came up during a seminar on warning labels in user manuals, too lazy to look for a web reference.)76.97.245.5 (talk) 15:30, 25 January 2009 (UTC)

<makes mental note to always remember to turn the toaster off at the mains when not in use> --Kurt Shaped Box (talk) 14:38, 25 January 2009 (UTC)

You could always get a pair of toaster tongs. I haven't had a pair since I was a kid but basically it's a pair of tongs that are made of plastic and you stick them in to get your bread, bagel, etc out. Since they aren't made of metal, they won't give you a shock. Dismas|^(talk) 16:50, 25 January 2009 (UTC)

Um...and who in the right mind would manufacture a knife without a non-metal handle?! ~AH1^(TCU) 17:51, 25 January 2009 (UTC)

All of our cutlery has metal handles. [28] for example makes steel-handled kitchen knives. They're pretty common. SteveBaker (talk) 20:31, 25 January 2009 (UTC)

Your have any dinner-knives in your flatware set? Also, it's not necessarily the knife itself that conducts via its handle to the person, it could just be the blade that shorts to other metal parts (as others mentioned) such as an outer metal surface, which is why chassis grounding (the "third prong" on US plugs) is an important safety feature. I've always heard it as "build something idiot-proof, and the world will build a better idiot". DMacks (talk) 17:55, 25 January 2009 (UTC)

The stovetop or "hob" heating element does not generally have the energized wiring exposed. Calrod heating elements have resistance wire (nichrome) insulated by ceramics from the outer metal shell. Only if the insulation broke down and the outer shell were not grounded would it be energized. In a toaster, by contrast, the nichrome resistance wire is directly exposed to the toast, for faster and more efficient heating. If your fork or knife touches the heating element in a toaster, and you are touching the knife metal and something grounded, you are likely to be electrocuted. Unplugging before toast extraction seems like a fine idea. Edison (talk) 23:23, 25 January 2009 (UTC)

I was wondering when someone was going to point out the difference in the heating elements. (Fixed your confusing typo in the first sentence.) --Anonymous, 04:57 UTC, January 26, 2009.

Re knives with plastic handles or other, I'd like to restate that it is inadvisable to use any implement with an increased danger of dislodging wires or damaging insulation inside a toaster, whether it is unplugged at the time or not. I lived in quite a few places where relying on the grounding of your home wiring system being up to code as DMacks suggested would have been folly. Even in "3-prong" outlets I've seen way too many that weren't connected, weren't connected properly or had a grounding wire from the patch panel ending somewhere in a wall after s.o. had done some remodeling. (Arguably the most egregious one.) In the US plugging in an adapter so you can plug in a 3 prong plug into an 2 wire outlet - without actually connecting the ground terminal - is an all too common practice. There are those little circuit tester plugs with LEDs that will help you verify your wiring. Using soft implements and thus reducing the risk of causing damage to the innards of your toaster seems like a hardship one can suffer. 76.97.245.5 (talk) 05:28, 26 January 2009 (UTC)

Choice of anticoagulant

Why is warfarin the anticoagulant of choice in the US and UK? What is its advantage comparing to heparin? What is its advantage comparing to acenocoumarol? --Mr.K. (talk) 12:27, 25 January 2009 (UTC)

I can't answer your question specifically, but a Google search reveals the advantages/disadvantages of both in different diseases such as venous thrombosis. Another two searches can show you the comparison between low-weight molecular heparin and warfarin against acenocoumarol. —Cyclonenim (talk · contribs · email) 12:41, 25 January 2009 (UTC)

Compared to heparin, the warfarin article states: "Warfarin is slower-acting than the common anticoagulant heparin, though it has a number of advantages. Heparin must be given by injection, whereas warfarin is available orally." -- Aeluwas (talk) 13:01, 25 January 2009 (UTC)

Is that a huge advantage? It looks like warfarin is just more convenient...Besides that is there any medical advantage?--Mr.K. (talk) 13:04, 25 January 2009 (UTC)

Of course it's a huge advantage! It's the difference between being able to walk around and carry out the daily activities of one's life, vs. lying in a hospital bed receiving intravenous fluids 24 hours a day! - Nunh-huh 13:46, 25 January 2009 (UTC)

It doesn´t say that it has to be intravenous. Heparin can be administered as subcutaneous injection. --Mr.K. (talk) 20:07, 25 January 2009 (UTC)

Subcutaneous heparin is sometimes used in bedridden or hospitalized patients as a means of preventing deep venous thrombosis or pulmonary embolism, but is not an effective means of fully anticoagulating someone - say in the setting of an artificial heart valve. In those settings - true anticoagulation, in which an actual change in blood parameters of coagulation can be measured - intravenous heparin is used because it has an immediate effect and is titratable to maintain an appropriate level of anticoagulation. After a few days, coumadin is started, because it - unlike heparin - has an oral dosage form which enables the patient to go home. Though they are both used for anti-coagulation, it's not like there's an actual "choice" between them: you use the one that the clinical situation dictates you use. - Nunh-huh 20:19, 25 January 2009 (UTC)

'More convenient' often equates to significant medical advantage. Patient compliance with a treatment regimen is often better when the treatment is less painful. Oral drug administration doesn't carry the same risk of infection associated with repeated (intravenuous or deep subcutaneous) injections. There are social benefits associated with lower cost-of-treatment, reduced packaging, and the elimination of biohazardous sharps waste. The patient can much more easily self-administer warfarin while working or travelling. Huge advantages. TenOfAllTrades(talk) 17:21, 25 January 2009 (UTC)

Drug interaction [29] and manufacturing defects [30] might sway the decision one way or another [31]. BTW. cinnamon contains varying amounts of coumarin. OR 2 years ago I asked the FDA whether they monitored levels and they answered "cinnamon is considered safe and is not tested" but coumarin as a food additive is prohibited! 76.97.245.5 (talk) 13:57, 25 January 2009 (UTC)

There are lots of natural food materials that are (un)regulated as food but that contain chemicals that are not allowable as additives. See Cyanide#Occurrence for example. DMacks (talk) 17:50, 25 January 2009 (UTC)

Regarding heparins vs. coumadin: Unfractionated iv heparin may be preferable in certain settings (ability to rapidly reverse anticoagulation being the primary one, some advantage in DVT's that extend on coumadin, etc.), but these are situations where patients should be in the hospital. In patients with cancer at high risk for deep venous thrombosis, low molecular weight heparin has been shown to be superior to coumadin in at least two prospective randomized control trials. Aside from these reasons, the convenience and other factors cited by others are the major ones. I'm not sure why other coumarins never made it to the forefront (cost? half life? developed later than coumadin?) -- Samir 08:21, 26 January 2009 (UTC)

help

While trying to get the tennis, my mother has managed to turn the normally colour digital TV through the set top box into black and white. Obviously she hasn't a clue how to undo this, and I have no idea how she did it, so how can this be undone? —Preceding unsigned comment added by 81.132.159.158 (talk) 15:00, 25 January 2009 (UTC)

Do you have a make and model ? There is likely a color setting which has been turned down to a very low level. StuRat (talk) 15:06, 25 January 2009 (UTC)

Turning the saturation setting down will turn a color image into a grey scale one. Check under the menu for image settings or the like. This seems more likely since it affects all the channels. I've also managed to lose color for certain stations when the receiving antenna was moved. (this was about 6 years ago on a homemade setup though.) I suppose you could try moving the set top box and making sure there is nothing sitting on it and checking to make sure the connectors are securely in place. I would check the color settings first. 152.16.15.23 (talk) 23:19, 25 January 2009 (UTC)

Check the cables between your set top box and the TV. Component cables carry brightness information on a separate cable from the color information. Also, S-video cables carry brightness information on a separate pin from the color information. If these kinds of cables are loose or damaged, this might cause the picture to become black and white. --Bavi H (talk) 04:44, 27 January 2009 (UTC)

communicating space tube

Following the "space tube" question above (Jan 24): Would the picture change if the tube ended in a U bend. (Provided such a tube could be constructed and wouldn't collapse due to the forces it was exposed to.) I was reminded of something , but had forgotten what it was called. I searched through 3 languages and I don't think we have a page. (Spanish and German do) We do have an image

could s.o. please link this properly

that says it's communicating vessels. (Should s.o. maybe do a page?) So would this be an effect to watch out for with that hypothetical space tube? 71.236.22.103 (talk) 16:35, 25 January 2009 (UTC)

Can you describe this tube a little more precisely? Where is the U bend and how big is it? Are you talking about a tube that has both ends in space, and just the bottom of the U in the atmosphere? Or something else? --Tango (talk) 17:10, 25 January 2009 (UTC)

The German article that image comes from is de:Kommunizierende Röhren which seems to be describing a tube linking two vessels which results in the liquid finding a common level in both vessels. It makes no difference, U-bend at the top, U-bend at the bottom, no atmosphere would leak out into space (other than what we are already losing by "evaporation"). The bottom line is that it requires energy to remove anything from earth and that energy has to come from somewhere. A passive tube, no matter how cleverly you bend it, can never provide any energy. This kind of thing is like perpetual motion machines, it can't be done because of a fundamental law of nature, but for each one you disprove, someone comes along with a more complex one that apparently allows it to work, but always there is a subtle, or sometimes not so subtle, flaw in the argument. And always it will come down to that same law of nature, conservation of energy. SpinningSpark 00:33, 26 January 2009 (UTC)

Yep - after enough years looking at silly ideas like this - you eventually learn that it's a waste of time to track down the root failure of the idea. The laws of thermodynamics say "No!" and that's all you need to know. We can say with utter, 100% confidence that there is no point in tracking down the specific flaw in the idea. It's there somewhere and we don't need to look further. SteveBaker (talk) 01:56, 26 January 2009 (UTC)

By the way, if you could actually manage to construct such a tube, you could use it as a space elevator. Most of the strength required of a space elevator cable is to support its own weight. That's the major stumbling block at the moment preventing anyone from actually doing it. SpinningSpark 00:38, 26 January 2009 (UTC)

(Actually - the current 'fatal flaw' is the modes of oscillation of the cable. A month or two ago it was proved that the cable would have fundamental instability issues that seem right now to be insurmountable without actively positioning rocket motors at many places on the cable - which would make it less effective than conventional rocketry. It's a serious blow to the future of mankind in space.SteveBaker (talk) 01:56, 26 January 2009 (UTC))

This was proposed as a thought experiment, and real world application was never the intention. I was just curious what the effect of the communicating vessels (es:Vasos comunicantes, de:Kommunizierende Röhren) would be. (The Spanish page actually has a nicer picture). I would not expect the specific properties caused by a U bend to have any effect if both ends end in space. If you had one end being shorter than the other though you should get different forces working on both sides and the liquid attempting to reach an equilibrium. Since Spinning Spark pointed out that atmosphere leaking out would not happen. Like in a Barometer you would get liquid pouring out till the pressure of the air on the short end would be the same as the sum of gravity "pulling down" on the liquid and the vacuum pulling it up in the other leg. But what would the influence of the vacuum be? Would you get a vacuum /near vacuum somewhere in the middle of the tube or would the liquid "stretch out" to fewer and fewer atoms per volume all the way up to space? Could we move the space elevator question to a separate item, please? Otherwise this item will get lost in Carbon nanotube feasibility and other unrelated stuff. (What happened folks? This is the first I've seen here that everyone seems to agree that pondering the specifics isn't worth the bother of explanation. :-( Everyone too tired?) 76.97.245.5 (talk) 04:53, 26 January 2009 (UTC)

power available from daylight

what is the power available from simple daylight say per square metre - i am aware that this will be a variable amount due to all the variabilities of geography-inclination-time of day-etc. as an instance i have a calculator that provides sufficient electrical power from light to run the electronic circuits and display module.Superbigleo (talk) 16:48, 25 January 2009 (UTC)

See insolation. --Tango (talk) 17:08, 25 January 2009 (UTC)

Gluten question

Does textured soy flour contain Gluten?Vanatthelake (talk) 17:36, 25 January 2009 (UTC)

No — the Soyfoods Association of North America says that soy flour and textured soy flour are gluten-free: [32]. TenOfAllTrades(talk) 22:16, 25 January 2009 (UTC)

Cosmic gods

Einstein spent a good deal of his life working on a Unified Field Theory in which he tried to reconcile the four fields we know of. If there were such a thing as a cosmic god who could turn out a "viable" part of the universe by selecting basic features for his creation from which all physical laws would follow as a consequence, what would such basic options be? 196.2.124.248 (talk) 18:04, 25 January 2009 (UTC)

Once you accept that God is messing with the laws of physics, then anything you can imagine is possible. This is the problem, actually, as it stops any need to figure out why things are they way they are (that would be science), if you can just say "that's the way God wanted it to be". StuRat (talk) 18:31, 25 January 2009 (UTC)

Only if one assumes an arbitrary and personified God, which is not what Einstein envisioned with his "Cosmic Religion", and not what most physicists postulate when they assume there is a divine order to the universe (which many believe in). --98.217.14.211 (talk) 23:11, 25 January 2009 (UTC)

Are you asking what is the simplest set of physical principles from which all known physical laws follow as a consequence? The answer is we don't know. Current physics is as simple as we know how to make it (pretty much by definition). -- BenRG (talk) 18:52, 25 January 2009 (UTC)

All else is the work of man

Even the gods must work within their limitations, so that the menu of permissible options is probably quite small (look what can happen with 100 odd elements, themselves logical consequences of simple arrangements, or just 5 nucleotides or 26 letters and a bit of punctuation). I think that a spartan elegance must be high on their list of priorities. 196.2.124.248 (talk) 21:07, 25 January 2009 (UTC)

Your cosmic gods aren't looking closely enough!

• up,down,top,bottom,strange,charm
• electron,tau,muon,
• electron-neutrino,tau-neutrino,muon-neutrino,
• a couple of weak-force bosons,
• the gluon and the photon
• and maybe we'll toss in a higgs boson or two.

The menu contains just 18 things - six quarks, six leptons and probably six bosons...and that's all ya need!

But then perhaps even that is too complicated and maybe we'll go with nothing more than a simple pan-dimensional vibration.

