Wikipedia:Reference desk/Archives/Science/2007 October 2

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October 2

Weighty of charge

I think about charge and current. what is weight of charge and current plese? —Preceding unsigned comment added by 88.109.239.189 (talk) 00:17, 2 October 2007 (UTC)

An electron has a mass of 9.109 382 15(45) × 10^–31 kg, but I'm unsure if charge has mass. Does the negative electrode of a capacitor gain mass when charged? anonymous6494 02:47, 2 October 2007 (UTC)

Along the lines of a capacitor gaining mass, I`ve wondered if a rechargeable battery is just a teeny bit more massive when fully charged compared to when it`s exhausted. I would have to guess yes. Is that correct? I suppose any kind of battery could also apply. Thanks, Dave 64.230.233.209 03:33, 2 October 2007 (UTC)

The electrons may be on the negative electrode, but they have been taken away from the positive electrode, so the net change in mass of a capacitor is nothing. However there will be some relativistic mass (E=mc²) due to the energy stored. The same will apply to the battery. Electrons are just mvoed from one place to another, so the mass of electrons in the battery is the same when it's charged as when it is empty. Graeme Bartlett 04:06, 2 October 2007 (UTC)

Could you not use a static-discharge to transfer electrons to one plate of a capacitor without having electrons drained from the other plate? Something like the active part of an electroscope. I don't think net total charge (i.e., electron count) needs to be conserved in a non-closed system, so how about looking at mass change in only one part of a closed system before/after creating electron imbalance of that part with respect to some other part. DMacks 04:27, 2 October 2007 (UTC)

Static charge capacitors with the other plate at infinity (or earth) have a low capacitance and cannot store much charge. You will be working hard to get a nanofarad of capacitance, and if you combine that with the mass of the electrons involved - you will get very little mass. Graeme Bartlett 00:11, 3 October 2007 (UTC)

Charge itself has no mass. Charge is a fundamental property of a particle, just like rest mass is. Asking what the mass is on charge is as meaningless a concept as asking what the mass of a velocity or the charge of a temperature is. They simply have no such inherent relationship. Someguy1221 04:49, 2 October 2007 (UTC)

According to our electron article, each electron has a mass of 9.109 382 15(45) × 10^–31 kg and a charge of –1.602 176 487(40) × 10^–19 C. This gives us a mass per charge of -5.7 x 10^-12 kg/C or -5.7 x 10^-9 g/C. The negative value means that you will subtract some mass for objects with a positive charge and add some mass for objects with a negative charge. This all assumes that the charge is in the form of ionized atoms, and/or free electrons. Free protons have a positive charge and are much heavier. StuRat 14:24, 2 October 2007 (UTC)

If you took an uncharged capacitor of huge capacitance, say of 1 farad and, and charged it with electricity, the energy stored in it would increase by 1/2*(capacitance)*(voltage)² Joules. The equation for mass and energy says E= mass*c² (where c is the velocity of light, approx 3 x 10⁸m/sec. If it were charged to 100 volts (a very high voltage rating for such a large capacitor), the increase in energy would be 5000 Joules, indicating a mass increase of 5.6 x 10^-14 kilograms, probably not detectable by any existing means, especially considering the mass of such a large capacitor. If it were charged to 1000 volts, the mass increase would be still only 5.6 x 10^-12 kg or a thousandth of a microgram, still unmeasurable in a capacitor probably weighing over a kilogram. (Please check the math, formulas, and analysis). Edison 14:39, 2 October 2007 (UTC)

I don't think that formula is applicable here. That only applies when mass is converted to energy (as in a nuclear reaction) or vice-versa. That doesn't happen in a capacitor. StuRat 14:54, 2 October 2007 (UTC)

It applies to everything. E=mc^2 is right no matter where the energy came from. Someguy1221 16:38, 2 October 2007 (UTC)

In a completely unrelated question, would that mean that a warm cup of coffee has a very slightly higher mass than a cold one? —Preceding unsigned comment added by 66.28.242.74 (talk) 17:40, 2 October 2007 (UTC)

Much higher since the cold one has already lost a lot of steam while it was hot and the hot one is still losing steam :D --froth^t 18:00, 2 October 2007 (UTC)

Yes. Ignoring evaporation, the hot cup of coffee will be very slightly heavier. If you want to think in terms of exactly where the mass is, the particles in the hot coffee will be moving faster, and therefore possess more relativistic mass. Someguy1221 00:23, 3 October 2007 (UTC)

If you wind as alarm clock, it gets heavier (by a tiny undetectable amount). If you accelerate a subatomic particle in a cyclotron, to an appreciable fraction of the speed of light, and fail to allow for the mass increase, your results will not be as anticipated (per old cyclotronists). The meaning of the "weight of current" is harder to interpret. Current into a conductor equals current out, so at first blush current would seem to have no weight. Edison 05:15, 3 October 2007 (UTC)

Another tick question I just thought of...

Is it possible for a tick to transmit HIV from one human to another? --Kurt Shaped Box 00:28, 2 October 2007 (UTC)

theoretically yes, practically no. Each individual tick (or mosquito or other arthropod vector) almost never attacks more than one human. Ticks in particular usually attack an animal host and then a human host. The chances of a particular human being attacked by a tick that had previously attacked a HIV-infected human are vanishingly small. A flea is theoretically more likely, but I have not seen any reports in the literature. -Arch dude 01:42, 2 October 2007 (UTC)

But leeches are another matter. Our article states that blood borne illnesses can be spread through a leech biting an infected person. --S.dedalus 01:45, 2 October 2007 (UTC)

Does water expand when heated?

