Wikipedia:Reference desk/Archives/Science/2007 October 23

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 23

Phase of quantum probability amplitude for reflection from a potential change

Part of my quantum mechanics assignment is to calculate the probability amplitude that an unbound particle will reflect back from a potential well. The final answer is given, and I keep getting an answer that differs from the given one by a constant phase factor but is otherwise identical. Am I correct in thinking that this phase difference is caused by considering the reflection as taking place at a different point within the potential well, and that the particle picks up the phase difference between the two nominal reflection points? If so, how is the phase relationship between the incoming and reflected wavefunctions usually specified? Do you always need to specify both a reflection probability amplitude and a nominal reflection point, or is there a simpler way? —Keenan Pepper 03:46, 23 October 2007 (UTC)

Let me guess: Does the phase factor that you've calculated make the answer a little less simple to express? In that case, my guess is that the difference between the answers is just a matter of a constant phase factor being considered unimportant to the problem at hand. After all, the overall phase of a quantum mechanical wavefunction is arbitrary. The only time a phase relationship between two unbound wavefunctions is important is when you're dealing with an interference effect between two parts of what's really one wavefunction, such as with a double slit experiment or something. An unbound particle reflecting back from a potential well is basically a scattering experiment, in which I don't think one usually cares about the phase relationship between the incident and reflected wavefunctions. The phase relationships between different parts of a bound state, however, is a different matter. MrRedact 05:39, 23 October 2007 (UTC)

Right, but our professor is very attentive to detail, even pedantic. I doubt he would just arbitrarily change the phase without telling us. Anyway, thanks for your answer. I feel confident it's not an error on my part now. —Keenan Pepper 12:38, 23 October 2007 (UTC)

Lobe-Finned Fish

My biology teacher owns a very peculiar preserved fish which appears to be a lobe-finned fish, though only the two front fins appear to resemble primitive limbs. It appears very primitive (non-bony, thick body and long thick tail) and is covered in large, thick, plate-like scales (the underside is bare and flat, and has two seemingly vestigial fins tucked flat against the body) and has a worm like lure on it's head. It almost resembles a frog without the tail, but with backwards bending knees (the limb like structer of the front fins is highly pronounced). The lobed-fins look like they were used for crawling, as the fish is most likely a bottom feeder. It is about 6 inches long, and the original color is no longer apparent. It was caught off the coast of florida on the ocean floor (unkown depth) and even after extensive research my teacher and the troller fisherman who caught it have found no-other like it nor anyone who is able to identify it's taxonomy. I'll try to get some pictures of it but for now I was wondering if anyone might be familiar with this description. BeefJeaunt 05:42, 23 October 2007 (UTC)

Part of the description sounds like some sort of angler fish - which have the bait, look a bit froggy, and despite not being lobe-finned fish have quite lobe shaped fins..87.102.17.104 11:16, 23 October 2007 (UTC)

Is it possible that your teacher is spinning you a story about what's going on here - "even after extensive research my teacher and the troller fisherman who caught it have found no-other like it nor anyone who is able to identify it's taxonomy". So your teacher somehow gets his hands on this bizarre unidentifiable fish, researches it with the troller (trawler?) fisherman, and then can't get it identified. Surely he would take it to a reputable university department or something like that to try to get identified professionally, and they would be very interested in it if it was really unable to be classified; I can't imagine them just shrugging their shoulders, saying they don't know, and giving it back to him to sit on a shelf (consider the reaction to the coelacanth when one was first caught in 1938 for example). --jjron 13:40, 23 October 2007 (UTC)

It seems reasonably improbable that the fish is actually lobe-finned (there are very few extant species). There are many species of fish, so finding one which even an experience fisherman is not familiar with is not terribly unusual. Your best bet is to take it to a fisheries collection (Florida Museum of Natural History is a good place to contact), but you'll probably need an expert to make the identification. --TeaDrinker 03:57, 25 October 2007 (UTC)

Speed of light

When we say that speed of light cannot be exceeded, what is the frame of reference? Keria 08:54, 23 October 2007 (UTC)

That's true in every inertial frame of reference! The speed of light is exactly the same in every inertial frame of reference. That's one of Einstein's postulates of special relativity. For more information, see the Introduction to special relativity article. MrRedact 10:16, 23 October 2007 (UTC)

And not to be totally pedantic, but the most simple and accurate way of stating it is the speed of light is independent of the velocity of the light emitter. The reason for the restatement is that 1. it emphasizes what is really going on in terms of its constancy (the speed of a wave is always independent of the velocity of its emitter; if it wasn't, the Doppler effect wouldn't work. Light isn't terribly special in THAT regard, though because it is light, it has very important implications for space and time, ergo Special Relativity) and 2. light can, in fact, vary in speed: the speed of light in a vaccum is different than the speed of light in a medium (that is, it can be slowed down in, say, water). So rather than saying it is "constant" I think it is a little more clear to say that it is "independent"—it also avoids the appearance of tautology that baffles many new physics students (the analogy with sound is an easy one), makes it more clear why Einstein and his buddies knew it was "constant" from a theoretical point of view, and reminds people that thinking of light as little particles only reflects some aspects of its nature. --24.147.86.187 12:01, 23 October 2007 (UTC)

