question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I recently heard about jet quenching concerning data taken by the experiments at the LHC. Apparently it is related to the existence to the quark-gluon plasma. As far as I understood this interpretation is an analogy to hydrodynamics (the jet is "blocked" by the plasma).</p>
<p>I would like to understand that in mor... | g17213 | [
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<p>Basic property of magnetic lines of force is that, they can never intersect each other. Among the two points given below, which one is correct?</p>
<ul>
<li>Magnetic lines of force of same magnet can't intersect each other, but magnetic lines of force of different magnets can intersect each other. </li>
<li>Magnet... | g17214 | [
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<p>I'm interested in the meaning of the phrase "continuum limit" specifically as it is often used in expressions relating to the ability of a quantum gravity theory to recover GR in the continuum limit.</p>
<p>I believe I understand the meaning but want to make sure I am not missing some important part of the precise ... | g17215 | [
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<p>Dear people in Physics Stackexchange,</p>
<p>My question is mostly related to the following papers:</p>
<ul>
<li>U. Seifert, <em>Z. Phys. B</em> <strong>97</strong>, 299 (1995). "The concept of effective tension for fluctuating vesicles".</li>
<li>U. Seifert, K. Berndl, and R. Lipowsky, <em>Phys. Rev. A</em> <stro... | g17216 | [
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<p>What ever happened to <a href="http://en.wikipedia.org/wiki/Action_at_a_distance_%28physics%29" rel="nofollow">"action at a distance"</a> in entangled quantum states, i.e. the <a href="http://en.wikipedia.org/wiki/EPR_paradox" rel="nofollow">Einstein-Rosen-Podolsky (EPR) paradox</a>? I thought they argued that in pr... | g61 | [
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<p>It's a Christmas time and so I hope I'll be pardoned for asking a question which probably doesn't make much sense :-)</p>
<p>In standard undergraduate nuclear physics course one learns about models such as <a href="http://en.wikipedia.org/wiki/Liquid-drop_model">Liquid Drop model</a> and <a href="http://en.wikipedi... | g17217 | [
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<p>In learning about relativity I've noticed that in the construction of Lorentz invariants (specifically four-vectors) two physical quantities that were previously considered distinct are instead treated as a single object. </p>
<p>Examples include position and time (spacetime), electric and magnetic fields, electric... | g17218 | [
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<p>In <a href="http://physics.stackexchange.com/questions/64578/is-there-a-way-to-see-light-frequencies-invisible-to-the-human-eye-without-the-u">this question</a> the OP is looking for a way to see light that is outside of the visible spectrum without using electronic sensors. This got me wondering about the visible s... | g17219 | [
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<p>Has there been any cases where the only explanation has been that at least one of the physical constants must have changed to explain an experiment/event/obervation? I am not intrested in large scale obsorvations such Gaolaxies holding together with insufficient obsorvable mass or stars seem to be moving at faster t... | g17220 | [
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<p>I do not understand how does the result of two vectors acting on a particle require me to take the cross product to find the resultant.</p>
<p>Won't the actual force on the particle be the result of the vectorial addition of the two vectors? How is it that result of two vectors on a charged particle in a magnetic f... | g17221 | [
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<p>first question here, so please be gentle!</p>
<p>I'm reading an entry-level engineering course book and am currently up to discussion of aircraft design.</p>
<p>There's one particular statement that is unclear to me:</p>
<p>Turning with the wing level is aerodynamically inefficient and the inner wing loses a lot ... | g17222 | [
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<p>I've been reading about the work of Marie Curie recently after a friend filled me in on what she did (never having had much of an idea previously) and it's all very interesting.</p>
<p>What I can't understand however is what real impact her discovery of radium had for the development of physics in general? I mean i... | g1020 | [
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<ul>
<li>A monatomic ideal gas is confined to move in two dimensions. What is the constant volume specific heat for this gas? </li>
<li>Consider a system of N independent harmonic oscillators moving in two dimensions. What is $C_v$ for the system.</li>
</ul>
<p>For the first case, I guess this one is $C_v = \frac{3}{2... | g17223 | [
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<p><a href="http://en.wikipedia.org/wiki/Physics" rel="nofollow">Wikipedia</a> definition: Physics (from Ancient Greek: φύσις physis "nature") is a natural science that involves the study of matter[1] and its motion through spacetime, along with related concepts such as energy and force.</p>
