question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>When a Hamiltonian operator apply to a wavefunction, how could we write the hamiltonian as,
$$H \psi = (E_n-\hbar \omega_0) \psi \ \ ? $$</p>
<blockquote>
<p>Is this because $E_n= H+ \hbar \omega_0$?</p>
</blockquote>
<p>where $\omega_0$ is the angular frequency.</p> | g14905 | [
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<p>I know that after invoking the Born-Oppenheimer approximation, the nuclei will move on the adiabatic potential provided by the electronic energy (also called potential energy surface (PES)). Such nuclear motions, can be described following quantum-mechanical, classical or hybrids methods on a fitted potential energy... | g14906 | [
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<p>Does the definition of an atomic explosion require the interaction of two or more atoms, or can a single atom be the source of an explosion?</p>
<p>Another way of phrasing the same question. Can there be an atomic explosion involving a single atom without any other atom involved in the start or chain reaction of th... | g14907 | [
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<p>At the time the Big Bang happened the matter had enormous density. According the GR (I may be wrong here) such density dilates time.</p>
<p>If so, could it be that the time periods just after Big Bang which are usually considered happening in small part of a second (such as the Planck epoch), in reaity took billons... | g700 | [
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<p>Grilling in the park today I started to wonder just how implausible a portable battery-powered grill would be. There are of course a lot of parameters in this question, so let's narrow it down for now: How much energy does it take to cook a steak?</p>
<p>To be a bit more specific let's say a 2.5cm thick steak to a ... | g14908 | [
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<p>This came from a physics wave book. I have a static, massive wire on the x-axis, with a y-displacement due to a force per unit length $F_y$. I start with the equation $F_y = T_0\frac{\partial^2(\eta)}{\partial(x)^2}$, where $\eta$ is a small displacement in the y direction and $T_0$, with units of force, is the tens... | g14909 | [
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<p>I'm reading articles about black body radiation and why classical mechanics fails to explain it. My question is:</p>
<p>Why do EM waves have to be standing wave in a cavity?</p> | g14910 | [
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<p>Consider a block of mass $m$ attached to a spring. Let it oscillate at a frequency $f$. Now each part of the spring is in SHM. so this means a wave is propagating through this spring.bCan this wave be reflected at the fixed end of the spring resulting in the formation of standing waves?</p> | g14911 | [
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<p>I am trying to clearly express in one or two sentences how increased evapotranspiration could cool a region. The audience is educated but non-scientific.</p>
<p>Is it accurate to say that the water vapor has removed latent heat? Is there a more clear explanation?</p> | g95 | [
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<p>What are the missing lines in the integration?</p>
<p>$$\frac{\text d \langle {p} \rangle}{ \text{d} t} $$
$$= \frac{\text d}{\text d t} \int\limits_{-\infty}^{\infty} \Psi^* \left( \frac{\hbar}{i}\frac{\partial}{\partial x} \right) \Psi ~\text d x$$
$$= \frac{\hbar}{i}\int\frac{\partial }{\partial t} \left(\Psi^*... | g14912 | [
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<p>Often in engineering physics, different vector spaces are used to visualize the trajectories (evolution) of systems. An example being the 6n dimensional phase space of n particles. It is not very clear to me if this space is Euclidean or has a meaning of distance. I understand the 2-norm when the physical quantitie... | g14913 | [
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<p>It’s easy, relatively speaking, to develop an intuition for higher spatial dimensions, usually by induction on familiar lower-dimensional spaces. But I’m having difficulty envisioning a universe with multiple dimensions of time. Even if such a thing may not be real or possible, it seems like a good intellectual exer... | g480 | [
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<p>I would like to migrate this <a href="http://math.stackexchange.com/questions/514/conjectures-that-have-been-disproved-with-extremely-large-counterexamples">Math</a> Question into physics. The question is:</p>
<ul>
<li>Are there conjectures in Physics which have been disproved with extremely large counterexamples? ... | g14914 | [
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<p>Do spacelike singularities really exist in quantum gravity? If the memory of anything which falls into a black hole can't get out, is there any sense in which the interior of the black hole is real? Similarly, if we don't have any direct records of the spacelike singularity in the past, is there any sense in which i... | g468 | [
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<p>I've heard that common way to get 354nm laser is to triple 1064nm Nd:YAG one.</p>
<p>But how to make non-linear crystal to do tripling instead of doubling?
