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November 2

Gravitational collapse

Hi, how big would a planet with the same composition as the Earth have to be before it collapsed into some kind of super-dense exotic matter? 86.151.118.165 (talk) 02:51, 2 November 2012 (UTC)

Well, something with the same composition as the Earth but with the mass to form a black hole wouldn't be a planet, it would be a star. That is, nuclear fusion would support it until everything that could fuse had fused, then it would collapse into a black hole. Around 10 times the mass of the Sun seems to be enough to form a black hole, but I'm not sure if the composition of that mass changes the equation. StuRat (talk) 03:07, 2 November 2012 (UTC)

I am not necessarily talking about a black hole. In fact, I specifically didn't mean a black hole. 86.151.118.165 (talk) 03:17, 2 November 2012 (UTC)

Like neutron stars? Plasmic Physics (talk) 03:45, 2 November 2012 (UTC)

Or white dwarfs perhaps... Whatever is the first stage of exotic matter that is far denser than any ordinary matter that we are familiar with on Earth could be. 86.151.118.165 (talk) 04:06, 2 November 2012 (UTC)

... also, I am specifically not asking about stars. I literally mean that you take a rocky planet, same composition as the Earth, scale it up by x amount, then how big before there's a big crunch and it squishes down to a lump of exotic matter. 86.176.211.219 (talk) 04:45, 2 November 2012 (UTC)

I just did a back of the envelope calculation which came as 78.2 times the radius of the earth for it to collapse into a neutron star (using 2.84 E 30 as the collapsing mass from the Netron star article and 5500 kg/m^3 as the density of the earth). But that doesn't sound right (also, apologies for the lack of math tags, its to early for me to remember how to do them) 80.254.147.164 (talk) 09:56, 2 November 2012 (UTC)

(edit conflict) Well, our white dwarf article says the smallest estimated mass for a white dwarf is 0.17 solar masses, which is about 56,000 Earth masses. So a rocky planet (I am assuming "rocky" means insufficient hydrogen or helium to support fusion reactions) with the same average density as the Earth but about 40 times the Earth's radius would collapse under its own gravity to form something like a white dwarf. I have no idea how such a massive "rocky planet" object would form in the first place - maybe we just have to assume it appears from nowhere. Gandalf61 (talk) 10:01, 2 November 2012 (UTC)

You don't necessarily need hydrogen or helium. Silicon and oxygen, the two most abundant elements in the Earth's crust, will undergo fusion if you get them hot enough and squeeze them tight enough.

Iron, on the other hand, will not, and I kind of doubt nickel will either; these are the main components of the core.

So the bottom line is that I kind of doubt StuRat's claim about fusion, but the question can't be disposed of completely trivially. --Trovatore (talk) 02:12, 3 November 2012 (UTC)

How's this for a paraphrase: How massive can a body be before degenerate matter appears at its core? —Tamfang (talk) 19:08, 2 November 2012 (UTC)

Metallic hydrogen is degenerate matter and is thought to be present in the cores of Jupiter and Saturn. Gandalf61 (talk) 19:24, 2 November 2012 (UTC)

Whenever the mass is large enough to cause a force that overcomes the atomic weak interaction ..?, But I also wonder what actually happens when a body of elements that are more dense than iron-26 gets forcefully compressed and heated ? Electron9 (talk) 18:29, 6 November 2012 (UTC)

Avalanche rescue

Is earth-moving equipment used to rescue avalanche victims? If so, how do they make sure that survivors are not accidentally killed by it? 24.23.196.85 (talk) 05:19, 2 November 2012 (UTC)

I've always wondered the same when it comes to rescuing survivors from debris after a tornado, building collapse, etc. Ks0stm ^{(T•C•G•E)} 05:27, 2 November 2012 (UTC)

Only a WAG, but I wouldn't think so. Time is of the essence and getting heavy equipment into position would take too much of it. Clarityfiend (talk) 07:35, 2 November 2012 (UTC)

Agreed, you have minutes, at most, to dig the person out. Also, if they are buried so deeply in snow that shovels won't work in time, then they are already dead, due to the pressure. And, the main problem isn't digging the hole to get them out, it's finding them in the first place. StuRat (talk) 17:28, 2 November 2012 (UTC)

The usual method is to for rescuers to form a line, poking through the snow with a long pole called an avalanche probe and hoping to be able to recognize the resistance when the probe hits a body. Trained dogs are used to refine the search. I found this photo of the Galtür Avalanche, which appears to be using this technique. This photo shows a dog guiding a team of rescuers armed with avalanche shovels. 20 people who had been buried were rescued but a further 31 died. Alansplodge (talk) 18:07, 2 November 2012 (UTC)

And I have just found our Avalanche rescue article. Alansplodge (talk) 18:08, 2 November 2012 (UTC)

Thanks for the input, everyone! Now, what if the avalanche also buries several buildings and cuts the only road into the area -- would a bulldozer be useful to uncover the buildings and/or clear the road, or would the same techniques be used as for the victims on the slopes? 24.23.196.85 (talk) 01:11, 3 November 2012 (UTC)

Yes, bulldozers or snowplows would be used to clear the road, provided there aren't any victims believed to be present, and in the area around buildings, but not the buildings themselves, if they were believed to contain victims. Buildings have more of a possibility of air gaps inside, so people might survive for quite some time. StuRat (talk) 01:18, 3 November 2012 (UTC)

Thanks a million, and clear skies to you! 24.23.196.85 (talk) 02:53, 3 November 2012 (UTC)

Mushrooms and mycelium

Hello there reference desk. I'm trying to work out what is known about fungal lifecycles in terms of the variety of types of mushroom a single 'lump' of mycelium can produce. I'm most interested in the Euholobasidiomycetes, as this seems to be the group containing most of the mushroom producing fungi.

I realise it's fairly hard to give good answers as the genetics of some fungi aren't that well understood at the moment. As far as I can tell, a single spore from a mushroom contains a haploid nucleus that will start a mycelium colony growing. Some species have asexual reproduction methods, but most will have to interact sexually with another 'compatible' mycelium colony before producing fruiting bodies. At this stage, I started getting bogged down in detail - but it seems that some species of mycelium have the ability to acquire and incorporate more and more genetic material. There was also talk about varieties of mushrooms previously though distinct that turn out to be genetically identical. My questions are:

1. When fungi are said to be sexually compatible, does this mean that they are the same species in a way analogous to plants and animals?

2. Many species seem to end up with multiple, genetically distinct, haploid nuclei in their cells after various complicated genetic processes. Will the spores dispersed by a mushroom represent the entire genetic material of a fungus, or are all spore from one mushroom the same (barring chance mutations.)

3. What kind of variety of mushrooms can one mycelium colony (assume indefinite sexual encounters if this is necessary) produce?

The main site I've been using is . I'm sure the information is in there, but it's very dense and I can only get comfortable with 10 or so terms of art per sitting...80.254.147.84 (talk) 08:46, 2 November 2012 (UTC)

1.Depends on how you choose to define species and what you mean by "sexual compatibility". Generally, a species is defined as "a group of organisms capable of interbreeding and producing fertile offspring". So...

• Yes, if by "sexual compatibility" you mean the capability of the individuals in the population to reproduce with another individual within the group (inclusive of mating type barriers between individuals among heterothallic fungi).
• No, if you mean sexual compatibility merely in the sense of individual mating type compatibility. In the same way that just because two human males can not reproduce with each other, does not mean they belong to different species (although the latter analogy is vastly oversimplified given that fungi can have thousands of "biological sexes").
• Overarching all that is the species problem. If you follow a morphologically defined concept of species, some fungi populations can remain morphologically identical (cryptic species), even when in truth they have diverged and achieved reproductive isolation from each other long ago. Indeed, until the very recently (2011 International Botanical Congress) fungi were given different scientific names for different morphs in their life cycles (see teleomorph, anamorph and holomorph), even if they are all the same species, largely because they can look radically different.

If you follow biological species concepts which relies on reproductive isolation, it can fail in complex reproductive relationships where some groups can reproduce with some other groups but not with others and vice versa; while others still are actually not reproductively isolated but will only mate under certain conditions that might be missed in laboratory environments; and it does not take into account where the capability of interbreeding may simply be the result of retained ancestral characters (plesiomorphy) when in truth the individuals themselves have become genetically isolated a long time ago.

Phylogenetic species concepts addresses the latter by restricting groupings based on shared ancestors, but it runs into the problem of where to place the boundaries. How do you divide into species what basically is a genetic continuum broken only by extinctions? The latter problem exists even in higher animals but is more evident among fungi, where even trying to define an "individual" itself is difficult due to the fact that they barely qualify as "multicellular organisms". So the similarities and differences on how higher organisms are classified depends on which system is followed or combinations thereof.

2.The most common, asexual spores, are of course geneticaly identical to the parent. Though apparently some long-lived fungi colonies have been discovered to essentially be genetic mosaics, possessing genetic variation within a sngle "individual", so spores from the same individual can be different in those circumstances even if produced asexually.

Sexual spores in contrast are the result of the meiosis of a typically brief diploid stage and thus will differ from each parent. Spores that result from mitosis after meiosis are of course genetically identical to each other, but not to the others.

Thus in Ascomycota, for example, the nuclei from the two parent individuals (not genetically identical) fuse to each other (karyogamy) and form the diploid zygote nucleus. The diploid zygote nucleus then undergoes meiosis, exchange genetic information here and there, and in the end divide into 4 genetically different haploid daughter nuclei. Each of the daughter nuclei then undergo mitosis, such that they create genetically identical copies of themselves. This usually results in 8 ascospores, with every two ascospore genetically identical with each other, but not to the other pairs. Basically, they're a set of 4 twins. This series of diagrams might help. Basidiospores are more or less the same, except that in Basidiomycota, the two haploid nuclei of the parent individuals coexist in the same cell (even vegetative ones) for a longer time without undergoing karyogamy.

3.I'm assuming you mean how many genetically different individuals can result from a single mycelium colony through sexual reproduction. Well as many as all the possible permutations I guess. :P That's a bit like asking how many genetically different children two human couples can produce assuming they have an indefinite number of sexual encounters. Barring twins, no two children will be genetically the same, though they can be genetically similar.

Disclaimer: not a mycologist, merely rehashing uni biology lessons. :P -- OBSIDIAN†SOUL 09:57, 4 November 2012 (UTC)

3d tracking tic-tacs

I have the following requirements. (Basically I would like to track the 3d location of a few things in near-field like bluetooth-distnace)

1. Glue ten tic-tac size devices to ten spots within a 40cm x 40cm x 40cm area.

2. Know in real time the location of each device #1 - #10 with a 2mm x 2mm x 2mm margin of error, within a 3m x 3m x 3m space (no tracking required if they leave this space). The response should be within 100 ms but preferably 15-20 ms.

Any technological solution could be considered.

--

My thoughts. The devices can be active (know their own location) or completely passive, like an RFID strip, and activated remotely by a reader or base station. It also doesn't matter if the location is only relative to some point of origin. And although the tic-tacs should be small, there can be a considerably larger base station or receiver.

Now, I realize there are many, many approaches here. Hollywood tends to use 3 or more cameras and interpolate exact position of the tic-tacs. The tic-tacs could have gps devices, then their precision and response is much, much worse than my requirements. The tic-tacs could be physically connected to rods that can move in 3d (in-and-out and pivot on a ball) that register their relative movements. Or they might somehow have radio signatures that the base station can interpret.

They could be magnetized and the magnetic signatures detected by a very large base station. They could be radioactive or emit xrays and be detected by their signatures on that basis. (Then the base station would have to have 3 planes, maybe).

What is the simplest, cheapest solution here? I would think that if there were some radiofrequency-based thing where there is a somewhat largish base station then it would work.

What do mimeo whiteboard digitizers use, for exmaple, like this - http://www.mimio.com/en-EM/Products/MimioCapture.aspx (scroll down)

or how do Wacom tablets digitize the location of a passive plastic stylus?

I don't really know the space of technologies that can meet the requirements. Your creativity is appreciated here, thank you. --91.120.48.242 (talk) 09:20, 2 November 2012 (UTC)

It sounds like a pretty traditional motion capture problem. I don't think there are many options out there other than optical systems like you mentioned. Does a marker and camera based solution work for your problem, or is there a reason you need something more technical? 209.131.76.183 (talk) 13:25, 2 November 2012 (UTC)

I just think that a passive radio emitter would be less technical, not more technical. RFID strips are incredibly low-cost. Isn't there a way to get a receiver to triangulate the position of a passive radio device? This seems like it's gotta be far less expensive from trying to get a line-of-sight and markets. I also just cannot believe that markers can be precise enough to my tolerances, e.g. 2-5 mm. --91.120.48.242 (talk) 14:58, 2 November 2012 (UTC)

That does sound like a sensible solution, though I think that's not "RFID" proper but some more basic type of radar signature - the key here is that waiting for digital operations to return a serial number seems like it should introduce too much timing uncertainty to measure the distance according to speed-of-light time delay. Triangulating the signal according to intensity or exact angle of displacement seems like it would be very tricky. But take what I say with a shaker of salt, because it's not my field. Wnt (talk) 18:06, 2 November 2012 (UTC)

You said they will be glued down, but glued down to what ? Rods ? StuRat (talk) 17:23, 2 November 2012 (UTC)

Hi! That is one possibility, but better is if they are just glued to the locations. The question is how to locate these in 3d space (not 6d, you don't need to know orientation at all). The rod idea is the worst one that I can think of, since it involves physically connecting these tic-tacs, instead of letting them move freely with the body they are on. 178.48.114.143 (talk) 17:47, 2 November 2012 (UTC)

What "body" are they on ? StuRat (talk) 18:02, 2 November 2012 (UTC)

Fine joints on a human body, glued on lightly thereto. In fact though they can be slightly tethered to some kind of slightly larger thing held on with a band, that is fine. this seems to be what the reference i found below was about. 178.48.114.143 (talk) 11:17, 3 November 2012 (UTC)

One potential problem, do we need to account for the possibility that one of the "tic-tacs" can be behind another, or behind a rod, from the POV of one of the detection devices ? StuRat (talk) 17:17, 2 November 2012 (UTC)

They can indeed be behind each other. I think something radio-based is the best idea. Does such technology exist? THey could be on different frequencies. So, the idea is if you have ten of these on ten unique frequency, say, and passive radio emitters that emit their frequency in response to a base frequency - then the receiver emits that frequency, and gets ten point sources corresponding to the ten different tic-tacs. THrough radio trangulation would it be possible to locate each to within 2mm by 2mm by 2mm? You don't need to know their orientation. 178.48.114.143 (talk) 17:47, 2 November 2012 (UTC)

The technology exists, but I don't think you can get that type of resolution out of it. Here's a company that offers such an RFID system, but to work on larger scales: [1]. StuRat (talk) 17:59, 2 November 2012 (UTC)

could you talk about the physics behind it ,and why it wouldn't work for radio, ultrasound, or magnetic-production and sensing respectively? 178.48.114.143 (talk) 11:17, 3 November 2012 (UTC)

The motion scan article claims that radio systems are less accurate, which makes sense when you start looking into the wavelength of the signals. Hollywood uses optical systems because they are relatively simple and have the best accuracy. Similar problems occur in industrial automation, and there is a large industry based around sensing locations in that market. If you have a good budget for this project, I recommend talking to motion capture or industrial sensing companies for ideas. If you're trying to make something from scratch on a low budget, optical is probably the simplest. 209.131.76.183 (talk) 18:08, 2 November 2012 (UTC)

This is an interesting contribution. Could you help me make sense of this research paper:

“ J Neurosci Methods. 1998 Sep 1;83(2):125-31.

Using miniature sensor coils for simultaneous measurement of orientation and position of small, fast-moving animals. Schilstra C, van Hateren JH. Department of Neurobiophysics, University of Groningen, The Netherlands.

Abstract

A system is described that measures, with a sampling frequency of 1 kHz, the orientation and position of a blowfly (Calliphora vicina) flying in a volume of 0.4 x 0.4 x 0.4 m3. Orientation is measured with a typical accuracy of 0.5 degrees, and position with a typical accuracy of 1 mm.

