Wikipedia:Reference desk/Archives/Science/2010 August 13

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August 13

Why expend effort finding pulsars?

According to this article, there are 262 000 computers running a program to locate pulsars in space. Is it worth the additional energy expenditure to know that there's a spinning star somewhere far away? We can't benefit from the information. We can't harness it in any way. If you're going to use energy in this way, wouldn't it be better to use it on something that can actually be used in the 21st century, like folding@home? ----Seans Potato Business 01:15, 13 August 2010 (UTC)

Probably the best answer would be a justification of theoretical astrophysics by some prestigious scientist. On the Method of Theoretical Physics. Are astrophysics, or high-energy physics, or other branches of theoretical physics useless? Probably, at this point in the development of our species and civilization, we are well past the regime where we can say that there is a practical engineering application to many of the remaining unsolved questions in physics. But we don't know for sure. And even if there is no practical purpose, there is still interest in finding answers to difficult questions; so there are still scientists working out on the far fringes of physics. Nimur (talk) 01:30, 13 August 2010 (UTC)

It looks like Einstein@Home is due for an update. PrimeHunter (talk) 01:43, 13 August 2010 (UTC)

Pulsars can be used to measure the motion of distant systems because their super-regular 'pulses' slowly change frequency due to relativity. Also, pulsars are known to be neutron stars - and those can be used as 'standard candles' (see Cosmic distance ladder for details) which allows you to measure their distances. I'm sure there are a bunch of other clever things that can be figured out from their properties. SteveBaker (talk) 01:55, 13 August 2010 (UTC)

As for the power consumption: The thing is that this program is running on the computers of private individuals when they aren't being used for something else...they run this program instead of running a screen-saver. There is a small amount of extra power consumed when they are running the program versus idling - perhaps 50 Watts. But that number of 262,000 computers is not the number that are running 24 hours a day - that's the number of people who've logged onto the site and signed up their computers to use the site. It's perfectly possible that only a small fraction of those are running the program at any given moment. This makes it really hard to estimate the amount of power they are consuming. But if (let's say) a quarter of them are running the program at any given time - and each one is consuming 50 Watts extra because of that - that's about 3 MegaWatts - about the same amount of power that a railroad locomotive produces. It's not all that outrageous if the result is useful. To put it in context, the power consumption of the entire world is about 15 TWatts - so this expenditure represents about one five millionth of humankind's power consumption. If we're looking to save energy, there are much better places to cut. SteveBaker (talk) 02:15, 13 August 2010 (UTC)

If we were to assume, for the sake of argument, that the information generated by Einstein@Home is completely and totally valueless to humanity in any objective sense, the question could generalized to, "Is it worth the additional energy expenditure for people to have hobbies and interests?" Sometimes, we just do science to satisfy curiosity. (Occasionally, that sort of bluy-sky curiosity-driven basic research does lead to important results, however.) For a project like this one, some people (some thousands of people, really) have decided that one of the ways they wish to spend their entertainment budget is on helping to map out features of our Universe. Their hardware cost is already sunk, and they figure that the marginal additional energy cost is, to them, a reasonable price of admission. Is that 'better' or 'worse' than using free time to play chess (with or without a computer...) or FarmVille? TenOfAllTrades(talk) 14:04, 14 August 2010 (UTC)

aspartic acid page

severl paragraphs down they state that aspartic acid contributes a nitrogen to inositol. Don't they mean inosine? —Preceding unsigned comment added by 71.136.2.238 (talk) 02:30, 13 August 2010 (UTC)

Good catch. You know you fix this stuff yourself, right? 99.183.166.165 (talk) 03:12, 13 August 2010 (UTC)

Bloodletting

Would bloodletting be an effective treatment for hypertension? Don't worry--Im not looking for medical advice ( and I certainly wouldn't try to exsanguinate myself, since I don't even have hypertension), it just occurred to me. —Preceding unsigned comment added by 99.183.166.165 (talk) 03:00, 13 August 2010 (UTC)

There are two major problems with this approach. The first is that the body is actually rather good at compensating for a loss of blood. Our article on hypovolemia discusses some of the physiological responses which occur in response to blood loss; blood pressure tends to be maintained through constriction of blood vessels and the migration of water from tissues into blood plasma. Remarkably, the body can handle the acute loss of up to about 15% of its blood (roughly 750 mL) before it starts losing the ability to regulate blood pressure. After that, the combination of constricted blood vessels with elevated heart rate actually leads to an increased diastolic blood pressure. It takes the loss of about a third of one's blood (about 1500 mL) before you start seeing consistent declines in blood pressure — and then you're in a really bad way otherwise.

