question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p><strong>Scenario 1</strong></p>
<p>Two identical and bilaterally symmetrical cars, driven by identical drivers in the exact center of the car and in the same body position, each traveling the same speed, collide exactly head on. (Essentially, eliminate all variables that would cause rotation or interpenetration dur... | g58 | [
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<p>Let's say I have an infinite line source in 3d wave medium, like a pulsating cylinder, emitting a broadband noisy signal. I know that the pressure falls off at 3 dB per doubling in distance, unlike a point source which falls off at 6 dB per doubling in distance, because the cylindrical wavefront is only spreading ou... | g15370 | [
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<p>Suppose you have two thermodynamical systems $X_1$ and $X_2$ (for example water and air) with different temperatures ($T_1 > T_2$). Now put them into thermal contact. Is there a formula which describes, how $T_1$ and $T_2$ changes with time?</p> | g15371 | [
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<p>What does it mean to "weakly gauge" a global symmetry in a gauge theory? I have seen this term used in a number of papers, but have not seen it defined.</p> | g15372 | [
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<p>If you take apart a syringe you are left with one piece that is a tube with a tiny hole in one end and the open end of a tube at the other. If you then submerge this underwater and cover the small hole, then lift out of the water, the water remains in the tube/syringe until you release your finger from the small hol... | g15373 | [
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<p>Tinker is a hero in the popular game Dota 2. He has a spell called 'March of the Machines' that creates a stampede of little robots in a rectangular area. The robots do damage on impact of an enemy unit. Basically this can be considered a vector field and enemy units are surface area. We want the maximum flux in ord... | g15374 | [
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<p>I have done my experiment using water ripple to study the behavior of waves. I know that the crest will absorb more light than the trough so that the image created on the white paper sheet appeared to be the troughs has darker lines than the crests. However now I wonder why the crest of water absorb more light than ... | g15375 | [
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<p>In discussion of LHC searches for SUSY particles, physicists seem to assume they will decay quickly to the lightest SUSY particle which then remains stable (at least within the time it takes to leave the detector). As an example: <a href="http://physics.aps.org/articles/v4/27" rel="nofollow">http://physics.aps.org/... | g15376 | [
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<p>I am trying to understand the derivation of the <a href="http://en.wikipedia.org/wiki/Einstein%E2%80%93Hilbert_action" rel="nofollow">Hilbert-Einstein action</a>. However it requires a knowledge about hyper-surfaces for the boundaries of the integrals and also about the normal to the hyper-surface $n^{a}$ for the de... | g15377 | [
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<p>In <a href="http://www.youtube.com/watch?v=Kw8dcb8iKSM&t=5m52s" rel="nofollow">this</a> video, Michio Kaku says </p>
<blockquote>
<p>"...general theory of relativity, where it is possible, we think, that you might be able to go faster than the speed of light..."</p>
</blockquote>
<p>Does GR really allow supe... | g15378 | [
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<p>I want to calculate the Dirac term from the canonical Kahler potential,
\begin{equation}
K = \Phi ^\ast \Phi \tag{1}
\end{equation}
but I'm coming across a pesky negative sign in the final result. I am finding (see derivation below),
\begin{equation}
- i \bar{\psi} \bar{\sigma} ^\mu \partial _\mu \psi \tag{2}
\en... | g15379 | [
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<p>Consider the following expression for a general QFT action:</p>
<p>$$ S ~=~ \int_0^t\mathrm dt~L
~=~\int_0^t\mathrm dt\int_\mathbb {R^3}\mathrm d^3x~\mathcal L
~=~\int\mathrm d^4x~\mathcal L.$$</p>
<p>Here we have clearly singled out time as the "worldline parameter" for calculating $S$, because we want to calcula... | g15380 | [
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<p>I am currently trying to determine the Schwarzchild radius of a star with solar mass 30. I am calculating it both with respect to solar mass, and w.r.t kilograms, however I am getting conflicting answers. (of a factor of 10)</p>
<p>$$
1 \text{ solar mass} \sim 1.9891 \cdot 10^{31}\,\text{kg}
$$
so I calulated </p>
... | g475 | [
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<p>Let there be a particle in a step potential: if its energy $E$ is higher than the step $V_0$, then it will have the momentum $\sqrt{2m(E-V_0)}$ and no more $\sqrt{2mE}$. (See <a href="http://en.wikipedia.org/wiki/Solution_of_Schr%C3%B6dinger_equation_for_a_step_potential" rel="nofollow">http://en.wikipedia.org/wiki/... | g15381 | [
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<p><img src="http://i.stack.imgur.com/t64Jh.jpg" alt="enter image description here"></p>
<p>I've no problems with the first part. However, I'm struggling with the last part of the question.</p>
<p>The first thing I did is to find the a new moment of inertia for the whole system including the mass attached at B which ... | g15382 | [
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<p>I am currently trying to determine the Schwarzchild radius of a star with solar mass 30.