This is accomplished by producing a time-varying magnetic field with three orthogonal pairs of field coils, driven sinusoidally at frequencies of 50, 68, and 86 kHz, respectively. Each pair induces a voltage at the corresponding frequency in each of three miniature orthogonal sensor coils mounted on the animal.

The sensor coils are connected via thin (12-microm) wires to a set of nine lock-in amplifiers, each locking to one of the three field frequencies. Two of the pairs of field coils produce approximately homogeneous magnetic fields, which are necessary for reconstructing the orientation of the animal. The third pair produces a gradient field, which is necessary for reconstructing the position of the animal.

Both sensor coils and leads are light enough (0.8-1.6 mg for three sensor coils of 40-80 windings, and 6.7 mg/m for the leads, causing a maximal load of approximately 5.7 mg) not to hinder normal flight of the animal (typical weight 80 mg). In general, the system can be used for high-speed recordings of head, eye or limb movements, where a wire connection is possible, but the mechanical load on the moving parts needs to be very small."

”

if I understand it correctly, this is sensors lead by a small wire. THis would be fine for me - the sensors would be attached to the fine joints and lead to a wire on a band around a heavier body part. Would this be doable? very expensive? Could you help me interpret the science in this article? THanks. 178.48.114.143 (talk) 18:46, 2 November 2012 (UTC)

• Hmmm, I'm thinking two bar code scanners, if you have one with a red laser, one with a green laser. The tic tacs contain photosensors that can tell when red or green is detected with very good temporal resolution. If they know when the laser beam is supposed to reach a certain spot in a 2-d grid pattern, and they can do it based on two separated points with the red and green, then they know their 3d location. This assumes the laser makes a thorough grid sweep (enough to hit any given spot a tic tac can be) and that you have enough understanding of the software to know when it hits that spot with great temporal precision - not sure either is true for a standard scanner. Wnt (talk) 17:55, 2 November 2012 (UTC)

This is an interesitng thought, I will keep track of it along with the others. I wonder if making the actual end-point "sensors" dumber however and the receptor smarter isn't the better way to go maybe? 178.48.114.143 (talk) 18:46, 2 November 2012 (UTC)

Heat transfer and temperature

I'd like to know if it is possible to estimate how hot an object will get over time when placed near a heat source. My specific problem is this: I have a wood stove that will have a surface temperature of about 300-500 C (?). I also have paint for a concrete wall behind the stove and the paint can take about 120 C. What I'm wondering is how close to the stove I can paint this wall and not burn my paint later. The shortest distance between wall and stove is about 30 cm, the longest (from top of the stove to top of the wall) about 150 cm, and there is some airflow between stove and wall. The max time the stove would be used would be around 2-3 hours/day (the time it takes to make food & heat the room). I'd like to paint as close as possible. I've read articles about heat conductivity, radiation etc but I'm none the wiser.

I don't know if this question is enough about science, but I couldn't figure out another place to ask this. --88.148.221.134 (talk) 13:09, 2 November 2012 (UTC)

I suspect that the paint will be fine, especially if it is white to help reflect the radiated heat. The concrete wall should be able to wick heat out of the paint surface pretty quickly, and circulating air will also help cool the surface. Intuitively, I think the wall will get hot, but not so hot that you can't touch it, and not hot enough to boil water, so it should be below 120C. Higher-temperature paints are also available, but are more expensive. The best way to answer the question for sure is to run the stove before painting the wall and measure the temperature directly. One of those IR "laser" thermometers would work great, if you use something (a board, tin foil, pretty much anything) to shade the wall from the stove's radiative heat just before measuring in order to prevent interference in the reading. 209.131.76.183 (talk) 13:21, 2 November 2012 (UTC)

It is possible to calculate the wall surface temperature by using airconditioning formulae. There are formulae for estimating the heat flow via air flow and formulae for direct radiation. You need to estimate the emissivity of the paint surface, and look up the thermal conductivity of the wall - tables for all sorts of walls are published in airconditioning manuals. You will need high school algebra capability to use such formulae.

While you said you intend to only use the stove for 2 to 3 hours a day, for safety you should assume continuous operation with the stove well stoked. From my own experience, I suggest you view paint temperature specs with a GREAT deal of suspicion. In any case, if the wall is any sort of timber product, plasterboard etc, you want to keep it to 50 C or less. Concrete walls 90 C or less.

However, I purchased a wood stove some years ago, and it came with installation instructions which gave the minimum distance from walls. So check with the manufacturer of your stove.

Ratbone 121.215.21.99 (talk) 15:08, 2 November 2012 (UTC)

I suggest you place something between the wood stove and the wall, to protect it, since, even if the paint doesn't scorch, the constant heating and cooling will cause it to crack and peel before the rest of the paint. A chunk of drywall covered with aluminum foil on the side facing the stove should do the job nicely and cheaply. If you want to spend more and make something fancier, you can do that, too. StuRat (talk) 17:06, 2 November 2012 (UTC)

people mover using air pressure

Somewhere in India or near India is a people mover that uses air pressure to push a large box around a circular path. The air boxes are higher up and is attached by an arm to a lower box fills up with riders. The circular route has segments. The air from one is pumped from a forward void into an aft void. Does anyone has a photo of this mass transit system or any other printed information? I think I read about it in the Whole Earth Catalogue back in the 70’s. I've google it extensively with no results. Thanks. Dennis — Preceding unsigned comment added by Jdenwyatt (talk • contribs) 13:54, 2 November 2012 (UTC)

You might be interested to know that some of the earliest subways were pneumatic, like this: Beach Pneumatic Transit. The problem is, it only works for a small distance. StuRat (talk) 16:45, 2 November 2012 (UTC)

Taman Mini Indonesia Indah (TMII, an Indonesian theme park) has an elevated Aeromovel transportation system that is close to the system that you've described, though with the positions of the pumped air and the passenger compartment swapped. In the TMII Aeromovel system, there is a hollow concrete pipe (beneath the elevated tracks) through which air is constantly pumped. The vehicles have large paddles or 'sails' that extend down into this pipe; when the sails are perpendicular to the direction of travel the train is 'blown' along, whereas when the paddles are turned parallel to the airflow the train coasts. I've read about similar systems in the past (I have a vague memory of a Popular Science article from about 20 years ago), but I'm having difficulty locating additional references. TenOfAllTrades(talk) 19:46, 2 November 2012 (UTC)

Although it doesn't address the OP's specific query, the general topic of atmospheric railways might be of background interest. (The poster formerly known as 87.81.230.195} 90.197.66.19 (talk) 13:14, 3 November 2012 (UTC)

Ball point pens and pull-cord light switches

Is there a name for, and do we have an article on, the alternating up/down mechanism found in ball point pens, which I'm assuming is similar to that found in pull-cord light switches? Rojomoke (talk) 14:09, 2 November 2012 (UTC)

Some poking around at google indicates that retractable ballpoint pens use a type of cylindrical cam follower/ratchet mechanism, sometimes called a "Ratchet spring". --Jayron32 14:26, 2 November 2012 (UTC)

Fat soluble medicine

If a medicine is fat soluble, will we absorb more of it taking it with fat or without fat (just water)? 80.58.205.34 (talk) 16:19, 2 November 2012 (UTC)

Most such medicines are advised to be taken with food, read the label and consult with a doctor, pharmacist, or nutritionist. See also, fat-soluble vitamins. (I support re-openning this since it is a general question, not a request for specific individual advice.) μηδείς (talk) 16:38, 2 November 2012 (UTC)

I know that medicines will explain how do you have to take it. But my doubt was rather general. The requirement "take with food" could be motivated by other causes, like to protect the stomach from some medicine. I just wanted to know how it works physiologically, not in a real life scenario. If a medicine gets dissolved in fat, will we absorb more or it or excrete more of it? 80.58.205.34 (talk) 16:42, 2 November 2012 (UTC)

It should help to dissolve it in fat. A normal person's digestive system is quite capable of digesting fat, so there's no problem with it passing out of the body like that. Being more diluted in all that fat would also help to avoid irritating the intestinal lining by being exposed to high concentrations. StuRat (talk) 16:53, 2 November 2012 (UTC)

• This section really does border on giving medical advice. What if the IP changed how he took his medicine according to what was stated here and it had negative effects? IRWolfie- (talk) 16:56, 2 November 2012 (UTC)

The IP is not asking to change anything. if the IP takes a medicine, he will follow the label. 80.58.205.34 (talk) 17:04, 2 November 2012 (UTC)

• If they said they wanted advice on how to take their own meds, then you'd have a point. StuRat (talk) 17:00, 2 November 2012 (UTC)

Yes, the reason is for the presumed fat content of the food, some medicines are also taken with milk. The body preferentially absorbs fat (fat digestion), so unless you are just drinking two quarts of vegetable oil daily, or a eating the un-absorbable Olestra, it should lead to better absorption, not excretion. Of course this is biology so there are all sorts of caveats. You will find most actual pharmacists enjoy discussing this sort of thing (not register clerks) so I would suggest approaching a consultation window if you have questions about any specific medicine. μηδείς (talk) 17:01, 2 November 2012 (UTC)

• It appears that the answer depends on the specific vitamin or drug in question. See [2] where lutein appeared to require fat, but vitamin E didn't (but then again, a preceding study found it did...). It's important to remember in all this that chylomicrons are made, they're not just bubbles of free fat that carry intestinal contents into the blood, which would be bad! So I think the effect is not one where the vitamins hitch along for the ride the whole way - rather, the vitamin has to get in as an individual molecule, and then, if there are more blobs of fat on the far side, it's more likely to stick and make room for the next molecule. So I don't expect super dramatic effects here, unless the biology is being particularly creative (something which it tends to enjoy doing often). There are some fun details, like Xenical can reduce the rate of absorption of some things. Wnt (talk) 17:34, 2 November 2012 (UTC)

Why does a dead body float on water ?

Why does a dead body float on water ? (Not Homework) Thanks! 106.209.2.66 (talk) 18:05, 2 November 2012 (UTC)

Gas builds up in the intestines (mostly, I think), bloating the corpse. There's a specific "floating decay stage" which takes anywhere from a day to a week to begin depending on temperature. [3] Wnt (talk) 18:11, 2 November 2012 (UTC)

A fresh corpse will immediately sink in water[4]. After a certain amount of decomposition the bloating will float the body back up. After all the gas-containing cavity rot enough for the gas to leak out, the body will again sink into the water. A8875 (talk) 21:10, 2 November 2012 (UTC)

Human bodies differ in density, but are generally slightly more dense than water [5], for example, for males. A very fat corpse might be less dense than water and float initially. Air or CO2 in the stomach from consuming fizzy pop could also add to bouyancy. [6]. I have observed that I float with lungs full of air, but sink if I expel sufficient air. Air retained in clothing could also make a fresh corpse float (Which sounds a bit like the world's worst soda fountain confection!) Edison (talk) 23:02, 2 November 2012 (UTC)

But wouldn't a body normally have lungs at least partially full of air ? StuRat (talk) 23:04, 2 November 2012 (UTC)

Once you're dead the diaphragm relaxes, and the lungs deflate. Rojomoke (talk) 23:35, 2 November 2012 (UTC)

Archemedes principle190.56.105.253 (talk) 15:21, 3 November 2012 (UTC)

Is that when he went to take a bath, found a body in his tub, and yelled 'Eureka !' ?" StuRat (talk) 23:33, 3 November 2012 (UTC)

Cell Biology

Hi! Which are the most important discoveries in history of cell biology, important for medicine? Please name 10 to 15. Thank you in advance! --Atacamadesert12 (talk) 19:23, 2 November 2012 (UTC)

As you have been previously informed, we do not do people's homework for them. Please refer to that prior response for the reasons for our position. — TransporterMan (TALK) 21:15, 2 November 2012 (UTC)

I am surprised we don't have an article on Metachlorians. μηδείς (talk) 21:37, 2 November 2012 (UTC)

Midichlorians. Someguy1221 (talk) 21:46, 2 November 2012 (UTC)

Thought I must be misspelling it but one gets quite a few hits on the other. μηδείς (talk) 01:19, 3 November 2012 (UTC)

That would be the citizens of the planet Midichloria. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:32, 3 November 2012 (UTC)

November 3

Time is an illusion

Back when I was at school (not "abducted", sorry auto-correct error 46.229.161.232 (talk) 18:50, 5 November 2012 (UTC)), I got into a conversation with, well lets just call him "Ted". At some point, the subject turned to reality and the meaning of life. Ted started to explain his understanding of Time. He said that it was just an illusion, and that what we were experiencing was our conscious movement through the multiverse. He said that there is an infinite number of static Universes and that the illusion of Time was in fact the changes noted when passing though these static universes. Was Ted pulling my leg, or could this be true? 46.229.161.232 (talk) 01:34, 3 November 2012 (UTC)

Welcome to the Science Reference Desk. Do you need help finding a reference to scientific question? If you need assistance finding a general forum for discussion, please see our article on internet chat room. Nimur (talk) 01:47, 3 November 2012 (UTC)

I'm un-hatnoting this. I see nothing medical involved. Besides, I agree with Ted. :) (Oddly enough, I just linked to my comments in this regard in the "free will" thread on the Humanities Desk) I should disclaim, however, that things beyond the universe tend to be inaccessible to scientific investigation, so this may not be the right subsection for the question. Wnt (talk) 02:26, 3 November 2012 (UTC)

Quoting from Scientific American,

...the true arena of events in a relativistic universe is a big four-dimensional block. Relativity appears to spatialize time: to turn it into merely one more direction within the block. Spacetime is like a loaf of bread that you can slice in different ways, called either “space” or “time” almost arbitrarily.

The concept of time that you describe is one that some physicists believe in, or believe is required according to certain models of how the universe works. However, it's not actually obvious that this interpretation is true, testable, or even meaningful. At this point in...time, it seems like just a philosophical interpretation of physics, and one that's not universally held. Someguy1221 (talk) 01:51, 3 November 2012 (UTC)

While physicists rely on time being real in many of their formulas, one thing that does seem odd to them is the unidirectional movement of time. Nothing in physics limits time in this way, and the 3 other dimensions go both ways. StuRat (talk) 02:19, 3 November 2012 (UTC)

Time is real, but in a couple of months Newsweek will be an illusion. As regards backwards time travel, has anyone found any evidence confirming it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:23, 3 November 2012 (UTC)

If the OP is suffering from illusions he needs medical attention, not bullshitting. μηδείς (talk) 02:35, 3 November 2012 (UTC)

Only if he's not making it up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:14, 3 November 2012 (UTC)

In other words, feed the birds, not the trolls. :-) 24.23.196.85 (talk) 03:35, 3 November 2012 (UTC)

Per Refdesk guidelines, please don't diagnose the visitors. The notion that a person must live his entire life in strictly the physical world, without ever experiencing a single vision, prophecy, revelation, or paranormal experience, or else be branded as permanently psychiatrically damaged, seems to me to be an extreme excess of materialism. Wnt (talk) 03:55, 3 November 2012 (UTC)

I much prefer this version of feed the birds ;-) Dmcq (talk) 10:35, 3 November 2012 (UTC)

Clearly a troll question, or at best a question with no good RD answer. Let's stop feeding please. Shadowjams (talk) 04:38, 3 November 2012Comment moved here after unhatting by Someguy1221 (talk) 04:53, 3 November 2012 (UTC)

Time is an illusion, in the sense that the traditional interpretation of time that the past and future are not real and only the present moment is real, is wrong (not just in relativistic physics, also in classical mechanics and quantum mechanics). The burden of proof is on those who believe that time does exist to prove this, not the other way around. If something does not exist, then there is nothing to prove.

Any set of laws of physics where information is conserved will have this property. If the information about the past exists in the future without any of that getting lost, then the past exists inside the future state. E.g., in principle you can measure who wins the US elections. The practical problem with performing such a measurement is that it involves a complicated interaction with every particle located in a sphere of about 4 lightdays radius. But the known laws of physics allow you to perform that measurement, which will collapse the wavefunction of the World into that state that under the time evolution will evolve to the state consistent with your measurement. Count Iblis (talk) 04:52, 3 November 2012 (UTC)

Time is an illusion; lunchtime doubly so. 82.131.132.190 (talk) 22:45, 3 November 2012 (UTC)

Time being an illusion is not an uncommon idea in philosophy. The nature of time is a complex topic, both in physics and in philosophy. You may find the following articles to be of interest: The Unreality of Time, Eternalism (philosophy of time), The End of Time (book), Arrow of time, Time in physics Red Act (talk) 00:07, 6 November 2012 (UTC)

A tidal dam for New York?

