question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>The true ground state of the anti ferromagnetic quantum Heisenberg Model (nearest neighbor only)is known to be a singlet (I think this is Liebs theorem.)</p>
<p>Since a singlet is invariant under rotations, the ground state doesn't break the rotational symmetry of the Hamiltonian (which the classical Neel state doe... | g17300 | [
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<p>I have used the rules for addition of angular momenta to work out the <a href="http://en.wikipedia.org/wiki/Clebsch%E2%80%93Gordan_coefficients" rel="nofollow">Clebsch-Gordan coefficients</a>, which all seem right except for state $\lvert0,0\rangle$:</p>
<p><strong>For n = 1</strong></p>
<p>\begin{align}
\lvert1,1... | g17301 | [
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<p>Say in a photoelectric experiment, we find a stopping potential of 1.85V for $\lambda=3000\overset{\circ}{A}$ and of 0.82V for $\lambda = 4000 \overset{\circ}{A}$.</p>
<ol>
<li>How can I get the Planck's constant from the above information?</li>
<li>Determine the work function of the sodium in electron-volts.</li>
... | g17302 | [
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<p>Can somebody provide a fairly brief explanation of what the chiral anomaly is? I have been unable to find a concise reference for this. I know QFT at the P&S level so don't be afraid to use math.</p> | g17303 | [
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<p>Can somebody help show me how a pulsed spherical wave has a wavefunction of the form U(r,t) = (1/r)a(t-r/c), where a(t) is an arbitrary function, r is the radius of the spherical wave, t is time, and c is the speed of light?</p> | g17304 | [
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<p>I'm trying to reconcile an apparent contradiction between explanations given by Dr. Cox in <a href="http://www.colbertnation.com/the-colbert-report-videos/253947/october-28-2009/brian-cox">2009</a> and <a href="http://www.youtube.com/watch?v=BeTjPsnzH-c&feature=related">2012</a>, and those given by a panel of <a... | g17305 | [
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<p>I have recently briefly read about new methods as the Britto-Cachazo-Feng-Witten (<a href="http://arxiv.org/abs/hep-th/0501052">BCFW</a>) on-shell recursion method.</p>
<ol>
<li><p>Can anybody please tell me about the essence of it? </p></li>
<li><p>What does it mean for the recursion to be on-shell? </p></li>
<li>... | g17306 | [
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<p>I'm trying to model the thermal noise from a capacitor. The capacitor is connected directly into an amplifier with resistance $R_{A}$ and capacitance $C_{A}$. A noisy capacitor is modelled as a thermal noise source $V_{J}$ due to a frequency-dependent resistor $R_{J}= 1/\omega C_{J} \tan \delta$ ($\tan \delta$ is th... | g17307 | [
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<p>Consider the plot below, showing the running of different masses due to renormalization for a certain point of the (c)MSSM. I am able to exactly reproduce the plot, including the running of M1, M2, M3. However, I can't get the running values of the actual particle masses (e.g. $m(\chi^0_1)$) from the generators. I t... | g17308 | [
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<p>If a splitting atoms / fusing isotopes (fission bomb, fusion bomb) yields more energy than chemical changes (TNT, et al) yields more energy than physical change (hydrogen bonds forming during water condensation), then why doesn't the trend continue BELOW the atomic level, or do physicists have no clue about that stu... | g17309 | [
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<p>Suppose there is a fully functional <a href="http://en.wikipedia.org/wiki/Space_elevator" rel="nofollow">space elevator</a> built on Earth. The base is attached to coordinates </p>
<p>$
(\lambda, \varphi) = (0,0)
$ </p>
<p>e.g., on the equator on the zero-meridian. </p>
<p>What would happen if we were to suddenly... | g17310 | [
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<p>is there a Hamiltonian reformultion of gravity ?=? if so if we use the usual Quantization scheme we can not we quantizy the gravity ??</p>
<p>in terms of a Gauge Theory with the potential $ A_{\mu}^{i} $ how can we get the Schroedinguer equation ??</p> | g17311 | [
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<p>Is there any way to add some type of 'optical brightener' to a PC+ABS molded part? I'm looking for something that will not affect the color / gloss. Ideally it will be a material that can be added during the molding process and only be seen by a camera with a UV light source + UV Pass filter. Does something like thi... | g17312 | [