Yes inded and that's exactly my problem (now I see I might have worded the quesion poorly): How do you know when the speed of an object or particule (say some intergalactic one) would be approaching the speed of light if we don't have a frame of reference to calculate from? Would we consider the known universe as stable and not moving so that all absolute speed should be seen as the speed relative to our universe? But then how can we be so sure our universe is not moving and say in one direction an object could go 1.5 times the speed of light relative to the universe and the opposite direction never more than 0.5 times the speed of light while never actually exceeding the absolute speed of light? Keria 12:15, 23 October 2007 (UTC)

Well, you can measure the speed of an object from any reference frame, but no matter what the case it will not bypass the speed of light. Which is to say, they will not be exceeding the speed of light in any reference frame. Sound a little weird? Well, that's sort of the essence of Special Relativity. Instead of another observer seeing them as bypassing the speed of light, they will have disagreements about the amount of space they have covered in that time, or the amount of time it took them to cover that amount of space. In either case they will never see them go faster than 300,000,000 meters per second. (At least, that's my basic understanding of it. Someone correct me if I am mistaken about my reasoning.)

In any case, you have to use a different velocity-addition formula when working within special relativity—it doesn't work quite the same way as it does with simple Galilean velocity additions. Unlike Galilean relativity, where you could have one observer see the other exceeding the speed of light, the relativistic velocity-addition formula has the inability to exceed the speed of light hard-coded into it in a rather elegant way. --24.147.86.187 13:07, 23 October 2007 (UTC)

To take the first part of your question, you can't. There's no absolute measurement of speeds in relativity—only (surprise) relative ones. If you take a sealed box that's travelling at some constant speed, there's no experiment that you can do inside that box that will tell you anything about how fast the box is travelling relative to anything outside the box. The idea of the luminiferous aether has no place in relativity.

If you have an intergalatic particle travelling at some constant speed, the physics works whether you say the particle is moving quickly and the galaxy it's passing is at rest, or if you say the galaxy is moving quickly and the particle is at rest. It's totally equivalent; you may run across the phrase 'There are no privileged frames of reference' in your reading.

In a larger sense, the Universe is just like that sealed box. We don't get any information about what's going on 'outside'; heck, there probably isn't any 'outside' to talk about. You can, if you wish, treat the entire Universe as moving with some constant velocity, and you'll get the same results out of your equations and experiments. (Indeed, all you accomplish is making the math slightly more complicated.) TenOfAllTrades(talk) 13:20, 23 October 2007 (UTC)

Perhaps the simplest way to say this is: For everyone and every thing in the universe, every other thing has to be moving slower than the speed of light relative to them (unless it's a photon when it's moving at exactly the speed of light). SteveBaker 14:05, 23 October 2007 (UTC)

Hm? No, an object farther away from you than the edge of your observable universe is moving faster than the speed of light relative to you. --Trovatore 15:43, 23 October 2007 (UTC)

Good luck ever observing that ;-) Someguy1221 17:22, 23 October 2007 (UTC)

That's not the point. Whether something is true of "every thing in the universe" is an ontological question, not an epistemological one. --Trovatore 17:37, 23 October 2007 (UTC)

If there were an object that was just outside my observable universe moving faster than light relative to me - then what do you imagine it and I would look like to an observer halfway between the two of us? For that observer, the laws of physics are the same as they are for me. SteveBaker 23:05, 23 October 2007 (UTC)

Who said they weren't? But I admit this does get a little tricky and I don't have it all worked out. The thing to keep in mind is that this is inherently a GR problem; you can't simply apply SR formulas like the addition-of-velocity one and expect them to work unmodified. On a related note, the choice of coordinate systems becomes somewhat less canonical -- we can't speak of an inertial coordinate system that extends from you out to near the edge of your observable universe. I think this is called lack of distant parallelism or some such. --Trovatore 23:14, 23 October 2007 (UTC)

I was hoping a real general relativity expert would step in and explain this, but that hasn't happened, so I'll go ahead and give it my best shot. Hopefully, the following doesn't have any errors that are too blatant:

If an object is farther away from you than the edge of your observable universe, then it's ambiguous as to how fast it's moving away from or toward you. However, it's definitely moving slower than the speed of light.

Speed is fundamentally a local phenomena. The only way you can unambiguously talk about the speed relative to you of something at a distance is if both you and the distant object share an inertial frame of reference. That is, you and the object have to be within a region of spacetime which is flat, or at least close enough that a flat spacetime is a good enough approximation for the problem at hand. But when you're talking about something beyond the observable universe, the curvature of the universe becomes a critically important part of the problem. The problem is that a speed is the spatial distance between two events, divided by the time difference between the two events. But when you're talking about large distances in a curved spacetime, it becomes ambiguous as to how to separate a distant spacetime interval into space and time components. In a curved spacetime, it's impossible to set up a distributed system of clocks that are all synchronized with each other, because the curvature of spacetime makes clocks at different points in spacetime run at different speeds. So unlike with special relativity, with a curved spacetime it's impossible to define any single global coordinate system that keeps time separate from space everywhere. Instead, what general relativity does is to "stitch together" a continuous set of inertial frames of reference, each of which is only used locally. The metric tensor defines the global geometry of the spacetime manifold, and is unambiguous everywhere. But the coordinate system in which one chooses to express the components of the metric tensor at a given event, which is what defines the difference between space and time at that event, varies from point to point, and is to a large degree arbitrary.