The second major issue is the chronic anemia that would result from the regular removal of so much blood. While the body can make up lost liquid (plasma) volume rather quickly, generating new red blood cells takes a bit more time. TenOfAllTrades(talk) 03:21, 13 August 2010 (UTC)

Bloodletting, however, has some positive effects on the renal system of a diabetic -- I asked about it in a lecture at Columbia University last October and the professor agreed with my assessment. That being said, there is this one benefit overpowered by many, many disadvantages unrelated to the way in which bloodletting can be beneficial, and since we can't isolate the benefit from the harm, bloodletting is not done in civilized medicine. DRosenbach ^{(Talk | Contribs)} 15:18, 13 August 2010 (UTC)

Interesting! What's the mechanism or specific beneficial effect here? DMacks (talk) 15:37, 13 August 2010 (UTC)

Wikipedia has an article about Bloodletting. Cuddlyable3 (talk) 22:58, 13 August 2010 (UTC)

I have to call a on that one, DRosenbach. Can you at least provide a hint of the mechanism for your claim? "The professor agreed with my assessment" isn't quite enough. --- Medical geneticist (talk) 00:02, 14 August 2010 (UTC)

I found [1] (I've only read the abstract). Note however that despite some favorable-sounding results, the author's conclusion falls well short of recommending the practice. Wnt (talk) 16:56, 15 August 2010 (UTC)

This article seems to have more to do with recovery from pre-surgical phlebotomy (for the purpose of banking blood for a potential autologous transfusion) in diabetic patients compared to normal individuals. It doesn't address at all the contention that phlebotomy would have a positive effect on the renal system in a diabetic person. --- Medical geneticist (talk) 17:56, 15 August 2010 (UTC)

Counteracting Diseases

Just out of curiosity, what would happen if you had AIDS and Lupus at the same time, or maybe even AIDS and Leukemia. 99.114.94.169 (talk) 04:40, 13 August 2010 (UTC)

What you describe appears to be the opposite of comorbidity, although I'm not sure whether it would apply to those diseases specifically. ~AH1^(TCU) 14:50, 13 August 2010 (UTC)

But what happen if you had both of these diseases? 99.114.94.169 (talk) 15:06, 13 August 2010 (UTC)

What would and does happen is that you would, first of all, suffer the effects of the Lupus or Leukemia. AIDS does not in itself primarily cause illness, it is a Deficiency in one's Immune system leading to a Syndrome of signs and symptoms caused by other diseases that one consequently catches, hence its acronymic name. (The Acquired part distinguishes it from an inherited genetic deficiency, also possible, since one acquires it from infection by the HIV virus.) Hence, the Lupus or Leukemia may well (though not certainly) be the consequence of having AIDS, and in addition one is quite likely to already have caught, or develop in the future, other illnesses as well. As the already-linked Comorbidity article describes, it's perfectly possible to suffer from two or more diseases simultaneously; the resulting signs and symptoms will depend on the particular diseases involved and may interact in unusual and/or unpredictable ways. 87.81.230.195 (talk) 12:41, 14 August 2010 (UTC)

I found a report about a man who had HIV, HBV, HCV, and lupus.[2] According to this, HIV generally protects against activation of lupus to some degree. But this person received interferon-alpha treatment - apparently good for HCV, bad for lupus. It's also interesting to note that HIV and lupus may have a lot more in common than you'd imagine - according to one idea [3] lupus may involve the response to a retrovirus already present in the human genome that can be set off by other viral infections! I suppose if we didn't have the technology to fight it, HIV would be part of the human genome also someday. Wnt (talk) 14:18, 14 August 2010 (UTC)

My info on lupus is about 10 years out of date (since the person i knew with lupus has died). The research then was that there was known to be 4 people with lupus and aids. The mechanism proposed to explain this was that many random antibodies were produced by people with lupus; and some of those antibodies were clearing up the HIV. Polypipe Wrangler (talk) 11:42, 16 August 2010 (UTC)

So if gravity is a pseudo force...

