question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Why does the azimuthal angle, $\phi$, remain unchanged between reference frames in special relativity?</p>
<p>Edit: Here is a link from "Radiative Processes in Astrophysics": <a href="http://i937.photobucket.com/albums/ad216/Kyanise/Capture-5.jpg" rel="nofollow">http://i937.photobucket.com/albums/ad216/Kyanise/Capt... | g12401 | [
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<p>In spin models, it is known that mean field becomes a better approximation as the connectivity increases. My question is: Is there an estimate for the threshold connectivity (as a function of the system size, $N$), such that for connectivites greater than the threshold, mean field is a good approximation?</p>
<p>Th... | g12402 | [
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<p>Let us consider the topological string A- and B-model (twisted SUSY non-linear sigma model on CY 3-manifold $X$). They are realization of $N=2$ SCFT and there are ground-states vector bundle $\mathcal{H}$ and vacuum line bundle $\mathcal{L}$ over the moduli space of the theory. In the A-model, $\mathcal{H}=H^{even}(... | g12403 | [
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<p><img src="http://i.stack.imgur.com/iQ5Zg.jpg" alt="enter image description here"></p>
<p>Sorry for the bad drawing, but I hope that this will help you get a hold of the problem.</p>
<p>Consider an Atwood Machine with a total of two blocks, a mass less pulley, ideal string. One block rests on the floor, while the o... | g12404 | [
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<p>Lately, I have some read some papers about the hidden sector of particle physics which combines with the Standard Model through the so-called Higgs portal. Let the Lagrangian for this be composed of two simple scalar fields like this:</p>
<p>$L=\partial_\mu \phi_{SM} \partial_\nu \phi_{SM} +\partial_\mu \phi_H \par... | g12405 | [
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<p>What is the extent of the <code>Galactic Magnetic Field</code>? What does the <code>Galactic Magnetic Field</code> look like from afar (such as half-way between the <code>Milky Way Galaxy</code> and <code>Andromeda Galaxy</code>)? Does the <code>Galactic Magnetic Field</code> interact with other galaxies's magneti... | g12406 | [
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<p>My textbook is using Faraday's law to explain the self inductance that happens in a solenoid with changing current.</p>
<p>According to Wikipedia, <a href="http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction" rel="nofollow">Faraday's Law</a> is:</p>
<blockquote>
<p>The induced electromotive force in any cl... | g12407 | [
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<p>I'm a bit stuck on a homework question that I've been assigned. The question is as follows:</p>
<blockquote>
<p><em>You are paddling a canoe at a speed of 4 km/h directly across a river that flows at 3 km/h. (a) What is your resultant speed relative to the shore? (b) In approximately what direction should you pad... | g12408 | [
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<p>In Coleman's paper, "Quantum sine-Gordon equation as the massive Thirring Model" (Link to the PRD paper <a href="http://prd.aps.org/abstract/PRD/v11/i8/p2088_1" rel="nofollow">http://prd.aps.org/abstract/PRD/v11/i8/p2088_1</a>), he pointed out that the massless Thirring Model is sensible only for coupling $g>-\pi... | g12409 | [
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<p>Imagine a perfect vacuum devoid of all matter and radiation. Irrespective of whether such a space can even exist, my intuition tells me that time would not exist within such a space. What this thought experiment tells me is that the human concept of time is basically that it's a measure of motion. Whether its a car ... | g12410 | [
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<p>A magnetic field $B$ can apply a force $X$ on a ferromagnet when there is no gap to separate them, $r$ = 0.
When that gap ($r$) is increased to 3 cm, the force drops to zero.