Given a local inertial frame of reference used in one place, like an inertial frame of reference in which the earth is more or less at rest, there isn't a single "correct" local inertial frame of reference that should be used at a remote location, such as near a star that's beyond our observable universe. You can arbitrarily choose a local inertial frame of reference near that star, in which the star is moving in any direction at any sub-light speed you want. But in whatever local inertial frame of reference you use for measuring the remote star's speed, it's moving at less than the speed of light in its local inertial frame of reference.

Although in an expanding universe, light from a distant star may never be able to reach us, it's not valid to say it's because the star is moving away from us at faster than the speed of light. Instead, a valid description is that the space in between us and the star is expanding faster than light can overcome. More technically, the metric tensor that describes the distance between nearby points in the space in between us and the distant star is changing over time, such that the distance between any two points gets bigger as time progresses. MrRedact 02:40, 24 October 2007 (UTC)

Well, the above seems a bit internally contradictory -- if speed is fundamentally a local phenomenon (please don't use "phenomena" as a singular), then how can it make sense to say that the star is moving away slower than the speed of light? I do think you're right that the situation is a bit ambiguous because there is no inertial frame including both objects, but that doesn't seem to stop people from describing stars at high redshifts as "moving away from us at 99.999% of the speed of light" or whatever. Whatever definition of speed is used in that description, must surely describe the star past the horizon as moving away faster than the speed of light. --Trovatore 02:49, 24 October 2007 (UTC)

Ah, poking around a little I found the basis of a good candidate for a notion of the speed at which the star is regressing. Give us, and an observer at the distant star, a time coordinate t equal to time since the Big Bang according to a comoving observer -- that is, an observer for whom the background radiation is isotropic; roughly speaking such an observer will be at rest relative to nearby stars or galaxies or maybe galactic clusters. At any t, draw a geodesic between the event point represented by us when we have time coordinate t, and the one at the distant star at time coordinate t. Let s be the length of this geodesic. Now consider ds/dt.

I think it will probably be at least approximately correct that this measure of speed will be less than the speed of light for stars within our observable universe, and greater than the speed of light for stars past the horizon. However it's not my field of expertise and I'm not sure of that. But at least there's a well-defined question on the table; maybe someone who actually does know can settle it. --Trovatore 03:16, 24 October 2007 (UTC)

I didn't actually say that the distant star is moving away slower than the speed of light, merely that the star is moving slower than the speed of light, meaning that in no matter what local inertial frame you use to measure the star's speed in, the star's speed is slower than the speed of light in that inertial frame.

It looks like you're right in that if you choose to define the speed of the star relative to us as being ds/dt, where s is the comoving distance between us and the star (just one of a number of distance measures that could be used) and t is the cosmological time (just one of a number of measures of time that could be used), then the speed of the star relative to us is greater than the speed of light. The principal that "nothing can move faster than the speed of light" isn't violated, however, because the "speed" involved is a measure of the metric expansion of space, not the speed of an object moving within space. Indeed, in the comoving coordinates, both us and the star are roughly at rest. MrRedact 11:48, 24 October 2007 (UTC)

After reading more closely, I see that the definition of the comoving distance is not the same as the length of a spacial geodesic measured along a hypersurface of constant cosmic time. The comoving distance is defined as not changing in time, and isn't even well-defined for an object outside of the observable universe, so it doesn't work to have s be the comoving distance in defining ds/dt as the relative speed. It does work to instead use the length of a geodesic, which is what you used in your definition. MrRedact 14:18, 24 October 2007 (UTC)

Thank you very much for all your answers. Keria 18:54, 24 October 2007 (UTC)

Tap water

hi, i'm now living in the UK, is it safe to drink directly from the tap? in countries i've lived in before it is always recommended to filter the water first... —Preceding unsigned comment added by 82.46.27.191 (talk) 13:37, 23 October 2007 (UTC)

Except under very unusual circumstances, yes, you can drink tap water in the UK (and most other European countries). If not (e.g. due to contamination), that information will be well advertised via TV, radio, and newspapers. You might want to check if you are living in a very old building where the piping may still contain lead. But even in that case, it the risk is only significant for long-term exposure. --Stephan Schulz 13:48, 23 October 2007 (UTC)

In buildings with lead pipes you just need to let the water run for a few minutes so that the water that's been sitting in the pipes for a long time is gone before you take some to drink. But aside from that, yes - it's OK to drink UK tap water. SteveBaker 13:59, 23 October 2007 (UTC)

Every country has its germs. Some more (and more dangerous ones!) than others, but you always run the risk of getting diarhoea when abroad, wherever you go. But at least in (western) Europe you're not likely to get anything serious, so don't worry and drink the tap water. Except when you're just there for a few days maybe, in which case only drinking bottled water would not be too much of a hassle. especially when you're on a business trip, and can't afford to get sick. But even then I would consider it rather over the top. Keep in mind that tap water in (western) Europe is meant to be perfectly safe to drink. I just pointed out the few minor reservations you might have. DirkvdM 19:08, 23 October 2007 (UTC)

Is it possible to use nanomachines instead of electricity?

