dialog listlengths 4 30 | title stringlengths 15 150 | category stringclasses 14 values | dialog_time stringdate 2016-01-21 01:59:30 2018-07-01 01:34:46 |
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[
{
"message": "The <a href=\"https://en.m.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment\" rel=\"nofollow noreferrer\">Stern-Gerlach experiment is a monumental experiment in quantum physics. It breaks the classical idea of spin and gives validity to the quantum nature of spin.But, if the spin of an electron... | Why aren't there two discrete infinitely narrow peaks in the Stern-Gerlach experiment? | physics | 2017-10-21T23:50:00.740 |
[
{
"message": "From a text of Richard Feynman:<blockquote> You know, of course, that atoms are made with positive protons in the nucleus and with electrons outside. You may ask: “If this electrical force is so terrific, why don’t the protons and electrons just get on top of each other? If they want to be in ... | Quantum effects limiting electrical attraction in an atom | physics | 2017-10-22T15:08:06.393 |
[
{
"message": "I'm looking for correlation function (i.e. $\\langle g \\rvert \\hat{S}_i^z \\hat{S}_{i+n}^z\\lvert g \\rangle$, where $g$ stands for ground state) for given Hamiltonian($\\hat{S}^z_i = \\hat{c}^+_{j} \\hat{c}^-_{j} - \\frac{1}{2}$):$$\\hat{H} = \\frac{-J}{2} \\sum_{j} \\left(\\hat{c}^+_{j+1} \\... | XXh model for $1/2$-spin chain | physics | 2017-10-22T15:19:58.540 |
[
{
"message": "If I understand correctly, graphite is made of sheets of carbon. <a href=\"https://i.stack.imgur.com/r3Oye.png\" rel=\"noreferrer\"> (from <a href=\"https://en.wikipedia.org/wiki/Graphite#/media/File:Graphite-layers-side-3D-balls.png\" rel=\"noreferrer\">Wikipedia)And when I write with a pencil, s... | Does pencil lead have a direction? | physics | 2017-10-22T23:55:33.067 |
[
{
"message": "How does the mass hanging down on the bottom (Assuming frictionless environment) apply a pull force to the car? How does the weight of the object transfer to the string (tension force and maybe the pulley does something?) which pulls the car?<a href=\"https://i.stack.imgur.com/ZESz4.png\" rel=\"no... | How does a weight connected to a string over a pulley pulling a cart apply force onto the cart? | physics | 2017-10-23T10:51:40.047 |
[
{
"message": "In the literature of field theories in flat spacetime, both forms of Euler Lagrange equation are used. e.g Consider a real scalar field $\\phi$ $$\\partial_\\mu\\frac{\\partial L}{\\partial \\phi,_\\mu}=\\frac{\\partial L}{\\partial \\phi}\\qquad\\text{where}\\qquad\\phi,_\\mu = \\frac{\\partial \... | Superscript vs. subscript indices in Euler-Lagrange equation in relativistic field theories | physics | 2017-10-23T17:49:13.860 |
[
{
"message": "In the Book \"Quantum Field Theory I\" by Manoukian, in section 4.3, from what I understood, he derived the quantum-action-principle of Schwinger only by using unitary time-evolution of the field Operators. At least I assume it to be like this, because for the proof he looked at the fields operato... | Derivation of Schwingers action principle from Heisenberg Equation and CCR - Why does it work with Anticommuting variations? | physics | 2017-10-24T00:19:28.877 |
[
{
"message": "It seems obvious that when a beam deforms under a point load, it deforms into a U-shape and when a cable deforms, it deforms into a V-shape.Is there any graphical method of understanding this beyond common sense?",
"role": "user"
},
{
"message": "When you say \"$\\mathsf U$-shape,\" yo... | Beams versus Cables | physics | 2017-10-24T10:44:23.327 |
[
{
"message": "After solving the eigenvalue equation for the momentum operator, I get $u(x)=Ce^{ipx/\\hbar}$, just like in Gasiorowicz's chapter 3. And then it says there: <blockquote> \"...and the eigenvalue $p$ real, so that the eigenfunction does not blow up at either $+\\infty$ or $-\\infty$....\". </blockq... | Momentum eigenfunction | physics | 2017-10-24T12:07:40.157 |
[
{
"message": "Is there quantitive data or equations matching the experimental data that can logically support Rutherfords model that there is a high mass dense nucleus? The only data i heard of was that one in 20000 alpha particles rebounded, but this is not published and their doesnt seem to be other results. ... | Where is the experimental data of Rutherford Gold Foil Experiments? | physics | 2017-10-25T05:50:16.220 |
[
{
