question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I came across this paper recently called <a href="http://arxiv.org/abs/1009.1136v1" rel="nofollow">The Small Scale Structure of Spacetime</a> and the following idea occured to me:</p>
<p>To uninformed humans the universe appears Euclidean but we know from GR that on a larger scale it behaves like a Riemannian manif... | g12118 | [
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<p>Can Einstein's equations in vacuum $R_{ab} - \frac{1}{2}Rg_{ab} + \Lambda g_{ab}= 0$ be treated as a Dirichlet problem?</p>
<p>I am thinking of something along those lines:
Consider a compact manifold $M$ with boundary $\partial M$. For a given metric $g_{ab}$ on $\partial M$, does a unique (up to diffeomorphisms) ... | g12119 | [
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<p><strong>The given state</strong>:<br/>
Let $\psi$ be a wave that passes from medium $a$ to medium $b$.<br/>
Let $A$ be the amplitude of $\psi$.<br/>
Let $R$ be the amplitude ratio of the reflected wave $\psi_r$ and the original one, and $T$ the amplitude ratio of the transmitted wave $\psi_t$ and the original one.<b... | g12120 | [
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<p>In an episode of Discovery's Curiosity with host Stephen Hawking, he claims the Big Bang event can be explained from physics alone, and does not require the intervention of a creator. </p>
<p>1) His argument is based on that, in the beginning, the universe is an equivalent of a black hole behaving as a quantum mech... | g12121 | [
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<p>I am not into all the tech details of communication via RF with implant chips (tracking chips) and so would like to ask how the known atmospheric pertubations of shortwave radio affect the distances over which one can closely and continuously track an animal with an implanted chip (e.g. a chip transmitting physiolog... | g12122 | [
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<p>More specifically, how does a wave-particle duality differ from a quasiparticle/collective excitation?</p>
<p>What makes a photon a gauge boson and a phonon a Nambu–Goldstone boson?</p> | g12123 | [
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<p>Power is known to be equal to the force x velocity (P=FV).</p>
<p>Im solving a question that states the following :</p>
<p>Car with engine working at 32 kW, mass of 1 tonne, travels at a constant speed of 40m/s along a level road.</p>
<p><strong>Given that the resistance to motion is directly proportional to the ... | g12124 | [
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<p>A 50.0 g Super Ball traveling at 25.0 m/s bounces off a brick wall and rebounds at 22.0 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 3.50 ms, what is the magnitude of the average acceleration of the ball during this time interval?</p>
<p>I am using the equation Aavg = (Vf... | g12125 | [
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<p>1) What does the <a href="http://en.wikipedia.org/wiki/Electric_potential" rel="nofollow">electric potential</a> at a point <em>exactly</em> mean? My teacher tells me that current flows from higher potential to lower potential but when I ask him the reason, he fails to give me a convincing answer. </p>
<p>2) And ca... | g12126 | [
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<p>We live in a dark world, and the light is results of big bang.
The world is really made mostly of <a href="http://en.wikipedia.org/wiki/Dark_matter" rel="nofollow">dark matter</a> and <a href="http://en.wikipedia.org/wiki/Dark_energy" rel="nofollow">dark energy</a>?