If a glass of water is heated from 20 Celsius to 80 celsius, does the water expand and become less concentrated? Acceptable 01:28, 2 October 2007 (UTC)

Yes the water will expand a very small amount and become less dense, if that is what you mean by concentrated. See the section on water density. Sifaka ^talk 02:05, 2 October 2007 (UTC)

The table in that article stops at 30°C, but I have here the CRC Handbook, 67th edition. It gives the density at 20°C as 0.99823 g/ml and at 80°C as 0.97183, so the "very small" increase in volume is more than you might think -- a bit over 2.7%. At the boiling point the density is 0.95838, so from room temperature to boiling, water expands by over 4%. This relatively large expansion is why it was possible for some early thermometers to use water as a working fluid; but of course they would not be usable with temperatures close to freezing, where water stops contracting as it gets colder and starts expanding again. --Anonymous, 13:48 UTC, October 2, 2007.

This is also (at the moment) the major contributor to sea level rise, not melting ice, as most people think, although that might become the major factor in the future. DirkvdM 07:42, 2 October 2007 (UTC)

This business of water expanding as it gets close to freezing is an extremely rare thing - there are only a handful of substances that do this. It's also the reason why your water pipes can split if they come close to freezing. The metal of the pipe is contracting with the cold - but the water expands and something has to give! But above those low temperatures water behaves like almost every other substance and expands as it gets warmer. SteveBaker 13:55, 2 October 2007 (UTC)

The water expands when heated alright, look at the overpressure valves dribble on hot water systems; or have a long, hot shower so the hot water system has only cold water in it, wait until the water is fully hot again then open a tap. The pressure is noticeably greater (the water spurts out at higher pressure than usual). This is particularly noticeably where the water pressure is normally fairly low.Polypipe Wrangler 06:50, 6 October 2007 (UTC)

FYI, I think some people may be confused about water expanding as it cools, and also expanding as it is heated. The most dense water (at least at normal atmospheric pressure) is I believe 4 Celsius. Many lakes are permanently 4 C at the bottom because it is heaviest and sinks. —Preceding unsigned comment added by 99.233.83.143 (talk) 16:19, 6 October 2007 (UTC)

I think that's rather the other way around. It's not like 4C molecules sink to the bottom (although there may be some of that too). It's more like the water at the bottom undergoes most pressure and therefore 'tries hardest' to be as compact as possible, so it gives off heat to the water above it. Unless the average temperature is lower than 4C, in which case it will absorb warmth, causing the water at the top to be coldest and freezing first. This is why fish can survive in a frozen lake for a long time - the water at the bottom will remain at 4C. I suppose that if it gets really cold, it might even absorb warmth from the ground underneath to stay as compact as possible. DirkvdM 07:42, 7 October 2007 (UTC)

Atoms

How can one determine the number of neutrons in an isotope. Marlith ^T/C 02:54, 2 October 2007 (UTC)

See mass number. --24.147.86.187 02:57, 2 October 2007 (UTC)

Wow, that page is amazingly verbose for such a simple concept. Let me summarize that page for you: atomic mass = protons + neutrons. DONE. Assuming you know the number of protons and the atomic mass, you should be in good shape. --Ybbor^Talk 03:01, 2 October 2007 (UTC)

Except that's not 100% true, especially for isotopes. Atomic mass is not the same thing as the mass number, which is simply a total of neutrons plus protons; atomic mass also has electrons involved, and the mass of isotopes can be slightly different than the mass number, and can deviate from their mass numbers based on their mass defect. So you have to make sure you are always rounding atomic masses, essentially, before you try to use them to calculate neutrons. --24.147.86.187 12:36, 2 October 2007 (UTC)

Yes - but the error is truly microscopic in all but the most exotic elements. We have:

• 'atomic number' -- the number of protons - which determines what we name the atoms and how many electrons they have when they are electrically neutral - which in turn determines most of their chemical properties).
• 'mass number' -- the number of protons+neutrons - which determines which isotope you have. Two atoms with the same mass number may have a different number of protons, so they may have wildly different chemical properties.
• 'atomic mass' -- the actual mass of an atom. The mass includes protons, neutrons and electrons. Since a proton weighs 1.007276 atomic mass units and a neutron is a little more at 1.008665 units and the electron is 0.000548 units - you can see that roughly, protons and neutrons have masses of almost exactly 1 and the electron weighs almost nothing - so the atomic mass is going to be almost exactly the same as the mass number but with a few extra digits after the decimal point.

So if you have the mass number and that atomic number, subtract them to get the number of neutrons. If you only have the atomic mass and the atomic number, then chop off all of the digits after the decimal point of the atomic mass to get the mass number and then subtract the atomic number. (This rule breaks for the very heaviest atoms - Darmstadtium for example has a mass number is 281 but it's atomic mass is 282 - but I think the rule works OK up to maybe Dubnium - you'll never care about this fact!)

SteveBaker 13:50, 2 October 2007 (UTC)

Also, in reference to the second answer, the mass number changes with each isotope. The atomic mass for any element is an average of all the possible isotopes' masses in relation to their abundance.Mrdeath5493 05:14, 3 October 2007 (UTC)

Foucault Pendulum Animation

I can't seem to wrap my mind around what this animation is trying to do. I think I understand foucault pendulums (it goes back and forth in the same plane relative to the stars, but since the earth is moving, the ground turns under it. Also the whole apperatus is moving around the earth's axis) but this image seems to contradict it. Shouldn't the the pendulum's swing be the same from the star's point of view? The animation is from the star's point of view so why does it spin? The spin would only be accurate if the earth were moving under it and the image was relative to the pendulum. Or is this only valid if the pendulum's on the north pole? Even so the image seems wrong. Aargh, it's hard to visualize things spinning while stuck on the surface of a rotating sphere.. can anyone help? --froth^t 04:33, 2 October 2007 (UTC)

I also wonder about the accuracy of that image. It's sort of hurting my head right now, so I'll think about it some more and report back. Nimur 04:49, 2 October 2007 (UTC)

I'm not going to view the image right now, but it's not correct in general that a Foucault pendulum goes back and forth in the same plane relative to the stars. Its initial plane of motion is determined by three points: the fulcrum F, the center of the Earth E, and the location B where the bob is released. As the Earth rotates, points E and F must remain in the pendulum's plane of motion, but point F is moving and will not (in general) remain in the original plane. The plane of motion thus rotates with respect to the stars as well as with respect to the Earth. --Anonymous, not moving right now with respect to the Earth, 14:00 UTC, October 2, 2007.

