question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>How do 3d <a href="http://en.wikipedia.org/wiki/Holography" rel="nofollow">holograms</a> work exactly? I read that there is a laser in use, but how are the multiple perspectives generated and how is the light <em>trapped?</em> in a certain area to create the effect?</p>
<p>Furthermore, how do you generate different... | g930 | [
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<p>How would a society go about either preventing our sun in its primary sequence from going into a Red Giant a billion years from now? Or perhaps, accelerating the process of going from main sequence of our start to a red giant prematurely. </p>
<p>What catalysts would have to happen, implemented by humans, so n... | g8434 | [
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<p>I googled the question and found no explanation. It seems that dog ears are inevitable (for paperbacks, notably) even if you've always been careful. From my experience, they are about equally likely to appear on the top corners as on the bottom corners (for both the beginning pages and the ending ones). Dog ears for... | g8435 | [
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<p>I am interested in (typically topological) field theories arising from Lagrangians of the form.</p>
<p>$f(\Phi) \lambda$,</p>
<p>where $\lambda$ is a Lagrange multiplier field not appearing in $f(\Phi)$. Perturbatively, the partition function just counts the solutions to $f(\Phi)=0$. What about nonperturbatively? ... | g8436 | [
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<p>This problem is puzzling me.</p>
<p>Scenario 1:
A certain sphere is having an innelastic collision with a plane of a very large mass. Let the angle between the sphere's velocity and the surface be 90 degrees. The escape angle will be the same as the incident angle, therefore the sphere velocity will be 90 degrees f... | g8437 | [
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<p>This must be the first question everyone asks when starting to study field theory at finite density and zero temperature. </p>
<p>To introduce a finite density one adds a Lagrange multiplier which fixes the number of particles in a non-relativistic field theory or the number of particles minus the number of antipar... | g8438 | [
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<p>Suppose I have an inertial frame with coordinate $\{q\}$. Now I define another reference frame with coordinate $\{q'(q,\dot q,t)\}$. I obtain the equation of motion in $\{q'\}$ in two different ways:</p>
<ol>
<li><p>First obtain the equation of motion in $\{q\}$ by the Euler Lagrange equation
$$\frac{d}{dt}\left(\f... | g8439 | [
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<p>I have seen on the internet that many times people assert that inside a cylindric <a href="http://en.wikipedia.org/wiki/Condenser" rel="nofollow">condenser</a> the electrostatic field is null due to the fact that the Gauss flux inside is null. But I wanted to make clear that this is not the reason. The reason lies o... | g8440 | [
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<p>I have a few questions about 3D waves:</p>
<ol>
<li>Are all 3D waves types of electromagnetic radiation?</li>
<li>Are all 2D waves mechanical?</li>
</ol> | g8441 | [
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<p>I am approaching this from an intuitive perspective and I don't speak the language. However, I have been doing a lot of reading about Bell's Theorum and how invalidates either locality or counterfactual definiteness. </p>
<p>From my point of view, locality is the concept that there is no way that two particles can ... | g8442 | [
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<p>When we study the interaction of the electromagnetic radiation with free electrons we can find two different approaches in the literature: for low frequency (RF, light...) a classical view is used and it is said that the electrons oscillates due to the electric field of the wave, but for high frequency radiation (X-... | g8443 | [
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<p>If we could irradiate a metal or a plasma with a coherent beam of hard X-rays, would the main effect be an ordered oscillation of the electrons like with a classical EM wave, or "compton-style" collisions?</p> | g8444 | [
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<p>Like any set of massive objects separated by distance, the Earth and Sun have a center of mass. How far in meters from the Sun's center is the Earth-Sun center of mass? Just curious? Also what percent of the Sun's radius is this distance?</p> | g8445 | [
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<p>Some of you may be familiar with the <a href="http://en.wikipedia.org/wiki/European_Union_energy_label" rel="nofollow">EU energy consumption classes</a> for domestic appliances (or equivalents in other areas).</p>
<p>Let's say we have a domestic appliance which was made before the energy directives were made active... | g8446 | [
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<p><strong>1. The problem statement, all variables and given/known data</strong></p>
<blockquote>
<p>Beam of electrons with energy $10eV$ hits the potential step
($8eV$ high and $0.5nm$ wide). How much of the current is
transmitted?</p>
</blockquote>
<p><strong>2. Relevant equations</strong></p>
<p>I know that... | g8447 | [
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<p>Only because</p>
<ol>
<li><p>Rep is unitary, so saves positive-definite norm (for possibility density),</p></li>
<li><p>Casimir operators of the group have eigenvalues $m^{2}$ and $m^2s(s + 1)$, so characterizes mass and spin, and</p></li>
<li><p>It is the representation of the global group of relativistic symmetry... | g8448 | [
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<p>Assume we had an elevator shaft long enough for a free-falling elevator to reach terminal velocity.</p>
<p>As I understand it, when the elevator begins to fall a person inside would experiences weightlessness because they would be accelerating downward at the same rate as the elevator. The rate of downward acceler... | g8449 | [
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<p>I am trying to determine if a radiant barrier on the inside of a hot water tank would increase its insulating value. Normally radiant barriers are used in house construction to reduce heat loss by reflecting radiant heat back into the house. The reflective surface is placed against an air gap on the exterior wall fa... | g8450 | [
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<p>The photon has a mass of 0, but it has energy because of its motion. When it is sucked into the black hole and becomes a singularity, it loses its energy because it is no longer moving. It is not possible for something to be sucked out of a black hole, so it has no potential energy that the kinetic energy could have... | g8451 | [