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<p>I heard that there have been some propositions about describing the collapse of the wave-function by adding non-linear terms, but I couldn't anything in any any textbooks or even articles (probably those propositions never reached a good level of consistency). However, I'd like to read about it. Could someone send m... | g17313 | [
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<p>Has anyone invented an optical waveguide that can "pipe" a scene from one place to another unaltered? More precisely, I want to displace (and/or rotate) a 4D light field.</p>
<p>An optical waveguide is an EM waveguide engineered to operate at visible wavelengths.</p>
<p>A light field is a computer graphics concept... | g17314 | [
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<p>I often heard AdS/CFT correspondence provides a powerful framework to study strong coupled system, which perturbation is not applicable. However, lattice method still works in non-perturbative domain. My question is, what is the advantage of AdS/CFT? Is there any example impoosible to access by lattice method (I don... | g17315 | [
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<p>We transmitted several messages to the space and listening to space for signs of intelligent life for years (SETI).</p>
<p>Assuming they have at least the same technology we have, could they detect these messages we sent out? </p>
<p>If not, how powerful transmitter is needed to make our word heard, let's say, fro... | g17316 | [
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<p>I was reading the article <em><a href="http://science.howstuffworks.com/moon4.htm" rel="nofollow">Moon Phases</a></em> on <a href="http://en.wikipedia.org/wiki/HowStuffWorks" rel="nofollow">HowStuffWorks</a>. In the picture, each moon has a dark green area which represents the shadow of the Sun. How is this shadow f... | g17317 | [
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<p>I was watching a show about the big bang theory. They were saying that in the beginning all that existed was energy. After the big bang that energy transformed into matter which then started forming into different elements. How exactly does energy change into matter and at what point does this happen?</p> | g17318 | [
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<p>Suppose we have a scalar field $\varphi$ with Lagrangian</p>
<p>$$ \mathcal{L} = \frac{1}{2} \kappa \left( \frac{\partial \varphi}{\partial x} \right)^2 + \frac{1}{2} \rho \left( \frac{\partial \varphi}{\partial t} \right)^2 \,. $$</p>
<p>Then the canonical momentum density is</p>
<p>$$ \pi = \frac{\partial \math... | g17319 | [
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<p>Vertical takeoff requires disposable rockets (would it a satellite rocket), which is a money loss, and also a lot of fuel, because initial velocity is zero. Also vertical takeoff seems risky, involves huge pieces of equipments, launch pads, to diminish risk.</p>
<p>Horizontal takeoff are done with a reusable aircra... | g17320 | [
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<p>Does fire create air resistance/drag? So, for example, would it be harder to swing a flaming sword than a normal one?</p> | g17321 | [
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<p>I am currently working on a data fit assignment for my class and ran into some confusion. I will post the entire question here so you can get some background but the only question I have is with what's given. As you can see we are given a frequency (120kHz) and the diamter of the source (6cm). What I need to continu... | g17322 | [
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<p>It is being said by some people, that quantum gravity entails that spacetime is an emergent phenomenon, and thus that the immaterial gives rise to the material. Is this what quantum graivty entails, or is this a bastardization of quantum gravity?</p>
<p>Further, is it true what Lee Smolin says that in order to unif... | g17323 | [
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<ul>
<li><p>How big should the black hole be so we can consider it to be classical? </p></li>
<li><p>When they claim that we can not probe shorter distances than the Planck length, can it be true? </p></li>
</ul>
<p>The argument says that, doing experiments with higher energies we would create even bigger black hole. ... | g17324 | [
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<p>I am looking for anexplanation of this phenomenon:</p>
<p><img src="http://i.stack.imgur.com/kCrBP.jpg" alt="sorry for bad drawing"></p>
<p>I was riding my bike, (not driving it, was sitting on the back seat) with the helmet on. While the glass of the helmet was intact, I could hear the sound of air striking my he... | g17325 | [
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<p>Two objects with half spin would consist of the elementary particles (i.e. quarks, fermions etc.) which are waves. Therefore all objects consist of several waves. Waves can exist at the same place at the same time. Depending on whether the wave is at a trough or a crest and the amplitude, the waves either cancel eac... | g17326 | [