*explodes* x_x I see how this is possible and I can look at the animation and imagine it making sense at the north pole where the earth is spinning under it and the fulcrum is stationary, but at an angle when the fulcrum is moving too, it... zomg I see it, it's working hah! thanks --froth^t 17:58, 2 October 2007 (UTC)

The surface of the Earth has intrinsic Gaussian curvature, so parallel transport of a vector around a closed curve may result in a net change in direction. See also Geometric phase#The Foucault Pendulum. —Keenan Pepper 02:45, 3 October 2007 (UTC)

Dimensions in a World

04:47, 2 October 2007 (UTC)210.0.136.138AHow many dimensions exist in the real world? And, how does this really mean to human beings? Can a specific person exist in a separte world of different dimensions, if that exists. Is it true that Eistein has already affirmed this?04:47, 2 October 2007 (UTC)210.0.136.138Allen Chau, from Hong Kong

There are as many dimensions as we define to exist. See degrees of freedom. One might say that the number of dimensions is equal to the rank of the system matrix. Alternatively, one might choose to describe the spatial extent of an object, which would only include three dimensions. One might also choose to represent system space in terms of phase or velocity - so we could easily have six dimensions. These concepts are quite complicated, but in short summary for layman's purposes, there are as many dimensions as we feel like adding to describe the situation at hand. Most systems can be easily described with three spatial dimensions (and often time as an additional dimension). Nimur 04:53, 2 October 2007 (UTC)

I think the OP was referring only to the commonsense meaning of "Dimension" as in space and time dimensions. We can plainly see three dimensions in space, and only three. As Einstein explained, time can be thought of as a fourth, somewhat wierd dimension. This gives our world four dimensions that we can observe. No higher dimensions have ever been observed, ever. Now, if a person were to exist in an "alternate set of dimensions" he'd better damn well be in another universe in the greater multiverse, or one of the many-worlds, because if he isn't, there's pretty much nothing but speculation to explain it (er, those first two were also speculation, but they've been floating around for quite a while). Now, the only remotely close to accepted theory that allows alternate dimensions to exist in our own universe without our observing them is string theory and its variants, but absolutely nothing can occupy these unobservable dimensions (except for strings themselves, which can sort of wiggle around in them). Everything you've seen on Sci-Fi shows about a person entering an "alternate phase" or something like that, and suddenly no one can see him, is entirely bullshit. Someguy1221 05:01, 2 October 2007 (UTC)

Mathematicians and scientists often deal in higher dimensions and calculate things using them. They can be assumed to exist on a theoretical level, in the same way that the square roots of negative numbers are assumed to exist on a theoretical level. These assumptions are useful in such contexts. But whether any human mind can actually visualise or even comprehend what they mean, outside of such theoretical considerations, is a moot point. -- JackofOz 13:05, 2 October 2007 (UTC)

Why do you say that? Have you ever read Flatland? The 2 dimensional people would have had 2 dimensional physics and called time the 3rd, and told their ref desk OPs that it's nonsense to think that you can just poof out into the 3rd dimension.. which of course the sphere does in the story, baffling their scientists --froth^t 18:05, 2 October 2007 (UTC)

Erm, what? Flatland is fiction, by the way. In modern physics, if a spatial dimension exists, there is utterly nothing to prevent any particle from moving through it. And so there would be some quite severe consequences. For example, chirality could not exist in three dimensional objects, which would conflict quite severely with many observations in chemistry. That's just the simplest to imagine example (in my opinion) of where the existence of a fourth spatial dimension would alter the laws of physics (er, chemistry, whatever). Now, string theory does allow wierdness like the existence of extra dimensions that are unobservable to only some observers. For example, every particle on in the universe could be bound to a "three dimensional surface" of a higher dimensional object. Thus, as if flatland were on the surface of a sphere, we would exist in a higher dimensional universe we could not observe. And this does not necessarily prohibit other objects, universes, whatever, from not being bound and limited by this three dimensional surface we are bound to. The problem is that string theory is presently unverifiable. So it is quite correct to say that there is no accepted theory in physics that would allow the existence of unobservable spatial dimensions. Someguy1221 20:08, 2 October 2007 (UTC)

You can define any point in space relative to some fixed coordinate system using three distances. This makes it a three-dimensional world. If you follow Einstein and wish to employ the mathematical convenience of talking about 'space-time' then you need to add one time measurement. This makes three or four dimensions depending on what you are trying to measure. Nimur's degrees of freedom argument is wrong because that's an argument about measuring things other than space itself. You can choose to measure space with things other than three distances - but no matter what, you always need just three numbers...so for example, you can measure every point in space using two angles and one distance ('spherical polar coordinates') or one angle and two distances ('cylindrical polar'). In space/time, you always need four numbers. The exact formulation doesn't matter - the dimensionality of space (or space/time) doesn't change depending on how you measure it.