Like, instead of electricity doing "work", the nanomachines do the work instead. Is this possible? 64.236.121.129 14:54, 23 October 2007 (UTC)

See mechanical work and nanotechnology for some articles that might be relevant. Something has to power the nanomachines, right? That might still be electricity. Friday (talk) 14:58, 23 October 2007 (UTC)

Firstly, we don't have nanomachines - and there are grave doubts that they are even possible. But if we do someday figure out how to make them, they'll need power from somewhere. Most likely we'd power them with laser light - but it's possible they could be powered from chemical sources in whatever media they are working. In that respect they are no different from normal-sized machines. Just as an industrial robot could be powered from electricity or gasoline or solar cells - it would be the same thing with nanomachines. So they aren't going to somehow "replace" electricity - although they may well be powered by electricity. Probably the best way to think of them would be as teeny-tiny robots - or perhaps like bacteria or virusses that we designed ourselves. SteveBaker 15:04, 23 October 2007 (UTC)

Yea I know we don't have nanomachines. If we did, I would already know the answer. Anyway, what powers the nanomachines doesn't necessarily have to be electricity. Hmm, I guess what I'm getting at is, is it possible to create something that is powered by something other than electricity (so it's impossible to be electrocuted) or something that can blow up like gasoline. Our bodies for example aren't powered by electricity (although there are electrical signals), nor by anything that is combustible. 64.236.121.129 15:39, 23 October 2007 (UTC)

Our bodies are powered by combustible materials, it's just mixed with water, so doesn't burn easily. If you take the water out, the remaining protein, carbs, fats, and alcohol burn quite nicely, and will even explode, if converted into an aerosol. StuRat 22:59, 28 October 2007 (UTC)

These machines would probably not carry "batteries" as such - and you wouldn't want to connect them up with wires - so electricity doesn't seem like the natural thing to power them with. They might maybe have an onboard chemical fuel supply - but more likely, I think we'll be powering them by shining laser light onto them from outside - or perhaps using chemicals in whatever fluid they are floating in to generate power. There are other possibilities though - they could be powered by something like a clockwork motor or something like a flywheel that stores energy and can be made to give it back as required. Things work very differently on a nano-scale and things that aren't considered very useful at the macro-scale are often extremely useful at the nano-scale (and vice-versa). For example, it's been widely suggested that nano-bots would use mechanical computing parts - like Babbages Difference engine or the TinkerToy computer that students put together at MIT. Pushrods and gears at that molecular scale would work more quickly than the transistors in an electronic computer! So it's possible that something like a clockwork motor could power such a machine.

But the bottom line is that we don't really know how we'll power these things...if indeed they are possible at all. SteveBaker 16:03, 23 October 2007 (UTC)

It has to be possible to power them. After all, viruses, bacteria, amoebas, cells, etc can utilize energy, so we know that it is possible. If they can do it, then it can be replicated. It's not easy to emulate, but it's possible. 64.236.121.129 16:40, 23 October 2007 (UTC)

Right - those things are (mostly) powered from chemicals in their environments and they have a small on-board chemical fuel supply to tide them over between meals. We could do the same thing. On the other hand single-celled plants are solar powered. We could do that too. If nanomachines are ever built 'for real', and if they are designed to self-reproduce (Drexler's "assemblers" for example) then there is the risk of Grey goo - when the machines go nuts and try to convert the entire planet into more machines! Having them powered by something that's not naturally "out there" is a way to prevent that. If you powered them by shining a laser of a specific frequency onto them - then if they went nuts, you could simply shut off the laser and they'd all switch off. Giving them a fixed internal power source (like a molecule-sized clockwork motor) would have a similar effect. But, as I said before, we are an awful long way from having such things - and it's a bit premature to be discussing details of things like power supplies when there are much more serious problems to be solved. SteveBaker 20:29, 23 October 2007 (UTC)

Grey goo. Pah. Amoebas are self powered and exist solely to make more amoebas. I see no grey ameobic goo. --Psud 10:23, 24 October 2007 (UTC)

See Micropower for a discussion of some nanomachines and nanogenerators (some recent articles on this topic are listed on the talk page but not yet incorporated in the article). Edison 17:01, 23 October 2007 (UTC)

density and volume of electron, proton (atomic structure)

dear sir

i am eswar .nice meeting you.

i would like to ask a question related to basic particles of atom

what is the numerical value of elctron and proton densities in kg/meter cube ?

what is the numerical value of elctron and proton volume in cubic metere ? —Preceding unsigned comment added by Eswar kumar p (talk • contribs) 15:05, 23 October 2007 (UTC)

The very first sentdnce of the Proton article tells you the size and mass. The Electron article also tells you the mass and has some discussion of the size (in terms of the "classical electron radius"). DMacks 15:14, 23 October 2007 (UTC)