What are the best crystals for tripling and what's the efficiency?</p> | g14915 | [
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<p>In the context of GTR spacetime, I'm trying to get the basic idea of a Riemannian manifold clear in my mind. Apologies for the longwindedness.</p>
<p>Question 1. Is this a reasonable, simplified summary of the steps needed to define such a manifold?</p>
<ol>
<li><p>Start with an amorphous collection of points.</p>... | g14916 | [
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<p>I am writing simple car simulation.</p>
<p>Assume non friction, then in straight line the car doesn't lose speed. But what if the car is turning, there should be some kinetic energy loses to change the direction of the car, so I should subtract some speed based on changing direction, isn't it right?</p>
<p>Deeper ... | g14917 | [
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<p>Quite a few of the questions given on this site mention a photon in vacuum having a rest frame such as it having a zero mass in its rest frame. I find this contradictory since photons must travel at the p of light in all frames according to special relativity.</p>
<p>Does a photon in vacuum have a rest frame?</p> | g94 | [
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<p>Can a functional derivative be calculated if we have a function of more than one variable? </p>
<p>The functional derivative of, for example, $F[b(x)]=e^{\int_0^{x'} dx a(x,y) b(x)}$ is </p>
<p>\begin{equation}
\frac{\delta F[b(x)]}{\delta b(z)} = a(z,y) e^{\int_0^{x'} dx a(x,y) b(x)}
\end{equation}</p>
<p>Bu... | g14918 | [
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<p>I have read how the <a href="http://en.wikipedia.org/wiki/BB84" rel="nofollow">BB84</a> protocol could work. However, I couldn't see a way to implement it in the laboratory, so that I could make a demonstration in the university's quantum optics laboratory. </p>
<p>From what I have read, I think that a way to demon... | g14919 | [
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<p>I am aware that the formula for <a href="http://www.google.com/search?as_q=Schiff+Equation" rel="nofollow">Schiff Equation</a> in used to determine frame-dragging is:
$$\boldsymbol{\Omega} = \frac{GI}{c^2r^3}\left( \frac{3(\boldsymbol{\omega}\cdot \boldsymbol{r})\boldsymbol{r}}{r^2}-\boldsymbol{\omega} \right).$$</p... | g14920 | [
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<p>The idea of “hadronic supersymmetry” originated in the mid-1960s and derives from the observation that baryons and mesons have similar Regge slopes, as if antiquarks and diquarks are superpartners. This is most efficiently explained by supposing a QCD string model of baryons in which a diquark substitutes for an ant... | g14921 | [
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<p>In the second chapter of Peskin and Schroeder, <em>An Introduction to Quantum Field Theory,</em> it is said that the action is invariant if the Lagrangian density changes by a four-divergence.
But if we calculate any change in Lagrangian density we observe that under the conditions of equation of motion being satisf... | g734 | [
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<p>i'm a high school student and i was reading about electromagnetic waves and how they transport energy and that the electric and magnetic fields sustain each other.</p>
<p>I have also read about longitudinal waves which travel due to contractions and rarefactions and also transport energy by changing the relative po... | g14922 | [
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<p>When light enters materials it slows down due to its refractive index (due to absorbing and re-emission of photons). </p>
<p>But, is there a way to increase the speed of light itself? Can there be some material which would increase rather than decrease the speed of light? </p> | g14923 | [
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<blockquote>
<p>A chain of mass $M$ and length $l$ is suspended vertically with its
lowest end touching a table. The chain is released and falls onto the
table. What is the force exerted by falling part of the chain on the
table?(Neglect the size of individual links)</p>
</blockquote>
<p>Here's what I did.
