Wikipedia:Reference desk/Archives/Science/2007 October 25

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 25

String Theory

There have been countless complaints all over the classroom. This weird, nerdy kid in my class is COMPLETELY and UTTERLY obsessed with string theory. He happened to ask every teacher he's met so far about string theory. What is string theory, anyways? Asking just out of curiousity, and a way to shut him up. I looked it up, but I eventually decided that if I devoted my life to deciphering that page, I'd be eternally confused. I'm no math or science geek here. Make your explanation simple enough for my simple mind to understand. Heh. Had to get all complaints out of my system. Sorry 'bout that. —Preceding unsigned comment added by 68.100.133.160 (talk) 02:06, 25 October 2007 (UTC)

No big problem but in the future please edit your posting rather than reposting the entire new version. I've deleted your earlier versions. Also it's a good idea to sign your posts with four tildes like this: ~~~~ . hydnjo talk 02:20, 25 October 2007 (UTC)

Wikipedia insisted that there was a problem when I tried to post my question. Lots of failed attempts.

As basically as I can put it...In physics, fundamental particles (like quarks and electrons, not protons and neutrons, which are made of quarks) are usually considered to be dimensionless (lacking extent in any direction) points in space (when it's a particle, and not a wave, but you wanted simple, so don't ask). In string theory, they are considered to have extent in one direction, making them little curved lines (or strings) instead of points. This leads to a number of very wierd predictions, like the existence of more dimensions than we can see or experience, and particles that have never been observed. The problem with string theory is that while it agrees with "normal" physics, its new predictions are entirely unprovable with any imaginable technology, let alone any existing technology. Someguy1221 04:06, 25 October 2007 (UTC)

I'll try to go even a little simpler, assuming very little knowledge of science: String theory deals with the very smallest parts that everything in the universe can be divided into. If you divide practically anything that exists, like your body for instance, into its very smallest parts, you'll get four kinds of parts: "electrons", which are the smallest pieces of electricity that there can be, "photons", which are the smallest pieces of light that there can be, and a couple other wierd parts called "quarks" and "guons". Those little parts are the smallest things that exist; you can't split them up into anything smaller. In fact, with the normal way that scientists make the most accurate possible calculations about how those parts behave, they treat those parts as not having any size at all. One of those little parts is treated as just being a point with no size.

String theory is a newer way of making calculations about how those little parts behave. In string theory, those little parts are no longer treated as being just a point with no size. Instead, the little parts are treated as being a little curvy line.

Another way that string theory is different from the normal way of making calculations about how the little parts behave is that according to string theory, there exist extra dimensions that we normally don't notice. A "dimension" can be thought of as a combination of a direction and the opposite direction. Space is normally treated as having three dimensions: up and down is a dimension, left and right is a dimension, and forward and backward is a dimension. Any other other direction in space can be treated as being a combination of directions in those three dimensions. Time also counts as a dimension: if you're sitting perfectly still, you can think of yourself as moving forward in the time dimension. Time works a little differently than space does, so space and time are two different kinds of dimensions. String theory says that there also exists a third kind of dimension, that is, a third kind of direction that something can move in. We don't normally notice those extra dimensions because the extra dimensions loop back around, such that if you go just a very little ways in one of the extra directions, you wind up right back where you started from.

To change the subject, if you have any interest at all in gaining some understanding about your classmate, you might want to check out Wikipedia's article on Asperger's syndrome. Weird, nerdy, and completely and utterly obsessed with a topic as geeky as string theory sounds an awful lot like someone who may have Asperger's syndrome. Asperger's syndrome is not too uncommon among people with ultrageeky occupations like mathematicians and physicists. MrRedact 06:17, 25 October 2007 (UTC)

If the questioner has any interest at all in gaining some understanding about their classmate, the best approach is to talk to him, treat him as a person, and drop the "weird", "nerdy", "geeky" labels, which are both insulting and stereotyping. Only a qualified professional can make a diagnosis of Asperger syndrome. Gandalf61 08:45, 25 October 2007 (UTC)

Oh, right, yes, talking to him would be much better than just reading an article that might apply to him. That option didn't even occur to me because I'm not into talking to people much. But that's just me.

It's kind of situational as to whether "nerdy" or "geeky" are insulting. I'm personally not offended at all to be called a nerd or a geek, especially since it's pretty much just me or other nerdy geeks who would call me that, and because I've grown to think of being a geek as being an acceptable, and even enjoyable way to be. But yeah, if those labels are applied to a high school kid who's struggling to try to fit in with the "normal" kids, then yeah, it's probably hurtful. MrRedact 18:33, 25 October 2007 (UTC)

If you indeed have a simple mind, then maybe the simple English Wikipedia article on String Theory is what you are looking for. :) DirkvdM 08:39, 25 October 2007 (UTC)

Well, you don't have to have a simple mind to have difficulty incorporating advanced scientific information. If you don't already know what a quantum and a quark are, much less are ready to accept the idea of 11 dimensions, then it's going to be hard to jump into an article on string theory. --24.147.86.187 12:46, 25 October 2007 (UTC)

Note that the questioneer himself said he had a simple mind. I wasn't being rude this time. :) DirkvdM 19:37, 25 October 2007 (UTC)

A nice, easy book you might recommend your inquisitive-yet-annoying friend is Brian Greene's The Elegant Universe, which is all about String Theory. If you are interested in getting the low-down without reading much, there is a PBS series by the same name which is totally online now. Check it out! --24.147.86.187 12:42, 25 October 2007 (UTC)

No, please don't watch the PBS series. It's shockingly bad. It's made with the visual and narrative aesthetic of a big-budget Hollywood movie, and it will fill your head with wrong and misleading ideas which will then be very hard to unlearn. It doesn't educate. You won't understand anything new after watching it; you won't be able to better evaluate claims about string theory or anything else. But you will think that the rubber sheet model of Newtonian gravity has something to do with general relativity. The book is better, but still pretty bad. I don't know what to recommend in its place, though.

I saw something on PBS that essentially said, over and over, "There are these strings, and they vibrate, and it's awesomely cool." Is that the one? —Tamfang 23:25, 25 October 2007 (UTC)

As for what string theory is, first of all, it's not a theory. It's a research program (that article should exist) whose goal is to find a theory of quantum gravity. The approach is to start with something sort of resembling Feynman diagrams, but using surfaces (manifolds) instead of points and lines. They're called string diagrams because cross-sections through the 2D surfaces look like 1D loops splitting and joining. Feynman diagrams represent a perturbative approximation to quantum field theory, and string diagrams might perturbatively approximate something too. The idea of the string program is to study the string diagrams in the hope of finding hints about, and eventually formulating, the theory that they approximate. The actual theory, if it exists, probably doesn't look much like the string diagrams; for one thing, you'd expect it to be background independent, which string diagrams aren't. The reason people are interested in this program is that there's a bunch of circumstantial evidence that string diagrams are related to quantum gravity, most obviously the fact that you get gravitons in them. People were also excited by the fact that most versions of this idea don't work at all. This is a good thing, because the fewer possibilities there are, the more strongly you're constraining the way the universe has to be. In fact there was a lot of hope/hype in the early days that string theory would constrain the universe so strongly that the standard model would fall out magically without any inputs. But that's not what happened; the general perception now seems to be that the theory has a huge number of effective parameters, leaving it less predictive than the standard model.