The extra dimensions that string theory predicts are claimed to be 'very small'. Understanding what this means is tricky - we have do take it in small steps:

• Suppose for a moment that we were observing some two-dimensional creatures - living on the surface of a flat piece of paper. In our present world view, the paper is flat and infinitely large. There is no 'up/down' dimension for them because they are 2D creatures - they only have left/right and forwards/backwards.
• But suppose one of those two spatial dimension (let's pick the left/right dimension) was 'small' - just a 10 miles across say. The universe can't have 'edges' - it has to 'wrap around'. By this, I mean that moving in the left/right dimension for exactly 10 miles would take you all the way around that dimension and back to where you started - for a 2D creature this would be a bit strange - but for us 3D creatures watching them, it would be like they were living on the surface of an infinitely long cylinder of paper that's just one mile in diameter. They could move as far as they wanted along the length of the cylinder - but if they moved a long distance in the other direction, they'd go all around the cylinder and back to the start. Because their 2D light beams are stuck in the 2D surface, if they looked off to the left or right using a pair of decent binoculars, they'd be able to see themselves 10 miles away.
• In a three dimensional universe like ours, if our up/down dimension was only 10 miles across then you'd be able to travel as far as you wanted left/right or forwards/backwards - but if you moved upwards by 10 miles (or downwards by the same amount), you'd be back where you started. Also, if you were out in space and looked up using a pair of binoculars, you'd be able to see your own feet, just 10 miles away. Looking left or right or forwards or backwards - and everything looks kinda normal.
• Now - imagine that third dimension isn't 10 miles across - but just one millimeter across. We would be almost like 2D beings - almost all of our existance would be in two dimensions since nothing in the universe could be more than a millimeter in height - and moving up or down would have almost no effect on your life. That third dimension exists - but it's hardly any use at all. We would have to be almost perfectly flat creatures - it would be ALMOST a 2D world...but not quite.
• Now imagine that instead of the up/down dimension being a millimeter across, it's much MUCH smaller than the diameter of an atom...in that case we'd have no way to know that there even was a third dimension - it would seem exactly like being in a flat, 2D world since any motion at all in the 3rd dimension would have no effect and no object could be as tall as even an atom...atoms themselves would have to be almost exactly 2D objects. We wouldn't even know that the up/down direction existed at all. It the third dimension were that small, we might as well be living in a 2D world for all that it would matter to us.
• OK - so back to a normal 3D world. What would happen if there were a 4th dimension? Well - we can't see it, measure it...it's not in any way detectable...so we might jump to the conclusion that there isn't one. But if the 4th dimension existed but was very small (much less than the diameter of an atom) - then it could very well be there but we'd be totally unaware of it...unable to detect it. It would SEEM like we were living in a 3D world.

The string theorists claim that there are DOZENS of extra dimensions beyond the three we can normally experience - but all but the first three are so small that we can't tell that they are there - even with the most sophisticated equipment we have. I've heard these extra dimensions described as being 'rolled up'. They might very well be correct - but we have no way to know.

SteveBaker 13:16, 2 October 2007 (UTC)

Just to note: dimensions aren't like they appear in cartoons. They aren't alternative worlds somehow layered on top of ours where aliens live (though note that in the many-worlds interpretation of quantum mechanics—something entirely distinct from the idea of "dimensions" in science—there can in fact be multiple layered realities). They aren't ways to conduct psychic or supernatural phenomena. They are different ways in which geometry can be expressed in the world in which we live, basically. The dimension of time can be as mundane as noting that things change — the apple disintegrates on your table as it moves through the time dimension. Dimensions are not all that exciting, from a science fiction point of view.

Einstein's work, via Minkowskii's interpretations of it, basically reduced discussions of time and space to questions of geometry, and emphasized that time has a geometrical, spatial component to it. This is why he is often credited with introducing the idea of time as a fourth dimension, though he was not really the first person to introduce such an idea and in fact most of our understanding of "Einstein's work" in this regard is through the filter of Minkowskii, who "geometricized" Einstein in really wonderful ways. --24.147.86.187 13:50, 2 October 2007 (UTC)

I'm not sure that I'd say that extra dimensions are not exciting in a science-fiction kind of way. If there are more than three spatial dimensions and they are 'small' (per string theory) then, indeed, they aren't much fun. But if there were a fourth dimension - but something about our minds/bodies/physics meant that we somehow couldn't percieve it - then indeed there would be sci-fi possibilities. An ability to move in that fourth dimension would allow you to do some pretty incredible tricks. Escaping from a locked (3-dimensional) room might be as simple as taking a step in the 'other' dimension, walking past the room then taking a step back again into our normal world. It would be like trying to imprison a 3D person in a 2D rectangle - they'd just step out of it using the 3rd dimension. You'd be able to tie knots that would be impossible to untie...all sorts of weird stuff. A lot of people worry about what the 4th dimension would look like - but that doesn't bother me at all - we can use computer graphics to simulate exactly how a 4D world would project onto 2D retinas just as we understand how a 3D world projects onto a 2D retina. The ikkier thing to contemplate is that some of the string theorists want more than one time dimension - and that's really hard to get one's head around. We can guess what 4D space would be like to 3D beings by analogy with how 3D space would seem to 2D beings. But we only percieve 1D time - and we can't use analogies to extrapolate out to 2D time...it's a real head-spinner. SteveBaker 15:19, 2 October 2007 (UTC)

There's a very clever little story along these lines by Heinlein, called ...and He Built a Crooked House. The opening half-page alone is worth the price of the anthology you get the story in. An LA architect builds a house in the shape of a tesseract, but cut open and unfolded into three dimensions, as you might cut a 3-d cube and unfold it into a 2-d shape. Then there's an earthquake....