Why the world is so deep and dark?</p>
<p><img s... | g12127 | [
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<p><img src="http://i.stack.imgur.com/neYV0.jpg" alt="enter image description here"><br>
I'm doing independent studies on electron-positron scattering, specifically the annihilation diagram contribution to the M matrix in Bhabha scattering, and this is the equation I recovered with the following initial conditions: An ... | g12128 | [
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<p>For example there are anti-particles to every particle we know, <p>
Similary in some sense, is there a possibility that we can charge photons..if not what are the reasons and has there been any attempt to do this experiment ? If it is possible to bend it than why not charge ?</p> | g12129 | [
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<p>I'm working in Taylor and Wheeler's "Exploring Black Holes" and on p.2-14 they use two honorary constants: Newton's constant divided by the speed of light squared e.g. $G/c^2$ as a term to convert mass measured in $kg$ to distance. </p>
<p>Without doing the arithmetic here, the "length" of the Earth is 0.444 cm; an... | g12130 | [
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<p>I have a 2D flow velocity field $\bar{V} = y^2\hat{i} + 2\hat{j}$. I'd like to find the equations for the streamlines and pathlines. Since $\bar{V}$ has 0 time derivative, the flow is steady, and so the equations for the streamlines should be identica, right?</p>
<p>Streamlines:
$$\left. \frac{dy}{dx} \right)_{stre... | g12131 | [
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<p>Does polarized light interfere?</p> | g12132 | [
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<p>Is it possible that if you have 2 ultraviolet lasers, that are invisible to the human eye, and if you aim their beams to intersect at some point, that the place of intersection will show a lower visible wavelength of light, caused by interference of the light freqency? Can any other form of heat or energy be genera... | g12133 | [
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<p>Let us take the standard QED ($e^-, e^+, \gamma$) as a model of QFT and ask what is its "short-distance" physics? </p>
<p>They say the UV infinities appear because we do not know the real physics of short distances and initially we introduce it wrong. OK, but after renormalizations, what physics does remain? Do we ... | g12134 | [
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<p>When a droplet is deposited on a surface with some surface roughness and subsequently tilted it can stick due to pinning (think of droplets on a window after rain).</p>
<p>What I am interested in is how/whether I can show that all the potential energy from tilting the droplet is converted in surface energy needed f... | g12135 | [
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<p>Given is a mechanical multiple degree of freedom system described by the following matrices and equation:</p>
<ul>
<li><p>mass matrix ${\bf{m}} = \left[\begin{matrix} m & 0 & 0 \\ 0 & m & 0 \\ 0 & 0 & m/2 \end{matrix}\right]$,</p></li>
<li><p>stiffness matrix ${\bf{k}} = \left[\begin{matrix}... | g12136 | [
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<p>I assume that all mass-objects curve time-space but the curvature is only measurable with celestial bodies large enough to be significant gravity-wells.
What you call "curvature" seems to me to be only a graphic representation-- a map-- of the varying thickness of time-space, a curve which being continuous can be re... | g12137 | [
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<p>I wrote a simple android app that shows the magnetic field(using the magnetic field sensor in the phone) in the current location. </p>
<p>When I place a two inch steel screw on the top of the phone (which is running the app), there is a change in magnetic field for a while. I'm guessing that it's due to the induced... | g12138 | [
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<p>This is a sample test question I've encountered twice in some practice chemistry finals. I'm a little bit confused about what it's asking. </p>
<blockquote>
<p>You are conducting an experiment on the photoelectric effect, and
observe that, at a certain frequency and intensity of light, no current flows. Accordi... | g12139 | [
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<p>I am considering a Lagrangian that is of the following form:
$$\mathcal{L}=-{1\over 2}\partial_\mu\phi\partial^\mu\phi+2\mu^2\phi^2+2\sqrt{6}{\mu^3\over \lambda}\phi + {9\mu^4\over 2\lambda} + \text{interactions}$$
Now, I am unsure what to do with a the term that is proportional to $\phi$: I think I heard at some po... | g12140 | [
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<p>I read somewhere that the earth has to be smaller than 1 cm to become a black hole, according to Schwarzschild. Since big bang came from a singularity, I am wondering, is there any minimum volume for anything? </p> | g12141 | [
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<p>Suppose that there is a quantity in Heisenberg picture as the following:</p>
<p>$A=u_1\Sigma_1 + u_2\Sigma_2 +u_3\Sigma_3$</p>
<p>I am not sure why $u_1,u_2,u_3$ is normalized to be ${u_1}^2 + {u_2}^2 + {u_3}^2 =1$. (The matrices $\Sigma$ are the Pauli matrices.) </p> | g12142 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/37571/formulas-for-compressibility-of-solids">Formulas for compressibility of solids</a> </p>
</blockquote>
<p>I have a question which is technically a physics question, but since I have yet to find a go... | g387 | [
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<p>My apologies for such a basic question--I am a musician, not a physicist. But I cannot anywhere find the word, if one exists, that describes that elegant pause of an object such as a ball, thrown straight up, as it reaches the apex of its trajectory's power and before it obeys the power of gravity commanding it to e... | g12143 | [
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<p>I am not sure if anyone has ever researched this but I am curious about underground reservoirs of natural gas and plate tectonics. Specifically, as the Earth's crust gets pulled down to the mantle do pockets of natural gas get ignited and explode? Or do these pockets of gas get pushed to the surface or further back ... | g12144 | [
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<p>I know this conclusion in topological order for a while: "the topological degeneracy on torus is equal to the number of quasiparticles types."</p>
<p>But can anyone give a physical argument that supports this conclusion?
