Wikipedia:Reference desk/Archives/Science/2010 February 4

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February 4

Symmetry

I am trying to derive a set of equations for how physics would behave in two large spatial dimensions (as opposed to our universes 3), I am trying to restrict myself to arguments from symmetry. I have isolated quantum and hamiltonian mechanics as the obvious generators for the laws (and since neither specify a dimensionality I think I am at liberty to do so), but am struggling to get a foothold in. How does one construct a hamiltonian, for eg. electrodynamics, from symettery. I managed to get an argument that the lagrangian (which is trivially related to the hamiltonian) would be a function ${\mathcal {L}}={\mathcal {L}}({\dot {\mathbf {x} }},\mathbf {A} ,\phi )$ for the velocity, vector potential and scalar potential respectively. From speaking to people, they seemed to imply that finding canonical momentum was simple, am I missing the point, or have they just assumed that the conserved quantities are the same in 2+1D as 3+1D? —Preceding unsigned comment added by 129.67.39.49 (talk) 01:45, 4 February 2010 (UTC)

I saw an argument somewhere that gravity would not work in a two dimensional universe. You may look into that for a proof by counterexmaple that physics as we know it won't work in 2D. Unless you'r aiming for something like the holographic principle. In any case, you'r not really asking a question about the real world here. EverGreg (talk) 11:17, 4 February 2010 (UTC)

In the truly awesome book "Planiverse" by A.R.Dewdney (which is a work of fiction about a 2D universe) there is an extensive appendix comprised of comments from scientists who contributed to the book after discussion of it in Scientific American. In there they talk about a wide range of things that makes 2D universes at best very boring places. I don't have the book with me right now - and I don't recall the conclusions about gravity - but one of the things I recall is that atoms cannot form in a 2D universe. SteveBaker (talk) 11:27, 4 February 2010 (UTC)

While not directly answering your question, I'd assume you can take pretty much the same equations as in three dimensions. Notice that the magnetic field becomes 1D; the electric field stays 2D as does the vector potential. Cut off the last row and column from the electromagnetic tensor (and B_z becomes the one-dimensional B). Icek (talk) 17:57, 4 February 2010 (UTC)

Constraining 3D equations to 2D would not work, the most obvious change for example is that flux density would tail off at 1/r not 1/r^2. —Preceding unsigned comment added by 129.67.119.199 (talk) 14:25, 6 February 2010 (UTC)

Yes, but that's not a fundamental equation - the fundamental equation is one of Maxwell's equations, $\nabla \cdot D=\rho$. In 2 dimensions, the divergence of D is zero (as it has to in charge-free space) for a 1/r field, not a 1/r² field. Other problems with electromagnetism: Faraday's law of induction is valid in the sense of:

${\frac {\partial E_{x}}{\partial y}}-{\frac {\partial E_{y}}{\partial x}}=-{\frac {\partial B}{\partial t}}$

I think Ampère's law will work the following way:

$c^{2}{\begin{pmatrix}{\frac {\partial B}{\partial y}}\\{\frac {\partial B}{\partial x}}\end{pmatrix}}={\frac {1}{\varepsilon _{0}}}{\begin{pmatrix}j_{x}\\j_{y}\end{pmatrix}}+{\frac {\partial }{\partial t}}{\begin{pmatrix}E_{x}\\E_{y}\end{pmatrix}}$

-Icek (talk) 19:04, 6 February 2010 (UTC)

Well no, because maxwells equations are for 3D, 2D isnt just a world where we go; ok so everythings the same except d/dz=0. Thats why in my question I explained I was starting from hamiltonian dynamics, as it is derived independentally of the dimensionality of the system. Unfortunately I couldnt think of a watertight argument for what a hamiltonian would be. Obviously T+V is of no help as conservation of energy is an empirical law of physics. Symmetry seems to be the only thing I can claim, but obviously more is needed to set up a system of dynamical equations. —Preceding unsigned comment added by 129.67.116.242 (talk) 01:10, 7 February 2010 (UTC)

For a 2D version of the Dirac equation, you can use the Pauli matrices instead of Dirac's α_k and β, so there will be 2-component spinors instead of 4-component spinors. For the 2D version of the γ^μ Dirac matrices in the covariant form, one representation would be $\gamma ^{0}=\sigma _{z}={\begin{pmatrix}1&0\\0&-1\end{pmatrix}}$, $\gamma ^{1}=\sigma _{z}\cdot \sigma _{x}={\begin{pmatrix}0&1\\-1&0\end{pmatrix}}$, $\gamma ^{2}=\sigma _{z}\cdot \sigma _{y}={\begin{pmatrix}0&-i\\-i&0\end{pmatrix}}$ Icek (talk) 18:24, 4 February 2010 (UTC)

concentrated alpha particles?

