question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>Is there a general theorem which gives some information about which influence have the lattice geometry (for example sub-lattice structure, square lattice, honeycomb lattice, lattice symmetries, ...) to the dispersion relation in the low-energy regime? </p>
<p>For example: graphene or magnons in antiferromagnets. B... | g9729 | [
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<p>Im studying anisotropic system composed by a elastic matrix (Young modulus $E_m$) filled with oriented rods. </p>
<p>Given this filler orientation, the material is elastic-anisotropic, with Young elastic modulus $E_\parallel$ in the direction of the rods orientation and $E_\perp$ in the transversal direction of the... | g9730 | [
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<p>The BICEP experiment's recent announcement included the preprint of their paper,</p>
<blockquote>
<p>BICEP2 I: Detection of $B$-mode polarization at degree angular scales. BICEP2 Collaboration. To be submitted. <a href="http://bicepkeck.org/b2_respap_arxiv_v1.pdf" rel="nofollow">BICEP-Keck preprint</a>, <a href="... | g9731 | [
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<p>In MRI we measure $T_1$ and $T_2$ relaxation times. $T_1$ relaxation time is defined as the time it takes for the longitudinal component of magnetization to recover $1-1/e$ of its original value, and $T_2$ relaxation time is the time it takes for the transverse component of magnetization to recover $1/e$ of its orig... | g9732 | [
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<p>The starting point and notations used here are presented in <a href="http://physics.stackexchange.com/questions/77758/two-puzzles-on-the-projective-symmetry-grouppsg">Two puzzles on the Projective Symmetry Group(PSG)?</a>. As we know, Invariant Gauge Group(IGG) is a <em>normal subgroup</em> of Projective Symmetry G... | g9733 | [
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<p>Landau Lifshitz claim in their Mechanics book (39.11) that for a uniform rotation we have </p>
<p>$ E = \frac{mv^2}{2} - \frac{m}{2} (\omega \times r)^2 + U,$
where the rotation is given by $v' = v + \omega \times r.$</p>
<p>This does not make sense to me, since this centrifugal term is negative( I mean, compared ... | g9734 | [
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<p>If the Higgs mass is in a certain range, the quartic self-coupling of the Higgs field becomes negative after renormalization group flow to a high energy scale, signalling an instability of the vacuum itself.</p>
<p>However, I don't know how to interpret the fact that the vacuum appears to be stable at a certain sca... | g9735 | [
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<p>I am looking for good and recent references to constructing twistor space for curved spacetime. This could be a general spacetime, or specific ones (say maximally symmetric spaces different from Minkowski). This could be in he context of the twistor correspondence, or the twistor transform of field equations, either... | g9736 | [
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<p>An important aspect of the AdS/CFT correspondence is the recipe to compute correlation functions of a boundary operator $\mathcal{O} $ in terms of the supergravity fields in the interior of the $AdS_{n+1}$ (as we approach the boundary). Namely, $\big< \exp \int_{\mathbb{S}^n} \mathcal{O} \phi_{0}\big > = \mat... | g9737 | [
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<p>Everytime I hear about adding torsion to GR, something struggles me: how do you create a kinetic term for the electromagnetic field that is still gauge-invariant? One of the consequences of torsion is that covariant derivatives no more commute on scalar functions, so by looking at the $F_{\mu\nu} = \nabla_{\mu}A_{\n... | g9738 | [
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<p>I've heard Astronomers talking about backlit CCD sensors, and talking about how much better they are than other types. What are they, why might I want to get one, and what are the pros/cons of this compared to related technologies?</p> | g9739 | [
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<p><a href="http://www.news.com.au/technology/sci-tech/magnetic-bubbles-160-million-km-wide-may-be-earths-first-defence-against-cosmic-rays/story-fn5fsgyc-1226072932809" rel="nofollow">This</a> article reported today, a finding from one of the voyager probes. It talks about magnetic structures at the (far) outer edge o... | g9740 | [