We have seen lately how vulnerable New York is to these types of hurricanes, especially thanks to global warming and sea-level rise.

I hope those subways and tunnels will get pumped out and operational again.

Especially since the hurricane, have the officials for the city of New York considered tidal dams to protect the city? London already has the Thames River Barrier so what obstacles must New York surmount in order to install such barriers of their own?

1. Do we have an article on such concepts?

2. How much would such a barrier be estimated to cost?

3. How big / what type of political obstacles are there?

4. What other obstacles and considerations would they need to evaluate and overcome in order to get the tidal barrier installed around the city?

Good golly, I really hope plans for such barriers are being put forth in city board meetings these days because we can't expect these storms to get any gentler in the future. The sea-level rise coupled with land subsidence due to heavy skyscrapers and etc. will make such sea barriers imperative for the city's future. --Let Us Update Wikipedia: Dusty Articles 07:35, 3 November 2012 (UTC)

It might help in the short run, but, eventually, any such barrier will suffer a catastrophic failure as sea levels rise and storms become more severe. So, it might result in a false sense of security, ultimately leading to more deaths, similar to the levee failures in New Orleans when Hurricane Katrina hit. A more sensible approach, IMHO, is to use any funds slated for a barrier to rebuild on higher ground, further inland, as anything that flooded this week will surely flood again, barrier or no barrier. StuRat (talk) 07:41, 3 November 2012 (UTC)

The Geography of New York City is very different from that of London. Where are you proposing to place your barrier(s)?--Shantavira|^{feed me} 08:03, 3 November 2012 (UTC)

There isn't much subsidence risk in NYC. London is built on clay, which is good for tunnelling, but only moderately good for skyscrapers. New York, on the other hand, is built on granite. This is why its underground network is so much shallower than London's, but it can support awesome skyscrapers. Even PATH, which is much deeper than most of the subway, is only as deep as the foundations of the WTC.

As for a barrier, well, one could put one in the Narrows, but that wouldn't protect Staten Island, southern Brooklyn, or Rockaway. If you put a much longer barrier between Sandy Hook and Rockaway, that might well worsen the flooding risk to Rockaway and coastal New Jersey, while costing a huge amount for something that's not used often. Obviously if the frequency of such storms increases, this might have to be reconsidered. AlexTiefling (talk) 09:56, 3 November 2012 (UTC)

Another solution is to let water flow freely. That has worked for Venice for ages. Comploose (talk) 13:24, 3 November 2012 (UTC)

No, it hasn't. See Venice#History and MOSE Project. Rmhermen (talk) 13:59, 3 November 2012 (UTC)

In fact, they had some serious flooding just this past week.[7] ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:50, 3 November 2012 (UTC)

See here. And along the coast line where you don't have harbors, you can build dikes in the sea like this, so that you still have a beach. Count Iblis (talk) 16:28, 3 November 2012 (UTC)

There was an interesting article in GSA Today just last month on optimizing mitigation. See this. Zoonoses (talk) 02:28, 4 November 2012 (UTC)

• Protecting Manhattan would require two such barriers, one at The Narrows to protect water entering New York Harbor from the south, and one to protect water from coming in at the East River, where there are several candidate locations: City Island, Bronx would provide probably the farthest practical point, beyond this Pelham Bay is probably too large to be feasible. Throggs Neck is also feasible, and would protect most of northern Queens and the South Bronx as well, while the confluence of Hell Gate and Bronx Kill near the northwestern tip of Randall's Island is probably the narrowest point, and closest to Manhattan, one could build it. Any flood control barrier south of the Narrows or east of the East River would likely cross too large a stretch of water to be feasible. --Jayron32 05:42, 6 November 2012 (UTC)

The best enzymes for ligating DNA:

The best enzymes for ligating DNA

Select one:

a. come from humans, as they are compatible with the most complex types of DNA.

b. come from bacteriophages, as they don't need to be incubated at a specific temperature to work.

c. come from thermophilic bacteria, as they need to survive thermocycling.

d. come from retroviruses, as they integrate their own DNA into a host's genome most efficiently.

(a) seems unlikely, but doesn't this seems like a subjective question anyway? 130.56.94.164 (talk) 13:17, 3 November 2012 (UTC)

(a) is clearly the correct answer, as humans are the most evolved species living on earth. Except for those who try having others do their homework. 77.3.129.83 (talk) 13:53, 3 November 2012 (UTC)

I don't know the answer, but our article on DNA ligase indicates that the most widely used type for lab work comes from bacteriophage T4. Looie496 (talk) 16:27, 3 November 2012 (UTC)

How would you do this?

You are given a plasmid with Ampicillin resistance, and a recombinant GFP gene engineered to only be expressed in the presence of lactose. Explain how you would get this vector into E. coli and screen for successfully transformed cells without using UV light. --130.56.94.164 (talk) 13:27, 3 November 2012 (UTC)

Not only does this question read as a homework question copied out, and we are not here to do your homework for you, it is impolite to post a question without giving a name. A psuedonym will do, but please assign yourself a name. Wickwack 60.230.220.27 (talk) 15:07, 3 November 2012 (UTC)

Is a name really a requirement here? It looks like new rules are generated every minute. But OK, I'll sign WickedWhack 77.3.129.83 (talk) 15:18, 3 November 2012 (UTC)

As far as I am aware there has never been a requirement for an IP to invent a name for the purposes of asking a question at the RefDesk. IP editors are just as welcome here as account holders. We won't do your homework for you, but you don't have to jump through any extra hoops in order to ask, and you were not being impolite. - Karenjc 19:05, 3 November 2012 (UTC)

We have articles on Ampicillin, I have made a redirect for Ampicillin resistance (which goes to a stub which you can expand given the inclination), and we also have articles on Beta-lactamase, there is a MeSH code: MeSH G12.392.269.347.500.600.050, pComb3H, pGLO, plasmid, Green fluorescent protein (for GFP) and Escherichia coli (molecular biology). Graeme Bartlett (talk) 04:09, 4 November 2012 (UTC)

Inoperability of back-of-neck skin?

"As he aged, starting in the late 1970s, Kim developed a growth on the right-back of his neck which was a calcium deposit. Its close location near his brain and spinal cord made it inoperable. Because of its unappealing nature, North Korean reporters and photographers, from then on, always shot and filmed Kim while standing from his same slight-left angle to hide the growth from official photographs and newsreels, which became an increasingly difficult task as the growth reached the size of a baseball by the late 1980s."

I'm missing something here. Why couldn't they just operate on it like any other skin condition? Nyttend (talk) 13:42, 3 November 2012 (UTC)

I'm not quite clear what is meant by a "calcium deposit" but I suggest that the reason they give is not the real reason, (North Korea has some history in this department) Maybe he had a surgery phobia. It is possible he had one of [http://www.ispub.com/journal/the-internet-journal-of-dermatology/volume-6-number-2/giant-sebaceous-cysts-of-scalp-a-case-report.html#sthash.8timQ2ox.dpbs these (scroll down a bit)]. By coincidence the first reference at the bottom of the page is from four Korean medics, so they are possibly common in Korea. Richard Avery (talk) 15:24, 3 November 2012 (UTC)

Are there any pictures? Given his obesity and habits it could also have been a gout tophus, although I think they are usually associated with joints. μηδείς (talk) 17:58, 3 November 2012 (UTC)

Sounds like an odd place for one, and when it is so far advanced as to lead to visible external tophi, gout is not a hard condition to diagnose or treat. I assume Kim had access to some kind of medical care. Wnt (talk) 13:36, 4 November 2012 (UTC)

Ko's

How come in a boxing or mma fight, when people who get hit in the exact same spot get knocked out, some of them go limp, and some of them get stiff and rigid? Shoulden't the body react the same if they are hit in the same spot? --Wrk678 (talk) 19:57, 3 November 2012 (UTC)

I don't see why the body would react the same. The damage done could be different, depending on the force of the impact, tiredness, or on previous injuries. Comploose (talk) 20:00, 3 November 2012 (UTC)

I have a semi precious stone and I want to know what it is.

I have a stone that is light blue that glows orange in the light. Can anyone tell me what it is? — Preceding unsigned comment added by 216.36.16.221 (talk) 20:36, 3 November 2012 (UTC)

I don't know, but if you can post a picture it may aid others. Falconus^{p t c} 20:43, 3 November 2012 (UTC)

Could you be a little clearer about what kind of light you are using to see the glow? Is it daylight, ultraviolet light, or light from an incandescent bulb or a fluorescent tube? - Karenjc 21:56, 3 November 2012 (UTC)

Sounds like fluorite to me, but it doesn't have to be. See what you think from the article. Wnt (talk) 22:08, 3 November 2012 (UTC)

I'm not absolutely sure that this is what the OP is talking about, but he or she may want to look at the lists in our pleochroism article. Deor (talk) 12:23, 4 November 2012 (UTC)

What is it the

As much as I try to understand what is it an electric charge, I can't understand it at all. What is it this charge? Is it a product or an effect of the magnet? מוטיבציה (talk) 21:07, 3 November 2012 (UTC)

It is a property of a particle, there are two kinds. Two electric charges of the same kind will push appart, two of the different kind will draw near. Unlike magnetism, the kinds electric charge can be found appart from one another. Plasmic Physics (talk) 22:34, 3 November 2012 (UTC)

Magnetism is caused by moving electric charge, so a magnet is an effect of charge not the other way around. As User:Plasmic Physics says electric charge is a property of some elementary particles. In most every day macro occurrences something that is negatively charged has an excess of electrons. Something that has positive charge has a lack of electrons (again I'm talking macro objects, this is due to protons, which have positive charge, being immobile in objects and electron being able to move). But there is only one type of electric charge (and it's anti charge) unlike colour charge which has 3 different types of charge (and there anti-charges).Dja1979 (talk) 01:04, 4 November 2012 (UTC)

Electric charge is something that causes an electric field. Electric charge is a property intrinsic to certain particles such as electrons, protons, and their antimatter equivalents. A moving electric field creates a magnetic field; conversly, a moving magnetic field creates an electric field. Without getting into the mathematics of the subject, there's not much point in trying to take it further than that. There are things that man does not have a visuallizable understanding of, and this is one of them. Physicists and engineers have long worked out mathematical models that verify and predict practical measurements. Once you have become accustomed to using the math, you become comfortable and confident with it, without ever really understanding the actual basis of the phenomena. Ratbone 124.178.138.168 (talk) 01:59, 4 November 2012 (UTC)

Thank you all for help. מוטיבציה (talk) 21:24, 4 November 2012 (UTC)

If you really want to get into it there's isospin and hypercharge, where I feel intuitively as lost as you do. Wnt (talk) 14:59, 5 November 2012 (UTC)

Gravitational potential energy

Start with two masses m1 and m2 at rest, separated by a distance r, and then release them.

At any subsequent (non-pathological) point, should the sum of the masses' kinetic energy (= 1/2*m1*v1^2 + 1/2*m2*v2^2) equal the change in potential energy, where potential energy is calculated using the forumla -G*m1*m2/r^2? 86.128.3.213 (talk) 21:47, 3 November 2012 (UTC)

The question appears to be asking if the sum of kinetic and potential energy in the system is conserved. In an ideal Spherical cow system, where there is no intervening gas or fluid and no electromagnetic effects, the sum of potential and kinetic energy should not increase or decrease. If the sum of potential and kinetic energy increased, we would seem to have a fine perpetual motion energy production device. The question does not specify that the masses are in a vacuum. If the total energy decreased, where did it go? If I release them in a zero G chamber filled with a gas or a fluid, they will do work as they converge and the sum of kinetic and potential energy at a subsequent point before impact would be decreased by the work done on the medium, which would heat the medium. Edison (talk) 22:55, 3 November 2012 (UTC)

Thanks, yes, I am aware of the principle of conservation of energy. My question is whether the numbers calculated by the above formulas ought to match, because in simulations I cannot get them to match. I wonder if there is some flaw in the reasoning of using those formulas in the obvious way, not whether there is some flaw in the principle of conservation of energy. You may assume no loss of energy due to other factors. The other possiblity is that I may be making a silly error that I cannot spot. Sorry if that was unclear. 86.128.3.213 (talk) 23:06, 3 November 2012 (UTC)

Yes, the numbers should add up. If they don't, please post your work, and we will see if we can find the error. StuRat (talk) 23:26, 3 November 2012 (UTC)

The program I am using is below. I am dumping it without a great deal of explanation, but I believe its operation should be fairly obvious to anyone who has a chance of finding the error which I have been unable to see. I do hope this isn't just some silly finger trouble.

G = 1.23 'arbitrary value; shouldn't matter
dt = 0.00001

m1 = 1
m2 = 10

'initial positions and velocities
x1_0 = 0
v1_0 = 0
x2_0 = 10
v2_0 = 0

'initial energies
ke_0 = 1 / 2 * m1 * v1_0 ^ 2 + 1 / 2 * m2 * v2_0 ^ 2
pe_0 = -G * m1 * m2 / (x1_0 - x2_0) ^ 2

'initialise variables
x1 = x1_0
v1 = v1_0
x2 = x2_0
v2 = v2_0
t = 0

Do

    r = Abs(x1 - x2)

    'calculate energies
    ke = 1 / 2 * m1 * v1 ^ 2 + 1 / 2 * m2 * v2 ^ 2
    pe = -G * m1 * m2 / r ^ 2
    dke = ke - ke_0
    dpe = pe - pe_0
    
'-----------------------------------------------------------
' at this point dke + dpe should equal zero (to reasonable accuracy), but it doesn't
'-----------------------------------------------------------

    'move one timestep
    t = t + dt
    F = G * m1 * m2 / r ^ 2
        
    a1 = F / m1 * Sgn(x2 - x1)
    v1 = v1 + a1 * dt
    x1 = x1 + v1 * dt
    
    a2 = F / m2 * Sgn(x1 - x2)
    v2 = v2 + a2 * dt
    x2 = x2 + v2 * dt
    
Loop

86.128.3.213 (talk) 02:22, 4 November 2012 (UTC)

This is expected, because you are calculating a solution using Euler's method. While this seems to be a simple and correct approach, it is well-known (amongst computational physicists, anyway) that Euler's method, applied to the formula for gravitation, propagates error, amplifying tiny calculation errors until they are exponentially larger than the quantities under consideration. Hold on, I'll dig up link to a page in our archives when I last discussed this topic. Nimur (talk) 11:57, 4 November 2012 (UTC)

Thank you for looking at this. I must admit that I am initially sceptical that the level of discrepancy I am seeing is due to numerical artefacts of the discrete approximation method. However, I know from seeing previous replies of yours at the ref desk that you are normally very knowledgeable, so I may have to stand corrected. 81.159.107.19 (talk) 12:07, 4 November 2012 (UTC)

Thank you for the compliment. But don't take my advice as authority: verify for yourself! Unfortunately, my link from the 2009 discussion is no longer active; the course website is now handwritten lecture notes with only a passing mention of Euler's method. There used to be an interactive applet, a breakdown of analytic and numerical sources of error, and all specifically for gravitation! No worries, there are other examples on the web, and I'll find some. And, all hope is not lost for your simulation: you'll just need to implement a different calculation method, such as a Runge-Kutta solver, that is appropriate for stiff equations like gravitation. The problem with numerical error isn't the roundoff or floating-point inaccuracy in any single calculation: it's the error that propagates from one step to the next. Each iteration of your loop amplifies a small deviation, and before long, you're very far from a reasonable solution. Let me keep looking for a suitable example on the web. Nimur (talk) 12:31, 4 November 2012 (UTC)

One of the reasons I am surprised is that I have used an essentially identical method to plot orbits, and it seemed to work very well (in terms of producing a sensible-appearing elliptic orbit). I have also used it to simulate n-body problems with visually sensible-looking results. See http://img834.imageshack.us/img834/5673/nbody.gif . 81.159.107.19 (talk) 12:50, 4 November 2012 (UTC)