How can that be solved? How can I expand the magnetic field so that it can be applied over larger distances? What methods are known to solve ... | g12411 | [
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<p><strong>The Question</strong> </p>
<blockquote>
<p>Between two rigid walls separated by a distance $l_1+l_2$, two rods of
equal cross-section area $A$, and length, coefficient of linear
expansion and Young's modulus $l_1, \alpha_1, Y_1$ and
$l_2,\alpha_2,Y_2$. Suppose the temperature of the entire system i... | g12412 | [
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<p><img src="http://i.stack.imgur.com/LW8GR.png" alt="enter image description here"></p>
<p>How exactly do you derive this result?</p> | g12413 | [
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<p>When we deal with Special Relativity and we start considering spacetime instead of space and time each at once, we usually see books saying that we consider a space with four coordinate $x^\alpha$ with $x^0 = ct$. We also consider this manifold to be $\mathbb{R}^4$ and give to it the metric tensor $g = \operatorname... | g12414 | [
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<p>We know that in the quantum harmonic oscillator $H=a^\dagger a$, $a^\dagger$, $a$, $1$ will span a Lie algebra, where $a, a^\dagger$ are the annihilation and creation operators, and $H$ is the Hamiltonian operator. </p>
<p>$$[H,a^\dagger\ ]= a^\dagger$$
$$[H,a]=-a$$
$$[a,a^\dagger]=1$$
So these four operators, $H=a... | g12415 | [
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<p>Why are the position and potential energy of a particle able to be measured precisely in Quantum Mechanics? I mean why do they commute with each other?</p> | g12416 | [
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<p>Referencing Stephen Hawking's recent paper <a href="http://arxiv.org/abs/1401.5761" rel="nofollow"><em>Information Preservation and Weather Forecasting for Black Holes</em></a> and <a href="http://physics.stackexchange.com/questions/95366/why-does-stephen-hawking-say-black-holes-dont-exist">this</a> question. I unde... | g12417 | [
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<p>I know that there's a lot of evidence for extremely compact bodies. But is there any observation from which we can infer the existence of an actual <em>horizon</em>?</p>
<p>Even if we are able to someday resolve directly the "shadow" of a possible black hole, isn't it still possible that it's just a highly compact ... | g12418 | [
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<p>Basically, I understand the difference between a "Theory" and a "Theorem" but I am quite confused when it comes to "Law", "Rule" and "Principle". Can you make the differences clear to me?</p> | g394 | [
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<p>It's known that gauge group for type-I superstring theory should be SO(32) for chiral anomalies to cancel. This is realized by presense of 16 space-time filling D9-branes, together with 16 space-time filling O9-planes with opposite charge: D9-branes bring U(16) gauge symmetry and due to orientifold planes the symmet... | g12419 | [
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<p>One often hears the words "string tension" in string theory. But what does it really mean? In ordinary physics "tension" in an ordinary classical string arises from the fact that there are elasticity in the string material which is a consequence of the molecular interaction (which is electromagnetic in nature). But... | g12420 | [
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<p>So I know the answer to this question varies widely across mass spec techniques, masses, and, of course, budgets, but my question is about the <em>best</em> case scenario for all of these variables (although I'm not really looking at proteins or anything of that size). I realize that the concept of depletion spectr... | g12421 | [
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<p>Eddy currents are induced in a metal plate when it experiences a changing magnetic flux. Is there a realistic visualization or simulation of eddy currents available? The only picture I found, on wikipedia, is a cartoon schematic. </p> | g12422 | [
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<p>In string theory , What exactly are right movers and left movers ?Are they waves propagating along the string to the right and to the left respectively ?
Can some-one please show me how to derive in details the general solution of the equation of motion for the string?</p> | g12423 | [
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<p>I read some articles saying that it is not obvious (or maybe impossible) to generate energy using capillary action. On the other hand in my understanding trees uses capillary action to extract water from the soil, but I guess the "trick" there is that the sun actually extract the water from the plants making it evap... | g12424 | [
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<p>I have a question about how to calculate the following expectation value:</p>
<p>$$\langle0|\mathcal{T}\{{a^{\dagger}}(0,0) a(0,0)\}|0\rangle$$
where $|0\rangle$ is the ground state and $a^{\dagger}(x,t)$ is the creation operator which creates a particle at position $x$ and time $t$. Is the answer just $0$ since ti... | g12425 | [