"message": "I'm watching a video about string theory, in which the fact that gravity is weaker than the other forces is explained in that gravitons aren't bound to our universe directly, and can flow across various branes. If this is the case, would that not mean that singularities would be like fixed points ... | Would black holes be present in all dimensions? | physics | 2017-10-25T15:42:39.867 |
[
{
"message": "Sorry about this question, but due to my limited background in quantum physics I wasn't able to figure out why in ALL the refs I have searched they state it as iffor sure:Why is the square of a creation/annihilation operator zero?Given that this is for a Fock space system.$$\\hat{a}^\\dagger~\\pro... | Square of annihilation operator | physics | 2017-10-25T17:47:58.247 |
[
{
"message": "I know that Stoke's flow (creeping flow) applies in the presence of low Reynold's number situations, i.e. $Re<<1$, which results in the following formula for the drag coefficient of a spherical object placed in the flow:$$C_d = 6\\pi\\eta a$$where $\\eta$ is the viscosity of the fluid and $a... | Does Stoke's drag formula apply even in the absence of flow? | physics | 2017-10-26T07:53:36.330 |
[
{
"message": "When looking at the Isospin representation of a proton-neutron system (with the notation $|I,I_3\\rangle$), you can go from an uncoupled to a coupled representation like this:$$\\textstyle|\\frac{1}{2},+\\frac{1}{2}\\rangle|\\frac{1}{2},-\\frac{1}{2}\\rangle=\\sqrt{\\frac{1}{2}}(|1,0\\rangle+|0,0\... | Why can a coupled wavefunction of 2 nucleons seemingly arbitrarily give two different expressions? | physics | 2017-10-26T12:40:38.963 |
[
{
"message": "I am trying to verify the computation of the commutator of the ladder operator for Klein-Gordon solutions, but it seems like I am unable to do it properly. Here is what I do:For,$$\\varphi(x^\\mu)=\\int\\frac{\\mathrm{d}^3p}{(2\\pi)^{3/2}\\sqrt{2p_0}}\\left(a(\\vec p)e^{-ip_\\mu x^\\mu}+a^\\dagger... | Regarding the commutator of ladder operator in QFT | physics | 2017-10-26T15:48:48.720 |
[
{
"message": "Suppose I have a setup where there are 2 mirrors parallel to each other and I let in a laser beam of a single wavelength of red color through a tiny little hole in one of the mirror so that the beam would strike the other mirror at right angle. Suppose the laser bounces back and forth and the mirr... | If monochrome laser strikes a mirror perpendicularly, how would I know whether there is destructive interference? | physics | 2017-10-27T01:45:18.250 |
[
{
"message": "I'm suddenly getting very confused about a basic question. Suppose somebody tells you that the action is invariant under the transformation $$x \\to x', \\quad \\phi(x) \\to \\phi'(x').$$I realize this notation is ambiguous, but it seems to be common. For example, one might define a Lorentz transf... | What does it mean for an action to be invariant under $x \to x'$, $\phi \to \phi'$? | physics | 2017-10-27T16:24:41.657 |
[
{
"message": "In <a href=\"https://arxiv.org/abs/1606.02946\" rel=\"nofollow noreferrer\">these notes on page 4 the author says that if a $2d$-dimensional phase space has $d$ conserved quantities $F_{\\mu}$ that Poisson commute, then $H$ can be written as a function of the $F_{\\mu}$. Why should this be the cas... | Maximal number of conserved quantities (classical integrability) | physics | 2017-10-27T17:11:56.500 |
[
{
"message": "<a href=\"https://en.wikipedia.org/wiki/Halo_nucleus\" rel=\"nofollow noreferrer\">Halo nuclei are generally very light nuclei with a significant neutron excess. These isotopes usually decay in seconds down to milliseconds, and so are often observed as individual ions in motion. Most of the data a... | Has a nuclear "neutron halo" been measured directly? Anything other than "breaks easily"? | physics | 2017-10-27T17:17:23.670 |
[
{
"message": "The article I’m talking about: <a href=\"https://www-ee.stanford.edu/~dabm/146.pdf\" rel=\"nofollow noreferrer\">https://www-ee.stanford.edu/~dabm/146.pdfIn this article, the author solves the main problem with Huygens Principle, which is that you have to ignore the backward wavelets, despite the ... | Isn’t this correction to Huygens Principle a little arbitrary? | physics | 2017-10-27T19:21:56.247 |
[
{