But note that the volume of an electron is not well defined. In quantum mechanics, it doesn't really behave much like a particle at all, but more like a wave, which only has a probability function, not a location and volume. StuRat 22:47, 28 October 2007 (UTC)

Anomalous hair

I have a hair follicle which is unusually long, some 2-3 times a normal hair and also white. It is notably to say that it always grows in the same place. I had asked my biology teacher if it was a case of mosaicism but he negated it without offering me an explanation. So guys, any ideas on what is it?—Preceding unsigned comment added by 193.188.46.61 (talk) 16:43, 23 October 2007 (UTC)

Your biology teacher isn't allowed to give out medical advice - and neither are we. SteveBaker 16:06, 23 October 2007 (UTC)

Lighten up. He isn't asking for medical advice. Theresa Knott | The otter sank 17:16, 23 October 2007 (UTC)

Your biology teacher is allowed to give out biological information, and so are we. Having a long white hair should not ordinarily make one suspect mosaicism. Why does a long white hair need explanation, anyway? - Nunh-huh 16:40, 23 October 2007 (UTC)

The melanocytes in this particular follicle have apparently ceased to function earlier than in your other follicles. If you were a mosaic or chimera, there would, I suspect, be a wide range of other readily observable manifestations. Gray hair says that white hairs can appear as early as childhood without any particular or worrisome cause. Just out of curiosity, is it growing more quickly than your other hairs, or is it more robustly rooted, and so does not fall out as readily? Eldereft 22:06, 23 October 2007 (UTC)

It is medical advice he is asking. He presents us with evidence and asks for a diagnosis. Please don't. Questions and answers removed. Lanfear's Bane | t 23:26, 23 October 2007 (UTC)

I felt the question was for an explanation of a biological phenomenon. The was no indication that the questioner regarded this as a medical problem in any way. Are we to assume that any and all questions of human biology are in future to be deleted? DuncanHill 23:39, 23 October 2007 (UTC)

Astonishing. Someone so unacquainted with what medical advice actually is that he removes a question about the causes of a white hair while leaving advice on how to remove ear-wax on the same page. This despite two people who had already indicated there was no advice. - Nunh-huh 00:17, 24 October 2007 (UTC)

I was going for 'here are some possibly related articles,' but fair enough. Eldereft 00:20, 24 October 2007 (UTC)

I agree that this is not a medical question, it's a biology question. I've noticed that people get more of those type of "rogue hairs", which never stop growing, when they get older. They especially appear in the eyebrows and on the ears of men, but can appear just about anywhere. They can be colored or white, but I've also noticed they tend to be thicker hairs. I'm not sure what biological mechanism causes this, but I'd suspect it's a malfunction of the mechanism which normally limits hair length in most places on our bodies. StuRat 22:37, 28 October 2007 (UTC)

safe fungi

how can I tell if fungi is safe to eat? —Preceding unsigned comment added by 213.228.203.153 (talk) 16:57, 23 October 2007 (UTC)

Eat it and see if you die. All joking aside, that's close to the answer. Try to find a local field guide. For instance, I have one for Colorado mushrooms. It lists a number of them, including their safety. It lists some as "Edible, but unsafe" because they are too easily mistaken for poisonous varieties. Failing that, there are methods to test plants for safety, of which you might be able to find in hard-core survivalist stuff. --Mdwyer 17:14, 23 October 2007 (UTC)

Assume it is unsafe unless you already know it is safe or if someone whose expertise you totally trust tells you it is safe. There are a lot of poisinous fungi out there and many of them look very similar to harmless ones. Theresa Knott | The otter sank 17:11, 23 October 2007 (UTC)

Short answer: There is no, clear, simple rule to tell the difference between poisonous and edible fungii.

Longer answer: When I was learning to program simple artificial intelligence systems, one class problem was to write a computer program that could take a lot of facts about classes of object and find rules to distinguish between them. So, for example, you could type in all of the information about 50 different kinds of car (top speed, fuel consumption, 0-60 time, number of doors, weight, etc) - then tell the system which cars were sports cars and which were not. The system would go off and work out which parameters about the car mattered and to what degree they mattered in classifying whether it was a sports car or not (so in this case, it would figure out that top speed and accelleration were important, having two doors was less important but still relevent - but fuel consumption had little or no bearing on how the car was classified). Then you could put in the data for a new car - and the program would unerringly be able to tell you whether it was considered a sports car or not by applying the rules. Anyway most of the class got good working programs to do this and at the end of the class, we were given a database containing all of the characteristics of a bazillion kinds of mushrooms and toadstools (including whether each one was poisonous or not) - and asked to "Find the rule to distinguish poisonous from edible". Nobody's program out of the entire class was able to find a common rule...and the reason for that is: There isn't one...it was a "trick question". SteveBaker 20:21, 23 October 2007 (UTC)

Off-topic: Did you do that in Prolog? I used that language once to write a program with which you could find the ideal place for you to live on Earth. Put in the characteristics and it gave the locations that had all those characteristics (well, actually it was limited to South America and had a very low resolution because I had to manually build the entire database). DirkvdM 09:29, 24 October 2007 (UTC)