Even if string diagrams are connected to the correct theory of quantum gravity (which they quite likely are) it's not necessarily in a way that anyone's going to find. It could be like monstrous moonshine, the famous unexpected connection between modular functions and the representations of finite groups. The connection is real (there's a proof now), but it wasn't discovered until these two branches of mathematics had developed independently and the same large integers suspiciously showed up in both. In principle someone could have discovered representation theory via this connection, but in practice that's not how people think. So I wouldn't be surprised if we found the right theory of quantum gravity by a totally different route, and only then (if ever) figured out how string theory relates to it. -- BenRG 19:17, 25 October 2007 (UTC)

Also, if you want to shut him up, just say, "Well, that sounds interesting, but until they come up with a way to test it, it might as well as be a religion as far as I'm concerned. An untestable theory is not much different than an article of faith." Which might drive him over the edge. ;-) One of the big issues with string theory is that at the moment there is no real way to determine whether it is correct or not; it doesn't make easily testable hypotheses. Some scientists see this as a temporary thing while others consider it to be signs of great flaws. --24.147.86.187 12:46, 25 October 2007 (UTC)

Probably the most time efficient way to get a feel for string theory are the results of a contest that Discovery channel organized recently, posted here. The contest asked people to make a video that explains string theory in two minutes or less. It should give you some idea what it's all about. risk 14:25, 25 October 2007 (UTC)

This one-panel cartoon seems to sum things up pretty well : [1] 69.95.50.15 15:37, 25 October 2007 (UTC)

OK - so we have two problems here: String theory and Annoying Geek.

Let's start with the first one: Annoying Geek...As others have suggested, this kind of obsession with one subject is a common thing with people with Asperger's Syndrome (which I happen to have...so I know what it's like). I didn't know I had it for the first 49 years of my life - but since realising the problem and getting it properly diagnosed - I can look back on some slightly puzzling things from my past and say "Holy Crap! That was me totally failing to get the message from everyone else!". This kid doesn't know he's being annoying - the obsession with one subject (and it could be anything from Dinosaurs to Internet Protocols - this time it happens to be String Theory) is very typical and right now it's the only thing he really cares about. He won't stop being interested in it until something else captures his attention - and that could take a lifetime.

This is bloody annoying for everyone else - but he probably hasn't noticed that yet. You need to try to imagine how he thinks (and since you are 'normal' - that should be easy for you!) The thing with us 'Aspies' is that we need to be told things of a 'social' nature that everyone else kinda somehow "just knows" (it's a complete amazing to me how you 'normal' folks "just know" that stuff). I literally cannot tell when someone is joking or not (particularly not if they can do it with a straight face). I have absolutely no 'innate' comprehension of body language (either my own or anyone elses). I had to LEARN those things...in classes...with an expert. It takes a conscious effort for me to maintain appropriate eye contact in a conversation. I have to think "Have I forgotten to look at people during the last few minutes?" and "Have I been maintaining eye contact for too long - so it's getting freaky for everyone?" and "How is everyone else holding their arms, how are they sitting? That person is sitting like I am - so they are probably agreeing with what I'm saying." Then..."Are my arms mimicking the poses of the people whom I agree with?" - "Could this slightly bizarre turn in the conversation be sarcasm or irony or something?".

So give the kid a break - help him out. Aspies are good at following clearly laid out rules - so if you explain to him (nicely - and directly) that this string theory obsession is annoying everyone and could he perhaps only mention it at most twice per day...then very likely, he'll do what you want. But he simply cannot work that out for himself - especially from things like you "zoning out" and rolling your eyes when he talks to you about it. He doesn't know that you are sick of the subject (after all, he finds it fascinating - and he can't tell that you don't unless you tell him).

OK - second thing: String Theory. Everything in the universe is made of teeny-tiny vibrating strings each much smaller than an atom. When I say "much smaller than an atom", I mean it in much the same way that I'd say that an atom is "much smaller than a galaxy" - just insanely tiny. The way that they vibrate gives them properties like "mass", "charge", "spin" and so on - and in order to have all of those interesting properties they need to vibrate in very complicated ways. Too complicated to do so in just 3 dimensions. Hence string theory says that there have to be something like a dozen dimensions (although some versions of the theory demand more or less dimensions - there are always a lot more than three). These 'extra' dimensions are very 'small' (about the same size as strings are) - which is why we've only noticed the first three. Sadly, all of these weird things happen on a scale that's not only smaller than we can see (even with our finest electron microscopes and such) - but on a scale smaller than we could even theoretically examine. This means that we can't currently prove whether string theory is true or not - we can't even think of ways to try to prove or disprove the theory...it's "unfalsifiable". Calling a scientific theory "unfalsifiable" is pretty much the most damning thing you can say about it. But if it's true, then it may be "The One True Theory Of Everything" - the ultimate explanation of all things. But we can neither prove that it's true nor that it's false. In that respect, it's like religion - you just have to believe in it. This is unsatisfying for scientists (including string theorists) - so the world of fundamental physics is torn between continuing to work on string theory in the hope of someday finding some way to either prove or disprove it - or giving up on it and looking for some other theory of everything instead. Personally, I'm in the latter school...we've spent enough valuable brain power on it...it's time to move on.

SteveBaker 16:52, 25 October 2007 (UTC)

One thing I don't quite understand is why don't the science and maths teachers offer some help. I presume that this is primary school so their level of science and maths may not be extremely high but I would assume they would be better able to learn about string theory then you Nil Einne 18:50, 25 October 2007 (UTC)

Ssshhh ... he really wanted to ask for himself, but was too ashamed, to he made up this boy .... and now this imaginary boy has Asperger's Syndrome ... DirkvdM 19:37, 25 October 2007 (UTC)

Steve, how can a dimension be small? The other dimensions stretch out pretty much into infinity. The universe may be finite (or it may not), but I mean in principle the dimensions themselves have no limits, do they? Except maybe time, but that also depends on the truth of the Big Bang and Crunch. Or does this have to do with MrRedact's remark about the dimension looping back on itself? In which case it's infinite in the sense that it's in an infinite loop, but we stand outside it, so to us it's small? But then each string has it's own dimension? Aaarghhh, that's not possible, a dimension is not a thing, it's something that contains things. Brainmelt .... DirkvdM 19:37, 25 October 2007 (UTC)

See Compactification (physics). MrRedact 20:15, 25 October 2007 (UTC)

(ec) The "extra" dimensions (according to the theory) loop back on themselves in a very short distance, but you're not "outside" them; quite the opposite. You occupy -- in fact, probably every proton in your body occupies -- the entire thickness of the universe in the direction of those dimensions. That's why you don't see any motion in one of those directions. There's nowhere to go. --Trovatore 20:18, 25 October 2007 (UTC)

For an easy to understand explanation, see Steve Baker's previous explanation here. I actually have that page bookmarked so I can find it again. I had always wondered how dimensions were supposed to curl up on themselves, and Steve explained the concept step-by-step in a way that I finally understood. 152.16.16.75 00:43, 26 October 2007 (UTC)

Ok, that put the idea clearer in my head. But it doesn't resolve my issue. Let's take one of those dimensions, say the 8th (which is nonsense of course - we can't point at 'the' 2nd dimension either - but for the sake of the argument). We can't perceive this 8th dimension, but the strings live in them. One for each string. right? Or is that where I go wrong? That 8th dimension is at the same time tiny, but all strings live in it, so it's also as big as the universe. I can't imagine this in any other way than that each string has its own 8th dimension. So that doesn't make it one dimension. By Steve's analogy, if a flatlander's '3rd dimension' were 1 km across, then he could live in it, but everyone would have his own 3rd dimension. The flatlanders would be able to see themselves through binoculars, but would they be able to see each other? DirkvdM 07:56, 26 October 2007 (UTC)