Then why is it considered one of the four fundamental forces? ScienceApe (talk) 04:47, 13 August 2010 (UTC)

Who said it was a pseudo force? --The High Fin Sperm Whale 05:24, 13 August 2010 (UTC)

Me too never heard that. It would be interesting to know where it says that.-- Jon Ascton  (talk) 05:33, 13 August 2010 (UTC)

Gravity is indeed one of the four fundamental forces. See Fundamental interaction. Gravity is definitely not a pseudo force. See Fictitious force#Fictitious forces on Earth. Dolphin (t) 07:23, 13 August 2010 (UTC)

I wouldn't describe gravity as a pseudo force because this description is normally used for fictitious forces in Euclidean space, and gravity is certainly a real force in Newtonian terms. In General relativity, gravity is not a force at all, of course, just a consequence of the curvature of space, but this is a non-Euclidean space (in fact a Pseudo-Riemannian manifold combining space and time). Dbfirs 07:33, 13 August 2010 (UTC)

See Fictitious force#Gravity as a fictitious force. Red Act (talk) 08:04, 13 August 2010 (UTC)

... an article which says that gravity is not really considered as a fictitious force within the meaning of the article. Dbfirs 07:43, 14 August 2010 (UTC)

Fictitious forces depend on the chosen frame of reference and in some reference frames they disappear altogether. First-order (local) gravitational effects disappear in a free-falling frame of reference. However, second-order (tidal) effects cannot be eliminated, so gravity does not fit the definition of a fictitious force. Gandalf61 (talk) 10:22, 13 August 2010 (UTC)

Ob.XKCD SteveBaker (talk) 00:32, 14 August 2010 (UTC)

I am certainly happy to be corrected on this, but isn't the whole point of GR that what Newton called the gravitational force (e.g. the G) is actually just the path of least resistance in spacetime, because mass warps spacetime? That is, there is no "force of gravity," there is just a warping of spacetime by mass, and following the subsequent curves. Yes? No? This is, I am fairly sure, what I was taught, though I am sure it is an abstraction. It seems like we are perhaps getting hung up on the "force" terminology in strange ways. --Mr.98 (talk) 14:24, 13 August 2010 (UTC)

This is exactly the impression I was under. ScienceApe (talk) 02:24, 14 August 2010 (UTC)

Let's be clear: the idea that there are "four fundamental interactions" is one effort to explain the universe in the most simplified terms possible. The grand unified theory (which does not yet exist) will hypothetically unite all forces into one fundamental force interaction (or something). At present, we have "four" (or "three", because of the electroweak unification at high energy). So we basically can say that there are four (or three) fundamental ways that the universe "behaves". Gravity (with its mind-bending and space-bending behavior) is one of those ways. The other forces behaviors (strong nuclear, weak-nuclear, & electromagnetic interactions) do not behave in the same way - they do not warp the geometry of space-time to actuate their matter/energy interactions. Note that most descriptions call these four properties of the universe "fundamental interactions" and not "fundamental forces" - they are not really "forces." They are abstract generalizations of the ways that matter and energy come together to change their distributions. For normal, reasonable, human-sized scales of size, time, energy, and so on, these interactions look like forces - that is, they follow a Newtonian relation between position, velocity, acceleration, and the gradient of a potential energy field. Nimur (talk) 17:02, 13 August 2010 (UTC)

I asked this question before (at Talk:Graviton) and received an interesting reply: that other forces also can be modeled as warping of spacetime in higher dimensions. But still don't really understand it. Though it appeals to my uneducated understanding of the topic, Fictitious force#Gravity as a fictitious force is actually an unsourced section - the "reference" is just more unsourced content. Always look for the sources for anything in Wikipedia before you put too much faith in it. Wnt (talk) 14:02, 14 August 2010 (UTC)

There are definitely efforts to describe other forces in a general-relativity framework (modeling them as tensors and so on); and there are parallel efforts to develop a quantum gravity theory. So far, the best of those efforts still have trouble consistently and accurately describing the behaviors of the universe, (in other words, describing the strong-nuclear force as a space-warping leaves some mathematical inconsistencies unresolved, or fails to match some experimental observation, etc). This is why mainstream physicists still consider there to be four fundamental types of interactions (or, three, depending how you want to count the electro-weak interaction). It is not widely agreed whether it is even possible to have a "grand unified theory". But there are definitely good efforts toward the goal, which is to describe all four fundamental interactions as different "versions" of the same behavior, using a single mathematical framework to describe all of them. Nimur (talk) 18:36, 14 August 2010 (UTC)

The Standard Model forces are all gauge forces, meaning that they are derived from a symmetry principle (gauge symmetry) that's analogous to background independence in general relativity. They do look a lot like general relativity applied to extra dimensions. In this thread, which I've been linking a lot recently, I talk about twisting circles at each point of spacetime. That's a geometric description of a U(1) gauge theory. If you replace the circles with spheres, you get an SU(2) gauge theory. So the idea of unifying gravity with the Standard Model by unifying the Standard Model gauge symmetries with the local symmetries of spacetime is an obvious one. For some reason, it has been incredibly difficult to get it to work. But it's always lurking in the background of discussions of quantum gravity. -- BenRG (talk) 21:26, 14 August 2010 (UTC)