From my first answer at 'Edible mold and fungus (mushrooms)' 10 threads up: "If you're not sure if something is edible, first rub it between your fingers, then under your armpit, then on your lips, then put some in your mouth, chew and spit. If any of these tests results in a unpleasant feeling, don't eat it. Then swallow a little bit and wait for a few hours (maybe longer). If you don't get sick, you can eat more and wait. If you still don't get sick, it's safe to eat." This info from a hard-core survivalist (no, not one of those idiots who stock up centuries worth of food in case the world ends). DirkvdM 09:29, 24 October 2007 (UTC)

Bad advise unless the other option is starving to death. The death cap, for example won't irritate your fingers, armpits or lips, but will quite cheerfully kill you a few days later unless you can get a liver transplant in a hurry. Half a cap will likely kill a person. Capsicums (or I think US of Aians call them bell peppers) are tasty and nutritious, and will fail the test. --Psud 10:39, 24 October 2007 (UTC)

It takes days to kill you? That's very unusual. DirkvdM 18:51, 24 October 2007 (UTC)

I agree. The death cap is deadly, but tastes good. Evolution at work right there. Eat food that you know is safe only. Leave the guessing to the starving person who has no choice. 64.236.121.129 13:57, 24 October 2007 (UTC)

So you're saying "look it up". Good advise, but I suppose the questioneer thought of that too. :) I got this from the SAS Handbook by John Wiseman. This time I bothered to look it up and under 'mushrooms' it says that there are no reliable general rules to identify edible mushrooms and boiling doesn't help either. You have to KNOW beyond doubt if it is an edible mushroom. And (translated back into English): "Unlike plants, for which the simple edibility test can be done, they have to be either identified or avoided. The deadly varieties don't taste unpleasant and the intoxication symptoms sometimes set in only after hours." So not days, but still, it turns out you guys are right. However, if identified beyond doubt as edible, they are a good food source which, in the right season, is available in abundance. Fortunately, they can also be easily conserved by drying. The book advises to learn a few real well and stick to those. It also advises to learn to identify amanites, the ones to particularly avoid. The most deadly is amanita phalloides, the death cap, followed by amanita virosa. Symptoms start slowly after 8 - 24 hours. After that a clear improvement, but in 90% of cases one will die after 2 - 10 days due to liver problems. No known antidote. Ah, so it does take days in this case, but it's not the poison itself that kills but the failing liver. Btw, the book also describes some nasty symptoms (including hallucinations) for the famous amanita muscaria, although one will generally recover. Note that I ate a whole muscaria once (for the hallucinations), but noticed nothing. However, that was a few days after I picked it, because I had started with tiny bits, ever bigger, until in the end I ate the remaining half. If only there weren't such idiotic drug laws, then people like me wouldn't do this sort of thing. Anyway, the muscaria article says "The effect is highly variable and individuals can react quite differently to the similar doses. Deaths from A. muscaria are extremely rare. [...] The amount and ratio of chemical compounds per mushroom varies widely from region to region, season to season, further confusing the issue. [...] The vast majority of mushroom poisoning fatalities (90% or more) are from having eaten either the greenish to yellowish to brownish mottled death cap (A. phalloides) or one of the destroying angels (Amanita virosa)." DirkvdM 18:51, 24 October 2007 (UTC)

I'd just like to agree that you should learn one or two easily identifiable species found in your area and stick to them. Use a book and a knowledgable friend if you can (you can get a book out of the library; friends who know about mushrooms may be rarer). For example, in the pine forests near where I live, one can find the delicious Boletus edulis, which is pretty distinctive, and what we call a pine ring (can't find it on wikipedia) whose stalk has a distinctive greenish-blue ring when cut. --Taejo|대조 10:27, 29 October 2007 (UTC)

Bathroom smelling of salt

Whenever I'm away from home for more than a day, when I come back home, my bathroom smells strikingly strongly of salt. The smell goes away by the next morning. What the heck is causing this? JIP | Talk 17:00, 23 October 2007 (UTC)

What does salt smell like? If the plumbing traps are drying out, it might be sewer gasses. It might be things growing in the traps. If you use those giant chlorine pills in your toilet tank, it could be chlorine gasses from it. In other words, I have no idea. --Mdwyer 17:09, 23 October 2007 (UTC)

It's like smelling something pulled up from under the sea. I do not think it's a problem with the house's plumbing, otherwise I would smell it constantly. I first experienced it when undergoing my civilian service training, which took three weeks in a training facility in another town. Weekends were free, so I came back home for every weekend. When I first opened my door on Friday evening, I was met with this salty smell. On Saturday morning, it was completely gone. It must be something related to my senses getting used to something, but how come I only ever notice it in my own apartment, not in my parents' apartments or at my workplace? JIP | Talk 18:47, 23 October 2007 (UTC)

Sounds like the smell of damp/cold places - which you probably get used to when you live there.. I seem to remember a pantry which was unheated having a smell that could be described as salty..87.102.10.72 22:10, 23 October 2007 (UTC)

Assuming you live near the sea, I have two theories:

1. The smell is always there. When you are at home, you get used to the smell and it disappears from your mind. If you go away for a while you get used to different smells so your mind really notices the natural sea smell when you return home.