Mom... | g14924 | [
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<p>If there are two cylinders (A and B) both with the same volume. B's radius is half of A's, so the length of B must be 4 ($2^2$) times that of A. </p>
<p>The uncertainty for the radius of A is the same as the for the radius of B, and the uncertainty is the same for the lengths. But the uncertainty of the volume isn'... | g14925 | [
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<p>I am wondering to what extent the flammability can be predicted from the statistical properties of an ensemble. Given the partition function of an ensemble, can we in principle predict this property? Is there a chance flammability is a classical property of matter?</p> | g14926 | [
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<p>I am trying to derive a formula to calculate the density of a irregulary shaped object.</p>
<p>I can measure the (<strong>false</strong>) weight of the object in pure air (of known density), and the (<strong>false</strong>) weight of the object in water (of known density).</p>
<p>I cannot measure (directly) the vo... | g14927 | [
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<p>Is the higgs field in space around us? </p>
<p>I understand it as that the higgs field has a constant value on every space time point, is that right?</p>
<p>And this value is the vacuum expectation value. This value is responsible for giving mass to the elementary particles, like the fermions, right?</p>
<p>In th... | g14928 | [
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<p>As discussed by Prof.Wen in the context of the <a href="http://arxiv.org/abs/cond-mat/0107071" rel="nofollow">quantum orders of spin liquids</a>, <strong>PSG</strong> is defined as all the transformations that leave the mean-field ansatz invariant, <strong>IGG</strong> is the so-called <em>invariant gauge group</em>... | g14929 | [
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-0.023960012942552567,
... |
<p>I have this question going in my mind from many days, i.e why brightness of light emitted from any light source around us decreases with distance? The brightness of light from tube light, streetlight, etc or any light from any source around us, decreases with the distance. As my teacher has taught me that light is a... | g14930 | [
0.01038885023444891,
0.0070113749243319035,
0.03209839016199112,
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0.029099253937602043,
0.02734271064400673,
0.046874865889549255,
0.0353... |
<p>In other words, does a finite set <a href="http://en.wikipedia.org/wiki/Correlation_function_%28quantum_field_theory%29" rel="nofollow">correlation functions</a> sufficient to determine a theory? Is there a chance correlation functions are more fundamental then the lagrangian?</p> | g14931 | [
0.04457852989435196,
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0.0013091510627418756,
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0.009407984092831612,
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0.0... |
<p>We are working on problem 6.12 from Griffiths Electrodynamics. It says that we have an infinitely long cylinder of frozen in magnetization of $M=ks\hat z$. We are trying to find the field. We have found:</p>
<p>$$J_b=\nabla \times M=-k\hat{\phi}$$
$$K_b=M \times \hat n=kR\hat {\phi}$$</p>
<p>Then we are stuck o... | g14932 | [
0.005911422893404961,
0.05896624177694321,
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<p>I have a homework problem that I can't get started on, below is the first bit. I feel like I should just be able to integrate to find $C$ but I get a divergent integral. Can someone give me a hint as to where to go here?</p>
<blockquote>
<p>A particle of mass m is in a one-dimensional infinite square well, with $U... | g14933 | [
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0.019063491374254227,
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0.017436547204852104,
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0.0... |
<p>This question is related to <a href="http://physics.stackexchange.com/questions/89969/6-independent-einstein-field-equations">my previous one</a> and it was a homework problem and was due two weeks ago.</p>
<p><em>Problem</em>：prove that four of Einsteins' equations
$$
G_{0\nu} = 8\pi T_{0\nu}
$$
have to 2nd order... | g14934 | [
0.007321775890886784,
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... |
<p>I'm in search of examples of Lagrangian, which are at least second order in the derivatives and are covariant, preferable for field theories. Up to now I could only find first-order (such at Klein-Gordon-Lagrangian) or non-covariant (e.g. KdV) ones. Also some pointers to the literature about general properties of su... | g14935 | [
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<p>When performing an experiment to observe electron spin resonance, we use DPPH molecules as they contain an unpaired electron on one of the N atoms. </p>
<p>My question is, why cant free electrons be used in this experiment? What is wrong with a beam of electrons or a metal?</p>
<p>Any help would be greatly appreci... | g14936 | [
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0.004887513350695372,
0.034077100455760956,
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0... |