Especially in Non-Abelian case.</p> | g12145 | [
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<p>A solid right cylinder of rock core is surrounded by four rods made of mild steel (all-thread rods). The rods are placed equidistantly around the core in a square formation. The tops and bottoms of the four rods are fixed to the top and bottom rigid plates, but the rock is just fitted snugly between the top and bott... | g12146 | [
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<p>This problem is about color science and it is short but tricky: Where do you get $I_p=\frac{P}{4 \pi r^2} sin \alpha$, where $I_p$ is radiant intensity(color science: radiometric quantities). Look at the link( exercise 2 a)): <a href="http://cs.joensuu.fi/~ot14/vo/IMG.jpg" rel="nofollow">http://cs.joensuu.fi/~ot14/v... | g12147 | [
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-0.009162668138742447,
0.0700947493314743,
-0.025101041421294212,
... |
<p>Is there any way to survive solarwinter like in Sunshine - movie?
Solar winter is where for some reason sun looses its capasity to produce radiation( heat etc.). It doesn't loose everything but some of its radiation energy( say 50 %) That causes earth to cool down causing next "ice age"</p> | g12148 | [
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<p>Having only really known two designs for paper airplanes since my days as a child, one which flies about eight feet and another which flies about ten feet, I have always wondered how people manage to come up with designs that are able to fly much, much further than that. Clearly, these have no propulsion after their... | g12149 | [
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<p>Can there be a charge configuration in space such that at any instant of time I can change the electric field at one and only one point?</p> | g12150 | [
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<p>I have been trying for hours and cannot figure it out. I am not asking anyone to do it for me, but to understand how to proceed. </p>
<p>We have the relations
$$[L_i,p_j] ~=~ i\hbar\; \epsilon_{ijk}p_k,$$
$$[L_i,r_j] ~=~ i\hbar\; \epsilon_{ijk}r_k,$$
$$[L_i,L_j] ~=~ i\hbar\; \epsilon_{ijk}L_k.$$</p>
<p>Now I a... | g12151 | [
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<p>Browsing Quora, I saw the following <a href="http://www.quora.com/Particle-Physics/Is-a-hard-drive-heavier-by-an-incredibly-tiny-amount-when-its-full-What-about-flash-memory">question</a> with contradicting answers.</p>
<p>For the <a href="http://www.quora.com/Particle-Physics/Is-a-hard-drive-heavier-by-an-incredib... | g442 | [
0.08943050354719162,
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<p>A light modifier that is commonly used in studio photography is a honeycomb grid. </p>
<p>It narrows the beam of light to a circle with soft edges, as it can be seen <a href="http://www.honeycombgrids.com/info/grid-diffusion-patterns" rel="nofollow">here</a>:</p>
<p>My question is: how is this happening? </p>
<... | g12152 | [
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<p>Given a certain running pace uphill, I want to be able to determine an equivalent pace running with no elevation change. Assumptions: similar effort in both cases (say for example running at 90% max heart rate), ignore wind, slope is constant for simplicity, ignore physiological and bio-mechanical factors, weight of... | g12153 | [
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<p>I was discussing the reason why we see beating from a Michelson interferometer, and one of my friend said it 's because the light have different frequencies, therefore, they would be out of phase.</p>
<p>But my argument is, Because two frequencies travel at the same speed, their phase difference remain the same. Bu... | g12154 | [
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<p>The statement of the time-reversal invariance of Maxwell's electromagnetism, as I understand it, is the following.</p>
<p>Given $\mathbf{E}(\mathbf{r},t)$ and $\mathbf{B}(\mathbf{r},t)$ that satisfy all Maxwell's equations (with $\mathbf{J}(\mathbf{r},t)$ and $\rho(\mathbf{r},t)$) and the boundary conditions, then ... | g12155 | [
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<p>Consider the well known demonstration of diffraction by a narrowing slit.