2. Sea water is mixing with the water in the sewerage system. Without a regular washing out by running water down the outlet and flushing the toilet, the sea water and it's smell seeps further up the drains and into the traps under the your sinks. If the traps are dry, the sea smell could easily escape into your bathroom.

Astronaut 17:11, 25 October 2007 (UTC)

Muscle cells

• On what factor does the strength of the muscle cells rely on ??
• can it be strengthened without increasing its size but by altering its components to make it strong as metal?

plz answer both Qs —Preceding unsigned comment added by 212.71.37.98 (talk) 17:12, 23 October 2007 (UTC)

A muscle's strength is dependent largely on how many myofibrils it contains. Now, saying "as strong as metal" is a meaningless comparison. The strength of a muscle is its ability to exert a force, whereas the strength of a metal is its ability to resist deformation. Someguy1221 17:28, 23 October 2007 (UTC)

The answer is no. The amount of force a muscle can exert is proportional to it's cross-sectional area. So bigger means it can exert more force - there isn't anything you can do to make it exert more force except by making it thicker.

"As strong as metal" is quite utterly meaningless. How strong is Mercury at room temperature? (Hint - it's a liquid!) Which metal are we talking about? What temperature? Are we talking about strength in tension or in compression or in bending? Take a length of electrical wire (copper) and try to snap it by just pulling on it...you'll never manage it. But bend it back and forth a few times and it snaps easily. Even your smallest muscles can be bent back and forth millions of times during your life and they don't snap.

Part of the trouble here is that you are using the word "strength" to mean two quite different things. When we talk about someone being "strong", we are probably talking about the amount of weight they can lift or something. That's a measure of the force your muscles can exert. When we talk about "strength" in metals, we're talking about the amount of weight they can passively hold without breaking. So whilst you MIGHT be trying to compare the amount of weight a steel cable could hold without snapping to the amount of weight a chunk of muscle could hold without snapping - that wouldn't be the same as the weight that could be lifted by contracting that same muscle. SteveBaker 20:05, 23 October 2007 (UTC)

Sanitation

(Aaw, lost what I wrote in an EC...) Is there anything I can do to sanatize my desk besides using clorox wipes and putting on GermX before eating, because we're having staph outbreakes at my school. I could probably get a hold of most things (disenfectants), but I need to know what they are. Thnx!YДмΔќʃʀï^→Г_C← 10-23-2007 • 19:36:16

While it's tempting to recommend that you use the time-honored method of subjecting it to a temperature similar to the inside the sun for a few seconds, I must regretfully assume that you are speaking in practical terms. "Creative" methods such as that excluded, I'd just recommend washing your hands a lot and using the disinfectants, etc you mentioned above. Maybe the article Staphylococcus could give some useful information as well.
Ah, here we go: this section talks about alcohol being a good disinfectant specific to the bacteria:

Alcohol has proven to be an effective topical sanitizer against MRSA. Quaternary ammonium can be used in conjunction with alcohol to increase the duration of the sanitizing action. The prevention of nosocomial infections involve routine and terminal cleaning. Non-flammable Alcohol Vapor in Carbon Dioxide systems (NAV-CO2 systems) have an advantage, as they do not attack metals or plastics used in medical environments and do not contribute to antibacterial resistance.

Hope this is useful. Pyrospirit (talk · contribs) 22:51, 23 October 2007 (UTC)

polymer

which materials are anti_markin about absorbing ink? —Preceding unsigned comment added by 85.133.156.36 (talk) 20:37, 23 October 2007 (UTC)

I'm not entirely sure what you're talking about. Could you provide more context to your question? Pyrospirit (talk · contribs) 23:01, 23 October 2007 (UTC)

You need something with a strong non porous surface, such as glass or metal. The ink will be erasable. FOr polymers you face the additional problem that the solvent in the ink may be able to dissolve the polymer or soften it, allowing the ink to pentrate the surface and be hard to remove. Melamine resin or Formica (plastic) are pretty good at resisting staining. Look at anything that might be used on a kitchen bench or whiteboard. Graeme Bartlett 01:34, 24 October 2007 (UTC)

Toadstools and snakes

I think I know two things: that no shelf mushroom is poisonous, and no snake with longitudinal stripes is venomous. Are these things true? --Milkbreath 21:23, 23 October 2007 (UTC)

There is no simple rule to distinguish poisonous mushrooms from edible ones - although what you say here isn't exactly that. Our article says that most shelf mushrooms are inedible - but doesn't say whether any are poisonous. I'd be VERY skeptical about that rule. About the snakes though. I find your claim here rather surprising too. I guess it depends on what you call a 'stripe' and just how 'longitudinal' it has to be. The Yellow bellied sea-snake is certainly pretty venomous - and I'd call that a black/yellow longitudinal stripe pattern...but maybe you can weasel out of that by saying that it's a 'sea snake' and you meant only land snakes - or that it's not really a "stripe" per-se but merely a top and bottom coloration. SteveBaker 22:37, 23 October 2007 (UTC)