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<p>What is spontaneous symmetry breaking from a classical point of view. Could you give some examples, using classical systems.I am studying about the 't Hooft and Polyakov magnetic monopoles solutions, which says that the SU(2) symmetry is spontaneously broken down to U(1) symmetry. What does this mean exactly? Also, ... | g12426 | [
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<p>Suppose we have a person <strong>A</strong> and a person <strong>B</strong>.</p>
<p>Person B travels very close to speed of light and never returns. He's constant in speed. Then, we can say two things:</p>
<ol>
<li>B is younger than A.</li>
<li>A is younger than B (since we can consider B's reference as inertial).... | g12427 | [
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<p>If our sense of contact temperature is influenced by the thermal conductivity of the material: </p>
<p><em>Can any solid material with a low heat capacity exist that feels closer to human body temperature than another solid material with a higher heat capacity; where both materials were previously kept in either a ... | g12428 | [
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<p>I'm confused by my books treatment of the Schrödinger equation. In steado f listing my questions at the end of my post, I'll add them as questions in parentheses after the line in question. </p>
<p>For a free particle: </p>
<p>$$i \hbar \left| \dot{\Psi} \right \rangle = H\left| \Psi \right \rangle = \frac{P^2}{2m... | g12429 | [
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<p>In almost all text, it uses the massless spring as example to illustrate the idea of elastic potential energy. I wonder what's really being changed if we consider the mass of the spring? I saw a problem on a text regarding the non-massless spring. It is said that the stretched spring (don't know the length) has unif... | g12430 | [
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<p>When the W boson was discovered in the 1980s, nobody spoke of sigmas. How many sigmas was it at that time?</p> | g12431 | [
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0.020178424194455147,
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0.010930878110229969,
0.012768637388944626,
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0.0018727610586211085,
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<p>Is the space unending, i.e it has no boundaries? If yes, how can a thing exist which is non-ending? Its impossible for me to imagine something like that. Secondly, if its not and has boundaries then it must be inside some other thing which is either non-ending or itself contained in another thing. Yet, again same pr... | g12432 | [
0.04848989471793175,
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0.0005040341638959944,
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<p>My question is specifically whether there exists a technique by which a <strong><em>single</em></strong> photon can be "tagged" or "encoded" in such a way that it can traverse our atmosphere and arrive at some sort of detector along with trillions of others and be singled out from the other photons. Would this be po... | g12433 | [
-0.045207880437374115,
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0.023004673421382904,
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0.012897291220724583,
0.03341588005423546,
-... |
<p>I have an argue with an ex-Doctor of Medicine about the amount of ultraviolet light reaching us under the clear day sun and under the 100% cloudy sky.</p>
<p>To what extent we can say that the sky clouds stops ultraviolet light from the sun?</p> | g12434 | [
0.002312424359843135,
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<p><img src="http://i.stack.imgur.com/oar2l.jpg" alt="enter image description here"></p>
<p>How to derive the equation in my question?</p> | g395 | [
0.014686394482851028,
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0.04693600535392761,
0.032667458057403564,
0.0... |
<p>I am wondering: The noble 'gases' are inert because they have closed shells and don't want to give that up. But the noble metals, such as Copper, Silver, Rhodium, Gold, don't seem to have this.</p>
<p>For example, Rhodium has electron configuration $4d^{8}\, 5s^1$. To me, this looks very similar to the alkali metal... | g12435 | [
0.028433945029973984,
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0.058017097413539886,
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... |
<p>I am looking for data sets which clock the time and precise location of free falling bodies in a vacuum. I have been told that the acceleration of gravity is not absolutely 100% uniform, and I would like to examine the data sets as to this question, particularly as to minute discrepancies. The more the better. Any... | g12436 | [
0.05927271768450737,
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0.... |
<p>Sorry if this is off-topic.</p>
<p>A question was recently asked on Musical Practice & Performance, asking what physical properties of silver would contribute to the sound of percussion instruments. It is likely to be off-topic there; I wondered if any of you physicists/material scientists would be able to offe... | g12437 | [
0.05397119000554085,
0.014639084227383137,
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0.05910951644182205,
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0.0482734777033329,