Forget all the responses above, or at least, forget them until you read this one. You are calculating gravitational potential energy incorrectly. It is -G * m1 * m2 / r, not -G * m1 * m2 / r ^ 2; you're off by a factor of r. --140.180.252.244 (talk) 00:21, 5 November 2012 (UTC)

Good eye! The above post is correct. Fix that error, and then we can consider other issues like numerical accuracy. Nimur (talk) 02:45, 5 November 2012 (UTC)

ARRRRGH!! 140, I am so grateful to you. Fixes it perfectly. You have no idea the number of times I have looked through that code without spotting that. When I say "perfectly", I mean up to my expectations of accuracy for smaller t. Nimur, you are correct of course that sooner or later the method would start to diverge considerably. 86.146.108.178 (talk) 18:18, 5 November 2012 (UTC)

Maximum Age for Becoming a Father

Is there a maximum age at which a man can become a father like there is for women/mothers? Futurist110 (talk) 22:25, 3 November 2012 (UTC)

No, not quite, but they do have a "best before" date. Plasmic Physics (talk) 22:37, 3 November 2012 (UTC)

So a man aged 115 could theoretically naturally become a father if he wanted to (and had the energy to have sex)? And what is the "best before" age? I know that it has to do with the condition of sperm deteriorating over time, but I don't know the exact age. Futurist110 (talk) 22:40, 3 November 2012 (UTC)

I doubt there is any "exact age". It would probably be a continous curve, which would in any case probably vary significantly from person to person. 86.128.3.213 (talk) 23:08, 3 November 2012 (UTC)

This page outlines some of the risks associated with being an older father. See also Man is 'world's oldest dad at 94'. Alansplodge (talk) 23:46, 3 November 2012 (UTC)

Thank you. Based on the info in your link, it would thus appear that someone like Jiroemon Kimura could still have another child if he had the energy to have sex right now, but that the odds of this would be pretty low due to sperm deterioration over time. I wonder if someone aged 95+ ever tried having a child or not? Futurist110 (talk) 23:51, 4 November 2012 (UTC)

One risk is confusing the baby's diapers with your own. :-) StuRat (talk) 00:33, 4 November 2012 (UTC)

Sperm don't sit around like eggs. They are produced and degrade regularly. If oldsters can still produce them they will be new sperm. μηδείς (talk) 03:52, 5 November 2012 (UTC)

Nevertheless, some evidence has been reported that the sperm of older men is more likely to contain mutations that affect the children to whom they pass than the sperm of younger men, although the overall risk is still small. - Karenjc 11:37, 5 November 2012 (UTC)

Yes, that's true, mutation load in the stem cells increases with age, and older men are more likely to be sterile for a host of reasons. Just want to make sure the OP is clear that unlike women's eggs they are produced anew at all stages of life and last for a short while, while eggs are produced early and once and then sit around for life til they are fertilized or go bad.

It has recently been reported that a 96-year-old man has fathered a child. Graham87 12:00, 5 November 2012 (UTC)

The original Dirty Old Man. -- Jack of Oz ^[Talk] 21:28, 6 November 2012 (UTC)

There were a Lot of dirty old men before him. StuRat (talk) 19:46, 7 November 2012 (UTC)

In fact, paternal age has been corelated with an increase of risk of the child being born with autism. Plasmic Physics (talk) 04:59, 7 November 2012 (UTC)

Yes, that's mentioned in the article that I linked above, It also mentions an increased risk of dwarfism, achondroplasia, schizophrenia and bipolar conditions, pre-term birth, genetic abnormalities and limb defects. It notes that in the US, there is an upper age limit of 40 for sperm donors. Alansplodge (talk) 14:12, 7 November 2012 (UTC)

November 4

Syria Rebels

I came across this YouTube video in which the Syrian rebels successfully attack and capture an army outpost, I am confused how they managed to do this because in similar situations in which the US and its allies encounter almost daily in Afghanistan, insurgents will try to attack army bases and the army will call in attack helicopters, which turn on their infrared cameras and can easily see the insurgents even in the day time and kill them with their 30 mm machine gun, or Rockets, Syria has some fairly advanced attack helicopters from Russia. I don't see why they can't do the same. Here is the video:

http://www.youtube.com/watch?v=IC8ENtjVp3I

--Wrk678 (talk) 00:03, 4 November 2012 (UTC)

Not really a science question, but there are several possibilities:

1) Attack is too rapid to allow such a response. Air responses take time, and the base must be able to hold out until then.

2) Communications are jammed or cut, so they can't call for air support.

3) Syrian outposts aren't designed to withstand attacks from all sides. Many outposts are designed just to defend against one type of attack. For example, posts on the border may be set up only to defend against cross-border attacks.

4) The Syrian air force is simply overwhelmed, and can't respond as quickly as is needed. Lack of spare parts and maintenance issues from constant use can have such an effect.

5) Multiple coordinated attacks stretch the Syrian air force too thin to respond.

Also note that often those bases are retaken by the Syrian military. In many cases, the rebels don't even attempt to hold them, they just raid them and then scatter. StuRat (talk) 00:29, 4 November 2012 (UTC)

Well, it looks like the attack lasts several hours, starting during the day and ending at dusk. Syria is a pretty small country so I think they could get their in time. I doubt the rebels have any kind of sophisticated jamming equipment that could jam military radios.--Wrk678 (talk) 09:35, 4 November 2012 (UTC)

Your premise that attacks on military posts in Afghanistan are always quickly suppressed by air attack may not be the whole truth. See 8 U.S. troops killed in Afghanistan, Militant attacks on two remote outposts also leave as many as half a dozen Afghan troops dead.; "It was precisely the kind of attack the top U.S. commander in Afghanistan is hoping to stave off by recently ordering troops to withdraw from such small outposts...". Also the Battle of Wanat and Siege of Sangin. None of these attacks were ultimately successful, but it was sometimes a "damned near-run thing"; although as yiou say, air power was used in a suppressive role in all cases, it's often hard fighting on the ground that wins the day. The training and equipment of the Syrian Army may well not be up to the standard of professional NATO troops. Alansplodge (talk) 10:07, 4 November 2012 (UTC)

Doing a quick search I find [8] "In recent days it has appeared that Syrian rebels have acquired heavy weapons that have forced the government's air force to bomb rebel-held zones from higher altitude, leading to claims of more indiscriminate bombing." The video shows a helicopter spiraling down and exploding in a ball of fire. Wnt (talk) 13:32, 4 November 2012 (UTC)

This outpost was a minor one possibly. I doubt they send even one aircraft to all fighting that is taking place. The Syrian_Air_Force#Aircraft_inventory Syrian Air Force has its limitations. What's the point of risking a crown jewel like an attack helicopter to save just half a dozen of trapped soldiers? Comploose (talk) 19:42, 4 November 2012 (UTC)

Well in Afghanistan fighting on the ground can stave off the assault but it's usually when the attack helicopters come that the insurgents will retreat. Usually there is a "Alamo" call that is given when the base is starting to become overrun that brings all airborne helicopters to the area.

Even though this was a small army base its capture involved the capture and probably the execution of several dozen or more Syrian army soldiers, so I would think the government would prioritize that and send attack helicopters over there. If you watch the end of the video after they capture the base, They hang around there for at least several hours afterwards and nobody shows up, if, for example, it was a priority issue, they probably would have shown up "late" a hour or so after the attack, which they did not.

The thing is I have watched numerous videos of these Syrian rebel attacks, many of them last for hours or more and it doesn't appear that any Syrian attack helicopters usually show up. This makes me wonder if in fact the attack helicopters the Syrians use do in fact have infrared cameras in them. Does anyone have any information on this? --Wrk678 (talk) 21:28, 4 November 2012 (UTC)

Attack helicopters are not an "I win" button, same as tanks. A chopper or a tank will rarely be sent to enter an engagement with no support. To be effective there has to be a co-ordinated attack. All it takes is one enemy soldier with a cold war era anti-air or a anti-tank weapon to be a serious threat to several million dollars worth of military hardware. With no ground support or good reconnaissance, sending a lone chopper might just be too risky. As is noted above, at least one chopper has already been lost and if I'm not mistaken there's been a few. Vespine (talk) 22:11, 4 November 2012 (UTC)

Well, it's pretty standard procedure to send attack helicopters to bases being attacked, regardless of anti-air weapons. They had those in Libya and Afghanistan too.--Wrk678 (talk) 22:55, 4 November 2012 (UTC)

That's an assumption on your part. I see no reason to believe it's "standard procedure". You don't know all the details, as I said, in the other circumstances, maybe there was ground support or reconnaissance available nearby, maybe the threat of anti-air was lower, maybe the pilots were more highly trained; there's just way too many factors involved to say something like "it's standard procedure". Warfare strategy is a very complex topic, it's not just a list of "standard procedures". Vespine (talk) 01:34, 5 November 2012 (UTC)

I disagree with that, military tactics are fairly universal. --Wrk678 (talk) 01:37, 5 November 2012 (UTC)

Well, this very scenario seems to disagree with your evaluation. There was a reason why they didn't send attack choppers, I suggested a few explanations, i'm not sure what other answer you would find more satisfactory. Short of asking the "people in charge", which no doubt would not tell you anyway.. I'm not saying that there aren't universal rules of engagement, I was trying to show that there would be lots of exceptions and finer details which civilains would not be privy to. Vespine (talk) 02:34, 5 November 2012 (UTC)

Well, I'm starting to suspect their helicopters are not equipped with infrared cameras, in which case they wouldn't be of much use in that scenario. If you read about the http://en.wikipedia.org/wiki/Battle_of_Kamdesh it talks about how the solders basically gave up and air support was the only thing that saved them. --Wrk678 (talk) 05:47, 5 November 2012 (UTC)

Oxidative stress and immune system

Hi all,

Can someone tell me in which treatise (hopefully up-to-date) can I find something about general relationships between the oxidative stress and the cells of the immune system? Thank you very much!

151.71.165.245 (talk) 10:12, 4 November 2012 (UTC)

This is a very general question, almost too general to answer. (Do you mean the effect of oxidative stress on invading cells, for example, and what level of review do you want?) Get to know http://www.ncbi.nlm.nih.gov/pubmed for making general queries and narrowing them down; http://scholar.google.com has become a very serious alternative. Leaf through oxidative stress, phagocytes including neutrophil, monocyte, and macrophage, phagocytosis, myeloperoxidase, reactive oxygen species, hydrogen peroxide, hypochlorite... it's no small topic, yet one key idea is very straightforward: the immune system recognizes invaders and puts them in special bins where they are bleached to death (and otherwise digested). Wnt (talk) 13:25, 4 November 2012 (UTC)

Thank you very much. My problem is exactly that I need a general approach to the topic, while the majority of papers I met on-line (including those found using the external links you seggested) is very specific. For this reason I was looking for a treatise. If you are so kind to seggest me a book about the immune system that covers the subject, it will be great!

Many thanks.

193.205.224.192 (talk) 12:54, 5 November 2012 (UTC)

Black holes at the speed of light

Hi, I have a sort of simple question. If you were to accelerate into a black hole would you travel at the speed of light as you cross the event horizon?

Or if you accelerated in at an angle, so your horizontal component of velocity would be say 100mph and your vertical component would be the increasing velocity due to the acceleration due to gravity of the black hole, could you even hit the speed of light before you hit the event horizon?

(This is assuming you have infinite fuel and are not crushed by the G-force and gravity) — Preceding unsigned comment added by 31.54.166.196 (talk) 14:51, 4 November 2012 (UTC)

From special relativity no particle with a rest mass can travel at the speed of light. So in answer to your question no you would not be travelling at the speed of light when you cross the event horizon.Dja1979 (talk) 15:58, 4 November 2012 (UTC)

What would your speed be as you crossed the event horizon? — Preceding unsigned comment added by 86.146.165.159 (talk) 16:17, 4 November 2012 (UTC)

For an outside observer your speed would be (surprisingly) equal to zero because of gravitational time dilation. Dauto (talk) 16:30, 4 November 2012 (UTC)

For this reason, it has been argued that black holes (as seen from outside) can never truly exist because they take forever to form! —Tamfang (talk) 20:12, 4 November 2012 (UTC)

In fact, any observer crossing the event horizon will travel exactly with the speed of light as measured in his own time. Ruslik_Zero 19:13, 4 November 2012 (UTC)

Is this so? From special relativity, we know that any thing in the universe, that has a rest mass, cannot travel at the speed of light. Thinking about it more, maybe the event horizon is outside the universe (i.e. it doesn't interact with the rest of the universe, it is inside the black hole), so special relativity doesn't hold.Dja1979 (talk) 20:27, 4 November 2012 (UTC)

So you would travel at the speed of light then? Also how long would it appear to the outside observer that you freeze for? — Preceding unsigned comment added by 86.146.167.230 (talk) 20:08, 4 November 2012 (UTC)

If an observer sees you freeze, then you never actually make it over in their reference frame, so the answer is forever. However the observation will be redshifted to extreme levels as well, with lower energy photons, and less of them, so eventually nothing will be observed. Graeme Bartlett (talk) 20:15, 4 November 2012 (UTC)

This has nothing to do with reference frames. No one outside the black hole will ever see you inside because light from inside can't reach the outside. It doesn't matter what speed they're going. -- BenRG (talk) 17:53, 5 November 2012 (UTC)

As time speeds up relative to how fast you are travelling, does time stop for the person at the event horizon travelling at the speed of light? — Preceding unsigned comment added by 86.146.167.230 (talk) 20:23, 4 November 2012 (UTC)

Black hole#Event horizon says

According to his own clock, [an observer falling into a black hole] crosses the event horizon after a finite time, although he is unable to determine exactly when he crosses it, as it is impossible to determine the location of the event horizon from local observations.

But Event horizon#Interacting with an event horizon says

An observer crossing a black hole event horizon can calculate the moment they have crossed it, but will not actually see or feel anything special happen at that moment.

"Unable to determine exactly when he crosses it" versus "can calculate the moment they have crossed it" is contradictory. Does anyone know which is right?

A related question: According to those articles someone inside the event horizon can see someone else who previously entered on the same path. Does the previous entrant appear to accelerate to infinite velocity or decelerate to zero velocity? Duoduoduo (talk) 23:49, 4 November 2012 (UTC)

The point is that the observer is unable to determine the location of the horizon with a local experiment but can calculate it's location if he has full knowledge of the black hole's mass, location, etc. For instance, we could at this very moment be crossing the horizon of a black hole so large that it's center is outside of the observable universe and therefore unknowable. There is no experimental test that we could use to find out whether that's true or not. BTW the guy falling in the black hole is not moving at the speed of light for any local observer as stated above by some people. That's just wrong. Dauto (talk) 00:01, 5 November 2012 (UTC)

Let's start with the basics. You have a gravity well, and the speed you gain when falling in is the speed you lose when falling out. If you fall into a black hole from a long way away, just barely miss the event horizon somehow and come back out, you should come to a stop at the same long distance away (ignoring gravity waves and such means by which you might lose energy!). Because only something travelling at nearly the speed of light can do this, the speed you must reach near the event horizon is almost the speed of light - relative to the outside observer. But of course, you're falling, so you're at rest the whole time as you see it. If you sped up on the way in though, that doesn't mean you'd be going faster than the speed of light relative to the outside - you'd just have more kinetic energy which, ultimately, would take you flying away from the hole at high speed when you got out. But since mass can acquire an arbitrarily large amount of kinetic energy by going just a little closer to the speed of light, you'd still be below that speed. Ultimately, the outside can only see you where you'd going slower than light relative to their frame of reference; after that, they see... an event horizon. Which is defined as a spot where the math breaks down - you don't really have infinite mass, they can't see you have infinite mass or that you're going at the speed of light, and they're unlikely to get your account about what you saw, though the whole time... you're still at rest. Wnt (talk) 15:10, 5 November 2012 (UTC)

The math doesn't break down at the event horizon. You can draw an event horizon anywhere in spacetime:

        _______________
       |         /     |   ^
       | inside /      |   |time
       |       /       |   |
       |      / outside|   |
       |_____/_________|    --------> space

If the diagonal line is moving right at the speed of light, it will "behave" just like a black hole event horizon. The inside region "attracts" objects from the outside: you will fall through unless you accelerate away, and the closer you are the larger the necessary acceleration. Nothing from the inside region can ever reach the outside, even light. If someone crosses from the outside to the inside, anyone who remains outside will never see them cross (they'll never see the light, that is). They will see the moment of crossing redshifted into the indefinite future. These makeshift event horizons even emit particles (Unruh radiation), just like black hole event horizons. You are falling through event horizons all the time. -- BenRG (talk) 17:53, 5 November 2012 (UTC)

Hey BenRG, I like your diagram. It really brings home to a lay person how trivial the concept of a horizon really is. Dauto (talk) 21:47, 5 November 2012 (UTC)

So why is the nootropic market kind of small?