<p>Topics in my physics bo... | g17224 | [
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<p>I have read that spacetime 4-vector is quite difficult to observe/explore and that energy-momentum 4-vector is much more appropriate for CERN etc. </p>
<p><strong>Why is that?</strong> Could anyone give me a brief explanation of the differences regarding exploration and observation?</p> | g17225 | [
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<p>So let's say I have a single ($N=1$) quantum harmonic oscillator and the energy is determined by $E_n = (n + 1/2) \cdot \hbar \omega$ (where $n$ is the quantum number and $n$ = $0, 1, 2, \ldots$)</p>
<p>What's the probability that the oscillator is in the state labeled $n$ at temperature $T$?</p>
<p>So according ... | g17226 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/19165/relating-milliampere-hours-to-watt-hours-for-batteries">Relating milliampere-hours to watt-hours for batteries</a> </p>
</blockquote>
<p>How can I figure out how many kWh's are in a battery using t... | g524 | [
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<p>Say I have a rotating torus filled with air at 1 atmospheric pressure at sufficient speed (and inclined along the direction of the force of gravity with respect to Earth). </p>
<p>If the rotation speed were sufficient, would I be able to simulate a free fall environment for an object suspended inside the spinning t... | g17227 | [
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<p>As you know, it is quite obvious that Bicycle spokes attach the hub in the centre to the rim. What else do they do? If you compare the wheels today with the ones from ancient times, there are more spokes now on motor bikes and bicycles than of a wheel of a chariot. Why is that? What effect does it have on the vehicl... | g17228 | [
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<p>I've noticed that if I shut my door when the window is open in a room, the door will tend to shut faster. If I shut the door when the window is closed with a normal force it will not fully close as if the air is cushioning it. I think when the window is open the door doesn't stop or slow down at all, it just slams.<... | g17229 | [
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<p>I am working on a practice exam for semiconductor physics. Can anyone help me figure out how to determine whether we have donor or acceptor impurity in Gallium Arsenide?</p>
<pre><code>Gallium is column 3 and (I think) it has a valence of 3.
Arsenide is column 5 and (I think) it has a valence of 5.
But it has a val... | g17230 | [
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<p>I've heard about the Trojan asteroids and there is the famous idea of putting a space colony at one of these points, but the explanations I see for how something is stable at those points it they are 'insignificant mass.' What does that mean? Insignificant to Earth could be pretty big, insignificant to the sun cou... | g17231 | [
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<p>Einstein states that a moving object's shape changes due to the length contraction. But people had done such an experiment: Taking photos to a moving object, but they didn't find Lorentz contraction, instead, the object on picture just takes a rotation, which is the aberration. I'm confused about the two effect. Is ... | g525 | [
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<p>A disk is rolling (not sliding) in the inclined plane with initial velocity of zero. So there is friction between disk and plane. But when we use the energy conservation rule, we consider as:</p>
<pre><code>gained kinetic energy + gained rotational energy = lost potential energy
</code></pre>
<p>So here is there n... | g526 | [
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<p>I own an old iPod Classic with original lithium-ion polymer battery and I use it primarily while running. Recently I discovered that when a temperature outside is low, usually below 5 C degrees, the battery goes flat really fast and I mean 10 minutes. It doesn't matter if it is fully charged or not, it always goes d... | g17232 | [
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<p>Does universal wave function exist? </p>
<p>What the science tells us?</p> | g17233 | [
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<p>Shouldn't it be possible for an incoming photon to excite one of the 1s electrons to a 2p state (or one of even higher energy) and then for the excited electron to drop back to 1s and kick out the 2s electron?</p>
<p>Is there some fundamental reason that prohibits this process, or is it just very unlikely, or is it... | g17234 | [
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<p>In a test I took recently in my beginning Physics class there was a question that really irked me: </p>
<blockquote>
<p><em>A man is swimming upstream at 10 mph. The water is flowing downstream at 5 mph.</em></p>
<p><em>How fast is the man moving?</em> </p>
</blockquote>
<p>Well, you can actually take this... | g17235 | [
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<p>I guess this is the same as for cylinders, when light is shone through parallel to the cross-section, but Google-ing this only turns up lenses like the ones used in glasses.</p>