Could alpha particles be concentrated enough by compression or supercooling to form a liquid, and what would its properties be if this state could be achieved, for example, would it destroy any matter it came in contact with like an acid, or have explosive properties?Trevor Loughlin (talk) 05:10, 4 February 2010 (UTC)

Alpha particles are nothing more nothing less than helium nuclei. Nothing fency about them. 68.56.16.165 (talk) 05:19, 4 February 2010 (UTC)

If you squished them together with enough force to overcome the electrostatic repulsion, then you'd probably have enough energy for Helium fusion. If you allowed them to recombine with electrons and form neutral atoms, then you'd have liquid helium, (not alpha particles). Nimur (talk) 06:22, 4 February 2010 (UTC)

If you concentrate alpha particles, the pressure will increase dramatically from electrostatic repulsion, so they will not form a liquid. The electrostatic energy of a single particle in a sphere (or some other shape) of alpha particles of a certain density is proportional to the number of particles to the power of 2/3, the total energy is proportional to the number of particles to the power of 5/3. As you see, the energy content increases faster than the number of particles at constant density. Icek (talk) 06:25, 4 February 2010 (UTC)

You'd have to mix in electrons, in which case you get a nice Bose–Einstein condensate of helium-4. EverGreg (talk) 11:40, 4 February 2010 (UTC)

I think that if you squash them together hard enough, you might get a substance made entirely of neutrons. I'm not an expert in this area, though. 24.23.197.43 (talk) 02:32, 7 February 2010 (UTC)

Experimenting with an 18V wall wort

Hi all,

This may be an odd question, but I'd like to know how risky it would be to use the output of an 18V (800 mA) DC transformer (connected to the wall through a grounded, fused strip) to power circuitry? If one were to cause, say, a short circuit, what's the worst that could happen? Blowing a fuse? Electrocuting oneself?

Thanks, — Sam 76.24.222.22 (talk) 12:23, 4 February 2010 (UTC)

An additional fuse or circuit breaker, that is a bit larger than the current you actually want to use, should be installed in series with the output of the DC supply. A short with no such fuse could damage the transformer. Since 120 V or 240 V (depending on your country) is present within the transformer, a damaged transformer could be quite dangerous. --Jc3s5h (talk) 15:43, 4 February 2010 (UTC)

See the article AC adapter. I assume you are asking about a "wall wart" ac-to-dc adapter which is more than just an ac-to-ac transformer. These devices are not well standardised but should have a Certification mark such as UL, CE, etc., etc. Check also that the adapter is labelled with the ac input voltage of your supply and the dc output voltage. You may have to find out the output polarity or fit a different output connector. You can use the adapter to power your circuits but there is no specification of the output regulation or ripple. It may not tolerate short circuits or more than the rated current (800 mA). Generally these adapters are sealed and have an internal fuse. They are not intended to be repaired. The certification mark is your best assurance that the dc output is properly isolated from the ac supply and cannot electrocute you.Cuddlyable3 (talk) 15:50, 4 February 2010 (UTC)

A lot of them are not true DC devices - they are often half-wave rectified AC, which is plenty good enough for things like charging batteries - but hopeless for driving "circuitry" in general. Even the ones that do full-wave rectification are not generally filtered well enough to give you a rock solid constant voltage. SteveBaker (talk) 22:52, 4 February 2010 (UTC)

One bad thing which could happen is that the internal fuse fails to protect against an overload (they are sometimes sensitive to short circuits but not prolonged overloads) and the device heats up and starts a fire. Edison (talk) 15:39, 5 February 2010 (UTC)

film versus HDTV

Which is the best, and what are the relative costs of buying or hiring 16 mm or 35 mm cine cameras, including developing and video transfer costs, compared HDTV or even UHDTV digital movie cameras such as Red? Dark scenes such as dimly lit musicians on stage seem OK on my semi-pro HDTV AVCHD video camera.But very bright beach scenes or sodium lamps shining on trees at night somehow seem to lack "atmosphere" despite plenty of detail. I cannot seem to find much cost information about film based movie cameras on the web.Trevor Loughlin (talk) 15:04, 4 February 2010 (UTC)

Could you please expand greatly on your question "which is the best"? It's impossible to answer without knowing a lot more about your budget and requirements. A film movie camera will be the best for many situations, and an HD video camera will be the best for many other situations. Tempshill (talk) 18:23, 4 February 2010 (UTC)