The story is very carefully constructed to be geometrically accurate and it's an interesting exercise to verify that. A few details, like what happened to certain walls, are sloughed over, but after all it's just a story. --Trovatore 17:34, 2 October 2007 (UTC)

As I linked above, you might too enjoy Flatland. Many people (including myself) report it being much easier to visualize and work in additional spatial dimensions after reading flatland. I disagree with 24.147 and the other guy that extra dimensions aren't like cartoons- stevebaker's got the right idea from a common sense approach, which is what I'm inclined to believe since string theory isn't really demonstrated by anything in our real world -froth^t 18:10, 2 October 2007 (UTC)

Yep - I agree, I'm quite doubtful that String Theory will ever be shown to be correct. It's a shame because it's very elegant - and correct things are usually elegant! But a theory that's unfalsifiable is not acceptable - so unless there is some kind of major new breakthrough, I think we have to put string theory back on the shelf and go back to looking for something else. SteveBaker 18:34, 2 October 2007 (UTC)

Despite all this talk of "rolling up" and string theory, I stand by my original assessment - there are exactly as many dimensions as we choose to model. I have worked physics problems which are not "wacky" (String Theory), but still imply high dimensionality - for example, a triple-pendulum can be described with six or 12 dimensions (perhaps each joint has a displacement, a momentum, and an acceleration; and maybe we want to throw in a nonlinear potential such as a magnetic attraction at each joint to an external magnet). Each one of these dimensions is a physical parameter where motion, displacement, energy, and other physical quantities can "go." We might start calling the dimensions (θ₁, θ₂, ...), (p₁, p₂...) and so forth. Dimensions can interact via the governing equations, derived from fundamental physical laws. We might take care to set up dimensions which are linearly independent and orthogonal, or we might not choose to do so. The system equations would be straightforward, and the dimensions would be quite complex.

I could just as well model the system in three dimensions of an absolute fixed frame, (X, Y, Z) and time (T). These dimensions are very straightforward, but the system equations would become much nastier, since the relationships would become very highly coupled. But, I could never reduce the complexity to fewer than the total number of variables in the system to begin with.

The same can be said of String Theory and any other "magic" theory which introduces a new variable. Decoupling complex interactions into "separate" dimensions is an operation on a mathematical model and does not change the system in any way. Simple transforms are heavily detailed in linear transform. More sophisticated decouplings are the crux of a lot of modern research topics. Nimur 17:34, 2 October 2007 (UTC)

There is a big difference between using multidimensional mathematics to solve a problem and saying that this many dimensions exist in space. It's not at all the same thing. I too have used as many as 14 dimensions to solve work-related problems in computer graphics...but the world still only has 3 dimensions.

Example: Computer graphics hardware really only draws triangles. If you want to draw a quadrilateral, it is usually split into two triangles. If you have two triangles that you think may originally have made up a quadrilateral - but you really wish (for various arcane reasons) that you could have split the quad along the OTHER diagonal, then you need to check that the two triangles lie in the same plane (if they don't then they didn't come from a quad and swapping the diagonal will do weird things to the graphics). This is a simple 3D problem as you might expect. However, if the triangles have (for example) smoothly varying colours that are linearly interpolated between their vertices - then swapping the diagonal can change the look of the final quad (imagine one triangle has three red vertices and the other has two red and one green - as is, the center of the line between the two triangles is red - but if you swap the diagonal, you get an orange colour in the middle - not at all the same thing). To check that it's safe to re-split it, you also need to check for "planarity in colour space" (Red/Green/Blue space) - so now you are doing a six-dimensional check in X/Y/Z/R/G/B space. But there are other parameters of a triangle in a graphics system such as texture coordinates, surface normal, transparency and so on - and to do a proper job, you need to know that ALL of them are 'planar'. I ended up with 14 per-vertex parameters - so I had to check for planarity in 14-dimensional space!

So yeah - it's easy to end up using math in higher dimensions as a convenient way of solving real-world problems - but that doesn't tell you anything about the number of dimensions of 'space'...which is still (seemingly) three. SteveBaker 18:31, 2 October 2007 (UTC)

Note that when I said extra dimensions weren't exciting, all I meant is "the current theories of extra dimensions are not that interesting when compared with the way that the idea of extra dimensions is invoked in popular fiction." You know, dimensional gateways, portals of alien worlds, etc. That's all. Sure, sure, Flatland, but that's not what most people have in mind when they talk about "dimensions". --65.112.10.56 20:41, 2 October 2007 (UTC)

I think we're largely in agreement, SteveBaker. Whether we are doing graphics or physics or string theory, adding new variables to the mathematics does not actually change the real system's dimensionality. It's only our model that changes. Nimur 16:01, 3 October 2007 (UTC)

Yeah - largely. I believe the string theorists claim that all of their extra dimensions are real, actual spatial dimensions - but 'curled up'. So small that we can never detect them. But they need the extra dimensions to give their strings the ability to vibrate in enough different modes to fulfill all of the things that are demanded of them in the theory. Super-strings are very tiny indeed - vastly smaller than an atom - so even the very tiny extra dimensions are large enough to let them vibrate in those directions as well as the usual three. SteveBaker 02:28, 4 October 2007 (UTC)

To Sweep Mercury

If a little mercury poured on ground and scattered, how can we completely remove it(in a normal condition and out of lab)?Flakture 13:20, 2 October 2007 (UTC)

http://www.epa.gov/mercury/spills/index.htm, from the article on, you guessed it, mercury. Lanfear's Bane 13:48, 2 October 2007 (UTC)

If you don't live in the US, you might also want to consult with your local authority or at least check out their website or other documents provided. There may be additional legal requirements or expectations. According to the EPA website, in the US you only have to report a spill of 1 pound/2 tablespoons or more. The minimum could easily be less in other countries and/or could vary depending on where it occurs. You probably should do this for anything more then a thermometer. Also in a lab in particular, there may be additional requirements imposed by whoever owns or is in charge of the lab. You should check with the lab's safety officer if that's not you (if it is you, it is doubly important you make sure you are aware of all legal requirements and check any existing in-lab regulations) Nil Einne 18:07, 2 October 2007 (UTC)

Check page 23 of Princo's mercury barometer guide. It says to NEVER sweep mercury, and not to use a vacuum. In general, use disposable paper, tape, droppers, etc to collect. --Mdwyer 19:50, 2 October 2007 (UTC)

calcium phosphate

what is the molecular formula (empirical would work as well) of the above compound? Our own wikipedia entry is kinda confusing. Am I supposed to combine the molecules it lists? --MKnight9989 14:02, 2 October 2007 (UTC)

The Oxford Concise Science Dictionary OUP, 1984, has the following:- "Calcium phosphate (V) A white insoluble powder, Ca₃(PO₄)₂; r.d. 3.14 It is found naturally in the mineral apatite, Ca₅(PO₄)₃(OH,F,Cl), and as rock phosphate ... The compound was formerly known as calcium orthophosphate." DuncanHill 14:09, 2 October 2007 (UTC)

Thanks mate. --MKnight9989 14:23, 2 October 2007 (UTC)

Which we have as tricalcium phosphate while calcium phosphate refers to a group of related compounds. Rmhermen 14:42, 2 October 2007 (UTC)

Propidium iodide stains only necrotic cells?