SteveBaker (talk) 23:07, 25 January 2009 (UTC)

You're basically asking the question that physicists have been asking since the 1980s—why are there X numbers of things and no more? Why are the values just such? Is there a reason? Can you reduce all of the possible variations of physics down to a few options, and can you find a theory which explains why those options had to be what they were and nothing else? The answer might be "yes", it might be "no", and it might be "we'll never know". --98.217.14.211 (talk) 23:11, 25 January 2009 (UTC)

There are 'levels' of power your cosmic gods might have - and the answer depends on where that 'level' is. If I had to invent my own degrees of omnipotence scale:

• Level 4 gods: Who can do things with technology that almost nobody can understand...yet falls within the bounds of 'known science'.
• Level 3 gods: There is the "any advanced technology is indistinguishable from magic" kind - where all you get to play with is the laws of physics and nature of matter that pertain to our universe - but with a complete knowledge of all of those laws.
• Level 2 gods: There is the ability to change the fundamental constants for which we have no real explanation (things like the charge on the electron and the speed of light).
• Level 1 gods: There would be the ability to change the equations that define the 'rules' of the game - so maybe changing gravity to work on the square of the mass instead of the mass.
• Level 0 gods: Then there is the kind of power that's hinted at in Carl Sagan's "Contact" (the book - it's not mentioned in the movie) where analysing the expansion of 'pi' as binary digits reveals a message embedded in the bits of the number...which decode to an image of a circle...implying that some "alien" or "god" put it there deliberately for us to find.

Each level produces a new degree of incomprehensibility on our behalf.

We've "proved" that pi is what it is from raw thought alone - we don't have to measure anything - just have the concept of a circle clearly in mind...and pi just pops out. It just "couldn't" be different. I maintain that this provides fundamental limits on the power of any god - which is why the idea of a christian 'level zero' god is tough to swallow! Level 4 gods are mere present day human scientists and technologists - for most humans, understanding how even the simplest childrens' toys really "work" is beyond them. Level 3 are credible aliens.

So if the OP's question has to be answered - we first need to know what degree of power is being envisaged.

• If our OP's cosmic gods are at level 4 - we know exactly what they can do - because they are out there doing it. It's what most people feel when the new iPhone comes out!
• At level 3 - we can list many of the laws of physics and particles that these 'gods' have to work with and we can certainly impose restrictions - they can't travel faster than light - they can't travel in time - they can't make perpetual motion machines.
• If the OP's gods are at level 2 - we've thought about what the universe would be like with different fundamental constants - and mostly we deduce that life could not exist if many things were much different - so our gods don't have a whole lot of wiggle room to change things without totally screwing everything up - butthe consequences of even the tiniest of change would probably produce profound effects that it's hard for us to predict. However, I think we could figure out (at least in principle) what that would do to the universe.
• At level 1, we're in deep trouble. Understanding what it would mean - even conceptually - to have fundamentally different laws of physics would be tough. So we can't answer the OP's question.
• And at level zero...there is no way to even form the thought of what the universe would be like if pi was 10% smaller. Truly omnipotent gods are meaninglessly unfalsifiable.

SteveBaker (talk) 01:48, 26 January 2009 (UTC)

I'm sure for some decoding mechanism there's an image of a circle embedded in the digits of pi. Level 0 gods would have some pretty staggering powers that approach paradoxical.. for one, the pi thing reminded me of this: take a deep breath and dive into it. How can that pi-encoded message even exist without some kind of decoding context? Could a level 0 god create such a message? I'd say no, but it has to be able to by definition, so that seems to imply the non-existence of a level 0 god. Could a level 0 god create a formal system not subject to the constraints of Godel's theorem? It's been proven impossible; what does that mean for a god that has to be able to do it? Of course this could all be subject to the constraints of our reason (including the maths we have proving it's not, heh)... this is all rather stale argument .froth. (talk) 23:10, 26 January 2009 (UTC)

It is conjectured that pi is normal, which would mean any possible message will be included somewhere in the digits. I think the idea behind Steve's "Level 0 god" is that they aren't even constrained by our concepts of logic, which makes it impossible for us to even contemplate them - they are impossible as far as we can tell, but they exist on some level beyond the ability of our logic to make sense of. Don't think about it too much - it will make your head explode. --Tango (talk) 01:03, 27 January 2009 (UTC)

Yes - actually, I had already realised that many years ago. There is indeed a perfect image of a circle embedded SOMEWHERE in the infinite digits of pi - because there are only so many patterns of digits possible and all of them must come up sooner or later. After I read the book ("Contact" by Carl Sagan) - I downloaded the longest available expansion of pi (which was then about a billion digits as I recall) and set about converting it to binary (non-trivial on a computer with less than a gig of RAM!) and looking for the largest square of zeroes with an acceptable approximation of a circle of 1's within it. My program crunched for about a month - and then another month looking for a circle of 0's in a sea of 1's. Within the first billion or so digits, the biggest such circle is only about 5 pixels across - and it's a huge stretch to call it a "circle". <sigh> It would have really screwed with people's heads if I had found one. But realistically, the probability of even an 8x8 pixel 'perfect' circle is the probability of a specific sequence of 64 consecutive bits having a specific pattern - and the odds of that happening at random is one in 16,000,000,000,000,000,000 - so we need at least 10¹⁸ digits of PI before we'll see even a circle the size of this letter 'o' popping out. Since that's vastly more memory than all of the computers on earth put together - the odds of ever seeing that circle is tiny.

So that (in some way) validates Carl Sagan's idea. Now, the message of the book is that science and faith both matter...or something like that. But, to quote from our article: "Ellie...computes the digits of π to record lengths and in different bases. Very, very far from the decimal point (10²⁰) and in base 11, it finds that a special pattern does exist when the numbers stop varying randomly and start producing 1's and 0's in a very long string. The string's length is the product of 11 prime numbers. The 1's and 0's when organized as a square of specific dimensions form a perfect circle.".

Well, the probability of what Ellie finds is actually suspiciously close to my estimate of it being pure chance - so perhaps Sagan has a hidden message BEHIND the message that most people read into the book - which is his old (and much quoted) claim that "Extraordinary claims require extraordinary evidence" may apply here. So perhaps he's hidden a message within his book - "Don't accept some wild-assed claim of there being a circle embedded in PI as evidence of there being a level 0 god out there - this could easily happen by chance alone". Sadly, the movie flushed away the hook in the tail of the story - it doesn't mention anything about PI or circles and punts for an easier ending.

But the probability of a sizeable circle image showing up inside PI as a matter of chance within the digits we're ever likely to be able to calculate is effectively zero (calculating 10²⁰ base-11 digits is far beyond what Ellie could do with the technology available to her) - so if it DID happen within the pathetically few digits we actually have to hand - we'd have to suspect some bizarre supernatural connection. However, these supposed "level 0 gods" don't ever seem keen on providing irrefutable proof of their existence...which is a shame because life on earth would be a lot simpler if they did! SteveBaker (talk) 16:06, 27 January 2009 (UTC)

The normality of pi is still just conjecture, so we can't be certain such a sequence will exist somewhere. Pi could be the sequence we've calculated so far repeated indefinitely with an ever increasing number of zeros between each repetition. If it is, that would be far more interesting than it being normal! --Tango (talk) 16:27, 27 January 2009 (UTC)

Truly omnipotent gods are incomprehensible and postulating their existence raises the age-old logical paradox of how they came about. So quite possibly one of the options that may be tickable, may be the causality/arrow of time feature. 196.2.124.248 (talk) 06:21, 26 January 2009 (UTC)

The trouble is that even 'level 3' gods (on my scale, above) are capable of manipulating your thoughts (heck, even us level 4 types get a shot at doing that). So you believe in L3/2/1/0 gods then you don't know what you do or don't know because the god(s) may be tampering with your thoughts. That's one of the things that makes them unfalsifiable. I say "God doesn't exist because I've managed to prove 'X'."...and you say "Aha! That's just because he wants you to think 'X' in order to test your faith."...so it's worse than "incomprehensible" - it's "meaningless - even in principle - to discuss it". At which point we wield our mighty 'razor of Occam' and end the speculation right there. SteveBaker (talk) 19:17, 26 January 2009 (UTC)

That's why religions often (always?) introduce the concept of "free will" even though their god(s) certainly have the power to influence our thoughts. Without free will, it just becomes impossible to have any meaningful theology. (Also, people like to feel in control - although, interestingly, they rarely like to actually be in control.) --Tango (talk) 19:45, 26 January 2009 (UTC)

While riding rollercoasters people like to be safe but dont like to feel safe. Sort of the same thing with control sometimes .froth. (talk) 00:34, 27 January 2009 (UTC)

To answer that - you have to realise that what god(s) say is mostly known because that's what the priests say. If people don't believe that have free will then if they screw up, it's God's fault. That's not good. Now people can (in practice) do what they heck they like and blame their local gods...and the priests can't do a damned thing about it. The priesthood lose power over the populace and it's all over for religion within one generation. On the other hand, if you are responsible for your own actions - then if you screw up, the priests can point out how the god(s) aren't going to be happy with you and you'd better sort out your behavior or you'll be banished to hell for eternity. This is an effective way to get your populace to knuckle under and do what the priests claim is god's will (and which, incidentally, allows them to carry on not having to do their share of the cleaning the cow shit out of the barn). SteveBaker (talk) 00:38, 27 January 2009 (UTC)

Watch out when people are under threat of social censure or eternal banishment and a convenient scapegoat is around.. Puritans believed that every little thing happened as a result of blesssing and punshment for the righteous and sinful.. if a cows milk is discolored, either the farmer sinned or SHES A WITCH! .froth. (talk) 00:50, 27 January 2009 (UTC)

mt st helens

Hi, I am investigating the eruption of Mt StHelens as part of my geography project.Is there a web address of the local newspaper from that area where i could learn first hand the timeline of the eruption? Thanks Quinnp (talk) 18:19, 25 January 2009 (UTC)

This was a national event, so you don't have to limit yourself to local sources for info about the timeline of Mount Saint Helens. See 1980 eruption of Mount St. Helens, which has many references at the bottom, and also contains a rough timeline. StuRat (talk) 18:28, 25 January 2009 (UTC)

http://www.oregonlive.com/oregonian —B00P (talk) 21:05, 25 January 2009 (UTC)

National Geographic. Twice, once soon after eruption and once a year or so later. Polypipe Wrangler (talk) 03:11, 27 January 2009 (UTC)

Which lightbulb?

Hi. Can anybody help me identify this lightbulb, please? As you can see from the picture it is just over 30mm long and is used in a 6 bulb "chandelier" light fitting, which is the main source of illumination in a room measuring 6m by 6m. Thanks CCorncob (talk) 18:51, 25 January 2009 (UTC)

Looks like some sort of halogen bulb. DuncanHill (talk) 20:21, 25 January 2009 (UTC)

I have managed to find some more info on one of the bulbs, that can be seen here. Not sure if it is helpful. Thanks CCorncob (talk) 21:30, 25 January 2009 (UTC)

I can make out "12V20W" on the bottom line of writing, this means that it is a 12 volt, 20 watt bulb. If I recall correctly these are quite common - your local hardware shop should have them if you need a replacement. DuncanHill (talk) 21:35, 25 January 2009 (UTC)

The letters "FSL" appear to be a trademark of Foshan Electrical and Lighting Co., Ltd. I think it is a G4 fitting (is it 4mm between the contacts? If so, it is a G4). DuncanHill (talk) 21:59, 25 January 2009 (UTC)

Yes the spacing is 4mm, so thanks for identifying them. I have seen these bulbs, but the contacts seem a bit thicker. Do you think they would still be appropriate? Thanks again. CCorncob (talk) 00:08, 26 January 2009 (UTC)

Probably, these things tend to be pretty standard. DuncanHill (talk) 00:10, 26 January 2009 (UTC)

OK great, thanks again for your help. CCorncob (talk) 00:18, 26 January 2009 (UTC)

If it's a 12v halogen - it's probably some variety of car headlamp bulb that they've adapted for this use. SteveBaker (talk) 00:53, 26 January 2009 (UTC)

They are used a lot in desk lamps and the like - I've just realized that the lamp on my computer desk uses one. DuncanHill (talk) 00:55, 26 January 2009 (UTC)

I have a set of these in some low-profile "hockey-puck" style lights I use around my house in a few applications. The local supermegahardwarestores (here Home Depot and Lowes) both carry LOTS of these kinds of bulbs in various sizes. Just take the bulb to the store and match the shape/size/markings. That's what I usually do. --Jayron32.talk.contribs 04:56, 26 January 2009 (UTC)

Identifying a street light bulb

So, the question above reminded me about this. The street light outside our kitchen window went out a month or two ago, and the bulb was replaced by some different kind. The light is quite blue-violet, making the white walls and the snow outside look bluish. When starting up, it starts out reddish, and then gradually moves over to the bluish color, in... say, 20-60 seconds. It seems to be pretty high-intensity, lighting a pretty large area. Any ideas what kind of lamp this is? The more important question is, though: do they flicker (like some fluorescent light bulbs)? -- Aeluwas (talk) 19:12, 25 January 2009 (UTC)

Possibly a mercury vapor bulb =- Nunh-huh 19:55, 25 January 2009 (UTC)

Or maybe a LED street light. Clarityfiend (talk) 20:03, 25 January 2009 (UTC)

No - it can't be LED - they don't shift color. SteveBaker (talk) 20:19, 25 January 2009 (UTC)

Egad, I've been LED astray. Clarityfiend (talk) 20:49, 25 January 2009 (UTC)

Water Clock Thingie Question

I am trying to build a water clock. My plan was to use a graduated tube and a valve and then have the valve drip at a constant rate. Then, i would measure how much water had drained and (using a graph) would be able to tell about how much time had passed. Unfortunately, after 30 mL have drained, the rate slows significantly. The articles i have read about water clocks say they use sloping sides. Does this help keep the flow constant? and if so, how could i change my plans to make it work accurately? Should i change from a straight tube to a funnellike tube? Any help at all would be appreciated.  Buffered Input Output 20:28, 25 January 2009 (UTC)

Using odd-shaped tubes doesn't change the rate at which water flows out - but it does change the rate at which the level in the container falls when a given volume of water has flowed out. So if you pick a container whose cross section at every height is proportional to the rate of flow when the water is exactly that deep - then the rate that the water level falls is more or less uniform even though the rate of water flow changes. Getting exactly the right container might be tough though - so for a practical project, you might want to look at other ways.

One other way I could think of to do it would be to graduate the time scale non-uniformly so that the distance between the marks indicating that the first minute has elapsed are further apart than the ones indicating the last minute...that makes it harder to read off the time - but at least then you can use a cylinder.

Another idea that comes to mind is to have three containers at different heights. The one at the top supplies water by pouring it into the second. The rate of flow into the second container is designed to be higher than the rate water drips out of it - so it always overflows into a suitable outlet. This wastes water but ensures that the second container is always 100% full - so the pressure inside doesn't change and the flow out of it is precisely constant. Sadly, because the water level in the second container never goes down - you can't use that level to tell the time...but you CAN catch the water that comes out of a spout to fill up a third cylindrical container and use the level in THAT one to tell the time.