<p>In <a href="http://motls.blogspot.de/2013/04/reframing-string-theory-in-terms-of.html?m=1" rel="nofollow">this</a> article discussing <a href="http://arxiv.org/abs/1304.0448" rel="nofollow">this</a> and related papers, it is explained among other things, how the neighborhood of an observer's worldline can be approxi... | g14937 | [
0.020338384434580803,
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0.008559177629649639,
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0.02... |
<p>I am interested in the link between the <a href="http://en.wikipedia.org/wiki/Black%E2%80%93Scholes#The_Black.E2.80.93Scholes_equation">Black & Scholes equation</a> and quantum mechanics.</p>
<p>I start from the Black & Scholes PDE
$$
\frac{\partial C}{\partial t} = -\frac{1}{2}\sigma^2 S^2 \frac{\partial^2... | g14938 | [
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0.06924063712358475,
0.05923008918762207,
0.031467217952013016,
0.005092012695968151,
0.0200... |
<p>A book by C. J. Ballhausen led me to believe that a quick way to check that I performed step operators properly was by observing that the "wave function should appear normalized," but I have found some issue applying this in practice and believe it is due to my misunderstanding of the underlying physics; I'm trying ... | g14939 | [
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0.02347933128476143,
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0.05349132791161537,
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0.0... |
<p>This may be a trivial question, but I cannot find a good answer to it.</p>
<p>What would happen if the size of everything in the Universe is multiplied by some constant factor at the same time, let's say everything doubles its size for instance. People double their size, houses double their size, streets, towns, Ea... | g14940 | [
0.057595930993556976,
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0.026647226884961128,
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0.01827186718583107,
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0.00849768053740263,
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0.05239778012037277,
0.02... |
<p>In a <a href="http://en.wikipedia.org/wiki/Tug_of_war">tug-of-war</a> match today, my summer camp students were very concerned about putting the biggest people at the back of the rope. Is there any advantage to this strategy?</p> | g14941 | [
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<p>I learned yesterday that the inverse of square roots is used to calculate the vectors of surface normals in 3d graphics. It seems like such a mind-bogglingly simple idea, and it leads me to wonder if it hasn't found use elsewhere. Is there anywhere in physics where one might need to calculate the reciprocal of a num... | g14942 | [
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0.038181353360414505,
0.03714829310774803,
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<p>I'm trying to properly understand the meaning of entropy, and how the universe is moving from an orderly state to a chaotic one.</p>
<p>If a glass of wine (for example) only has meaning to a human, what makes a shattered spilled glass any less orderly than a full whole glass?</p>
<p>Or if a particle is observed, a... | g14943 | [
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0.07945923507213593,
0.022... |
<p>Consider an outdoors scenario, with good weather and no sensible air currents at the floor level. How turbulent or laminar is the air surrounding this environment?</p> | g14944 | [
0.021112516522407532,
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<p>It is known that for any smooth, orientable, compact manifold $X$ without boundary and $\alpha \in \Omega^{r}(X), \beta \in \Omega^{r-1}(X)$ it holds </p>
<p>\begin{equation}
(d\beta,\alpha)= (\beta, d^{\dagger}\alpha),
\end{equation}</p>
<p>where </p>
<p>\begin{equation}
(d\beta,\alpha) = \int_X d\beta \wedge \s... | g14945 | [
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0.0123923160135746,
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0.03802042454481125,
0.0036298164632171392,
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<p>With my little knowledge of optics I have come across some 'known' designs such as the Double Gauss for example, is there a 'beam compressor'.</p>
<p>My requirements are to reduce an incoming parallel wavefront (source at infinity) to either an outgoing parallel beam (ie afocal), by a factor of around 100 within 10... | g14946 | [
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0.04198222979903221,
0.008430843241512775,
0.00... |
<p>Here's how my book explains mass defect:</p>
<blockquote>
<p><em>Particles inside the nucleus interact with each other - they feel attraction. The potential energy $U$ of such attraction is negative, because in absence of these forces we consider the potential energy to be zero. So we can write the total energy a... | g14947 | [
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0.031148921698331833,
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0.014734150841832161,
0.016076434403657913,
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... |
<p><img src="http://i.stack.imgur.com/xRtob.png" alt="two different spring systems"></p>
<p>Two identical springs with spring constant $k$ are connected to identical masses of mass $M$, as shown in the figures above. The ratio of the period for the springs connected in parallel (Figure 1) to the period for the springs... | g14948 | [