I am calculating it both with respect to solar mass, and w.r.t kilograms, however I am getting conflicting answers.</p>
<p>If someone could work this out and help me clarify I would be very grateful!</p> | g475 | [
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<p>Hypothetically, suppose there is a situation where the Earth's moon gets neatly sliced into two equal hemispheres, and the force responsible for this slicing also creates a distance between the two halves of say, half the (average) distance from the Earth to the Moon, as it originally stood.</p>
<p>Do the two halve... | g15383 | [
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<p>I'm currently interested in this subject but all I can see is about neural networks and I'm more interested on the Theoretical point of view: "how can a system (Lagrangian/Hamiltonian) alter it's geometry by external perturbations?" (If I got that right... of course)</p>
<p>Some directions here?</p> | g15384 | [
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<p>I would like to clarify my question. I have numbered them to be independent questions</p>
<ol>
<li><p>For any conservative fields, $\vec{F} = -\nabla U$. Which means the restoring force is opposite to the increasing values of the potential energy. If it so happens that $F = \nabla U$, does that mean the restoring f... | g15385 | [
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<p>Apologies if this is stating the obvious, but I'm a non-physicist trying to understand Griffiths' discussion of the hydrogen atom in chapter 4 of Introduction to Quantum Mechanics. The wave equation for the ground state (I believe) is:$$\psi=\frac{1}{\sqrt{\pi a^{3}}}e^{-r/a}$$ </p>
<p>where $a$ is the Bohr radius ... | g15386 | [
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<p>I would like to express the wave functions for three identical particles, each with orbital angular momentum $L=1$ and spin angular momentum $S=1/2$, in terms of single-particle wave functions. In other words, I would like to obtain the Clebsch-Gordan coefficients for this problem.</p>
<p>The problem is discussed ... | g15387 | [
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<p>Imagine a sphere of uniform density with similar volume and average density of our Earth. There is a bore leading to the center of the sphere from the surface with a scale at regular intervals. At what part of your journey towards the center would the scale read your greatest weight?</p>
<p>There are some caveats t... | g15388 | [
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<p>Since I studied General Relativity I had this question running on my mind. As I see it (just taking lectures of Quantum Field Theory right now)</p>
<p>"Why you need a gauge boson for gravity when the higgs brings things mass?"</p>
<p>You know, mass is the cause for physicist to study differential geometry so why w... | g598 | [
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<p>Look at this: <a href="http://en.wikipedia.org/wiki/Gross-Neveu_model" rel="nofollow">http://en.wikipedia.org/wiki/Gross-Neveu_model</a></p>
<p>Wikipedia sais "When N=1 it reduces to the integrable Thirring model". but the aditional term in thirring model is $\frac{g}{2}\left(\overline{\psi}\gamma^\mu\psi\right) \l... | g15389 | [
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<p>It seems like it should due to bremsstrahlung, since we're talking about electrons with 5-7KeV of energy slamming into the walls of the device, but I've found no information about this online, so I'm assuming something else must be happening. CRT-style TVs and computer monitors both have this problem, so my guess is... | g15390 | [
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<p>Note $\hbar = 1$.