Sieve Map

I was reading up on urban planning and the services (such as water, medical etc) requirements involved and I came across the term "sieve maps" listed as a tool to enable analysis of services requirement, without any further explaination of what they are. I have carried out wikipedia and google searches for this term but nothing jumps out. Any ideas? Thanks 150.49.180.199 (talk) 05:09, 13 August 2010 (UTC) Mark

Perhaps a map that cross references with sieve analysis for each area? I'm not certain either, but that seems like a possibility. Killiondude (talk) 06:54, 13 August 2010 (UTC)

Spectrum

What is the difference between bandwidth and spectrum? —Preceding unsigned comment added by Kiranpatel1038 (talk • contribs) 08:12, 13 August 2010 (UTC)

In what context? Both are words that have a wide variety of related meanings - when you're talking about a range of frequencies available for transmitting data, the two can be roughly equivalent - but in other circumstances they can mean very different things indeed. Could you clarify? ~ mazca ^talk 14:07, 13 August 2010 (UTC)

"Bandwidth" specifically refers to a measurement of the amount of spectrum that a signal occupies. Most commonly (i.e., for simple signals), "bandwidth" refers to the "3-dB bandwidth", i.e. the span of frequencies that the signal falls to to 50% of its peak power. In more specialized contexts, "bandwidth" can refer to other numerical measures of a signal. (This is especially true of complicated signals that do not have nice, peak-like spectra). "Spectrum" usually refers to the frequency spectrum, which is the representation of a signal in the Fourier domain (or frequency domain). These terms can often be used loosely and interchangeably, so if there is not much clarification provided, you should assume that these terms are referring to the vague concept of the frequency-representation of a signal. Nimur (talk) 16:56, 13 August 2010 (UTC)

Quantum mechanics and predicting the future.

Let's suppose you knew everything about the current state of the universe. Would the stochastic nature of quantum mechanics still render you unable to predict the future? Or is the future state of the wavefunctions deterministically dependent on its current state in this sense?--Alphador (talk) 09:17, 13 August 2010 (UTC)

Well one huge problem is you cannot "know everything about the current state of the universe" – there is a fundamental principle called the uncertainty principle that limits the detail to which you can "know" the state of the system. Physchim62 (talk) 09:48, 13 August 2010 (UTC)

"Knowing everything" in this case means knowing the wave function. And yes, if you know the full wave function of the world at the present time you can predict (via Schrödinger's equation or the like) the wave function at any future time. The results of any particular measurement will of course be stochastic, with probabilities dependent on the wave function and subject to the uncertainty principle for non-commuting observables. --Wrongfilter (talk) —Preceding undated comment added 10:07, 13 August 2010 (UTC).

I've heard about the schrödinger equation, but I only have a rudimentary understanding of it. Could you give me an example of how you could use the schrödinger equation to predict the future state of the wavefunction?--Alphador (talk) 11:05, 13 August 2010 (UTC)

Well, it is a differential equation like so many others in physics. The equation itself tells you the rules of the game, i.e. in what state will the system be in a moment when it is in such and such a state right now. Schroedinger's equation contains the Hamiltonian operator which defines the system that you're looking at, how it interacts with the outside world and so forth. To solve any differential equation you need to specify initial conditions, that would be the state (the wave function!) now (or at any given point in time). The solution will then tell you what state the system will be in at any other time in the future (or in the past). --Wrongfilter (talk) 13:41, 13 August 2010 (UTC)

(ec)This is one of the Big Questions, isn't it, that people come to rather different positions on.

My understanding is that the wavefunction is presumed to evolve in a deterministic way (otherwise, where would the new information come from?), so if like some updated Laplace's demon you could have a complete knowledge of the wavefunction now, and could somehow iterate that forward, then you would have a complete knowledge of the wavefunction at a particular time in the future.

However, you would then have the question of interpreting what that wavefunction meant. Specifically, according to decoherence, it is suggested that that evolved wavefunction is likely to evolve into an almost perfect product of factor wavefunctions for a number of essentially disjoint non-interacting separate distinct "histories" -- the multiple universes in many worlds interpretation language.

You would therefore be able to predict these different, effectively disjoint, outcomes; and even assign them probability-like weights; but not say which one your own future consciousness will associate with.