(See for example the demonstration at the 30 minute mark of <a href="http://ocw.mit.edu/high-school/physics/physical-optics/interference-diffraction/" rel="nofollow">this lecture</a> at MIT by Walter Lewin)</p>
<p>It is my (possibly mistaken)... | g12156 | [
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<p>A while ago, <a href="http://arxiv.org/abs/0802.2041v1" rel="nofollow">there was some conspicuous evidence that supermassive black holes didn't seem to be eating dark matter at the expected rate of 70%-30%, in fact, only 10% of the black hole mass increase could in principle be attributed to non-baryonic mass</a>.</... | g12157 | [
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<p>I have been told (not sure if it is true), that mirror (and glass) do not allow to pass the electromagnetic signals of mobile signals. </p>
<p>but for a standard mirror what type of wave can pass through it? </p>
<p>thanks</p> | g12158 | [
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<p>I'm trying to make a program that simulates shadows in a 2D environment and I need some help in determining how things should look.</p>
<p>For example, if my light source is red and the illuminated object is blue (only radiates light in the blue frequency), how should it look when I shine red light on it?</p>
<p>H... | g12159 | [
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<p>I am curious what the electric and magnetic field's of light look like when time is stopped. A "photograph" or illustration/description of these fields at a moment in time is what I desire. </p>
<p>Also, does the picture change at various points in the wave?</p>
<p>I assume that <a href="http://physics.stackexchan... | g12160 | [
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<p>I heard on a podcast recently that the <a href="http://en.wikipedia.org/wiki/Supermassive_black_hole" rel="nofollow">supermassive black holes</a> at the centre of some galaxies could have densities less than water, so in theory, they could float on the substance they were gobbling up... can someone explain how somet... | g12161 | [
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<p>Does gravity effect the "sphericalness" of the Coulomb force?</p>
<p>For example, is the field 1 meter above a charge weaker than the field 1 meter below the charge?</p>
<p>Could a 0.014% difference in the field be detected?</p>
<p>Have there been any such experiments run?</p>
<p><strong>Edit:</strong></p>
<p>I... | g12162 | [
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<p>In the electron double slit experiment, why is it not, in principle, possible to know which slit the electron went through by the electron's effect on the surrounding EM field? As the electron travels, it would disturb the field, and presumably this disturbance measured at a point far from the experiment would be s... | g12163 | [
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<p>I'm very new to the topic of surface plasmons and I have been reading about different methods of exciting them. There is one method in which a prism is set up to allow phase matching of an incident light ray to the required wave vector for exciting a surface plasmon. The light goes through total internal reflection ... | g12164 | [
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<p>This question has been bugging me for a while now. I am not sure this is the correct forum to ask, please close if it is not the right forum.</p>
<p>Lets say a bus is traveling at $60\: \mathrm{km/h}$ and there is a mosquito flying inside the bus. Since the mosquito's speed is considerably less than that of the bus... | g12165 | [
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<p>I've got to teach the concepts of "Electric Potential" & "Potential Energy" to 10th grade students. I don't understand how to express these things and make them understand.</p>
<blockquote>
<p>“If you can't explain it simply, you don't understand it well enough” ~ Albert Einstein</p>
</blockquote>
<p>Probab... | g12166 | [
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<p>If the space of universe is expanding at fast rates..(even faster than light)</p>
<p>Why we do not see the trace of the stars?</p>
<p>A possible answer could be that the stars are only moving away but mantaining in geodesic respect earth and each other, that is strange, in a 2D model of an inflating balloon with d... | g12167 | [
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<p>What are the real dates that are represented in the figure 10, page 17, in the <a href="http://static.arxiv.org/pdf/1109.4897.pdf" rel="nofollow">OpERA paper</a> </p>
<p>Imo the X axis labels are inconclusive, or absent. </p>
<p>(in the investigation of a crime it is relevant the place and the time of the even... | g12168 | [
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<p>On damnlol.com, I came across this picture:</p>
<p><img src="http://i.stack.imgur.com/Bwxxl.jpg" alt="enter image description here"></p>
<p><a href="http://www.damnlol.com/hello-god-i-have-a-fault-to-report-7549.html" rel="nofollow">http://www.damnlol.com/hello-god-i-have-a-fault-to-report-7549.html</a></p>
<p>My... | g12169 | [
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0... |
<p>I know the basics, that by measuring how much x-ray signal reaches each 'pixel' on the receiver we can measure how much has been absorbed. But this gives only a single channel of information, e.g a greyscale image.