According to WP: "Propidium iodide (or PI) ...can be used to differentiate necrotic, apoptotic and normal cells." According to my understanding, PI stains necrotic but not apoptotic and normal cells. Can someone corroborate this? --137.120.3.217 16:46, 2 October 2007 (UTC)

My first Google hit.....there are others. --JWSchmidt 17:01, 2 October 2007 (UTC)

patents::??

hey friends i have thought of a completely new way of ignition in ic engine.i am sure that it would increase the efficiency and would be able to every problem related to spark plugs.but i cant experiment on it since it require quite costly trials,what should i do.how/which company.how to get a patent .please help.

regards Reveal.mystery —Preceding signed but undated comment was added at 17:04, 2 October 2007 (UTC)

Contact a Patent attorney in your area. -- JSBillings 17:26, 2 October 2007 (UTC)

Or, you might just choose to put this detail on your resume and apply for a job in research as a mechanical engineer. If your system is truly innovative, you should have no trouble finding employ as an engineer. You will probably have an easier time funding your idea if you are part of a corporate, academic, or institutional research group. Most importantly, you will gain the insights of expert peers who can examine your system and help you improve it. Science and engineering, especially in the 21st century, is a collaborative effort. Nimur 17:43, 2 October 2007 (UTC)

"Science and engineering, especially in the 21st century, is a collaborative effort." — what planet are you living on? Science and engineering in the 20th century is marked by increasing patents, defensive monopolies, and a total fear of litigation. Universities push researchers to patent anything and to patent broadly. True collaboration and free IP sharing on profitable technologies takes place only in fields heavily influenced by the ideology of the open source movement (basically fields with close connections to computer science) and even then they wring their hands constantly about whether or not they should patent or how they are going to avoid patent wars and the like. Whether you think science and engineering should be collaborative in this economic sense does not have any bearing on whether it really is collaborative in this sense. --65.112.10.56 20:37, 2 October 2007 (UTC)

You can patent it yourself - you don't need a company to do it for you. However, it can be a little tricky to get the language right when you write your patent - it's very easy to not quite patent enough, so that someone can come along with a small variation of your idea and dodge the patent, rendering it useless...or to somehow misword it in some other way that allows a loophole to be exploited. If you are really convinced that this is something special - then certainly you should consult a patent lawyer. I strongly disagree with User:Nimur. Once you have presented your idea in public - without the protection of a patent - they can just take your idea and use it without paying you a cent. So for chrissakes don't put it into a resume or send it to anyone else without having at least applied for a patent. Note that it's enough to have applied for one - it doesn't have to have been granted yet. You can wait YEARS between applying and completing the process. Personally, I would be quite surprised if you could improve on a simple spark gap as an ignition source - and if I were you, I'd DEFINITELY want to do some basic experiments just to prove that it works at all. You ought to be able to do that with something like a small motorbike engine that you could pick up on the cheap. Just to prove that it works - not that it's efficient or better or anything - just to convince yourself that it'll work. If necessary, find someone you trust with the right skills to help you do this. If your idea is truly better/cheaper than spark ignition, you'll make enough millions from it that splitting the rewards with a close collaborator won't be so terrible. The process of patenting something in a bullet-proof manner with lawyers and such isn't cheap - and you wouldn't want to waste that money on an idea that has a fatal flaw. SteveBaker 18:08, 2 October 2007 (UTC)

The premise of course, is that owning a patent provides legal protection. Gauging the cynicism which pervades the above posts, what makes you think a well-worded patent will protect you from large corporations? You must understand that to defend a patent requires a lengthy legal battle with a very high budget. Even if you are completely legally protected by your fully-encompassing patent, a large legal team may still beat you in court or bankrupt you through legal process. Sometimes that may even be part of the strategy - large legal firms do not have to win, they just have to out-live your budget. A patent is among the most exposing ways to demonstrate your technology - you must carefully detail every mechanism of your system, explaining to the whole world how your system works, and hoping that infringers will be prosecutable. Alternatively, by engaging work as a researcher, you can build up a trusted network of colleagues who will support you, and gain the business infrastructure of a larger organization. These people will be on your side, collaborating with you, you make your product more successful.

When I say "collaborative," I do not mean "open-source" at all. I mean that large engineering projects cannot be operated by a single person. You need a team of engineers, a legal team, a finance team - there are so many tasks, one person cannot make it all happen alone. Competition is certainly a key element of the modern technology economy. But when you face the whole world alone, you are competing with everyone. Nimur 16:09, 3 October 2007 (UTC)

The usual trick if a large, rich company infringes on your patent is to let them get away with it until a year before the patent is due to expire - and then sell it to their biggest competitor. Patent law is nasty. SteveBaker 19:15, 3 October 2007 (UTC)

Laches? TenOfAllTrades(talk) 12:27, 5 October 2007 (UTC)

I am doing some reading on patents, so I'll tell you some of what I've learned so far. But if you're not exaggerating about your idea you should indeed consult a patent consultant, because the wording in the patent is very essential to the protection you get. It's a legal thing, so there are loads of loopholes for others to legally steal your idea. This is the reason to patent broadly, as the anon pointed out.