The strings live in all of the dimensions at once - just as we do. Our bodies take up space in all 15 (or so) axes at once - and so do the strings. But for all practical purposes, we are vastly too big to do or see or measure anything interesting in the 'extra' dimensions because there just isn't room in them. So while we exist in all 15 (or so) dimensions, we only NOTICE the three three huge dimensions. Even things as small as atoms don't have 'room' to do anything in the extra small dimensions. But the super-strings (which you'll recall are AMAZINGLY tiny, even compared to an atom) have plenty of room to vibrate in those directions. So they can vibrate up and down (1st dimension) and left and right (2nd dimension) just like a plucked guitar string. They can also vibrate 'in' and 'out' (like a slinky or a sound wave in the 3rd dimension) and they can vibrate squark and floop (sorry - I had to make up two new words for vibrating in the fourth dimension), snork and wibble (5th dimension), finque and gnort (6th dimension)...and so on. So there isn't one dimension per string or anything like that. I don't quite understand how you are misconstruing my flatland analogy...but it is hard to convey these things accurately. SteveBaker 19:00, 26 October 2007 (UTC)

Thank youfor those new words. :) But the problem is I can't see how a dimension can be at the same time small, so that only strings one string can live in it, and as big as the universe, so all strings can live in it. I can accept the idea that a dimension ends where the universe ends (although that is already rather strange (a dimension is a mental construct, a way to look at things - you can't point at it). But if it is smaller (irrespective of how small), then what lies outside it has to have its own version of that dimension to live in. And I can't understand more than one version of a dimension - one for each string in this case. DirkvdM 06:42, 27 October 2007 (UTC)

Consider an ant farm; specifically, consider one not quite as thick as I remember mine having been, so you have lots of available up/down, plenty of left/right, but there is insufficient room for two ants to pass in the in/out dimension. The grains of sand, however, have an extra degree of freedom - they can be displaced in this funny extra dimension that has no meaning for the ants (ok, it does for actual ants, but these are "special" ants). Everywhere an ant-physicist goes in the enclosure, she can measure her familiar two dimensions, but the sand still can be displaced in depth - it is the same direction everywhere even though there is not far to go in it. Eldereft 01:57, 28 October 2007 (UTC)

Ah, I think I've finally got it. The dimension is very small in its own dimension (however weird that sounds), but still stretches out over the entire universe in the other dimensions. I'm ashamed it took a silly ant farm analogy to get it through my thick skull. Now that I get it I don't understand how I didn't before. So the dimension loops back into itself, forming a circle. Add another dimension and you get a tube. Add yet another dimension and the tube gets thickness? I can't imagine that stretching into infinity, though. Btw, that second dimension looping back into itself would result in a torus. And the third one? Oh dear, I guess topological dreams will be keeping me awake tonight (...). DirkvdM 07:48, 29 October 2007 (UTC)

Amateur pyschological evaluations continued

I made a separate header to keep the discussions separate. DirkvdM 07:58, 26 October 2007 (UTC) ps Someone changed the header, so don't blame me. :)

..what if I said that he does this purposely and is fully aware that his classmates are glaring and rolling their eyes or looking for the nearest fire escape or something? He's also one of the best students in the class. I doubt that he has trouble catching up. But he is obsessed, though. I'm pretty sure he doesn't do it just to annoy us. ~~Questioner~~

Maybe he's concerned more with gaining knowledge than with what others might think of him. If he has high self esteem then he might figure everyone already thinks of him as a nerd (which is a good thing), so there is no reason he should impose artificial restrictions on his opportunities for learning. Maybe he has low self esteem and he's seeking acknowledgement of his intellectual abilities. Maybe self esteem doesn't play into it and he's just showing off - "Look at how intelligent I am." Maybe he's simply a genius. Geniuses tend to make their own rules. Maybe you could strike up a friendly, non-confrontational conversation and bring the conversation around to asking him. His actions may annoy you, but imagine how boring life would be if everyone felt an overwhelming need to conform. Personally, I think we need more young people ardently studying the science behind the mysteries of the universe. Go nerds! 152.16.188.107 06:58, 26 October 2007 (UTC)

Changed sub-head. Only a qualified professional can make a diagnosis of Asperger syndrome or any other pyschological condition. We cannot conclude anything on the basis of a few sentences from the original questioner, neither should we try to. This whole sub-thread is inappropriate for the RDs. Gandalf61 09:00, 26 October 2007 (UTC)

Acceleration to near-light speeds

What's the speed of an object moving with a constant acceleration (from its point of reference) with respect to time from its point of reference and from the starting point of reference (when its speed was zero)? Does this question fit better on the mathematics page? — Daniel 03:27, 25 October 2007 (UTC)

It's not terribly hard to work it out -- start from the relativistic addition-of-velocities formula, figure out the change in velocity-in-lab-frame with respect to time-in-ship-frame at a particular velocity (remember to take the existing time dilation into account!) and integrate. From memory I think it may be tanh(at), where a is the acceleration, t the time, "tanh" is the hyperbolic tangent, and you're working in a system of units where the speed of light equals one. But I'd have to re-derive it to be sure. --Trovatore 03:34, 25 October 2007 (UTC)

I just did the integration without assuming special units, and got c*tanh(at/c), which works out to tanh(at) once you put it in said special units. Someguy1221 04:13, 25 October 2007 (UTC)

No, no - everybody knows that the speed of light is 137. In units with ħ and e set to one but the Fine-structure constant retaining its required dimensionless value, that is. For anyone wandering through wondering what is the deal with the funny units, they are useful because physicists like to be lazy efficient. Trovatore's answer is patently dimensionally incorrect to anyone dragging the constants along, but the result must have units of velocity (there is Someguy's first c), and the argument of tanh must be dimensionless (at has units of velocity, so the must be another c to cancel). This only works if both the original formula and the subsequent math are correct, but using c = 1*(3*10¹⁰ cm/s) units actually makes the algebra less cumbersome and clarifies the presentation without sacrificing accuracy or rigor. Eldereft 06:03, 25 October 2007 (UTC)

I really can't tell -- are you trying to make a joke, or are you genuinely crusading for the units that you prefer, or what? For dealing with a relativistic but presumably non-quantum problem, it's much more common, convenient and sensible to choose units such that c=1, rather than to sacrifice the convenience of c=1 in order to make ħ and e be 1. Trovatore's answer is perfectly correct using the very commonly used choice of units for this type of problem. I'm not trying to start an argument or anything; I genuinely just don't understand why you made this comment. MrRedact 06:58, 25 October 2007 (UTC)

See hyperbolic motion (relativity). -- BenRG 13:02, 25 October 2007 (UTC)

I assume the answer given is in respect to time from the point of reference of the observer. What's the answer with respect to the time from the point of reference of the one accelerating? — Daniel 20:20, 25 October 2007 (UTC)

This happens to be equivalent to the same situation as before, except the observer is now sitting in a gravitational field pointing towards the accelerating object, a field of magnitude equal to the acceleration. I'm not so good at GR, so I'm not sure how this affects the observed v/t curve. Someguy1221 20:35, 25 October 2007 (UTC)

You don't need GR here; SR works just fine for this question, acceleration or no. However I don't remember if the "tanh(at)" answer is for t in the lab frame or in the ship frame. Whichever it is, though, you can convert to the other one using purely special-relativistic techniques. --Trovatore 20:43, 25 October 2007 (UTC)

Alright, so I was thinking about this, and I believe that the only difference between the two observers (due to time dilation) is that the accelerating observer should observe the velocity between himself and his starting point to be accelerating at a higher rate than the non-accelerating observer observes...I think. And I think tanh(at) is in the lab frame. Someguy1221 21:15, 25 October 2007 (UTC)

In the equation v=tanh(at), the v is obviously in the lab frame, since in the ship's frame the ship's velocity is just 0. And FWIW, the starting point's velocity in the ship's frame is just -v. However, the t is in the ship's frame. I just derived the tanh(at) from the velocity addition equation myself, so I'm sure of this. An intuitive way to remember that the t is in the ship’s frame is because it’s getting multiplied by a, which is definitely measured in the ship’s frame, since in the lab frame the ship’s acceleration isn’t a constant. It would be weird for there to be an equation that multiplied an acceleration in one frame by a time in another frame, without there being a factor of gamma in there somewhere. —Preceding unsigned comment added by MrRedact (talk • contribs) 20:54, 26 October 2007 (UTC)