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<p>This may or may not be the appropriate scientific discipline to ask this question of, but I'll give it a shot. I'll happily invite chemists to chime in as well.</p>
<p>It's time to tap sugar maples in the North East USA once again. What we essentially pull from the trees via taps is a sugar solution that, using rev... | g12438 | [
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0.024426842108368874,
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... |
<p>my teacher gave me this analogy to the electric current , the wire is like a pearl necklace where the pearls can move, the current or the movement of electrons is like putting your fingers between 2 pearls separating them then you start taking one pearl from the right of your finger and push itto the left of your f... | g12439 | [
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0.04441223666071892,
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0.03242463245987892,
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0.0... |
<p>The equation for the instantaneous displacement of a traveling wave at time $t$, and at any position $x$ along the wave is:</p>
<p>$$y(x,t) = A_{max}\sin(kx +\omega t + \phi)$$</p>
<p><img src="http://i.stack.imgur.com/nxG3P.gif" alt="enter image description here"></p>
<p>But this is only valid when the traveling... | g12440 | [
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<p>What do Allowed and Forbidden transitions tell us about the properties of a photon? </p>
<p>Allowed transitions have the change in angular momentum $\ell=1$, all the others are forbidden. But what does it tell us?</p> | g12441 | [
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<p>I have a question about the concept of measurement and observable in quantum mechanics. I'd like to fist explain my understanding of it and then ask the question.</p>
<p>First we have a system and its state function $\psi(x)$ and naturally it means there are two mutually incompatible observables $x$ and $\omega$ (... | g12442 | [
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<p>I have often seeen statements on physics.SE such as,</p>
<blockquote>
<p>The only consistent theory of everything which we know of to date (2013) is string theory.</p>
</blockquote>
<p>Why exactly is this so? Adding the Loop Quantum Gravity Lagrangian Density (the Einstein-Hilbert-Palatini-Ashtekar lagr... | g12443 | [
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0.052... |
<p>I want to find the Taylor expansion of $y=\frac {V_t^2}{g} \ln(\cosh(\frac{gt}{V_t}))$</p>
<p>I have tried using the fact $\cosh x= \frac {e^x}{2}$ for large t, which works, I just need help on small values for t.</p>
<p>Using maple17 for small t, I was able to see it expands to $\frac{1}{2}gt^2 - \frac{1}{12}\fra... | g12444 | [
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0.02076067216694355,
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0.... |
<p>I was watching a video about the swarzchild radius and it said that potential energy is $gmm/r$. This cannot be right though because potential energy goes up with distance not down. I'm assuming he meant motion due to potential energy. Also what is the intuition behind the equation $gmm/r$?</p> | g12445 | [
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0.03783183544874191,
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<p>As, using the fact that E*A stays constant for a point charge ( E= electric field, A=area of sphere centered on charge touching the point where we have to measure E) , we can prove that E falls by 1/r^2 . Is there any basic method for the Magnetic field?</p> | g12446 | [
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0.007355255540460348,
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<p>I fail to understand what the electron clouds actually signify. Such as the $p$ orbitals, which have a dumbbell like shape. Now I am aware that they aren't actual trajectories of electrons, but what is their need? Does it indicate the highest probability of finding an electron? </p>
<p>And also, concerning the Zeem... | g12447 | [
0.001683801063336432,
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0.07552482187747955,
-0.00... |
<p>So, I have a (confusing) Hamiltonian:</p>
<p>$$H = \int \mathrm{d}k\,\omega_{k} a^{\dagger}\bigl(\vec{k}\bigr)a\bigl(\vec{k}\bigr)$$</p>
<p>where $\omega_{k} = \sqrt{k^{2} + m^{2}}$ and the measure is $\mathrm{d}k = \frac{\mathrm{d}^{3}k}{(2 \pi)^{3} 2 \omega_{k}}$. </p>
<p>I want to find the energy of a single p... | g12448 | [
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0.016584884375333786,
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0.02755913697183132,
0.0012433663941919804,
0.013904902152717113,
-0.0003746383881662041,... |
<p>So given the angular momentum operator:</p>
<p>$$L_{z} = - ih\biggl(x \frac{\mathrm{d}}{\mathrm{d}y} - y \frac{\mathrm{d}}{\mathrm{d}x}\biggr)$$</p>
<p>I know how to write these in terms of polar coordinates (obviously). But say I want to work in complex coordinates, such that:</p>
<p>\begin{align}
z &= x + i... | g12449 | [
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0.026671702042222023,
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0.03868049010634422,
-0.0... |
<p>I've been taught that diffraction is the reason why we can hear around corners, since the wavelength of sound is approximately 10 cm (smaller than a door or a window).</p>