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<p>I am a layman, so take this with a grain of salt.</p>
<p>I saw a TV show the other day which showed a Russian Cosmonaut who had spent more time in space than any other human. The relativistic effects of the low gravity and extreme speeds at which he had spent a decent part of his life had pushed him a small, but s... | g8452 | [
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<p>What is a good way to block neutrons and what is the mechanism that allows this? It's my understanding that polyethylene is somewhat effective. Why?</p> | g8453 | [
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<p>Assume that we have access to a computer with unlimited computing power.</p>
<p>As with the Lattice QCD can try to prove that we live in a simulated universe?</p>
<p>Apparently, one may use the issue of cosmic rays.</p>
<p><a href="http://www.wired.co.uk/news/archive/2012-10/11/universe-computer-simulation" rel="... | g8454 | [
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<p>I'm reading through Vol. 1 Chaper 18, and Feynman says that in the system:</p>
<p><img src="http://i.stack.imgur.com/G3AZG.png" alt="enter image description here"></p>
<p>(<a href="http://www.feynmanlectures.caltech.edu/img/FLP_I/f18-01/f18-01_tc_big.svg" rel="nofollow">See here</a> for a higher resolution copy - ... | g8455 | [
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<p>This is really a question to get a little more insight about a homework exercise.</p>
<p><strong><em>1.</em></strong> In my text book, the sum of multiplicities for all possible macrostates is given to be:</p>
<p>$$\sum \Omega_\mathrm{total}=\binom{N_A+N_B+q_\mathrm{total}-1}{q_\mathrm{total}}$$</p>
<p>For two Ei... | g8456 | [
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<p>Reading Landau's Statistical Physics Part (3rd Edition), I am trying to calculate the answer to Chapter 39, Problem 3.</p>
<p>You are supposed to calculate the total kinetic energy of the particles in an ideal gas hitting the wall of a vessel containing said gas.</p>
<p>The number of collisions per unit area (of t... | g8457 | [
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<p>Do we know exactly the difference between <a href="http://en.wikipedia.org/wiki/Particle" rel="nofollow">particles</a> and <a href="http://en.wikipedia.org/wiki/Quasiparticle" rel="nofollow">quasiparticles</a>? Is Higgs boson a particle or a quasiparticle? I ask this because if I understood well, Higgs boson created... | g8458 | [
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<p><a href="http://en.wikipedia.org/wiki/Noether%27s_theorem">Noether's (first) theorem</a> states that any differentiable symmetry of the action of a physical system has a corresponding conservation law.</p>
<p>Is the converse true: Any conservation law of a physical system has a differentiable symmetry of its action... | g740 | [
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<p>Good afternoon everybody.</p>
<p>I am reading on a book about semiconductor mobility. I have fully understood the definition, but I also noticed that often one talks about high or low mobility. My question is: what are the <strong>advantages</strong> of having a <strong>high</strong> mobility? I mean, in the techno... | g8459 | [
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<p>Recall the first law of BH thermodynamics</p>
<p>$ dM=\frac{\kappa}{8\pi} dA + \Omega dJ + \Phi dQ $</p>
<p>Now, let's consider the Reissner-Nordstrom solution $J=0$ such that $m>Q$ but only slightly greater. Suppose I have a small bit of charge $dQ$ which I bring in from infinity to the BH horizion. </p>
<p>1... | g8460 | [
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<p><a href="http://en.wikipedia.org/wiki/Maxwell_equations" rel="nofollow">Maxwell's equations</a> allow for wave solutions via oscillations between electric and magnetic field content.</p>
<p>Couldn't we generate electric waves also if that solution didn't exists?
Imagine there was no magnetic field, only the electri... | g8461 | [
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<p>I'm pretty ignorant regarding neutron and nuclear transport modelling, but i'm interested in trying to pursue it for a particular pet project. It regards modelling of nuclear reactions like those required for NERVA-like rockets or <a href="http://path-2.narod.ru/design/base_e/nswr.pdf" rel="nofollow">this one</a>.</... | g8462 | [
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<p>Water falling from a tap eventually breaks into droplets at a particular distance from the tap. The distance(from the tap) at which it breaks into droplets is observed to be an increasing function of the volume flux of the water flowing out of the tap. What is the valid explanation for this phenomenon?</p>
<p>My ow... | g8463 | [
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-0.01915392093360424,
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0.0... |
<p>I'm learning quantum mechanics on my own. I've known that energy is quantized and I've started wondering about temperature. From thermodynamics we have:
$$U=\frac{3}{2}NkT $$
(for ideal gas, of course)<br>
Both U and N aren't continous, so i think T shouldn't be, too. Is that formula correct also for quantum mechani... | g8464 | [
0.05213490128517151,
-0.026821672916412354,
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0.016089284792542458,
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0.03563883900642395,
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-0.0023604833986610174,
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0.019486984238028526,
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... |
<p>I'm trying to program an $N$-body simulation and I'd like to be able to test it with a known solution to a simple, two-body problem. I've looked at multiple sources, but I just don't know how to apply it to my simple test case.</p>
<p>Two objects at rest placed 10 meters apart with mass of 1. The force between them... | g134 | [
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<p>What is the Quantum Boltzmann equation and what does it describe? I think it describes the propagation of electrons and photons but I am not sure.</p> | g8465 | [
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-0.045753467828035355,
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0.06687366962432861,
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<p>Why will the resulting force lines of two positive point charges be like this:</p>
<p><img src="http://i.stack.imgur.com/3jnkx.jpg" alt="enter image description here"></p>
<p>I would expect this:
<img src="http://i.stack.imgur.com/KIltz.jpg" alt="enter image description here"></p> | g8466 | [
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<p>Approaching the following question</p>
<blockquote>
<p>Imagine we have a collection of $N = 100$ simple harmonic oscillators.