However I'm sure I've seen images where there are opaque white parts (bones) and opaque black parts (m... | g12170 | [
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<ol>
<li><p>What are <a href="http://en.wikipedia.org/wiki/Lagrangian_point" rel="nofollow">Lagrange points</a> in gravitation fields? </p></li>
<li><p>Additionally, what are their properties? For example, if a satellite or asteroid rested at a Lagrange-point.</p></li>
</ol> | g12171 | [
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<blockquote>
<p>There are m*n identical cells of emf E and internal resistance r connected in parallel rows. This combination of cells is connected across an external resistance R. For what arrangement of the cells will the current through R be maximum?</p>
</blockquote>
<p>I don't understand when the current will b... | g12172 | [
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<p>In an alternating current, how are frequency, voltage, amperage, and watts related?</p>
<p>For instance, imagining the power as a sine wave, what is amperage if voltage is the amplitude? Is there a better analogy than a sine wave?</p>
<p>EDIT: One of the things I specifically wanted to know is whether frequency a... | g12173 | [
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<p>Lets deal with wave propagation in a cylindrical duct. </p>
<p>We ask the question: "what is the general form of a pressure wave which can propagate through the duct?" In answering this, we assume that the pressure wave in question has harmonic time dependence, i.e. $\exp(i\omega t)$ dependence.</p>
<p>The critica... | g12174 | [
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<blockquote>
<p>Water, dripping at a constant rate from a faucet, falls to the ground. At any instant there are
many drops in the air between the faucet and the ground. Where does the center of mass of
the drops lie relative to the halfway point between the faucet and the ground? (a) Above it
(b) Below it (c) E... | g12175 | [
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<p>Can anyone explain how photogenerated current in the base gets amplified in a <a href="http://www.google.com/search?as_q=phototransistor" rel="nofollow">phototransistor</a>.
If you use band energy diagram, then I would understand more quickly and clearly.</p>
<p><img src="http://i.stack.imgur.com/Bljdo.png" alt="e... | g12176 | [
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-0.... |
<p>If a wave packet is given by: </p>
<p><img src="http://i.stack.imgur.com/AItyP.jpg" alt="enter image description here"></p>
<p>My question is basically how do we choose the write $A(k)$ to fit the particle we are looking at, or does it not matter (as my matter as my textbook seems to imply) which seems counterintu... | g12177 | [
0.046855613589286804,
0.023683641105890274,
0.003906880505383015,
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0.07714812457561493,
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0.026400061324238777,
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-0.026019984856247902,
0.046711623668670654,
0.028735745698213577,
0.06399355083703995,
0.04... |
<p>How exactly is the <a href="http://en.wikipedia.org/wiki/Weyl_tensor" rel="nofollow">Weyl tensor</a> is connected with information about <a href="http://en.wikipedia.org/wiki/Gravitational_wave" rel="nofollow">gravitational waves</a>? And what are physical reasons for that?</p> | g12178 | [
0.01247072871774435,
0.0861925259232521,
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0.013807... |
<p>I am trying to follow a book (Introduction to Ligand Field Theory by Ballhausen in 1962 on pg 15), but it isn't clear how they make a particular leap.</p>
<p><strong>Background</strong>
I want to find the wave function for the term $^1 D$. We know that $\psi(L,M_L,S,M_S) = \psi (2,2,0,0)$ is made up of three micro ... | g12179 | [
0.016195934265851974,
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0.015982061624526978,
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0.02079560048878193,
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0.028813673183321953,
-0.05395185947418213,
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0.07013405859470367,
0.05583121255040169,
-0.06... |
<p>This question was prompted by <a href="http://physics.stackexchange.com/questions/79054/can-matter-really-fall-through-an-event-horizon">Can matter really fall through an event horizon?</a>. Notoriously, if you calculate the Schwarzschild coordinate time for anything, matter or light, to reach the event horizon the ... | g12180 | [
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0.009808647446334362,
0.02346074767410755,
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0... |
<p>This is a question I've had a while about quantum theory.</p>