Actually, the "a" is only in there as a simplification of f/m, which is what I actually worked with. F and m can certainly be measured from the lab's frame as constant, and the factor of gamma got disected by the integration. Someguy1221 06:49, 27 October 2007 (UTC)

No, that's all wrong. Neither F nor m are constant in the lab frame. As the ship goes faster, the mass of the ship as measured in the lab frame increases. And the equation F=ma doesn’t work at relativistic speeds. See the "Relativistic mass" and "Force" sections of Special relativity. MrRedact 19:27, 27 October 2007 (UTC)

P.S. An intuitive way of knowing that the acceleration of the ship can’t possibly be constant in the lab frame is because if the acceleration were constant in the lab frame, then the ship would reach and exceed c in a finite amount of time (lab time, not proper time). In the lab frame, the ship’s acceleration must asymptotically approach 0 to keep the ship from exceeding c. MrRedact 20:51, 27 October 2007 (UTC)

Yes, I'm well aware of all that, thank you. My "m" refers only to rest mass, which is constant. Thus, we can retain "f" as a constant, or rather, dp/dt as a constant, where "p" is relativistic momentum. It works. Someguy1221 21:24, 27 October 2007 (UTC)

OK, it looks like this was mainly just a misunderstanding. You said that m is measured in the lab frame, which made it sound to me like you were viewing m as being the mass in the lab frame, i.e., the relativistic mass, which certainly isn’t constant.

I’ve figured out to my surprise that F actually is constant in the lab frame, and is the same value as F in the ship’s coordinates. F is obviously constant in the ship’s coordinates, so it’s surprising to me that F happens to also be constant in a frame with respect to which the ship is moving at relativistic speeds and accelerating.

As noted above, the t in v=tanh(at) is the proper time. In terms of the lab’s time, I calculate v=at/sqrt(1+a²t²), where as always c=1 and a is the ship’s acceleration as measured in the ship’s coordinates. MrRedact 18:53, 28 October 2007 (UTC)

I think you’re right about the magnitude of the acceleration of the ship’s starting point as measured in the ship’s coordinates being greater that the magnitude of the acceleration of the ship as seen in the lab frame, at any given event on the ship’s world line. Consider two nearby events on the ship’s world line. The two coordinate systems will agree on the magnitude of the change in velocity that occurred between the two events. But the time measured between the two events will be less in the ship’s coordinates that in the lab frame due to time dilation, so the magnitude of the acceleration will be greater as seen by the ship. MrRedact 05:56, 27 October 2007 (UTC)

TERRESTRIAL PLANT GROWING COMPLETELY IN WATER

I FOUND THAT A TERRESTIAL PLANT IS COMPLETY SUSTAINING IN WATER EVEN IF COMPLETELY DETACHED FROM SOIL.ANOTHER THING IS THAT IT DOESNT HAVE ITS NORMAL ROOT WHILE FALLING INTO WATER.BUT ALSO IT GREW ADVENTITIOUS ROOTS AND SURVIVED.ANOTHER PLANT OF SAME SPICIES GREW ADVENTITIOUS ROOTS EVEN IF IT HAD ROOTS IN SOIL,WHEN ITS SHOOT IMMERSED IN WATER. MY QUESTION IS THAT HOW DO A TERRESTRILE PLAND SHOW SUCH A VARIATION IN CHARACTER? HOW CAN IT GROW IN WATER WHILE IT IS CMPLETELY DATACHED FROM SOIL AND WITHOUT ROOTS? IS IT SHOWING ANCESTRAL CHARACTER? —Preceding unsigned comment added by 59.93.40.184 (talk) 05:21, 25 October 2007 (UTC) --59.93.40.184 05:31, 25 October 2007 (UTC)

Such a plant could grow for a while on the minerals dissolved in the water or stored already in the plant. If the water is ground water, it may in fact have similar minerals available to the plant as it would have in soil. Even rain water will have some nitrates dissolved. However in pure water the plant will eventually suffer mineral deficiency and go yellow, and die. It would not be due to ancestral throw back, but due to the fact that the main ingrediantes plants need are water and air. Graeme Bartlett 05:54, 25 October 2007 (UTC)

Don't shout. Shouting is rude. You are rude. I refuse to read your question. DirkvdM 08:59, 25 October 2007 (UTC)

What Dirk means is that typing in ALL CAPITAL LETTERS is frowned upon in online discussions. It is more difficult to read large blocks of text that are in all caps. On the internet, words in all caps are usually interpreted as 'louder', or 'shouting'; as in the real world people online are more inclined to stand and listen to you if you 'speak' clearly and quietly. I hope you'll keep that in mind in the future, and I'm sorry that Dirk bit your head off. TenOfAllTrades(talk) 13:45, 25 October 2007 (UTC)

I find it extremely unlikely that anyone who knows how to post a question on the ref desk (has found it and discovered how to post a question) has such a limited knowledge of computers (combined with a total lack of common sense) that they don't know that all caps is not normal. It is extremely likely that he intended to draw extra attention, which is rude. Btw, all caps is not harder to read for me. DirkvdM 14:32, 25 October 2007 (UTC)

That's nice, but my experience is otherwise and so apparently is other people's. Skittle 17:17, 25 October 2007 (UTC)

Right, I take that back. Especially when glancing over a text, I pick up less when it's in all caps. DirkvdM 08:03, 26 October 2007 (UTC)

This phenonoma is well known - try hydroponics - also try a web search for "hydroponics + adventitious root"87.102.94.16 12:39, 25 October 2007 (UTC)

The main idea behind hydroponics is that plants don't need soil to grow. All they need is access to certain minerals (about 13 different ones), oxygen and water. If you can get these minerals to the roots, the roots only need to stay dark and moist for the plant to survive. There are many ways of accomplishing this, you can hang the roots in moving water (with minerals dissolved in it). you can let the water flow by the roots on a light slope, you can even hang the roots in a dark chamber and spray them lightly with the mineral solution. The main advantage of hydroponics is that the roots don't need to search for water through the soil, so they have to grow less. That energy can then go into the plant. Also, you need less water to grow plants this way. risk 14:48, 25 October 2007 (UTC)

Power lines noise

Hi,everyone. Whenever I walk under the highly raised power transmission lines,I hear some humming sound(not birds),but it seems to come from the vicinity of the wire circumference.I thought it was because of rainy season.but it appeared in summer too,and in all seasons.later I guessed it couldbe due to capacitance effect, but I'm unsure.Anybody can prove this?.. —Preceding unsigned comment added by Balan rajan (talk • contribs) 05:42, 25 October 2007 (UTC)

Corona discharge. There might be other contributing effects, I'm not sure. Someguy1221 05:58, 25 October 2007 (UTC)

It gets worse where there is salt on the power lines, after rain it can wash off the contamination. This also casues EMI electomagnetic interference. Graeme Bartlett 06:02, 25 October 2007 (UTC)

How did you get salt on the power lines!87.102.94.16 12:37, 25 October 2007 (UTC)

Really long, non-conducting salt shakers, of course! Seriously, in any area near the sea coast, there's actually a surprising amount of salt in the air as a result of droplets of seawater evaporating and leaving microscopic nuclei of salt. These microscopic bits of salt accumulate, partly as a result of electrostatic effects.