That at any rate seems to be a thumbnail sketch of one answer that some people seem to find acceptable.

But I suspect it depends on quite another set of cans of worms -- for example, with reference to what is your wavefunction of the universe defined? What absolute scales or place or time? They surely don't exist. How can such a wavefunction have any information content? Information implies the reality of counter-factual states from which the current state can be distinguished. But how can states that are by definition counter-factual have any reality? etc, etc.

To do physics, we essentially have to make approximations -- separating the "system of interest" from the "background", and then assuming the background is homogenous, uninteresting, unimportant -- an external scale through which we can define place, time, or any other variable of the system of interest. And of course most of the time this works brilliantly. But I suspect that it becomes a serious problem, if we want to start talking about a "wavefunction of the universe", which properly would have to absorb all of that background into itself - leaving what to define the wavefunction against? Such questions may even become significant, even if we do not go to such lengths. For example, I suspect we regularly make a change in the system/background approximation when we introduce a "measuring apparatus", and that is why that appears to produce a distinct break in determinism.

So: decoherence gives one answer to your question, but the terms in which you ask it perhaps in themselves open up deeper questions.

I'm interested to see what comments other answerers give. Jheald (talk) 10:12, 13 August 2010 (UTC)

The uncertainty principle come from my opinion from movement back and forth to the past and the future . thanks —Preceding unsigned comment added by 84.228.231.7 (talk) 13:39, 13 August 2010 (UTC)

Science is not interested in your opinion. It is interested in clearly defined theories that explain empirical results. --Tango (talk) 00:12, 14 August 2010 (UTC)

If you know the future , you can explain results in any way you like . thanks —Preceding unsigned comment added by 212.199.175.93 (talk) 04:18, 14 August 2010 (UTC)

Even if you did know everything about the curent state, determinism is not proven so it would be near-impossible to predict anything with 100% certainty and accuracy. ~AH1^(TCU) 14:47, 13 August 2010 (UTC)

Indeed. Also, this recent article has a very interesting perspective on quantum mechanics in an infinite universe. Count Iblis (talk) 14:55, 13 August 2010 (UTC)

You don't need to invoke quantum mechanics to prove the impossibility of this. Even in a perfect 'clockwork universe' where you somehow had perfect knowledge of the initial state of things - there are two major problems with predicting the future:

1. (As we discussed a few days ago) How are you going to store the perfect knowledge of the current state of the universe? You can't build a computer big enough to do it because your computer is a part of the universe and in order to do a perfect prediction, it has to factor in it's own influence on the universe. Every bit of memory in the computer needs at least a bit of memory to describe its own state. In fact, no computing device can have perfect knowledge of even its own state as well as having knowledge about anything beyond that.
2. Consider the time it would take to run these calculations. The physical processes used in the computer would have to run faster than the real universe or else your "prediction" would arrive considerably later than the events they were predicting. Again, to produce a perfect prediction, the computer would have to predict it's own answer before the answer would become available because the nature of the answer includes the effect of giving that answer on the progress of the universe.

So the answer is a clear "No". However, having said that, we most certainly can make some predictions of the future - but they must definitely either be imperfect (like weather forecasting) or very limited in scope (like predicting that the sun will rise at such-and-such time tomorrow morning). Quantum mechanics isn't a necessary consideration here - it merely makes perfect future prediction more impossible than just straightforwardly impossible. Chaos theory also imposes sharp limitations on our ability to predictions.

SteveBaker (talk) 14:13, 14 August 2010 (UTC)

Frog with yellowish stripes

I occasionally find frogs with two yellowish stripes running down their backs. It mentions them in the grass frog article, but does not give any specific species. All I have to give for pictures is these two blurry pictures to give. Can anyone identify them? I do not see anything in Frogs in New Jersey or in the NJ.gov index of frogs and toads in New Jersey. Thank you. --Chemicalinterest (talk) 12:36, 13 August 2010 (UTC)

It seems to be a Pickerel Frog, where maybe its a morph that does not have dominant spots or maybe its a young frog where the spots have yet to completely fill in. 99.114.94.169 (talk) 15:28, 13 August 2010 (UTC)

Pickerel frogs are common (this picture is a clear example). That's how they normally look. --Chemicalinterest (talk) 15:50, 13 August 2010 (UTC)

What primates other than humans are good swimmers?

