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July 28

Force particles

When a force particle collides with another particle, it changes the velocity of the other particle, right? If so, there must be a constant stream of force particles coming out of an object that makes that force (such as photons out of electrons and gravitons out of everything). If each force particle has energy, where is the energy coming from? Also, are gravitons effected by gravity the same way everything else is? Where does it go when it hits the other object? Is there anything I can read that I don't have to pay for that talks about that stuff? — Daniel 00:21, 28 July 2007 (UTC)[reply]

I don't know what you've been reading, but ~~unless I'm badly mistaken, there's no such thing as a "force particle", and~~ we've never detected or even proven the existence of the mythical graviton~~, either~~. ~~So there really aren't any answers to your questions.~~ —Steve Summit (talk) 01:06, 28 July 2007 (UTC)[reply]

The theory of gravitons is basically just theoretical (read: made up) at this point.. they thought "we discovered a particle for every other force so lets make one up for gravity". Very little is even guessed about them at this point- come back when we discover a unified field theory. IMHO certainly there's a better way of describing gravity than infinite numbers of noninteracting particles flooding every point of the universe. --⁪froth^t 01:16, 28 July 2007 (UTC)[reply]

The proper term is messenger particle or force carrier. In my experience, all explanations of their function that don't invoke quantum gibberish, yet more quantum gibberish, or the pinnacle of quantum gibberish are all actually incorrect. So unless you plan on devoting several years of higher education to the field, it is hard to develop an actual understanding. It's not your fault, though, it's the fault of quantum for being such complete and utter gibberish. Someguy1221 01:27, 28 July 2007 (UTC)[reply]

You're right that force-carrying particles can carry energy and change the velocity of other particles. You can draw Feynman diagrams that show exactly that happening. However, there is not a constant stream of photons carrying energy away from every electron. Instead, there's a photon field that has some properties in common with the electric field and magnetic field in Maxwell's equations, some properties in common with a particle in ordinary quantum mechanics, and some properties that are new to quantum field theory. If the electron is minding its own business, not accelerating or interacting with anything else, then the photon field doesn't carry away any energy. If it gets accelerated, it will radiate some energy in photons. If it passes by some other particle, it may scatter and lose some energy through interactions mediated by photons. And yes, we expect that gravitons should also interact with gravity like everything else does. --Reuben 01:42, 28 July 2007 (UTC)[reply]

Why does the electron need to pass by something? If there are two electrons, no matter how far apart they are they repel each other. Is this just an inaccuracy of classic physics? Does an electromagnetic wave have a chance of collapsing so the photon that it is has never been emitted? Is it impossible for an object to emit a force carrier so it never hits anything. If gravitons are effected by gravity, wouldn't it be impossible for gravity to escape a black hole? I guess in that case the gravitons couldn't actually hit each other, but if two bodies emit gravitons at each other, would the gravitons from each body increase the energy of the gravitons from the other body? — Daniel 02:01, 28 July 2007 (UTC)[reply]

That's still true, but it's not at all simple to understand in terms of quantum field theory. You have to describe it in terms of the photon fields, or very very many (in fact, an indeterminate number of) virtual photons, which don't have the same properties as "real" photons. Believe it or not, the question of whether or not it's possible to emit a photon that never gets absorbed is a famous and subtle question! I would have to search for more information about it. I'm not sure it's settled on a fundamental level what the answer is. As for gravitons near a black hole, our models break down. Fortunately, people have found ways to calculate most of what we need to know based on considering what happens just outside the event horizon. So it may be that black holes have exactly the gravity you expect, even if no gravitons can actually get out. It's likely to be very very difficult to understand any measurable gravitational phenomena in terms of individual gravitons. You'd have to go to graviton fields, or (again, indeterminately many) virtual gravitons. And these calculations will not be easy. --Reuben 04:22, 28 July 2007 (UTC)[reply]