There are lots of other ways. SteveBaker (talk) 20:52, 25 January 2009 (UTC)

While the above approaches work for a few hours (or days using large enough tanks), you might need an automatic method of refilling the tank to make this a permanent clock. The method used in a toilet tank, with a float valve which connects to a tube of pressurized water, is probably the simplest. This still allows the tank volume to vary somewhat, so the drips won't be exactly constant, but you can just average the length of time between drips and use that. Another approach is just to use a dripping faucet, which, being connected to a constant water supply, should only vary if the pressure changes. StuRat (talk) 01:58, 26 January 2009 (UTC)

Of course - all clocks need a source of power - and that might well be a natural stream or river. But the idea of a constant-pressure tank that's allowed to overflow (with the overflow flowing away someplace) is a really simple way to get constant pressure with the primitive means available to water clock designers. The only real problem is the waste of water - but if you're feeding fountains and such it's a very small deal. The flow rate into the constant-pressure container only has to be a tiny percentage more than the clock's 'useful' outflow rate - just enough to cover the variability in pressure of your ultimate waters source. Kinda like we use zener diodes to limit voltages for our electronics. We are always using the hydraulic analogy to describe electronics - well, you can reverse the analogy to make a water clock using the ideas from electronic clocks! SteveBaker (talk) 02:19, 26 January 2009 (UTC)

Our article on water clocks has some OK descriptions of some ancient designs and it is also QUITE well referenced with some external links and books. You may find some good information starting there and taking it where it leads you. --Jayron32.talk.contribs 04:53, 26 January 2009 (UTC)

I'm sorry i wasn't really clear on my question. My question was if i NEED a sloped-side container to make this work with some degree of accuracy.  Buffered Input Output 13:48, 26 January 2009 (UTC)

Then no, you don't . StuRat (talk) 17:04, 26 January 2009 (UTC)

Definition of Work

Why is work defined as Fd and kinetic energy as 1/2 mv^2? Why not use work=2Fd and KE=mv^2? Is it simply because Fd is more concise than 2Fd, or is there a better reason? --99.237.96.81 (talk) 23:00, 25 January 2009 (UTC)

It seems to be a matter of how the units of work and energy are defined. If force is mass times acceleration, then in the metric system it can be given as kilogram meters per second squared. Then force times distance is kilogram meters squared per second squared, which is the definition for Newtons. You could have measured force in a new unit called "figs" where two "figs" equals 1 Newton, and then force would be 2Fd. Edison (talk) 23:10, 25 January 2009 (UTC)

(edit conflict) You are right that it is a matter of definition. However, it is not the units, but rather the quantities. In most areas of physics, formulas don't change with the change of units. Velocity, for instance, is always simply distance/time, no matter if you use meters, kilometers, or miles for the distance and hours or seconds for the time. (To avoid using higher math, I used the formula for no acceleration.) The situation is rather like that of a circle. We know that the circumference is equal to 2πr, where r is the radius. If you don't like the factor 2 there, just use the formula πd, where d=2r is the diameter. — Sebastian 23:38, 25 January 2009 (UTC)

Suppose that I don't change the units of measurement. I'm under the impression that although Fd=(1/2) mv^2 can be derived from Newton's second law, work and kinetic energy are equal to Fd and (1/2) mv^2 only by definition. If that's the case, why can't I multiply both sides of Fd=(1/2) mv^2 by 2, call the left side "work", and call the right side "kinetic energy"? The units are still consistent; just as multiplying the diameter of a circle by pi doesn't mean a new unit has to be invented for the circumference, 2Fd can still be measured in kilogram meters squared per second squared. --99.237.96.81 (talk) 23:32, 25 January 2009 (UTC)

Yes, you could build a system based on what you suggest, but it is not very useful. Putting aside the issue that ${1 \over 2}mV^{2}$ is only an approximation in the first place, and there are higher order terms if relativistic effects are considered, you will still cause problems. You will be building a factor of two into all sorts of equation, many not obviously related. For instance, it will affect the definition of electrical potential difference which now becomes $-2\int E\cdot dl$ instead of $-\int E\cdot dl$, unless of course, you change the definition of the volt, but then you will have to mess with equations like $P=IV\,$. This factor of two is a dimensional constant. The SI system has gone to great lengths to eliminate as many dimensional constants as possible from the system of units. Before then engineers and scientists were required to remember a great number of them. It is a step backwards to start putting them back in. SpinningSpark 00:11, 26 January 2009 (UTC)

This is kinda silly - you can do this with almost anything. If I decide to measure distances as the "extent as measured from the midpoint" instead of from one end to the other (analogous to measuring the radius of a circle rather than its diameter) - then you end up with velocity being twice the "distance" divided by the time (v=2d/t). To get rid of the 2 you can choose to redefine the meaning of velocity - but you then need to go off and fix a bunch of other things...2's and 0.5's pop up in some places - and disappear in others. Some equations will get more complicated - others will get simpler. I suspect (because we've been doing this for a LONG time) that overall things would get more complicated. But we don't fundamentally gain or lose anything - no additional insight results. We happen to have picked one 'meaning' for work, force, energy, etc - you COULD pick a different one - but that just causes everyone to have to reprint an awful lot of textbooks. You can see this happening in all sorts of areas of engineering where a factor of 'g' (9.8 meters per second per second) creeps in to simplify equations that involve 'weight' rather than 'mass'. The result is generally a lot of confusion...so we work hard not to do that. SteveBaker (talk) 00:51, 26 January 2009 (UTC)

OK, so a joule is defined as "work done by 1 N over one meter". If energy is discussed in the context of thermodynamics, relativity, quantum mechanics, or anything else, one joule has to be the equivalent of 1 N over one meter. Is that correct? --99.237.96.81 (talk) 01:49, 26 January 2009 (UTC)

The definition of the unit doesn't change - but you have to be careful because in the context of things like relativity, measuring things like mass, length and time gets tricky - and lots of our basic equations of dynamics and energy are simplified Newtonian equations that are only approximations when you start to consider relativistic objects. At the quantum level, everything gets kinda fuzzy - so again, the definition of what a Joule is doesn't change - but the ability of objects to not be in one place makes measuring properties and plugging them into fundamental equations really tricky. This is dangerous territory for 'armchair physicists'! SteveBaker (talk) 02:10, 26 January 2009 (UTC)

January 26

Air pressure or surface tension

Have any of you ever noticed this? Let's say you have a plastic cup and a large basin of water. You put the cup in the water sideways so that some water goes into it. Then you turn the cup upside-down and submerge it. When you try and pull it out again (keeping the cup upside-down), it sticks a little at the surface and you have to apply a little extra force in order to pull it out completely. Is that due to surface tension, or have I somehow decreased the amount of air inside the cup (perhaps having displaced some of the air with water), creating a slight vacuum effect? howcheng {chat} 02:51, 26 January 2009 (UTC)

Surface tension is probably a factor. Another factor could be that the water falling out of the cup creates a vacuum behind it, that vacuum is going to try and hold the water in. It could be the combination of the two, actually - surface tension tries to hold the water together, the air pressure tries to keep the water in the cup, so you have to add extra force to overcome that. --Tango (talk) 03:36, 26 January 2009 (UTC)

The water you let into the cup is staying in there while the upside-down cup is part way out of the water, because of the pressure of the surrounding air. The force you're feeling is simply the weight of that water. The reason you didn't notice it before you lifted the cup out of the water was that it was buoyant while it was submerged. If you try filling the entire cup with water and lifting it out udside-down, the force at the moment you lift it out of the water will be exactly the same as if you lifted it out right-way-up, also full of water. Surface tension is not involved in any significant way. --Anonymous, 05:24 UTC, January 26, 2009.

Interesting. Will have to try that when bathing the kids tonight. Thanks. howcheng {chat} 19:25, 26 January 2009 (UTC)

Catching the milk

When heating milk for cocoa, I have noticed that skimmed or semi-skimmed milk is more likely to catch (burn on the bottom of the pan) than full-cream. Why would this be? DuncanHill (talk) 04:13, 26 January 2009 (UTC)

Because the fat in the cream provides some burning protection to the milk solids (mostly sugars and proteins). Without the fat coating these particles, they are much more susceptible to being affected by the heat. The burning of the milk is a varient of the Maillard reaction, though in this case, its a rather unwanted one. --Jayron32.talk.contribs 04:49, 26 January 2009 (UTC)

Fat/oil has a much higher boiling point, so I figure this is part of the reason. BTW, try microwaving the milk to avoid burning it. StuRat (talk) 17:00, 26 January 2009 (UTC)

Just last night, I was reading some related advice in Cook's Illustrated. They suggested putting a small amount of water to cover the bottom of the cold pan, heating that water (to boiling, if I recall correctly), and then adding the milk. This method is supposed to prevent the problem you describe. -- Coneslayer (talk) 14:04, 27 January 2009 (UTC)

There's even a device to do just that, called a double boiler, where water boils in the bottom part, and the steam then heats the milk in the top part, but not hot enough to burn it. Before microwave ovens, this was the best way to heat milk. StuRat (talk) 16:46, 27 January 2009 (UTC)

We call them bain maries in English :) DuncanHill (talk) 16:57, 27 January 2009 (UTC)

Actually - we call them bain marie's in French - even though we're English! SteveBaker (talk) 18:05, 27 January 2009 (UTC)

A double boiler is a similar idea, but not quite the same thing, since the top pot sits in boiling water in a bain marie, while the top pot is held out of the water in a double boiler. StuRat (talk) 21:14, 27 January 2009 (UTC)

Or just stir constantly - always works for me. --Tango (talk) 14:12, 27 January 2009 (UTC)

• Thanks for all the answers - very interesting. I prefer full cream milk because it tastes nicer, but circumstances sometimes dictate the use of the watery stuff. I've tried using a microwave, but it is hard to get the milk boiling without it overboiling. DuncanHill (talk) 16:57, 27 January 2009 (UTC)

The car of the future!

I remember reading back in high school about guys that had developed engines with unheard of efficiency and gas mileage and such. This was usually in magazines such as Popular Science and Popular Mechanics. I haven't picked up either magazine in quite a few years but I would guess that they still publish these stories from time to time. What happened to these engines? I was told by various cynical and pessimistic people over the years "The oil companies bought the patents to keep people buying more gas!" although, I've never been one to believe in too many cabals. So what's the story with these things, these wonder engines? Where are they? Were they always just figments? Or were they not commercially viable for one reason or another? Dismas|^(talk) 06:24, 26 January 2009 (UTC)

What you're remembering is known as the "Pogue carburetor." This is what Snopes has to say about it. Also read about the Pogue patents. Interestingly, the only article we have for a Charles Pogue is not this Charles Nelson Pogue. 152.16.59.190 (talk) 09:41, 26 January 2009 (UTC)

Well now we have Charles Pogue (disambiguation), so if someone writes an article about the Pogue Carburator or that Pogue, it can hang off there. DMacks (talk) 04:30, 27 January 2009 (UTC)

Free energy suppression and fuel saving devices are an interesting read. DMacks (talk) 14:33, 26 January 2009 (UTC)

A lot of the inefficiency in car engines comes from running them at variable speeds and temperatures. If an engine could be run continuously, at a constant speed, and was tweaked to perform optimally at that speed and temperature, it would get much better efficiency numbers. Electric/gasoline hybrids, which run the engine at a constant speed to charge the batteries, do get better mileage, but still suffer from temperature changes from starting and stopping the engines periodically. StuRat (talk) 16:54, 26 January 2009 (UTC)

One point of clarification, as StuRat's commas make this unclear: Hybrids which run the (gasoline) engine at a constant speed, which are presently a very small subset of all hybrid cars, are applicable to this statement. These "series hybrids" include models like the not-yet-released Chevrolet Volt. They do not include the Prius or any other mass-distributed hybrid, in which the gasoline engine still connects directly to the drivetrain. — Lomn 18:27, 26 January 2009 (UTC)

Thanks for the clarification. Your right, my wording didn't make that clear. StuRat (talk) 21:38, 26 January 2009 (UTC)

Some of those things have definitely made it - the Wankel engine, for example, had horrible lubrication problems when it was first described (probably in Popular Mechanics!) - but that was solved after maybe 30 to 40 years of engineering effort - and now you can buy several Mazda's that have Wankels in them. But many of these ideas (the Scuderi Engine for example) fall by the wayside for reasons of practicality that the original inventor didn't consider: Cost of manufacture, reliability, wear, pollution, noise, smoothness, overheating on hot days, failure to start on cold days...many of those ideas simply didn't prove practical. Also: If you see some engine that seems impressive because it did 55mpg back in the early 1960's - remember that lots of engines could do that when pulling cars of that era. My 1963 Mini does 55mpg with it's little 37hp engine. My 2007 MINI does barely 40mpg...which is considered pretty good by modern standards. That's not because some mysterious magic thing happens in the 1963 engine - to the contrary, it's crude and horrible in many ways. It's because the '07 car is exactly twice as heavy and can do 140mph and 0-60 in 6.5 seconds with it's 170hp engine, while running the airconditioner, the radio, the computer and so on. The '63 can just barely break 70mph and has a 0-60 time around 12 seconds - no radio, not much of a heater, no A/C, etc. The '07 car needs its first service at 20,000 miles - the '63 requires the owner to do work every 1,000 miles with an oil change and full service every 3,000. So you have to be careful. MPG numbers from old magazines probably have to be halved before you can compare them with modern engines - and MPG is not the only consideration. SteveBaker (talk) 19:08, 26 January 2009 (UTC)

What's this about cars being heavier today? It was my impression that they were considerably lighter, unless you count things like SUVs and Hummers as cars. You know, to economize on fuel and all that. I remember hearing 2 tons as the typical weight of an ordinary car circa 1970 and 1 ton today. Am I that far off base? --Anonymous, 09:40 UTC, January 27, 2009.