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<p>It seems obvious why mercury has no atmosphere, given its proximity to the sun--but yet Venus is also fairly close, and has an extremely dense atmosphere. Titan is a large moon with an atmosphere thicker than Earth's, and then Triton, a more distant large moon, has only a tenuous Nitrogen atmosphere. Why aren't more... | g9741 | [
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<p>It's not going to last forever - Jeans Escape is going to eventually act on the atmosphere after trillions of trillions of years: see <a href="http://faculty.washington.edu/dcatling/Catling2009_SciAm.pdf" rel="nofollow">http://faculty.washington.edu/dcatling/Catling2009_SciAm.pdf</a></p> | g9742 | [
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<p>There is the specific universe we live in, the "actual" universe with planet Earth, humans evolving, and us discussing metaphysical debates on physics.se in 2012, etc. There might or might not also be other possible/potential worlds out there, some differing majorly, like in the laws of physics, or minorly, almost ... | g9743 | [
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<p>Work is expressed as <code>W=F*d</code>, where the <code>F</code> is in Newton, <code>d</code> is in meters and result <code>W</code> is in <strong>Joules</strong>.
For example, if I take <code>1N</code> on earth and lift it <code>1m</code> up in the air I have done <code>1J</code> of work.</p>
<p>Kinetic energy is... | g9744 | [
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<p>For a <a href="http://rads.stackoverflow.com/amzn/click/B0061DSNCC" rel="nofollow">typical flourescent light available in the United States</a> on a a standard 120V 60Hz line, is there information available on the decay time of the light? For example, if I am running the light a full power (ON) and shut off power (... | g9745 | [
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<p>I am going through Sakurai's quantum mechanics, and at one point the solution to a problem says:</p>
<p>$(\sin(\beta)\cos(\alpha)-i\sin(\beta)\sin(\alpha))b+\cos(\beta)a=a$
$(\sin(\beta)\cos(\alpha)+i\sin(\beta)\sin(\alpha))a-\cos(\beta)b=b$</p>
<p>$a,b$ are the complex coefficients for some state, so we have:</p>... | g9746 | [
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<p>The exact solution representing a FLRW universe with $k>0$ and dust (p=0), and $\Lambda=0$, is described by a cycloid. What is the exact solution for dust, in the presence of a positive cosmological constant $\Lambda>0$? Could you give references?</p> | g9747 | [
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<p>What, fundamentally, is an electromagnetic wave? As far as I know, all wave phenomena are derivations of an oscillating processes, e.g. particles vibrating in a medium. I can't imagine a wave process which couldn't be explained as moving particles: sound wave - movement of gas molecules, waves on the water - movemen... | g9748 | [
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<p>Does anyone know where I can find the analytical expressions of the scattering amplitude in second Born Approximation for the Yukawa potential? I need it for the both cases of the method of partial waves and the Born series as defined to solve the Lippmann-Schwinger equation. In general the second term is unimportan... | g9749 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Lennard-Jones_potential">Lennard-Jones potential</a> has the form:</p>
<p>$$U(r) = 4\epsilon\left[ \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^{6} \right]$$</p>
<p>The (attractive) $r^{-6}$ term describes the dispersion force (<em>attraction at long ... | g9750 | [
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<p>Once an object reaches terminal velocity in free fall, is there a point in time when the object actually starts slowing down due to resistance, or does it stay constant?</p> | g9751 | [
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<p>What causes ice to melt in these patterns?</p>
<p><img src="http://i.stack.imgur.com/WlcMR.jpg" alt="Melting Ice"></p>
<p>And why does this always happen when the ice is covered in snow?</p> | g9752 | [
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<p>Lightning contains a lot of energy, so where does this energy go after lightning has hit the ground? </p>
<p>Does it travel all the way to the core? What happens after that?</p> | g9753 | [
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<p>So consider the case where there is a particle and a moving telescope:
<img src="http://i.stack.imgur.com/HD5xk.jpg" alt="enter image description here"></p>
<p>If the particle is located at position 1, and the telescope is moving horizontally as shown, the EM radiation appears to be coming from position 2, from the... | g9754 | [