If I'm understanding the OP correctly, that's a good question, and one which caused Einstein and others to come up with the idea that gravitational, electromagnetic, etc. fields have to change the "geometry of space", so that they can affect the movement of other objects without having to continually supply energy from somewhere. Of course, this unfortunately reminds me of the original theory of colloids, where scientists couldn't figure out how enzymes would give a glass of water the ability to digest protein, for instance, so they decided that dissolving the enzyme in the water somehow changed the structure of the water so as to make it digest proteins.Gzuckier 17:27, 30 July 2007 (UTC)[reply]

Brain Memory

Memory is stored in brain cells but ? In What forms is that memory stored ?

Memory isn't stored. Experiences are stored and that's what we call memory. So the question is then "how does memory work", and I don't think there is anything near a conclusive answer to that. At the cellular level, very roughly speaking, neurons receive signals from other neurons and send signals to other neurons in response. How strong the signals they send are depends on the strength of the signals they receive and the history of received signals. That last bit is the memory bit. How those actions by individual neurons combine to form memories at a higher level is where it gets trickier. DirkvdM 05:28, 28 July 2007 (UTC)[reply]

At the neuron level, memory is stored via synaptic plasticity. See Long-term potentiation and Hebbian theory. MrRedact 05:38, 28 July 2007 (UTC)[reply]

For bonus points, how many petabytes of information can a human brain hold? Including corruption and fragmentation over a lifetime, of course --L^ie! 05:43, 28 July 2007 (UTC)[reply]

It’s hard to give an accurate answer to the "bonus" question, because a brain and a computer store information very differently. But as a rough approximation, the information content in a brain could be viewed as very crudely being similar to the information content in a matrix, where the matrix indices specify presynaptic and postsynaptic neurons, and the non-zero matrix elements specify the efficacy of a synapse connecting the two neurons. With one byte to specify the efficacy of a synapse, and 5 bytes to specify the index of a neuron, an efficient sparse matrix representation of the matrix would require about 6 bytes per synapse. If a brain has about 10¹⁵ synapses (I’ve seen estimates between 10¹⁴ and 10¹⁶), that would correspond to the brain holding about 6 petabytes of information. However, that number is a very rough estimate. I think some neurobiologists would argue that that number should be considerably higher, because there’s a lot of weird stuff that goes on at the neuron level that doesn’t map well to an artificial neural network model of the brain. And some AI researchers would argue that that number should be much lower, because it’s possible to represent some of the information that we use our brains to store much more efficiently than with a neural network. MrRedact 07:00, 28 July 2007 (UTC)[reply]

I have a suspicion that memory, as distinct from the processes that govern reason and handle inputs and outputs, is actually quite limited. How much independent information can a human actually recall? Is it more or less than the amount of information written in Wikipedia (for example)? Wikipedia has a few hundred gigabytes. If one lives 70 years, you could devote 20 minutes per article to learn all of Wikipedia's content (ignoring details like sleep and food). If we limit the discussion to just the facts and information that humans can recall, then I would not be surprised if that could be compressed into a terabyte or so. This excludes the highly complex operational hardware and software that allows us to process this information and sensory input into that thing we call consciousness. Dragons flight 08:18, 28 July 2007 (UTC)[reply]

I could question whether it make any sense to limit the discussion to just the 'facts and information'. Humans appear to remember a very large variety of sensory experiences in a large variety of detail. A lot of that may not even be easily accessible to the human but is clearly stored since it may be remembered if a certain trigger is present. Bear in mind most of wikipedia is text. If wikipedia's content was all in video form for example, the data storage requirements would be vastly different. In the end, I don't think any comparison makes sense. You simply can't talk about the human memory in bytes since it does not work in bytes. Nil Einne 15:46, 28 July 2007 (UTC)[reply]