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0.033131878823041916,
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0.02295602671802044,
0.022954672574996948,
0.... |
<p>I have an important doubt about the nature of canonical transformations in hamiltonian mechanics.</p>
<p>Suppose I have a one-degree-of-freedom lagrangian system, whose hamiltonian depends explicitly on time:</p>
<p>$$\frac{\partial{\mathcal{H}(p, q, t)}}{\partial{t}} \neq 0$$</p>
<p>so <em>in principle energy is... | g14949 | [
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0.... |
<p>I'm sorry for this lexical, probably extremely elementary, question. But what is a pseudo-rotation? I just read this term for the first time, in the beginning of the 4th chapter book of CFT by Di Francesco & al. I would say it may be an hyperbolic rotation or a rotation followed by a parity operation (with deter... | g14950 | [
0.03847586736083031,
0.07203588634729385,
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0.02911381609737873,
0.03482283651828766,
-0.059199... |
<p>In 2-d, one ripple would mean the velocity of water particles move out radially forming a circular wavefront. The Navier Stokes equations say the divergence of velocity has to be zero, but this circular radiation pattern has nonzero divergence. What am I missing here, since water ripples clearly exist?</p> | g14951 | [
0.0312618725001812,
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0.026829572394490242,
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0.0371992... |
<p>I have been reading about symmetries of systems' actions, e.g. the Polyakov action, and I have encountered Lorentz transformations of the form: $\Lambda^{\mu}_{\nu} X^{\nu}$. I am moderately familiar with $\Lambda$, the Lorentz matrix. If the indices are in superscript then it is the inverse of $\Lambda_{\mu \nu}$. ... | g14952 | [
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0.10620247572660446,
0.0007515057804994285,
... |
<p>Consider all of sudden the sun vanishes. What would happen to planetary motion. Will it continue to move in elliptical path or move in a tangential to the orbit immediately after sun vanishes or move in elliptical orbit for some time after the vanishing of sun or any other cases?</p>
<p>If so, please explain...</p> | g4 | [
0.07408048212528229,
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0.005841840989887714,
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0.027046525850892067,
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0.0024506670888513327,
-0.007672655396163464,
-0.003221239196136594,
0.022549500688910484,
0.04347353056073189,
-0.... |
<p>Here on Earth we are blessed with being able to see some other planets, Mars & Venus etc, with the naked eye on a fairly regular basis thanks to the distance between the planets.</p>
<p>What about from Mars? What planets would be visible to the naked eye on a regular basis from Mars?</p>
<p>Earth would obviou... | g14953 | [
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0.016204718500375748,
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0.04762626066803932,
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0.003719829488545656,
0.048151567578315735,
-0.014858529902994633,
0.10711102187633514,
0.026279473677277565,
0.06648977100849152,
0.027... |
<p>If you take any large nucleus and add protons to it, the electrostatic repulsion between them will make the nucleus more unstable, because the electrostatic force between them is more repulsive at a greater distance than the strong force is attractive</p>
<p>So how come if you add more neutrons, which dont have a c... | g14954 | [
0.0009017513948492706,
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0.006175653077661991,
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0.0... |
<p>Is there an updated version of the cosmological triangle with recent PLANCK results included?</p>
<p><img src="http://i.stack.imgur.com/Q31Pq.png" alt=""></p> | g14955 | [
0.013085982762277126,
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0.05238007381558418,
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0.01925753988325596,
-0... |
<p><a href="http://www.msnbc.msn.com/id/42044156/ns/world_news-asia-pacific/" rel="nofollow">The recent news</a> says that</p>
<blockquote>
<p>Japanese authorities confirmed Saturday that radiation had leaked from a quake-hit nuclear plant after an explosion destroyed a building at the site.</p>
</blockquote>
<p>Wh... | g14956 | [
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0.035087354481220245,
0.013796977698802948,
-0.03200880065560341,
0.014692670665681362,
0.004574075806885958,
0.0008214123663492501,
-0.02... |
<p>How can i derive the dynamic of a relativistic charged particle in a uniform magnetic field $B=(0,0,B)$?</p> | g14957 | [
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0.01023206114768982,
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0.012486273422837257,
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0.04646344855427742,
-0.03367987275123596,
-0.007... |
<p>I know that we can calculate the maximum potential of a van de graaff generator by ( radius* electric field in which corona discharge begin to form in the surrounding gas( according to wikipedia 30 kv/cm)).