Atlant 12:58, 25 October 2007 (UTC)

It's almost certainly 50 or 60 Hz mains hum - just like you can hear from a transformer (power pack) - the interaction of the oscilating current with the earths magnetic field causes a 50 or 60Hz physical vibration. Add the sound of corona discharge (crackly) - and that should be it...87.102.94.16 12:36, 25 October 2007 (UTC)

• I once read that if you ask a person to make a constant hum without specifying the pitch, some high percentage of people will hum at whatever pitch their country's electrical equipment hums at. No sources, of course. :( --Sean 13:14, 25 October 2007 (UTC)

Unlikely. 50 or 60 Hz is a very low bass note. It's well below the lowest notes required of an operatic bass singer. A harmonic of 50 or 60 Hz is slightly more believable. --Robert Merkel 21:19, 25 October 2007 (UTC)

Salt can also of course speed up rusting, so presumably powerlines and the apparatus that holds them near coastal areas not only rust more quickly but hum more frequently and louder on average. Lanfear's Bane | t 13:25, 25 October 2007 (UTC)

Where this salt buildup is a real problem, you'll occasionally see a bizarre-looking power-company tower truck spraying water on the insulators to wash the salt off. (How they avoid causing short circuits with this stunt, or electrocuting themselves, I'm not 100% sure.) —Steve Summit (talk) 00:18, 26 October 2007 (UTC)

To electrocute themselves, they would need to make a path between power line and ground, and put themselves in that path. Same reason crows don't fry when they stand on power lines awaiting their opportunity to strike. --Psud 11:08, 26 October 2007 (UTC)

If you haven't seen a crow fry while trying to land on a power line, you need bigger power lines. I think Steve was thinking that the path of water would form a circuit just like peeing on an electric fence will make a circuit. --DHeyward 07:24, 27 October 2007 (UTC)

("You need bigger power lines." Grin.)

As someone who has grabbed an electric fence, walked on a third rail, and held a live wire in my mouth (and felt pain in only one out of the three), I do understand about completing circuits! I shouldn't have said "avoid electrocuting themselves"; that was for cheap effect. There are lots of varieties of insulated-boom cherry pickers from the buckets of which you can safely work on live wires bare-handed. But it's harder to imagine keeping a powerful pump and a big tank of water (presumably mounted down on the chassis of the truck) adequately isolated from ground. Perhaps they don't try, and use distilled water (which is not significantly conductive) instead. —Steve Summit (talk) 17:47, 27 October 2007 (UTC)

I feel a maxim coming on - The Science Desk, peeing on electric fences on an encyclopedic scale since 2001. Lanfear's Bane | t 13:37, 29 October 2007 (UTC)

color vision

sir, I would like to know more about color vision in different animals.For eg.do bulls and cows recognise differen colours? —Preceding unsigned comment added by 59.93.24.4 (talk) 12:02, 25 October 2007 (UTC)

Have you looked at our color vision article yet? Do you have further questions?

Atlant 13:03, 25 October 2007 (UTC)

Bulls and cows do not have color vision, according to the science podcast Vanguardia de la Ciencia - I'm not able to locate the exact file where I heard this although I have it on my computer (mp3 files aren't easily searchable...). The information is confirmed by this website, which also contains information about other animals.

The description of how color vision "works" in our article is somewhat technical. I'll try to explain it in (hopefully) simpler terms. The reason why we can reproduce just about any color using three primary colors is that our retina has three types of cones, each of which responds to a different range of wavelengths. With the exception of lasers, light is composed of a mixture of wavelengths. Any mixture of wavelengths which stimulate each type of cones by an equal amount, will be perceived as the same color. Thus, two colors that appear identical, may correspond to two quite different mixtures of wavelengths. If a person had a mutation which slightly shifted the response optimum of one of his types of cones, he might be able to distinguish two colors, which appear identical to "normal" people. Even more surprisingly, in some instances, a person who lacks one type of cones is able distinguish colors that appear identical to someone with normal color vision. Check out the reference in the article color blindness. The reference is from 1992, yet I heard about color blind individuals being used by the military for spotting camouflages as a child sometime in the 1960's, and it greatly intrigued me. Many birds have four or even five different types of cones, and experience a world of color that we cannot possibly imagine. --NorwegianBlue ^talk 14:12, 25 October 2007 (UTC)

Just a moment, Mr. Blue! If you're a bird yourself, why aren't you saying that "you" humans can't possibly imagine it? Hmmmm? --Anonymous, 1:43 UTC, October 26, 2007.

Expanding Universe...Are we all getting bigger?

In the ant on a balloon model of the expanding universe is the ant getting bigger too or just the balloon? Sappysap 13:34, 25 October 2007 (UTC)

I've always heard it as just the balloon; e.g. it was the space in between matter that was expanding, not the matter itself. I'm not sure whether that makes total sense though, esp. when talking about large amounts of diffuse matter (e.g. clouds of hydrogen gas out in space). --24.147.86.187 15:13, 25 October 2007 (UTC)

Yeah - just the balloon. If the ant got bigger - then so would the ant's measuring stick - so the little guy would have no idea that his balloon was expanding. Here in the real universe, we can easily measure the expansion of space - so it follows that we are not expanding along with it. Diffuse gas clouds might expand because there is very little in the way of forces holding them together. But the strong, weak and gravitational forces keep things like planets, solar systems and ants firmly glued together. SteveBaker 15:18, 25 October 2007 (UTC)

OK, that makes sense. So basically the expanding action is not very powerful over small distances (like gravity), but does a lot of work over large distances (like gravity). So locally things stay more or less together while the space around them expands. --24.147.86.187 00:05, 26 October 2007 (UTC)

Of course that's for now. --Trovatore 22:39, 25 October 2007 (UTC)

An equally valid explanation would be that the universe remains the same size but matter itself is shrinking. Weird, but is it weirder than an expanding universe? After all, it's the universe, so we can't measure it against anything, so shouldn't we assume it to be of constant size? DirkvdM 08:09, 26 October 2007 (UTC)

Yes, it would be weirder (in my subjective opinion). The "size" of matter, or more specifically the seperation between its consitutient parts, is governed by by equilibrium states among the various relevant forces, especially electromagnetism. The strength of the electromagnetic force governs the size of atoms and the seperation between them in ordinary matter. The strength of the weak and strong forces play similar roles in defining the properties of matter, albeit in more esoteric ways. In order for matter to be shriking (but still appear to have all the same properties), you'd have to posit that all the basic force laws are changing with time. That is much weirder than saying that the average density of the universe is decreasing (which is the effect of the expansion) in a way that is consistent with time invariant physical laws. It's like placing a drop of oil on a sheet of paper: it will spread out over time so that it's average density descreases, but none of that physical processes governing its behavior have changed. It is more aesthetically satisfying to say that physics is fixed and the universe evolves within a physical framework than to say that that universe is fixed and hence physics must be changing. Dragons flight 09:43, 26 October 2007 (UTC)

I agree, from what I've read of Stephen Hawking's work, the universe, not the matter within it, is changing. The matter is just becoming increasingly spaced out. Midorihana_{(talk)(contribs)} 09:48, 26 October 2007 (UTC)

Right, of course, the simplest solution is the one to go for, and constantly changing laws of physics doesn't quite fit that. But then we have a problem with the Big Bang, or, rather, the 'time' before that (or how was that?). Don't the laws of physics even break down there? DirkvdM 07:12, 27 October 2007 (UTC)

I have a problem with the claim that space gets bigger but we don't. As a thought experiment, consider two spherical objects in space 1 million meters apart with a radius each of 1 meter. With the claimed "expanding balloon, nonexpanding ant" model, over time the distance between the objects should increase, say, to 1.1 million meters, but each object would still have a 1 meter diameter. Now place a 1 million meter cable of negligible tensile strength (so it does not forceably prevent the expansion) between them. Its length would have to increase over the time period to 1.1 million meters. Next to it, place 1 million replicas of the standard meter. As individual oblects, each would remain of constant length. But there is no difference between the million meter cable and the million meter sticks. Ergo, the earth, and we ourselves, should expand if the universe expands. Edison 15:35, 26 October 2007 (UTC)