This depends on the location and date, of course, in that those things effect the price of fuel. Europe was known for small cars, and the US for large cars, traditionally, but they are becoming more similar now, due to globalization. As would be expected, large cars were common where and when fuel prices were lowest (as adjusted for inflation): [33]. The biggest cars in the US were perhaps from the early 1970's, right before the 1973 oil crisis, which stopped all our fun. Also, you can't exclude SUVs, minivans, trucks, etc., as more people drive those now than did back then. StuRat (talk) 15:30, 27 January 2009 (UTC)

The first generation VW Polo was below 700kg and the newest version is 1100kg.--Stone (talk) 10:24, 27 January 2009 (UTC)

My '63 Mini comes in at 1300lbs - my '07 MINI Cooper weighs 2600lbs - exactly twice as much - and until the SmartCar came on the scene, the modern MINI was the smallest car on sale in the USA. Ironically - there is more luggage space AND more rear legroom in the '63 car...and it handles better. Most cars that were around 20+ years have gained about 50% in weight. Most of that is because of the legal requirements for crash survivability, plus air conditioning, plus higher performance expectations (it really is a pain driving a car with a 72mph top speed on a Texas freeway!), plus luxury, plus emissions control. I'm not saying that the weight gain is necessarily a bad thing - but it does explain why the performance numbers for these bizarro-engines tend to look so good from a modern perspective. Some of them genuinely DO have better power-to-weight or fuel efficiency than conventional otto-cycle engines - but many are not that great. Those that are better on a purely fuel/power basis tend to have other (fatal) practical problems. The [Scuderi Engine]] for example has twice the usual number of cylinders - set up in pairs so that one is hot and the other cold. The latter collects water and corrodes - and the temperature difference between them causes stresses in the engine block which cracks very easily - also, the conduit between the two cylinders gets fouled easily and is almost impossible to clean. So while the Scuderi gets almost twice the power than a conventional engine - it would cost close to twice as much to make and it would fail very easily. SteveBaker (talk) 15:22, 27 January 2009 (UTC)

With twice the power, it seems like you could use some of that extra power to heat the cold cylinders, using the exhaust, and cool the hot cylinders, using air and unburned fuel, to equalize the temps. Has this been tried ? StuRat (talk) 20:57, 27 January 2009 (UTC)

Einstein Field Equation

Is the Einstein field equation G_ab=8πKT_ab or G_ab=8πT_ab or G_ab=T_ab(G is the Einstein Tensor, K the Gravitational constant and T the Strees-Energy Tensor)?The Successor of Physics 06:43, 26 January 2009 (UTC)

Doesn't really matter, does it? You can get rid of K through a redefinition of your units, see Natural units and Geometrized unit system. In SI units, the factor is actually 8πK/c⁴ and you seem to have set c=1 already. You could get rid of 8π by a redefinition of either G_ab or T_ab or both, if you wanted to, but that's rather uncommon, I think. There's no "wrong" or "right" here, it's just a matter of convention. Check in your text book what convention they use. --Wrongfilter (talk) 17:52, 26 January 2009 (UTC)

Remember, if you remove a pi from the field equation, it will be at the expense of adding pi's to other equations. --Tango (talk) 23:28, 26 January 2009 (UTC)

Thanks!!!The Successor of Physics 04:50, 27 January 2009 (UTC)

Drake equation with infinite L

I think I've found a flaw in the Drake equation.

Suppose that it is possible with non-zero probability for a civilization to break the law of entropy and continue to exist and release radio signals forever. Then the term L in the Drake equation, as an average, is infinite. Since the existence of Earth rules out a zero value for any other term in the equation, this in turn implies that N must be infinite as well. But in reality, this will be true only once the universe is infinitely old.

Would it be possible to adjust the Drake equation to account for the finite age of the universe? NeonMerlin 09:34, 26 January 2009 (UTC)

I don't think you need to adjust anything. The maximum L cannot be infinity; max L is equal to the age of the universe, although in my unprofessional opinion it is unlikely anything got started for at least the first billion when everything was getting settled out into galaxies and such. If 1% of alien civilizations builds a broadcaster that lasts for 10 billion years and the rest will communicate for 1000 years on average then we get an L of 10,000,990. 152.16.15.23 (talk) 10:14, 26 January 2009 (UTC)

Reading your question over again I realize that I may have not given you the answer that you wanted. Are you looking for a way to express the Drake equation as a function of time passed since the first possible civilization could have formed with the assumption that a fixed fraction of the civilizations that form continue broadcasting for the rest of eternity and thus accumulate? 152.16.15.23 (talk) 10:29, 26 January 2009 (UTC)

That's not even the big effect. If civilizations are arising at a uniform rate (in fact, you'd want to tie it to the star formation history of the universe in some entirely unknown way - life as we know it won't arise until you produce some metals), you'd just use half the hubble time as an average age. WilyD 15:03, 26 January 2009 (UTC)

This is a problem with most predictive mathematical models — they can lead you astray if you don't pay attention to their limitations. In the original Drake formulation, there are just two terms that aren't unitless constants: L, which is the average lifetime of a broadcasting civilization; and R^*, the average rate of star formation in our galaxy. (Note that Drake only contemplates civilizations within our own galaxy, not across the entire Universe.)

Implicit within those terms is the assumption that L will be less than the age of our current galaxy (civilizations require some time to evolve), or at the very least, less than the age of the Universe. Pushing the formula back further in time (with a larger L) would imply that civilizations had been developing around stars that had not yet formed. The alternative form of the Drake equation (Drake equation#Alternative expression) described in our article incorporates this restriction a bit more explicitly. There, the final term L/T_g – the average lifetime of a communicating civilization divided by the age of the galaxy – should end up as not more than 1. (Give or take some fudging I don't want to get into, if that ratio is 1 then every civilization that starts broadcasting continues to do so forever.)

Of course, that formulation falls down on very long time scales, too — as L approaches the lifetime of the average star, species with interstellar capability begint to settle 'new' stars (increasing the odds that a given star system will harbor life). Species without interstellar capability, meanwhile, will tend to get wiped out as their stars go out. TenOfAllTrades(talk) 14:46, 26 January 2009 (UTC)

The trouble with this hypothesis is the setting of the other attributes to 1.0 because Earth represents one example. Doing that tells you that either:

• Earth is eventually able to learn to broadcast radio forever...hence WE are the cause of L=infinity...but N_e (the average number of civilisations per suitable planet) could still be one-over-infinity (there are an infinite number of planets and we are the only one with life). Then the equation boils down to infinity over infinity - which tells you nothing...we may still be alone in the universe.

• The various 'N' terms in the equation strictly refer to the number of suns/planets/civilisations THAT ARE CAPABLE OF ACHIEVING LIFESPANS OF DURATION 'L'. Now, you can't count the Earth as 1.0 for any of those N terms because we may never defeat entropy - so any one of the N's could go to zero - and we're back with no aliens out there.

But the Drake equation really needs be used to count the number of civilisations that are NOT us - otherwise it's not very interesting. If you exclude Earth from the math - then the answer can still be zero - even with L=infinity.

But in any case, the idea of a civilisation being able to 'defeat entropy' is kinda silly...as far as we know, entropy can no more be defeated than time travel or superluminal travel be achieved. If you assume that science-fiction physics is allowed - then you need to rewrite the equation to include time travel and instantenous travel. If we aren't talking about "known physics" - but instead "unknown physics" (in which entropy can be defeated for example) then the Drake equation itself is incorrect and would have to be severely amended. The whole POINT of the equation was to estimate the number of civilisations we might hear from given our present knowledge of the universe. Once you start throwing in alternative physics models - all bets are off.

SteveBaker (talk) 15:54, 26 January 2009 (UTC)

There seem to be several flaws, all dealing with levels of technology reached by other civilizations:

1) I agree with your concept, that, if a civilization survives beyond some length of time, they may have overcome all the problems which tend to cause extinction, like warfare and living on a single planet.

2) They may also develop ways to communicate instantly with other civilizations, over vast distances, and in different times, say by using wormholes.

3) There seems to be an implicit argument in the Drake Equation that only our galaxy matters, while I can imagine a civilization in another galaxy that could spread to ours, either physically, or virtually.

4) There may also be life forms in other dimensions/parallel universes, which manage to develop a technology which allows them to communicate with us. StuRat (talk) 16:46, 26 January 2009 (UTC)

I would argue that if communication between "parallel universes" is possible, then they aren't really separate universes. I can't think of a reasonable definition of "universe" which would consider them separate. --Tango (talk) 00:53, 27 January 2009 (UTC)

We may indeed want to redefine the word "universe" at some point if that happens, but my point is that the Drake Equation doesn't consider this possibility. StuRat (talk) 15:18, 27 January 2009 (UTC)

For a civilization to survive the possibility of extinction, it must be far more advanced than us, and it must also have learned how to keep its civilization alive if its own actions start destroying its environment. Our own species might not even survive 3 million years, and most scientists agree. The Fermi paradox really isn't such a paradox. ~AH1^(TCU) 18:17, 27 January 2009 (UTC)

Whether civilizations self-destruct has a lot to do with what nasty weapons science brings us in the future. Nuclear weapons may be capable of destroying all human life on a planet. And perhaps more powerful anti-matter weapons (which may be available in a century or so) might be capable of destroying the planet itself. However, once people have spread to many planets, moons, asteroids, and space-stations, in many solar systems, and floating between them, even this won't be enough to wipe us out. So, we might be safe, unless there's some new super-weapon that will allow anyone to wipe out the galaxy or universe, then self-extinction will become virtually inevitable. StuRat (talk) 20:52, 27 January 2009 (UTC)

In dogs, say a Great Dane and a Chihuahua were to breed through artificial insemination...

What would the offspring look like? Would this even be possible? This article shows how big the size difference can be. So what might be the effect if the mother was a Great Dane and the father was Chihuahua, and vice versa?--'Cause It's No Good (talk) 11:25, 26 January 2009 (UTC)

I don't think it is possible to say what they look like, we simply don't know enough about the genetics. Besides it will almost definitely vary a fair amount from cross to cross. I don't however see any reason why it would be impossible if the mother was a great dane. I'm somewhat doubtful the mother and/or puppies will survive if if the chihuahua is the mother however. Nil Einne (talk) 11:51, 26 January 2009 (UTC)

Couldn't they be prone to sympatric speciation, where the two dogs, currently physically incapable of mating, eventually become speciated where they cannot reproduce genetically? Or does them being in the environment of dog breeders prevent this from happening? -- MacAddct1984 ^{(talk &#149; contribs)} 14:43, 26 January 2009 (UTC)

I think this is just another example of why the standard definition of "species" doesn't really work. Breeding between Great Danes and medium sized dogs and Chihuahuas and medium sized dogs (which will presumably occur naturally) means there will be an exchange of DNA between the two breeds even though they can't breed together easilly. --Tango (talk) 19:38, 26 January 2009 (UTC)

I think it is fair to say that the size would be somewhere in between the two, though I doubt it be right in the middle, I'd assume the hight would take after one more than the other. That being said, the father would have to be the Chihuahua since if the Chihuahua was the mother it would not be big enough to carry a baby that potentially would be so much larger than itself. It does matter which one is the mother as you keenly asked. We know some human traits we have are more from our mothers, like baldness in males (That is why they tell men to look at their mother's father to see if they'll be bald). I assume there are similar gender specific attributes in dogs, though there probably hasn't been as much research on it. Anythingapplied (talk) 20:40, 26 January 2009 (UTC)

I wouldn't be quite so fast to say it's all in the genes. It has been found that many features in fetal development are heavily influenced by conditions in the womb (do you also call it that in dogs?) like e.g. available nutrition, what chemicals are released to trigger certain cellular activities. It may still be that a Great Dane mix cub might grow too big for a Chihuahua mother, but I'd consider it more likely that it would fail to develop because something in the fetus growth pattern would not be compatible it might even be that the cub would drain resources the mother could not afford to lose. Another possibility might be that instead of carrying a litter of several pups most of the fetuses would fail to develop and only one would be carried to term. If the mother then can't birth it and no vet is available to do a C section they'd both die. Her birthing one rather big, but still manageable pup that then grows to something odd looking and significantly larger than a Chihuahua. A lot of a puppy's growth, size wise happens after it's born. So, a Chihuahua as mother has fewer chances, but it's not all because of genes. 76.97.245.5 (talk) 21:51, 26 January 2009 (UTC)

I think it's unlikely the bitch would die, I would expect the fetus to be aborted if it got bigger than was safe. I guess it's possible the bitch's body wouldn't notice the fetus was too big to be delivered until too late (since it can probably fit in the womb without being able to fit through the cervix), but it seems unlikely to me. --Tango (talk) 23:24, 26 January 2009 (UTC)

OOhhh. If I ask a question about donkeys, can I use the word "ass" in a totally non-ironical way too? --Jayron32.talk.contribs 15:04, 27 January 2009 (UTC)

If you want, although donkey is the more common term. --Tango (talk) 15:48, 27 January 2009 (UTC)

Throw the British term for a Rooster into the question for maximum linguistic titillation on this side of the pond. Edison (talk) 17:45, 27 January 2009 (UTC)

As for the OP, see a report of such a mix at [34]. This is certainly not a confirmed report, and I could find no such reports at Google News archive or Google books. Might be some discussion in the veterinary literature. Edison (talk) 17:53, 27 January 2009 (UTC)

Progesterone receptor A - isoform

I would like to know what is the molecular weight of (human) progesterone receptor A (PR-A)? There are a lot of reports that looked at PR expression using western blotting but it is for me still unclear what the 'real' molecular weight is. Some studies report 94 kDa, others 81-82kDa (in both cases there is a single PR-A band visible). Many thanks in advance. Ana. —Preceding unsigned comment added by 131.211.166.194 (talk) 14:37, 26 January 2009 (UTC)

Estimating the molecular weight of a protein on a western blot is a bit dicey. First, the molecular weight markers that are run alongside the sample are just meant to give an approximate reference point to estimate the sizes of the bands of interest. Second, a gel can run unevenly, throwing off the size estimates. Third, the size markers would typically be invisible on a western blot (since you're using an antibody that should only react with your protein of interest) so in practice one marks the position of the MW standards on the transfer membrane after visualizing the transferred proteins using a stain like Ponceau S. Fourth, the lanes containing the size standards are usually cropped out of the published photos and replaced manually with the approximate molecular weights. Fifth, sometimes only the band of interest is shown and reported to be at some particular MW for which you just have to take the author's word on it.

Now, if you were talking about a protein gel stained with Coomassie or Silver stain to visualize all the proteins, then you would only have the first 2 problems. However, you would still have the universal problem of post-translational modifications, which can either increase the apparent molecular weight (by adding on a phosphate, acetyl, ubiquitin, or lipid side chain, etc.) or decrease the molecular weight by cleaving the protein.

The "real" molecular weight of the A isoform of the progesterone receptor? You can get a predicted MW based on the weight of each individual amino acid in the chain (see http://ca.expasy.org/ for a good set of proteomics resources). In this case, the predicted MW of PGR-A is ~99 kDa. Of course, then you have the final problem with proteins... sometimes they don't behave themselves and they run out on the gel faster or slower than you expect them to. --- Medical geneticist (talk) 15:26, 26 January 2009 (UTC)

greatest possible scientific progress 40 years ago from single twitter?

thinking of working scientists with a 50+ year career:

if they could, today, send back 1 twitter's worth* of information (a clue) to themselves of 40 years ago regarding what to explore, what is the greatest progress they possibly could have made (early) as a result?

Actually I am interested by discipline: chemistry; biology; physics; mathematics; economics; medicine

Thank you!