What if i covered the sphere with Mica with a dielectric strength ( according to wikipedia) 1.18 Mv/cm , will ... | g14958 | [
0.0343310721218586,
0.009291483089327812,
0.013294145464897156,
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0.01868574135005474,
-0.003934452775865793,
0.022612493485212326,
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-0.0... |
<p>I'm trying to obtain <a href="http://en.wikipedia.org/wiki/Euler_equations_%28fluid_dynamics%29" rel="nofollow">Euler equation</a> for a perfect fluid in laminar or stationary flow. A particle fluid is submitted at volume forces and surface force. The fist, in my case, is giving only by gravity and the second by pre... | g14959 | [
0.06409884989261627,
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0.09811832755804062,
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0.06675880402326584,
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-0.012071730569005013,
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0.02289024367928505,
0.023415639996528625,
0.03... |
<p>It is generally assumed that there is no limit on how many bosons are allowed to occupy the same quantum mechanical state. However, almost every boson encountered in every-day physics is not a fundamental particle (with the photon being the most prominent exception). They are instead composed of a number of fermions... | g14960 | [
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<p>When a wheel is rolling, not skidding, and its axle moves at velocity $\vec{v}$, then a point on the top of its circumference will move at velocity $2\vec{v}$, shown below.</p>
<p><img src="http://i.imgur.com/qLXEZ.gif" alt="Velocity wheel top and wheel axis" title="Can't embed image, sorry. Hosted on imgur."></p>
... | g14961 | [
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<p>I found this nice <a href="http://cadcam.eng.sunysb.edu/~purwar/MEC501/report.pdf" rel="nofollow">paper</a> about RB convection. However I am confused by what is going on page 6. In particular why we are suddenly using Helmholtz equation to find spatially periodic solutions. Aren't we working with convection, so why... | g14962 | [
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<p>This is a problem (Problem 3.16) from the book Statistical Mechanics 2nd Ed. by Pathria.
In the problem I have to calculate the partition function of an ultra-relativistic 1D gas ($E_i=cp_i$) consisting in $3N$ particles moving in one dimension. I know that the partition function is given by</p>
<p>$$Q_{3N}=\frac{1... | g14963 | [
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0.0072120... |
<p>Currently I am planning to get masters degree. So I am thinking about a subject in which I have to get masters degree. Following are my questions to leading physicists..</p>
<ol>
<li>Which technology is the future of telecommunication? Currently electromagnetic waves only rules the world for telecommunication. But ... | g14964 | [
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<p>First of all, I know almost nothing about physics. I was reading Kontsevich´s paper on <a href="http://arxiv.org/abs/q-alg/9709040" rel="nofollow">Deformation quantization of Poisson manifolds</a>, however I could not figure out what´s the intuition for such operation. </p>
<p>Why there is the word "quantization" a... | g14965 | [
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<p>I have a vehicle traveling at initial speed $100\:\mathrm{m/s}$.
Expected destination speed is also $100\:\mathrm{m/s}$.
Maximum deceleration is $3$.
Maximum acceleration is $10$.
Distance to the target is $2000\:\mathrm{m}$.
The vehicle should reach the target in 40s.</p>
<p>The vehicle should follow a linear path... | g14966 | [
0.012503064237535,
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<p>Once a quantum partition function is in path integral form, does it contain any operators?</p>
<p>I.e. The quantum partition function is $Z=tr(e^{-\beta H})$ where H is an operator, the Hamiltonian of the system.</p>
<p>But if I put this into the path integral formalism so that we have something like $Z= \int D(\b... | g14967 | [
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<p>I've read over the decades that a magnetic shield might protect a spacecraft from cosmic radiation. Its a fascinating idea that might only be theory or science fiction at the moment. In regards to that here is an article just in case someone isn't sure what I mean:</p>
<p><a href="http://physicsworld.com/cws/arti... | g14968 | [
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<p>Suppose a vibrating tuning fork compresses air molecules.And for this it has to do work.As compression occurs,its temperature increases.Does the energy spent by the fork go as the increased internal energy of the molecules?If so,then which energy goes as sound energy?As the process is adiabatic,does this given energ... | g469 | [
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<p>I often see the expression $W = V \Delta P$ for the work of a constant volume compression where there are a fixed number of moles and the compression is caused by heating. Is this the work equation for a constant volume, isothermal process where the pressure is increased by adding moles of a gas?</p> | g14969 | [
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<h2>Background</h2>