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<p>In semi-empirical quantum chemistry, one frequently encounters the so called <a href="http://en.wikipedia.org/wiki/Zero_differential_overlap" rel="nofollow"><em>zero differential overlap</em></a> approximation</p>
<p>$$\langle \mu \nu | \lambda \sigma \rangle = \delta_{\mu\nu}\delta_{\lambda\sigma} \langle \mu \mu ... | g9755 | [
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<p>Right after take-off (which means an airplane already exceeded V1) it is recommended that an airplane keeps climbing even when emergency occurs. Beside worries of crashing into houses and buildings by flying low altitude, why should an airplane not stop climbing up? Why should it climb up and then, lowers to some al... | g9756 | [
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<p>Can someone explain the difference between hopping and tunneling? The context I'm considering is conduction in semiconductors, specifically between impurity states within the bandgap. It's always been my understanding that hopping <em>is</em> tunneling. Variable range hopping and nearest neighbor hopping, as I un... | g9757 | [
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<p>Light has a dual nature, one of photons and the other of waves. But energy doesn't really travel in waves. So what do the wave represent?</p> | g9758 | [
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<p>I was wondering as how would appear the interference pattern of a double-slit experiment moving at a relativistic speed v, 1) in the case of light and, 2) in the case wave matter (i.e. electrons for instance) as seen in comparison between rest and moving reference frames (respectively S and S’). </p>
<p><img src="h... | g9759 | [
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<p>In an answer to <a href="http://physics.stackexchange.com/questions/101766/does-any-material-glow-under-appropriate-conditions/101768#101768">this SE question</a>, the respondent explains that heating a perfect diamond will not cause it to glow with thermal blackbody radiation. I don't quite follow his explanation.... | g9760 | [
0.03648146614432335,
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0.01203907560557127,
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0.020837031304836273,
-0.018... |
<p>Assume a test charge with charge $Q$ is placed at the center of a 13-sided regular polygon, the vertices of which are charges with equal charge $q$. What is the electrical force on the center charge?</p>
<p>To start we write this as our electrical force...
$$ \vec{F}_{Q} = \sum^{13}_{n} \frac{1}{4\pi\varepsilon_{0}... | g9761 | [
0.02968464605510235,
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<p>I've read <a href="http://physics.stackexchange.com/q/44457/41825">this question and answers</a>, but neither of the posts does seem to address my concerns. The problem is as follows:</p>
<blockquote>
<p>Assuming a device that keeps something in a gravitational field on a constant height, like an electromagnet, h... | g315 | [
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0.04314865544438362,
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-0.05230824649333954,
-... |
<p>I have been told that the a freezer will freeze food slower if:
a) the product load is greater then the capacity
b) the capacity is greater then then the load.</p>
<p>In a) I think this means if a freezer can freeze 2kg of food in 12 hours, using more food will cause the freezer to work slower and so freeze slower.... | g9762 | [
0.04306695982813835,
0.10066494345664978,
0.02196139097213745,
0.03441297262907028,
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0.03822870925068855,
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0.000668... |
<p>Does anyone know any materials that have an electroluminescent threshold in the millivolt or microvolt range?</p>
<p>Specifically, a stable solid state material. I hope to deposited the material as a thin film.</p>
<p>Thank you for the help!</p> | g9763 | [
0.0346234068274498,
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0.011805976741015911,
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0.020185... |
<p>After reading a very informative tutorial on elementary particles physics over at <a href="http://www.particleadventure.org" rel="nofollow">http://www.particleadventure.org</a>, I have a question I can't figure out.</p>
<p>I understand the need to accelerate a particle to high energy level, as it allows to view "sm... | g9764 | [
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<p>There are people proposing the possibility of using entropic force to explain the gravity force between objects.