$$H = H_0 + \lambda V =\frac{p^2}{2m} + m\omega^2x^2 + \lambda m^2\omega^3 x^4$$
Supposedly the perturbation expansion diverges. We are supposed to estimate for what order we have a correction to the ground state energy which is comparable in magnitude to the unperturbed ground state energy itself.... | g15391 | [
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<p>My experience with solitons is restricted to the classical setting, namely solutions to the quartic interaction $\phi^4$, the Sine-Gordon equation, and Korteweg–de Vries equations. I was explicit to show the boundary on my solitonic knowledge so that I could ask for an interpretation of the recent paper <a href="htt... | g15392 | [
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<p>I am not a physics student. In one of my courses, some fundamental concepts of Quantum mechanics were needed, so I was going through them when I stumbled upon this.</p>
<p>It says</p>
<p>$$\text{probability} = \int_a^b\Psi^*\Psi\mathrm{d}x\quad\biggl(= \int_a^b\Psi^2\mathrm{d}x\text{ if }\Psi\text{ is a real funct... | g15393 | [
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<p>I am worried here about specific supersymmetric scenarios in which an energy scale above the TeV is introduces. An example would be the Seesaw extension of the Minimal Supersymmetric Standard Model. My questions is:</p>
<p>In such a scenario, and even though SUSY guarantees a cancellation of the quadratic divergenc... | g15394 | [
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<p>Always while studying I was told that if two identical spheres, one charged and the other uncharged, are brought together the charge in each one of them is halved.
However, why does it happen?</p>
<p>Is it because the electrons repel each other in the the charged sphere and shift to the other sphere, which is uncha... | g15395 | [
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<p>If you matched the yellow light of one prism to that of the green light of another prism, say through a thin glass pane, what would be the resulting color?</p> | g15396 | [
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<blockquote>
<p>This post generalizes the posts:<br>
- <a href="http://physics.stackexchange.com/questions/29537/proportion-of-dark-matter-energy-to-other-matters-energy-at-the-beginning-of-the">Proportion of dark matter/energy to other matters/energy at the beginning of the universe?</a><br>
- <a href="http://ph... | g15397 | [
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<p>I have a link hinged at one end and attached to a rectangular object via another hinge in the other end as shown. Now, I was wondering how would I maintain the orientation of the rectangular object regardless of the rotation of the link. </p>
<p>I know this sounds like a vague question but I am just out of ideas on... | g15398 | [
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<p>We were asked to try to make a theoretical description of the following phenomenon:</p>
<p><em>Imagine a 2D Bose Einstein condensate in equilibrium in an harmonical trap with frequency $\omega$. Suddenly the trap is shifted over a distance a along the x-axis. The condensate is no longer in the center of the trap an... | g15399 | [
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<p>Did I missed something in angular momentum definition?
Two identical bodies rotate around mass center.
Now I invented anti-gravity and turning gravitational switch off.
Those two bodies will move now in straight line with constant velocity and angular momentum conservation is compromised.
Turning the gravitation off... | g476 | [
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<p><a href="http://en.wikipedia.org/wiki/Electric_dipole_moment" rel="nofollow">Electric dipole moment</a> says $p = qd$. Which charge does the $q$ equal to?</p> | g15400 | [
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<p>I have been trying to find the correct method for determining the outflow force resulting from a certain amount of air being forced into a pipe of a certain dimension. Essentially i'm trying to determine muzzle velocity/force/pressure. I'm sure this is incredibly simple, but I have been looking around and cannot f... | g15401 | [
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<p>In october,1707 four British warships ran aground because of error in position,sparking the effort to produce a marine clock that would be accurate to locate a position with in 30 miles after sailing from England to the West Indies & back again (a)What daily accuracy for such a clock would be required? (b)What d... | g15402 | [
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<p>Ideally 2 objects of different mass and weight will hit the floor at same time because they face same gravitational pull and accelerate. Will the <a href="http://en.wikipedia.org/wiki/Terminal_velocity" rel="nofollow">terminal velocity</a> of both objects be same also? and with that theory does terminal velocity of ... | g15403 | [