<p>I'm looking for something like what's described in this article: <a href="http://spie.org/x34513.xml" rel="nofollow">http://spie.org/x3... | g17236 | [
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<p>The source of Sun's incessant energy is hydrogen; which is continuously converting to helium through nuclear fusion reaction releasing energy. Why does not all hydrogen convert into helium in one big explosion just like a man-made bomb or cracker explodes?</p> | g17237 | [
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<p>I am conducting an experiment that requires comparison to models for a water droplet's change in size due to evaporation. I've found plenty of papers, but they all seem to require measurement of the drop's radius and/or height. </p>
<p>For the purposes of the experiment, I need a rate of change of the drops volum... | g17238 | [
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<blockquote>
<p>Consider a straight wire which runs along the y-axis. A B-field exists which is uniform and only in the x-direction:</p>
<p>$$\vec{B}=(B(t),0,0)$$</p>
<p>The B-field at time $t_0$ is 'switched off' in a sharp step, which will be modelled by the tanh function:</p>
<p>$$
B(t)= \begin{case... | g17239 | [
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<p>Please forgive me if I'm wrong, as I have no formal physics training (apart from some in high school and personal reading), but there's something about Heisenberg's Uncertainty Principle that strikes me as quite obvious, and I find it strange that nobody thought about it before quantum mechanics development began, a... | g17240 | [
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<p>Interstellar space propulsion...if a spaceship were to get beyond our Sun's gravitational pull and since there is no atmosphere/wind/friction in space...does that mean, if an engine was constantly thrusting, that the spaceship would continue to accelerate to the speed of light, as long as the engine was propulsing f... | g17241 | [
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<p>Physics me this:</p>
<p>The <strong>equivalence principle</strong> has rigorous physical definitions that say, for one, that the laws of physics are the same in all inertial reference frames. This is to say that <em>the behavior of the universe</em> is the same for any system regardless of velocity $(\vec{v})$ and... | g17242 | [
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<p>I just started my class on fluid mechanics. There's a problem that requires absolute viscosity $u$ of water at 25C. I looked up my table in the book and I only have it for water at 20C and 30C. I figured we had to manually calculate it in this case.</p>
<p>The school notes only have Andrade's equation $u = D \times... | g17243 | [
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<p>We Now From Information Theory That Entropy Of Functions Of A Random Variable $X$ Is Less Than Or Equal To The Entropy Of $X$.</p>
<p><img src="http://i.stack.imgur.com/RNkQo.jpg" alt="enter image description here"></p>
<p>Does It Break The Second Law Of Thermodynamic?</p> | g17244 | [
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<p>Suppose we have some function of time and space (1-D for simplicity) $G(x, t)$ which, by considering some equation relating $G$ to other quantities we know to be dimensionless. We now conclude that the argument of $G$ must be dimensionless, else we have a contradiction. So let us suppose that $G(x,t) = G(\zeta)$ for... | g17245 | [
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<p>1 - Has anyone ever measured the one way speed of photons traveling perpendicular to the Earth at the Earth's surface?</p>
<p>2 - Given our current understanding of Physics is there any way both the upward and downward speed would not be $c$?</p>
<p>3 - If the measurement were made and the downward speed were foun... | g17246 | [
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<p>Quite often (see, for example, this <a href="http://jila.colorado.edu/Chem4541/Born%20Oppenheimer%20p1-7.pdf" rel="nofollow">PDF, 50 KB</a>) when discussing the Born-Oppenheimer approximation the following assertion is made: any well-behaved function of two independent variables $f(x,y)$ can always be expanded over ... | g17247 | [
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<p>While I was studying <strong>beats</strong>, I tried to find a displacement function of any particle in the most generalized form. I ended up with $$y=2A\sin(\pi(t-x/v)(f_1+f_2))\cos(\pi(t-x/v)(f_1-f_2)).$$</p>
<p>Now, given such a function wherein you cannot compare to a general equation, how do you find the wave ... | g17248 | [
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<p>For the sake of this question we are inside the EH and a sound wave enters from our perspective as the sound moves closer to us at the EH would it speed up. </p>
<p>Specifically how would the extreme expansion of physical space lower the frequency of an incomming sound wave?</p> | g17249 | [
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<p>If it was possible to place a single gas molecule in a cell and freeze it to near absolute zero.