The emphasis is that entropy is more fundamental than energy.
It is the closest study as entropy is closely related to information.
What is Mathematical formulation of <a href="http://en.wikipedia.org/wik... | g751 | [
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<p>Essentially, there is a beam of length L and negligible mass sticking out of a wall with a mass Mg hanging at the end of it. We are given an equation for elastic energy (which I don't think needs to be modified), and we have to come up with the potential energy contribution from the mass, and then hopefully be able ... | g9765 | [
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<p>I've found this interesting paper that mentions another possible way to interpret the recent BICEP2 results, and that hadn't been ruled out yet <a href="http://arxiv.org/abs/1403.5166" rel="nofollow">1</a>. As interesting as the possibility that the BICEP2 team has observed CMB polarization due to gravitational wave... | g9766 | [
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<blockquote>
<p>When I see <a href="http://en.wikipedia.org/wiki/Harmonic_coordinates" rel="nofollow">harmonic coordinates</a> used somewhere, what should my association be? </p>
<p>Is there some general use or need to consider the <a href="http://en.wikipedia.org/wiki/Harmonic_coordinate_condition" rel="nofollo... | g9767 | [
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0... |
<p>Would it be possible to determine the rest mass of a particle by computing the potential energy related to the presence (existence) of the particle, if this potential energy could be determined accurately enough?</p>
<p>I noticed from the answers to a recent question that I always assumed this to be true, without e... | g9768 | [
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0.033872343599796295,
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<p>For someone who likes learning about astronomy what are the blogs and/or podcasts that I should be following?</p> | g9769 | [
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<p>Or in other words, are there differences in average Lyapunov timescale between orbits interior to Jupiter and orbits exterior to Jupiter? I'm trying to answer a question at <a href="http://www.quora.com/Why-does-Pluto-have-so-many-satellites/answer/Alex-K-Chen">http://www.quora.com/Why-does-Pluto-have-so-many-satell... | g9770 | [
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<p>Is there a general way to calculate the magnetic field for a time dependent current of a long thing wire?</p>
<p>For ex:</p>
<p>If the current is</p>
<p>$$
I(t)=I\sin wt,
$$
is there a general method to use in order to calculate the magnetic field? </p>
<p>I know for time-independent currents we can use
$$
\int... | g9771 | [
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<p>I believe earth-based detectors measure mainly solar neutrinos, which have energies on the MeV scale of nuclear physics, are directed from the sun, and have flavors determined by the sun's nuclear reactions plus neutrino oscillations. In addition to this, I recently learned from a physics.SE answer that the universe... | g9772 | [
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<p>I was recently overviewing various <a href="http://en.wikipedia.org/wiki/Massive_compact_halo_object" rel="nofollow">massive compact halo object</a> studies (the Anglo-Australian MACHO collaboration and the French I/II EROS collaboration), and they frequently reference "blue bumper stars," irregular variable stars w... | g9773 | [
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<p>I'm not going to post the full question, I just want a general idea of how I should go about solving this type of problem. </p>
<p>There is a square with 4 charged masses on each of the corners, in the center of the square, there is a fifth charged mass. I am supposed to find the net force acting on the center mass... | g9774 | [
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0... |
<p>I have question related to electromagnetic Spectrum.</p>
<p>If energy of photon is $E=m_e c^2$, to which part of the electromagnetic spectrum does it belong ? </p> | g9775 | [
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<p>In a paper by Gregory and Laflamme (<a href="http://arxiv.org/abs/hep-th/9301052" rel="nofollow">http://arxiv.org/abs/hep-th/9301052</a>) in 1993, it was demonstrated that black strings and $p$-branes which were solutions to certain low energy string theories were unstable by searching for solutions to the perturbat... | g9776 | [
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<p>I have often heard it said that several problems in the theory of electromagnetism as described by Maxwell's equations led Einstein to his theory of Special Relativity. What exactly were these problems that Einstein had in mind, and how does <a href="http://en.wikipedia.org/wiki/History_of_special_relativity">Specia... | g9777 | [