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<p>Sometimes in quantum cosmology, when we are thinking about 'wave functions of the universe' we have in mind some sort of formal path integral, where we include not just the variations in the dynamical fields (metric and so forth), but also possibly some sort of prescription for summing over all possible topologies. ... | g17327 | [
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<p>I am stuck on a homework question, all because I dozed off in class.</p>
<p>I understand what a stream function is but I don't know how to apply it to calculate the flow in pretty much anything.</p>
<p>Here's the problem I am stuck on. I choose to not give out the question in it's entirety.</p>
<blockquote>
<p>... | g17328 | [
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<p>Borrowing from Laughlin's argument on quantum Hall effect, Kane and Mele argued why there must be edge states in graphene with spin-orbit coupling in one paragraph, which is above the one with equation (6), of this paper:</p>
<blockquote>
<p>C. L. Kane and E. J. Mele. “<a href="http://arxiv.org/abs/cond-mat/04117... | g17329 | [
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<p>I'm currently studying for an exam, where I'm looking into decays and gamma radiation. I then have a diagram where there are stuff like "Compton scattering", "Single Escape Peaks", "Double Escape Peaks" which all are calculated if I know the value of the photopeak. And all these three are actually quite well explain... | g17330 | [
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-0.04020298272371292,
-0.024183237925171852,
0.0017457276117056608,
0.06976702064275742,
0.022208... |
<p>I am trying to understand torque on a current loop which is placed in a uniform $\vec{B}$-field.</p>
<p><img src="http://i.stack.imgur.com/LSN6w.jpg" alt="Image">
(<a href="http://i.stack.imgur.com/oNO8a.jpg" rel="nofollow">http://i.stack.imgur.com/oNO8a.jpg</a>)</p>
<p>It says that $\vec{F}_2$ and $\vec{F}_4$ hav... | g17331 | [
0.010637965053319931,
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-0... |
<h2>Introduction</h2>
<p>Let say we have some stars and their spectral classification in the MK index. (not all HD stars)</p>
<ul>
<li>HD xxxx - B3</li>
<li>HD yyyy - O7</li>
<li>HD zzzz - F0</li>
<li>....</li>
</ul>
<p>If the stars share the same spectral type, then <strong>they share the same superficial temperatu... | g17332 | [
0.007815231569111347,
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<p>Pardon the misleading title.</p>
<p>It is to my understanding that moving/heavy clocks run slow. The Earth itself is under gravitational influence from many sources, and is moving. Is there a way to know how much 'faster' a clock would run if those influences were removed? I don't need a precise number, an order of... | g310 | [
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<p>I am getting quite confused with this terminology when I read the papers. Like while constructing the near horizon $AdS_3$ in the $D1-D5$ system one considers $IIB$ on $R^{1,4}\times M^4 \times S^1$ and one "wraps" $N_1$ D1 branes on the $S^1$ and $N_5$ D5-branes on $M^4 \times S^1$. What does it exactly mean? </p>
... | g17333 | [
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0.003499276703223586,
... |
<p>Chern-Simons Forms appears in several places in physics for examples, </p>
<ul>
<li><p>Fractional Quantum Hall Effect, </p></li>
<li><p>response of Topological Insulator, </p></li>
<li><p>invariant of knot, </p></li>
<li><p>electromagnetism in 2+1 space-time, and so on. </p></li>
</ul>
<p>I need to know about: </p... | g17334 | [
0.030844923108816147,
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0.009707990102469921,
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... |
<p>I need someone to clarify a conceptual problem I can't seem to surpass. Image there is a rollercoaster loop and a rollerbcoaster car enters the loop at high speed.</p>
<p>Once the car completes the full loop and is then at the last point at the bottom of the loop, I am trying to understanding the forces at play.</p... | g17335 | [
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<p>I was wondering how strong a magnet should be in order to be able to horizontally attract 0.2 Kg of pure iron at a distance of 0.3 M. Since I know nothing about magnets, I started looking for companies that provide magnets, and what different ones they offer, and I decided to pick a bar magnet. My problem here is th... | g17336 | [
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<p>I am supposed to calculate the electric field due to the charge density $\rho(x) = Ax e^{-\lambda |x|},$ where the density is supposed to be homogenous in $y,z$ direction. </p>
<p>The problem is, that the integral $$\phi(x) = \frac{1}{4 \pi \epsilon_0 } \int_{-\infty}^{\infty} \int_{-\infty}^{\infty} \int_{-\infty}... | g17337 | [