What would the molecule do as it thawed out?</p>
<p>Would it translate the heat energy into it's electrons and nucleus into vibrations and remain where it was? Would these vibrations cause it to start bouncing off the... | g17250 | [
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<p>On a systems level, I understand that as electrons are pushed into a wire, there is a net field and a net electron velocity. And I've read that the net electron drift is slow. But electricity travels through the wire, essentially at c, and I want to understand that mechanism. My apologies if my question is poorly... | g174 | [
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<p>I'm currently studying electric potential, and I'm having trouble with one of the problems on my homework:</p>
<blockquote>
<p>A) A point particle with charge $+q$ is on the x-axis at a distance $d$ from the origin, and another point particle with charge $-q$ is on the x-axis at a distance $-d$ from the origin. A... | g17251 | [
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<p>From One of My Unpublished Papers
$$\frac{d^2 x^{\alpha}}{d\tau^2}=-\Gamma^{\alpha}_{\beta \gamma}\frac{dx^{\beta}}{d\tau}\frac{dx^{\gamma}}{d\tau} \tag{1}$$ </p>
<p>For radial motion in Schwarzschild’s Geometry we have,</p>
<p>$$\frac{d^2 r}{d \tau^2}=-\frac{M}{r^2}\left(1-\frac{2M}{r}\right)\left(\frac{dt}{d\ta... | g17252 | [
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<p>I'm studying QFT from Le Bellac's book, but I can't understand very well his proof for the generator of proper vertices. Can someone give a more readable and/or understandable proof?</p> | g17253 | [
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<p>Is there any non-trivial many-body system for which the exact solution to Schrödinger's equation is known? (By non-trivial, I mean a system with particle-particle interactions.) Perhaps something like positronium, or two electrons in a box.</p> | g17254 | [
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<p>I am trying to deposit zinc metal from zinc chloride using chemical vapor deposition. But it is thermodynamically feasible to obtain zinc from zinc chloride?</p> | g17255 | [
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<p>I know that centrifugal is labeled a fictitious force only arising in a rotating reference frame, but I still struggle to understand the forces at play intuitively in tethered rotating bodies. </p>
<p>I've always been told that the reason a slingshot works is because the ball wants to go in a straight line. "Yeah c... | g17256 | [
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<p>In Perkins `Particle Physics', to compute the baryon-antibaryon-ratio, he uses that for $Mc^2\gg kT$:
$$E= Mc^2 + \frac{p^2c^2}{2m}.$$
I realize that the approximation comes from $E^2=M^2c^4 + p^2c^2$ and that it is perfectly allright in the ground of the dimension...</p>
<p>But how can one derive this approximatio... | g17257 | [
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<p>After researching through the web, I can't figure out how to express into a differential equation a coupled mass spring system with damping and initial values. Two masses and two springs, no external forces, just gravity because of vertical position. I know that $mx''+cx'+kx=f(t)$ is used for single spring systems, ... | g17258 | [
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<p>Exactly the title. There needs to be a pressure to prevent gases from perpetually expanding, right? Bear with me, I'm not a physicist or studying to be one.</p> | g17259 | [
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<p>I'm reading a book <em>Lie groups, Lie algebras, cohomology and some applications in physics</em> by Azcarraga and Izquierdo, and on page 347, when deriving the exact form of the central extension term I came to a bit which I don't understand how they got it.</p>
<p>The algebra is given by</p>
<p>$$[L_m,L_n]=(m-n)... | g17260 | [
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<p>Topological insulator is a fermion system with only <em>short-ranged entanglement</em>, what does the <em>entanglement</em> mean here?</p>
<p>For example, the Hilbert space $V_s$ of a lattice $N$ spin-1/2 system is $V_s=V_1\otimes V_2\otimes...\otimes V_N$, where $V_i$ is the Hilbert space of the spin on site $i$. ... | g17261 | [
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<p>Let's say we have a stuff that consists only of hydrogen (H), then we add a single atom of oxygen (O) and they interfere - we get a water molecule where atoms are arranged in a particular way. Then we add salt (NaCl) where Na may take some O and Cl may take some H. </p>
<p>What was described might be rough or incor... | g17262 | [
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<p>Vacancy Generation/Annihilation Time, Recombination Time and Relaxation Time ($\tau$) are all synonymously used in atomic physics literatures. They're defined as the time that it takes for vacancies and atoms to position in steady state sites and reach a thermo-mechanical equilibrium concentration. The relaxation ti... | g17263 | [