Wikipedia has articles on Comparison of movie cameras (film-based) and Professional video camera (digital) that may help. Since a film camera consumes filmstock only once while a video camera can reuse (overwrite) a recording medium many times it is impossible to compare overall developing and video transfer costs without knowing how much you plan to use the camera. The light from a Sodium-vapor lamp is monochromatic while human Color vision is trichromatic (our retinal cones have 3 different bandpass responses). Colour photography makes an imperfect emulation of human vision and it has no way to adapt to sodium lighting. Cuddlyable3 (talk) 01:55, 6 February 2010 (UTC)

Four-dimensional universe

What would a four-dimensional universe be like in terms of physics, chemsitry, biology, etc.? --J4\/4 <talk> 16:50, 4 February 2010 (UTC)

It is common to refer to our universe as being four-dimensional: length, width, height, and time. Physics easily works with time as a dimension. So, there is no change there. Chemicals change over time without a problem. Biological things age without a problem. So, I can't really see much of a difference from what we experience every day. -- kainaw™ 17:11, 4 February 2010 (UTC)

Our article, Fourth dimension, contradicts you in paragraph #3. Comet Tuttle (talk) 17:27, 4 February 2010 (UTC)

That paragraph contradicts itself. It needs to be better written to state whatever it is attempting to state. -- kainaw™ 17:58, 4 February 2010 (UTC)

maybe that paragraph has changed already, but what it means (meant?) is that time is not a fourth dimension in an euclidean space, but it is a fourth dimension in a Minkowski space, i.e. time is distinguishable from the other three dimensions. —Preceding unsigned comment added by 83.134.175.84 (talk) 18:13, 4 February 2010 (UTC)

So, a smart-ass answer to the original question would be: It will make Euclidean space look like Minkowski space. -- kainaw™ 18:44, 4 February 2010 (UTC)

That's like asking what a cat would be like if it was really a dog. For all intents and purposes, our three-dimensional universe is the only one that ever could exist, so any speculation beyond that is mere fluff. Vranak (talk) 17:53, 4 February 2010 (UTC)

I meant what a universe with four spatial dimensions would be like. I know that some people have done something similar with two dimensions, predicting what its physics, chemistry, biology, etc. would be like. --J4\/4 <talk> 19:57, 4 February 2010 (UTC)

Read flatland, and extrapolate (it's basically required reading for anyone speculating about more dimensions). I have a feeling that the world is 3d because it's the lowest practical number of dimensions - going higher is "cool", but not necessary for a universe to exist. The universe usually chooses the lowest energy for anything. (This is just speculation, I don't have specific arguments.) Ariel. (talk) 20:07, 4 February 2010 (UTC)

NO! Please don't read flatland - it's a terrible book that not only doesn't describe a 2D world at all well - but completely messes up the few things it does describe. It's also painfully sexist, classist, elitist and just about every other kind of 'ist'. Some people claim that's a satire on the sociology of the times...but it's still horrible to read. Read Planiverse instead - that's a superb book - it's very consistent, it has characters and plot and stuff - and even contains a comprehensive appendix that describes where they had to cheat on the physics to make a workable story. The drawings are a lot of fun - you can spend ages looking at the 2D steam engine to try to figure out how it works. SteveBaker (talk) 22:48, 4 February 2010 (UTC)

What, Flatland might corrupt the mind of J4V4, so he shouldn't read it? I agree that it's probably not the most scientifically grounded examination of worlds with a different number of dimensions, but it is an entertaining read. And it's more a commentary on Victorian society and culture, rather than its "sociology" (not sure if you intended that word or not). Buddy431 (talk) 00:23, 5 February 2010 (UTC)

I don't think it would corrupt anyone's mind - but it would severely disappoint anyone who is trying to understand what a 2D world might be like. If that's what you're trying to understand then reading flatland is just a total waste of your time. Planiverse, on the other hand, really makes you think - and gives you a real feeling for the difficulties of 2D. In flatland, men are geometrical figures - the lower classes of society have few sides (triangles and squares) - higher classes more - all the way up to the circles. Women on the other hand are like needles - effectively 2-sided - lower than the lowest of the low men. If this kind of thing feels kinda nasty...welcome to flatland. Planiverse, on the other hand explains how a being from that world can eat and poop without falling in half (think about that!) - how fluids can circulate within it's body. How it is impossible for them to make practical wheeled vehicles - but how it's easy to travel by balloon. What music sounds like - and how the instruments work. How wars can be fought when only one warrior can fight at a time. It's an amazingly clever book. So, yeah - if you're interested in struggling through a turgid, wincingly nasty Victorian diatribe - you need flatland. If you want to get your head stretched into thinking in 2D and have an actual plot with characters and stuff - get Planiverse. SteveBaker (talk) 02:51, 5 February 2010 (UTC)