* (140 characters) —Preceding unsigned comment added by 82.120.111.130 (talk) 17:37, 26 January 2009 (UTC)

Thats an interesting question. My first inclination would actually be for social purposes. Instead of giving them what we value the most, give them what they could use the most at that time in history. To me, the answer to that question would be something to try and prevent the cold war or any of the other wars that have occured in the last 40 years. Science will always move on. The fact that we would be sending them something we now know is proof that we would have will be eventualling have been going to learn it, and thus isn't necessarially of a crucial need to transmit, where as the lives lost in wars or the recources lost in economics collapses maybe of more importance. That said: In the field of math I'd probably transmit hints to the proof for Fermat's Last Theorem. Anythingapplied (talk) 17:56, 26 January 2009 (UTC)

I doubt you could get a significant amount of useful information about FLT into 140 characters. Wile's proof built upon large amounts of recent work - all Wiles actually proved was "All elliptic curves are modular." (although one shouldn't diminish the significance of that proof), that only proves FLT because of lots of work done before. I guess you could say "The proof of Fermat's Last Theorem involves modular forms." so people have an idea of what stuff to study, but that's about it. --Tango (talk) 18:14, 26 January 2009 (UTC)

I have a truly marvellous hint to give you which this SMS sized mesasge is too small to contain. --LarryMac | Talk 18:35, 26 January 2009 (UTC)

I think I'd go with "Fermat's last theorem didn't fit in the margin!"...well, if I were sending back something about Fermat...which I think would be a waste. 40 years ago is 1969 - that's around the time when most of the fundamental physics stuff had already been figured out. Look at the MANY Wikipedia timelines - it's tough to find a suffiently compelling single breakthrough since the mid-1970's. Using our one super-valuable 'twitter' to save them 5 years by mentioning Quarks or Dark Matter seems like a wasted opportunity. I wonder if there is enough space in our 140 characters to tell them how to send twitters back in time - it would be good to tell Newton to give up Alchemy or to tell Einstein about Quantum theory while he was still young enough to work on it...but if we're really stuck with 40 years then neither of those things is any good. I'd be awfully tempted to say "Make REALLY SURE that the 'twitter' standard allows unlimited-length message attachments" - then go on to dump all of Wikipedia and the results of the Human genome project onto the end of the message. But I sense you're not going to let me do that...so we're down to: "Arrest G.H.W.Bush'sOldestSon&BillGates.GlobalWarmingCausedByCO2-SERIOUS!!TellSteveBaker:BuyGoogle,DiseaseOfRobert R. don'tLetItSpread.". But specific scientific advice is tricky in so few characters. SteveBaker (talk) 18:48, 26 January 2009 (UTC)

The OP let us have one twitter per discipline, so you don't need to be quite so careful about what you choose. I'm struggling to think of good things, though - it seems there have been disappointingly few major discoveries in the last 40 years... There has been lots of incremental development, but few major breakthroughs. The biggest development in the last 40 years has to be computers, but even the major breakthroughs for that were made more than 40 years ago, it's just been incremental development since (pretty rapid incremental development, sure, but not anything a twitter is likely to help with). You could send back warnings about various disasters, of course, but I don't think that's really what the OP had in mind. --Tango (talk) 19:03, 26 January 2009 (UTC)

How about a message on the importance of the Internet, using words they would understand at the time, like "ARPA-NET, on home personal computers, will revolutionize how people communicate". Be sure to send it to Al Gore, so his claims to have invented the Internet will then become true. :-) StuRat (talk) 20:47, 26 January 2009 (UTC)

Would knowing how important the internet will become actually help develop it? It moved pretty quickly as it was... --Tango (talk) 21:45, 26 January 2009 (UTC)

It took from the 1960's to the 1990's for the Internet to become widely available for home users. I suspect that this could have happened a couple decades earlier, although, due to bandwidth limitations on dial-up modems, that text-only pages would be all that could be passed easily between computers at that time. Still, that could have been quite useful, and Wikipedia could have even started in the 1970's. StuRat (talk) 03:41, 27 January 2009 (UTC)

I think the essentials of the Polymerase chain reaction could be boiled down to 140 characters.-gadfium 23:07, 26 January 2009 (UTC)

"Useful fluorescent protein for tagging in Aequorea victoria" => Win Nobel Prize. Dragons flight (talk) 23:16, 26 January 2009 (UTC)

Apparently I need a better time machine. GFP was first isolated in 1962. Dragons flight (talk) 23:19, 26 January 2009 (UTC)

I'm also partial to sending lottery dates and numbers but that's not very scientific. Dragons flight (talk) 23:16, 26 January 2009 (UTC)

Computer science: "32 bit network addresses are too small, but go for a flat 32 bit memory model for RAM. Emacs, not vi, and never NotePad!" --Stephan Schulz (talk) 23:26, 26 January 2009 (UTC)

Er - you mean "vi, not emacs" - right? SteveBaker (talk) 00:18, 27 January 2009 (UTC)

Will all of the women please leave the audience? Now where did I put that bag of stones... --Stephan Schulz (talk) 10:20, 27 January 2009 (UTC)

Eighty Megs And Continually Swapping - Ha!! (Oh - it's OK - the chicks have left - we can just pretend like we're doing a bunch of macho/geek posturing).OW! That rock really stung!<wink, wink> SteveBaker (talk) 15:07, 27 January 2009 (UTC)

Plastics. -- Coneslayer (talk) 12:46, 27 January 2009 (UTC)

Nylon:1935, Polystyrene:1839, Polypropylene:1951...nope. (Oh, wait - I just followed your link - Hahahaha!). SteveBaker (talk) 15:11, 27 January 2009 (UTC)

What about 200 years?

Since we seem to be struggling with 40 years, how about 200 years? "The speed of light in a vacuum is constant for all inertial observers." has to be pretty high on the list of options for physics - once you have that, you can work out most of special relativity in an afternoon. Is there a similarly short statement that sums up quantum mechanics? What about for other disciplines? --Tango (talk) 19:15, 26 January 2009 (UTC)

Forget pure science. Go for technology: "Wires carrying current have a magnetic field. Conductor cutting through magnetic field gets voltage induced. Build motors and generators." Edison (talk) 19:54, 26 January 2009 (UTC)

I certainly would not send anything back. Humanity has teetered on the edge of self-annihilation too long for me to be comfortable making sweeping changes in the discipline that has defined the last 200 years. 200 years isn't long at all anyway; let them work it out for themselves. Who knows what kind of other advances were made trying to solve problems that we might spoil for them. The key article here is Serendipity. And don't even think of trying to avert wars or disasters; I'd argue confidently that nothing has more impact on the future than war. For one, the modern large-scale conflicts have marked remarkable leaps in manufacturing technology, not to mention paradigm shifts in popular culture- billions of people thinking and behaving differently. Yes the price was unimaginable suffering and the blood of millions, and the world might be better if things had happened differently, but we're not talking about a stable, post-scarcity world culture; we're talking about an era in which the world is stockpiling enough nuclear weaponry to turn the earth into molten slag, we're talking about progressive changes positively straining at the fabric of society to change slavery and torture into equality and humanitarianism and to accept radical changes in our way of life. That may be the best or the worst time to confront Earth with a greeting from the future, but it's certainly not the best time to meddle with things. .froth. (talk) 21:06, 26 January 2009 (UTC)

And anyway don't assume the message has to tell the truth.. Seldon lies to the Foundationers to great effect, and telling them the truth would have destroyed them, although a little 40- or 200- year hop is hardly comparable. .froth. (talk) 21:06, 26 January 2009 (UTC)

I'd go with disease prevention: "Boil water before you drink it and surgical instruments before you use them; eat fruits, veggies, grains, milk, and meat to be healthy." Alternatively: "Don't poop into rivers you drink from, bury it instead" (although they might have figured that out by then). StuRat (talk) 20:51, 26 January 2009 (UTC)

Except those things aren't sufficient. The link between peaches and cholera was real when they were being washed in contaminated water; someone who knows eating fruit has an unhealthy effect will discount the rest of your advice. You'd need to give them some clue as to what your motive was for boiling the water; it's not just something you do before drinking it. And sticking to the old-fashioned American food pyramid groups might make healthy eating easier in modern-day America, but it isn't an absolute healthy diet guide. There's no reason to add milk to an adult's diet if they're already getting what they need elsewhere, particularly if they don't retain the ability to digest lactose into adulthood. There's no need to tell them to eat meat if they're eating enough protein without it, and if they aren't they probably can't afford meat anyway. If they're getting enough carbs elsewhere there's no need for grains. Etc. Find an influential person and seed them with germ theory instead - "Miasma theory is onto the right idea, but it's tiny creatures not bad smells and they can travel through water too. Look into it." 79.66.105.133 (talk) 21:53, 26 January 2009 (UTC)

I believe germ theory goes back further than 200 years, and the invention of the microscope allowed people to actually see bacteria. Saying "boil water before you drink it, wash food with it, or wash dishes with it" might be a good addition, though. StuRat (talk) 03:36, 27 January 2009 (UTC)

Yes, but it wasn't taken seriously until the mid 19th century. Seeing micro-organisms doesn't tell you they cause disease. By giving someone the reassurance it would prove to be right 40 years before it was being seriously explored, you could provoke research that would save thousands of lives. 79.66.105.133 (talk) 18:38, 27 January 2009 (UTC)

"Marie, use a much longer stick when stirring the pitchblende" . DuncanHill (talk) 16:47, 27 January 2009 (UTC)

obviously this isn't working - so how about without a length limit

obviously I'm not getting answers about physics, chemistry, etc, and 40. So what if you can only relate one discovery, but without length limit. What discovery of the past 40 years would have the biggest impact 40 years ago?

We're talking about biggest impact now? Hm, I'd have to go with "you can't tell now, but the sun has become unstable and will destroy the entire earth in 40 years and there's absolutely nothing you can do about it. make your peace." 72.236.192.238 (talk) 22:09, 26 January 2009 (UTC)

I think you mean you have no chance to survive make your time. --Trovatore (talk) 23:13, 26 January 2009 (UTC)

"Rub sticks together"? --Tango (talk) 23:16, 26 January 2009 (UTC) Sorry, I wasn't reading properly... --Tango (talk) 00:21, 27 January 2009 (UTC)

I really don't think 40 years is enough. It's not the length of the message (well, not within reason) - even with a couple of pages, I doubt we could make a big impact. Part of the problem is that most of the work we do these days requires modern technology. It's no use telling them to look for the Higgs boson because the technology to do that simply wasn't there in the 1970's. Even if we tell them that computers are seriously important and the internet matters and to use open systems to allow scientists (and laymen) to collaborate on writing an encyclopedia...they simply couldn't do that back then because first you had to make smaller/cheaper computers - then you could use those to push the technology - which in turn allows still smaller/cheaper computers - which means that more people have them - which turns computer networking from a cliquish "UseNet" into the Internet and thence into the world-wide-web. Back when I was in college in the mid 1970's, we couldn't have built the internet if our lives depended on it. Sure, we can tell them about the rise of text messaging - but without the battery technology and the mass-production of tiny RAM chips - they couldn't make the cell phone to exploit that. Some things just have to evolve slowly.

That's why Tango's idea to stretch the time limit to 200 years has started to provoke some interesting answers while increasing the message length has not. If we had something important to say - I'm sure we could figure out a way to say it in 140 characters and add enough information to speed up the work...but we just don't have anything profound to say. I think a global warming warning would be the best thing we could do. What we're trying to do now would have been so much easier if we'd had another 40 years to do it in.

So (within limits) it's not the length of the message - it's the amount of time we can send it back. If the limit TRULY is 40 years - then the idea of telling some scientists how to make a ridiculous amount of money on the stock market isn't so silly - lack of funding has probably done more to limit our technological progress than anything else...fix that and everything moves faster. SteveBaker (talk) 00:18, 27 January 2009 (UTC)

Re the Higgs boson: the theory was pretty well understood forty years ago. I don't think there's much we could send. Algebraist 00:22, 27 January 2009 (UTC)

If there's no size limit to the message, perhaps the people of the late sixties would enjoy a copy of the human genome. APL (talk) 06:14, 27 January 2009 (UTC)

Physics and chemistry like most technical things advance gradualy and if you lift somebody up 200 years in knowledge in a small area he has no foundation to stand on. The design of a microchip is usles in 1809, same with airplanes. Penicillin extraction from fungus might work even with technics in 1809 and this will make the differnce in the growth of the nations. The ammonia synthesis of Haber Bosch is complicated, but if you get this running in 1809 the food production would increas drastic. To chnge the outcome of the wars in the 19th century would have the largest impact. Machinegun design to one of the fighting groups in a war done in the old fashoned way would make clear winners. The French under Napoleon would be my choice before or after Watergate the map of Europe would be a lot different than. The composition of sulfur mustard or chlorine gas might be a good tip to the armies of the world too. --Stone (talk) 10:15, 27 January 2009 (UTC)

I believe the main threat to humanity is our technology outpacing the social structures necessary to survive it (nuclear weapons in the last century, probably nanotech and biotech in this one). I would send something like "it is a sin to put the tools of adults into the hands of children", and then maybe some lotto numbers so they'd know I wasn't just some goofball. --Sean 13:51, 27 January 2009 (UTC)

You're just guessing, though, they can do that just as well. We've had nuclear weapons for over 60 years and haven't destroyed ourselves yet, so the benefit of hindsight should make you less concerned about such things than someone 40 years ago rather than more. --Tango (talk) 14:10, 27 January 2009 (UTC)

The problems of technology outpacing our ability to deal with it were well known in the late 1960's - there is nothing we can possibly tell them about that except, perhaps, "You were right about that". That's not going to change anything that happened. As for the nuclear weapons thing - it was only the presence of all of those nukes that prevented a third world war. Trust me, I was there. Everyone was so freaking terrified that the end of the world was coming that we were forced to work with the 'enemy' to make sure that it didn't. The result was exactly what the pre-nuclear weapon people said: A policy of mutually-assured destruction works. That surprised me at the time - but hindsight helps a lot! If we told them it would all turn out OK in the end - they might have caused one side or the other to drastically scale back weapons production before the moment of reconciliation - and THAT could easily cause the very thing we'd be trying to avoid. Besides - we're talking 1969 - by which time the worst of the madness was over. We were much more concerned then about the Soviet's conventional army nibbling away at the edges of Europe and our inability to prevent that OTHER than by starting a nuclear exchange that would end the world. Fortunately, the soviets had much the same concern...(see how that works?!). 14:59, 27 January 2009 (UTC)

In what way were they "right about that"? People fear problems with too advanced technology all the time (and have done for centuries), but can you give an example of a time they were actually right? --Tango (talk) 15:13, 27 January 2009 (UTC)

Internal combustion engines and global warming? SteveBaker (talk) 16:40, 27 January 2009 (UTC)

That's still a fear about the future - global warming hasn't done any major damage yet (a few extra hurricanes, maybe, but nothing on a global scale) and we may yet get emissions under control and prevent a complete disaster. --Tango (talk) 16:45, 27 January 2009 (UTC)

Just a guess - you aren't a polar bear are you?