<p>I wonder how can this be correct, since I can hear even when a room is closed (walls are not completely rigid), althought the sound will be l... | g12450 | [
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0.04422903060913086,
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<p>From string theory, the vacuum field equations obtain correction of the order $O[\alpha'R]^n$ such that they can be written as</p>
<p>$$
R_{\alpha\beta} -\frac{1}{2}g_{\alpha\beta}R + O[\alpha'R] = 0
$$</p>
<p>where $\alpha' = \frac{1}{2\pi T_s}$, when including just the first order term for example.</p>
<p>What ... | g12451 | [
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0.015320303849875927,
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... |
<p>I am trying to evaluate a diagram that looks like </p>
<p><img src="http://i.stack.imgur.com/9lbyJ.png" alt="Feynman loop diagram"></p>
<p>The middle of the diagram is a fermion loop. I know that the coupling between the $Z^0$ and fermions depends on the fermions' helicities, so it would be nice to evaluate the d... | g12452 | [
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0.008614103309810162,
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... |
<p>If I launched a Satellite into orbit and dropped a silver wire caged in carbon fiber with aerodynamic wings (for support), would the Faraday effect of the wire traveling through earth's electromagnetic atmosphere (as the satellite orbits earth) generate a lot of electricity? </p>
<p>Also, would the wire being in th... | g82 | [
0.041316766291856766,
0.060593754053115845,
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0.001039023045450449,
0.0022893501445651054,
0.014471819624304771,
-0.01014429796487093,
0.02... |
<p>Are Ising spins scalar or operators? I am not a condensed matter physicist hence having some confusion. I have learnt about Ising models from adiabatic quantum algorithm papers. For example <a href="http://dwave.files.wordpress.com/2007/03/20070301_demo_slides.pdf" rel="nofollow">this presentation</a> or <a href="ht... | g12453 | [
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0.07329423725605011,
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0.08233629912137985,
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0.0179... |
<p>Assuming that the earth is spherical, that its temperature is continuous, and that some other more or less realistic conditions hold, we might think that the Earth's core temperature should be about the average of its surface temperatures. </p>
<p>This is not the case, as the core is hotter than all but a few spots... | g12454 | [
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0.031180081889033318,
0.0... |
<blockquote>
<p>Someone holds a 2kg weight in their hand at a distance of 35cm from the elbow (fulcrum) and the downward force (load) due to the weight is 20 Newtons. Calculate the effort in Newtons that the muscles of the forearm must apply at a distance of 5cm from the fulcrum to hold the weight up. Show calculatio... | g12455 | [
0.022832058370113373,
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0.0028716784436255693,
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0.009312299080193043,
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... |
<p>Previously, on <a href="http://physics.stackexchange.com/q/86509/33806">Save us from swallowing baby universes, please!</a>, I asked how we can be saved from false vacuum decay assuming we are living in a false vacuum.</p>
<p>What if we are living in a stable vacuum after all, and string theory actually describes t... | g12456 | [
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0.0010161855025216937,
0.029640069231390953,
... |
<p>Suppose you prepare a two-particle system such that $\Psi(\vec{r}_1,\vec{r}_2, t_0) = \Psi_1(\vec{r}_1, t_0)\Psi_2(\vec{r}_2, t_0)$.</p>
<p>So then, initially $\Psi(\vec{r}_1,\vec{r}_2,t_0) - \Psi_1(\vec{r}_1, t_0)\Psi_2(\vec{r}_2, t_0) = 0$</p>
<p>But now you let the system evolve in time and $\Psi(\vec{r}_1,\vec... | g12457 | [
0.0047730072401463985,
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0.02484862133860588,
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0.025650011375546455,
0.009860837832093239,
-0.0... |
<p>While taking thermodynamics our chemistry teacher told us that entropy is increasing in day by day (as per second law of thermodynamics), and when it reaches its maximum the end of the world will occur. I didn't see such an argument in any of the science books, is there any probablity for this to be true?</p> | g12458 | [
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-... |
<p>Suppose a rigid body is invariant under a rotation around an axis $\mathsf{A}$ by a given angle $0 \leq \alpha_0 < 2\pi$ (and also every multiple of $\alpha_0$). </p>
<p>Is it true that in this case the axis $\mathsf{A}$ is a principal axis of the rigid body? </p>
<p>If so, how to prove it? Do you have any refe... | g12459 | [
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-0.036005184054374695,
-... |
<p>The phenomenon I'm talking about is <em>positive feedback</em>, as known from control engineering: when the microphone is too close to its speaker, it can "hear itself", so the signal will be infinitely amplified. This can be very irritating e.g. during a concert.</p>
<p>But I wonder: why do you only hear a high-pi... | g12460 | [
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<p>this is <a href="http://en.wikipedia.org/wiki/Planck_length" rel="nofollow">Planck length</a>:
$$\ell_p=\sqrt {\frac {G.\hbar}{c^3}} .$$</p>
<ol>
<li><p>How much is important the role of this length in the strings theory?</p></li>
<li><p>is this planck's length or newton's length! or maybe both of them!?</p></li>
<... | g12461 | [
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<p>Well in a problem I had to calculate the maximum amount of "reflections" in a glass fibre optic pipe (index of refraction = 1.3, width of 20 micrometer and length of 1 meter). I am a bit blocked on how to calculate this.</p>
<p>I considered first the critical angle $sin(\theta_{cr}) = \frac{1}{n}$ Which came out to... | g12462 | [
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<p>In <a href="http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.1692.html">a fascinating 30 June 2013 article</a> in <em>Nature Chemistry</em>, researchers from the University of Leeds found that when molecules of hydroxyl (<strong>OH</strong>, a fairly stable radical) and methanol (<strong>CH$_3$OH</strong... | g12463 | [
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<p>Due to light travel time, we observe astronomical objects as they were in the past. If we knew objects' motion (relative to us), it seems like we could extrapolate to their present positions, but I can't remember ever reading about anything like this. Has there been any work like this done--or is there some reason w... | g12464 | [
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<p>I am familiar with the casual dichotomy in QFT between coupling with positive dimensions in energy implies relevant operator on one side and negative dimension implies irrelevant operator on the other side (forgetting about marginal operators) once you have set $\hbar$ and c equal to 1, and then I thought than in a ... | g12465 | [
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<p>If I'm a tyro and have a latitude, longitude, time, date, height from the horizon, and compass direction, what means can I use for identifying what I see there?</p>
<p>Realize that, as a tyro, I don't have any astronomy books or programs, and don't want to buy any; I might download a free program for my occasional ... | g12466 | [
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<p>Could you please help me understand how one can measure output frequency of free electron laser <strong>(provided that we know size of magnetic domains and electron energy)</strong>? This should be a function of magnetic domains size & electron velocity? But electron velocity should drop due to photon emission -... | g12467 | [
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<p>Backstory: When I learned about chemical reactions, there were two types of molecular bonds: Ionic, where an atom or compound molecule with a low valence number loses those valence electron(s) to one or more other compounds with a high valence number, which it then bonds with; and Covalent, where valence electrons a... | g12468 | [
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<p>I've been using this online calculator to work out the difference in pressure and flow between two ends of a pipe:</p>
<p><a href="http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm" rel="nofollow">Pipe Friction Calculation for Fluid Flow in a Pipe</a></p>
<p>So far most of it makes sense, and I've manag... | g12469 | [
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<p>One of the great unheralded advances made in the history of science was the ability to determine the age of Earth based on the decay of isotopic uranium. Based on the apparent abundance of uranium in the early Earth, what conclusions can be drawn about the star that preceded the Sun?</p> | g645 | [
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<p>The propagator of a QFT is known to have a branch cut as a function of the (complex) external momentum. The branch point (as done by, say, Peskin & Schroeder in eqn.7.19 section 7.1) is identified as the root of the argument of the logarithmic piece. Is this not a scheme dependent piece? At least, at the outse... | g12470 | [
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<p><em>As the title goes, what are <a href="http://www.google.com/search?as_epq=threshold+corrections" rel="nofollow"><strong>threshold corrections</strong></a> in quantum field theory?</em> </p>
<p>In particular, I would be glad if a good reference is provided. Standard QFT books such as Peskin, Weinberg, etc seem to... | g12471 | [
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<p>I have a question about the spinor helicity formalism from arXiv:1308.1697</p>
<p>Denote the massless spin-1/2 fermions as Eqs. (2.10)-(2.11) in that paper
$$v_+(p)= \begin{pmatrix} |p]_a \\ 0 \end{pmatrix} $$
$$v_-(p)= \begin{pmatrix} 0 \\ |p \rangle^{\dot{a}} \end{pmatrix} $$
$$\bar{u}_-(p)= (0, \langle p |_{... | g12472 | [
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<p>This question is motivated by <a href="http://physics.stackexchange.com/questions/76941/big-bang-physics-cosmology">Big Bang Physics/Cosmology</a>. If eternal inflation is a good description of the universe and we live in a bubble universe then presumably our bubble nucleated at a spacetime point. Does this mean it ... | g12473 | [
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<p>Now that we don't have permeating Ether anymore, why don't we consider the omnipresent Cosmic background radiation in place of it? and measure Speeds with respect to the CMBR?