Drifting waaay off topic, but: Steve, I recently re-read Flatland, and it's clearly a satire against the 'traditional Victorian values' of its time, not an affirmation of them. I agree that Planiverse is better in several ways, but that's partly because it's able to build on both the pioneering example of Flatland itself and on a century of further thinking on the topic - "on the shoulders of giants" and all that.

While we're making recommendations to J4V4, may I nominate The Fourth Dimension, a non-fictional work by Rudy Rucker, himself a Professor of Mathematics, a successful (Science Fiction) writer and a fan of Flatland's author. [/sercon litcrit]. 87.81.230.195 (talk) 10:04, 5 February 2010 (UTC)

I didn't get a satirical feel from flatland. It didn't seem to be making fun of the concept at all - it was all delivered with a perfectly straight face and seemed to go out of it's way to demean women. I knew it was claimed to be a satire before I read it...but I just couldn't see that in the book - it seemed to simply be promoting this view of the world. I've read "The Fourth Dimension" too - it's not bad - but I found it a little disappointing. I guess it didn't tell me anything I didn't already know - but it's probably a good introduction for someone who hasn't thought a lot about 4D already. One book to avoid like the plague is "Flatterland - a romance in many dimensions" which kinda claims to be a sequel to flatland or something like that. It delves into 0D, 1D, 2D and 4D worlds as well as universes with non-Euclidian geometries, etc. It ought to have been interesting - but it really wasn't. For example, in the 0D world, he explains that there is only one entity in the world and it is the king of 0D-land. Well, no! How can you have a thinking being in a literal singularity - how could its brain possibly work...it's kinda getting across the rough idea of a zero dimensional world - but not explaining how anything whatever could possibly exist in such a place. Bleaugh! Simply awful. SteveBaker (talk) 14:49, 5 February 2010 (UTC)

Good Lord! You thought Flatland was supposed to be serious? No wonder you didn't like it. Did you take Gulliver's Travels at face value to? 86.179.145.61 (talk) 16:56, 5 February 2010 (UTC)

I have to disagree with your interpretation of Flatterland as well. It's more looking at the mathematics of different types of spaces, rather than the scientific plausibility of them. J4V4 is clearly interested in the latter here, so I agree that it probably wouldn't be the best book to read. But if someone is interested in a lighthearted, and not-too-painful introduction to non-Euclidean geometry and other fun math topics, Flatterland is worthwhile to read. Buddy431 (talk) 00:31, 6 February 2010 (UTC)

The OP asks about 4 dimensions, not 1, 2 or 3. SteveBaker thank you for your book reviews, but how often must your faulty grammatical contractions such as "within it is body" be rebuffed before you allow yourself to conform to this aspect of the English language? In mitigation you have occasionally used it's = it is correctly, if rarely on your web site to which you sometimes link. Cuddlyable3 (talk) 19:30, 5 February 2010 (UTC)

You would have some difficulty tying your shoelaces. Gandalf61 (talk) 20:28, 4 February 2010 (UTC)

I read in one of the literary excerpts from the Portable Atheist (I forget who) an interesting theory by one of the characters. I don't know if it's really supported at all by evidence but three dimensions is supposedly the only space in which you can tie a knot and not have it just all back apart. And so by some convoluted logic that's the only dimension that a universe could start itself up in and survive. -Craig Pemberton 04:47, 5 February 2010 (UTC)

Mathematicians can measure things in a 4-dimensional universe by using Quaternions. Non-mathematicians may find it strange that a solid object can have a different shape depending on which direction you look at it. Here is a video. Cuddlyable3 (talk) 20:42, 4 February 2010 (UTC)

Computer graphics tech tends to represent everything in four dimensions (4x4 matrices) and uses affine geometry and homogeneous coordinates to move stuff around gracefully. You might have fun learning linear algebra and how it views the concept of dimension. Also, we have some nice animations of stuff like hypercubes and four dimensional simplicies. We have a page on the fourth dimension. A 0 simplex (point) has 0 borders. A 1 simplex (line) has 0 borders (points). A 2 simplex (triangle) has 3 borders (lines). A 3 simplex (tetrahedron) has 4 borders (triangles). A 4 simplex (pentachoron) has 5 borders (tetrahedra). Look carefully at the animation and you can count all five. -Craig Pemberton 21:18, 4 February 2010 (UTC)