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<blockquote>
<p>We have a point charge $q>0$ in vacuum at a distance $a$ from the center $M$ of an isolated metal sphere that has a total charge $-q$ and radius $R$. ($a>R$)</p>
<p>A) Use the method of images to find a charge configuration that has the same boundary conditions. (hint: you need 3 charges)</... | g9778 | [
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<p>In my experiment, I use a laser beam with wavelength $\lambda=894 \text{nm}$ for some magnetic resonance experiment. Right now, I'm doing some calculation using Quantum Mechanics, which requires the amplitude of the electric field to be inserted to my Hamiltonian.</p>
<p><strong>My question is basically: How do I g... | g9779 | [
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<p>If there exists a natural magnetic field due to the metallic core of the earth... could we then extract and get free energy from the earth core ??</p> | g82 | [
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<p>In the usual $(x,y,z)$ system of coordinates, if we expand the Maxwell's curls equations for phasors</p>
<p>$$\nabla \times \mathbf{E} = - \mathbf{J}_m - j \omega \mu \mathbf{H}$$
$$\nabla \times \mathbf{H} = \mathbf{J} + j \omega \epsilon \mathbf{E}$$</p>
<p>we obtain equations like the following:</p>
<p>$$\disp... | g9780 | [
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0.011609933339059353,
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0.0083... |
<p>We have notions of derivative for a continuous and differentiable vector fields. The operations like curl,divergence etc. have well defined precise notions for these fields.</p>
<p>We know electrostatic and magneto static fields aren't actually well behaved. They blow up at the sources, have discontinuities and yet... | g9781 | [
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0.04441472142934799,
-0.00... |
<p>Energies of wind and water can produce electricity. But, can sound energy also be used to produce electricity?</p> | g9782 | [
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<p>I know this is an already answered question, but I couldn't make head or tail of it, and it's bugging me. I know I'm probably asking a silly question, but please bear with me as I'm 14 and this is my first post. </p>
<p>I saw this perturbation while studying up a bit of linearised gravity:</p>
<p>$$g_{\mu\nu} = \e... | g9783 | [
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0.08792506158351898,
0.057682886719703674,
-0.007... |
<p>I am looking into Landau Levels and keep coming across a magnetic length defined as follows for a 2D system:</p>
<p>$l_B=\sqrt{\frac{\hbar c}{e B}}$</p>
<p>I have seen numerous sources say this is:</p>
<p>$l_B\approx 26nm \sqrt{B[Tesla]} $</p>
<p>But by plugging those numbers in I don't see how this is the case ... | g9784 | [
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0.017... |
<p>The oil drop experiment performed by Robert Millikan in 1909 enables us to calculate the elementary charge.</p>
<p>The following forces have effect on the droplet:</p>
<ol>
<li>$F_\mathrm{G} = m g = \frac{4}{3} \, \pi r^3 \rho_\mathrm{Oil} g$</li>
<li>$F_\mathrm{A} = \frac{4}{3} \, \pi r^3 \rho_\mathrm{Air} g$</li... | g9785 | [
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0.007100635673850775,
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0.013129877857863903,
... |
<p>I came across a New Study at : <a href="http://arxiv.org/PS_cache/arxiv/pdf/1101/1101.2565v1.pdf" rel="nofollow">http://arxiv.org/PS_cache/arxiv/pdf/1101/1101.2565v1.pdf</a> . Which talks about Time like quantum entanglement. What does that mean? </p>
<p><strong>Comment added by L.Motl</strong>: The same preprint h... | g9786 | [
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<p>Currently I am learning <a href="http://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution" rel="nofollow">Maxwell-Boltsmann distribution</a> (MBD) and in that I am learning about <a href="http://en.wikipedia.org/wiki/Microstate_%28statistical_mechanics%29" rel="nofollow">microstate</a>, macrostate and the... | g9787 | [
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0.09349148720502853,
-0.008... |
<p>Are there any good theories on inverting the law of physics?</p>
<p>To make physics work the opposite way of what it does.</p>
<p>Please ask question if this is unclear! I'll answer as well as I can. </p>
<p>Ok, I'll try to explain better. I was taking a smoke break and started thinking about time travel, and som... | g9788 | [
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-... |