The total internal energy is $U = q \epsilon$ where $q$ is the number of energy
quanta. Assume $q >> N >> 1$. If we double the internal energy, by how
much will the entro... | g8467 | [
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0.028634022921323776,
-... |
<p>I would like to ask if there is any Nuclear process which can be used to produce a <a href="http://en.wikipedia.org/wiki/Wireless_power" rel="nofollow">wireless power</a> ? </p>
<p>Is there any nuclear process can be radiate to the environment with no harm to human beings?</p>
<hr>
<h1>How can I use the photo ele... | g8468 | [
0.005591431632637978,
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0.05795668065547943,
0.05442827567458153,
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0.0216... |
<p>The Lagrangian density for QED is</p>
<p>$$ \mathcal{L}=-\frac{1}{4}F^{\mu\nu}F_{\mu\nu}+\bar{\psi}(i\gamma^{\mu}D_{\mu}-m)\psi $$</p>
<p>with</p>
<p>$$F_{\mu\nu}=\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu} $$
$$ \bar{\psi}=\gamma^{0}\psi^{\dagger}$$
$$D_{\mu}=\partial_{\mu}+ieA_{\mu}$$</p>
<p>$U(1)$ local gauge... | g8469 | [
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0.07429398596286774,
0.04375302419066429,
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0.03085116669535637,
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0.0081635825... |
<p>Can someone kindly help me to know how can i get electron momentum density for one orbital like home?
what is the theory of electron momentum density? how can I derive electron momentum density from real electron density?
how can i use Fourier transform?</p> | g8470 | [
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<p><strong>Can a student with a heavy math background start learning physics with Goldstein's "Classical Mechanics"?</strong></p>
<p>Or is the book too obtuse with basic physics that I need to start elsewhere?</p> | g277 | [
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<p>I want to know about the importance of the stability,
generally,why is stability important in super-gravity?
and why do we like these solutions?</p> | g8471 | [
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<p>We know that nuclear magnetic moment can be expressed in terms of the expected value for nuclear spin as:</p>
<p>$$\langle\mu\rangle =[g_lj+(g_s-g_l)\langle s_z\rangle]\frac{\mu_N}{\hbar}$$</p>
<p>(Cf. Krane), where $\vec{j}$ is the <em>total</em> angular momentum, $\vec{l}+\vec{s}$.</p>
<p>How does the expected ... | g8472 | [
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0.015862256288528442,
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... |
<p>How deep can I go if jumping from 50m?</p> | g8473 | [
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0.019329356029629707,
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0.03308030962944031,
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-0... |
<p>The electric field of a point charge goes like $\displaystyle\frac{1}{r^2}$</p>
<p>The electric field of an infinite line goes like $\displaystyle\frac{1}{s}$</p>
<p>The electric field of an infinite plane is constant</p>
<p>Is there an intuitive way or some insight to understand such results and realize that the... | g8474 | [
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<p>I'm very young so know no calculus whatsoever.</p>
<p>I want to be able to calculate uncertainties for a Physics course I'm doing online, but I believe you need to have knowledge of differentials to do this in some cases.</p>
<p>Do you need knowledge of calculus to be able to calculate with differentials?</p> | g8475 | [
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0.005458842031657696,
0.014306332916021347,
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<p>I have earlier posted the same question <a href="http://math.stackexchange.com/questions/117876/conversion-of-motion-equation-from-cartesian-to-polar-coordinates-is-covariant">here</a> on <code>math stackexchange</code> but without any answer. As the question concerns tensors, I guess that I have come to the right p... | g8476 | [
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0.012763059698045254,
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0.00784586276859045,
0.049144111573696136,
-0... |
<p>When I first studied friction I faced f = $\mu$ N where f is force of friction, $\mu$ is coefficient of friction for the surface considered and N is the normal force for the body on surface. Now f is a force so it must be a vector which means it has a direction. N is normal force so it has direction too. But both f ... | g8477 | [
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0.001940... |
<p>Can you explain, please, <strong>step-by-step</strong> how an <a href="http://en.wikipedia.org/wiki/Electronic_filter" rel="nofollow">electronic filter</a> does work?