It's completely UTTERLY incorrect to say that global warming hasn't done any major damage yet. There is strong evidence that the number of hurricanes is increasing due to global warming - and that means that the victims of Katrina and the total annihilation of Galveston could easily be suffering those consequences. Low lying island communities all around the world are actually starting to notice the sea level rise and a few are losing crops due to salt water getting into the groundwater beneath their fields. Plants that live on mountain slopes are vanishing from the lower slopes and being found at higher altitudes. Migratory birds are being found further North than they've ever been seen before - and in other areas, whole populations of animals and plants have simply 'vanished' because one species growth spurt or breeding cycle that is triggered by temperature are appearing out of sync with other species who time their young based on day-length - so one species thrives to 'plague' proportions while the other starves. Heck - find a photo of ANY glacier in the world as it was 10 years ago and as it is today! If that's not "major damage" - I don't know what is! SteveBaker (talk) 17:50, 27 January 2009 (UTC)

Oh - and to your other comment: getting emissions under control ain't enough. A big climatology study that came out a few weeks ago reported that the timescale for the atmospheric CO2 level to return to 'normal' even if we went back to a pre-fossil-fuel economy overnight (yeah...right!) would be on a scale of thousands of years and that indeed CO2 levels will continue to climb slowly for decades - even after we stop making matters worse. That's because of the knock-on effects of the temperature rise slowly feeding back into CO2 release from the oceans. Even if we "get emissions under control" - we are still in for a disaster. At this point it's more about the depth of the disaster we're just starting to head into than whether it gets worse or not...it's definitely going to get worse no matter what we do. SteveBaker (talk) 17:58, 27 January 2009 (UTC)

Well, if the human race gets wiped out in the next 50 years, I'll buy you a pint! ;) I take all claims of impending doom with a very large pinch of salt - none of them have been correct so far, what makes this one any different? Once it gets bad enough that people can't get away with just doing it lip service, we'll find a workable solution - we always do. --Tango (talk) 18:04, 27 January 2009 (UTC)

I guess it depends on your definition of "major". None of those things are even remotely comparable to a nuclear winter, which was the main fear regarding technology getting out of hand 40 years ago. Also, such statements are only meaningful if compared to non-global warming figures - there are always lots of hurricanes, there are always lots of species going extinct, glaciers have been melting for the past 10,000 years, etc.. There is undeniably an increase in those things and it is undeniably getting worse, but it isn't easy to actually make a meaningful comparison which you need to do before you can claim that global warming (particularly, man-made global warming) has already caused major damage. --Tango (talk) 18:04, 27 January 2009 (UTC)

Displacement, s

Why is displacement notated with the letter s? Any particular reason, or just what ended up as convention in the end? --80.229.152.246 (talk) 19:49, 26 January 2009 (UTC)

Not much more than guessing: Latin la:spatium denotes the length of a path. v is velocitas, t is tempus. --Wrongfilter (talk) 20:02, 26 January 2009 (UTC)

Thanks, that sounds extremely plausible. --80.229.152.246 (talk) 22:50, 26 January 2009 (UTC)

I'm also going to pipe in with my opinion. Notation varies from place to place, but in my experience, the most uniform and consistent systems always use "X,Y,Z" as the standard Cartesian grid, because they are the last letters of the English alphabet. When we do a $\mathbb {R} ^{3}$ to $\mathbb {R} ^{3}$ mapping to some other abstract coordinate system, we generate other coordinates in $\mathbb {R} ^{3}$, so we just count back three more letters and get "U,V,W". These are common notations in computer graphics - "UVW" Mapping. Now, we're running out of letters at the end of the alphabet, (U-Z are taken), and t is usually reserved for "time", so we now have to step back one more letter... "S" - for a mapping of $\mathbb {R} ^{3}$ to $\mathbb {R} ^{1}$. I actually came up with this explanation for myself; I had a similar question about this notation during my first vector-calculus classes. This explanation seems to make the most sense to me. Nimur (talk) 18:01, 27 January 2009 (UTC)

viscosity vs. temp

Is it safe to assume that the viscosity of an aqueous solution will drop as its temperature goes up? ike9898 (talk) 20:21, 26 January 2009 (UTC)

Temperature dependence of liquid viscosity. But I'd keep an eye on Evaporation, Vapor pressure.76.97.245.5 (talk) 21:30, 26 January 2009 (UTC)

Alternating current outlet

Why do outlets have one hole larger or different than the other so you have to put the plug in a certain way? I thought that alternating current, well you know, alternates; the only difference between putting it in one way or the other is a tiny (1/60 second in america I believe) phase change.. I read Neutral_wire and it confused me. It seems to suggest that AC comes in on a live wire and out on a neutral wire, like direct current. I thought the relative safety and interesting electrical properties of AC were precisely due to it not flowing in any particular direction for more than a tiny fraction of a second.. 72.236.192.238 (talk) 20:30, 26 January 2009 (UTC)

Here, I think, is an explanation, from our article on AC power plugs and sockets:

Polarised plugs and sockets are those designed to connect only in the correct orientation, so the hot and neutral conductors in the connected equipment are connected to the hot and neutral poles of the outlet. Polarisation is maintained by the shape, size, and/or position of plug pins and socket holes to ensure that a plug fits only one way into a socket. This is so that switches, for example, interrupt the live wire of the circuit. If the neutral wire were interrupted instead, although the device would deactivate due to the opening of the electrical circuit, its internal wiring would still be energised. This can present a shock hazard if the device is opened, because the human body would create a circuit — a path to a voltage different from that of the live wire. In toasters and other appliances with exposed heat elements, reversed polarity can cause the elements to be electrically live even when they are cool to the touch, posing the risk of electrocution even if the device is not deliberately disassembled or otherwise tampered with.

Reverse polarity can also create a hazard with screw-in light bulbs, where the shell of the socket may be energized even though the lamp is switched off.

Interchange of the live and neutral wires in the behind-the-walls household wiring can defeat the safety purpose of polarised sockets and plugs; a circuit tester can detect swapped wires.

ike9898 (talk) 20:49, 26 January 2009 (UTC)

That can't possibly be right. If you interrupt the circuit then there's no current, correct? It doesn't matter where you interrupt it. And again, how is there a hot lead and a neutral lead if alternating current just goes back and forth through the whole circuit? Every lead is hot, or rather each lead alternates between being the + and the - 72.236.192.238 (talk) 21:14, 26 January 2009 (UTC)

The hot lead alternates, yes. But both + and - will flow to ground. It doesn't have to be the ground in that particular socket. It could be the ground from some other socket, or can be the ground in the actual ground. APL (talk) 21:27, 26 January 2009 (UTC)

I understand that both leads (1 and 2) flow to the ground (3) but why are 1 and 2 different sizes as if it matters which is which? ( http://img220.imageshack.us/img220/2696/782455zp3.jpg ) 72.236.192.238 (talk) 21:39, 26 January 2009 (UTC)

Because only one lead is "hot" (Alternating from + to -). The other is neutral, similar to ground. APL (talk) 22:01, 26 January 2009 (UTC)

There is one hot lead which alternates between positive and negative. The other lead remains at (or near) 0v, so the effective voltage and current change directions (signs), but the second lead is never hot. You could theoretically implement a system where both leads changed voltages, but it wouldn't provide any real advantages and it wouldn't allow simple safety measures like polarised plugs. -- 74.137.108.115 (talk) 21:53, 26 January 2009 (UTC)

How can the other lead remain at 0v? Volts are electric potential, it has to be measured between two different points. So the hot lead is +120v relative to neutral, then -120v relative to neutral. Which should be another way of saying hot is +120v relative to neutral, then neutral is +120v to hot. Which should be another way of saying the two leads are identical except for phase, so it shouldn't matter which is which. We can ignore the additional grounding lead since it isn't used unless there's a problem. I really don't know where you're coming from saying "the effective voltage and current change directions (signs), but the second lead is never hot" ... if the current is flowing into the hot lead that means it's coming out of the neutral lead, and uh isn't current coming out of a lead the definition of hot? The electrons have to come from somewhere; you're not pumping charge into and out of a giant tank, you're dealing with a giant electrical circuit starting and ending at the power plant. 72.236.192.238 (talk) 22:05, 26 January 2009 (UTC)

You just explained it well, actually. Ground really can act as a "giant tank". The neutral wire does not go back to the power plant. It is simply connected to ground. (There is no 'complete circuit' between your lamp and the power station.)

So if you imagine two hoses, one constantly vibrating between pressure and suction, and another connected to the infinite "tank" of ground-water at neutral pressure, you can see how it makes a difference which "hose" you accidentally tap into. APL (talk) 22:30, 26 January 2009 (UTC)

Hm ok it's not a circuit But if ground can act like a giant tank then -120v on the hot (relative to 0v on the neutral) really is equivalent to 120v on the neutral (relative to 0v on the hot). That's the only thing I was worried about being wrong about, but apparently I'm not. Think about it... if the live wire is alternating between 0 and 120 relative to ground, and the neutral is equivalently alternating between 120 and 0 relative to ground, then they're the same.. :( 72.236.192.238 (talk) 22:49, 26 January 2009 (UTC)

Oh oh oh I see. As explained above it's useful for breaking the connection before the appliance instead of after. I was assuming that it's a circuit and it wouldn't matter which side, but I see now that I learn that one end is just ground, not a circuit back to the power station: your body could be that one end! Whew that was a doozy. I have no non wikipedian training in electricity and it shows im afraid 72.236.192.238 (talk) 22:55, 26 January 2009 (UTC)

There is a hot lead, a neutral lead and often a ground. The voltage is from hot to neutral or ground. Where there is a power switch, it must interrupt the hot line; interrupting the neutral would turn the device off, but would leave live power. Devices such as a GFCI work by detecting residual current; reversing the leads render them useless. --—— Gadget850 (Ed) ^talk - 20:48, 26 January 2009 (UTC)

Of course, I usually just file those polarized plugs down so that they'll fit into older sockets. APL (talk) 22:02, 26 January 2009 (UTC)

Let me try to clear this up a bit. If you live in the U.S., you have 2 lines coming into your house: One is at +120 V (relative to ground) and one is at -120 V (relative to ground). Now, in your house, there are two types of plugs. You major appliances, which draw lots of current, like the dryer, are likely hooked up to the +120, -120, and ground. This supplies a net voltage of 240 V across the appliance. These are those funny round fat plugs. The normal "frowny-face" outlet is hooked up to one of the two "hot" wires (either +120 or -120, it doesn't matter which) a "neutral" wire (which is hooked up to ground at the breaker box) and a "ground" wire, which is generally grounded firectly at the junction box. So, at this outlet, the net voltage is 120 V, because the appliance you attach is hooked into the hot wire and the neutral wire, and the two are 120 V apart relative to each other. The deal with alternating (rather than direct) current, is that the "direction" or "sign" of the current flow doesn't matter. The sign only effects the wave function of the current (i.e. a +hot wire has a mirror image wavefunction profile to a -hot wire) and as such, all that usually matters is that the hot wire is hooked up to where the appliance expects it to be. It doesn't matter whether its the +hot or -hot. In fact, for some applications (like a regular incandescent bulb, or a toaster) it doesn't even matter which wire gets the hot, and which gets the neutral. --Jayron32.talk.contribs 22:10, 26 January 2009 (UTC)

There is no + or - in an AC line. If you measured across +120 and -120 DC, you would get 0. Residential U.S. power is two 120 volt hot leads and a neutral. In a standard breaker box, odd numbered breakers tap onto one hot and even the other hot, balancing the load. 220v breakers are double and tap into both hots. --—— Gadget850 (Ed) ^talk - 23:29, 26 January 2009 (UTC)

I'm sure he meant instantaneously one is + while the other is - (on a sine curve), even though overall both average 0 .froth. (talk) 00:29, 27 January 2009 (UTC)

As I actually explained in my own words, the +120 and -120 refer to the sign of the wavefunction. The neutral, of course, is a flat line at 0. The two lines have an alternating wave function which are mirror images of each other, so arbitrarily one can be called + and one -. Tapping into these two lines will give a net difference of 240 V relative to each other, which is used for high demand appliances like you drier. --Jayron32.talk.contribs 16:38, 27 January 2009 (UTC)

Nit: US breakers aren't "odd-breakers one hot, evens the other". It would sure make running the two internal bus-bars easier (one feed to the left column, other to the right), but makes it much harder to configure a "two-hot" (240V) breaker. See Breaker box#Breaker arrangement. DMacks (talk) 17:25, 27 January 2009 (UTC)

Ah, that helps a lot. But doesn't that prove my point? Like you said it doesn't matter for frowny face sockets which house line you connect the hot lead to. Equivalently it doesn't matter which direction you plug your power cord into, for any application, not just lamps and toasters. By connecting to only one house line (and the neutral goes to 0v, ground) you change nothing except the net voltage. Instead of 240v you have 120v. But it can't matter which side you connect the live wire to, because electrically the live and neutral are only distiguishable by phase, exactly the case with the two lines coming into the house! One end of the cycle the live is +120 (relative to the neutral being 0v) the other end of the cycle neutral is +120 (relative to the live being 0v). 72.236.192.238 (talk) 22:42, 26 January 2009 (UTC)

The holes are different sizes so that if you plug in a device the off switch, fuse and breakers are interrupting the circuit on the live side. If you have a short in the device and the off switch only disconnected the neutral line you could still get power flowing from your hot lead to whatever ground (e.g. your body) was available. If the disconnecting element is where the hot line connects to the device and will effectively interrupt the circuit. Some devices are designed to disconnect both poles. For those it would not matter which way you plug in the plug. So don't reshape your plugs or widen your outlet holes.76.97.245.5 (talk) 22:16, 26 January 2009 (UTC)

Let's say you have a toaster. The lever on the toaster turns on the hot lead. When it is off, you can jam a fork in it all you want to get that last bit of bagel off. If hot and neutral are reversed, then the lever only turns off neutral. If you stick that fork in while you are grounded (touching the fridge, oven, sink, etc.) then you are going to get toasted by that hot lead. --—— Gadget850 (Ed) ^talk - 23:29, 26 January 2009 (UTC)

As an added precaution to the polarized plugs, you should install the sockets with the grounding plug *up*, not down (i.e., not a frowny face). That way when a picture frame or some other metal object slides down the wall it won't have any chance of being energized. --Sean 16:51, 27 January 2009 (UTC)

Compact fluorescent light bulb hooked up backwards

If a CFL is hooked up with the hot and neutral wires reversed, would it work correctly? I have a lightbulb socket that causes otherwise normal CFLs to light up dimly and flash. I'm wondering if reversed wiring is a possible explanation. ike9898 (talk) 20:45, 26 January 2009 (UTC)

Do you have it on a dimmer switch? Sometimes if you have an ordinary fluorecent tube fixture in the same circuit this can also happen.76.97.245.5 (talk) 21:06, 26 January 2009 (UTC)

No but it is on a circuit with a GFCI breaker (a breaker, not an outlet). Does that matter? ike9898 (talk) 17:26, 27 January 2009 (UTC)

Reversing hot and neutral wires cannot possibly affect operation of any device. It can only increase safety hazard for some (improperly designed) devices. -Yyy (talk) 07:51, 27 January 2009 (UTC)

Certainly reversing the hot and neutral can affect the operation of a device. My home had some light fixtures with an obsolete scheme of three-way switching which could energize the light socket with the tip of the bulb connected to neutral and the shell of the socket at 120 volts from neutral. The hot part was separated from a grounded metal outer surround of the socket only by paper, as in the normal construction of such a socket. One time when it was switched on, the 120 volt potential difference arced across the old paper insulation and before the breaker operated a glob of molten metal fell on the carpet. Had the phase and neutral been connected to the socket properly, such a large voltage difference from shell to surround would have not occurred. I rewired the circuit for modern 3-way switching, which required an additional conductor, and replaced the light fixture. Edison (talk) 17:32, 27 January 2009 (UTC)

Why do octane raings vary?