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<p>This is a made-up example, just to understand a concept. If changing the probability values aids your explanation, that's fine by me.</p>
<p>Say you have a physical quantity $E$ that can take values 1, 2, 3 with probabilities 0.4, 0.25, 0.35 respectively (working in a quantum framework). You have a positive operato... | g15404 | [
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<p>So there's the classic example of the relativity of simultaneity involving two people on a train, with a light source exactly between them. Moments after the lights turn on, observers on the train will say the light struck the passengers simultaneously, while folks on the ground looking into the train will see the l... | g15405 | [
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<p>I was sent here from mathoverflow, hoping for a complete answer to this:</p>
<p>===</p>
<p>A friend of mine asked me what is the flux of the electric field (or any vector field like
$$
\vec r=(x,y,z)\mapsto \frac{\vec r}{|r|^3}
$$ where $|r|=(x^2+y^2+z^2)^{1/2}$) through a Mobius strip. It seems to me there are... | g15406 | [
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<blockquote>
<p>A horizontal force is used to pull a $5.0\text{ kg}$ cart at a constant speed of $5.0\text{ m/s}$ across the floor. The force of friction between the cart and the floor is $10\text{ N}$. </p>
<ol>
<li>What is the magnitude of the horizontal force along the handle of the cart? </li>
<li>Calc... | g15407 | [
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<p>Is there any reason to believe that any measure of loudness (e.g. sound pressure) might have an upper boundary, similar to upper limit (c) of the speed of mass?</p> | g15408 | [
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<p>From the one-band Hubbard model, $H=-t\sum\limits_{<ij>, \sigma}c_{i\sigma}^{\dagger}c_{j\sigma}+U\sum\limits_{i}n_{i\uparrow}n_{i\downarrow}$, we know if $U\gg t$, the energy cost of two electrons staying on the same site is too high, so there the band will be split into two bands with gap U. How to prove thi... | g15409 | [
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<p>What is the maximum time for an HF radio wave to reach its destination regardless of propagation mode? Since electromagnetic waves' speed is close to the light speed in the air, can we say it is always lower than e.g. 1 second? Or, atmospheric conditions, reflection etc. may cause it to be as long as 10 seconds or m... | g15410 | [
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<p>The answer to <a href="http://physics.stackexchange.com/questions/104513/derivation-of-eulers-equations-for-rigid-body-rotation">physics.stackexchange.com/questions/104513</a> gives the following derivation of tensor $I$:</p>
<p>$\begin{align}
\frac{\text{d}}{\text{d}t} I &= \frac{\text{d}}{\text{d}t} (E\,I_{\t... | g15411 | [
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<p>The problem I have today is to determine the differential equation for a square fin protruding from a wall that experiences surface to ambient radiation and has an internal heat generation of $\dot q$ per length. The fin does not experience convection. I performed an energy balance on a differential element of the f... | g15412 | [
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<p>I read a statement in Becker and Becker's <em>String Theory and M-Theory</em> page 2. After pointing out the non-renormalizablity of GR by the dimension of gravitational constant, it is said:</p>
<blockquote>
<p>Some physicists believe that perturbative renormalizability is not a fundamental requirement and try t... | g15413 | [
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<p>In calculating the total-momentum operator of the real Klein-Gordon field, I end up with an equation like
$$ \vec P = \frac{1}{(2\pi)^3}\int d^3p \mspace{9mu} \vec p\Big(a_pa_{-p} + a_pa^\dagger_{p}-a_{-p}^\dagger a_{-p} - a_{-p}^\dagger a_p^\dagger\Big) $$</p>
<p>and it seems the first and the last integrals van... | g15414 | [
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<p>Could you please recommend any good texts on algebraic geometry (just over the complex numbers rather than arbitrary fields) and on complex geometry including Kahler manifolds that could serve as an informal introduction to the subject for a theoretical physicist (having in mind the applications in physics, e.g. in ... | g15415 | [
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<p>In the turbulent transport of a scalar field, $\Phi$, decomposed into mean and fluctuating components, $\Phi=\left<\Phi\right>+\phi^\prime$, the scalar variance is defined as $\left<{\phi^\prime}^2\right>$.</p>
<p>Today I got a bit reamed out in an academic meeting for using the variance to synonymously... | g15416 | [