<p>Many times when I look at books and equations about this subject matter I see that the use many concepts in probability. (Correct me if Im wrong) Like how the movement of atom can be modeled using probability distributions. So I was wondering when phy... | g12181 | [
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<p>I would like to do a calculation of an expanding balloon represented by a triangular spring-damper mesh system. Also the behavior of the balloon when it is put in a container, where its shape conform to the shape of the container while expanding. Can anybody point me to any studies being done?</p> | g12182 | [
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0.0655367448925972,
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<p>The common perception regarding what happens when two objects of equal sizes but unequal mass are allowed to fall freely towards the ground is that - both the objects make contact with the ground at the same instant.</p>
<p>This is attributed to the fact that the acceleration of both the objects towards the earth a... | g12183 | [
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0.021687... |
<p><a href="http://en.wikipedia.org/wiki/Quantum_electrodynamics" rel="nofollow">Quantum electrodynamics</a> (QED) is the relativistic quantum field theory of electrodynamics that is the first theory where full agreement between quantum mechanics, special relativity and electrodynamics is achieved.</p>
<ul>
<li>What i... | g12184 | [
0.03400467336177826,
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<p>In the following lecture, starting at minute 29:00 and going further, the professor resolves the Twin Paradox using Lorentz velocity addition. I have a question about this:</p>
<p>Isn't the figure given below (taken from a slide in the lecture, at time 37:50) referring to the case where there is an independent obje... | g12185 | [
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0.03991810232400894,
0.001... |
<p>What exactly is a lepton number of a particle? With the charge (eg proton is just 1, not the exact charge), I can understand because it's a physical property, put a particle with charge + next to another particle with charge + and they will repel.
What is the lepton number in similar terms? Or is it just a conventi... | g12186 | [
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0.0... |
<p>The rate of change of magnetic flux through a surface (open) is related with the line integral over the closed loop binding the selected surface by one of the Maxwell's equation. But that means even if a changing magnetic flux is present anywhere on the surface such that the electric and magnetic field at the chosen... | g12187 | [
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0.014140... |
<p>I have some questions about renormalization. To my understanding, in order to deal with infinities that appear in loop integrals, one introduces some kind of regulator (eg, high momentum cutoff, taking $d\to d+\epsilon$, etc.) so that we get a finite answer, which blows up as we remove the regulator. Then we renor... | g12188 | [
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0.009536005556583405,
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... |
<p>In many countries, solar panels are heavily subsidized because they replace fossil fuels that apparently cause global warming. A mirror of the same size would - through a completely different effect - also reduce some global warming by reducing the solar energy reaching the earth. Considering that mirrors are much c... | g12189 | [
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0.028... |
<p>Are there any interesting, important or (for the non physicist) astonishing examples where the recoil principle (as special case of conservation of linear momentum) is applied beside rockets and guns?</p>
<p>I am teaching physics in high school and was just wondering if there are any more interesting examples than ... | g12190 | [
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0.02428797259926796,
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0.02358887903392315,
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<p>Every morning, when I ride my bicycle, there is a very loud squeak coming from the brakes. I have an aluminum rim (I think that they are of the sprint type) and rubber pad brakes. A couple of brake events afterward end that and after that the breaks are silent. I suspect it has something to do with the morning plump... | g12191 | [
0.06965797394514084,
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0.004253490827977657,
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0.04353755... |
<p>I have a little trouble with the <a href="http://en.wikipedia.org/wiki/Stimulated_emission" rel="nofollow">simulated emission</a>. I know of the <a href="http://en.wikipedia.org/wiki/No-cloning_theorem" rel="nofollow">no-cloning theorem</a> which states that it is not possible to duplicate any state.</p>
<p>One the... | g12192 | [