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0.018... |
<p>I think you can detect a neutron event with a scintillator (neutron to photon), photomultiplier tube (photon to electric signal) system, but how would a fusion neutron's energy (2.45 MeV) be typically measured?</p> | g17338 | [
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<p>I've been asked to draw a free body diagram of the following stepped bar setup:</p>
<p>$ P = 10kN \;and\; Q = 30kN$</p>
<p><img src="http://i.stack.imgur.com/1ajRX.png" alt="Stepped Bar"></p>
<p>The one shown in the answer is the following:</p>
<p><img src="http://i.stack.imgur.com/xU2p1.png" alt="Free Body Diag... | g17339 | [
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-0.04... |
<p>(1) Are there lexical/semantic knowledge bases for physics that can be used for automated reasoning and AI (like Princeton's <a href="http://en.wikipedia.org/wiki/WordNet#Database_contents" rel="nofollow">Wordnet</a> and MIT's <a href="http://en.wikipedia.org/wiki/Open_Mind_Common_Sense#ConceptNet" rel="nofollow">Co... | g17340 | [
0.04902101680636406,
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<p>I've implemented a fluid simulation based on the paper <a href="http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/ns.pdf" rel="nofollow">Stable Fluids</a>.</p>
<p>It works quite well, except I would like to have the velocity at the "upper" edge just to outflow and not to re-enter on the lower(opposite) ed... | g17341 | [
0.009502645581960678,
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<p>I have some questions about the history of <a href="http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation" rel="nofollow">Newtons law of universal gravitation</a>.</p>
<ol>
<li><p>Did Newton discover his <a href="http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion" rel="nofollow">three laws of mot... | g17342 | [
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0.026575403288006783,
0.0046... |
<p>I've been trying to simulate a spacecraft entering a circular capture orbit about Mars using Mathematica, but am having a little trouble. The simulation starts when the spacecraft enters Mars' sphere of influence. In order to find the correct positions and velocities for a circular orbit, I calculated the point of c... | g17343 | [
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0.00377... |
<p>So I was thinking about sound - and how anything below 20Hz is basically inaudible to humans (because it is too low of a frequency to be recognized), as well as anything above around 20KHz (because it is too high of a frequency to be recognized). I was thinking about this in terms of sight (light particles/waves), a... | g17344 | [
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-0.028635645285248756,
0.0005745167145505548,
0.0031363721936941147,
0.02442632056772709,
0... |
<p>Most high school textbooks distinguish several forms of energy.</p>
<ol>
<li><p>Mechanical:</p>
<p>-Kinetic</p>
<p>-Potential</p></li>
<li>Chemical </li>
<li>Electromagnetic</li>
<li>Nuclear</li>
<li>Gravitational</li>
<li>Thermal</li>
<li>Hydraulic</li>
<li>Electric</li>
<li>Mass</li>
<li>...</li>
</ol... | g17345 | [
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-0.021662823855876923,
0.04450925439596176,
-0.042473431676626205,
0.030635077506303787,
-0.... |
<p>I am trying to read Kittel for a project, and he mentions the properties on silicon and germanium so briefly, that I don't understand it at all. He talks about p states, and I don't really know what that means. I've taken quantum mechanics, but I don't understand what is actually being said. I hope someone with expe... | g17346 | [
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0.038151584565639496,
0.01592140831053257,
-0.... |
<blockquote>
<p>Given $\mathbf{F}=\langle 7.20,−12.0,28.2\rangle\text{ Newtons}$, find the component of $\mathbf{F}$ that acts perpendicular to member DA such that the vector addition of the perpendicular and parallel components of $\mathbf{F}$ ($\mathbf{F}=\mathbf{F}_\perp + \mathbf{F}_\parallel$) with respect to DA... | g17347 | [
0.039409369230270386,
0.0006332676857709885,
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0.029032276943325996,
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0.036808814853429794,
0.019532982259988785,
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-0.021509375423192978,
0.02743379957973957,
0.02598745748400688,
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... |
<p>If our Lagrangian is invariant under a local symmetry, then, by simply restricting our local symmetry to the case in which the transformation is constant over space-time, we obtain a global symmetry, and hence a corresponding Noether charge.</p>
<p>Because, however, this Noether charge didn't come from just any old... | g17348 | [