In that way an object moving through the space, can be said to have at least a 'kind-of' absolute velocity w.r.t Background radiation? I.O.W ... | g396 | [
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<p>What is the purpose behind <a href="http://en.wikipedia.org/wiki/Weak_formulation" rel="nofollow">weak formulation</a> of PDEs? I have read in the book by Zienkiewicz and Taylor that a weak formulation is more "permissive" that the original problem in the sense that it allows for discontinuities in coefficients of P... | g12474 | [
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<p>In this <a href="http://physics.stackexchange.com/questions/60715/is-newtonian-gravity-consistent-with-an-infinite-universe">PSE post</a> the issue is about the stability of an infinite universe under Newtonian gravity.<br>
Here I'will drop the Newtonian constraint because we know of the finite speed of interactions... | g12475 | [
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<p>In each of the uncertainty relations $$\Delta p_x \Delta x \geq \hbar/2$$ $$\Delta p_y \Delta y \geq \hbar/2$$$$\Delta p_z \Delta z \geq \hbar/2$$$$\Delta E \Delta t \geq \hbar/2$$
the second term on the left side is one of the compoments of a position 4-vector, while the first term seems to be the corresponding com... | g12476 | [
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<p>Does the warp drive allow to travel between universes? Even in a level 2 <a href="http://en.wikipedia.org/wiki/Multiverse" rel="nofollow">multiverse</a>?</p> | g12477 | [
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<p>As far as i understand, for an object to have a fixed quantity of potential energy, it must be in current equilibrium and have no net force applied to it (otherwise the potential would convert to kinetic). For example, i picture a ball on a hill as a classical example.</p>
<p>And as far as i know, potential energy ... | g12478 | [
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<p>In most textbooks on field theory you read that "<a href="http://en.wikipedia.org/wiki/Spontaneous_symmetry_breaking" rel="nofollow">spontaneous symmetry breaking</a>
implies degeneracy of the ground state". (Like for example in <a href="http://www.itp.phys.ethz.ch/research/qftstrings/archive/13FSQFT2/Chapter07.pdf"... | g12479 | [
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<p>My Physics teacher was reluctant to define Lagrangian as <em>Kinetic Energy minus Potential Energy</em> because he said that there were cases where a system's Lagrangian did not take this form. Are you are aware of any such examples?</p>
<p>Update: Here I'm of course assuming that $T$ and $U$ stands for the kinetic... | g12480 | [
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<p>What is the ratio between horizontal and vertical kinetic energy in the ocean and what is the scale dependencies of this ratio ?</p> | g12481 | [
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<p>My question is about figure3 (page 8) of this paper
<a href="http://arxiv.org/abs/hep-th/9705131" rel="nofollow">hep-th/9705131</a>.