The size of physical objects is governed by chemistry (i.e. electromagnetic forces). As long as the expansion provides neglible force compared to that of chemical bonds, physical objects will continue to maintain the same length, though the spaces between them may increase. Dragons flight 16:34, 26 October 2007 (UTC)

Edison's thought experiment is interesting - but I think the cable would either snap under the "expanding universe tension" or it would have sufficient strength to hold the two balls together or it would simply stretch like a piece of elastic. Since the amount of growth is very small indeed on a scale of a mere million meters, this would have to be an exceedingly fragile or stretchy rope for it to do anything other than keep the two balls a constant distance from each other. There is indeed a difference between your standard meter sticks - they are not attached to each other - so gaps will obviously form between them. I don't see any problem with that. SteveBaker 18:35, 26 October 2007 (UTC)

Actually I don't think the standard meter sticks will separate, at least not for this reason. They aren't attached per se, but the gravitational attraction between them will massively swamp any tendency for them to move apart due to universal expansion.

Here's a very naive calculation -- it may not be accurate, but if it's not completely meaningless, and I don't think it is, then it'll show my point. Consider two particles at distance r from one another, moving along with the Hubble flow, no interaction between them. They move apart at a velocity v = Hr, where H is the Hubble constant. The acceleration is dv/dt = Hdr/dt = Hv = H²r. So the force required to divert one of the particles from that course, and keep it at a constant distance from the other, is just H²rm, where m is its mass.

According to our article, H is about 70 km/sec/megaparsec, and a megaparsec is about 3x10¹⁶ km, so H is about 2x10^-15 sec⁻¹. So at a million meters the acceleration to be overcome is 4x10⁻²⁴ m/s². On the other hand, if one of the meter sticks weighs a kilogram, then the acceleration due to its gravity at a distance of a million meters is 6.7x10⁻²³ m/s², an order of magnitude more. Maybe the meter sticks are lighter than that, but that's going to be completely overwhelmed by the fact that there's a million of them, and they're much closer together. --Trovatore 18:02, 27 October 2007 (UTC)

pH

Can pH be less than zero? One of the articles here says so.

Deepti —Preceding unsigned comment added by 61.2.66.136 (talk) 14:19, 25 October 2007 (UTC)

Yes, see here. --NorwegianBlue ^talk 14:30, 25 October 2007 (UTC)

See also superacid. TenOfAllTrades(talk) 16:17, 25 October 2007 (UTC)

Doesn't this mean pH is ill-defined? Can't it be reduced to SI units? I suppose not, because it is operationally defined. Is it a 'real' unit of measurement (whatever that means)? Oh, hold on, it's a unit-less quantity, or better dimensionless quantity, right? DirkvdM 08:20, 26 October 2007 (UTC)

I don't think pH is really operationally defined. It's defined in terms of the activity of hydrogen (or hydronium) ions through a mathematical formula (see pH). The issue is that most solutions in everyday life are between 0 and 14 and since it's a log scale, that's a large range (10^14) that can usually cover almost everything. But there's nothing that says it has to be within that range. --Bennybp 15:13, 26 October 2007 (UTC)

I did see pH. That's where I got the 'operationally defined' from. I wouldn't have used that expression because I didn't know it, but the nice thing about science-speak is that I instantly understood what it meant. :) DirkvdM 19:11, 26 October 2007 (UTC)

Jeez, maybe I should read the articles I link to rather than skimming :) It looks like it could be defined mathematically (for some solutions) or operationally. Interesting, I'll have to do more research on that :) --Bennybp 00:57, 27 October 2007 (UTC)

giardia parasite

we live in the arctic of alaska and because of the global warming we have experienced an increase of beaver population in our region, which we never use to have before. all the lakes and ponds and rivers are full of more beaver every year, can we drink ice water? is the parasite able to live in the ice? and does it still live after the ice has melted? we do already have a filter that can kill the giardia, i just want to know if we need to use it for the ice water too?

Inupiaqbelle78 15:35, 25 October 2007 (UTC)inupiaqbelle

Giardia can live in ice (and ice cubes), if that is what you are asking. Any water that you may consume that might have giardia in it should be either filtered or boiled first, whether it is in ice or even just used to wash off food. --24.147.86.187 17:01, 25 October 2007 (UTC)

Welcome to Wikiopedia, the encyclopedia that anyonee can edit. The answers you get here can come from anyone. including editors who have no expertise whatsoever that relates to your question. Your question relates to a potentially life-treatening issue. Please seek a professional opinion, Someone in your community could die if you act on the wrong response. That said: if you kill and eat the beaver, the you muwst cook theme completely. duh. -Arch dude 03:28, 26 October 2007 (UTC)

Go away! And stop spreading false medical info. Giardia lethal? Where did you get that idea from? And read the question. And learn to spell. Dude. DirkvdM 08:26, 26 October 2007 (UTC)

I'd say it's a no-brainer that you must always sterilize water from rivers and lakes before drinking it, and this hardly qualifies as "medical advice", it's just plain common sense. Untreated water is potentially dangerous, just about everywhere. StuRat 20:00, 28 October 2007 (UTC)

Where it gets tricky is, is it more or less dangerous than dehydration? In extreme cases the answer is obvious, but the borderline may be tough to define. Suppose you're ten miles into a twenty-mile hike and you twist your ankle; you think you can make it out but you're not sure. You don't have any disinfectant or anything to start a fire with. You have a two-liter canteen, one-third full. Should you fill it up from the running stream, possibly the last one? What about if there's no stream, but there's a pond? My guess is that many people would overestimate the dangers of the water relative to not having the water. --Trovatore 21:16, 28 October 2007 (UTC)

Especially with giardia. It isn't much more than a bloody nuisance, with some sickness and especially foul smelling diarhoea (I speak from experience). The diarhoea dehydrating you then becomes the problem, of course, and I suppose drinking more of the infested water won't matter at that point. Btw, StuRat, the safety of river water depends largely on the presence of humans upstream. And the water in national parks in New Zealand used to be perfectly safe to drink, until it got infested with ... yep, giardia. DirkvdM 07:57, 29 October 2007 (UTC)

I would expect that humans will be present just about anywhere a human is likely to visit. And, even if they aren't, plenty of other animals also carry waterborne diseases that humans can contract. Glacial meltwater coming out of a river from under the glacier ought to be relatively safe, I suppose, but there could still be a thawed/rotting animal corpse in there somewhere, so I'd boil it anyway. StuRat 17:38, 29 October 2007 (UTC)

I was talking specifically about hiking national parks, where normally no-one lives. Then again, if it is a much used national park, as are many in New Zealand, only the water at the highest hut might be considered safe. But then, if there's a track further up (eg crossing a pass) then someone with giardia might have felt a sudden urge and not observed the rule of shitting far away from the river. Point taken. DirkvdM 08:31, 30 October 2007 (UTC)

Dirk, I'm sure we're all happy that you got through your encounter with Giardia with nothing worse than that, but you shouldn't assume that that's the worst that can happen. With GI pathogens particularly (cf Salmonella and Listeria) it often turns out that healthy young adults get a little sick and then get over it, but young children, older people, and the immunocompromised, may die. I never actually heard of anyone dying specifically from Giardia but that doesn't mean it can't happen -- and there are other nasties in water also, like cryptosporidium.