Any information can be measured in bytes. If you take the negation of the binary logarithm of the probability of a certain state, that is the information of that state. For example, if there is a one in a million probability of me winning the lottery, the information that I didn't is -lg0.999999=0.00000144269576 bits. The information that I won would be 19.9315686 bits. If the information was a bit fuzzy, and it only said there was a 50% chance of me winning, that would be one less bit of information. The actual act of measuring a person's memory like this is incredibly difficult, but it still theoretically can be measured in bits. Changing this to bytes is trivial. It should be noted that information stored on your computer rarely if ever has perfect compression, and the amount of memory used is more than you'd calculate. — Daniel 20:27, 28 July 2007 (UTC)[reply]

I disagree although I admit I don't understand most of the mathematics of what you're talking about or informationa theory very well. I don't think you can give any numerical figure to the 'information' that the human brain stores precisely because it does not work like that. Human memory is closer to analog then digital, although it's neither AND both IMHO. Also, I don't think it makes that much sense to talk about compression let alone perfect compression when it comes to human memory. Human memory isn't compressed so to speak, at least not in the way we think of when it comes to digital compression. The level of detail stored of course varies. (However as I mentioned above, it's important to consider that even determing the level of detail is difficult as we often 'store' more then we normally remember). I'm not sure but I think you may have missed the main point I was trying to make. It seems to me you're still just thinking of the human memory as pure information which IMHO is too simplistic and doesn't make sense. even if to some extent, you can argue that all memory is basically information. Perhaps there are things that I don't understand but really, I wouldn't trust any answer coming from someone without a detailed knowledge of information theory and the extremely complicated human neural system (which we are only just beginning to understand). Most answers I've read (in general, not here) usually seem to be coming from one or the other. One answer I came across was this one [1] which is interesting more in how poor the figures are. While the Landauer work is interesting (and the experiments analysed described only in minimal detail so perhaps it's better then what it appears although I'm somewhat doubtful you can come to any meaningful conclusion about how much someone remembers about a picture from a true & false/MCQ test), it appears to be highly flawed in that it was only really only looking at very simplistic memory and very simplistic information. Nil Einne 01:49, 30 July 2007 (UTC)[reply]

Yeah; the classical example is the grandmother cell where the memory of your grandmother was stored; if anything happened to it, people would ask you "who's your father's mother?" and you'd be stumped. No, the mind doesn't store things that way, on any level except perhaps the most simple. Gzuckier 17:30, 30 July 2007 (UTC)[reply]

chicken skin

I started having chicken skin on my neck. I wonder how i got this. can be from eating chicken? what must i do to make it disappear. Thank you for any answer you may provide. —The preceding unsigned comment was added by 124.104.136.216 (talk • contribs) 12:12, 28 July 2007 – Please sign your posts!

Whatever it is, it is definitely not from eating chicken. My guess is that it is a rash or chafing, but I'm not a doctor and not qualified to give medical advice. 72.148.109.119 13:05, 28 July 2007 (UTC)[reply]

Please take the time to read the guidelines above. Wikipedians don't give medical advice. Sorry Nil Einne 15:40, 28 July 2007 (UTC)[reply]

You may be referring to Keratosis pilaris. You may also want to see a dermatologist. Someguy1221 21:28, 28 July 2007 (UTC)[reply]

Or pseudofolliculitis barbae, since you mention it is on the neck. This is most likely if you are a male of African descent. If this is the case, it should go away as your beard grows out. To prevent it, just avoid shaving so close so hairs don't get ingrown. HYENASTE 01:23, 29 July 2007 (UTC)

If you get chicken skin on your neck from eating chicken, you need to use your napkin. Gzuckier 17:31, 30 July 2007 (UTC)[reply]

Or aim a little higher. Capuchin 10:32, 1 August 2007 (UTC)[reply]

does photon move in straight line ?

i've always taught that photon's move in straight line . but i've also learnt that sometimes photon is of dual nature . sometimes they move in wave form . but the front of a wave always changes direction so the path can't be said straight . enlighten me if i'm wrong .