The pit viper Trimeresurus popeorum has ventrolateral stripe. I also came across this bizarre image of what the photographer claims is the deadly Bungarus fasciatus which normally has striking yellow and black lateral stripes, but in this case sports black and yellow longitudinal stripes. The picture has the accompanying text: "Bungarus fasciatus : mutazione genetica. Raro esemplare con una lunga fascia dorsale nera al posto della tipica colorazione ad anelli." I caught the word genetic mutation but that is a pretty drastic change from the normal patterning. Mistaken identity possibly? EDIT: It appears to be the venomous elapid Hemibungarus sauteri an "Asian coral snake" Sifaka ^talk 04:20, 24 October 2007 (UTC)

Actually it seems like a few of the "Asian coral snakes" in the venomous genus Calliophis seem to be longitudinally banded and strikingly colored. See this picture of Calliophis bivirgatus. Sifaka ^talk 04:51, 24 October 2007 (UTC)

Followup: [1] says that the Sulphur Shelf mushroom (Polyporus sulphureus) poisoned seven members of the The Mycological Society of San Francisco (who REALLY ought to know better!). Our article Laetiporus confusingly describes it as edible (and gives it a totally different Latin name?!?) - but then goes on to say "About half of the population has an allergic reaction to this type of mushroom, with cases being more pronounced in older mushrooms."...yeah - so it's edible, but you have a 50/50 chance of being allergic to it. Hmmm - I call your claim "Busted". SteveBaker 22:45, 23 October 2007 (UTC)

Right you are. But, heyyyy...does ya got sumpin against weasels? --Milkbreath 23:00, 23 October 2007 (UTC)

To my knowledge none of the bracket fungi appear to be truly deadly poisonous, but then again some dangerous fungi can grow in a manner where they superficially resemble bracket fungi. It also doesn't help that most bracket fungi taste like tree bark with similar toughness. Incidentally Chicken of the Woods (Laetiporus sulphureus is the correct name for Polyporus sulphureus) is actually very commonly eaten and supposedly tasty; however it needs to be cooked before eating. The poisoning described above was probably at worst an upset stomach, vomiting, and maybe some diarrhea, nothing requiring any hospital attention. Sifaka ^talk 03:16, 24 October 2007 (UTC)

Hmmm - so what you are saying is that it may be true that bracket/shelf mushrooms are not poisonous - but there is no good rule for identifying that something actually is a bracket/shelf mushroom and not a look-alike. OK that makes our OP technically correct - but not usefully/safely correct! If 50% of people have an allergy to the mushroom - I'd be surprised if the symptoms were upset stomach, etc - we'd see allergic reaction symptoms. Of course an allergic reaction doesn't mean that the mushroom is 'poisonous'. But I don't think I'll be eating them anytime soon! Bottom line has got to be that it's just not safe to use this 'rule' to identify edible mushrooms. SteveBaker 04:28, 24 October 2007 (UTC)

Steve you appear to be right. I read it over and found this [[2]], but it seems only mature specimens cause the trouble. Sifaka ^talk 04:36, 24 October 2007 (UTC)

• It's too bad 'shroom-hunting is so tricky. I wonder if you couldn't just come up with some type of litmus test for the most popular substances these things use to kill you. --Sean 21:27, 24 October 2007 (UTC)

internal violation

My big brother wants to join the army but his mates keeps teasing him that during his medical he's going to be internally violated. But I'm to sure about this, I want to know (1) does the doctor internally violate recruits and (2) what purpose does this serve? —Preceding unsigned comment added by Everyone knows someone called Dave (talk • contribs) 22:29, 23 October 2007 (UTC)

What country/army are you asking about? - hydnjo talk 22:47, 23 October 2007 (UTC)

Probably doing a Rectal examination - possibly for Prostate issues. SteveBaker 22:54, 23 October 2007 (UTC)

If that is violation, then I have once been violated by a woman (a doctor). (no prostrate problems, I can happily tell you.) DirkvdM 09:45, 24 October 2007 (UTC)

To paraphrase Tony Soprano, "I don't even let people wag their finger in my face!". 38.112.225.84 15:26, 24 October 2007 (UTC)

• I would be very surprised to learn that young men receive prostate exams in a standard recruiting physical. It's much more likely that your brother will just receive a check for any weaknesses around the inguinal canal, which could lead to an inguinal hernia. This exam gets quite personal, but it's no "unsolicited finger in the anus". --Sean 19:19, 24 October 2007 (UTC)

Is that the legendary stand-in-a-line-and-"please cough whilst I hold your testicles" thing? --Kurt Shaped Box 20:41, 24 October 2007 (UTC)

Yes, although they don't actually hold your testicles. Rather, they "slide" a finger or two up alongside the spermatic cord. Only for some reason, "slide" usually turns out to mean "jam". :-) --David Iberri (talk) 21:14, 24 October 2007 (UTC)

• I get my revenge by turning my head towards the doctor. --Sean 21:29, 24 October 2007 (UTC)

The U.S. Army does do a hemorrhoid check, but it is a visual check and does not involve any probing. These mates are high school students aren't they? --— Gadget850 (Ed) ^talk - 08:10, 27 October 2007 (UTC)