Still, there are lots of scenarios where I'd drink the water rather than go without. I suspect that a lot of people overestimate the risks. But that's just me, and I don't really know much about it, so I offer no warranties of any kind. --Trovatore 20:07, 29 October 2007 (UTC)

Yes, of course, in combination with weakness, caused by whatever, anything can be lethal. I've also had cholera, which is a notorious killer, but mainly because it often breaks out under conditions where people are already weak, such as in refugee camps. But an otherwise healthy person should survive it. DirkvdM 08:31, 30 October 2007 (UTC)

What do beavers have to do with giardia? Dismas|^(talk) 12:28, 26 October 2007 (UTC)

Beaver's pooping in a river where you get your water supply is one of the more common ways to get infected with it. 38.112.225.84 14:42, 26 October 2007 (UTC)

Sounds like we need a global campaign to put diapers on beavers. :-) StuRat 17:40, 29 October 2007 (UTC)

Note that the filter probably doesn't kill giardia. This may be of relevance concerning what you do with the filter. I don't know, just thought I'd point this out. DirkvdM 07:21, 27 October 2007 (UTC)

Why are videogames fun?

What causes the brain to enjoy it? All you are doing really is just pressing buttons. But if you stare at a blank screen and use your imagination, it's no where near as fun. So what's gives? 64.236.121.129 17:38, 25 October 2007 (UTC)

The suspense, the feeling of accomplishment, the entertainment from good storylines? Playing with your friends, the challenge, the anxiety? This is why I play video games. Beekone 17:55, 25 October 2007 (UTC)

I'd agree with this. The conclusion, then, is that you're obviously not "just pushing buttons". While pushing buttons is the physical activity, it's in response to the stimuli that a blank screen does not provide. The same holds true for a great many things: baseball is more fun than batting practice, giving a concert is more fun than solo karaoke, and so forth. — Lomn 18:18, 25 October 2007 (UTC)

Aspects of the most popular video games are basic aspects of classical conditioning. See something flashy, hit the right button, and you get rewarded (praise, adulation, the death of your enemies, etc.) or punished (sad music, game over). Repeat. Obviously it's not just the pushing of buttons — it's the whole context of the system of interactions between your brain and the reward system. In any case though it is worth noting there are very different types of games and they probably appeal to different parts of the brain: pinball, Counter-Strike, and Police Quest all use functionally similar hardware but utilize very different faculties (and don't necessarily appeal to the same people). --24.147.86.187 23:56, 25 October 2007 (UTC)

I think games have a strong biological advantage. We're not the only animals that play games. I remember a scene from the blue planet, where killer whales spend hours tossing a dead seal back and forth with the children. My guess is that these kinds of games provide a safe environment to train motor skills, reflexes and coordination. Of course, for any animal there needs to be a strong biological imperative to perform these mindless repetitions without getting bored, so nature has made these things fun, and made us want to be good at it. Playing the whole thing out in your imagination does not provide most of the benefits of games. First of all, these skills are mostly low level neural processes (like muscle memory), so you need to actually do them to get better at it. Second, it's good to have some independent verification of how good you are at something. In my mind, I can be a fantastic hunter that always catches the prey and never dies, but unless I get actual real world feedback on these skills, I may just be kidding myself (and die the first time I actually try to hunt). That's why nature wants us to play real games, instead of just using our imaginations. risk 03:11, 26 October 2007 (UTC)

I fixed your link. Algebraist 21:28, 26 October 2007 (UTC)

Menopause

Do a) pregnancies, b) oral contraceptives influence the onset of menopause in any way? --KnightMove 19:02, 25 October 2007 (UTC)

I don't know if prenancy has an effect, but taking oral contraceptives will have no effect. However, taking oral contraceptives can hide the symptoms of menopause, and even allow a woman to continue to have periods, even though her ovaries have stopped putting out eggs. [2] Someguy1221 19:09, 25 October 2007 (UTC)

Decibel Meter

Is there any way to make a homemade decible meter? Thanks Deltacom1515 19:03, 25 October 2007 (UTC)

If you had some sort of calibration standard for sound power, you could calibrate any arbitrary microphone, amplifier, and ac voltmeter as a sound meter. Alternatively, if you can borrow a sound level meter, you could calibrate your homemade device against that meter.

Atlant 23:39, 25 October 2007 (UTC)

Sure - a microphone and a voltmeter should do just fine. I bet you could find some freeware software that would let you plug a mike into your computer's sound card and read off the sound levels. But for it to be accurate you'd need a way to calibrate it. If you can borrow a decent sound level meter you could play the same sound into that machine and your home-made contraption and calibrate it like that. The only other way would be to have a sound source of known loudness and set it up that way. I can't really think of anything like that. My HiFi/Home Theatre system has decibel numbers it displays as you wind the volume up and down - but that can't be accurate because it depends on how loud the thing you are playing was recorded at. SteveBaker 23:58, 25 October 2007 (UTC)

Your hi-fi is displaying "relative" decibels (decibels of attenuation); absent a calibration microphone (which some high-end receivers provide), there's no way it can know the absolute sound pressure being produced. As for calibrating sound level meters, ours actually came with a calibrator that, when closely coupled with the meter's microphone, puts out a 94 dB 1000 Hz tone (or, with a switch press, a 114 dB tone). It's that sort of gadget you'd need to calibrate a home-made meter, but even then, there'd still be questions of how well-coupled the calibration source and microphone are and what the frequency response of the microphone is. It'd be far easier to borrow a calibrated meter against which to calibrate the home-made meter.

Radio Shack, by the way, sells sound level meters for not very much money; the meter I use at home came from there (whereas the work meter and calibrator that I was describing above is a very nice Brüel and Kjaer [3]).

Atlant 12:12, 26 October 2007 (UTC)

The above proposals to use a calibrated sound level meter to calibrate a home-brew combination of microphone and amplifier is flawed. Sound pressure level meters have a defined frequency response curve which the home-brew system would lack, so the improvised calibration would be accurate only for the particular frequency used. Edison 15:26, 26 October 2007 (UTC)

I assumed that one would calibrate the home-brew meter using a variety of different single frequencies (tones).

Atlant 23:01, 28 October 2007 (UTC)

You would need a logarithmic amplifier to display the results in the usual decibels if you were to merely use a voltmeter. —Preceding unsigned comment added by 88.109.17.174 (talk) 00:51, 27 October 2007 (UTC)

Or a VU meter or a voltmeter with a "decibel" scale as most analog multimeters (VOMs) used to have.

Atlant 11:48, 30 October 2007 (UTC)

Why do humans rarely eat gull meat?

There are gulls everywhere. The gulls are large and fat. Why do people not shoot them for food like they do with wild duck, pheasant and pigeon? --81.77.116.167 19:25, 25 October 2007 (UTC)

Isn't it said to be bad luck to shoot gulls? Either that or they taste of rancid fish :-) Astronaut 19:43, 25 October 2007 (UTC)

Seagulls are often culled as in many areas they are classified as vermin and can be very aggressive (particularly Herring Gulls. Why they are not used for food is a good question as the largest ones can be bigger than a chicken.GaryReggae 19:56, 25 October 2007 (UTC)

• Avoidance of bad karma, see Jonathan Livingston Seagull. --JWSchmidt 21:15, 25 October 2007 (UTC)

Three reasons:

1. Gulls are scavengers. This means they're likely to carry all sorts of bacteria and parasites, and by eating them, you're likely to get infected.
2. Gulls are scavengers. This puts them very high up on the food chain, so toxic chemicals are likely to bioaccumulate to high levels.
3. Gulls are scavengers. Meat tends to pick up the flavor of whatever the critter eats. Gulls tend to eat decaying food, so guess how gull meat tastes?