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<p>I have a doubt regarding this problem:</p>
<blockquote>
<p><em>Two large identical flat metal plates are placed parallel to one another, seperated by a small distance compared to their linear size. One plate is given a charge per unit area $-5.50 \times 10^{-5} Cm^{-2}$ and the other a charge per unit area $+5.50... | g15417 | [
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<p>I would like a suggestion on a price-efficient way of experimenting with spontaneous down-conversion and single-photon counting. The simple dual-slit experiment could be one part of an application although there are many, but I'm mainly asking about the key components which are similar - the laser that pumps a SPDC-... | g15418 | [
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<p>I studied that electronics is the branch of physics which deals with the practical applications of moving electrons through vacuum, semi-conductors and gasses. Can electrons move through vacuum? </p> | g15419 | [
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<p>if an atom in its ground state is coupled to an electromagnetic field it can absorb a photon if the EM field contains one with the right frequency. These transitions depends on $⟨f|H_i|i⟩$ (from <a href="http://en.wikipedia.org/wiki/Fermi%27s_golden_rule" rel="nofollow">Fermi's golden rule</a>) with $|i⟩$ the initia... | g15420 | [
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<p>As a reference, see this question: <a href="http://physics.stackexchange.com/questions/22876/does-a-photon-exert-a-gravitational-pull">Does a photon exert a gravitational pull?</a></p>
<p>It turns out the answer is "Yes" -- but this does not seem consistent with light being wave-like.</p>
<p>I am imagining a extr... | g15421 | [
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<p>I am familiar with the way we derive the form of the FRW metric by just using the fact that we have a maximally symmetric space i.e the universe is homogeneous and isotropic in spatial coordinates. Similarly, how do I get the Poincare patch of $AdS_{p+2}$ i.e
\begin{equation}
ds^2 = R^{2}\left(\frac{du^2}{u^2}+u^2(-... | g15422 | [
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<p>On which factor does the electrical conductivity of an intrinsic semiconductor depend? It doesn't have an excess of charge carriers in fact, does it? </p> | g15423 | [
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<p>My knowledge on this particular field of physics is very sketchy, but I frequently hear of a theoretical "graviton", the quantum of the gravitational field. So I guess most physicists' assumption is that gravity can be described by a QFT?</p>
<p>But I find this weird, because gravity seems so incredibly different ... | g15424 | [
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<p>There are many different detectors for different radiation,such as NaI,HpGe,CsI for $\gamma$ detection,and ionization chamber,proportional counter,Geiger counter for $\alpha$, $\beta$ detection,but how to select a suitable detector for different radiation?I mean compare between them,what is the advantages and defect... | g15425 | [
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<p>$\beta$ in statistical mechanics is equal to $\frac{1}{k_BT}$ in in thermodynamics, but I do not understand why $\beta\propto T^{-1}$ instead of, say, $\beta\propto T$?</p> | g15426 | [
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0.02668924815952778,
0.011318805627524853,
0.00... |
<p>As the Lagrangian in classical mechanics corresponds to energy, it must be real. But is that the case in quantum field theory? I mean, it should still correspond to some sort of energy, but what about all the "$i$"s here and there, such as in the Dirac Lagrangian $i\bar{\psi}\gamma^\mu\partial_\mu \psi$ and the curr... | g15427 | [
0.07310037314891815,
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0.014594988897442818,
0.01606498286128044,
-0... |
<p>Assume I have a solid grasp of undergraduate physics. From what I've read the warp field interferometer is supposed to be a sort of Michelson interferometer, except instead of adjusting the displacement of one mirror, you have a toroidal capacitor that... somehow expands space? </p>
<p>Edit: I am talking about the ... | g15428 | [
0.013203568756580353,
0.08885318785905838,
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-0.05272563546895981,
0.0497206449508667,
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0.049137432128190994,
-0... |
<p>I need help to solve this problem related with the N-Body problem, i dont understand quite well what I need to define or to express in order to solve it.</p>
<p><em>We assume a particular solution to the N-Body Problem, for all $t>0$, and $h>0$, where $h$ is the total energy of the N-Bodies, show that $U\righ... | g15429 | [
0.027485700324177742,
0.05699021741747856,