Why are students not tested for doping? Is there any genius known for taking nootropics. I know that the mathematician Erdos was known for taking amphetamines, and some artists do not hide their past consume of drugs (although art is an entirely different field, you can fuck up with your brain and still be among the best in the field). Comploose (talk) 20:04, 4 November 2012 (UTC)

At the moment, there are no prohibitions against taking "cognitive enhancers", even for standardized testing. If there are no prohibitions, there is no testing. If, at some point, the use of these is banned — a big if, as it is a complicated issue of performance, mental health, doctor's recommendations, and so on — then presumably testing will have to become part of any effective enforcement regime. --Mr.98 (talk) 20:47, 4 November 2012 (UTC)

Mathematicians and artists do not really compete with each other as directly as people do in sports, that's why I think perhaps our society doesn't see cognitive enhancement in as bad a light as physical enhancement. Whatever competition there is amongst artists and scientists, it's not the "ends" of those pursuits. Sure you compete indirectly, but you compete indirectly by being born. In competitive sport on the other hand, winning against your opponents IS why you play the sport in the 1st place. I suppose students at one stage will compete for university places and scholarships, but you don't get professional "test takers" who make a living just by taking tests. Vespine (talk) 22:00, 4 November 2012 (UTC)

Nootropics are generally debatable. Why would there be a way for a drug to improve on intelligence, that nature doesn't already take advantage of? I suppose that if they increased calorie expenditures or something it would be conceivable ... still, what we see are more often things like modafinil. Tell me ... if much of sleep can be conveniently avoided with a little pill, why does every animal species from fruit flies to man go through the process, despite obvious vulnerability to predation and decreased opportunity for food gathering? Wnt (talk) 22:06, 4 November 2012 (UTC)

Isn't that appealing to nature? The same argument could be made against the bifocals that I'm wearing right now: "Why would there be a way to compensate for myopia, that nature doesn't already take advantage of?". I concur with your overall stance, I just think a different argument would be more convincing.A8875 (talk) 22:34, 4 November 2012 (UTC)

When we are awake we are on natural stimulants. The reason why animals sleep is due to competetion. If you have some machine that has to repair itself that is performing at some level, then you can put it on stimulants and let it perform better at the expense of its repair capacity. So you need to balance that by having a downtime for repair. Also, performing repairs in downtime is more efficient. Count Iblis (talk) 23:02, 4 November 2012 (UTC)

I see this less as appealing to nature as appealing to evolution. Evolution, however, is notably poorly tuned for ages that people rarely reached in primitive times, or for activities like reading that were not important many millennia ago, hence the bifocals. Wnt (talk) 01:27, 5 November 2012 (UTC)

The analogous argument could be made about studying: "Evolution is poorly tuned for activities like memorizing large amounts of information.".A8875 (talk) 03:21, 5 November 2012 (UTC)

Well, that's a valid point. The idea of general intelligence is a peculiar one, central to understanding humanity, and utterly mysterious. Why did humans evolve so many different skills that everyone has - why aren't there genotypes, families or even races that don't understand how to work calculus, but can do everything else just fine? But we digress... Wnt (talk) 15:34, 5 November 2012 (UTC)

(after ec) Add to this that the enhancing effect of drugs, any drugs, is rather dubious. That's no drug that will make you wiser. Some will make you kind of restless, reduce your fatigue, keep you awake and so on. But, in my personal experience, people who use them are the kind who need to spend the night awake before exams or people who have mental problems and need to function normally. These groups are not really skewing things to their benefit. OsmanRF34 (talk) 22:12, 4 November 2012 (UTC)

Ritalin lengthens attention span, and as any student knows, not being distracted while studying is the most important factor in doing well. Some of that is due to the placebo effect, but there's a statistically significant portion that isn't. Testing students for doping is infeasible because students don't confine their studying to a single 1-minute competition every month or year; they study 6 days a week, for half of their waking lives. --140.180.252.244 (talk) 00:14, 5 November 2012 (UTC)

• Come to think of it, a main reason why nootropics are not yet popular is that there has been little effort to wage a "war" on them. (Unless you count methamphetamine, which has much in common with Ritalin, if that counts) I think if we had a major DEA push to put people selling modafinil in jail for twenty years, the merchants with good police connections would make a huge profit, giving them a motive to hype it as a "hip" thing in the media and on the street; before long people would be coming up with super-potent addictive analogs to take by injection and we'd be hearing stories of people going without sleep for six months until their brains turn to tapioca. After that a multibillion-dollar trade in it would never end. Wnt (talk) 01:27, 5 November 2012 (UTC)

I am not sure why you would conclude they are "not yet popular." Amongst those with money and incentive to do well academically, they are immensely popular. A ridiculous percentage of kids at any high-end private high school has prescriptions to them, and many others purchase them illegally from those who do. They are not recreationally very popular, but in terms of getting ahead at the junctures in life that make quite a lot of difference — standardized testing, getting into a "good" school, etc. — and are actually competitive (which is to say, zero-sum — there are winners and losers), there is a quiet little arms race going on. I do suspect that someday there will be some consensus about some standards here, about whether the ability to pay for concentration tilts the scale too much in favor of those with means, but we aren't there yet, just the early murmurs of ethical concern. The issue is a genuinely complicated one, ethically and medically speaking. --Mr.98 (talk) 13:20, 5 November 2012 (UTC)

The question is open to discussion from a medical standpoint, but I don't see that it skews the playing field towards privileged people. I don't believe many people are not able to pay for generic Ritalin. Filling a prescription through Walmart costs only $4/month, and maybe the poor at the bottom won't be able to buy this generic Ritalin, but most people would be able to afford it, if they want to.

Ritalin has the same problem as other nootropics. Although they might help you perform better if you are late for preparing yourself for one of the 'junctures', I do not believe it will make you any better long term regarding developing and using certain abilities like writing, knowledge acquisition, social abilities, creativity, planning. I am not trying to say that nature made us perfect the way we are, but Ritalin specifically, which works in a similar way to cocaine and amphetamine, has many drawbacks, and the effects on long term users are not well understood yet. It certainly makes you more awake for a certain time, but I believe this is probably at cost of your memory, health (mental and physical), and a rebound effect. I don't see the advantage here. It looks like a real arms race, when both sides invest lots of resources in things that they need, just because the other side have it. OsmanRF34 (talk) 14:53, 5 November 2012 (UTC)

Coffee and tobacco? μηδείς (talk) 02:24, 6 November 2012 (UTC)

engine diagram

Hi : Looking for a engine diagram and info.for a toyota avalon xl 2006 . Thank You — Preceding unsigned comment added by Carol9905 (talk • contribs) 20:28, 4 November 2012 (UTC)

Your local library may have repair and service manuals for that car. Libraries often buy volumes that cover repair procedures for a manufacturer's entire line over 4 years or so. If it is a vehicle that you plan on self-servicing on a regular basis, you might want to look into buying the book made specifically for that car from an auto parts store. 209.131.76.183 (talk) 13:43, 5 November 2012 (UTC)

Also, have a look at this Google Image search and see if there's anything helpful there (not much of a mechanic myself). Alansplodge (talk) 16:24, 5 November 2012 (UTC)

Confusion about how telescopes work

I don't really get how a Newtonian telescope works.

Rays of light reflecting off the object we're attempting to view enter into the telescope tube effectively parallel because of its huge distance from us. The rays then reflect off of a parabolic mirror, which focuses all the rays to a point. At least it would, were it not for another mirror obliquely oriented, which reflects these rays to the telescope's eyepiece, which magnifies the image.

Here's my problem: if all the rays are focused to the same point after reflecting off the parabolic mirror, how can we distinguish between different points on the object? Wouldn't the image of the object just be a point? 65.92.7.202 (talk) 22:25, 4 November 2012 (UTC)

All parallel rays focus to the same point. Non-parallel rays do not. If you imagine 100 rays travelling perpendicular to the mirror's axis, they focus at a certain point on the focal plane. If you imagine 100 rays travelling at an angle of alpha to the perpendicular, those rays focus to a different point on the focal plane. The distance between these 2 focal points is proportional to alpha. --140.180.252.244 (talk) 00:04, 5 November 2012 (UTC)

Even your eyeball focuses light into a point, but unless there's something wrong with your eye, the point isn't on your retina. Maybe an image like this will help. I think a similar thing happens in the telescope. Vespine (talk) 05:06, 5 November 2012 (UTC)

Are you sure you don't have it backward? Unless there's something wrong with your eye, the image is on your retina. If it's not, you either have myopia or hyperopia --140.180.252.244 (talk) 07:52, 5 November 2012 (UTC)

Yes, the image is on the retina in a normal eye, but Vespine's point is that the focal plane lies between the lens and the retina. This whole thread arises from mistakenly assuming that the focal plane is the image plane. Gandalf61 (talk) 14:55, 5 November 2012 (UTC)

In a Newtonian telescope the focal plane is the image plane. The first answer by 140.180.252.244 is correct, and Vespine's followup isn't helpful as far as I can tell. -- BenRG (talk) 18:04, 5 November 2012 (UTC)

Ah, right — in astronomy the image plane "is" the focal plane because the objects viewed are "at infinity", unlike in most daily uses of the eyes. —Tamfang (talk) 19:57, 5 November 2012 (UTC)

Hang on, the focal point is different then the focal plane. The OP was talking about the focal point. You know, the spot where the light focuses to a point if you shine the sun through a magnifying glass. In a Newtonian telescope, that point doesn't fall on your retina. That's what I was trying to show with the image I linked. Vespine (talk) 21:37, 6 November 2012 (UTC)

Light slow motion

Is this real http://www.youtube.com/watch?v=SoHeWgLvlXI&feature=related. If it is I want to see the effects of relativity. I'm sick of hearing "oh yea relativity has been experimentally verified countless times" I want to see it with naked eyes. Why didn't they do that? Money is tight (talk) 22:42, 4 November 2012 (UTC)

I don't think that clip shows anything not explicable by classical electrodynamics; you see a light wave propagating, which is impressive, but not so much related to relativity. The easiest way to observe relativity with your eyes would probably be like they did it in 1919. You'd need to observe the stars around the sun (with a telescope ofc) during a total solar eclipse, and then compare the positions of the same stars with a picture you took at night when there was no eclipse. You should see the effect of the sun bending the light of the stars. - Lindert (talk) 23:13, 4 November 2012 (UTC)

The most dramatic visual demonstration of relativity is probably the Einstein ring. That article has lots of photos. --140.180.252.244 (talk) 00:00, 5 November 2012 (UTC)

Einstein's prediction before the eclipse was not that gravity would bend light – that was predicted classically – but how much. An Einstein ring doesn't tell us anything about general relativity unless we know the mass of the galaxy in front — or does it? —Tamfang (talk) 00:10, 5 November 2012 (UTC)

They can get a source traveling at half the speed of light and emits light together with a source that stays still, I want to see these two light beam travel at the same speed. Money is tight (talk) 05:51, 5 November 2012 (UTC)

To accelerate a macroscopic object (a light source) to such speeds is impractical if feasible at all with our current technology. And where would you film such an event? The light source would leave earth sooner than you can blink your eyes. - Lindert (talk) 08:59, 5 November 2012 (UTC)

It takes around 0.155mc² to accelerate an object to half the speed of light (γ=1/√0.75), so around 3.32 kilotons of TNT for a 1g object. Given enough time and monetary resources, getting an undersized LED throwie to 0.5c should be right near the edge of humanity's current technological capabilities, but unless you have Scrooge McDuck-levels of wealth, it's just not going to happen. And even if you do happen to have that kind of wealth, you're going to need to pull some strings with the UN, because I doubt they'll think "because I don't believe in special relativity" is a good enough reason to allow you build what is essentially a weapon of mass destruction.--Link ^(t•c•m) 15:22, 5 November 2012 (UTC)

Assuming your LED can survive 1,000,000 g acceleration, it will take around 15 seconds to accelerate it to 0.5c, during which time it will move about 1.5 million km. This is not within the capabilities of the human race now or in the foreseeable future. -- BenRG (talk) 17:32, 5 November 2012 (UTC)

Would you be satisfied with the Advanced Light Source, where the light is emitted by charged particles travelling at >99% of c, or the Large Hadron Collider, where collisions happen at such a rate (~1 billion per second) that they have to take careful account of the light-speed delay in order to correlate the results from different parts of the detectors?

Anyway, there's nothing strange about the speed of a wave being independent of its source. The same is true of sound waves, for example. -- BenRG (talk) 17:32, 5 November 2012 (UTC)

Yes the invariance of speed of light is very strange, because it predicts things like length contraction and time dilation. I just find it very difficult to believe and want to see it for myself. Money is tight (talk) 01:02, 6 November 2012 (UTC)

Unfortunately the speeds and energies involved are so incredibly high that there aren't many good ways to easily observe the effects directly. I recommend you look through Tests of general relativity and Tests of special relativity, and attempt to understand how some of the experiments worked and why the results confirm relativity. If there are tests with methods that you doubt or ones where you don't understand what the test is supposed to be doing, people here will be more than happy to help you work out the details. Some of the tests are pretty simple, but still very difficult to pull off on your own due to the precision required. 209.131.76.183 (talk) 15:32, 6 November 2012 (UTC)

The reason it's hard to see evidence of modern physics is that if it were easy it would have been noticed much sooner, and hence wouldn't be modern. -- BenRG (talk) 22:26, 6 November 2012 (UTC)

November 5

Impulse (physics)

In this article, it states there are 2 different units. I don't understand how those 2 different units can end up expressing the same thing in the end?174.20.101.190 (talk) 01:21, 5 November 2012 (UTC)

They are equivalent: ${\rm {N\cdot s=kg~{\frac {m}{s^{2}}}\cdot s=kg~{\frac {m}{s}}}}$A8875 (talk) 01:50, 5 November 2012 (UTC)

And, they help remind physicists about the two commonplace ways we calculate impulse: the impulse of an event is often computed by multiplying the net force by the duration of the event; or, the impulse of an event is calculated by multiplying a mass by its total change in velocity. Nimur (talk) 03:07, 5 November 2012 (UTC)

Mechanism from DNA to proteins etc?

Is the mechanism between DNA and actual proteins etc that are created mapped out?, such that one can use the DNA to calculate (dry run a cell) how the produced protein etc looks like? Electron9 (talk) 03:58, 5 November 2012 (UTC)

See Transcription (genetics), Translation (genetics), Genetic code, Protein structure prediction. It's probably best for you to make a quick first pass through these articles and say what parts of the topic still confuse you after that. Wnt (talk) 04:16, 5 November 2012 (UTC)

Yes, specifically genetic code. The genetic code is the recipe for translating from sequences of DNA bases to the sequences of amino acids that make up proteins. It is astonishingly simple. If you know the code, you don't have to know anything about the mechanism that implements it in order to predict the result. (Well, there are a few complications, but they can be ignored on a first pass.) Looie496 (talk) 05:12, 5 November 2012 (UTC)

Yes, the genetic code is astonishingly simple. But you also have to take into account post-transcriptional modifications and posttranslational modifications. And when you have done that, you only have a protein's amino acid sequence. Inferring a protein's structure and function from its sequence is very difficult. Then you need to work out how it interacts with other proteins and chemicals in metabolic pathways. Then there are the complications of gene regulation. Taking all that into account, being able to "dry run a cell" (however we interpret that) is going to be a massively complex undertaking. The genetic code is just a snowflake on the tip of the iceberg here. Gandalf61 (talk) 12:17, 5 November 2012 (UTC)

The idea (dry run) is to make a computer simulation that is feed with the DNA code. Once the proteins etc has left the cell other software can simulate the chemical reactions. As for fenotypic gene enable/disable I guess those are in turn controlled by other genes and their resulting structures interacting with environmental chemistry as a feed back loop. Is that mechanism fully understood? Electron9 (talk) 16:12, 5 November 2012 (UTC)

No I don't suppose it is "fully understood", or even close to that, except in very limited cases. The cellular model article makes interesting reading. It says "The complex network of biochemical reaction/transport processes and their spatial organization make the development of a predictive model of a living cell a grand challenge for the 21st century.". According to this report, the best we can do so far is to build a computer model of mycoplasma genitalium, a bacterium with just 525 genes. Gandalf61 (talk) 17:11, 5 November 2012 (UTC)

(e/c) The DNA will tell you the order of amino acids, but knowing the order of the amino acids tells you very little about the functionality, which is often determined by the shape of the resulting protein. There's some active research on exactly how that folding works and how those shapes are determined, including a distributed computing project for the "heavy lifting" of just crunching how all of those pieces fit together. In all likelihood there are important mechanisms we aren't even aware of. 150.148.0.65 (talk) 17:34, 5 November 2012 (UTC)

Maybe not a science question?