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<p>Specifically, during the moves towards <em>Le Système international d'unités</em> in the 18th and 19th centuries, why didn't anyone attempt to move us away from the definition of there being 24 hours in a day?</p>
<p><a href="http://en.wikipedia.org/wiki/Second#History" rel="nofollow">Wikipedia informed me</a> that... | g17264 | [
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<p>I understand how the wave equation works, and therefore how light moves through the EMF; this question is not about that mechanism.</p>
<p>But when a charge moves in space, information about its location travels outward at the speed of light, altering the field strength of the EMF. What is the mechanism by which th... | g17265 | [
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<p>On the Page 385 of Goldstein's Classical Mechanics book (third edition), it starts to talk a bout the canonical transformation with time as an explicit parameter.</p>
<p>But I don't quite under understand the following argument:</p>
<blockquote>
<p>Considering a canonical transformation of the form
$$\zeta(t)... | g17266 | [
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<p>Transparent materials let photons through because the energy gap of electron is so large that the photons cannot be absorbed. If the material absorbs a photon, the photon disappears; does this mean that its appearance is opaque? How about the colour white? In this case, does the material absorb photons?? Because whi... | g17267 | [
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<p>I've heard it mentioned many times that "nothing special" happens for an infalling observer who crosses the event horizon of a black hole, but I've never been completely satisfied with that statement. I've been trying to actually visualize what an infalling observer would see (from various angles), and I'd like to k... | g17268 | [
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-0.003669740166515112,
0.031760990619659424,
0.0... |
<p>There are three variables, $X_t$, $Y_t$, and $Z_t$ that are dependent of each other, and I have the time series data of those variables from replicated experiments. The stochastic dynamics look quite persistent and repeat some patterns. Based on my subjective view, it looks like there is some weak attracting force t... | g17269 | [
-0.00476683396846056,
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0.015392179600894451,
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0.03285056725144386,
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0.0... |
<p>See <a href="http://physics.stackexchange.com/q/2378/">What is our location relative to the Big Bang?</a>, which contains the following: </p>
<blockquote>
<p><em>The conclusion is that the Big Bang happened everywhere, all at once.</em> Phys.SE users Ali and WernerCD reached this same conclusion.</p>
</blockquote... | g17270 | [
0.038787756115198135,
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0.04527564346790314,
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0.02... |
<p>If the sun's surface was ~ 4000K (and earth closer to compensate), the UV component of the radiation would be less. However, UV makes ozone via photolysis of oxygen. Also, the stratosphere would probably start up higher (and contain less mass) because UV heating is what's responsible for the inversion. So what is th... | g17271 | [
0.003809296526014805,
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0.0469224788248539,
0.01670166291296482,
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0.06839805841445923,
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<p>We normally write down the Dirac Lagrangian as
\begin{equation}
{\cal L} _D = \bar{\psi} ( i \partial _\mu \gamma ^\mu - m ) \psi
\end{equation}
but are the Lagrangian's,
\begin{equation}
\bar{\psi} ( i \partial _\mu \gamma ^\mu \gamma ^5 - m ) \psi , \quad \bar{\psi} ( i \partial _\mu \gamma ^\mu - m \gamm... | g17272 | [
0.05596257746219635,
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0.07685375958681107,
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0.03700226917862892,
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-0.023764770478010178,
0.02571399137377739,
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-0.022108620032668114,
0.02853... |
<p>As I understand, an object with mass cannot reach the speed of light because its (relativistic) mass increases "exponentially" as it approaches light speed.</p>
<p>So there is a relation between mass and speed. But if speed is a relative measurement (it depends on a point of reference) how does that affect the mass... | g17273 | [
0.004872176796197891,
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0.05679864063858986,
0.0207... |