20.137.18.50 (talk) 14:34, 13 August 2010 (UTC)

Humans are not good swimmers -- as list of drowning victims clearly shows. 99.137.221.46 (talk) 14:35, 13 August 2010 (UTC)

What primate species have the capacity to be good swimmers? 20.137.18.50 (talk) 14:38, 13 August 2010 (UTC)

Our article on primate mentions the "Proboscis Monkey, De Brazza's Monkey and Allen's Swamp Monkey, which has developed small webbing between its fingers". ---Sluzzelin talk 14:40, 13 August 2010 (UTC)

Possibly the Steller's Sea Ape, if it exists. ~AH1^(TCU) 14:44, 13 August 2010 (UTC)

Sea Monkeys? Staecker (talk) 11:38, 14 August 2010 (UTC)

The article on aquatic locomotion also mentions the crab-eating macaque and the Rhesus macaque. ---Sluzzelin talk 14:46, 13 August 2010 (UTC)

If you want to talk about 'capacity' that's a rather difficult question IMHO. I wonder whether you could teach a chimpanzee or orang utan or gorilla to be good swimmers with enough effort. This [4] claims orang utans and gorillas can't because of their centre of gravity is in their necks and sternums, but as with the person writing, I'm sceptical whether that's the whole story. These two refs have various discussions of swimming chimpanzees, the general conclusion I draw from that is it's likely to be possible [5] [6] and a chimp may even be able to outswim an olympic swimmer. Note that if you can't teach an animal to swim, it may as much as anything be because the animal lacks the learning capacity or intelligence necessary for you to be able to teach it. It's also likely to be difficult to prove whether or not you can teach whatever animal how to swim without significant effort, which would likely have to start at learning to teach the animal effectively. In other words, the best answer may be most primates may have it, but we'll probably never really know. Nil Einne (talk) 17:17, 13 August 2010 (UTC)

Long-distance swimming says that a few humans are capable of swimming 100km without a break - over 800 people have completed 30+km swims across open ocean and there are many Marathon swimming competitions in which hundreds of people are able cover 5 to 10km distances in open water. Ironman Triathalon events involve 3 to 4km swims (along with biking and running) and are fairly commonplace events that most moderately fit humans could train to complete. Almost all of us can comfortably swim a hundred meters. Can anyone name one other primate that can come even close to doing that? No? Me either. I conclude that we are likely to be by far the best adapted primate for this kind of thing. We have long limbs - we are mostly hairless (we don't get water-logged) - we have our center of gravity in the right place and we have vast amounts of stamina for covering long distances. SteveBaker (talk) 00:28, 14 August 2010 (UTC)

How large a factor is behaviour, though? Humans can only swim several kilometres following extensive and specialised training and only do so with the motivation of challenging themselves and proving their abilities. I can't see a wild primate attempting such a thing. They might well be capable of it if they did train for it and actually attempted it. --Tango (talk) 00:38, 14 August 2010 (UTC)

You don't need particularly specialized training. You just need to learn how to swim, and then get in really good shape. It's true that swimming is a skill sport, but you don't need that much skill to swim 4000m — just basic competence plus good physical condition and a willingness to grind it out. --Trovatore (talk) 06:46, 14 August 2010 (UTC)

In addition, swimming for so long is as much about endurance as anything. I've seen it suggested humans are one of the primates with the best endurance/stamina so we can run marathons or more importantly chase prey over very long distances and stuff like that. I'm not offering any opinion on the validity of this claim but if it is true, it may be one of the reasons why we can swim for such long distances. But you could just as well say we are the primates best adapted for having sex that lasts several hours or for jumping up and down in one spot for hours. Nil Einne (talk) 06:39, 14 August 2010 (UTC)

I agree that it might not only be about the distance one can swim - which is evidence of a more general high level of stamina in humans rather than specific swimming ability. But can other primates swim more quickly? Can they dive deeper? Stay submerged for longer? See better underwater? Stay in the water for longer? Survive in cold water better? I don't think so. I can't think of a single aspect of the art of swimming that other primates are better at. So while stamina is the easiest measure of this ability - I'm pretty sure we win on most of the other criteria too.