One way I've seen it nicely explained... The photon is moving in a straight line from its point of view. It may be moving like a wave from your point of view. -- Kainaw^(what?) 13:56, 28 July 2007 (UTC)[reply]

Consider this as an analogy. Take a boat trip directly across a harbour from one dock to another. You regard yourself as travelling in a straight line across the water. But the water has a bit of chop on it creating small waves that move the boat, and therefore you, up and down as you travel in your straight line path from dock to dock. This is like the photons moving as a wave front. There's a couple of other things to consider. The wave–particle duality is a model that helps us understand the behaviour of things like light, not an exact description of reality. And, light does not always travel in straight lines, it can be bent by extremely large masses; see for example gravitational lens. --jjron 14:40, 28 July 2007 (UTC)[reply]

Electromagnetic waves don't wiggle back and forth as they move! The field strength oscillates perpendicular to the motion, but that's not a spatial displacement.

In quantum field theory, the only place where the word has a well-defined meaning, a photon is a quantum of energy in the electromagnetic portion of the overall quantum field. If you have two liters of water in a container, you can't say which parts of the water correspond to individual liters, and it's the same with two photons in the electromagnetic field. Photons are quanta of waves, definitely not particles in the ordinary English sense of the word. The reason photons often seem to move in straight lines is the same reason classical geometric optics is a valid approximation. -- BenRG 16:01, 28 July 2007 (UTC)[reply]

The photon is itself like a wave, it is not moving along a wave. --24.147.86.187 21:21, 28 July 2007 (UTC)[reply]

Photons do not have to travel in a straight line, it's that is the more likely route. They are subject to the uncertainty principle where you cannot measure the momentum (say direction as the speed is known) and its location precisely at the same time. GB 22:16, 28 July 2007 (UTC)[reply]

^{Fixed your uncertainty principle wikilink — Matt Eason ^{(Talk  Contribs)} 23:00, 28 July 2007 (UTC)}[reply]

Artificial lung

Why can't a machine similar to a dialysis machine remove blood from the body, add oxygen, remove carbon dioxide, then return the blood to the body ? Such an artificial lung could replace normal lungs when they are damaged by smoke inhalation or disease, or recovering from surgery. StuRat 20:33, 28 July 2007 (UTC)[reply]

Such a machine exists - see Oxygenator and Heparin-coated blood oxygenator. -- Finlay McWalter | Talk 20:52, 28 July 2007 (UTC)[reply]

See ECMO for an even more advanced version. alteripse 02:42, 29 July 2007 (UTC)[reply]

There is such a thing as a heart-lung machine, but this is not used unless the patient is undergoing heart surgery or a heart transplant.

Lightning

Are there any warning signs (say a few seconds in advance) that allow you to tell that you are going to get hit by lightning? And if you did know, would there be anything you could to to prevent it from happening? 71.38.188.212 20:36, 28 July 2007 (UTC)[reply]

This NOAA page says your hair might stand on end, and suggests a crouch that might minimise the danger of your being struck. -- Finlay McWalter | Talk 20:49, 28 July 2007 (UTC)[reply]

Lower your highest point as much as possible and keep contact with the surface to a minimum (lightning travels through the ground after it has struck). So squat. Wearing the right kind of soles on your shoes might also help. So don't touch the ground with your fingers (to keep balance, for example). DirkvdM 08:20, 29 July 2007 (UTC)[reply]

The advice I heard was to squat with both feet together. Wrap your arms round your knees and tuck your head in as much as possible. I'm not so sure though - wouldn't lying as flat as possible be better? Astronaut 16:35, 29 July 2007 (UTC)[reply]

The concern with lying flat on the ground is that lightning current can pass through the ground (for example, lightning strikes a nearby tree and disperses throughout the surrounding ground). If YOU are lying on the ground, then you, as a bag of mostly salty water may provide a better conduction path across that five or six feet of ground than the soil does. For this reason, the advice is to crouch with your feet together so that you're less likely to form part of the current traversing the ground.