For example, high pass filter. I know It's a trivial things, but I can't get it completely. Don't bring me formula and etc. Just explanation in three ... | g8478 | [
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-0.05878005549311638,
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0.08188290894031525,
0.0137... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2219/beginner-physics-resources">Beginner Physics Resources?</a><br>
<a href="http://physics.stackexchange.com/questions/12175/book-recommendations">Book recommendations</a> </p>
</blockquote>
<p>I'm w... | g98 | [
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0.013829582370817661,
0.03114432841539383,
0.050515566021203995,
0.02650926448404789,
0.006763909477740526,
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-0.027507713064551353,
0.009678046219050884,
0.015582690015435219,
0.03187807276844978,
-0.0... |
<p>When considering the 'Heisenberg' picture of the harmonic oscillator, I've come across the step:
$$\begin{align}
\left\langle n\left|(\hat{q_H}\hat{H}-\hat{H}\hat{q_H})\right|k\right\rangle &= (E_k-E_n)q_{nk}
\end{align}$$</p>
<p>where $\hat{q_H}$ is a position operator. I realise that this must be a pretty s... | g8479 | [
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0.023263538256287575,
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-0.027002088725566864,
-0.009006580337882042,
... |
<p>From Wikipedia (http://en.wikipedia.org/wiki/Water_electrolysis#Efficiency):</p>
<blockquote>
<p>The electrolysis of water requires a minimum of 237.13 kJ of electrical energy input to dissociate each mole.</p>
</blockquote>
<p>Each mole of water gives you 2 grams of Hydrogen and 16 grams of Oxygen (http://www.l... | g8480 | [
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0.012885996140539646,
0.034077469259500504,
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0.06668403744697571,
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-0.0018148041563108563,
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-0.020640823990106583,
-0.03188600391149521,... |
<p>Static electric fields are supposed to be conservative in nature and therefore give $0J$ work if traversed over a loop. However in the following problem I got non zero work by a static electric field. How can I explain this work ?</p>
<p><img src="https://lh4.googleusercontent.com/-S3oWGGy_30Y/UuLvVIXZnFI/AAAAAAAAA... | g8481 | [
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0.059918344020843506,
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-0.043926190584897995,
0.005389141384512186,
0.003814536379650235,
-0.004143642261624336,
-... |
<p>The question is to finde the initial horizontal velocity of the ball at end of the ramp, where it is released.</p>
<p>I know how to do this using gravitational potential energy and kinetic energy ($v=\sqrt{2gh}$), assuming all potential energy is converted into kinetic energy but the question is asking me to find t... | g8482 | [
0.08551327884197235,
0.02655821479856968,
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0.026562398299574852,
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0.03509971499443054,
0.008054223842918873,
0.0134... |
<p>White light is always said to contain all the different wavelengths of light. Why, then, can we 'make' new colors simply by adding wavelengths? Is it just a matter of our perception, that, when two colors are added together, they appear to be the wavelength of another color. Or are the waves actually forming into an... | g8483 | [
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0.006914319936186075,
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0.... |
<p>For the same speed and inclination, is the physics acting on the body equivalent? Lets assume the person keeps pace with something that moves perfectly uniformly.</p> | g8484 | [
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-0.00... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/21851/prove-that-negative-absolute-temperatures-are-actually-hotter-than-positive-abso">Prove that negative absolute temperatures are actually hotter than positive absolute temperatures</a><br>
<a href="ht... | g278 | [
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0.010347283445298672,
0.010644334368407726,
0.029547693207859993,
0.03844556584954262,
-0.0741933137178421,
0.03123536705970764,
-0.03916247561573982,
-0.021610703319311142,
-0.004823841620236635,
0.03391565382480621,
0.008454455062747002,
0.005... |
<p>I'm an aspiring physicist who wants to self study some Quantum Physics. My thirst for knowledge is unquenchable and I can not wait 2 more years until I get my first quantum physics class in university, so I want to start with a self study. I am enrolled in a grammar school and the most gifted among the gifted (not m... | g1004 | [
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0.021231312304735184,
0.0180213563144207,
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0.005319610703736544,
0.000322075531585142,
0.05300034210085869,
0.019557930529117584,
0.0... |
<p>I'd like answers both in the more intuitive side an on the more precise side. </p>
<p>Thinking of water as "cubes" of water, for example, would allow pressure in the z axis to be independent of the y or x axis. Choosing other "shapes", like a triangular prism, yield different results. Will this fact, then, be depe... | g8485 | [
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<p>I was trying to find out the cause behind the Explosion at petrol pump due to the Mobile phones but eventually it turns out it is not Radio Frequency which may cause the explosion rather it is totally the static electricity which may cause serious explosion and ignition of vapors,
The other reason I found is, due t... | g8486 | [
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0.038530319929122925,
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-0.01... |