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0.01142542902380228,
-... |
<p>Parametric resonance is a situation where the driving frequency is a multiple of the eigenfrequency. Various people say that using a swing and propelling it oneself is such a case, with the driving frequency being the double of the eigenfrequency. But when I use a swing, as I did today, my own motion has the same fr... | g12193 | [
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0.005037777591496706,
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0.01... |
<p>What is the simplest derivation of the following two well-known formulas that work for crystal lattice [1]:
$$
F[f(\mathbf{x})] \equiv \tilde f(\mathbf{G})
= {1\over\Omega_\mathrm{cell}} \int_{\Omega_\mathrm{cell}} f(\mathbf{x})
e^{-i\mathbf{G} \cdot \mathbf{x}}\,d^3 x
$$
$$
F^{-1}[\tilde f(\... | g12194 | [
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0.08393439650535583,
0.028786439448595047,... |
<p>Any metal conductor such as aluminium or copper is a conductor because of the free electrons in such metals. </p>
<p>Plasma also has free electrons so I would like to know if you can repel plasma the same way as aluminium is repelled when near an AC electro magnet?</p>
<p>If so how come when I spin a magnet near m... | g12195 | [
0.05514960363507271,
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0.01965203508734703,
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0.06150953844189644,
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-0.0... |
<p>What is a good, single, "periodic table" of all the particles of the <a href="http://en.wikipedia.org/wiki/Standard_Model" rel="nofollow">Standard Model</a>?</p>
<p>I thought <a href="http://pdg.lbl.gov/" rel="nofollow">Particle Data Group</a> would have a single-page PDF of this, but I couldn't find a single table... | g12196 | [
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0.04414216801524162,
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0.014956029132008553,
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0.021166518330574036,
0.054977305233478546,
-0... |
<p>As the title suggests I was wondering why the International Bureau of Weights and Measures
decided a mole to be a standard <a href="http://en.wikipedia.org/wiki/SI_units">(SI-)unit</a>. After some research I found I was not alone with this problem.</p>
<p>The core of my question is: </p>
<ol>
<li>How is the unit ... | g12197 | [
0.014793448150157928,
0.022613689303398132,
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-0.020203815773129463,
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0.020935993641614914,
0.02573612704873085,
... |
<p>Does anyone take the <a href="http://en.wikipedia.org/wiki/Wightman_axioms" rel="nofollow">Wightman axioms</a> seriously? Mainly with respect to quantum gravity or gauge theores, abelian or non-abelian?
Anyone doing any research on axiomatization of QFTs in some way?</p> | g12198 | [
0.005965287797152996,
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0.... |
<p>In Lagrangian Mechanics we choose the path of least action. </p>
<p>Given a uniform gravitational field, and a particle of finite mass; and fixing two points the start & end-point we consider all paths connecting the two points and minimise the action. This turns out to be a Brachistone, as first shown by Berno... | g12199 | [
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<p>I'm currently trying to solve a problem that involves estimating the minimum energy of a particle in the potential:</p>
<p>$$
V(x) = \frac{-V_0a}{|{x}|}
$$</p>
<p>I'm quite confused about how to handle the absolute value in the potential. So far I know that the total energy of the particle will be </p>
<p>$$
E =... | g12200 | [
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0.014116935431957245,
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-... |
<p>I'm looking for the <a href="https://en.wikipedia.org/wiki/Critical_mass" rel="nofollow">critical mass</a> of <a href="https://en.wikipedia.org/wiki/Polonium" rel="nofollow">Polonium</a>; is there a formula? E.g.:$$\text{Neutrons / Protons}\cdot\text{ Constant = X kg}$$</p>
<p>There is a little table in the Wikiped... | g12201 | [
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-... |
<p>I have a question about the pressure placed on a plate of material X, how the force is distributed and what would be the material property that would determine its failure. </p>
<p>To simplify things "suppose" I wanted to build a vacuum chamber with a viewing window made of material X, that could handle a external ... | g12202 | [
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0.0... |
<p>Well I'm not sure how many people remember the crazy ball - a small ball made of rubber which bounced like crazy. What I noticed is that the ball seemed to bounce higher than the point from which it was actually dropped. How is this possible? Doesn't this violate the law of energy conservation?</p> | g12203 | [