Atlant 00:24, 30 July 2007 (UTC)[reply]

Another way to look at that is that at the precise point where the lightning strikes (maybe a centimeter across) - the voltage at the ground is a bazillion volts - but 10 meters or so away, it's grounded (so pretty much zero volts) - the number of volts per meter of ground is insanely high. When you touch more than one point on the ground - the voltage between those two points on the ground is probably going to flow though your body (which is nicely conductive) rather than through the ground (which probably isn't). If your feet or hands were touching the ground at points one meter apart - then you'd be taking 1/10th of the 10 meters of voltage difference through your body. If you could get your points of contact within 10cm of each other - then you only take 1/100th of the voltage. The smaller the area you cover - the less of a belt you get - hence the advice to keep your feet together. You also want to avoid touching the ground with your head or your hands because a shock across your heart or through your brain is much more likely to kill you than one that can take a short cut without going that way. In the canonical 'stuck out on a golf course' scenario, I'd be tempted to place a golfclub on the ground and to stand on that - on the grounds that a nice metal shaft would probably conduct the electricity directly rather than it going through my body at all. But then given how little time you have to think about it and act - all of this advice is probably entirely pointless. SteveBaker 04:23, 30 July 2007 (UTC)[reply]

?????

I know this seems impossible but science taught us to exclude the word impossible from our dictionary ..... anyway the use of nanotechnology to upgrade parts of a human, such as memory, strength, iq ..... etc Can this be real ??????

It's hard to say what future technology will bring, and what will prove to be very difficult or entirely impossible. If you look at science fiction films from the 1950s people can fly and zap one another with ray guns, but still have big fat curvy tv sets with no remote control. So who knows. You might want to read Technological singularity. -- Finlay McWalter | Talk 22:45, 28 July 2007 (UTC)[reply]

As one might imagine, the most amazing-seeming technologies that will become available in the future are going to be things no one ever thought of. Before the science of genetics was well understood, it was likely inconceivable to most people that organisms could be "engineered" to express a desired trait. And before E=mc², it was likely equally inconceivable that a large ship could be powered for years with only a baseball sized volume of fuel. 151.152.101.44 23:58, 28 July 2007 (UTC)[reply]

It is impossible for the laws of physics to be broken. If they could be they wouldn't be the laws of physics. I suppose it's possible that the universe is totally indeterministic, and nothing is totally impossible, but you couldn't get certain things to happen consistently. — Daniel 03:21, 29 July 2007 (UTC)[reply]

Daniel, you obviously haven't read the latest research in improbability. Someguy1221 10:11, 29 July 2007 (UTC)[reply]

On a serious note, though, there are some things that physics would simply prohibit. I believe the more accurate phrase would be, "the appearance of anything is possible." Someguy1221 10:11, 29 July 2007 (UTC)[reply]

I strongly disagree with our OP here "science taught us to exclude the word impossible from our dictionary" - certainly not! Quite the opposite in fact - put the word "impossible" back into your dictionary and apply it liberally where the science indicates that it's appropriate! There are certainly well-established laws of physics that make some classes of thing impossible. Travelling faster than light is impossible, perpetual motion machines are impossible, knowing both the position and speed of a particle to more than a certain precision is impossible.

Then we have "I know this seems impossible" when referring to using nanotech to improve human performance. That doesn't seem impossible at all. There are a lot of people working in the field of nanotechnology - and lots of people working on human-implantable-technology - and if their work comes to fruition, we'll see things that are as much like magic to use today as Wikipedia would have seemed to Newton.