Clinical laboratory science, and maybe more of a legal question than anything else, but every set of clinical laboratory results I've ever seen has a statement that says that partial reproduction of the test report is not permitted. Is this just a "don't interpret single test results without seeing context" warning? 150.148.0.65 (talk) 17:34, 5 November 2012 (UTC)

Is a full reproduction allowed, and a partial not? Otherwise, if neither a full nor a partial reproduction is allowed without consent, that would be a common copyright notice. OsmanRF34 (talk) 18:02, 5 November 2012 (UTC)

To quote some sample text "Partial reproduction of this Test Report is not permitted" (at top of each page of a set of test results). The sample is from a Indian reference laboratory, but I've seen a lot of the same in American test results. It says nothing about prohibition of full reproduction. Looking at a couple of other things I have lying around it isn't 100%, one of the ones I found (American) just explicitly labels full and partial reports. 150.148.0.65 (talk) 18:29, 5 November 2012 (UTC)

I think any claim that partial reproduction is forbidden may be void due the "Quotation#Copyright law". In addition foreign law isn't likely enforceable in another country. Electron9 (talk) 18:59, 6 November 2012 (UTC)

November 6

Dichromacy and Trichromacy colorblind

I was aware some people are colorblind. I was wondering if there is any difference between dichromacy and trichromacy is any difference. If people are having trouble seeing green are they also unable seeing red. is there any difference between red and green colorblindness. I have never heard about anybody having trouble seeing yellow although Color blindness mentions blue-yellow colorblind they basically having difficulty seeing violet hues, but I never heard anybody who is disrupted on yellow hues. I am guessing most people I was aware of is Anomalous trichromacy, but I was wondering how Anomalous trichromacy works on blue-yellow sensors? Are they totally unable to see blue-yellow sensors on Anomalous trichromacy or they just see those as shades of brown. I have met one people on the bus is totally deficient on red, green, and blue they can see grayscale and shades of brown and pink, what type of colorblind is that?--69.226.43.174 (talk) 00:38, 6 November 2012 (UTC)

I think you misunderstand the meaning of the word colorblindness. It means an inability to distinguish colors that most people can tell apart, not an inability to see colors that most people can see. Looie496 (talk) 00:56, 6 November 2012 (UTC)

This page purports to show you how your favorite webpage looks to several common kinds of colorblindness. —Tamfang (talk) 01:03, 6 November 2012 (UTC)

I got the better understanding now about how colorblind works now. I bookmarked the Colorblind Webpage Filter (All I got to do is to type it on Google), and first I went through my favorite websites to play around with the colors. Anomalous colorblind is the less serious type and it is less noticeable unless under certain lighting conditions where certain cones may be skewed and interrupted. Dichromacy means people can only see two or three general colors, and their perceptions are reduced to whatever sensors are remained in their cones.--69.226.43.174 (talk) 04:45, 6 November 2012 (UTC)

Reason why we don't fall through the floor

I was having a discussion with someone on why matter doesn't simply pass through other matter (given the fact that normal matter is mostly empty space). I was under the impression that it was due to the electromagnetic force. He said that's a common misconception and it is due to the pauli exclusionary principle. Is he correct? ScienceApe (talk) 00:45, 6 November 2012 (UTC)

I have looked at Pauli exclusion principle and I am confident it isn't reasonable to apply this principle to explain why matter doesn't simply pass through other matter. Dolphin (t) 00:49, 6 November 2012 (UTC)

(This is incorrect—see below.) -- BenRG (talk) 23:13, 6 November 2012 (UTC)

It's because those atoms are bonded together as a solid (if the atoms or molecules aren't bonded together, then you have a fluid). Think of a hammock. It's mostly empty space, but nonetheless stops you from falling on the ground, because the threads are all tied together. StuRat (talk) 01:50, 6 November 2012 (UTC)

You are correct, he is wrong. The exclusionary principal describes why other electrons can't fill already occupied orbitals, hence limiting atomic bonding to specific valences. Sheesh, the things people come up with! μηδείς (talk) 02:18, 6 November 2012 (UTC)

(This is incorrect—see below.) -- BenRG (talk) 23:13, 6 November 2012 (UTC)

The Pauly exclusion principle: "Anyone with taste will exclude themself from any movie staring Pauly Shore." StuRat (talk) 03:26, 6 November 2012 (UTC)

The last exclusionary principal I encountered was my high school headmaster who kicked me out of the class for ... well, I'd better not say. -- Jack of Oz ^[Talk] 05:23, 6 November 2012 (UTC)

Wouldn't you think the "headmaster" would be tolerant of such things ? StuRat (talk) 05:47, 6 November 2012 (UTC)

Only if Jack was disciplined for being a cunning linguist. --Jayron32 05:51, 6 November 2012 (UTC)

I think they invented tolerance one Monday in 1983, well after I went to school. -- Jack of Oz ^[Talk] 06:20, 6 November 2012 (UTC)

The other person in the discussion is referring to electron degeneracy pressure, which only manifests itself in extreme examples such as the core of a collapsing star. The electron degeneracy pressure between your feet and the floor is negligible. Someguy1221 (talk) 03:22, 6 November 2012 (UTC)

(This is incorrect—see below.) -- BenRG (talk) 23:13, 6 November 2012 (UTC)

This is what he said, "The electrostatic force behaves completely differently from the contact forces we're used to. The floor pushes back exactly as much as you push on it; contrariwise, the electrostatic force's push depends entirely on the distance. You can derive Hooke's Law from the basic kinematics of QM - the compressing of the states by Pauli exclusion causes a corresponding increase in momentum as per the uncertainty principle. I'm sorry to break it to you but you've been taught a wrong fact for a long time." ScienceApe (talk) 03:32, 6 November 2012 (UTC)

From our article: A material subjected to ever increasing pressure will become ever more compressed, and for electrons within it, the uncertainty in position measurements, Δx, becomes ever smaller. Thus, as dictated by the uncertainty principle, the uncertainty in the momenta of the electrons, Δp, becomes larger.. In short, your friend doesn't know what he's talking about. The pressure exists as he suspects, but its value is insignificant outside of extremely dense matter. Someguy1221 (talk) 03:42, 6 November 2012 (UTC)

Also note that "The floor pushes back exactly as much as you push on it" is true for any explanation of a static situation. --Stephan Schulz (talk) 06:56, 6 November 2012 (UTC)

---

Solids and liquids are incompressible because of electron degeneracy pressure, and you don't fall through a solid floor (as opposed to a liquid floor) because of the intermolecular bonds. This has been asked before on the ref desk. -- BenRG (talk) 07:03, 6 November 2012 (UTC)

Yea Newton. The third law applies here: The weight of an object pressing upon another is countered by an equal and opposite force exerted by the electrostatic interaction between electric fields of atoms. Plasmic Physics (talk) 21:12, 6 November 2012 (UTC)

No, as I said above, it's electron degeneracy pressure that presses upwards on your feet, though it is horizontal electrostatic tension that prevents the floor from breaking apart under your weight. Newton's third law applies everywhere, but doesn't explain why you don't fall through the floor. You would fall through a floor made of jello, though the third law applies there too. -- BenRG (talk) 23:13, 6 November 2012 (UTC)

I just don't buy it, Ben. At normal densities, long-distance molecular interactions can be explained just fine without invoking degeneracy pressure. I don't see a need for it in this situation. Someguy1221 (talk) 00:58, 7 November 2012 (UTC)

Exactly. Where does compressability of solids fit into the degeneracy idea? Plasmic Physics (talk) 01:48, 7 November 2012 (UTC)

I would be surprised if it was correct, it would turn my understanding of atomic-force microscopy upside-down. Plasmic Physics (talk) 01:51, 7 November 2012 (UTC)

People talking alone

What's wrong with these people? I know that they are not necessarily mentally ill, some just take drugs, also legal drugs like coffee. But, what has happened in their brain, what is the brain mechanism of "mental talk, but not aloud"? Comploose (talk) 00:59, 6 November 2012 (UTC)

Please see Intrapersonal communication. Specifically: "Simon Jones and Charles Fernyhough cite research suggesting that our ability to talk to ourselves is very similar to regular speech. This theory originates with the developmental psychologist Lev Vygotsky, who observed that children will often narrate their actions out loud before eventually replacing the habit with the adult equivalent: sub-vocal articulation. During sub-vocal articulation, no sound is made but the mouth still moves. Eventually, adults may learn to inhibit their mouth movements, although they still experience the words as "inner speech"."A8875 (talk) 01:40, 6 November 2012 (UTC)

It can also be helpful in some cases, like repeating something out loud to remember it. I believe this trick works because more of the brain is involved in speaking and hearing the words than just thinking them. There's also the issue of people who aren't able to read or count silently. This could, indeed, in some cases compensate for a deficiency in their brain, by using different neural paths to bypass the non-functional portion. StuRat (talk) 01:44, 6 November 2012 (UTC)

what is the brain mechanism of "mental talk, but not aloud" - How else does one think, except as mental talk, but not aloud? All my thoughts that are not pictures are words, sentences, paragraphs, even dialogues. How else do you reach conclusions, consider options, assess situations, except as words not spoken aloud? Have I missed something? There are people who process things externally. I worked with one who drove most of us into any room in the building where she could not be heard. Is that what you mean? Bielle (talk) 02:03, 6 November 2012 (UTC)

I wanted to contrast people who are "mental talk, in silence" to others who are "mental talk, aloud". Something is different in the second case: too much coffee, stress, some drugs sometimes makes some people be in the second group, even if they are normal under other aspects. I was not asking about any contrast in terms of "mental talk" / "no mental talk". Comploose (talk) 02:19, 6 November 2012 (UTC)

My mom always used to say "People who talk to themselves are either crazy or have money in the bank." To which she would always add "And I'm flat broke." Of course, it isn't any sign of being mentally defective in any way to occasionally talk to yourself aloud. People who aren't under the influence of drugs or stress or who are otherwise perfectly normal, mentally (for any given standard of "normal"), do sometimes speak to themselves out loud. Of course, people carry on all sorts self-talking, whether it is internal monologue, keeping a diary or journal of some sort. One journal articles I found on actual talking out loud to oneself is [9].--Jayron32 03:35, 6 November 2012 (UTC)

Unfortunately, when I engage in an internal monologue, I always end up heckling myself. StuRat (talk) 03:23, 6 November 2012 (UTC)

At least that won't make you go blind. Be grateful for the respite.  :) -- Jack of Oz ^[Talk] 05:18, 6 November 2012 (UTC)

Isn't heckling yourself by definition internal dialogue? -- Q Chris (talk) 13:47, 6 November 2012 (UTC)

Maybe we should all get in touch with our inner StuRat and have a good old chinwag. I'll get round to it when I've finished my current vitally important project (transplanting Mt Everest to the Antarctic a teaspoon at a time). -- Jack of Oz ^[Talk] 21:26, 6 November 2012 (UTC)

"I used to be poor and crazy, but now I'm rich and eccentric." Someguy1221 (talk) 03:19, 6 November 2012 (UTC)

It's entirely natural to talk out loud, whether there is someone there to listen or not. "How can I know what I think until I hear myself say it?" The discipline of speech is good for ordering internal thoughts. --TammyMoet (talk) 10:13, 6 November 2012 (UTC)

Nature of sound

If a car crashes in the forest and nobody is there to hear it, does it still make a sound? Bonkers The Clown (talk) 07:53, 6 November 2012 (UTC)

Yes. HiLo48 (talk) 08:03, 6 November 2012 (UTC)

And what makes you say so? Can you elaborate as to why "yes" and not "no"? Bonkers The Clown (talk) 08:05, 6 November 2012 (UTC)

The Laws of physics. HiLo48 (talk) 08:14, 6 November 2012 (UTC)

Well the driver would presumably hear something. But this is essentially the same question as If a tree falls in a forest, where this is discussed. (I changed the title of your question to something more meaningful.)--Shantavira|^{feed me} 08:27, 6 November 2012 (UTC)

This depends on your definition of "sound". The way physicists define it, as a pressure wave, does not require an observer. Indeed, we would need to change much of physics to allow for a collision, in air, which does not produce a pressure waves. Now, if a philosopher wants to define sound as only existing when it is heard, that's fine, but has nothing to do with science. StuRat (talk) 19:55, 6 November 2012 (UTC)

What if it is a superpositional Schrodinger soundwave? Plasmic Physics (talk) 20:59, 6 November 2012 (UTC)

In that case, only dogs can hear it. And Schrödinger. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:20, 6 November 2012 (UTC)

I mean, if the crash was initiated by a quantum trigger, would it still make a definitive sound if there is no observer? Assuming unrealistically perfect conditions. Plasmic Physics (talk) 01:42, 7 November 2012 (UTC)

protons

Is the proton a fundamentally stable particle? Or does it have a finite lifetime as predicted by some extensions to the standard model? What explains the anomalous spin of protons? :) Bonkers The Clown (talk) 08:39, 6 November 2012 (UTC)

If you're aware that physicists can't decide whether the proton is fundamentally stable, why would you bother asking a bunch of random people on the internet? Someguy1221 (talk) 09:47, 6 November 2012 (UTC)

Additionally, our article on the Proton spin crisis mentions that this is an unsolved problem, which I'm sure you were already aware of. Someguy1221 (talk) 09:51, 6 November 2012 (UTC)

A lower limit for the half-life of the proton is 2.1 × 10²⁹ a, but proton decay has never been observed. Double sharp (talk) 14:05, 6 November 2012 (UTC)

The proton is almost certainly unstable, the only question is how large the half life is. Hawking has argued that the proton would at least have to decay via making a transition to a virtual black hole which then evaporates via the Hawking process.

Also note that the deuteron is known to be unstable in the standard model with a half life of about 10^(218) years. Count Iblis (talk) 16:18, 6 November 2012 (UTC)

Proton decay does or should have the relevant ideas covered. DMacks (talk) 16:29, 6 November 2012 (UTC)

Worried to death?

I was thinking about a phrase my mother used to use "I was worried to death!" and wondered if, in fact, it was possible to shorten your life - or at least adversely affect it - by worrying! Is there any good scientific research on the deleterious effects of worry on human beings? I don't mean the mental illness anxiety, by the way. Just plain, old fashioned worry. --TammyMoet (talk) 10:15, 6 November 2012 (UTC)

Worrying causes negative thoughts and negative thoughts translate into depression. And you'll die sooner or later if you worry daily. Don't worry. Be happy. :) Bonkers The Clown (talk) 13:38, 6 November 2012 (UTC)

Citation needed. AlexTiefling (talk) 13:41, 6 November 2012 (UTC)

If you mean worry v.tr. 3 a (To seize with the teeth and shake or tug at repeatedly) then you certainly could be worried to death rather quickly! -- Q Chris (talk) 13:44, 6 November 2012 (UTC)

Topical question, apparently empirically answered this week in a rather tragic death. well, okay, it was 'heartbreak', but that has to be a near-cousin of worry, non? --Tagishsimon (talk) 14:59, 6 November 2012 (UTC)

That looks like hearsay to me. AlexTiefling (talk) 15:05, 6 November 2012 (UTC)

Here's a news article, with links to a scientific article [10]. It explains how grieving can greatly increase incidence of heart attack. I don't know if "grieving" is similar enough to "worry" for your purposes, but there it is... SemanticMantis (talk) 17:18, 6 November 2012 (UTC)

Not grieving? Keeping it all inside? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:18, 6 November 2012 (UTC)

Stress certainly has negative effect on health, and thus can reduce your lifetime. Not sure if that's what you mean by worry. - Akamad (talk) 17:41, 6 November 2012 (UTC)

To clarify, what I meant by "worry" is something like sitting envisioning a future event that might or might not actually happen and all its ensuing ramifications. You know, the sort of unproductive thought processes you indulge in at 3 am... --TammyMoet (talk) 20:47, 6 November 2012 (UTC)

As with "Future Events Appearing Real". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:18, 6 November 2012 (UTC)

how to be more powerful (literally, not philosophically)

EDIT: First of all this question had been misinterpreted. This is not a philosophical question but purely practical. I hope you are able to follow my reasoning, and what the question is.