0.0035536244977265596,
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0.056388504803180695,
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-0.04140550270676613,
... |
<p>This may be a naive question, but after the Fukushima Daiichi partial meltdown and studying the aftermath of Chernobyl it seems they could be helped by this idea.</p>
<p>In Chernobyl, the liquidators that cleaned up the disaster tunneled concrete under the reactor core and covered the whole complex in a big contain... | g15430 | [
0.031460605561733246,
0.01031927764415741,
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-0.0... |
<p>I am having trouble understanding the reasoning behind the solution in this Irodov General Physics problem. The problem is 1.6:</p>
<blockquote>
<p>1.6. A ship moves along the equator to the east with velocity
vo = 30 km/hour. The southeastern wind blows at an angle Θ = 60°
to the equator with velocity v = 15... | g15431 | [
0.0479385182261467,
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<p>Is there an pptimal temperature for the <a href="http://en.wikipedia.org/wiki/Mpemba_effect" rel="nofollow">Mpemba Effect</a>? Is there an optimal initial water temperature for speedy freezing? If so, what is it?</p>
<p>If a specific example is needed: There is a 100 milliliter sphere of water floating in air at -1... | g15432 | [
0.03060918301343918,
0.030082765966653824,
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0.03426405414938927,
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0.005558902397751808,
0.031055... |
<p>How do small perturbations around the compact dimension affect T duality. What happens if I chose a compactification of the nature $r+\delta r$. And what keeps the compact dimension stable, i.e from expanding into a large dimension or imploding into itself. </p> | g15433 | [
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<p>I understand the meaning of pressure on a surface to be force acting per unit area.</p>
<p>But when it comes to understanding pressure in the context of fluids in motion or at rest I think I am having some trouble grasping the concept.</p>
<p>When we say the pressure of a gas in a container (which may be of any ar... | g15434 | [
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<p>Suppose that we have 2 objects next to each other.The object at the left is A and the object at right is B.now we have these situations:
1) we push B to the left.
2) we pull A to the left.(in this case A and B are stuck to each other.)
Do the forces A exert on B have the same magnitude and direction in both situatio... | g15435 | [
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<p>Suppose I have a function of time $t$ and position $(x,y)$ such that
\begin{equation} p_t \,dt = p \,dy - p_x (1-x) \,dx + p_y \,dy\end{equation}
where the subscript denotes a differentiation. In this case, I am able to derive a (partial) differential equation from this form.</p>
<p>I'd love to have your help to ... | g15436 | [
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... |
<p>If the theory of everything indicates a singularity-free and finite universe, will <a href="http://en.wikipedia.org/wiki/Poincar%C3%A9_recurrence_theorem">Poincare recurrence</a> be relevant to the universe? If so, is there any interesting physical consequence, e.g. in superstring or quantum gravity?</p> | g15437 | [
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0... |
<p>I want to understand the efficiencies of separating mixed gases, and for that I want to understand the thermodynamic limit case. Looking at the <a href="http://en.wikipedia.org/wiki/Entropy_of_mixing#Gibbs_free_energy_of_mixing" rel="nofollow">wikipedia page for entropy of mixing</a>, I find the following formula:
$... | g15438 | [
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-... |
<p>Given a needle of mass $m$ modeled by a cylinder of length $l$ and radius $r$ placed on an infinitely large water surface, what is </p>
<ol>
<li>The maximum depression in the water surface; and</li>
<li>The equation of the shape of the water surface when depressed?</li>
</ol>
<p>I'm quite sure this is a simple que... | g15439 | [
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-... |
<p>How is the sun's equatorial circumference measured by scientists? </p> | g15440 | [
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0... |
<p>Is work on solitons in QFT's focused on finding solutions that could represent the fundamental particles of the Standard Model, or is the work focused on finding particles Beyond The Standard Model? If the work is primarily BTSM, is it still possible that solitons represent the SM particles?</p>
<p>My related quest... | g15441 | [
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-0.0... |
<p>Wikipedia <a href="https://en.wikipedia.org/wiki/Specific_impulse#Specific_impulse_in_seconds" rel="nofollow">defines</a> specific impulse as:
$$