Start from Seiberg-Witten theory, integrate out the charged
high energy modes down to Higgs scale and we get a $U(1)$ gauge
theory without matter. Then the author claims that the beta... | g12482 | [
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<p>I've look into the hydrogen state diagram, and it seems that it can be frozen under pressure.</p>
<blockquote>
<p><strong>Question:</strong> Does this mean that hydrogen cannot be kept frozen in a vacuum chamber?</p>
</blockquote> | g12483 | [
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<p><img src="http://i.stack.imgur.com/5rbRT.png" alt="Enter image description here"></p>
<p>Gate (poly-Si + $SiO_2$) and $p^{-}$ silicon operate as capacitors.</p>
<p>But how are voltages and charges applied? In order for inversion to occur, there should be charges formed in poly-Si, right? How does it work?</p>
<p>... | g12484 | [
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<p>First of all, note the qualifier "residual". The present question is not the same as that asked, and answered, in the StackExchange question "<a href="http://physics.stackexchange.com/questions/8452/is-there-an-equation-for-the-strong-nuclear-force">Is there an equation for the strong nuclear force?</a>" which was ... | g12485 | [
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<p>My textbook has two instances of rolling bodies (smooth rolling). In the first, the body is rolling on the horizontal floor with some acceleration of its centre of mass. In this case, the book says that the friction will act in the direction the ball is accelerating. </p>
<p>In the other instance, the ball is rolli... | g12486 | [
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<p>From what I'm understanding about Dirac spinors, using the Weyl basis for the $\gamma$ matrices the first two components behave as a left handed Weyl spinor, while the third and the fourth form a right handed Weyl spinor. By boosting in a direction or in the opposite, I can "asymptotically kill" either the left or r... | g12487 | [
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... |
<p><a href="http://www.scientificamerican.com/slideshow.cfm?id=a-do-it-yourself-quantum-eraser" rel="nofollow">Click here</a> for the publication.</p>
<p>Having performed this experiment, I have gotten clean results. Essentially, a double slit is made by putting an photon beam in the way of a wire with orthogonal pola... | g12488 | [
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-0.026229210197925568,
0.04011930525302887,
0.04983343556523323,
-0.021663833409547806,
... |
<p>How would a physicist measure temperature of molten metals in 1850-1920s? What equipment would be used?</p> | g12489 | [
-0.012458463199436665,
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0.026662269607186317,
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0.01803302951157093,
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0.0004418821772560477,
0.01... |
<p>If we take the Minkowski metric, $\eta_{\mu\nu}=(1,-1,-1,-1)$, instead of the usual $(-1,1,1,1)$, does this change the form of the Lorentz Transform? I think the standard Lorentz Transform looks like:
$$
\begin{matrix}
\gamma & -\gamma\beta & 0 & 0\\
-\gamma\beta & \gamma & 0 & 0\\
0 &a... | g12490 | [
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-0.... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/29794/why-are-coordinates-and-velocities-sufficient-to-completely-determine-the-state">Why are coordinates and velocities sufficient to completely determine the state and determine the subsequent motion of a... | g397 | [
0.05041762813925743,
0.05081123858690262,
-0.00463460199534893,
0.04675984010100365,
0.05155711621046066,
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0.06597151607275009,
0.013090922497212887,
-0.005768525879830122,
-0.013609047047793865,
-0.051048748195171356,
-0.013288402929902077,
-0.016776110976934433,
0.0... |
<p>I've noticed that in the discussion of the fine structure of Hydrogen atom standard QM texts claim that the Darwin term, which corrects energy of $\ell=0$ (or $s$-) states only, is related to the zitterbewegung of the relativistic electron.</p>
<p>I'm quite familiar with the zitterbewegung phenomenon, but it is not... | g12491 | [
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-0.0107314083725214,
0.00035329043748788536,
-0.020128412172198296,
0.030667198821902275,
... |
<p>I'm trying to do the following problem:</p>
<p>A lever $ABC$ (see figure) has weights $W_1$ and $W_2$ at distances $a_1$ and $a_2$ from the fixed support $B$. Using the principle of virtual work, prove that a necessary and sufficient condition for equilibrium is $$W_1a_1 = W_2a_2$$
My attempt:</p>
<p>Now, the prin... | g12492 | [
0.01763593591749668,
0.030634775757789612,
-0.015530040487647057,
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0.014052739366889,
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0.0163776483386755,
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0.06149652972817421,
-0.05004517361521721,
0.023157386109232903,
-0.045263081789016724,
-0.009... |
<p>Nearly all gauge-fixing prescriptions are based upon setting some function involving the gauge fields to be zero. That function is continuous and varies over the real/complex numbers. Trying the same trick for discrete gauge symmetries break down because we have no continuity, and hence, no implicit function theorem... | g12493 | [
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0.019086793065071106,
-0.... |
<p>The density of states (DOS) is generally defined as $D(E)=\frac{d\Omega(E)}{dE}$, where $\Omega(E)$ is the number of states. But why DOS can also be defined using delta function, as
$$D(E)~=~\sum\limits_{n} \int \frac{d^3k}{(2\pi)^3}\delta(E-\epsilon_n(\mathbf{k}))?$$ </p> | g12494 | [
-0.0012155309086665511,
0.05762037634849548,
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0.1275905817747116,
-0.... |
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