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0.04761817678809166,
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0.039035506546497345,
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0.033643... |
<p>I have a book question I'm trying to understand:</p>
<p><img src="http://i.stack.imgur.com/LJCeE.png" alt="http://i.imgur.com/IqmS9OB.png"></p>
<p>The first bit is easy enough. The second part I was confused so I checked the solution:</p>
<blockquote>
<p>B is into the page. The flux increases as the bar moves t... | g17349 | [
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0.03588854894042015,
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0.035644516348838806,
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-0.029287563636898994,
-0.0678873211145401,
0.08689474314451218,
0.00481477240100503,
0.01617... |
<p>In <a href="http://www.goodreads.com/book/show/8514649-quantum-mechanics" rel="nofollow">Zetilli's</a> book author says that we can interpret an inner product $\langle x | \psi(t) \rangle$ as a wave function $\psi (x,t)$ and i understand this.</p>
<p>Next he talks about how a state of the system $|\psi(t)\rangle$ c... | g17350 | [
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-0.015410738997161388,
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-0.03553253784775734,
0.011374590918421745,
0... |
<p>Given a Hilbert space of finite dimension $N$ with an orthonormal basis $\mathcal{B}=\{|0\rangle,\ldots,|N-1\rangle \}$ what is the most general unitary operation that commutes with the projector onto one of the basis elements (say $|0\rangle$), \emph{i.e.}, what is the most general $\mathcal{U}$ such that $\mathcal... | g17351 | [
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0.044565875083208084,
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0.04938076063990593,
0.014808151870965958,
0.0... |
<p>D-wave claims to have built 128 qbit quantum computers which are commercially available?</p>
<p>What I don't understand is that have they <em>really</em> been able to do this given that the scientific community is still struggling to make a quantum computer realizable (from what I have gathered)? </p>
<p><strong>I... | g528 | [
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-0.0740886926651001,
0.02233930490911007,
0.03874942660331726,
-0.005812784191220999,
-0.0167... |
<p>I don't understand at all what the time operators are in quantum mechanics. I thought that given a wave function, because it's a function of time, we could simple put in any time in the future to find it's time evolution. What is this time operator, why is it unitary, and how does it work?</p> | g529 | [
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0.01... |
<p>In an optics lab, where all optical beams pretty much reside in a plane, it is fairly simple to describe (linear) polarizations as vertical or horizontal (or s and p).</p>
<p>When we start talking about light coming from any angle (say, from any sky position), we now need a basis of polarization states <em>at every... | g17352 | [
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0.024961145594716072,
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0.004491377156227827,
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-0... |
<p>I know that <a href="http://en.wikipedia.org/wiki/X-ray" rel="nofollow">X-rays</a> can be detected by various ways, like ionizing of air particles.</p>
<p>Is there a way to detect X-rays,which are photons, by detecting? Can something absorb the energy of the X-rays and detect if it is there?</p> | g17353 | [
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0.0056932... |
<p>Today I read an introduction on an optical device called an <a href="http://en.wikipedia.org/wiki/Acousto-optic_modulator" rel="nofollow">acousto-optic modulator</a>, which is used in many optical experiments. It is the first time I have heard of this element. The material showed one example of having a laser beam s... | g17354 | [
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<p>An arbitrary qubit is represented as $\alpha|0\rangle+\beta|1\rangle$ with $|\alpha|^2+|\beta|^2=1$. If we know either $\alpha$ or $\beta$, the state can be completely identified. The 'arbitrariness' of an arbitrary qubit thus can be said to be '1'. For a known state this is '0'. Now if we consider an arbitrary two ... | g17355 | [
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0.003531441558152437,
0.019690237939357758,
-0.02121925726532936,
... |
<p>I know we can't move at the speed of light, but if we were to travel on a photon how fast would we see other photons going? The speed of light is constant... So do photons see other photons moving at the speed of light?</p> | g17356 | [
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0.006893510930240154,
0.03826073929667473,
0.04560529813170433,
0.004287533927708864,
-0.00446225... |