I_\mathrm{sp} = \frac{F_\mathrm{thrust}}{\dot{m} \cdot g_0}
$$
The $g_0$ is said to be <em>the acceleration at the Earth's surface</em>.</p>
<p>So is it actually the acce... | g15442 | [
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0.004008... |
<p>apart of the 't Hooft diagrams that you all love (and find all sort of dualities starting with them) one of the venues 't Hooft works nowadays is apparently some sort of "deterministic representation of quantum mechanics". I avoid saying "the world is classical" in a broad sense because it is my feeling that this is... | g15443 | [
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-0.... |
<p>I am looking for any available measured solar-cell datasets (Voltage/Current) especially for organic photovoltaic cells for the testing of a software unfortunately I am unable to get the measured values. Please mention if anyone knows about any on-line available data set ?</p> | g15444 | [
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0.012780552729964256,
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0.0033503284212201834,
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<p>We know that density of ice reduces by about 8% during freezing, this means it expands to have little higher volume. But if I fill water in a container (entire volume) which has very low coefficient of thermal expansion at 0 $^\circ$C, will the space constraints stop water from freezing?</p> | g477 | [
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0.013627642765641212,
0.024055879563093185,
0.025209899991750717,
0.00805194... |
<p>I don't have much of an idea of how to draw causal sketches. I know that you need to work out the gradient of the light cones, which can be done using a given metric and using null vectors. But how do you use null vectors to work out the gradient of metric? </p>
<p>I've got a metric of $ds^2=-dt^2+(e^t)(dx^2)$ that... | g15445 | [
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0.006057844962924719,
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0.11162276566028595,
0.0084... |
<p>I recently visited my child's elementary school to speak to a science classroom about rocks and minerals. While trying to explain what a crystal is, I got sloppy and mis-spoke that an atom was the smallest possible piece of matter (rather than an element!) I was quickly stopped and corrected by a 9-year-old that tol... | g15446 | [
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0.018949560821056366,
0.005497014615684748,
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-0.00... |
<p>A homework question that I don't conceptually understand:</p>
<p>A quantum particle of mass M is trapped inside an infinite, one-dimensional square well of width $L$. If we were to solve Schrodinger's wave equation for such a particle, we could show that the minimum energy such a particle can have is </p>
<p>$$E_... | g15447 | [
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... |
<p>Peskin in his QFT page 334 argued that $Z_1=Z_2$ to all orders in QED perturbation theory, but I couldn't understand his argument:</p>
<blockquote>
<p>... With a generalization of the argument given there (section 7.4 for Ward identity), on can show that the diagrammatic identity (7.68) holds for digrams that inc... | g15448 | [
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0.005311568733304739,
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0.034872666001319885,
0... |
<p>I understand why the pressure is reduced above the wings of aircraft, but when I read books and look for information, it says that the air is compressed below the wings, I do not understand why it is? Could you tell me what makes the air compressed below the wing, and how is it compressed?</p> | g15449 | [
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0.... |
<p>The KLT relations (Kawai, Lewellen, Tye) relate a closed string amplitude to a product of open ones. While I get the physics behind this I don't really understand the derivation in the original paper (see <a href="http://www.sciencedirect.com/science/article/pii/0550321386903627">http://www.sciencedirect.com/science... | g15450 | [
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0.0... |
<p>From the Wikipedia entry on Electrochemical cell (<a href="http://en.wikipedia.org/wiki/Electrochemical_cell" rel="nofollow">http://en.wikipedia.org/wiki/Electrochemical_cell</a>):</p>
<blockquote>
<p><em>An electrochemical cell consists of two half-cells. Each half-cell
consists of an electrode, and an electro... | g15451 | [
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0.03084808960556984,
0.030330374836921692,
0.0098... |
<p>Any opinions if the equation 13.115 of Peskin and Schroeder is true on arbitrary manifolds in arbitrary dimensions for the same Lagrangian? I a priori see no problem.</p>
<p>The point I also want to ask is - if one evaluates that equation for spacetime >2 then one will miss the symmetry broken phase of the theory -... | g15452 | [