<p>How does <a href="http://en.wikipedia.org/wiki/Annihilation" rel="nofollow">annihilation</a> work? I'm wondering why matter and antimatter actually annihilates if they come into contact. What exactly happens? Is that a known process? Is it just because of their different charges? Then what about neutrons and anti-ne... | g935 | [
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0.01189708337187767,
0.007875420153141022,
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<p>I recently heard about the possibility of the creation of a "baby" universe or "pocket" universe from our space time,the theory says that concentrating enough mass into a tiny volume of space (like in black holes) a pocket of false vacuum would form e perhaps it'll continue to expand following it's own inflation per... | g8487 | [
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0.0685211569070816,
0.0244... |
<p>It seems impossible for an ice cube to contain bubbles. the ice should freeze far too slowly for a bubble to get trapped within it. However, virtually all ice (that I have seen in my freezer) contains gas bubbles. How is this possible? </p> | g279 | [
0.003561601974070072,
0.08101401478052139,
0.004364926367998123,
0.0555550642311573,
0.023475052788853645,
0.04012944549322128,
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0.046751562505960464,
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0.04975243657827377,
-0.019333112984895706,
-0.01... |
<p>In our quantum optics lecture we derived the formula for the <a href="http://en.wikipedia.org/wiki/Casimir_effect" rel="nofollow">Casimir force</a> between two plates (or at least the force per unit surface, since for two infinite plates we would have an infinite force). It was then said, that in experiments one oft... | g8488 | [
0.022325905039906502,
0.028935693204402924,
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0.00828818790614605,
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0.02651057206094265,
0.011928229592740536,
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-0.006655804812908173,
-0.03103514574468136,
0.055028609931468964,
-0.04424687847495079,
0.0... |
<p>What what I understand, hydrostatic pressure is the "weight" of the water pushing against objects. But if this is true, why is hydrostatic pressure perpendicular to the surface it acts on instead of always going down?</p>
<p>For example, if you placed a book on a desk, the book's weight would push against the desk,... | g8489 | [
0.07296154648065567,
0.0282610971480608,
0.010385299101471901,
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0.04210783168673515,
0.0818987786769867,
0.02608896605670452,
0.021117420867085457,
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-0.03748386725783348,
0.01115353498607874,
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-0.005255580879747868,
0.002156514... |
<p>Actually I am not a physics student but I have to give a lecture about Fluorescence lifetime imaging(FLIM). I am thinking of comparing this techniques to another imaging techniques.
Does anyone know what is the best imaging techniques that is comparable to FLIM?
Thank you</p>
<p>Soha</p> | g8490 | [
0.02856980450451374,
0.007802653592079878,
0.012906376272439957,
0.021337304264307022,
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0.004861123859882355,
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0.06747668236494064,
0.009873568080365658,
0.025627627968788147,
0.00... |
<ol>
<li><p>What is the precise definition of <a href="http://en.wikipedia.org/wiki/Unified_field_theory">unification of fields</a> (in classical and quantum mechanics)?</p></li>
<li><p>In general, does unification of a field mean that we can write both of them at both sides of an equation (like Maxwell's laws)? Or doe... | g8491 | [
0.029149143025279045,
0.035601235926151276,
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0.08347538113594055,
0.03376420587301254,
0.010381004773080349,
0.0857870802283287,
0.015445580706000328,
-0.008578971959650517,
-0.06291921436786652,
0.00803463440388441,
-0.007692985702306032,
-0.0174... |
<p>I've spent some time reading wiki etc. What I get now is that apart from the normal light amplitude information, <a href="http://en.wikipedia.org/wiki/Holography" rel="nofollow">holograms</a> also record the phase information of light. But this is so difficult for me to understand. In my understanding to display the... | g8492 | [
0.006602445151656866,
0.05539175868034363,
0.0060373712331056595,
-0.008804310113191605,
0.0020860519725829363,
0.02795250341296196,
0.040197014808654785,
0.017390692606568336,
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0.017286408692598343,
-... |
<p>I am a physics enthusiast and I have a question: Why is it meaningless to express the '$\pm$' (standard deviation) value as a percentage?</p> | g8493 | [
0.04963541030883789,
0.005401881877332926,
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0.02415631338953972,
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0.044671643525362015,
0.006820992100983858,
0.0035668727941811085,
-0.05942844972014427,
0.04326385259628296,
0.003672993276268244,
-0.016977323219180107,
-0.00... |
<p>let $|\psi\rangle = a_0|0\rangle + a_1|1\rangle \in H$. Show that there are 3 real $r_x,r_y,r_z$ s.t. $$|\psi\rangle \langle\psi|= \frac{1}{2}(I + r_x\sigma_x + r_y\sigma_y + r_z\sigma_z.)$$</p>
<p>Any suggestions on where to start with this?</p> | g280 | [
0.022199271246790886,
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0.00014415866462513804,
0.03816258907318115,
-0.03427726402878761,
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0.02168728969991207,
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0.017486052587628365,
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0.00791256595402956,
-0.009515532292425632,
... |
<p>I have an idea of making a tennis serving machine. I will briefly describe what it is:</p>
<ul>
<li>The machine is configured to serve the ball at a fixed speed to the center of the left (or right) service court</li>