<p>In <a href="http://physics.stackexchange.com/questions/16638/is-it-only-red-green-and-blue-that-can-make-up-any-color-through-additive-mixtu">this</a> thread, I asked whether it is true that the colors red, green and blue, through additive mixture, can make up <em>any</em> color. Turns out they ... | g14970 | [
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0.02780... |
<p>The equation of motion for the density matrix of a many body isolated quantum system is the von Neumann's equation: $\dot{\rho }(t)=i[\rho (t),H]$. How about the equation of motion for the reduced density matrix of one particle, is there a general procedure to obtain it?</p> | g14971 | [
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<p>I came across these swimming goggles with a LCD display integrated right on the goggle itself. </p>
<p><a href="http://www.psfk.com/2011/09/smart-goggles-enable-swimmers-to-track-and-record-swim-pace.html/my_pace_goggles2" rel="nofollow">http://www.psfk.com/2011/09/smart-goggles-enable-swimmers-to-track-and-record-... | g14972 | [
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0... |
<p>I know I should be able to piece together some basic Newtonian equations for this, but I'm not sure where to start. I want to be able to choose one planet as the center and calculate its distance from another planet over time as they both rotate the sun. </p>
<p>First I need to even find equations for the motion ... | g14973 | [
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<p>Discussing with colleagues (mostly condensed matter ones), we were astonished there is no mention about the work by Larkin in the <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2013/advanced.html" rel="nofollow">announcement of the Nobel Prize committee</a> this year.</p>
<p>The title of the Lark... | g14974 | [
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<p>Since neutrinos</p>
<ol>
<li>have a small mass and</li>
<li>are affected by gravity,</li>
</ol>
<p>wouldn't it be theoretically possible to have such a large quantity of them so close to each other, that they would form a <em>kind</em> of a stellar object, i.e. one that would keep itself from dissolving due to th... | g14975 | [
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<p>Why does mode hopping occur when the temperature of a diode is changed?</p>
<p>Why is a similar effect seen when we change the electric current?</p> | g14976 | [
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<p>Before I take P-Chem I would like to understand how physicists view the same material. What Physics course(s) should I take and/or books should I read to learn the same material from a physicist's perspective? Would thermodynamics be equivalent?</p>
<p>Background: I have done the math: Calculus 1-3 and differential... | g14977 | [
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<p>Why isn't pressure used as flight?</p>
<p>I've heard that 2L bottles can hold a pressure of up to 90 PSI safely. Since $F = PA$, if the nozzle of a pressure rocket is about 4 inches squared in area, that would be a thrust of 360 pounds!? Is there something wrong with my math, or why don't we just pressurize air and... | g14978 | [
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<p>I am calculating the action of the conformal generators on fields, to be more precise on wavefunctions. For now, I'm classical. I will just paste the part of my report on this to show what I am talking about:</p>
<p>Now let us use the fact that $\Phi_a(x) = U_P(-x)\Phi_a(0) = e^{iP_\mu x^\mu}\Phi_a(0)$. We can writ... | g14979 | [
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0.... |
<p>I am talking here about dry friction between solid objects, for example a ruler and a table, not anything lubricated or fluid.</p>
<p>I noticed that with a ruler and a table for example, if you drag the ruler like it was a knife, it is much easier to do it than if still holding the ruler in the same position you dr... | g14980 | [
0.04456329345703125,
0.03258277475833893,
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<p>Since a particle in one dimension can only move in a straight line. Is it possible to have potential energy? And how would the kinetic energy and potential energy differ in higher dimensions?</p> | g14981 | [
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<p>I have read a lot on Higgs bosons, yet I do not fully comprehend how they are created and how they are "flicked off" the Higgs field. I have also had trouble comprehending why a Higgs boson quickly becomes unstable and decays into more common particles.</p>
<p>How is a Higgs boson created and how and why does it qu... | g14982 | [
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<p>According to <a href="http://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofollow">Noether's theorem</a>, every continuous symmetry (of the action) yields a conservation law.</p>
<p>In fluid, there is a local particle number conservation law, which is $$\partial{\rho}/\partial{t}+\nabla \cdot \vec{j} ~=~0,$$ wh... | g14983 | [
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<p>A stationary observer very close to the horizon of a black hole is immersed in a thermal bath of temperature that diverges as the horizon is approached. $$T^{-1} = 4\pi \sqrt{2M(r-2M)}$$ The temperature observed by a stationary observer at infinity can then be obtained through the gravitational redshift formula (see... | g14984 | [