<p>I'm programing simulation software for solenoid and hemholtz coils, where I have to calculate <strong>B(x,y,z)</strong>. I have found dozens of variations of <a href="http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law" rel="nofollow">Biot-savart law</a> for determining B on axis. But how about <strong>outside of t... | g9789 | [
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<p>I would like to know what is the energy needed <strong>considering the air resistance</strong> to shoot from ground to the orbit a 100g object (even if it vaporizes in the process). </p>
<p><strong>Variables to make approx calculations:</strong>
Lets assume it has a <strong>pointy bullet shape</strong> (best know s... | g9790 | [
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<p>How to mathematically formulate the Two Slit Experiment in a Lorentz invariant framework.</p>
<p>Is there a paper about this?</p> | g9791 | [
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<p>Once I discussed cars and there was a question about rate at which the car gains its speed ($100\:\mathrm{km/h}$) from standstill (i.e. acceleration).
At some point of conversation it came up that cars cannot gain their $100\:\mathrm{km/h}$ speed for such tiny time interval I proposed (less than $3$ seconds),
becaus... | g9792 | [
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<p>This question is regarding a definition of Tensor product of Hilbert spaces that I found in Wald's book on QFT in curved space time. Let's first get some notation straight.</p>
<p>Let $(V,+,*)$ denote a set $V$, together with $+$ and $*$ being the addition and multiplication maps on $V$ that satisfy the vector spac... | g9793 | [
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<p>Before using anticommutation relatives the energy, momentum, charge and number operators of the Dirac field have following expressions:
$$
\hat {H} = \int \epsilon_{\mathbf p}\left( \hat {a}^{+}_{s}(\mathbf p )\hat {a}_{s}(\mathbf p ) - \hat {b}_{s}(\mathbf p )\hat {b}_{s}^{+}(\mathbf p ) \right)d^{3}\mathbf p,
$$</... | g9794 | [
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<p><a href="http://en.wikipedia.org/wiki/2013_Ashes_series" rel="nofollow">The 2013 Ashes series</a> (a cricket thing between England and Australia) are underway as of today and it seems they have a new (to me) gimmick. It appears that they are now able to measure almost instantaneously (within a few seconds) the rotat... | g9795 | [
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<p>I am a physicist who is not that well-versed in mathematical rigour (a shame, I know! But I'm working on it.) In Wald's book on QFT in Curved spacetimes, I found the following definitions of the direct sum of Hilbert spaces. He says - </p>
<blockquote>
<p>Next, we define the direct sum of Hilbert spaces. Let $\{ ... | g9796 | [
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0.03031318634748459,
-... |
<p>I am a Physics undergraduate, so provide references with your responses.</p>
<p>Landau & Lifshitz write in page one of their mechanics textbook:</p>
<blockquote>
<p>If all the co-ordinates and velocities are simultaneously specified, it is known from experience that the state of the system is completely dete... | g397 | [
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<p>The Hubbard model reads
$$H = -t \sum_{\langle ij \rangle, \sigma} c_{j\sigma}^\dagger c_{i\sigma} + U\sum_i n_{i\uparrow}n_{i\downarrow} $$</p>
<p>In the large $U$ limit and at half-filling, the Hubbard model tranforms to $t$-$J$ model
$$H = -t \sum_{\langle ij \rangle, \sigma} c_{j\sigma}^\dagger c_{i\sigma} + J\... | g9797 | [
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<p>If I now see the <a href="http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation" rel="nofollow">Schrödinger equation</a>, I just see a bunch of weird symbols, but I want to know what it actually means. So I'm taking a course of Linear Algebra and I'm planning on starting with PDE's next month. What 'other math' is ... | g9798 | [
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<p>So I was operating a Laue machine recently which generates x-rays and fires them at a sample, and I noticed that there was a high-pitched whine coming from the instrument (nothing abnormal, just something I noticed). Both the current and the voltage could be set separately; typically values are 10 mA and 20 kV. I no... | g9799 | [
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<p>The black hole at the center of the Milky Way is believed to have erupted as an active galactic nucleus (AGN) approximately 2 million years ago, at which time <a href="http://www.newscientist.com/article/dn24257-early-humans-saw-black-hole-light-in-the-night-sky.html" rel="nofollow">it would have been visible to ear... | g9800 | [