<p>I am stuck on a few issues in <a href="http://youtu.be/w5rCn593Dig?t=5m14s" rel="nofollow">this video</a>. (Note: It is at the frame concerning this question.)</p>
<p>In it, from what I understand (which could be wrong) we first apply the Hadamard gate to a qbit in the $\lvert 0 \rangle$ state. Then on that we use ... | g17357 | [
0.007313033100217581,
0.021556496620178223,
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0.0... |
<p>The question is very simple:</p>
<ol>
<li><p>Why does the moon or the earth or any another planet revolve <strong>anti-clockwise</strong>? </p></li>
<li><p>And can any planet (or satellite) revolve <strong>clockwise</strong>? </p></li>
<li><p>What is the physical law for this phenomenon?</p></li>
</ol> | g17358 | [
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<p>Let's say we have a magnet stuck to a metal bar, suspended above the ground. If I attach a paperclip to the magnet, where is the energy to hold the paperclip coming from (against the force of gravity), and for how long will the paperclip remain there - will it remain there forever?</p> | g17359 | [
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<p>I know that what <a href="http://en.wikipedia.org/wiki/Planck_length">Planck length</a> equals to.</p>
<ol>
<li><p>The first question is, how do you get the formula
$$\ell_P~=~\sqrt\frac{\hbar G}{c^3}$$ that describes the Planck length?</p></li>
<li><p>The second question is, will any length shorter than the Planck... | g870 | [
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<p>All objects above absolute zero emit radiation due to random collisions between the atoms they are made of. The spectrum of radiation emitted varies according to the temperature of the object, I believe because of the random speeds at which atoms hit each other, producing photons of random energies/wavelengths that ... | g17360 | [
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<p>General relativity tells us that what we perceive as gravity is curvature of space-time. </p>
<p>On the other hand (as I understand it) gravity can be understood as a force between objects which are exchanging (hypothetical) virtual particles called gravitons, similar to the way electromagnetic forces are due to ob... | g131 | [
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<p>Can gamma rays of high enough energy entering our planet's atmosphere reach the surface (50% probability)?</p>
<p>Or, in other words, is there a window for extremely high-energy gamma rays like for the visible spectrum and radio?</p>
<p>This figure, from <em><a href="http://imagine.gsfc.nasa.gov/docs/science/know_... | g17361 | [
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<p>A symmetry is spontaneously broken by an operator $\hat{O}$ which acquires a non-zero vacuum expectation value. This is expressed as </p>
<p>$$ \langle 0 | \hat{O} | 0 \rangle = v$$</p>
<p>The parameter $v$ is said to have dimensions of mass. Can someone demonstrate why this is the case? It makes intuitive sense, ... | g17362 | [
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<p>Obviously the question's title has an unspecified subtext: intuitive <em>to me</em>.</p>
<p>Some background to pitch the discussion appropriately: I have a broad understanding, more qualitative than quantitative, of the Lagrangian formulation of the standard model. My General Relativity is pretty vague. I have a po... | g17363 | [
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<p>How would I find the mass of "pure" matter, that is, non-quantized matter, for a given volume?Let's say I have a volume equal to 1 meter squared, and I completely filled it up with matter - that is, no space in between. What would be it's mass? </p> | g17364 | [
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<p>Almost every physical equation I can think of (even though I don't actually feel comfortable beyond the scope of classical mechanics and macroscopic thermodynamics, as that's enough for dealing with everyday's engineering problems) is expressed assuming continuous domains at least for one variable to range over; tha... | g17365 | [
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<p>Here is the problem:</p>
<p>A boy stands at the peak of a hill which slopes downward uniformly at angle $\phi$. At what angle $\theta$ from the horizontal should he throw a rock so that it has the greatest range? </p>
<p>I realize that the same question is posted here: <a href="http://physics.stackexchange.com/que... | g17366 | [
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<p>I've run into a conceptual road block. I'm coming to you guys because I think my adviser is getting annoyed with me. The concept involves a meniscus being pulled up a cylinder. I understand that the main force "pulling" on the meniscus at the contact line is due to the difference between the static and dynamic co... | g17367 | [
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<p>How we know that the spin of fundamental particles?