<p>For a while I've been trying to write a simple geometric derivation of the Lorentz transformation, based only on the second postulate. Although I'm able to successfully derive the Lorentz transformation, the geometry of that derivation is always a combination of relativistic effects (ie. Lorentz contraction and time... | g17274 | [
0.04630575329065323,
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0.007373865228146315,
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0.0018109960947185755,
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<p>We have an ice cube in a tray in a space shuttle. As the ice cube melts, the centre of mass shifts downward, so the tray should move downward to maintain the position of the centre of mass. Now, <em>some</em> force is required to move the tray, right? Where is this force coming from? Where does it transfer energy fr... | g17275 | [
0.018609970808029175,
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0.008851257152855396,
0.005167440976947546,
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<p>I've heard the total energy is zero, but I've also heard it cannot be said to be zero since there's so much unknown stuff in the universe. Is that true? </p> | g27 | [
0.03479619324207306,
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<p>Following on from <a href="http://physics.stackexchange.com/questions/48116/pictures-of-nuclear-explosions-some-milli-nano-seconds-after-detonation">this question</a>, here is a high-speed photograph of a nuclear explosion, taken about 1 ms after detonation: (<a href="http://commons.wikimedia.org/wiki/File%3aTumbler... | g17276 | [
0.047753944993019104,
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<p>I read the following on Wikipedia regarding <a href="http://en.wikipedia.org/wiki/Fluorescence" rel="nofollow">fluorescence</a>,</p>
<blockquote>
<p><em>Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation... The most striking examples of fluorescence occ... | g17277 | [
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0.038170... |
<p>I once saw on TV that the moon is slowly drifting away from the earth, something like an inch a year. In relation to that the day on earth what also increase in time.
I wonder why is that?</p> | g221 | [
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0... |
<p>We are all told at school water vapour and carbon dioxide are the top two greenhouse gases, and that they absorb thermal infra red radiation, trap heat and warm up the Earth. My question is how do they do that? Why can't Oxygen or Nitrogen or any other gas not absorb infra red radiation as well as water vapour or CO... | g504 | [
0.026632273569703102,
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<p>If we bring a floating balloon in a accelerated train, the balloon will move forward in the same direction as the acceleration as shown in the following figure. </p>
<p><img src="http://i.stack.imgur.com/dRTb2.png" alt="enter image description here"></p>
<p>However if a pendulum is hung on the train ceiling, the b... | g527 | [
0.05778059363365173,
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0.03547677397727966,
0.03538515418767929,
-0.0203711... |
<p>I read a news article about how they were able to create a negative temperature, below absolute zero, and my question is how does this work?</p>
<p>I know that there are different definitions of temperature, and for the negative temperature, it's referring to entropy, the disorder.</p>
<p>Can someone explain to me... | g278 | [
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0.0003297555958852172,
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-0.... |
<p>When an light travels in free space, it has a velocity of propagation equal to the speed of light.</p>
<p>However, then the light enters a medium with a refractive index of n, the velocity of propagation changes to </p>
<p>$\ v_p = c / n $</p>
<p>Is this change in velocity instant? Or is there a gradual decelerat... | g17278 | [
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0.04480325058102608,
-... |
<p>It's known that the emission from Blazars is highly polarized. WHat does that mean? Is it simply another way of stating that blazars have highly collimated and beamed emission?</p> | g17279 | [
0.03403516486287117,
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<p>I 'get' Newton's third law of motion, except for one thing. We know that if we let an apple fall to the Earth, the earth will fall to the apple, because the Earth must experience the same force in the opposite direction (the third law).</p>
<p>This I cannot imagine. Is there a possibly intuitive way to explain this... | g17280 | [
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0.03735513240098953,
0.0... |
<ol>
<li><p>Mathematically, how does a $\pi$ phase shift appear upon reflection of light off a optically denser medium?</p></li>
<li><p>Why is it always $\pi$?</p></li>
<li><p>If the medium is absorptive it is no longer $\pi$?</p></li>