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<p>It is well known that if the compactification manifold of a supergravity theory has non-zero Betti numbers, this may lead to the so called Betti multiplets in the spectrum of the low dimensional theory. A famous example is compactification of IIB supergravity on $T^{1,1}$, where a Betti multiplet shows up because of... | g9801 | [
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<p>I have a (probably) simple question regarding boundary conditions. In electrostatic simulations, the relevant Maxwell equation is $\nabla \cdot \mathbf{D}=\rho$ where $\mathbf{E}=-\nabla V$, and $\mathbf{D}$ is related to $\mathbf{E}$ through any applicable constitutive relations. When a floating-potential metal obj... | g9802 | [
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<p>What is the reason for the observation that across the board fields in physics are generally governed by second order (partial) differential equations?</p>
<hr>
<p>If someone on the street would flat out ask me that question, then I'd probably mumble something about physicists wanting to be able to use the Lagrang... | g257 | [
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<p>I want to understand what is wrong with the following argument:</p>
<p><em>in a topologically compact spacetime, a closed 3D boundary separates the spacetime in two connected components, because of this continuous symmetry, either one of the two things must happen</em></p>
<p>1) <em>the stokes theorem is not valid... | g9803 | [
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<p>Every Solution of the Dirac Equation is also a solution of the Klein-Gordon equation.</p>
<p>So the K-G equation does not necessarily represent particles with non-zero spin.</p>
<p>Would it be incorrect to conclude that KG equation relates solely to zero-spin particles?</p> | g9804 | [
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<p>Is there any difference between using a positive versus a negative charge to test an electric field?</p> | g9805 | [
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<p><img src="http://i.stack.imgur.com/vBxf1.jpg" alt="enter image description here"></p>
<p>(a) I am a little confused about this part. The point at A to B isn't radial. The electric field is radially outward, but if I look at the integral</p>
<p>$$\int_{a}^{b}\mathbf{E}\cdot d\mathbf{s} = \int_{a}^{b}\frac{\rho r}{3... | g9806 | [
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<p>Where is the source of the photon. </p>
<p>If the photon propagates from within the electrons transit does this point to some sort of field?</p>
<p>Does the energy come from a boundary being broken in laymens terms a sound barrier type effect the electron performs on its shell as it changes orbit?</p> | g9807 | [
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<p>There are a decent number of complex mathematical descriptions of the zero-dispersion wavelength online, but I can't seem to find any basic explanations. So to be redundant, what is it?</p> | g9808 | [
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<p>Is perturbation theory usually taught in undergraduate physics, and how much of it is taught in quantum mechanics courses?</p>
<p>Also, how much of quantum field theory would be taught in undergraduate physics?</p> | g9809 | [
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<p>Are the gravity waves detectors all working on the same
principle/effect ?</p> | g9810 | [
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<p>1: Do neutrinos undergo <strong>elastic</strong> collisions with fermions?</p>
<p>2: Would this imply a <strong>variable</strong> speed for neutrinos?</p>
<p>3: Can neutrinos transfer <strong>momenta</strong> in interactions?</p> | g9811 | [
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<p>I came across a very recent paper by Gerard 't Hooft
The abstract says: </p>
<p>It is often claimed that the collapse of the wave function and Born's rule to interpret the square of the norm as a probability, have to be introduced as separate axioms in quantum mechanics besides the Schroedinger equation. Here we s... | g9812 | [
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<p>Is charge of something for (e.g.) an electron related to electromagnetic space if it exists due to energy, due to which it may have mass? I don't know about quantum mechanics or advanced particle models. Can anyone just simply give an intuitive idea? </p>
<p>EDIT
I want to mean what actually gives electron charge i... | g189 | [
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<p>This titled position of the earths axis is known as inclination of the earths axis.