<li>Based on the rotation in 3 directions (X,Y,Z) of the ball, the machine would let the ball land ... | g8494 | [
0.047923605889081955,
-0.014565185643732548,
-0.014063859358429909,
-0.04596497118473053,
0.010675033554434776,
0.017876407131552696,
0.06114821881055832,
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0.015345841646194458,
-0.03615335375070572,
0.026241783052682877,
0.08708304911851883,
0.0... |
<p>What really is <a href="http://en.wikipedia.org/wiki/Reflection_%28physics%29" rel="nofollow">reflection</a>? Is it just the reemission of EMR? I asked my teacher, he said in quantum sense, it is true. But when I read something about emissivity in Stefan Boltzmann's equation, it states that if an object reflects mos... | g92 | [
-0.009937508963048458,
-0.0035227376502007246,
-0.005815513432025909,
0.0051635331474244595,
0.06926241517066956,
0.060123179107904434,
0.028224170207977295,
0.028631217777729034,
-0.0029874362517148256,
-0.04385834187269211,
-0.03846955671906471,
0.03295525163412094,
0.05150086060166359,
... |
<p>The tensor of inertia of a solid sphere is $I_{ii}=\frac{2}{5}MR^2$ about an axis passing through its CM. Why would the tensor of inertia of each hemisphere about that axis be $I_{ii}=\frac{2}{5}mR^2$, where $m=\frac{M}{2}$ is the mass of the hemisphere? Is it because the tensor of inertia of each hemisphere would b... | g8495 | [
0.025889774784445763,
-0.010272267274558544,
0.002914970740675926,
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0.011816911399364471,
0.022211264818906784,
0.12877987325191498,
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-0.0008638114668428898,
-0.054856326431035995,
-0.012424042448401451,
0.008601479232311249,
... |
<p>The escape velocity of Earth is $v=\sqrt{\frac {2GM}{R}}$, where $M$ is the mass of the Earth and $R$ it's radius (approximating it as a sphere), and is much less than light speed $c$.</p>
<p>But I want to know the escape velocity of black holes. Is it much more than light speed?</p> | g281 | [
0.0033662759233266115,
0.06929954886436462,
0.015716277062892914,
0.024461908265948296,
0.015154674649238586,
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0.07842311263084412,
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0.0005143510061316192,
0.016172129660844803,
0.027003418654203415,
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0.... |
<p>First, I would like to apology for my lousy English used here, as being a non-native english speaker, </p>
<p>I am currently using Classical Mechanics as a tool to learn how to construct a theory as an end. Therefore, I have a few questions, and a few reasonings behind them (I only consider reality, not imagined wo... | g8496 | [
0.037545543164014816,
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0.050468116998672485,
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0.048331987112760544,
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-0.031562790274620056,
-0.01035173237323761,
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0.030844591557979584,
... |
<p>I always think that it is not possible to escape from within event horizon. However, some one recently told me with deep conviction that it <em>is</em> possible with sustained energy output. I countered with calculations in Schwarzschild metric showing that any objects below event horizon in the simplistic black hol... | g8497 | [
0.0025025794748216867,
0.024991996586322784,
0.01735207624733448,
0.052380356937646866,
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0.003031219355762005,
0.0326225683093071,
0.01541901659220457,
-0.0888640433549881,
0.02418600022792816,
0.016713032498955727,
0.018209237605333328,
-0.020177925005555153,
-0.0359... |
<p>I'm a little unclear as to how <a href="http://en.wikipedia.org/wiki/Quantum_field_theory" rel="nofollow">QFT</a> differs from Elementary <a href="http://en.wikipedia.org/wiki/Particle_physics" rel="nofollow">particle physics</a>. They both use pictorials of Feynman graphs, is it that Elementary particle physics ass... | g8498 | [
0.042942073196172714,
0.03767647594213486,
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0.061596594750881195,
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0.024320198222994804,
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-0.027623668313026428,
0.02588416449725628,
-0.010262647643685341,
0.01291521918028593,
-0.0... |
<p>I'm afraid this question is a little too open-ended, but bear with me while I find a better formulation.</p>
<p>carbon allotropes (like fullerenes and graphene) are regular patterned. Conduction bands of electrons in graphene in particular, have energy-momentum relationships that make them behave as massless carrie... | g8499 | [
0.06572474539279938,
0.033806171268224716,
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0.04347814992070198,
0.036562737077474594,
0.01806672289967537,
-0.024815907701849937,
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-0.02943379431962967,
0.022160619497299194,
-0.03176754340529442,
0.013686208054423332,
-0.0... |
<p>What are some good lecture notes to learn quantum field theory from, available online?</p> | g282 | [
0.020797979086637497,
0.0013782146852463484,
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0.042938537895679474,
0.007345591206103563,
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0.004686895292252302,
0.05407429113984108,
0.005236365366727114,
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0.014342044480144978,
... |
<p>I have a top of unknown mass that has a moment of inertia $I=4\times 10^{-7} kg \cdot m^2$. A string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 m.</p>
<p>Could somebody help me derive some equations to help with this? Or to get me in the right direction? I have... | g894 | [
0.010805455036461353,
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0.0027573835104703903,
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0.05114263296127319,
-0.015508556738495827,
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0.01744554005563259,