</ol> | g358 | [
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0.014200392179191113,
... |
<p>I know that if we are given a stress tensor that is diagonal, the sign on the diagonal entries tell us whether we have traction or compression. </p>
<p>Now, imagine that we are given a non diagonal stress tensor, and we wanna know the only traction and only compression directions. Those are of course the principal ... | g17281 | [
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0.03457249328494072,
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<p>Suppose we have a Lagrangian that depends on second-order derivatives:</p>
<p>$$L = L(q, \dot{q}, \ddot{q})$$</p>
<p>If we're working on the variational problem for this Lagrangian, then I know that we'll wind up with the following <a href="http://en.wikipedia.org/wiki/Euler%E2%80%93Lagrange_equation" rel="nofollo... | g17282 | [
0.09709072858095169,
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0.06649753451347351,
0.0398414172232151,
0.0783... |
<p>I am given the following coupled Hamiltonian
$$H=\hbar\omega[a_x^\dagger a_x+a_y^\dagger a_y+1+K(a_x^\dagger a_y+a_y^\dagger a_x)]$$
Which I can decouple into two different oscillators
$$H_u=\frac 12 \hbar \omega(1+K)(a_u^\dagger a_u+1)$$
$$H_v=\frac 12 \hbar \omega(1-K)(a_v^\dagger a_v+1)$$
I am then given that the... | g17283 | [
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0.02882159873843193,
0.015936270356178284,
-0.054823316633701324,... |
<p>Excuse me for my ignorance but I really couldn't find a solution. According to Einstein, every happening is possible to describe by both of interacted objects.</p>
<ol>
<li>Is there any other way to describe the Big bang than the one that describes the rapid expansion of the universe?</li>
<li>I just read that Kepl... | g17284 | [
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0.07922632247209549,
0.03971... |
<p>My question is, where could I get some more info on how the Euler-Lagrange equations are related</p>
<p>$$ \delta S [y(x)] =0 $$</p>
<p>with the Feynmann path integral formulation $ \int D[y(X)]e^{iS[y(x)]/\hbar} $</p>
<p>I believe that when $ \hbar \to 0$ (semiclassical), only the points that satisfy (1) contrib... | g141 | [
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0.014247365295886993,
0.02797689288854599,
0.077... |
<p>I saw <a href="https://www.youtube.com/watch?v=tmNXKqeUtJM">this video</a>, but I had the impression that orbiting in an ellipse or a circle is quite a coincidence - it depends on how the planet got into the Solar System. Because I think that either all active forces balance in a circle, or simply all the planets wi... | g17285 | [
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0.0091885756701231,
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<p>Is there any publicly accessible data that shows quantum entanglement empirically.</p>
<p>I want to see what these researches are seeing that is showing them that indeed this phenomenon is real.</p>
<p>Also, any explanation of such data would be greatly appreciated, ie. what instruments are used to measure what as... | g17286 | [
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0.011604483239352703,
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0... |
<p>I was told that Lorentz' force is given by </p>
<p>$${\bf F}= q{\bf v} \times {\bf B}.$$</p>
<p>But I have read that it is given by $${\bf F}= \frac{q}{c}{\bf v} \times {\bf B}.$$</p>
<p>Why have these two relations different forms if they represent the same force? Thanks for any help!</p> | g17287 | [
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... |
<p>I figure that Mie scattering is best for finding the scattering when the wavelengths are between 1/10th to 10x the particle diameter. However, is there an upper limit to this? If I send 2.8cm microwaves into a 10cm sphere, will it scatter according to Mie Scattering?</p> | g17288 | [
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<p>I have an electron in a 3D space and there is a uniform constant magnetic field $B$, oriented according to z-axes.</p>
<p>At $t=0$, we have $z=0$ and $\dot z =0$.</p>
<p>I have proved that the trajectory is a circumference and that the motion is uniform. Now I have to find the center of the circumference. </p>
<p... | g17289 | [
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<p>I'm trying to solve a homework problem as review for an exam I have tomorrow and I was wondering if someone could help explain it to me. It is as follows:</p>
<blockquote>
<p>You are at Lowe’s shopping for bricks with your best friend. You fill your cart and put the remaining bricks in your friend's cart. As it t... | g17290 | [
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<p>For a certain pair of rigid bodies, I have the gradient of energy in terms of Euler angles. I want to transform this gradient to the gradient of energy in terms of rotations about the $x, y, z$ axes (the very useful gradient known as torque). </p>