But why invoke nanotechnology here? It seems to me that the work to interface fairly normal computer electronics into the nervous system is coming along rather quickly. I don't think it's at all far-fetched that one could have a large implanted memory subsystem with (say) enough capacity to hold everything that's currently on the Internet - plus the ability to record everything you've ever seen, heard, touched or smelled in your life from the point of implantation onwards. Having 100% perfect recall of all of those things would certainly give the impression of superhuman abilities - with no nanotech required. Increasing IQ is a little more controversial - but someone with the ability to do lightning-fast mental arithmetic, to be able to speak every language, recite every poem, play, film script or song by heart (because they have a calculator, a translator and the library of congress embedded in their brain) would certainly seem pretty smart to us. SteveBaker 13:14, 29 July 2007 (UTC)[reply]

100% perfect recall with a memory storage may however be something like hypnopædia (sleep teaching), where phrases can be memorized but there is no comprehension. As for upgrading parts of a human, I read somewhere about a new technology that enables blind people to "see" by use of a device that you stick on your tongue. This was 4 or 5 years ago too, so I don't see why human "enhancements" are not possible.--GTPoompt (talk) 12:42, 30 July 2007 (UTC)[reply]

FM signals

Ok I am 12 years old so I know barely anything about radios and how humans cross between them so here is my question.

So I was practicing guitar right, and then when I was done I took the cord out of my guitar but didnt turn the amp off. I noticed that when I touched different objects with the tip of the cord some objects would make buzzing sounds (out of my guitar amp) so then I realised that the sounds only came when I touched something metal or my body. Then I was testing different parts of my bady when I put it on my hand. Then the amp was buzzing a bit but I could hear some sounds changing. Then I swore I heard some english words and knew it was a radio. I startewd walking around my room with the cord to my hand (trying to get a good signal) when all of a sudden the rock station 103.9 The Hawk* came on and I could hear people having a conversation in somewhat fuzzy sounds (like when you are leaving a town and the station fades out but you can still understand everything). So my question is obviously, How is this possible?!?

103.9 The Hawk is a London ontario station and I do live in London Ontarioand with a radio get a clear signal

I'm not sure of what causes it but I understand people have picked up radio signals with their metal-fillings. The signal itself carries power which is how those old-radios that kids used to build (crystal radio) worked. It my be worth looking at radio waves radio and articles linking from this. I remember reading somewhere that people have inadvertently picked up old radio broadcasts from the 40s/50s/60s - not sure if it is true though. I expect your setup is because the cord is acting as an antenna and the amp as a speaker (presuming the amp has a speaker built in). Similarly it's my understanding the individual's mouth acts as the speaker in the somewhat odd radio from dental-work situation. ny156uk 23:16, 28 July 2007 (UTC)[reply]

If anyone actually picked up radio broadcasts from the 40s/50s/60s it's because they picked them up in the 40s/50s/60s, or someone rebroadcast them. Radio signals don't remain detectable after 40 years of bouncing around. Unless, of course, you're 40 light years away, and you're aiming a football-stadium sized radio telescope at the Earth. 151.152.101.44 23:48, 28 July 2007 (UTC)[reply]

(this is made by the person who started it) But when the metal part of the guitar/amp cord (with the other metal part in the amp and it's turned on) is not touching my hand it just makes a loud buzzing noise and only when I poke my hand with it does it tune in.

Radios work by having a resonant circuit that can be adjusted to pick up only a particular carrier frequency. Such circuits are actually quite simple in design and depend on details like the resistance in the circuit. It is concievable that by "poking" it, you alter the current loop, so that you are turning into a particular resonance corresponding to 103.9. Dragons flight 10:23, 29 July 2007 (UTC)[reply]

I"m a little surprised that you'd pick up an FM station that way - but AM radio is pretty easy to pick up accidentally in wires that happen to be the right length to act as an antenna. By touching the end of your guitar cord to different objects, you are changing the effective length of the antenna and thereby 'tuning in' different frequencies. If you happen to hit the exact frequency of a reasonably powerful AM radio station, then you'd certainly be able to pick out the audio given a sufficiently powerful guitar amp. But FM radio doesn't work like that - and I don't see how you'd get it that way. Are you 100% certain it was an FM station that you picked up? SteveBaker 12:57, 29 July 2007 (UTC)[reply]

There are two ways you could receive an FM station using a guitar amp:

The FM station simulcasts on an AM station; it's very easy to receive AM radio using devices that aren't really intended as radio receivers, especially if we're talking about most-powerful AM station in your neighborhood.
Slope detection allows an amplitude-sensitive detector to receive an FM signal. But that's asking for a pretty odd set of circumstances to come together in your guitar amp and cable.