-0.07347960025072098,
0.01774052157998085,
-0.013961578719317913,
-... |
<p>Where/what is emitting cosmic background radiation, and when did it come into existance, was immediately after the big bang?</p>
<p>I know that the universe isn't 3D in the traditional sense, and I don't pretend to understand it. However if the big bang originated from a single point, and the cosmic radiation was e... | g8500 | [
0.06843017041683197,
0.0025277533568441868,
0.030854325741529465,
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0.036288924515247345,
0.016563059762120247,
0.04704912006855011,
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0.0017494611674919724,
0.07260841876268387,
0.032741282135248184,
0.0... |
<p>Recently I got the book "On the Shoulders of Giant" from Stephen Hawkings. It consists of more than 1000 pages of classical publications in physics. However 900 pages are given to the work of Copernicus, Galilei and Newton and 100 pages are given to the papers of Einstein. Therefore I think this books gives a wrong ... | g8501 | [
0.02751452662050724,
0.045319247990846634,
0.005402067676186562,
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0.0348883792757988,
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0.005555721465498209,
0.06874243170022964,
0.04764118418097496,
-0.06047797575592995,
0.033720772713422775,
-0.007... |
<p>So I know that conduction is transfer of thermal energy by direct contact via molecular collisions. </p>
<p>For conduction, $Q/t$ is the rate of heat flow and is heat current ($I$). My textbook says that the rate of heat flow is constant across any number of slabs between 2 heat reservoirs, and I understand why thi... | g8502 | [
0.09503520280122757,
0.017452850937843323,
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0.04707135260105133,
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0.05116770789027214,
0.024545244872570038,
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0.01719176210463047,
-0.0370730422437191,
0.05137518793344498,
0.013595569878816605,
-0.0017... |
<p>Why sometimes we remember that "classical" lagrangians of fermions are constructed from grassmann numbers, while sometimes don't? </p>
<p>For example, for Majorana's field in terms of 2-component spinors (you can read about this representation <a href="http://www.mdpi.com/2073-8994/5/4/271" rel="nofollow">here</a> ... | g8503 | [
0.06101047620177269,
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0.0001674076629569754,
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0.059069421142339706,
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0.09516309201717377,
0.04352070391178131,
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0.0028800086583942175,
-0.011702596209943295,
0.019977634772658348,
-0.0012589988764375448,
... |
<p>What is the modern mainstream way to deal with the <a href="http://en.wikipedia.org/wiki/Measurement_problem" rel="nofollow">measurement problem</a>? For this question, the measurement problem is the problem of formalizing wave function collapse when the observer is part of the model (say I want to simulate an obser... | g8504 | [
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0.015984823927283287,
-0.04746319353580475,
0.02674408070743084,
0.0... |
<p>This might be a stupid question, but nonetheless, it has been bothering me.</p>
<p>If you take a photon, make it go through some atoms in a solid, liquid or whatever, then you have the chance of this photon being absorbed by an electron, and thereby exciting the electron. This requires the photon to have enough ene... | g723 | [
0.008613675832748413,
0.0344960018992424,
0.00841339398175478,
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0.047770120203495026,
0.0006235654000192881,
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0.034923069179058075,
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-0.013657023198902607,
-0.0017266180366277695,
0.01285537239164114,
-0.004257898312062025,
0... |
<p>I started studying the BMS symmetry in connection with the paper:
<a href="http://arxiv.org/abs/1312.2229" rel="nofollow">http://arxiv.org/abs/1312.2229</a>
and there are a few strange things I noticed.</p>
<p>First of all, from reading the original papers by Bondi, Metzner and Sachs, I know that the "BMS symmetry"... | g8505 | [
0.010440417565405369,
0.008840128779411316,
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-0.02829204685986042,
0.03936688229441643,
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0.00727741327136755,
0.06668177992105484,
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0.007285681553184986,
-0.0158291757106781,
0.03499927744269371,
0.0372522696852684,
0.0017000... |
<p>Consider the standard map (also known as <a href="http://www.scholarpedia.org/article/Chirikov_standard_map" rel="nofollow">Chirikov map</a>):
$$
p_{n+1} = p_n + K \sin(\theta_n) \\
\theta_{n+1} = \theta_n + p_{n+1}
$$</p>
<p>I know that the diffusion coefficient according to the Einstein relation is defined t... | g8506 | [
-0.02161182463169098,
-0.008767884224653244,
-0.03582596406340599,
0.02711840346455574,
0.06350667029619217,
0.05083465203642845,
0.07131753116846085,
0.05371281877160072,
0.007637249771505594,
-0.025580400601029396,
-0.023461509495973587,
0.033800043165683746,
0.03684898838400841,
0.01104... |
<p>Imagine you have a sealed cylindrical vessel with a given radius with a compressed gas inside. Let's give some numbers, 5 cm radius and 100 atm pressure. You poke a hole in the vessel and the gas will flow out, propelling the vessel in the opposite direction with a given force. Intuition tells me that this force dep... | g8507 | [
0.044190287590026855,
0.04657455161213875,
0.0199635848402977,
-0.02076045237481594,
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0.03146027401089668,
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-0.016972649842500687,
0.07648617774248123,
0.033447012305259705,
-0.017752567306160927,
0.0004... |