<p>Performing the analogous transformation between, say, spherical c... | g17291 | [
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<p>It's possible that this question is too soft or even quite senseless for this forum, but I will ask nevertheless.</p>
<p>Everyday (macroscopic) things, like a grandfather's pendulum clock or the grandfather himself have age, which can be determined in several (not independent) ways:</p>
<p>1, <strong>testimony of ... | g17292 | [
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-0.004831445869058371,
-0.0002986107429023832,
-0.002872948069125414,
0.04423758387565613,
0.03... |
<p>I have a state $\Psi (x,0) = \sum_{n=0}^{\infty} c_{n}u_n(x)$ and want to find the expectation value of any observable A at time t, $\langle \Psi(t)|\hat{A}|\Psi(t)\rangle$.</p>
<p>I know that I should apply the time evolution operator to find $\Psi(t)$ but am not sure how to find the expectation value when I'm not... | g17293 | [
-0.029091263189911842,
0.025340044870972633,
-0.022885356098413467,
-0.08275698125362396,
-0.0018352855695411563,
0.0034523559734225273,
-0.004552212078124285,
0.0391666553914547,
-0.04564362391829491,
-0.031048834323883057,
-0.006751798093318939,
-0.028575323522090912,
0.015281178057193756,... |
<p>I have been trying to understand total internal reflection (and have read several posts on this site already). Mathematically, I feel that I understand how the evanescent wave decays exponentially as it crosses a boundary surface and why there is no transmission. However, I have no intuition as to why it happens. Is... | g17294 | [
0.00004409320899867453,
0.0444851778447628,
0.009836028330028057,
-0.012279236689209938,
0.05202726274728775,
0.07540945708751678,
0.06391619890928268,
0.04017962887883186,
0.0008998481789603829,
-0.06326554715633392,
-0.013899083249270916,
0.003527258522808552,
0.02975865639746189,
-0.018... |
<p>In my book about quantum mechanics they give a derivation that for one particle an area of $h$ in $2D$ phase space contains exactly one quantum mechanical state.
In my book about statistical physics they do exactly the same, but now for $6D$ phase space (now one quantum mechanical state covers a volume of $h^3$).</... | g17295 | [
0.0035471851006150246,
-0.023637566715478897,
-0.021183788776397705,
-0.003642949741333723,
-0.0031688017770648003,
0.0682334154844284,
0.028795698657631874,
0.06341762840747833,
-0.019359782338142395,
-0.04544815793633461,
0.02662636712193489,
-0.06009601429104805,
-0.03940855339169502,
-... |
<p>I've seen references to some sort of black hole (or something) referred to as a <a href="http://www.google.com/search?q=sudden+singularity">sudden singularity</a>, but I haven't seen a short clear definition of what this is for the layman. </p> | g17296 | [
0.031487561762332916,
0.04022324085235596,
0.009927971288561821,
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-0.0007134041516110301,
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0.011864220723509789,
0.026062773540616035,
0.0064423950389027596,
-0.033550407737493515,
0.024729426950216293,
0.012376325204968452,
0.07966453582048416,
... |
<p>I am playing around with an Navier stokes solver and I'm having trouble introducing heat.</p>
<p>Am I right in thinking this would be introduced in the ${\bf f}$ term of ${\partial{\bf u}\over\partial t} = -({\bf u}\cdot\nabla){\bf u}+v\nabla^2{\bf u}+{\bf f}$?</p>
<p>I find the lack of mass term disturbing. Pleas... | g17297 | [
0.024896126240491867,
0.003268092405050993,
-0.024958837777376175,
0.013808638788759708,
0.01380909513682127,
-0.037335190922021866,
0.050141576677560806,
0.020435180515050888,
-0.0533820241689682,
-0.04602300003170967,
0.004019307438284159,
0.005010079592466354,
0.018173685297369957,
-0.0... |
<p>I saw this symbol like:</p>
<p>$$\lambda=3000\overset{\circ}{\text{A}}$$</p>
<p>and I don't know what this means. Is it a frequency? (since $\lambda$ is usually used for frequency)</p> | g17298 | [
0.01067857164889574,
0.03808332979679108,
-0.007035666145384312,
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0.03518369048833847,
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0.028815485537052155,
0.026946159079670906,
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0.08226245641708374,
-0.0016963053494691849,
-0... |
<p>I read that an alcubierre drive would get destroyed by hawking radiation inside the warp bubble. Where does this hawking radiation come from? And why does it only happen to objects inside the bubble? </p> | g17299 | [
0.05463946610689163,
0.03492339327931404,
0.0026142001152038574,
-0.013337045907974243,
0.04239160194993019,
0.06252548843622208,
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0.047442030161619186,
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0.011049719527363777,
0.029179668053984642,
0.02422383613884449,
0.01212488766759634,
-0.0365... |
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