"message": "When dealing with the problem that femtosecond laser pulses interact with atoms, the semi-classical method is usually used: we describe the atom as quantized and describe the pulse classically.I find myself cannot classically describe the formation of absorption spectra! I'm reading <a href=\"http... | How can we classically describe the formation of absorption spectra? | physics | 2017-10-28T06:25:59.353 |
[
{
"message": "I am wondering about this. I have often encountered a claim that the electrons in an atom have an \"orbital speed\", and in some cases that even so much as a number is assigned to this supposed \"speed\", like that the electron in hydrogen at the 1s ground state \"orbits\" at a very specific numbe... | What does it mean to talk about electron's "orbital speed", quantum mechanically? | physics | 2017-10-28T06:27:46.783 |
[
{
"message": "I've seen angular momentum defined as: $$\\ L=I \\omega\\ $$In dynamics, the notation is different and states: $$\\ L_o = r × (mv) \\ $$How are these definitions related, if they are describing the same thing?",
"role": "user"
},
{
"message": "<a href=\"https://i.stack.imgur.com/2curx... | How are these two definitions of angular momentum related? | physics | 2017-10-28T18:05:12.767 |
[
{
"message": "Is it possible for a place to exist with zero Higgs field, by kind of shielding it or something(theoretically)?",
"role": "user"
},
{
"message": "The simple answer is no, though as always the answer is more involved than this.I would guess you are thinking of the way that a <a href=\"h... | Higgs field shielding possibility | physics | 2017-10-28T18:15:22.213 |
[
{
"message": "I have 2 questions i would really like to find an answer to:if we have a quantum pair, we can determine whether 2 quanta are entangled or not assuming that we have access to the information of both of them. so if we have a quantum \"trio\" instead of a quantum pair, does the information about 2 ou... | quantum entanglement of 3 or more quanta | physics | 2017-10-29T08:16:27.753 |
[
{
"message": "If a small creature moves in a vertical circle, will its shadow formed on a horizontal plane, because of the sun, move in a simple harmonic motion?I'm considering it to be a small circle so that the altitude of the sun doesn't have any role in this. What I had in mind was that the shadow would be ... | Would this be considered simple harmonic motion? | physics | 2017-10-29T11:55:34.230 |
[
{
"message": "I am working on a physics simulator of rigid bodies. I am currently struggling with calculating friction of a rigid body with multiple friction points. The simulator is 2 dimensional and from top down view.The things that I know:Current speedForce applied to the center of massCurrent rotational sp... | Calculating friction on a rigid body with multiple friction points | physics | 2017-10-29T14:54:37.587 |
[
{
"message": "During the process of a pendulum swinging it is performing work done in between potential and kinetic energy on a continuous basis as long as a small force, small amount of work, is continuously supplied to it.For instance let's say that there is an initial amount of energy used in lifting the 10 ... | Does a Pendulum do more work than what's going into it? | physics | 2017-10-29T15:50:56.837 |
[
{
"message": "The normal mode of spin for an electron is spin down:<a href=\"https://i.stack.imgur.com/5isZj.png\" rel=\"nofollow noreferrer\">with angular momentum L pointing in the opposite direction of motion V (right)but, when a free electron approaches , say, a Helium ion it must , according to Pauli's, fl... | What makes an electron flip to spin-up? | physics | 2017-10-30T06:32:38.703 |
[
{
"message": "Atoms as we know are the structural unit of everything. As i know that atoms are 3D objects, they have length breath and height (they have thickness).Everything is made up of atoms means everything is 3D. So why do we say that any triange ABC drawn on a piece of paper is a 2D figure?",
"role":... | Does second dimension exist? or any other dimension? | physics | 2017-10-30T14:58:32.337 |
[
{
"message": "While learning General Relativity, we always use the Levi-Civita connection, which has the special property of being torsion-less.<br>My question is: Do we need to use a torsion-less connection to study General Relativity? If so, why is it essential? What does a torsion-full connection change phys... | Do we $\textit{need}$ to use a torsion-less connection(Riemann-Levi Civita) in General Relativity? | physics | 2017-10-30T15:22:33.510 |
[
{