0.0700974091887474,
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0.0893382728099823,
-0.01742... |
<p>I had a <a href="http://math.stackexchange.com/questions/431126/laplace-beltrami-operator-on-sphere">question</a> at MSE which gave a rise to another question.</p>
<p><a href="https://en.wikipedia.org/wiki/Maxwell%27s_equations#Alternative_formulations" rel="nofollow">Maxwell equations</a> can be written in form $$... | g12204 | [
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0.008983057923614979,
0.03318316116929054,
0.00489087775349617,
0.057... |
<p>I know Einstein was great and all. Why is it that exactly at the speed of light is where infinite energy is required to accelerate any object with mass? Is it simply because the math of relativity checks out and explains most of everything? Are there any physicists who disagree with Einstein's theory? </p> | g122 | [
0.04491554573178291,
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<p>Very often when people state a relaxation time $\tau_\text{kin-kin}, \tau_\text{rot-kin}$,, etc. they think of a context where the energy relaxation goes as $\propto\text e^{-t/\tau}$. Related is an approach to compute it via
$$\tau=E(0)/\left(\tfrac{\text d E}{\text d t}\right)_{E=0}.$$</p>
<p>Both are justified... | g12205 | [
0.021554989740252495,
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0.007... |
<p>OK, lets formulate it differently and say water works as a blue passing / red restricting filter.</p>
<p>It is actually observable. Just do a dive in a swimming pool with white light (maybe even at night) and a pool with a metal casing or white tiles. The further you look, the more blue it is.</p>
<p>So why is thi... | g12206 | [
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<p>I understand that evaporative cooling takes place thanks to small pores contained in the pot and that allow some water to go through and evaporate. However I couldn't understand clearly whether water inside the pot stays at its original temperature or would it cool further?
If it will become cooler then how?</p> | g12207 | [
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<p>In an article from the <a href="http://fisica.ciencias.uchile.cl/~gonzalo/cursos/termo_II-05/seminarios/AJP_Callen-relativistic-thermo71.pdf" rel="nofollow">reference</a> there are following words (page 2):
"...pressure P is a Lorentz invariant... the result follows from standart properties of the relativistic stres... | g12208 | [
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<p>Is it possible to consider <a href="http://en.wikipedia.org/wiki/Gravitational_constant" rel="nofollow">Newton's universal gravitational constant</a>, $G$, as inverse of vacuum permittivity of mass?</p>
<p>$$\epsilon_m=\frac {1}{4\pi G}$$</p>
<p>if so, then vacuum permeability of mass will be:</p>
<p>$$\mu_m=\fra... | g12209 | [
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<p>I remember reading about the groundbreaking experiment by <a href="http://arxiv.org/abs/hep-ph/0502081" rel="nofollow">Nesvizhevsky (et al. 2001)</a> some 12 years ago using ultra-cold neutrons which showed the first experimental evidence of quantum gravity. It is my understanding that these experiments has been rep... | g12210 | [
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<p>What (if any) is the relationship between the conserved (non-topological) noetherian charges and <a href="http://en.wikipedia.org/wiki/Topological_quantum_number" rel="nofollow">topological charges</a>? Namely, is there any "generalization" of the <a href="http://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofol... | g12211 | [
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<p>How can Hawking radiation with a finite (greather than zero) temperature come from the event horizon of a black hole? A redshifted thermal radiation still has Planck spectrum but with the lower temperature (remember CMB with temperature redshifted by expansion of the universe). Now, redshift at the event horizon is ... | g12212 | [
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<p>A sinusoidal oscillator has :</p>
<p>$$x=x_{max} \cos(\omega t - \varphi )$$</p>
<p>Period is 2, initial displacement is 100mm
initial velocity is 200mm/s</p>
<p>What is the phase angle assuming $-\pi < \varphi < \pi$</p>
<p>How do I go about solving this?</p>
<p>Is the phase $(\omega t - \varphi)$? But I... | g12213 | [
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<p>One example of a <a href="http://en.wikipedia.org/wiki/Nonholonomic_system" rel="nofollow">nonholonomic</a> constraint is a disk rolling around in the cartesian plane that is constrained to not be slipping.</p>
<p>These leads to the constraint $dx - a \sin\theta d\phi = 0$ and $dy - a\cos\theta d\phi = 0$ Where $\p... | g12214 | [
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