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<p>Suppose that the physical system is in generic state $|\psi\rangle$. Show that $\sum_{\lambda}p^2_{\lambda} = 1$ to an observable $O$, if and only if $\Delta O = 0$. ($\Delta O$ is a standard deviation).</p>
<p>Using the probability measure definition $p_{\lambda} = \langle\psi|P_{\lambda}|\psi\rangle$. Using hypot... | g15453 | [
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0.022418301552534103,
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... |
<p>I am trying to calculate the "relative linear velocity" of a particle moving over a rotating object.</p>
<p>According to <a href="http://www.sciencedirect.com/science/article/pii/S0304389411006637" rel="nofollow">this paper</a> (section 2.2) I am reading the relative linear velocity is calculated by:</p>
<p>$$
v'=... | g15454 | [
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-0... |
<p>One of my more recent hobbies is making "swords" out of PVC conduit, foam, and duct tape. As all the weight is forward of the cross guards, I needed to put some amount of some substance inside the hilt to counter-balance it. Curious as to how much counter-weight I needed, I decided to see if I could develop a contin... | g15455 | [
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... |
<p>Does anyone know how the Breit-Rabi formula (energy dependence of the hyper-fine splitting in presence of any external magnetic field for alkali atoms when $F=I \pm 1/2$) is derived, or where to find a reference for it? It doesn't seem to be in the original paper from 1931, or in the textbooks I've looked at.</p>
<... | g15456 | [
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<p>Maxwell's equations are nearly symmetric between $E$ and $B$. If we add magnetic monopoles, or of course if we restrict ourselves to the sourceless case, then this symmetry is exact. This is not just a discrete symmetry of exchange. A "duality rotation" of $(E, B) \rightarrow (E \cos \theta - B \sin \theta, B \co... | g15457 | [
0.05930250883102417,
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0.044601161032915115,
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0.006656101439148188,
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<p>I have a quick question that just came up in my research and I could not find an answer anywhere so I thought I'd try here.</p>
<p>So one of the definitions of the Dirac Delta is the limit of the <a href="http://mathworld.wolfram.com/LorentzianFunction.html" rel="nofollow">Lorentzian function</a> with $\epsilon$ go... | g15458 | [
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0.025049174204468727,
0.024... |
<blockquote>
<p>The diameter of a cylinder is measured using a Vernier Callipers with no zero error. It is found that the zero of the Vernier scale lies between 5.10 cm and 5.15 cm of the main scale. The Vernier scale has 50 divisions equivalent to 2.45 cm. The 24th division of the Vernier scale exactly coincides wit... | g15459 | [
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0.0037321322597563267,
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0.014125287532806396,
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0.019639993086457253,
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0... |
<p>Years ago there was some hype around <a href="http://en.wikipedia.org/wiki/Heim_theory" rel="nofollow">a theory that would supposedly allow for FTL</a>. But I have since heard nothing of this. </p>
<p>Is anything happening with the theory? How would a magnetic field allow us alter spacial dimensions?</p> | g15460 | [
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<p>An alkali atom has a single outer electron that interacts with incoming photons of the right wavelength (for alkalies it's in the visible & IR range). If there is an external magnetic field, the electron has a well defined quantization axis and the the incoming light can be separated into three components: linea... | g15461 | [
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<p>I'm not sure whether I'm asking the right question here. I am simply a physics admirer!</p>
<p>Alright. So my question is, is it possible to create nothing?</p>
<p>Lets say you take a cube serving only as a a shell. Then expanded the cube.</p>
<p>Or a balloon, the size of really really small. Then expanded the ba... | g15462 | [
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<p>In the semi-classical treatment of the ideal gas, we write the partition function for the system as $$Z = \frac{Z(1)^N}{N!}$$ where $Z(1)$ is the single particle partition function and $N$ is the number of particles. It is semi-classical in the sense that we consider the indistinguishability of the particles, so we... | g15463 | [
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0.... |
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