The earth's rotation axis makes an angle of about 66.5 degrees with the plane of its orbit around the sun, or about 23.5 degrees from the perpendicular to the ecliptic plane</p>
<p>what is the scientific reason for the inclination o... | g9813 | [
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... |
<p>Could I ionize a gas using an electron gun and knock off electrons in the gas to make plasma?</p> | g9814 | [
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<p>In QM, the state vector $|\psi\rangle$ seem to have various dimensions under different representations: (only in space of continuous dimension)</p>
<p>$$\langle x|\psi\rangle = [\frac{1}{\sqrt{Length}}]$$
$$\langle p|\psi\rangle = [\sqrt\frac{time}{{Mass Length}}]$$
etc, and $|\psi\rangle$ can equal to $|x'\rangle$... | g9815 | [
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<p>In the comments to this <a href="http://quantumfrontiers.com/2012/09/24/the-allure-of-elegance/" rel="nofollow">post</a>, it was hinted that proving that the force acting on a charge at a vertical distance from a uniformly charged plane is independent of that distance can be done by recalling the scale invariance sy... | g9816 | [
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<p>I just came across this Wikipedia article on pn-junctions:</p>
<p><a href="http://en.wikipedia.org/wiki/P%E2%80%93n_junction#Equilibrium_.28zero_bias.29" rel="nofollow">pn junction</a></p>
<p>What I don't get is why the negative charge density is narrower/smaller than the positive one in Figure A. I'm guessing the... | g9817 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/11820/what-really-cause-light-to-appear-slower-in-media">What really cause light to appear slower in media?</a> </p>
</blockquote>
<p>This came to me as a question from one of my friend while I was convi... | g298 | [
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<p>A chain 64 meters long whose mass is 20 kilograms is hanging over the edge of a tall building and does not touch the ground. How much work is required to lift the top 3 meters of the chain to the top of the building? Use that the acceleration due to gravity is 9.8 meters per second squared. Your answer must include ... | g9818 | [
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<p>We were learning about Boyle's law (pressure is inversely proportional to volume of a gas) and in the experiment to prove the law, we were told that we cannot change the volume of a gas too rapidly without affecting its temperature.</p>
<p>I have two questions about this:</p>
<ol>
<li>Why does temperature of a gas... | g9819 | [
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<p>I was watching The Return of the King and just after Frodo and Sam destroy the One Ring, they run out of the mountain and hide on top of a rock as the volcano erupts and lava flows past them. Is this actually feasible or would they have been roasting alive?</p>
<p>Here's an image for reference.</p>
<p><img src="ht... | g9820 | [
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<p>Why are 11 dimensions needed in <a href="http://en.wikipedia.org/wiki/M-theory">M-Theory</a>? The four I know (three spatial ones plus time) have an intuitive meaning in everyday life. How can I think of the other seven? What is their nature (spatial, temporal, ...) and is there an <strong>intuitive</strong> picture... | g9821 | [
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