Atlant 00:33, 30 July 2007 (UTC)[reply]

Well, an FM station broadcasting on the AM band is what I would call "An AM Station" - but then I'm a traditionalist! For slope detection to work, the AM reciever would have to be very finely tuned such that as the frequency moves around due to modulation, the amplitude of the reception drops off rather rapidly as a function of frequency. That's totally not going to be the case with a guitar cord touching something metallic because the irregular shape of the final antenna would have a pretty flat frequency response. So I think we're talking about a radio station that maybe broadcasts on both FM and AM at the same time. SteveBaker 04:10, 30 July 2007 (UTC)[reply]

When you dismiss slope detection, you're ignoring the possibility of resonance.

Atlant 11:55, 30 July 2007 (UTC)[reply]

Unshielded cables, like those used for guitars, can pick up all kinds of electromagnetic interference, like radio signals. This is why most microphones, and lots of other audio gear, use shielded cables (often with XLR connectors) and a balanced audio system, to keep outside signal interference to a minimum. Pfly 05:18, 30 July 2007 (UTC)[reply]

Was the guitar amp on the distortion channel? — Omegatron 23:35, 30 July 2007 (UTC)[reply]

Animals eating their waste

Why is it that some animals, including humans eat or lick their waste? (vomit, urine, or shit) For some reason, I've only noticed it in mammals.

Ive seen videos of dogs licking their vomit. Chimps drinking their pee. Gorillas eating vomit AND their shit. And we all know theres humans that enjoy drinking urine. And humans that enjoy being pissed on, or shitted on for sexual excitement.

Waste has a lot of bacteria and eating it can be fatal, so why do animals do it? Is it another one of those weird rare things that people just do? Were supposed to think it's nasty (im thinking because of psychological evolution), so is it another one of those rare traits that some animals in a species have? PitchBlack 23:41, 28 July 2007 (UTC)[reply]

Animals will eat vomit as the food is not fully digested, so they eat it again as it still has nutritional value. The same is sometimes also applicable to excrement if not fully digested, they give it a second go. A puppy will somethimes learn to eat excrement as a behaviour - when you clear it away it considers you to be taking something belonging to it. What better way to stop you than scoffing it back down again? Lanfear's Bane

Animal waste is a rich source of pheromones. Some animals will lick it either to aid detection of the chemical cue of another animal, or to spread their own cues around. Rockpocket 00:26, 29 July 2007 (UTC)[reply]

On a side note: one of my terriers constantly tries to disguise his scent by rolling in other animals excrement, he is always a pleasure to take walking... Lanfear's Bane

See Coprophagia -Arch dude 01:01, 29 July 2007 (UTC)[reply]

Ha, thanks for the info. Makes sense. But none of you mentioned humans. I'm pretty sure humans dont eat their crap because it still has "nutritional value", they GOTTA have some poptart lying around somewhere. But anyway, is it possible that some humans got it as a result of evolution? Somehow us getting it from past mammals? PitchBlack 05:12, 29 July 2007 (UTC)[reply]

Why do humans have any kinks? Its a type of paraphilia. Rockpocket 07:27, 29 July 2007 (UTC)[reply]

Most of it is probably caused by either folk medicine or lore, or fetishism. Taken from one of my Bathroom Readers, some of the following inventive usages:

India - The Vedas call urine a nectar of the gods and fountain of youth.
Rome - The emperor places a tax on the commercial sale of urine. People with ulcers and cancers think ingesting urine will cure them, and showering in urine is a popular practice (Gives new meaning to the term golden shower, huh?)
China - Believed to make medicinal herb potions more potent.
Egypt - "Urine is drunk down, rubbed on, bathed in, and stared at". Also used as an early form of pregnancy test.
Germany - Urine boiled lightly with honey is popular as an eye curative (? no idea what they mean there)
England - After overindulging, people rub their urine on themselves immediately after they produce it, to avoid "the shakes". Gargling urine with saffron is used to avoid throat inflammation.