For example spin-0, 1/2, 1,2.. What is the experimental facts about spin?</p> | g211 | [
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<p>Eddy currents are setup in any metallic block which is in the vicinity of changing magnetic fluxes. These primarily cause heat losses, and in certain cases causes damping of the relative motion between the metallic block (where the currents are induced) and the magnet producing the field.To reduce these effects, we ... | g17368 | [
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<p>Does the Earth's rotation affect an object in the stratosphere?</p>
<p>Example: I attach an object to a weather balloon and let it go at latitude +40.7, longitude -73.9 (New York). It goes up until it hits the stratosphere (about 40 km up). Then the air is not dense enough for the balloon to go any higher so i... | g17369 | [
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<p>Previously I asked a question <a href="http://physics.stackexchange.com/questions/3442/question-on-dimensions-of-cft-operators-ref-magoo-hep-th-9905111">Question on dimensions of CFT operators (ref: MAGOO, hep-th/9905111)</a> here and it was (correctly of course) answered by Motl. I realized I didn't understand a p... | g17370 | [
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<p>Technically, 4 AA batteries will give out ~5V, which is equivalent to USB. Can you use 4 AA batteries to charge an iPhone, without messing up the Li-Ion cells used on iPhone?</p>
<p>So my question really has 3 parts:</p>
<ul>
<li>Do the Amps add up with each battery? So if one battery is 2000 mAh, will 4 batteries... | g17371 | [
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<p>I read a lot in <em>Road to Reality</em>, so I think I might use some general relativity terms where I should only special ones.</p>
<p>In our lectures we just had $\partial_\mu$ which would have the plain partial differentials. On a problem set, the Bianchi identity for the Maxwell field tensor is given as:
$$
\pa... | g17372 | [
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<p>The charge of a fundamental particle is a mysterious but obvious and well-known property of every non-neutral particle.</p>
<p>I can understand how, if a particle is an object, or thing, for want of a better word, in its own right, then it can have a property of charge, because it would just be a property that's at... | g17373 | [
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<p><strong>Prigogine's Min. principle</strong> states that in steady-state non-equilibrium systems the entropy generation rate is at a minimum, i.e., a system will seek a steady-state that has min entropy generation. This principle has a well-established proof, but applies to systems so close to equilibrium that there ... | g17374 | [
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<p>Proper time is used to parameterize the world line of a moving particle in a way which is Lorentz invariant, which is elegant and powerful. Since space and time are usually treated on the same footing, I'd expect proper length to be a powerful parameter of some sort, yet I've never come across it being used in this ... | g17375 | [
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<p>In an ideal environment with no friction, in a vacuum, what happens to the velocity of the spin of two spheres spinning in perfect parity at two different velocities when they come into contact?</p> | g17376 | [
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<p>We have the following circuit: </p>
<p><img src="http://i.stack.imgur.com/VtWeT.jpg" alt="enter image description here"></p>
<p>A neon lamp and a inductor are connected in parallel to a battery of 1.5 $V$. The inductor has a 1000 loops, a length of $5.0 cm$, an area of $12cm^2$ and a resistance of $3.2 \Omega$. T... | g17377 | [
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<p>Have you realized, that often the photo of a star shows 6 rays spreaded symmetrically around it, independently of the camera chosen? Do you have idea of what kind of optical phenomena is behind it?</p> | g17378 | [
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<p>I am practising to Tfy-0.1064 -elementary-physics-exam and doing this practise -exam <a href="http://tenttiarkisto.fi/exams/9916.1.pdf" rel="nofollow">here</a>. The problem in Finnish goes like this:</p>
<blockquote>
<p><em>"Selosta lyhyesti sähkömagneettisen säteilyn lähettämisen ja vastaanottamisen peria... | g17379 | [
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<p>I have doubts with the following problem:</p>
<p>A projectile is fired from the top of a mountain that has a downward slope with angle $\phi$ from the horizontal. The initial velocity of the projectile is $v_{0}$ and has a angle $\theta$. Show that the range $R$ (maximum horizontal distance traveled) is related to ... | g17380 | [
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<p>For a hypothetical vehicle traveling in an <a href="http://en.wikipedia.org/wiki/Alcubierre_drive" rel="nofollow">Alcubierre bubble</a> at <a href="http://en.wikipedia.org/wiki/Faster-than-light" rel="nofollow">faster-than-light</a> (FTL) velocities, what would happen when the leading edge of the bubble encounters i... | g17381 | [
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... |
<p>My question is related to the first page of <a href="http://science.howstuffworks.com/dictionary/astronomy-terms/before-big-bang.htm" rel="nofollow">this article regarding the big bang theory</a> and refers to this specific sentence:</p>
<blockquote>
<p><em>Armed with the best physics of the 20th century, Albert ... | g530 | [
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<p>When you bite something in two pieces, e.g. a piece of hard candy, you hear the sound through two sources: vibrations in the air, entering your ears from the outside and internal vibrations in your skull. </p>
<p>What I have noticed is that there is a difference in (the way I perceive*) the sound intensity when my ... | g17382 | [
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<p>I have a question about the generalization of gauge transformation with two antisymmetric indices.</p>
<p>Starting from Eq. (3.7.6) in Polchinski's string theory book p. 108.