Firstly, laws differ from country to country, but in general they work roughly the same. The most important deviation is (again) the US, where patents are given out more liberally. There, 'anything under the sun made by man' is supposedly patentable. You could go for a national patent (not necessarily in your own country and possibly in several countries) or a PCT patent, which is a wider international patent (there is as yet no such thing as a worldwide patent). In Europe you could also go for a European patent. In that case, the more countries you want to cover, the more it will cost of course. Per country, count on a few thousand euro, more if you want it properly done (researched well and written by an expert). But if in Europe you want a patent in at least 3 or 4 countries, then it is cheaper to get a 'European patent', which is basically a collection of national patents. But the research into patentability only needs to be done once, which saves money.

As I understand it, it makes sense to apply for a patent in one country first to have it researched by the patent bureau. It might turn out to have been thought of before, in which case there is no point in taking it any further. But it may also turn out not to be patentable for various other reasons, such as it following logically from the state of technology; if for an expert in the field, it is a logical solution to a problem then it is not patentable. Then again, if that has been the case for several decades and no-one has patented it yet, then it apparently breaks with some rusty line of thinking and it is patentable again. The loopholes can work both ways, so to say. After you have applied for a patent, it will be kept secret for one year, to give you time to decide on further patents and maybe start setting up your business. Also because any competitors might violate the patent, hoping you won't have the time or money to sue them, as Nimur pointed out. Not uncommon, as I understand it, so even if you have a patent, you're still not in the clear. But that year might give you a decisive head start if you use it wisely.

About getting a job through your idea, keep in mind that if you're hired for the specific purpose of being inventive then your employer gets the patent - all you get is the bone he throws you. Speaking of which ... if you happen to live in the Netherlands, drop me a note. I'm trying to get together some inventive minds with the idea to make money out of patents. Don't worry, I wont' hire you. :) It'll be a joint venture of sorts, something along the lines of what Nimur was talking about (still working on the legal aspects of that - damn, I just want to be an inventor).

But like I and others said already, get professional advise. This is a tricky business (which sort of takes the fun out of inventing if you want to make money out of it). Btw, this is a legal question, so count yourself lucky no-one has bitched about that yet. :) (Damn, now I just did.) DirkvdM 18:45, 3 October 2007 (UTC)

It's certainly no fun being the lone inventor in the face of gigantic multinational corporations and truly pathetic patent offices. You spend a fortune on getting your patent through the process - but yet the patent office probably didn't spend more than a couple of minutes looking at your patent - just barely enough to read through it. So there is no guarantee that your patent is meaningful - or that it'll stand up in court. You won't know that until someone infringes on it and you have to get big expensive law firms on your side to defend it with no real guarantee of winning. SteveBaker 19:15, 3 October 2007 (UTC)

Update on defending the patent before court: for a European patent that only happens in 10% of the cases. The explanation for this is probably that for a European patent an extensive research is required. In the US, a different system is used. Like I said, patents are given out much more liberally. This is possibly the 'declaratory system' (literal translation from Dutch), in which one only needs to apply and pay a sum. The European ('attributive') patenting system gives much more legal certainty. But of course the extra research means it's more expensive. Too bad one doesn't always have a choice between the two. In the Netherlands, one can also apply for a 'small patent', which is cheaper and faster and more appropriate for small inventions that might not be worthwhile for potential competitors to go to court for. This doesn't appear to apply to your invention, so a European or PCT patent (the latter of which leads to an 'International Search Report') might make more sense for you. DirkvdM 11:45, 5 October 2007 (UTC)

Carbonated Water

Is drinking carbonated water (as in, just plain seltzer water) bad for you? The articles on it and soda seem kind of fuzzy on this, and one of my friends claims that the acid they use to carbonate water leeches calcium from bones. 66.28.242.74 17:38, 2 October 2007 (UTC)

Osteoporosis lists the risk factors for calcium loss - it does mention soft drinks as one of the possible causes - but in the context of phosphoric acid - which isn't present in plain carbonated water. Your friend is probably thinking about Carbonic acid - which is certainly present in plain seltzer water because it's formed whenever you dissolve CO₂ in water. However, carbonic acid is floating around in your blood quite naturally - it's the way that CO₂ gets carried from the cells that produce it back to your lungs. Transporting the stuff around is an important blood function - just as carting loads of oxygen around is - so it's hard to imagine it would be a problem. The osteoporosis article also says (in effect) that if you drink lots of soft drinks (with no calcium in them) then maybe you are drinking less of things that provide calcium (milk for example) - but you'd have the same problem if you drank un-carbonated water. It doesn't mention carbonation as being a specific problem though. The article gives some useful links - you should probably read those too. If you are concerned about a health risk - or if you have any symptoms - you should (of course) consult a doctor. SteveBaker 17:56, 2 October 2007 (UTC)

The acidity of carbonated beverages has been implicated in some tooth decay as it may contribute to erosion of tooth enamel. — Scientizzle 19:28, 2 October 2007 (UTC)

The acidity may lower the pH of your blood, eventually leading to metabolic acidosis. In reality, the body's Bicarbonate buffering system is more than sufficient to handle soda water... or lemons... --Mdwyer 19:41, 2 October 2007 (UTC)

Michoud Fault article

http://en.wikipedia.org/wiki/Michoud_fault

I know enough about geology to know that there are not two tectonic plates involved in this fault as it states in the article. I don't know enough to rewrite it. I put a link to a good paper in the external links section. Dansample 18:53, 2 October 2007 (UTC)

You should leave a note on the 'discussion' page relating to that article. List your concerns there. Someone will come along and take note of it. SteveBaker 19:24, 2 October 2007 (UTC)

And you might tag the article as needing expert attention, using {{expert}} . --Anonymous, 21:48 UTC, October 2.