Why do unbranched hydrocarbons have lower octane ratings that branced or cyclic ones. Andy (talk) 22:01, 26 January 2009 (UTC)

They are easier to burn, probably due to more surface area exposed to oxygen. Graeme Bartlett (talk) 23:11, 26 January 2009 (UTC)

Cheers Graeme. Andy (talk) 07:11, 27 January 2009 (UTC)

Skin temperature and freezing

Hot water freezes faster than cold water.[35] Does the same hold true for flesh? In other words, if you were to sit in a sauna for a while and then go out naked into crazy cold temperatures, roll in the snow, etc. would you develop frost bite FASTER than you would with a normal skin temperature? --S.dedalus (talk) 22:09, 26 January 2009 (UTC)

I read that article and it looks like most of the proposed explanations are specific to it being a jar of water. Anyway, I'm certain that the determining factor in this case is how the wind flows past your body, which parts of yourself you rub deepest and more often into the snow, which parts of the snow are colder, which parts of your body were warmer than others to start with... the effect you referenced is only reliably measurable in consistent laboratory conditions; there's no way you could possibly roll around in the snow consistently. .froth. (talk) 22:25, 26 January 2009 (UTC)

The effect that makes hot water freeze faster almost certainly doesn't apply to flesh. However, other effects could cause you to get frostbite quicker after being very hot - your body will be adjusted to stay cool, so when you suddenly go outside it will take just time for your body to adjust to staying warm and you will lose a lot of body heat very quickly (I'm not sure how much "a lot" is - it depends on how quickly the body can adjust). --Tango (talk) 23:18, 26 January 2009 (UTC)

Your body works hard to maintain its temperature - going into a sauna makes it work harder to do that - but if you take your body temp with a proper core-temp thermometer - it's not going to vary by so much as one degree between the sauna and the snow...at least not until you're in a lot of distress. Also, the thing about hot water freezing faster than cold isn't REALLY true...at least not in a proper controlled experiment where the ONLY difference between the two pots of water is their initial temperature. If you think about it, it couldn't be any other way. Hot water has to first turn into cold water before it freezes! There are some rather specific circumstances where the nature of the stuff dissolved in water boils off and the nature of the cooling happening from the outside in when something is cooled rapidly rather than slowly CAN make it happen - but none of those special effects are true of your body. So not directly. However, one of the CRUCIAL things they tell you about being out and about in very cold conditions is not to work up a sweat - because as soon as you stop exercising, the sweat freezes and puts you in a lot of danger. So while a hot/dry body should do no worse than a cold/dry body, a hot/sweaty body will indeed be WAY more susceptible to the cold than a cold/dry one. SteveBaker (talk) 00:01, 27 January 2009 (UTC)

But the initial temperature apparently changes something about the chemical properties of the water to make it freeze faster. Or as the article said, convection currents (as parts of the water cool, the warmer water rises.. aka closer to the surface, so it can be more efficiently cooled) could play part .froth. (talk) 00:18, 27 January 2009 (UTC)

Yes indeed - all kinds of things that are not true 'in general' (and certainly aren't true for the human body). SteveBaker (talk) 00:48, 27 January 2009 (UTC)

The Mpemba effect really is true, you don't need really obscure circumstances, just two beakers of water and a freezer. --Tango (talk) 00:08, 27 January 2009 (UTC)

Actually - if you read the acticle - you'll find that 'special' circumstances are indeed needed. It just happens to be that the 'special' conditions are two cups stuck in a freezer! "The Mpemba effect is the observation that, in certain specific circumstances, warmer water freezes faster than colder water" - it's definitely not true in general. SteveBaker (talk) 00:46, 27 January 2009 (UTC)

Sure, but they aren't obscure circumstances, which is what I said. In fact, they are exactly the circumstances you would first use if you wanted to test for such an effect existing. --Tango (talk) 00:50, 27 January 2009 (UTC)

Yeah - I absolutely agree that the conditions aren't "obscure" (in the sense that you don't need a titanium klein-bottle in a helium/neon atmosphere with exactly 3.4 parts per million of iodine dissolved in the water) - but they are SPECIFIC - in that if you vary the conditions of the test to even a fairly small degree - the effect completely goes away. It's one of those odd coincidences that the simplest possible test of the effect works just fine - but any significant variation on the experiment fails to demonstrate it...and that's what matters here. An exposed human body out in the snow is not at all like a cup of tap water placed into a freezer (it's salty - it has an irregular shape - the liquid inside can't use convection to move around - it has an internal homeostatic heat source...you name it). Hence it's exceedingly unlikely to meet the SPECIFIC (but not OBSCURE) conditions of the Mpemba experiment and we can be reasonably confident (certainly to the degree required in a WP:RD response) in saying that the Mpemba effect does not apply in the situation our OP describes. SteveBaker (talk) 14:46, 27 January 2009 (UTC)

So can we say with confidence that, when thoroughly dried with a towel, a person immerging from a sauna will take slightly longer too developed frostbitten than a person with a normal skin temperature? --S.dedalus (talk) 19:31, 27 January 2009 (UTC)

January 27

Errors in casting plastics

Hi - I need a piece of terminology - what's it called when a mold produces a bad casting and you get something that's not the shape you intended?

Thanks,

Adambrowne666 (talk) 00:55, 27 January 2009 (UTC)

A dud ? I'm not sure if a malformed plastic casting has a specific name. StuRat (talk) 03:28, 27 January 2009 (UTC)

One type of imperfection in casting is flash, though this may be removed to obtain the shape you intended. -- KathrynLybarger (talk) 03:39, 27 January 2009 (UTC)

Thanks, yeah, probably there's no global term - I'm gonna go for a 'miscast', I think. Adambrowne666 (talk) 04:14, 27 January 2009 (UTC)

Spontaneous absorption of water waves

What is the formula for the rate at which deep water surface waves (both gravity and capillary) are absorbed by the water and the air above it, if they do not run into anything?

129.2.43.42 (talk) 01:22, 27 January 2009 (UTC)Nightvid (unregistered)

soap

Good day!

I would like to ask what is a germicidal soap and what are its effects?! or shall we say what are its applications-for what and for whom...

Your answer would be greatly appreciated.

Thank you and God bless! —Preceding unsigned comment added by 125.5.144.109 (talk) 02:50, 27 January 2009 (UTC)

An antibacterial soap is one that tends to kill bacteria. This is usually unnecessary, as washing bacteria off your hands is sufficient. There are some negatives, as well:

1) It can kill off helpful bacteria that control other health threats, like fungus.

2) It can kill off helpful bacteria in septic tanks, which decompose waste.

3) It can cause bacteria to develop a resistance, which makes it more difficult to kill them when they really do pose a threat. StuRat (talk) 03:23, 27 January 2009 (UTC)

That's why there's an increasing move to switch to bacteriostatic rather than antibacterial soap. 76.97.245.5 (talk) 03:46, 27 January 2009 (UTC)

Soap was invented around 3000 BC, During the 1970's someone thought "why don't we make soap that's BAD for bacteria." Apparently up to that time soap was enjoyed by bacteria as a nutritious food stuff. Bacteria fought back, hiring lobbyists who argue that use of antibacterial soaps should be restricted. —Preceding unsigned comment added by 76.125.8.141 (talk) 13:42, 27 January 2009 (UTC)

antibiotic resistance

Something has long bothered me about the antibiotic resistance discussions as applied to hand soap. The active ingredients usually used in antibacterial soap are triclosan or ethanol. However, it is physically impossible to use either of these compounds as internal antibiotics. The ratio required for ethanol (>60% by volume) would be fatal in the bloodstream, and triclosan is too insoluble in water to reach bactericidal concentrations in blood (normally it is suspended in an nonpolar solvent). Further, my understanding is that their chemistry and method of action is simply not related to any of the widely used internal antibiotics, so the risk of cross-resistance ought to be very low.

Hence my question is: Should people really worry about bacteria developing resistance to triclosan or ethanol? Would it matter? It would appear that even if bacteria developed resistance to hand sanitizer it would have little to no relevance in deciding how to fight an infection of that bacteria. Sure, it might be a little bad if hand soaps and the like lost their edge, but in the grand scheme of things being resistant to hand soap would appear to be independent of and far less troubling than resistance to things like methicillin. Dragons flight (talk) 05:36, 27 January 2009 (UTC)

No, the issue of resistance doesn't pertain, as the agents in hand soaps are antiseptics rather than antibiotics. - Nunh-huh 06:05, 27 January 2009 (UTC)

I think it's just a case of mislabeling. What they probably mean is that any surviving pathogens are likely to be very hardy and might be harder to kill with conventional methods. I agree that there is a lot of confusing (confused?) info out there. I read an article (reputable science site) where the interviewed researcher within 4 sentences first complained that increasing use of antibacterial cleaning agents in households would influence bacterial susceptibility to drugs, then he stated that although that had been shown in a petri dish an experiment conducted on an actual kitchen countertop failed to yield the same result. He followed that by saying if it were up to him he would only advocate use in hospitals because in a household you wouldn't need it anyway because the bacterial load was rather low whereas in hospitals it was high. Somewhere lower down was a comment that hospitals are breeding grounds for drug resistant strains. (So he advocates use of chemicals he suspects of increasing drug resistance in a place that already has a lot of that, instead of where it could not be shown to develop?) I read it several times, and then actually went and looked the guy up. He really was a researcher in a university lab. 76.97.245.5 (talk) 10:01, 27 January 2009 (UTC)

I have to disagree with both of the two previous posters.

@76.97.245.5: Sure - that was a bad report - but it doesn't mean that what the guy is saying isn't true - and it CERTAINLY doesn't mean that the reverse of what he says IS true!

@Nunh-huh: Your distinction between antiseptics and antibiotics is irrelevent.

But in general:

Whenever we provide some kind of stress factor in the life of a creature (be it a bacterium or an aardvarq), we're going to be affecting it's evolutionary development in such a way that it'll tend to be better at surviving in that stressed environment in the future. That's absolutely unavoidable - and it doesn't matter whether it's an "antiseptic" or an "antibiotic" - the result is the same. (From the lead paragraph of our Antiseptic article:

"Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. They should generally be distinguished from antibiotics that destroy bacteria within the body, and from disinfectants, which destroy microorganisms found on non-living objects. Some antiseptics are true germicides, capable of destroying microbes (bacteriocidal), whilst others are bacteriostatic and only prevent or inhibit their growth. Antibacterials are antiseptics that only act against bacteria. Microbicides which kill virus particles are called viricides."

But it really doesn't matter. Antiseptics, antibiotics, disinfectants, germicides, bacteriocides, bacteriostatics, antibacterials, microbicides AND viricides - all apply stress to their intended targets and if they are anything less than 100% effective at preventing their chosen victims from ultimately reproducing - they WILL cause evolutionary pressure. (It's tough to be 100% effective because at the boundaries of the area the substance was applied over, there is guaranteed to be some place where it's present in non-lethal doses - and right there, a creature can survive and evolve tolerance)

Once you have evolutionary pressure - you'll tend to get resistant strains developing.

Hence, the rule is that you shouldn't use ANY of those things unless you actually need to. We got along just fine without antibacterial/whatever soaps, baby-wipes, TOYS(!), etc - and introducing them is a bad idea regardless of whether you happen to be able to induce evolutionary effects in the lab. Evolution is a valid scientific theory and you don't need to keep doing experiments to prove it. Just as we know that brand X bowling balls will fall if you let go of them without having to do the experiment - so we know that creatures will tend to evolve without doing the experiment. If you can't reproduce it in the kitchen but you can make it happen in the petri dish then you certainly need to ask why that is and set up experiments to find out why - but it shouldn't lead you to conclude that evolution doesn't work in the kitchen because extraordinary claims require extraordinary evidence. We should behave as if the hypothesis that evolution doesn't work on kitchen countertops is false until such time as someone proves it and manages to explain why.

So, with what we currently know (which is all we ever have to go on) - we shouldn't use these products in the kitchen because the consequences of failing to do so are not severe. But we may be forced to use them in hospitals where the consequences of infection are vastly more serious because of all of the sick people spreading nasty bacteria everywhere - and all of the open wounds and so forth. Resolving the issue of bacterial and viral resistance to antimicrobials in hospitals is a serious one - but it's not relevent to the question of whether we should make matters worse by using them when we don't need to in our own homes.