$$S_{\sigma} = \frac{1}{4 \pi \alpha'} \int_M d^2 \sigma g^{1/2} \left[ \left( g^{ab} G_{\mu \nu}(X) + i \epsilon^{ab} B_{\mu \nu} (X) \righ... | g17383 | [
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<p>I found this problem in Landau-Lifschitz vol.1 (Mechanics)</p>
<p>A simple pendulum of mass $m$, length $l$ whose point of support moves uniformly on a vertical circle with constant frequency $\gamma$. </p>
<p><img src="http://i.stack.imgur.com/CSo8C.png" alt="">
$$$$
The problem is, of course, to find the Lagrang... | g17384 | [
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0.010797002352774143,
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0.0104235... |
<p>Let's have Lorentz group with generators of 3-rotations, $\hat {R}_{i}$, and Lorentz boosts, $\hat {L}_{i}$. By introducing operators </p>
<p>$\hat {J}_{i} = \frac{1}{2}\left(\hat {R}_{i} + i\hat {L}_{i}\right), \quad \hat {K}_{i} = \frac{1}{2}\left(\hat {R}_{i} - i\hat {L}_{i}\right)$ </p>
<p>we makes algebra of ... | g17385 | [
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<p>Are there any open problems in physics involving Lie groups and differential equations for a phd theses. </p>
<p>Some applications are say, Noether's theorem in classical or quantum field theory. But I am not sure if those topics lead to any research problems. </p>
<p>So any idea about prospective research problem... | g17386 | [
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... |
<p>I have a proton, how do I know that it is made of 2 up quarks and 1 down quark or if it is made of 3 anti-down quarks, each with different color charges?</p>
<p>This question is also applicable to the antiproton, is it made up of 2 antiup and 1 antidown or of 3 down quakrs? </p> | g17387 | [
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<p>I'm working on a problem involving a silicon semiconductor. A PN junction is created with $N_a = 5\cdot10^{14}$ throughout the entire semiconductor, and is doped with $N_d = 2\cdot10^{15}$ on the N side.</p>
<p>I'm asked to calculate the Diffusion Constant $D$, carrier mobility, and carrier lifetime for both sides ... | g17388 | [
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0.0004003892536275089,
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0.04105997458100319,
0.024945778772234917,
0.00... |
<p>We know that every moving clock with respect to some clock A, is running slower than A. My question is simple - why it does not contradict the principle of relativity? Why can't we say that the clock which runs faster than any other clock is at absolute rest?</p>
<p>I remember that I've read in some book that its b... | g17389 | [
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0.014... |
<p>Yesterday I learned about optimum speed. My teacher told that optimum speed is the speed with which one can take turns on banked road without wear and tear. </p>
<p>$v_0=\sqrt{rg\tan\theta} $, $v_0$= optimum speed, $r$= radius, $g$= gravitational constant </p>
<p>Then he asked us to find out what will happen if... | g17390 | [
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0.0... |
<p>Kip Thorne has <a href="http://www.its.caltech.edu/~kip/scripts/ClosedTimelikeCurves-II121.pdf" rel="nofollow" title="Kip Thorne - Closed Timelike Curves">shown</a> that in order to create closed timelike curves (CTCs), one needs stress-energy tensor $T^{\mu\nu}$ that violates averaged null energy condition (ANEC).<... | g17391 | [
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<p>Hi is there any possibility that you located between 2 sound sources and u hear nothing?
as we know 2 wave in opposite direction will destroy each other... </p> | g531 | [
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0.0076... |
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