We should perhaps mention the highly controversial "Aquatic ape hypothesis". That suggests that perhaps humans specifically evolved for a semi-aquatic lifestyle. However, that hypothesis is certainly not mainstream science and has to be considered skeptically. SteveBaker (talk) 03:34, 15 August 2010 (UTC)

I suspect the biggest factor is that humans choose to swim the distances and speeds they do. It's only after choosing to swim for competition or pleasure that we also choose to develop the skills and stamina required. (Or we force our kids to.) I suspect that the average gorilla would see little point in swimming backwards and forwards 20 times up and down that 50m pool every day. So the major difference is that other animals would generally only swim for survival reasons, while humans do it for "fun". HiLo48 (talk) 03:49, 15 August 2010 (UTC)

My labrador puppy definitely does it for fun...or perhaps because he has some evolutionary need to have a layer of mud and dog fur in the back of my car? SteveBaker (talk) 05:05, 15 August 2010 (UTC)

It's a good thing your puppy isn't a primate, or it would have destroyed my argument!. Of course, you're right. I will be one of the first to agree that other creatures, mammals and birds in particular, do things for fun. I don't think many have taken organised competition quite as far though. HiLo48 (talk) 05:16, 15 August 2010 (UTC)

Personally I would say having partially webbed feet like the Allen's Swamp Monkey as mentioned by someone above is one aspect which one primate has over humans. In addition as I mentioned earlier, it's been suggested that chimpanzees could outswim an olympic swimmer (I presume over a short distance) if you could convince them to and this wouldn't surprise me. Note that swimming speed is a complicated thing anyway and probably should have some connection to size anyway. I'm pretty sure humans could outswim a number of fish or aquatic birds for example.

In any case, I would suggest this is getting partially OT, the original question was which primates other then humans are good swimmers which changed into 'capacity to be good swimmers'. My point above and I haven't seen anything to really change it is that even if it's true we're capable of being good swimmers, the question of whether other primates are capable of being 'good swimmers' is difficult to answer, perhaps unanswerable (well maybe some sort of biomechanics analysis could answer it).

Unless you set 'humans' as the cut off point for good swimmers, which is a questionable decision, then even if primates particularly the other great apes are universally worse then us even if you could somehow convince them to try, if they aren't that much worse is it really accurate to say they aren't capable of being good swimmers simply because they are (slightly?) worse then us? In other words we get into the problem of defining a 'good swimmer' (but IMHO being worse then us doesn't mean they definitely aren't capable of being good swimmers).

The problem is that when it comes to humans we're capable of a lot of things as others and I have been saying because we have a great learning capacity and the willingness to do things for a variety of reasons which simply have limited applicability to other animals, even ones generally considered highly intelligent like the great apes.

An interesting test particularly for the original wording would be to drop a diverse bunch of fit adult humans who have never learnt to swim or even float (perhaps never been near a large body of open water) and the understanding they will not be saved into a body of water with clear visibility of land say 100 metres and see how many of each survive i.e. make it to land. Repeat for a bunch other primates including great apes in a similar situation with some adjustment of distance for body size. Ethical issues would prevent such an experiment being carried out and even if you did there are a lot of confounding factors. E.g. perhaps humans are less able to deal with such a stressful situation since they panic more easily and are better able to understand their perilous situation but on the flipside perhaps the primates aren't able to comprehend so well that they just need to make it to the land and they will be safe. But despite all that I'm far from sure that humans would win.

Nil Einne (talk) 20:16, 15 August 2010 (UTC)

The whole mental aspect of this is indeed tricky. Animals use instinctual skills where humans don't/can't. My dog was never taught to swim - he just waded out into the water and started swimming. He had no concept of not being able to swim. He'd never seen another animal swim - certainly not a dog. But it was no problem for him whatever. Humans often drown in pathetically small amounts of water because they haven't learned how to swim. But that's just how our brains are wired. We've traded intelligence for instinct. I guess, if you talk about untrained skills then it would be true to say that humans can't swim at all...so we're the worst at it of all primates...but then by that measure, maybe we're the worst at doing math, the worst at language, etc. SteveBaker (talk) 03:11, 16 August 2010 (UTC)

Test on toes

What is the name of the test or sign whereby the doctor holds one toe and pushes it up or down while the patient's eyes are closed. The patient then advises whether it was moved up or down. Kittybrewster ☎ 15:55, 13 August 2010 (UTC)

Never heard of that test, but the concept of what it's testing for sounds like proprioception.20.137.18.50 (talk) 16:04, 13 August 2010 (UTC)

A video of the test being done. Cuddlyable3 (talk) 22:44, 13 August 2010 (UTC)

I believe that's called the "this little piggie" test. sorry... Vespine (talk) 23:56, 13 August 2010 (UTC)

Many such signs are mentioned at plantar reflex, and quite a few have their own stub articles. I won't try to name the specific sign from this, but if this test isn't listed there it should be. Wnt (talk) 17:00, 15 August 2010 (UTC)

Cheap vehicles

what is the cheapest best quality used car saying all are taken care the same? Ford,chevy,mustang,honda,etc.? —Preceding unsigned comment added by 98.221.179.18 (talk) 15:56, 13 August 2010 (UTC)