SteveBaker (talk) 14:24, 27 January 2009 (UTC)

Steve, There's some kind of flaw in this argument, in its most general form, isn't there? I see some sort of assumption that organisms have an unlimited capacity to cope with any number of evolutionary pressures. In practice if you put a pressure on a zillion parameter system sure it will adapt to that pressure but the adapted point will not be as optimal at some other things as the unpressured system. So your bacteria may adapt to survive repeated exposure to 55% alcohol when it couldn't before but it will be worse at something else. Which depending on your reliance on the hard soap may or may not be a worse situation than before. Sure if you are talking about an antibiotic you need to cure someone you don't want to stress it that way but if you are talking about something which doesn'r really matter I find it hard to buy the argument.--BozMo talk 15:03, 27 January 2009 (UTC)

Sure - the bacterium that's resistant to dilute alcohol will be worse at something else - but in evolutionary terms, it only has to be better off than it's competition. So every time you use dilute alcohol, you'll wipe out more of the 'capable' bacteria and give the resistant (but otherwise worse) ones room to grow and thrive. The problem is that the 'worsening' may be (say) the loss of the ability to metabolize pink food coloring or something. That loss isn't measurably to our gain - and we can't control or (easily) predict what that 'worsening' might be. Worse still, when you set loose a new set of genes, you don't know WHAT the effect will be. It could just as easily result in a change of the 'coating' of the bacteria and thereby cause all of us humans to lose our antibody-resistance to the darned thing. SteveBaker (talk) 16:36, 27 January 2009 (UTC)

Agree but AFAICT in general "big" stresses (e.g. surviving in salt water or Dettol) seem to take a lot out of bacteria: they don't seem to ever manage one of these and still be able to compete with other bacteria well when the stress is absent. --BozMo talk 21:05, 27 January 2009 (UTC)

Lots and lots of things can place an evolutionary pressure on bacteria though, and almost no one worries about their impact. For example, ordinary (non-bactericidal) bar soap, dish soap, and laundry detergent will all remove bacteria. Presumably this creates an evolutionary pressure for bacteria that cling more firmly to their environment to avoid being washed away. However, you'll never hear people advocate that we stop using soaps entirely. Similarly, the wide spread use of food preservatives presumably encourages "preservative resistant" bacteria, but I've never seen people get crazy about preservative resistance the way some people do about hand soap. It just strikes me that the way some people focus on antibacterial hand soap is way out of proportion to the danger. Dragons flight (talk) 15:41, 27 January 2009 (UTC)

That's true - but the things you've described are truly necessary to us. Antimicrobial washing up liquid is of negligable benefit - it's purely an advertising bullshit thing - and we don't need to use it. Food preservatives, however are necessary to our way of life. SteveBaker (talk) 16:36, 27 January 2009 (UTC)

For an example of where antibacterial soaps should be used, hand-washing in areas prone to MRSA comes to mind: MRSA#Hand_washing. StuRat (talk) 15:14, 27 January 2009 (UTC)

question about HIV/AIDS

how does science, technology and communications address issues of HIV/AIDS and gender mainstreaming —Preceding unsigned comment added by 196.33.11.13 (talk) 12:21, 27 January 2009 (UTC)

This sounds like a homework question to me. On the off chance it isn't, perhaps you would care to provide a little more information about what, specifically, you're interested in? -- Captain Disdain (talk) 12:47, 27 January 2009 (UTC)

Writing a college essay involves first determining what the question means. College professors are often not models of clarity. I think they sometimes get fed up and try to trip the class up. Sometimes they actually think what they wrote makes sense, not realizing that they're begging the question. Sometimes they're drunk when they write it, I suppose, which would explain a lot. The second step is to guess what the professor wants to see. This is important only to the extent that your grade is important. You can learn the material thoroughly and become the most proficient person in the world in your pursuit and still get only a "C" if you don't follow this second step. Often, too, your paper will be graded by a graduate student with a checklist looking for key concepts and facts, and you should try to guess what these will be. In this case, we start at a disadvantage because the grammar of the question is bad ("does" should be "do"), so we can look forward to getting marked off for correct English, always frustrating. Another problem is the jargon. What is an "issue"? Professors love that word. I've never been able to tell whether they use it because they think it has a meaning, because they want to leave things open-ended, or because they're just being bloody-minded. And good luck figuring out what "gender mainstreaming" is. That really pisses me off. I'll bet your professor just got done having a big argument with his mistress over the term, and he wants to see what you'll all say about it so he'll have more arrows in his quiver the next time it comes up in a symposium. Anyway, good luck, and don't sweat it. Think it's easy, and it will become easy. --Milkbreath (talk) 12:57, 27 January 2009 (UTC)

...OR...

You could just say:

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

SteveBaker (talk) 14:03, 27 January 2009 (UTC)

There's nothing wrong with telling people generally how to go about thinking of how to answer questions when it is clear that's probably what is at stake here. Saying "do your own homework" is concise but it isn't always the most useful answer (and I mean "useful" here in the true sense, not in the sense that giving them the answer would be "useful" in the long run). Teach a man to fish, and all that. --140.247.241.150 (talk) 17:51, 27 January 2009 (UTC)

I too thought "gender mainstreaming" was just meaningless jargon, but truly we have an article on everything. Gandalf61 (talk) 17:01, 27 January 2009 (UTC)

Silly me. Now that I know it's about differential implications.... --Milkbreath (talk) 17:28, 27 January 2009 (UTC)

If it was about differential integrations it would be much easier, by the Fundamental Theorem of Calculus. You could probably submit the question, (+C), and not get a C+ ... Nimur (talk) 18:32, 27 January 2009 (UTC)

Vines climbing around a tree

Why do vines climb upwards around a tree in a clockwise direction(if looked from above)? —Preceding unsigned comment added by 202.70.74.137 (talk) 15:15, 27 January 2009 (UTC)

You may have selection bias. I spent three years trying to tame the wisteria on my trees. It grows wherever it likes, in whatever direction it likes. -- kainaw™ 15:17, 27 January 2009 (UTC)

Apparently this is an active area of research; try googling "vines clockwise". It seems most vines twist counterclockwise, but that we haven't figured out why yet. Perhaps something to do with the chirality of biological molecules. --Allen (talk) 15:37, 27 January 2009 (UTC)

Why are 90% of people right handed? Why do most sea shells twist in one direction? Why do (nearly) all of us have our hearts, livers and pancreases on one particular side? Why do ALL animals and plants have the same chirality of biological molecules? If there is not advantage to one asymmetry over the other - why isn't there a 50/50 mix? The reason is that we're all descended from a single individual. So in this case, once the gene for a particular direction of twist got to become the ancestor of all modern vines - only an evolutionary change in the twist-direction gene could cause opposite-direction-twist to happen. Since there is likely to be ZERO evolutionary benefit to twisting in the opposite direction to all of the other plants - that gene would not reproduce preferentially to the 'normal' direction and could easily simply fade from the gene pool because it's so rare. Genes only spread when there is some benefit to the creature that possesses that gene. Left-handedness in humans is a bit different - it is thought to hang around because we are tribal creatures and there is a benefit to every community of humans to have a few left-handed people because our brains are wired up differently. Hence communities in which left-handedness dies out are at a disadvantage compared to those where it remains - and hence there are always a few lefties around (including an unreasonably large percentage of US presidents, architects and 3D computer graphics people!). SteveBaker (talk) 16:23, 27 January 2009 (UTC)

Before we compare to handedness, we could at least provide a non-google reference that it's intrinsic to the plant and not the environment. There seem to be a lot of news stories re-hashing this same research. [36] [37] APL (talk) 17:12, 27 January 2009 (UTC)

I agree with APL. Steve's explanation sounds plausible, with the quibble that vines are not a monophyletic group, so any shared twist-direction gene would probably be doing more than determining twist-direction. But most researchers seem to agree that vine twining is an unsolved question. Same with handedness... there seem to be multiple active hypotheses for the proportion of left-handedness. And Steve's explanation requires group selection, which is controversial. --Allen (talk) 20:24, 27 January 2009 (UTC)

I wonder if the OP is from a hemisphere opposite Kainaw's, though; there's part of me that remembers an experiment with toilets flushing a different direction in the northern hemisphere from the southern, and wondering if vine growth has to do with the rotation of the earth. —Preceding unsigned comment added by DTF955 (talk • contribs) 17:59, 27 January 2009 (UTC)

Er - you do know that the toilet-flushing thing is a myth don't you? The coriolis forces are VASTLY too tiny to produce either that - or the vine rotations...so no. SteveBaker (talk) 18:31, 27 January 2009 (UTC)

Ohh, now I donno about that…surely if the [[Coriolis forces] are strong enough to create left- rather than right-hand traffic in Australia and New Zealand, they're strong enough to make water spiral the wrong way down the sink. ← The preceeding text is a joke. It is not intended to inform or educate. —Scheinwerfermann ^T·_C21:01, 27 January 2009 (UTC)

Vine-twisting direction seems to have been noticed only quite recently. I wonder why botanists did not notice it generations ago. What else is being overlooked in botany? And what is being overlooked in other branches of science? Medical school students are told to pay attention to details about a patient and his ailment; but that does not seem to be stressed for college students in other areas of learning. In everyday life we ignore many, many, small details - we would go nuts if we paid great attention to everything. But in science, and in professions, attention to details within the area of interest is needed. (The transistor was discovered by investigating a small detail in the action of diodes.) On the other hand, a scientist should not become so immersed in details that he overlooks the big picture. In this regard, details may be sought in order to support a pre-existing conjecture. For instance, Darwin studied details in biology with a predetermined objective. He wasn't just accumulating facts (though that can be useful to aid further work in science by others). Darwin's predetermined objective was to place evolution on a firm basis. Thus, there are two goals in science. One is to accumulate facts. The other is to put 2 and 2 together to make 5 (idea synthesis). Sometimes the "accumulating" approach in science leads to the other approach – the very act of accumulating related facts can bring to light an overall concept that was not seen at all before. Even in everyday life a serendipitous juxtaposition of seemingly unrelated facts will occasionally reveal an overall concept not seen before. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:22, 27 January 2009 (UTC)

It's not a recent discovery, Charles Darwin wrote about it. I always thought it was because the plant was phototropic following the sun as it went around the sky. Graeme Bartlett (talk) 20:12, 27 January 2009 (UTC)

Surely that would only work if they were growing an entire loop around the tree each day? I don't think they grow that fast. --Tango (talk) 20:19, 27 January 2009 (UTC)

No, it could just be that they're influenced at some critical point. But the articles I link indicate that the influence of the sun's motion has been ruled out as the cause. APL (talk) 20:25, 27 January 2009 (UTC)

Help on Forces

Does Contact force exist even when there is no gravity. Bold text CAN YOU DIFFERENTIATE NORMAL CONTACT FORCE FROM CONTACT FORCE??? And further more...what is the newtons third law pair for contact force acting on the feet of a gecko that clings to a wall which is perpendicular to the ground??? —Preceding unsigned comment added by 123.49.43.236 (talk) 17:52, 27 January 2009 (UTC)

Certainly. Gravity is just a force - you could substitute a different force. Magnetism, say. Also, that nice Mr Einstein told us that acceleration and gravity are indistinguishable for all laws of physics - so in deep space an object accelerating at 1g would produce exactly the same effect. The teeny-tiny hairs in the gecko's foot are sticking to the glass through Van-de-Waal's forces at the atomic level. SteveBaker (talk) 18:30, 27 January 2009 (UTC)

It seems really unlikely that in any circumstance, the Contact Force would be in any other direction than normal. Does anyone know of any counter-examples? If there are any, they are probably not in macroscopic, "standard" situations. Nimur (talk) 18:39, 27 January 2009 (UTC)

Most stuff eaten at once and eating things whole

Since I'll be gone on April Fools Day, I ask this question now that was on my mind.

The song about the old lady who swallowed a fly has her eating huge amounts of things at once, apparently whole (though it's not said for sure; she's likely nuts as it is, so she could have odd ideas about what can catch what, but anyway...).

My questions are: 1. How much is the most one person has eaten at one time? I've heard of ten-pound burgers someplace, I think. 2. I doubt one could even get a cat down one's throat, so we'll go with a bird; suppose someone was able to swallow a very small bird whole; how long would it survive in the stomach before being attacked by the stomach fluids and killed? Long enough to find the spider?

Take note - anyone who claims this question is asking for medical advice will be laughed at for days. :-)Somebody or his brother (talk) 18:08, 27 January 2009 (UTC)

Well, our stomach article states "in humans, the stomach has a relaxed volume of about 45 ml, it generally expands to hold about 1 litre of food, but can hold as much as 4 liters." Certainly the limiting factor is the circumference of one's esophagus. According to this article average diameter is 2-3cm (.78-1.1 in), so 6.3-9.4 cm (2.4-3.5 in) circumference. -- MacAddct1984 ^{(talk &#149; contribs)} 18:30, 27 January 2009 (UTC)

Surely the esophageal cross-section is not of fixed size? Nimur (talk) 18:37, 27 January 2009 (UTC)

Yeah, it must expand to a point, I couldn't find much about it though. If a bird did manage to get down someone's throat, I'm sure finding and eating an already decomposing spider is the last thing on its mind. Also, we happen to have an article on There Was an Old Lady Who Swallowed a Fly. -- MacAddct1984 ^{(talk &#149; contribs)} 18:43, 27 January 2009 (UTC)

Wow, there is an article on everything here. :-)Somebody or his brother (talk) 19:21, 27 January 2009 (UTC)

Not forgetting 'a papper theen waffer' [[38]] Laughed at for days, eh? - ooh, blimey!! Richard Avery (talk) 19:41, 27 January 2009 (UTC)

66 hot dogs in one sitting. You might also want to check competitive eating. Clarityfiend (talk) 20:04, 27 January 2009 (UTC)

Please see the International Federation of Competitive Eating Records List. These guys are pretty much the authority. The most impressive item on the list in my opinion is the 21 lbs of grits eaten in 10 minutes. Anythingapplied (talk) 20:51, 27 January 2009 (UTC)

Does this count as "whistling"?

Hi. I know a method of "whistling" different from conventional whistling. Place the tip of your tongue loosely on top of your lower teeth, then place your upper teeth loosely on top of your tongue, and very slightly behind your lower teeth. Pucker your upper lips up towards your nose, close your jaws slightly, then blow a steady stream of air through your upper teeth and the gap in your lips, while slightly puffing your central and upper cheeks. It should make a high-pitched sound. Now, I find that using this method, I cannot control the pitch of the whistled note, and it isn't always continuous. However, would this still count as whistling or not? Thanks. ~AH1^(TCU) 19:17, 27 January 2009 (UTC)

See Whistling#Types. Seems to me like it's still whistling, unless by "still count" you mean you're planning to enter a whistling contest and don't want to be disqualified. Coreycubed (talk) 19:50, 27 January 2009 (UTC)

Autoclaving liquid

When autoclaving liquid, one is always instructed to use an oversized container so that the liquid will not escape if it starts to boil. When you use the 'liquid' cycle on the autoclave, at the end of the cycle the pressure drops slowly to prevent boiling over.

My question is, in practice does liquid (an aqueous solution such as microbial media) commonly boil in a autoclave run on the liquid cycle? That is, is the oversized container really just a redundant precaution, and the liquid will not boil as long as the autoclave works correctly? ike9898 (talk) 21:08, 27 January 2009 (UTC)

osmole confusion

I`m just reviewing some renal stuff, and I`ve realized I`m confused on a pretty question:

If I took 500 sodium molecules and put them in 1 L in one container. In another contained, I put 500 glucose molecules.

Which would have the greater osmolality?

--Cacofonie (talk) 21:39, 27 January 2009 (UTC)