So uh, now you know, I suppose. They also make points afterwards such as urine not being toxis, it being 95% water and 2.5% urea, and 2.5% minerals, salts, hormones and enzymes, and that urea is poisonous in large amount, but "the small portions present in urea actually purify the body, clear up excess mucus, and purify the skin, which is why it's a main ingredient in women's cosmetics", that urine is sterile, and that it contains antibodies that can help to ward of diseases. They know way too much, if you ask me --L^ie! 07:30, 29 July 2007 (UTC)[reply]

Urine isn't necessarily sterile, or so someone here once pointed out to me. But it is less likely to carry diseases than feces. An important point here, though, is that if one consumes one's own urine or feces, any diseases in it will come from oneself, so there is no added infection (in some cases it might aggravate it, though, not sure about that). And if excrement from other animals contains a disease, it's not likely to be a disease one can get oneself. It's the excrement of others of one's own species that is most dangerous. Which is why it is safe to use cow dung to fertilise foodcrops, but not human droppings. (Notice how I nicely avoided the word 'shit' :) - damn, used it after all ... ). DirkvdM 08:14, 29 July 2007 (UTC)[reply]

Yeah, excuse me for not thinking of another word at the time. I was thinking too quickly and I couldnt think of anything else.

E.coli is safe in our bodies, to decompose the waste I guess. But it's dangerous to eat. So how would you explain that? PitchBlack 08:44, 29 July 2007 (UTC)[reply]

Escherichia coli isn't always safe in our bodies: it depends on where it is (normal flora of gastrointestinal tract as opposed to causing a urinary tract infection), and the occurence of disease also depends on which strain it is. Recurring dreams 12:11, 29 July 2007 (UTC)[reply]

Well, I think that was PitchBlack's point. You can't assume something is safe just because it comes from you (DirkvdM's opinion). We're pressing close to medical advice ("Can I drink my own pee?"), so I think it's a good time to point out that both urine and excrement can be dangerous to consume, even if they are your own. Matt Deres 01:54, 30 July 2007 (UTC)[reply]

There is an abnormal condition known as Coprophagia that exists in many animals (even humans) in which they desire to consume there own feces.Mrdeath5493 17:04, 29 July 2007 (UTC)[reply]

Rabbits (and maybe similar animals?) eat their own poop because that's how they "chew their cud". Unlike cows, which have evolved a special place to store the grass they eat to let it ferment, then burp it back up to chew and swallow for keeps, rabbits have to do the double pass thing. (I'm not sure if the poop they eat is different from their regular poop, never watched that closely).

According to The Private Life of the Rabbit, the two types of droppings are indeed different. We may have information in rabbit, but I'd have to check. Skittle 20:35, 30 July 2007 (UTC)[reply]

On another note, many animals eat cat poop, whether house cat or lion; the cat digestive system is so inefficient, and their diet so high-protein, that their poop ends up being quite high in protein itself. Gzuckier 17:36, 30 July 2007 (UTC)[reply]

Some dogs also seem to have a particular fancy for horse faeces, presumably due to the efficiency of the equine digestive system leaving useful nutrients behind. Martinp23 20:43, 30 July 2007 (UTC)[reply]

Oddly enough, I've just noticed that this question was one of the very first questions asked on the Reference Desk, ever. See this archived version. —Steve Summit (talk) 15:42, 4 August 2007 (UTC)[reply]