Let us begin with the observation that with a coffee mug or any other object in front of you (try it!) you can cause the coffee mug to move simply by selecting a new location for it, picking it up, and moving it.

The proximate cause of the move or displacement was your own thought. Since, for example if you moved it with your right hand, if after that thought you found your right hand encumbered by something you forgot about, you would have just moved it with your left hend. It is really your thought that caused the change.

So, a thought is a very powerful thing.

But, on the other hand, there are thoughts that do not cause a change in the world. They come and go, like an old man's erection. They affect nothing.

I would like to know how to make my thoughts more powerful. To begin with, by increasing their effectiveness on my own body, and then on my team, organization, country, world. What do you suggest is an appropriate way to increase the leverage of my thought, so that I can not only move a coffee mug, but reshape my life, country, or world? Please be detailed.--91.120.48.242 (talk) 13:19, 6 November 2012 (UTC)

Begin by making good use of your time. Spend less of it asking unproductive questions on RefDesk.

In all seriousness - economic privilege will make more difference to the 'power of your thoughts' than anything else. If you're white, male, American, upper- or middle-class, able-bodied, neurotypical, not subject to mental ill-health, heterosexual, and not too outspoken about your religious views, you'll go far. As to what you can do, yourself - there are many things, but the degree to which they're effective correlates to the extent that you match the privileged profile described. (Obviously this is socially determined; if you're Japanese rather than American, then being ethnically Japanese rather than white is the appropriate factor, etc.) AlexTiefling (talk) 13:34, 6 November 2012 (UTC)

I really did not mean on this level, I meant on an everyday level, hence the example of a coffee mug. I mean things like translating from "having a product idea" to actually shipping it, much like translating from "I want to move this cup over" to it actually being moved over. Can you address it in more practical terms? --91.120.48.242 (talk) 14:10, 6 November 2012 (UTC)

If you mean literally then a Powered exoskeleton would do it for you. -- Q Chris (talk) 14:25, 6 November 2012 (UTC)

That must be one massive mug. Plasmic Physics (talk) 20:53, 6 November 2012 (UTC)

You talked about your ability to "reshape my life, country, or world" - that sounds like going beyond the immediately physical effect of your thoughts. 'Reshaping the world' doesn't sound like 'an everyday level' to me. If you do mean things like translating product ideas to manufactured products, then my earlier comments still stand. AlexTiefling (talk) 15:04, 6 November 2012 (UTC)

Try reading How to Win Friends and Influence People by Dale Carnegie. StuRat (talk) 19:50, 6 November 2012 (UTC)

or Power for Success by Frank Haddock. Also speaking the truth can garner other's support. and being able to find hidden truths is very powerful as it is difficult to deny/ignore GeeBIGS (talk) 01:19, 7 November 2012 (UTC)

Air quality in Prometheus

During landing (minute 23 and about three quarters) on the foreign planet, the readings of the gases comprising the atmosphere are given as 79% nitrogen, 21% oxygen and trace argon -- something very similar to earth's atmosphere. But a scientist on board then says that CO₂ readings are three times what they would be on earth -- about 3% -- and she explains that one would die after only a few minutes of exposure to such an atmosphere without a protective suit (and, I'm assuming, a breathing device). Why would triple the amount of CO₂ necessitate a protective suit? DRosenbach ^{(Talk | Contribs)} 14:35, 6 November 2012 (UTC)

Not surprisingly our article Carbon dioxide#Toxicity mentions some of the effects of an increase carbon dioxide:

In concentrations up to 1% (10,000 ppm) will make some people feel drowsy.[78] Concentrations of 7% to 10% may cause suffocation, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.

It also links to Hypercapnia, which is our article on the condition of excessive carbon dioxide in the blood. 3% seems to be in the range of starting to get close to dangerous but perhaps not quite there yet and I'm not sure that dying within a few minutes is likely. I'm not even sure it's likely at 7% although I would't want to risk it particularly if anyone who could try to save me is going to be exposed to the same conditions. Perhaps the producers were thinking of carbon monoxide?

BTW our article also mentions something which you can check in Atmosphere of Earth. Either your memory of the movie is wrong, or there's something seriously wrong with it. 3% carbon dioxide is not triple the concentration of earth (which isn't 1%, that's well over 1 order of magnitude wrong).

Nil Einne (talk) 14:47, 6 November 2012 (UTC)

You're right -- all she said was "[it's only like earth] if you're breathing through an exhaust pipe. CO₂ is 3%. Two minutes without a suit and you're dead." DRosenbach ^{(Talk | Contribs)} 14:50, 6 November 2012 (UTC)

The exhaust pipe bit makes me think it even more likely the producers were confusing carbon monoxide and carbon dioxide. Nil Einne (talk) 14:52, 6 November 2012 (UTC)

This source also mentions [11] that the planet in question was most likely supposed to be carbon monoxide as it's been suggested before that the planet is polluted with carbon monoxide. (I'm not entirely sure why that would be the case, if the planet has similar atmospheric conditions and temperature to earth, you would expect any carbon monoxide would be oxidised to carbon monoxide so there needs to be a constant high source or some reason why this is not happening, see Carbon monoxide#Atmospheric presence. You could get something like Venus where photodissociation produces carbon monoxide but I'm not entirely sure how likely that is if you otherwise have similar conditions to earth. At the very least the high levels of UV may be an additional concern.) Nil Einne (talk) 15:02, 6 November 2012 (UTC)

Using the figures in Hypercapnia, 10kPa will cause acute symptoms shortly leading to death--that's about a 10% concentration. Chronic respiratory acidosis will set in at about half that concentration. The 3% number is probably global warmist propaganda to make CO2 sound more dangerous than it is. CO2 and CO are odorless. Given how bad that movie stank, I suspect they meant to say it had a 3% concentration of flatus. μηδείς (talk) 15:02, 6 November 2012 (UTC)

Don't assume malice when stupidity will suffice.-- OBSIDIAN†SOUL 16:45, 6 November 2012 (UTC)

All of the above explains why you would need breathing apparatus; but not why a full-body suit would be needed. One reason would be solar radiation or protons, but as space exposure notes, that's a long term concern, not a 3-minute-death issue. Another would be very low pressure - if the ambient pressure was very low (cf Armstrong limit) an explorer would develop ebullism (as Kittinger did on his hand during his record dive), even if she was breathing air at 1 bar. But the planet exhibits a dense cloud layer miles above the surface, suggesting the surface pressure is pretty high. So that leaves the possibility that the atmosphere contains something so unpleasant that even a few minutes of it touching exposed skin would be fatal. Skin is pretty good at keeping out the environment, so that would necessitate the atmosphere was significantly acidic, caustic, or otherwise significantly toxic - something much worse than exhaust gas. Under relatively normal pressure and the specified air contents, they'd just need a respirator - which is exactly what the human characters wear in Avatar. I fear the suits are there for the theatrical "let's suit up" effect they provide. -- Finlay McWalterჷTalk 16:58, 6 November 2012 (UTC)

And breathing specifically is the express purpose of the suits - Holloway asks David why he's wearing a suit when "you don't breathe" (0:25:38) - not pressure, toxicity, or biosecurity. -- Finlay McWalterჷTalk 17:05, 6 November 2012 (UTC)

Actually, about %5 carbon dioxide is needed to cause chronic acidosis, so short exposures of 3% to healthy people should be harmless. The purpose of the suits was to show the contrast between the inside and outside environments, to give the alien something to break through--to allow the use of the suits as props. μηδείς (talk) 18:05, 6 November 2012 (UTC)

Alcoholism - Biological process

Hi all, First, please note that this is not a request for medical advice, but a question about specific biological process inside the body. Please do not give any specific medical advice. I have read places that alcoholism/recovering from alcoholism can cause the following 2 effects:

1: Extremely bad body odor 2: External bruises around the liver, external scarring.

I was wondering how it is that the body/the alcohol ingested can cause these problems - and what is the chemical/biological reason for this on a fairly simple level. There doesn't seem to be anything lited in the article on Alcoholism. Please do not give advice on how to treat these as it consitutes medical advice and I don't want my post deleted. 80.254.147.164 (talk) 15:08, 6 November 2012 (UTC)

1. Alcoholism causes a deterioration in self-care, drunks don't shower as regularly as non-drunks in a given population.
2. Alcohol impairs blood clotting - bruising anywhere on the body may be exacerbated. Roger (talk) 18:14, 6 November 2012 (UTC)

1) Alcoholics may also sweat alcohol, which smells unpleasant to most, and also readily evaporates, taking regular body odor with it. StuRat (talk) 19:45, 6 November 2012 (UTC)

Death determination in Sherlock Holmes

Maybe we're all just a little too informed these days because of shows like CSI, but shouldn't Watson have been confused by the hanged man's lack of rope marks on the neck that usually occur during a hanging. It seems awfully sloppy for him to have overlooked such a thing, especially since both he and Holmes are so astute in so many other scientific findings? I mean, sure, it would disrupt the entire plot, but it seems to undermine it just a tad too much -- they could have had him executed in another fashion to preserve his apparent death and subsequent resurrection. DRosenbach ^{(Talk | Contribs)} 14:54, 6 November 2012 (UTC)

It was somewhat sloppy, but Watson was only there to pronounce death, not perform an autopsy or otherwise determine cause of death. IIRC, he checked for pulse and maybe made a mirror test, but that was it. The guy who cut Blackwood down should have been the one to mention the oddity, I would think. Matt Deres (talk) 15:35, 6 November 2012 (UTC)

The entire premise of Sherlock Homes is faulty, that every clue leads you down a single path. For example, "no sign of a break-in" = inside job. Instead, every clue only alters the probabilities, and you never can absolutely conclude anything, only that certain chains of events are more likely than others. StuRat (talk) 19:42, 6 November 2012 (UTC)

Cloning in animals Vs. plants

A gene of interest has been isolated via restriction enzyme digest and amplified using polymerase chain reaction (PCR). We want to clone this gene of interest by inserting it into a plasmid vector, making a recombinant DNA molecule. What differences in the cloning method would we want if we wanted to express the gene of interest into a plant? — Preceding unsigned comment added by 150.203.114.11 (talk) 15:02, 6 November 2012 (UTC)

I'm sorry, but this (to me) a very general and vague question. Can you clarify? In case it helps, one simple difference between cloning in animals and plants is that many plants naturally clone themselves, see vegetative reproduction. In animals, natural asexual reproduction is highly restricted, mostly to little things like hydras. How is this relevant to gene insertion? SemanticMantis (talk) 17:10, 6 November 2012 (UTC)

Maybe some context will help. That question is the last in a sequence. Here it is:

A gene of interest has been isolated via restriction enzyme digest and amplified using polymerase chain reaction (PCR). We want to clone this gene of interest by inserting it into a plasmid vector, making a recombinant DNA molecule.

What features of a plasmid are necessary for this molecular cloning to work?

How do we get the gene of interest into the plasmid vector?

The gene of interest is inserted into the plasmid. Describe two methods by which the plasmid can be transformed into E.Coli.

How do we know which transformed E.Coli cells are the desired clones?

Describe any differences in the cloning method if we wanted to express this gene of interest into a plant.

--150.203.114.11 (talk) 17:16, 6 November 2012 (UTC)

Ok, that looks like homework. If you want more help, you'll have to explain how you've started, what sources you've looked at, and where you are stuck. We generally have a rule against doing people's homework for them, see the disclaimer at top. SemanticMantis (talk) 17:20, 6 November 2012 (UTC)

It's not homework; it's pracice questions for the examin. And besides, this is biology; there is no such thing as "being stuck" like there is with maths or physics; you either know the answer a priori or you don't; it's not something you can deduce or work out.--150.203.114.11 (talk) 17:31, 6 November 2012 (UTC)

Thank you for being honest. Practice examination questions are clearly a form of homework. If we work out the answerr for you, that helps us get smarter, but doesn't help you. Your claim about being stuck is nonsense. Floda 121.221.77.87 (talk) 00:26, 7 November 2012 (UTC)

American Bison Furs

With the Ameican Bison once numbering 30 to 60 million, and hundreds of thousands to millions of hides being shipped back to the east coast every year in the second half of the 1800's, what happened to all the furs, rugs, robes, etc...? A majority would be lost, worn out, thrown away, but with untold millions of hides processed into some sort of product shouldn't they still be a realitively common item in the United States? Or do treated hides just not last long enough? Beach drifter (talk) 15:44, 6 November 2012 (UTC)

Would not much of the hides be turned into leather? I'd guess 100+ year old shoes, suitcases, etc, are relatively common, but equally that the source - bison, or cow, for instance - less obvious. --Tagishsimon (talk) 16:00, 6 November 2012 (UTC)

I don't think furs last all that long, at least if you use them. If stored in a refrigerator for a century they last, sure, but not many people did that. StuRat (talk) 19:36, 6 November 2012 (UTC)

What is a major disadvantage of PCR compared with in-vitro replication?