<p>Imagine there's a sphere of radius $R$ which has constant density $\rho$ and you can stand anywhere inside of the sphere. Wherever you stand within the sphere, you'll only feel gravity coming from the mass at smaller radii than the point at which you're standing. That is, you could be standing at some point with ra... | g8508 | [
0.006180732976645231,
0.03173753246665001,
-0.010352297686040401,
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0.014832397922873497,
0.059408023953437805,
0.044595181941986084,
0.049304600805044174,
-0.05773089453577995,
-0.020674103870987892,
0.0007488090195693076,
-0.04469434171915054,
-0.03160388767719269,
0... |
<p>could exist 2 different Hamiltonians $ H1 $ and $ H2$ so</p>
<p>a) The SEMICLASSICAL eigenvalue staircase is equal i mean the expression $$ \oint _{C} p.dq = n+\alpha $$</p>
<p>but the real eigenvalues $ E_{n} (1,n) $ and $ E_{n}(2,n) $ are completely different</p> | g8509 | [
-0.023667743429541588,
-0.026327235624194145,
-0.005528355948626995,
0.03569072112441063,
0.04480721801519394,
0.023905500769615173,
0.037319499999284744,
0.03492295369505882,
0.03814564272761345,
0.015269295312464237,
-0.004034901037812233,
0.027686428278684616,
-0.014223053120076656,
0.0... |
<p>I am studying the transition from the second excited electronic state of molecular oxygen, $b^1\Sigma_g^+$ , to the ground state, $X^3\Sigma_g^-$. I know that the ground state has total angular momentum $J=1$, total spin $S=1$, and three spin sublevels $(m_s=-1,0,+1)$. The upper state has $J=0$, $S=0$, and one suble... | g8510 | [
-0.023142972961068153,
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0.008724558167159557,
0.09599291533231735,
0.023322362452745438,
0.026107173413038254,
-0.023054247722029686,
-0.05455981194972992,
0.05577627569437027,
0.026090538129210472,
-0.... |
<ol>
<li><p>All the linearly independent eigenfunctions of the parity operator $\mathcal{P}$ form an infinite set and all the linearly independent eigenfunctions of the unit operator $\bf 1$ also form an infinite set. Is the cardinality of these two sets same or different? </p></li>
<li><p>Every function is an eigenfun... | g8511 | [
0.025899801403284073,
0.017373714596033096,
0.01643914170563221,
-0.03603746369481087,
0.042781658470630646,
-0.05243435874581337,
0.011195824481546879,
0.06469248980283737,
0.009204640053212643,
-0.039325740188360214,
-0.0436987541615963,
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-0.0055185225792229176,
-0.0... |
<p>I am using <a href="http://chipmunk-physics.net/" rel="nofollow">Chipmunk</a>'s physics engine to simulate 2D classical mechanics of solid polygons (excellent by the way!). The only way you can alter the spontaneous behaviour of the the simulated objects is to apply <a href="http://chipmunk-physics.net/release/Chipm... | g8512 | [
-0.021401457488536835,
0.02463465742766857,
-0.005879542790353298,
-0.027836496010422707,
0.0012840143172070384,
-0.061757516115903854,
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... |
<p>I am trying to find the energy of a wave travelling through a solid material in a 2D Finite Element Method (FEM) - Simulation. </p>
<p>As a general approach I would try to use $E_{kin}=\frac{1}{2}mv^2$ at the highest particle velocity $v$, as this would be the point, where all the energy in the wave is kinetic and ... | g8513 | [
0.1054317057132721,
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-0.009915380738675594,
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0.0016926868120208383,
0.03462951257824898,
-0.005282551050186157,
0.035181544721126556,
0.03... |
<p>If I stick a metal and insulator together, will the Fermi level of the metal align with the insulator?</p>
<p>When people draw a band diagram for a metal-oxide-semiconductor heterostructure, I never see them label the Fermi level of the oxide. What is the Fermi level of the oxide relative to the metal and insulato... | g8514 | [
-0.02716023474931717,
0.04627545550465584,
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0.0... |
<p>The standard lore in relativistic QFT is that poles appearing on the real-axis in momentum-space Green's functions correspond to particles, with the position of the pole yielding the invariant mass of that particle. <em>(Here, I disregard complications tied to gauge-fixing and unphysical ghosts)</em></p>
<p>Schema... | g8515 | [
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0.032625712454319,
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0.0096... |
<p>Upon reading about the principal bundle picture of (quantum) field theory I encountered two different definitions of the gauge group:</p>
<ul>
<li><strong>Local gauge group $G$</strong>. Corresponds to the fibers of the $G$-bundle. Local gauge transformations correspond to the change of coordinates in which fields ... | g8516 | [
0.01505094114691019,
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-0.028479043394327164,
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-0.01857396587729454,
0.019346879795193672,
0.032818980515003204,
-0.003585868515074253,
-0.0512357... |
<p>What happens when the explosive energy of a grenade or a bomb is contained in a container, if you will, and no energy can be released through the container in the form of heat or sound etc...? Just theoretically asking?</p>
<p>I just want to know what happens when we take a huge explosion or any explosion and shrin... | g8517 | [
0.02823490835726261,
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-0.033996... |
<p>Usual central potentials produce quantum spectra with energy levels going as $n$, $n^2$, $n^3$ and so on, being $n$ the quantum number of the orbit. In the other extreme we have "dirac-delta" potentials which have only a single discrete eigenvalue. I was wondering, what kind of potential do we need for producing an ... | g8518 | [
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0.010284487158060074,
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0.04724933207035065,
0.0... |
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