You need to think what the purpose of the car is. Reliability wise Honda are very reliable, well made cars (at least the ones we get in the Uk). It really depends on the use though - there will be a number of bests - small-car, the best 4x4, the best people carrier, the best pick-up and so on. That said any 'best' is really just a matter of opinion, but I would recommend using something like Parkers Guide (or whatever the US equivalent is - assuming US based on Chevvy/mustang). ny156uk (talk) 16:39, 13 August 2010 (UTC)

Consumer Reports publishes a list of used car reviews. And Kelley Blue Book provides a list of market-prices for virtually every make and model. These two resources are commonly the "first stop" to assess the value and cost of a vehicle. Nimur (talk) 16:46, 13 August 2010 (UTC)

Effects of Tramadol same as codeine?

This question has been removed, per the medical advice guidelines.

We cannot offer medical advice. Please see the medical disclaimer. Contact an appropriate medical professional. We have articles about the various drugs so you can learn about them and maybe find links to more information about them. DMacks (talk) 16:27, 13 August 2010 (UTC)

This is about as clear a violation of our medical-advice guidelines as ever. You need to consult with your doctor to discuss any effects of any medication the doctor has prescribed to you. Your doctor can help you decide the right course of action. Nimur (talk) 16:49, 13 August 2010 (UTC)

Note that adverse effect and drug interaction provide useful external links for further information, though such issues are surely worth tracking down the miscreant who produced the prescription without discussing the issue, if possible. Wnt (talk) 01:04, 15 August 2010 (UTC)

Floating islands

Are there any inhabited islands that float around the sea? I don't mean like plate tectonics where everything is moving because of lava 82.43.88.151 (talk) 18:00, 13 August 2010 (UTC)

Sure enough we have an article on Floating islands. Some of those are inhabited, see the second part of the article. --Dr Dima (talk) 18:17, 13 August 2010 (UTC)

Also take a look at houseboat. ~AH1^(TCU) 22:59, 13 August 2010 (UTC)

Finding a wavefunction

How do people find the wavefunction of an elementary particle? Often in quantum mechanics problems you are simply told what it is, I would like to know how people determine the wavefunction.--Alphador (talk) 22:03, 13 August 2010 (UTC)

Wavefunctions are linear combinations of the eigenfunctions that solve Schrodinger's equation. Solving the latter in any particular case requires specifying the Hamiltonian operator, which includes a generic part related to kinetic energy and specific part related to how the particle(s) potential energy can be expected to change as a function of position and/or time. In most cases, the potential part is specified by the solver in terms of the fundamental forces involved (e.g. electromagnetism) and the details of the larger environment within which the particle is being studied. Once the potential field is specified, finding the eigenfunctions is an exercise in solving partial differential equations (i.e. pure math). Exact solutions generally only exist for fairly simple systems, so often the eigenfunctions are found either via numerical approximation or by approximating complex systems in terms of simpler systems that are analytically solvable. Finding a precise wavefunction to match the system's state is then a problem of finding the precise linear combination of eigenfunctions that match some specified initial conditions, i.e. a boundary value problem. Dragons flight (talk) 22:33, 13 August 2010 (UTC)

If I may be so bold as to ask, is the OP asking how one measures the wavefunction experimentally?--Leon (talk) 06:34, 14 August 2010 (UTC)

It is impossible to measure the wavefunction experimentally, as it is not an observable quantity. Some functionals of the wavefunction have a physical meaning of observable quantities (energy, momentum, angular momentum, etc. in a given system of reference), those can be measured; but not the wavefunction itself. For example, if you consider a wavefunction in coordinate representation, absolute value squared of the wavefunction at a given point correspond to the probability density of finding the particle there, and the phase of the wavefunction does not correspond to anything observable. Probability is not an observable quantity, either (indeed, in any single trial an outcome is either 0 or 1; the probability is only determined in many trials). However, if you can prepare many identical systems, and perform many identical trials, this may -- at least theoretically -- allow you to map the probabilities of finding an electron at different locations. This gives you the amplitude of the wavefunction of that state, in coordinate representation, with a desired precision. --Dr Dima (talk) 10:24, 14 August 2010 (UTC)

Short answer: You will know the wavefunction of a system after you have measured a complete set of commuting observables of the system. The state of the system will then have collapsed in the simultaneous eigenstates of the observables determined by the measured eigenvalues of all the observables. Count Iblis (talk) 14:46, 14 August 2010 (UTC)