We do use 4x4 matrices and affine geometry - but that's not to represent things in 4D - it's so we can compute the effects of visual perspective using a single matrix operation. Also, it's convenient to use the same 4D hardware to store RGB colors with an 'alpha' field to approximate translucency. But we're not generally doing 4D geometry. SteveBaker (talk) 22:48, 4 February 2010 (UTC)

Right. I literally meant that the representation is four dimensional. The thing modeled is probably going to be three or two dimensions.-Craig Pemberton 04:40, 5 February 2010 (UTC)

I recall reading that in a 4-dimensional universe, gravitational and electromagnetic forces would diminish with the cube of the distance. The inverse-square law becomes the inverse-cube law. This may present some problems for atoms, molecules and stable orbits for planets. Please correct me if I'm wrong. 78.176.30.155 (talk) 21:26, 4 February 2010 (UTC)

Yes, that's a reasonable assumption. Also, in 4D it's much harder to enclose a hyper-volume - so making things like plant and animal cells and tubes for containing liquids and gasses is harder because you need a greater amount of material to enclose whatever is inside. Think about drawing a 2D circle on paper - the actual outline is a tiny amount of 'stuff' compared to what's inside. But in 3D, with like a balloon, there is far more 'skin' required to hold in the contents. This gets worse in four spatial dimensions and upwards.

Indeed, while sealing eg. a 3D jar, you need to seal the 2D circle between the jar and its cap. But for a 2D 'jar' you only seal 2 points. For 4D, you'll need to seal a 3D volume. Btw, I asked another question about dimensions before, and interestingly Steve had bashed 'Flatland' back then! 78.176.30.155 (talk) 23:53, 4 February 2010 (UTC)

What about hypercube and Roman surface? ~AH1^(TCU) 02:19, 5 February 2010 (UTC)

Since no one has answered yet, I'll have a go. A 3D cube consists of 6 squares and has 12 edges. To create an air-tight cube, one must seal these edges, which are 1 dimensional lines (please disregard my previous post saying that sealing the jar needing a 2D circle etc, my bad). A hypercube consists of 8 3D cubes (cells) and these are connected by 24 2D faces that need to be sealed, which is harder to do. I don't know what to make of the Roman surface as I, a non-mathematician, can't grasp how it is constructed. It looks like a Klein bottle which has no volume, so what to seal? It is not a useful container anyway! Then again, someone who is much more knowledgeable (read: Steve) can maybe enlighten us on these matters. 78.176.30.155 (talk) 15:26, 5 February 2010 (UTC)

The Roman surface is a realizable 3-D object. It has a real volume divided into 3 similar compartments and it could therefore be constructed as a container. Its 9 edges are all concave. Cuddlyable3 (talk) 19:41, 5 February 2010 (UTC)

Given the length of this section, it's odd how few people have actually tried to answer the question... You can easily change the number of dimensions in our physical theories and see what happens, since it is just a parameter that is determined empirically. As has been mentioned above, all the inverse-square laws would become inverse-cube laws, and that does mess everything up. Under Newtonian gravity, there would be no stable orbits - objects would either spiral in or out (if you know basic calculus, you can go through the standard derivation of Kepler's laws from Newton's universal theory of gravity changing the square to a cube and see what happens, it's easy enough to see that, while the maths works fine, the results are completely different). Under General Relativity, it apparently gets even worse - gravity wouldn't be able to extend outside a solid object (I haven't seen that derived, though). Under Quantum Mechanics, we find that atoms can't form. We also find that light can't exist (you can have electromagnetism, but it can't propagate as waves). Basically, a universe with anything other than 3 spacial dimensions (and the same fundamental laws of physics as ours) would be very boring (the problems I've mentioned apply to higher dimensions than 4 as well, and there are also problems with fewer than 3 dimensions, some the same as those I've mentioned, some different) and life couldn't arise (so we can use the anthropic principle to explain the number of dimensions we observe). You could, of course, come up with different laws of physics which would give interesting results with other numbers of dimensions, but if you are allowed the change the laws of physics you can do almost anything! --Tango (talk) 15:29, 6 February 2010 (UTC)

cyanide poisoning or other deadly poisonous gases & residue

Greetings!

I am gathering data because I believe I am being poisoned via gas. Are gases likely to leave a residue in the filtration in my home? I have kept sources to submit but do not know if they are worthwhile in proving my case.