The Michoud fault is a normal fault. DuncanHill 23:36, 2 October 2007 (UTC)

Fungus fungus

Can a fungus get a fungus infection? --Milkbreath 21:49, 2 October 2007 (UTC)

Interesting question. Can whatever 'drug' utilized to treat first infection be considered a fungus on the fungus? Sorry if that`s just stupid. Dave 64.230.233.209 22:11, 2 October 2007 (UTC)

Only if that drug was a fungus which lived on the fungus. I doubt that it was :) 79.65.119.193 22:46, 2 October 2007 (UTC)

Hi again 79.65.119.193. Just as I thought, hence I wrote 'drug' as I did. I didn`t think that answer was very smart. Not my forte. I should stick to high-school-level physics' problems. lol Dave 64.230.233.209 22:58, 2 October 2007 (UTC)

Mushrooms can go mouldy. DuncanHill 23:37, 2 October 2007 (UTC)

Ah. Good. That's what got me wondering in the first place; I don't remember ever seeing that in my fridge, and there's ample reason to suppose I would have. --Milkbreath 00:27, 3 October 2007 (UTC)

Yay, a mycology question, I'm so happy! Absolutely, it happens all the time although the parasitism may be out of sight underground. Most of the species in the genus Hypomyces participate in some form of fungus on fungus action. Hypomyces includes the tasty lobster mushroom (Hypomyces lactifluorum) which basically takes over its host fungus's mushroom and replaces all its tissue with its own. Asterophora lycoperdoides actually grows mushrooms out of other mushrooms, especially the Russulas. (more pictures of this here and here.) The fungal world is full of strange surprises. Sifaka ^talk 01:04, 3 October 2007 (UTC)

Excellent. Thanks. So nobody's safe. Cool links. I'll have to try that microphotography trick. --Milkbreath 01:18, 3 October 2007 (UTC)

This process helps get rid of that fungus among us. Edison 05:08, 3 October 2007 (UTC)

Even better, the fungal fungal infection could be treated with an antifungal medication isolated from a fungus. Most of the antifungal drugs were isolated from bacteria, and others are synthetic, but some, such as griseofulvin, were originally isolated from specific fungal microorganisms (in this case, Penicillium griseofulvum. - Nunh-huh 05:28, 3 October 2007 (UTC)

Do "voices in one's head" ever engage one in normal "small talk"

Are "voices in one's head" seen as negative just becasue a person decided, say, to go around shooting because of them, and the times people hallucinate innocent things don't get attention? Do voices in one's head ever engage in small talk. You know, "Hey, Jim, how are you doing? Nice day, huh? How 'bout that game last night? Our quarterback stunk." I suppose it's possible that such a hallunciation could come from an imaginary friend, but from the article, I don't thikn so, because my understanding of imaginary friends is that they're always internal - i.e.: The person knows they're an imaginary friend, even if it's an adult who has adopted one for some reason, such as Asperger's Syndrome. I could be wrong on that, though. I also am not talking about hypnogogia, as from what I read that usually isn't understandable, it sounds more like mumbling if it's audible. It does seem strange, though, that the only thing one hears about hallucinations is bad stuff, though, never just innocent stuff like, "The voices in my head and I are discussing what we want for lunch." Something which sounds very normal for a young child with an imaginary friend, which as I say, I suppose to be internal, even if the child talks as thought it's external.209.244.187.155 23:24, 2 October 2007 (UTC)

There was a rather long feature article in the New York Times not too long ago about the Hearing Voices Movement, which was basically people arguing that hearing voices is not necessarily something that needs to be medicalized or medicated or something like that. I seem to recall some of the people in the article saying that the voices weren't always abusive or malevolent though I also got the impression that most of the time they were, that something about whatever it is that creates the voices seems to make them focus on the negative. But that was just my impression. Here's the article, in any case, though I last read it last March so my memory of the details might be foggy. --24.147.86.187 02:16, 3 October 2007 (UTC)

(Also, I had never heard of hypnogogia before—how interesting. I've had the "tripping" feeling many times while waking up, and was always shocked by how violent it felt in comparison with other dream-like sensations, but never realized there it was a general phenomena by the name and that it was basically the strange border line between being awake and asleep. How interesting.) --24.147.86.187 02:19, 3 October 2007 (UTC)

It gets better. "Hypnogogia" is specifically the strange border line between being awake and asleep when falling asleep. "Hypnopompia" is specifically the strange border line between being awake and asleep when waking up. - Nunh-huh 05:24, 3 October 2007 (UTC)

Have anyone ever subjected those "voices" to an IQ test? or get the "voices" to write up a scientific paper on Quantum Physics? After all if God is speaking to you, he must know some serious shit. 202.168.50.40 04:21, 3 October 2007 (UTC)

If voices in one's head say innocuous things like "Looks like it might rain today" they probably get little noted nor long remembered. Edison 05:07, 3 October 2007 (UTC)

Thanks, all; especially for the article. I'm trying to do research into a possible novel idea I have, a pitcher with mental challenges who makes the majors, sort of a modern day Rube Waddell but without the alcoholism; so any eccentric behavior is straight mental condition. In a way, one might say it's a cross between Rube Waddell and Harvey (film) —Preceding unsigned comment added by 209.244.187.155 (talk) 12:38, 3 October 2007 (UTC)

Richard Rhodes' fascinating book Why They Kill, while not addressing mental illness as such, spends on a good deal of time on Lonnie Athens' research into violent criminals' "internal community" of voices. --Sean 13:20, 3 October 2007 (UTC)

Another area to research might be Dissociative identity disorder, previously known as "Multiple Personality Disorder." It is a controversial diagnosis, but I am just offering it as another topic that might have some relevance. While fictional, Matt Ruff's excellent novel Set This House In Order contains a protagonist who is a "multiple" and there are depictions of two or more of his "alters" in conversation. Finally, I feel the need to mention that Elwood P. Dowd was a bit of souse, if not an alcoholic himself. --LarryMac | Talk 20:02, 3 October 2007 (UTC)

Thanks.209.244.30.221 13:55, 4 October 2007 (UTC)