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<p>I need help with the following problem. I think I almost have it . . .</p>
<p>A parachutist bails out and freely falls a distance of $y_1$. Then the parachute opens and thereafter, the parachutist decelerates at a rate of $a_2$. She reaches the ground with a speed of $v_2$. Find her average speed for the fall. (The... | g14985 | [
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0.... |
<p>In a rainbow the colors order is red then orange (made from red and yellow, thus making sense that it appears in between them) the yellow followed by green after which comes blue (again green formed from yellow and blue). The final color is purple, which is next to the blue' but not in any contact with the red.</p>
... | g14986 | [
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<p>I am trying to understand the application of the operator product expansion to calculate the radially ordered product in the complex plain of $T_{zz}(z)\partial_w X^{\rho}(w)$ which should result in</p>
<p>$$
\langle R(T_{zz}(z)\partial_w X^{\rho}(w))\rangle = -l_s^2\frac{1}{(z-w)^2}\partial_w X^{\rho}(w) - l_s^2\f... | g14987 | [
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<p>A <a href="http://www.universetoday.com/85927/australian-student-uncovers-the-universes-missing-mass/" rel="nofollow">recent article from a popular astronomy website</a> tells of discovery of missing mass (not dark matter) that has puzzled astronomers for some time. Apparently, the discovery involves enhanced electr... | g14988 | [
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<p>It might be a silly question, but I was never mathematically introduced to the topic. Is there a representation for <a href="http://en.wikipedia.org/wiki/Grassmann_number" rel="nofollow">Grassmann Variables</a> using real field. For example, gamma matrices have a representation, is it not possible for Grassmann Vari... | g14989 | [
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... |
<p>A person wants to throw an object from the top of a tower $9,0m$ high towards a target which is $3,5m$ far from the place where the person is launching the object. Suppose that this object is thrown horizontally.</p>
<p>What I want to find out is:</p>
<ol>
<li>What initial speed does the object need to have in ord... | g14990 | [
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0.00032325979555025697,
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0.06552944332361221,
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0.01... |
<p>What observables are indicative of BCS Cooper pair condensation?</p>
<p>"Thought" experiments and "numerical" experiments are allowed.</p>
<p>This question is motivated by the question <a href="http://physics.stackexchange.com/questions/43876/has-bcs-cooper-pair-condensate-been-observed-in-experiment">Has BCS Coop... | g14991 | [
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0.05017... |
<p>In my quantum mechanics class, my professor explained that the Hamiltonian along with position and momentum operators can be represented by matrices of countable dimension. This is especially usefull in harmonic oscillator problems. My professor explained that the eigenvalues of the Hamiltonian are (of course) the d... | g632 | [
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0.029686875641345978,
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0.004006082657724619,
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0.03... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/14968/superluminal-neutrinos">Superluminal neutrinos</a> </p>
</blockquote>
<p>An article in the newspaper a few months ago said that Neutrinos travel faster than Light. Another article then said that th... | g83 | [
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-0.03488150238990784,
0.0134322140365839,
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0... |
<p><strong>My question:</strong> What (physical or mathematical) reasons (not philosophical) do some physicists ('t Hooft, Penrose, Smolin,...) argue/have in order to think that Quantum Mechanics could be substituted by another theory in the future? Namely...Why should it be an effective and non-fundamental (``non-ulti... | g14992 | [
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0.012... |
<p>I want to know if you could theoretically travel from your house to work via a wormhole but stay in the present day...without changing time. Kind of like teleportation but harnessing the energy of a black hole or wormhole. My background is chemistry not physics so I'd prefer a mathematical explanation. Thanks.</p> | g14993 | [
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... |
<p>I am having a problem with reflection on an acrylic surface, in the IR part of the spectrum. This reflection is interfering with an algorithm that looks at objects, as it makes two show up when only one exists.</p>
<p><strong>Some background:</strong></p>
<p>An IR sensitive (and IR filtered) camera must view an IR... | g14994 | [
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0.021203195676207542,
0.08392395824193954,
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0.022... |
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