Also is there a source for submitting prescriptions to verify if they have been laced with poison?

Anyones input would be greatly appreciated.

Thanks! —Preceding unsigned comment added by Vickie Bragg (talk • contribs) 18:40, 4 February 2010 (UTC)

If you suspect that you are being poisoned, go see a doctor. If you suspect someone is trying to intentionally poison you, as it sounds like, also go to the police. Asking for information to anonymous people on a reference desk about this stuff is probably not a safe way to handle the situation. Falconus^{p t c} 18:53, 4 February 2010 (UTC)

Please call your doctor immediately to ask these questions. I agree with Falconus that researching this on the Internet is not going to help you at all. Comet Tuttle (talk) 18:58, 4 February 2010 (UTC)

For the non-medical part of your question - no, a gas won't leave a residue on your filters - precisely because it's a gas. If the suspected substance were an airborne powder (such as the spores of something nasty or a very finely ground chemical agent) or perhaps even very fine liquid droplets - then maybe it would. SteveBaker (talk) 22:33, 4 February 2010 (UTC)

That's not necessarily true. Depending on the filter and the gas you may get a chemical reaction, or even simple adsorption, that leaves behind some residue. Dragons flight (talk) 18:11, 5 February 2010 (UTC)

This is not medical advice but an observation on probabilities. Some symptoms have many possible causes (e.g., itching) and no single diagnosis stands out as more probable without far more details and sometimes testing or treatment trials. Other symptoms are so specifically characteristic and have such a narrow range of possible explanations that a single diagnosis is far more likely than all others. In western societies the fear that one is being deliberately poisoned repeatedly or chronically by gas is not all that rare and in nearly all cases indicates a very specific problem for which there is a treatment. Fears will not be allayed by poison testing. The advice: Please see a doctor and explain your fears and follow through with seeing the specialist she or he refers you to. Good luck. alteripse (talk) 00:03, 5 February 2010 (UTC)

Name That Beetle

My friend lives in Berkeley, California. She has been finding some of these beetles in her house. I think they might be devil's coach horses, but she thinks they're too narrow and not the right colour. They're not earwigs: they don't have the pincers. Does anyone know what they might be, and whether they pose any sort of threat? Marnanel (talk) 19:49, 4 February 2010 (UTC)

Someone else has suggested Jerusalem crickets. Marnanel (talk) 20:04, 4 February 2010 (UTC)

Looks like it could be, but it's hard to tell with that image and the coloration is normally a bit redder? Get a better image. Try using [bugguide.net] to key it. The website is highly effective. -Craig Pemberton 21:27, 4 February 2010 (UTC)

BTW, in order to be a beetle it needs to have elytra (the front wings which have been modified into shields for the back wings). The scientific name for beetle is "coleoptera" which literally means "wing cover". So if you think it's a beetle look for them to make sure. -Craig Pemberton 04:53, 5 February 2010 (UTC)

Unless they only have a half-cover, in which case they are Hemiptera or true bugs. Also, the Devil's Coach Horse IS a beetle but flightless, and only has little residual wings and wing-cases that aren't really obvious. Alansplodge (talk) 16:21, 5 February 2010 (UTC)

I am reasonably certain that that is a Jerusalem cricket, not a beetle, and certainly not a rove beetle. Jerusalem crickets often wander into houses in California.--Eriastrum (talk) 18:52, 6 February 2010 (UTC)

Right hand exposed to gel extraction's UV ray for 2 minutes non-stop.

While having green UV ray on, I cut a gel using a blade with my bare right hand. I later found out that my hand for holding the blade and being exposed to UV during cutting the gel should be worn a glove. How serious of a damage might have this caused? —Preceding unsigned comment added by 142.58.43.215 (talk) 19:51, 4 February 2010 (UTC)

This is medical advice, which is against policy to answer here on Wikipedia. If you are concerned about it, the only advice that we are allowed to give is to consult a doctor or other medical professional. Sorry about that! Falconus^{p t c} 19:54, 4 February 2010 (UTC)

That's right; you are asking a bunch of anonymous people on the Internet; we cannot possibly give an accurate diagnosis. Please call your doctor. Comet Tuttle (talk) 20:03, 4 February 2010 (UTC)

Nonsense removed - Nimur (talk) 22:13, 4 February 2010 (UTC)

One question, how is a UV ray green? I thought UV was invisible or maybe purple? Googlemeister (talk) 22:04, 4 February 2010 (UTC)