--Carnildo 23:38, 25 October 2007 (UTC)

Sorry, this is bad science. Think chickens and ducks which are covered in bacteria, think crabs which scavenge on carrion. Both widely eaten with minimal detrimental effects. That is one reason why we cook food. Richard Avery —Preceding comment was added at 07:43, 27 October 2007 (UTC)

Yeah I suppose so although I'm not too sure about the last point, pigs used to eat all sorts of junk (eg pigswill) but they are still eaten and sheep/cows don't taste like grass either! Pigeons are also eaten sometimes and they eat rubbish off the streets and carry disease too. I would have thought that cooking the bird properly would destroy any bacteria. PS why all the recent questions about gulls? This is the third one I've seen in the last week or so! GaryReggae 12:19, 26 October 2007 (UTC)

Slight note, most beef consumed in the U.S. is from corn-fed cows raised in CAFOs and grass-fed beef does in fact taste appreciably different and is one of the things that distinguishes Argentinian beef, for example. Read The Omnivore's Dilemma for more information on the consequences of raising ruminants on a corn versus grass diet. One of the regular editors/contributors here is some kind of seagull fanatic or something, so the gull questions might be light-hearted trolling of him or something related, FYI. 38.112.225.84 14:37, 26 October 2007 (UTC)

FYI, the pigeons we usually eat are not (usually) the type that scavenge the rubbish in our streets. --Kurt Shaped Box 18:50, 26 October 2007 (UTC)

I always assumed the feral pigeons were Wood Pigeons - you learn something every day!GaryReggae 19:37, 26 October 2007 (UTC)

In my experience, you very rarely get to see Woodpigeon close up - they're very nervy, flighty birds. I suppose that they've learned to beware the hand of man over the years - as it often holds a shotgun. --Kurt Shaped Box 06:57, 27 October 2007 (UTC)

Pffft! Maybe where you live. The woodpigeons in my garden barely move until you're a couple of metres away. Very fat, lumbering things they are. Look quite tasty. Skittle 15:19, 28 October 2007 (UTC)

Shoot a few. Then watch their expressions change when they see you going out. --Kurt Shaped Box 22:26, 28 October 2007 (UTC)

The only real answer here is because chickens are bigger, easier to grow, easier to feed, taste better (apparently), survive much healthier without eating meat etc. It is the same reason why we keep cattle/pigs over any other animals for food - they 'farm' better. There aren't really any wild land animals that most humans eat anymore. Eating small birds was extremely common throughout history (typically the only meat the poor/slaves would eat right up till late 18th century etc). Usually they would eat pigeon or birds that were easier to capture and net. Homeless people in most countries still eat birds like gulls and pigeons, most typically capture by throwing metal pipes at end, believe it or not.--Dacium 00:17, 29 October 2007 (UTC)

-enic vs -eic suffix on acids

I was editing pinolenic acid. It is frequently called pinoleic acid. I'm pretty sure that's a mistake (rather than just an alternative spelling.) That is, pinolenic acid has three double bonds and I think that a compound called pinoleic should have two. I wanted to provide a cite a definitive guide to the chemical notation. But I struck out in the IUPAC Gold Book [4]; maybe I didn't know what term to search for.

Can somebody point me to an authoritative statement about -eic vs -enic, as used in fatty acids? David.Throop 20:45, 25 October 2007 (UTC)

Actually, the suffix is "ic" for carboxylic acid. So the question is whether the proper prefix is "pinole" or "pinolen." Someguy1221 21:04, 25 October 2007 (UTC)

Amphisbaena

I've got to write a report on an animal with near nothing about it, so could someone tell me What signs of health and illness in an amphisbaena would be, and mabey how long it is? I've goth this much so far, but I've got to do a "rehabilitation" thingy for it.

Habitat - Desert Cage - Heavy cage, snip wings, lead under cage, poison fangs Consider - can become two halves Food - Ants

en.wikipedia.com/wiki/amphisbaena http://www.eaudrey.com/myth/amphisbaena.htm

Habitat - Desert Cage - Heavy cage, snip wings, lead under cage, poison fangs Consider - can become two halves Food - Ants Similar in color and appearance to a worm; it can slither in either direction well; medismal uses; 50 feet long, with two heads at each end. It has large bird-like feet and a pair of feathered wings, making it quite an unusual sight to behold; The amphisbaena is a very rare creature that supposedly descends from a legendary serpent that was once long enough to encircle the entire globe and powerful enough to kill gods; An amphisbaena sees four times as well as a human in low-light conditions and twice as well in normal light; An amphisbaena can ascertain other creatures by smell and hearing within 30 feet; According to Greek mythology, the mythological amphisbaena was spawned from the blood that dripped from Medusa the Gorgon's head as Perseus flew over the Libyan Desert with it in his hand; it can't be determined which is the rear head; egenerative abilities - if the amphisbaena is cut in half, the two parts can rejoin venomous fangs - the amphisbaena is venomous, as Pliny the Elder indicates: "The amphisbaena has a twin head, that is one at the tail end as well, as though it were not enough for poison to be poured out of one mouth." efficient duplicity - the amphisbaena's heads can handle more than one task at once. speed - according to some accounts, the amphisbaena can slither (or run) very quickly, and, in the case of the limbless amphisbaena, it can slither in either direction, as Isidore of Seville indicates: "It can move in the direction of either head with a circular motion." The poet Nicander, however, describes the amphisbaena as "slow in motion". rolling - by locking the jaws of its two heads or holding the neck of one in the mouth of the other, the amphisbaena can roll like a hoop, as depicted by medieval artists warmbloodedness - unlike most serpents, the amphisbaena was apparently unperturbed by the cold, as Isidore of Seville indicates: "Alone among snakes, the amphisbaena goes out in the cold." pregnancy - pregnant women wearing an amphisbaena around their necks would supposedly have safe pregnancies; in accord with this, women in power would wear bracelets in the shape of amphisbaenae arthritis - wearing a dead amphisbaena or its skin would cure arthritis chilblains - wearing the skin of an amphisbaena will reduce this swelling of the hands caused by cold cold - wearing a dead amphisbaena or its skin is a cure for a cold woodcutting - nailing the skin of an amphisbeana to a tree before cutting it down will make it easier to fell the tree and keep the lumberjack warm

http://en.wikipedia.com/wiki/amphisbaena http://www.eaudrey.com/myth/amphisbaena.htm http://www.pantheon.org/articles/a/amphisbaena.htm http://www.uvm.edu/~chmartin/amphisbaena.htmll http://www.monstropedia.org/index.php?title=Amphisbaena YДмΔќʃʀï^→Г_C← 10-25-2007 • 21:00:36

Amphisbaena is a mythological animal - there is no such thing! So asking these kinds of question is not going to get you any clear facts because there aren't any facts...all there is is fiction. So all you are doing is reading about the mythology that other people have written. So solid things like how long it is or how you know it's getting sick are going to be figments of someone elses imagination. It's very likely that if you've been given an assignment to write about this creature, then in all likelyhood your teacher is trying to get you to use your imagination. So go nuts! Think up some cool things and write about them (as had all of the other people you've found writing about it). I would like to know how they poop without the necessary apparatus!SteveBaker 23:11, 25 October 2007 (UTC)

Well, the assignment might be a cultural study, in which case all claims need to be sourced. As for the pooping question, maybe the head that doesn't eat, vomits, and they spend all their time trying to out-eat the other head, so they're not the unlucky end. risk 03:18, 26 October 2007 (UTC)

This could be a misspelling of Amphisbaenia which appears to be the real animal from which the mythical one was born (figuratively speaking, of course. Literally speaking the mythical creature was born of the blood of the Medusa). --Psud 09:46, 26 October 2007 (UTC)

Remember, rover gets the pill and fido gets the suppository. (a joke from Futurama) -- Diletante 16:20, 26 October 2007 (UTC)

Hmmm CatDog? SteveBaker 18:22, 26 October 2007 (UTC)