What is a major disadvantage of PCR compared with in-vitro replication?--150.203.114.11 (talk) 16:50, 6 November 2012 (UTC)

What did your teacher say was a major disadvantage, or what was written in your textbook? That's where you will find the answer to your question. --Jayron32 18:40, 6 November 2012 (UTC)

Science fiction question regarding physics

I'm hoping to get a realistic physics viewpoint on a fictional event. Say there is a person who is, for one reason or another, trapped between two different timelines. Their body rapidly phases between the two, leaving a vacuum during the infinitesimally short time they are not present. Would such a vacuum be extremely cold? For directly, would the person be cold to the touch? Thanks in advance for anyone who answers. --Ghostexorcist (talk) 17:56, 6 November 2012 (UTC)

The process you are describing would cause the conservation of matter and energy to be violated in each timeline. This is such a wild deviation from normal thermodynamics, I don't think we can easily speculate. But how rapid is the oscillation? Will Brownian motion convey air molecules into the vacated space prior to the person returning? Because if so, that space might be expected to get very hot, rather than cold - with consequent danger to the oscillating person, not just bystanders. AlexTiefling (talk) 18:01, 6 November 2012 (UTC)

Well, just as physics was modified to allow for the conservation of total mass and energy, versus each separately, let's imagine that it's again modified to allow for conservation of the total mass and energy in all possible timelines. In this case, assuming the person does not materialize in a vacuum, the air where they appear needs to go somewhere. The most elegant solution is to send that air the other way, so no vacuum is created. If, instead, you suddenly blow the air out of the way, then that will create a minor explosion where the person arrives, and a sudden implosion where they left. Both would result in an increase in temperature. The place they left would have a net reduction in air pressure and the place where they arrived would have an increase. In an enclosed space, this could pop your ears. If you are the person being transported, this might pop your ears in any case. So, sending the air back the other way is the best solution (although this could introduce bacteria, pregnant mosquitoes, and such into the other environment). StuRat (talk) 19:29, 6 November 2012 (UTC)

This is just basically nonsense. Any one contradiction logically implies all other contradictions. You might as well ask if 2=3, then does 5=6? The answer can be yes (if 2=3, then 2+3=3+3, or no, because 2x2=3x2, i.e. 4=6, not 5. Or does it? It is utter bullshit, so make up whatever ad hoc nonsense (like air switching) you want. μηδείς (talk) 19:50, 6 November 2012 (UTC)

Medeis put it a bit impolitic, but she's essentially correct. It was stated much better by Arthur C. Clarke, who had Clarke's three laws, the third of which is very germane to the question. What Clarke said was "Any sufficiently advanced technology is indistinguishable from magic." Which is to say that, when writing speculative fiction of any sort (either fantasy or sci-fi), it isn't really necessary to be entirely correct with regards to the laws of physics, indeed it is better to not even try at all, since any half-assed kludge attempting to explain FTL communication or teleportation or any of a number of other common sci-fi tropes will necessarily invite criticism (justly so) as being completely incompatible with the known laws of physics. So Clarke's solution was to just not try: let the magic be magical. Also relevent: when writing about the present, we don't spend any time explaining TV or the internet or any of a number of other technologies that would have seemed quite "magical" to anyone living, say, 300 years ago. We all know TV works, and many of us know why it works, and even if we don't it is common enough to be accepted without an exhaustive discussion of how the laws of physics allow it to work. In the same way, there's no need to make room in your science fiction writing to allow for lengthy explanations of how physics allows for some bit of sci-fi technology: the characters in the story will accept it, so there's no real need to explain it to the readers, and again, any attempt to explain it to the readers will only come off as clumsy and essentially wrong. --Jayron32 20:06, 6 November 2012 (UTC)

I disagree. I like my sci-fi to at least be within the realm of possibility. Take the Stephen King book The Stand. It started out about something possible, an out-of control disease spread from a germ warfare lab, then became an absurd tale about the devil. At that point I lost interest. Also note that real sci-fi occasionally gets it right, with Clarke predicting communication satellites and even The Jetsons predicting the microwave oven. StuRat (talk) 20:19, 6 November 2012 (UTC)

De gustibus non est disputandum. Clarke has sold a book or two in his day, and may have something relevent to say on writing successful science fiction. --Jayron32 20:22, 6 November 2012 (UTC)

Not to mention that The Stand really isn't science fiction, at least not the type of "spaceships and robots" science fiction that both the OP and Clarke are discussing here. Applying his law requires sufficiently advanced technology, and absolutely nothing in The Stand is really advanced technology. It is essentially set in the 1970s. Finally, not liking Stephen King is fine: many people don't like him. But not liking The Stand merely because you didn't expect anything supernatural in it seems incongruous. The supernatural is kinda his thing. I mean, even assuming you read The Stand the year it came out, there were previous books about A telekinetic teenager, a town of Vampires, and a telepathic child and a haunted hotel. It took him until Cujo before he wrote a book entirely devoid of the supernatural, and even after that, the vast majority of his books feature it prominently. --Jayron32 21:12, 6 November 2012 (UTC)

I have to agree with Jayron re The Stand. King almost always writes fantasy dramas. The Stand succeeds briliantly as a Drama. (I am not a huge fan of King's, but his good books are good.) The Tommyknockers is pure science fiction, and it's crap. 11/22/63 is almost pure science fiction, and succeeds brilliantly. King has a thing for ghosts or devils opening doors. he does it in The Shining and The Stand, which are both successful dramas. He needs to be judge within universe and onthe basis of a drama writer.

If you want hard sci-fi read the early Larry Niven. For example, his teleportation boothes are subject to the conservation of momentum and require oceanic buffers to prevent zoom-splatification. As far as I am concerned, a good human conflict is the essence of drama. If you want good sci-fi then look for good drama. Miven could do this and Heinlein was the best. No one ever gave a whit about the Dean's bull ...shit. μηδείς (talk) 21:48, 6 November 2012 (UTC)

I liked Heinlein's supernatural stuff as much as his hard SF. I mean the early supernatural stuff, like Gulf and The Unpleasant Profession of Jonathan Hoag. Stranger is OK but it's on the border of where he abandoned tight plotting for having his characters explain things to each other. --Trovatore (talk) 21:57, 6 November 2012 (UTC)

Other good examples: Lost Legacy, Waldo, Magic, Inc. --Trovatore (talk) 23:24, 6 November 2012 (UTC)

One of the things to remember about good science fiction writing is that it is good writing first and good science fiction second. What makes some of the best science fiction is the sort of universality of themes and novel approaches to them, which isn't something that is strictly confined to science fiction, but is what makes all quality literature worth reading. In good science fiction, the "science fiction" elements blend in or melt away in ways that make them part of the background of a really good story. Which isn't to say that such elements are unimportant, but there's a certain MacGuffin-like quality to science fiction: If you strip away the sci-fi bits and still have a good story and compelling characters, and if the sci-fi itself doesn't distract from it, you have a great book. I mean, what is The Moon is a Harsh Mistress if it isn't a work of revolution fiction or a critique of colonialism. How is the theme of A Space Odyssey all that different from the Genesis narrative of Adam and Eve in the Garden of Eden? Isn't the Monolith merely the Tree of Knowledge? Isn't the Foundation Trilogy basically a fanciful version of Gibbon's Decline and Fall... mixed with a healthy dose of Ludwig Boltzmann? Ben Bova's works are a socialist critique of modern capitalist excesses. It goes on and on: well respected sci-fi can always be reduced to core themes that are universal to the human condition. There's rarely been a well respected and well read work of science fiction which is just a series of fanciful inventions that goes nowhere interesting. They can be adventure stories, social critiques, religious allegory, whatever, but science fiction is merely a setting and not a theme unto itself, at least not when it is done by those that critically and commercially are regarded as doing it best. --Jayron32 22:17, 6 November 2012 (UTC)

RE: 'In good science fiction, the "science fiction" elements blend in or melt away in ways that make them part of the background of a really good story'. I disagree. I want the sci-fi elements up front. One thing I disliked about the original Outer Limits was how they often felt the need to put some type of "human interest" story up front, like whether two of the characters will rekindle an old romance. If I wanted to see that, I'd watch a soap opera or read a Danielle Steel book. StuRat (talk) 22:59, 6 November 2012 (UTC)

Mixing Oort clouds

I came across this diagram showing that in approximately 25,000 years Alpha Centauri will make its closest approach to the Sun - approximately 3 light years. The diagram indicates that the Oort cloud is about 1.5 light years in radius (somewhat more than the Oort cloud article says). Assuming that Alpha Centauri also has an Oort cloud similar in size to the solar system's Oort cloud, it seems possible the two clouds might over overlap to some extent. Is there likely to be any mixing of material between the two systems? Astronaut (talk) 18:53, 6 November 2012 (UTC)

Possibly, but the extreme low density of both means that gravitational interactions will be minimal, much less any actual collisions. However, the orbital periods of Oort cloud objects around the Sun are so slow, that even the slightest deflection could have noticeable impact after a few such rotations (which is many thousands of yeas). StuRat (talk) 19:17, 6 November 2012 (UTC)

The orbit of Proxima Centauri is not known or even confirmed, so guesses about an Oort cloud around the Alpha Centauri trinary are beyond speculative. μηδείς (talk) 19:45, 6 November 2012 (UTC)

By "not even confirmed" do you mean it's not known whether Proxima has positive or negative energy with respect to Alpha A/B, or what? —Tamfang (talk) 20:03, 6 November 2012 (UTC)

Sources I have read, including our own article, which was the most recent, say that it is not yet confirmed whether Proxima Centauri is gravitationally bound to Alpha Centauri A and B. I unreservedly, and wholeheartedly, recommend The Sparrow. μηδείς (talk) 21:35, 6 November 2012 (UTC)

How do you define over-overlapping, is it a synonym for superoverlapping or repeat overlapping, what is the difference between overlapping and over-overlapping? Plasmic Physics (talk) 20:47, 6 November 2012 (UTC)

IQ/social group

Are there any serious studies regarding IQ by social group. Like IQ of Christians/Jews/Muslim, IQ of women/men. I know that such things would make many people ruffle their feathers, but it could be perfectly scientific. Comploose (talk) 19:06, 6 November 2012 (UTC)

Those aren't "social groups". And, you're right that it would be far too controversial. Scientists don't enjoy having their motives and research questioned, and much less do they death threats. StuRat (talk) 19:13, 6 November 2012 (UTC)

What are they then? Comploose (talk) 19:20, 6 November 2012 (UTC)

Religion and gender. Not sure if there's a good collective term for them. Under anti-discrimination laws they are sometimes called "protected groups" (along with race, national origin, and maybe sexual orientation). StuRat (talk) 19:33, 6 November 2012 (UTC)

Please refer to race and intelligence.A8875 (talk) 19:18, 6 November 2012 (UTC)

Well, most of such studies of race are pretty dubious. It's easier to define gender than race.

First of all, you're not talking about gender; you're talking about sex. But anyway, it isn't necessary to have a precise definition of race to do a statistical study on what variables correlate with it. If you can get all observers to agree most of the time on what category someone belongs to, that's enough to see whether other things are correlated. The weakest part of such studies is probably trying to figure out what exactly you're measuring, not whom to count. --Trovatore (talk) 19:46, 6 November 2012 (UTC)

Maybe. Maybe not. A small, but not insignificant number of people are intersex or transgender (of various types). And that's not even getting into whether to categorize the various kinds of homosexuals and bisexuals in there somehow. Any time you try to categorize people in pretty much any way, you're going to find it stickier going than you could have imagined at the outset. Matt Deres (talk) 19:51, 6 November 2012 (UTC)

But once again, it really doesn't matter. The existence of intersex folks makes it problematic to claim that sex is a completely well-defined category, but it poses almost no problems for studying what correlates with sex, because the percentage of intersex persons is very small indeed. --Trovatore (talk) 19:53, 6 November 2012 (UTC)

Read The Bell Curve, if you dare. μηδείς (talk) 19:52, 6 November 2012 (UTC)

In addition to race and intelligence (already mentioned), we also have sex and intelligence and religiosity and intelligence. Dragons flight (talk) 20:06, 6 November 2012 (UTC)

Coming soon: Cat/dog preference and intelligence. Evanh2008 ^{(talk|contribs)} 21:07, 6 November 2012 (UTC)

Cats can live with their cerebra removed, dogs die. QED. Arrfff! μηδείς (talk) 21:31, 6 November 2012 (UTC)

It's clear that cats are smarter than dogs. A dog will do whatever you want him to do. How many intelligent people do you know who'll do that? --Trovatore (talk) 21:47, 6 November 2012 (UTC)

It depends on whether you consider members of a political party to be "intelligent". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:12, 6 November 2012 (UTC)

Ha! I always knew rebelliousness was a sign of intelligence. Thanks for that insight, Trovatore. -- Jack of Oz ^[Talk] 23:46, 6 November 2012 (UTC)

cats aren't rebellious. (Neither are dogs, unless they've been mistreated, in which case they're usually just crazy.) The former are just to stupid in most cases to know what is wanted of them. Note that dogs are aware there' "master's" eye direction, while cats are oblivious. Might as well brag about your pet tape worm's independent streak. μηδείς (talk) 01:39, 7 November 2012 (UTC)

Tipler Cylinder

The maths behind the Tipler cylinder seems to be very hard to find both on wikipedia and elsewhere. What exactly would happen to an object, say a rocket of some sort, that approaches it? The article says it can travel backwards in time, does this mean it exceeds the speed of light in some form? Wouldn't the rocket be affected by G-force and/or pressure and gravity?

I found out about the Tipler cylinder through a horizon documentary and it said it provided a possible way to travel back in time as oppose to a black hole, in which you cannot escape the event horizon. Does this mean that if a Tipler cylinder existed it would not have any form of event horizon? And that at any point the rocket could leave it's orbit? Does this mean light can escape it too? — Preceding unsigned comment added by 109.153.170.218 (talk) 21:59, 6 November 2012 (UTC)

Also some sources say it has to be infinitely long whereas others say it just has to be sufficiently long for the rocket to ever avoid the ends of the cylinder. Which are correct? — Preceding unsigned comment added by 109.153.170.218 (talk) 22:05, 6 November 2012 (UTC)

Does a full moon cause higher tides, and if so, how much higher?

This was part of the story of Hurricane Sandy. Many tellers of the story included the "fact" that the full moon would make the flood water levels higher. Does it? How much? HiLo48 (talk) 22:53, 6 November 2012 (UTC)

Spring tide has the details. It's a well-known and well-studied phenomenon. AlexTiefling (talk) 22:58, 6 November 2012 (UTC)

As for "how much", I think it's generally in the 20% ballpark (with a corresponding reduction for neap tides), though I'm sure it varies by locale. You can look up tide gauge data for the US from NOAA; here's the Atlantic City, NJ gauge for the coming month. Tide range on the 15th is about 6.5 feet, contrasted with 3.5 feet on the 8th (still for the larger tide; the smaller tide that day is only 2.5 feet). — Lomn 23:26, 6 November 2012 (UTC)

(ec)Oh, and clarifying: the moon making the flood levels higher is, for all practical purposes, strictly a matter of the spring tide. The storm surge is over and above the normal tide level to yield the total flood height, but a hurricane producing an 8 foot surge at full moon will still produce an 8 foot surge at a half moon, too. Sandy was particularly bad in that landfall near NYC coincided with high tide and spring tide, though it fortunately didn't coincide with the higher high tide (see this plot from Sandy Hook, NJ right up to failure). — Lomn 23:33, 6 November 2012 (UTC)

It may be well known and well studied, but from my perspective, it's rarely well explained and often misunderstood. The only quantitative measure I can see in the Spring tide article is "causing tidal differences of inches at most". I have the impression that there's a popular misconception that because the full moon is brighter, the moon somehow causes much bigger tidal differences. The discussion at Talk:Hurricane Sandy#Should the Full Moon be mentioned? gives me just that impression. HiLo48 (talk) 23:30, 6 November 2012 (UTC)

Well, note that "inchest at most" is specifically referencing perigean spring tide particularly, and is "inches" with regards to an average spring tide. Spring tide vs average tide can be quite substantial. Another popular misconception (or just a factoid that's easy to miss) is that the full moon and the new moon produce identical extreme tidal effects. — Lomn 23:35, 6 November 2012 (UTC)

Making eggs on an industrial scale

How do egg farmers get roosters to service the massive quantities of hens on an industrial scale? Or do hens make eggs without getting any sex that cannot become chicks? Or can chickens reproduce parthenogenetically? 67.163.109.173 (talk) 00:10, 7 November 2012 (UTC)

hens make eggs without getting any sex that cannot become chicks. Dauto (talk) 00:19, 7 November 2012 (UTC)

What are you trying to say Dauto + OP? I suppose you both meant: "hens lay eggs without sex." — Preceding unsigned comment added by OsmanRF34 (talk • contribs) 00:24, 7 November 2012 (UTC)

You just have to insert proper punctuation to make it make sense: "hens make eggs – without getting any sex – that cannot become chicks". Someguy1221 (talk) 00:51, 7 November 2012 (UTC)

OK, that sounds like a cautionary tale about how important punctuation is. There is still the problem of saying "make eggs" instead of "lay eggs", as if the chicken were preparing the eggs. OsmanRF34 (talk) 00:56, 7 November 2012 (UTC)

I guess you're on my mother's side of a minor dialect divide between us: it grates on me when she says "make a potato" to mean "cook a potato". —Tamfang (talk) 01:06, 7 November 2012 (UTC)

I'd use parens: "Hens make eggs (without getting any sex) that cannot become chicks." Or, if we don't want such a clumsy sentence: "Unmated hens lay infertile eggs." StuRat (talk) 01:01, 7 November 2012 (UTC)

The hens will lay eggs without ever mating. Presumably they have been bred for enhancement of this trait. The vast majority of eggs you buy at the grocer's will be unfertilized and contain no embryo. At a low rate, unfertilized chicken eggs will begin development through parthenogenesis, but they almost always fail before hatching. We have little bit at Parthenogenesis#Birds. Someguy1221 (talk) 00:24, 7 November 2012 (UTC)

It's worth remembering that human females create eggs without having sex too. They're generally not much use though. (The eggs, not the females.) HiLo48 (talk) 00:43, 7 November 2012 (UTC)

Meh, the females aren't of much use either. Yes, but the intact egg never leaves a human female's body. It disintegrates in the fallopian tubes if it isn't fertilized within a day or so. --140.180.252.244 (talk) 01:59, 7 November 2012 (UTC)