Likely a secondary green light to indicate visually whether the UV light is on or not. Ginogrz (talk) 22:08, 4 February 2010 (UTC)

Or it may just be part of the spectra for whatever compound they use to create UV light (e.g., it radiates in green visible light and in UV, and possibly other energies such as infra-red - does the light feel warm?) --Ludwigs2 23:11, 4 February 2010 (UTC)

The types of damage that can be caused by ultraviolet light are well known, but to find out what may have happened in your particular case, you should talk to your local workplace safety officer or a doctor. --Carnildo (talk) 01:12, 5 February 2010 (UTC)

Incidently, I'd caution against using a bare hand for cutting a gel, especially if it's stained with ethidium bromide, which can cause heritable mutations. Use nitrile gloves; apparently the EtBr can get through latex. Other dyes (e.g. SYBR Green I) are also toxic, even if less so than EtBr. -- Flyguy649 ^talk 05:05, 5 February 2010 (UTC)

If you do talk to an outside doctor, you'll probably want to first figure out the type of light source, its power, and its wavelength spectrum. UV refers a large range of wavelengths and the potential hazard can differ by orders of magnitude depending of the particular wavelengths involved. A local safety officer might be able to tell you more, since he may already be familiar with the equipment and its hazards. Dragons flight (talk) 05:43, 5 February 2010 (UTC)

[Removed medical advice. 86.179.145.61 (talk) 13:57, 5 February 2010 (UTC)]

I must say that if you ask the typical MD about some physics question like the health effects of exposure to some particular UV wavelength at some intensity for some time, you might get a blank stare. Unlike TV shows would indicate, they are not all experts in every branch of science. Edison (talk) 15:36, 5 February 2010 (UTC)

What's the power rating of the UV source? If it's a relatively low-power UV lamp for fluorescence observations (like we use in our lab to check TLC plates), then you'll be fine -- we don't have to wear gloves or anything when marking the plates. If it's a higher-powered source, sunburn might happen on prolonged exposure -- but unless it's a very high-power source, a two-minute exposure prob'ly won't cause any harmful effects. The reason for wearing gloves was probly because of toxic/irritating chemicals involved, rather than UV exposure. FWiW 24.23.197.43 (talk) 02:52, 7 February 2010 (UTC)

life possible on other gas giant moons

Is this possible Callisto and Ganymede also have ocean underneath the black icy surface. And Encladeous the whitest moon on Saturn the artlce also said they have a ocena beneath the surface. Did any of article said Europa once had ocean without ice, if the information I had is original sorce.--209.129.85.4 (talk) 20:56, 4 February 2010 (UTC)

Speaking speculatively, life is possible on any number of bodies in the solar system. All that's required (even with the restrictive presumptions of terrestrial life) is trace amounts of liquid water as a medium and sufficient access to 'organic' compounds that could serve as building blocks for cellular processes, and those are fairly widespread in the system. However, no one has any idea what the necessary (much less sufficient) conditions for the commencement of life are - we can't even really define when more or less normal chemical reactions transform into more or less stable self-replicating chemical reactions (which is maybe the minimal quality that any living thing needs to have). --Ludwigs2 23:07, 4 February 2010 (UTC)

You must add to this that Life could be of a diffrent form than Organic life. It maybe a case were life is of Gas or any compound/substance it is just our understanding of Organic life that we currently refer to.Chromagnum (talk) 07:02, 7 February 2010 (UTC)

Where does the momentum go when I put on the breaks?

If I understand the conservation laws correctly, momentum is always conserved but kinetic energy can easily be lost when it is converted to other forms of energy. So when I am traveling along in my car and apply the breaks, I understand that the kinetic energy of the system (my car and everything in it) has been converted to heat (which is just undirected kinetic energy of the breakpad molecules, right?). Where did the momentum go? Isn't it an internal force that caused me to stop? Or was it an external force exerted by the earth? If I measured the earths momentum with arbitrary precision would I find the car's momentum had been transferred to the Earth? Thanks 128.223.131.109 (talk) 21:36, 4 February 2010 (UTC)

Hitting your brakes makes your wheels stop rotating. If you were floating in your car, they would stop rotating and your momentum would not change. You are focusing on the relationship between the road and the tires. The car has forward momentum. The tires try to move with the car (without rotating). The friction between the tires and the road tries to keep the tires and road as one body. Therefore, the car is trying to pull the road. The road pulls back with an equal and opposite force (assuming you don't start skidding). That is an instantaneous stop. For a slow stop, it is the same. Car pulls on wheels which pulls on road and road pulls back. Interestingly, busy intersections with stop lights often have rippled roads, cause by many vehicles stopping (pulling) on the pavement. -- kainaw™ 21:43, 4 February 2010 (UTC)

The momentum goes into individual atoms in the road, air, brakes, chassis, etc (heat). Also slightly into the rotation and momentum of the planet but such effects are swamped by the size of the Earth. And your acceleration would tend to cancel the effects of your deceleration. -Craig Pemberton 22:04, 4 February 2010 (UTC)

The momentum doesn't become heat; heat is more or less defined as molecular motion (kinetic energy) without (net) momentum. It's very quickly correct to say that the momentum is entirely sunk in the (rest of the) planet's net rotation (speeding it up or slowing it down, or turning its axis of rotation). --Tardis (talk) 23:10, 4 February 2010 (UTC)

Yes, that's right. Craig was thinking of the kinetic energy, not the momentum. --Anonymous, 02:02 UTC, February 5, 2010.

You are literally changing the rotation speed of the Earth. But because the mass of your car is utterly microscopic compared to the mass of the planet - the effect is too small to measure. Also, when you first speeded up, you altered the rotation speed of the planet in the opposite direction - so the net result is zero. There have been numerous uses of this for joke purposes - the Car Talk show on NPR advocated that everyone should live to east (or was it to the west?) of where they work so that the combined effect of commuters speeding up as they leave home and slowing down when they get to work would shorten the working day. (Yes, it's silly). SteveBaker (talk) 22:24, 4 February 2010 (UTC)

I have pondered this while driving more than a few times (Ohio roads are notoriously boring.) Say that if you take your car, accelerate in a straight line (pushing off on the planet) to get up to 60mph, then apply the brakes (grabbing onto the planet) until you stop, where exactly does all the energy come from/go to along the way? You accelerate using fuel, to increase the net difference in momentum between you and the planet. That makes sense. You stop by using your brakes, but what determines the relationship between heat generated through friction, and momentum exchange with the planet? Do you have to give back 100% of the momentum you took from the planet? If so, where does the heat come from (since we are 'conserving' energy)? --Jmeden2000 (talk) 14:09, 5 February 2010 (UTC)

You are getting confused between conservation of momentum and conservation of energy. Both things are perfectly conserved - but separately. Momentum is conserved because the planet is being slowed down or speeded up in the opposite direction to motion of your car. Energy is conserved because chemical energy in the gasoline is turned first into the kinetic energy of the car (as you accelerate) and then as you brake, the kinetic energy turns into heat in your tyres, in the road and in your brake disks/drums/pads. Eventually, that heat dissipates into the ground and into the atmosphere - and (because both are gigantic) ends up making very little difference to the overall temperature of the world. Both things are conserved but in totally unrelated ways. SteveBaker (talk) 14:28, 5 February 2010 (UTC)

So it is correct to say that 100% of the energy put into your car during acceleration (stored as a difference of momentum) is returned in the form of heat or other energy dissipated by your brakes? So, no material 'efficiency' is employed in determining how much heat energy your brakes need to dissipate, since it all has to go out this way? --Jmeden2000 (talk) 14:41, 5 February 2010 (UTC)

Nearly 100% yes. On a flat road your car would eventually stop without using the brakes because its kinetic energy is slowly dissipated in air resistance and rolling resistance (see article). Cuddlyable3 (talk) 19:57, 5 February 2010 (UTC)

Yeah - it all ends up as heat - but not necessarily in the brakes. The air resistance results in the air heating up, other internal bits of the car will get warm, some energy will go into distorting (and then heating) the tires and the springs and the oil in the shock absorbers. Some of it even winds up being absorbed by stretching the material in your seat belts. But the VAST majority of the energy ends up in the brakes. The only way it wouldn't would be if you started off at the bottom of a valley and drove to the top of a nearby hill and stopped at the top. In that case, some of the energy would wind up in the gravitational potential energy of your car...but as soon as you drive down the other side and stop again, that too has turned into heat. It's worth remembering that when you consume gasoline getting your car up to 70mph and then use your brakes to stop from high speed, the heat generated in the brake disks is about the same as if you poured the same amount of gasoline on them and set fire to them in some confined space!! Little wonder then that the brake disks of race-cars often end up glowing cherry-red by the end of the race - and failing to down-shift as you drive down a long hill can overheat your brakes to the point where the brake fluid boils and the brake disks warp from the heat! SteveBaker (talk) 23:14, 5 February 2010 (UTC)