"message": "How do I calculate the gravitational potential energy between two objects that are separated by near to infinite distance? I would like to know if the two objects are kept at near infinite distance, then at what kinetic energies would they come and collide into each other. The way to calculate gra... | How do I calculate the actual gravitational potential energy between two objects $m_1$ $m_2$ that are at zero distance? | physics | 2017-10-30T15:49:38.197 |
[
{
"message": "I have read and heard numerous times that a vector field in nonabelian gauge theory which has gained mass through the Higgs mechanism decreases in strength exponentially with distance as it propagates. I would be thankful for a brief explanation of the approach and result and, if possible, a refer... | How to understand why massive fields decay exponentially with distance? | physics | 2017-10-31T01:43:08.927 |
[
{
"message": "I'm a student studying on engineering (typically chemical), I came across this question which I do not understand - Suppose the pressure at a point within a column of mercury in a tube is $74$ mm Hg . What is the pressure $5$ mm Hg below this point . This is talking about pressure as the head of f... | Pressure in a tube - principles of engineering | physics | 2017-10-31T13:58:26.777 |
[
{
"message": "In gauge theory, physical states are often said to be characterized by equivalence classes of gauge field configurations that differ by gauge transformations. But according to <a href=\"https://physics.stackexchange.com/questions/72815/large-and-small-gauge-transformations\">Large and small gauge ... | Experimentally distinguishing between topologically inequivalent physical states in gauge theory | physics | 2017-11-01T05:45:18.140 |
[
{
"message": "If my frame is moving with uniform acceleration and so is another frame, then for me that frame should be stationary,i.e acceleration should be zero.Then why is acceleration considered a relative quantity?",
"role": "user"
},
{
"message": "No, acceleration is not relative in classical ... | Is acceleration relative in classical physics? | physics | 2017-11-01T06:38:31.487 |
[
{
"message": "I was doing Kepler's first law (basically that is the only law in which I have a problem) other two laws are easy to understand). During the explanation of the first law my instructor said that we need to establish the fact that angular momentum does not change per unit time i.e. stays constant.Pr... | Kepler's law and my problem | physics | 2017-11-01T06:53:31.297 |
[
{
"message": "I am a bit confused by how Peskin & Schroeder describe the corrections to the two point function of the linear sigma model from the second functional derivative of the effective action. Without going into too much details on p386 (Eq. 11.103) they derive the second functional derivative of the... | Peskin and Schroeder Eq. 11.103: how does it relate to one-loop diagrams? | physics | 2017-11-01T10:39:25.407 |
[
{
"message": "(once again this question is not a duplicate of any other question to my knowledge, and this should actually help alot of people trying to ionize air)<br>for one you can easily figure out that nitrogen is 15.58eV and oxygen is 13.6eV, but the problem is in the air nitrogen bonds with another nitro... | Electron Volts in Covalent Bonds of Nitrogen | physics | 2017-11-01T13:16:53.237 |
[
{
"message": "How do these both detectors separate from each other? Of course I can derive the terms and this is, more or less, all I can look up: In an electromagnetic calorimeter the particles interact mostly electromagnetically and in a hadronic calorimeter they will do it via the strong force.This rises the... | Difference between hadronic and electromagnetic calorimeter | physics | 2017-11-02T14:53:37.047 |
[
{
"message": "The standard heuristic argument for why quantum effects of gravity become important at the Planck scale is to consider the length scales at which both quantum field theory (QFT) and general relativity (GR) become crucial in order to explain physical phenomena. For QFT this is when the length scale... | Why do quantum effects of gravity become important at the Planck scale? | physics | 2017-11-02T16:02:24.013 |
[
{
"message": "I have recently started studying particle physics, and I was surprised by the description of hadrons. At first I was told that the $\\Delta^0$ baryon was composed by one up and two down quarks, and that was fine. But then I saw this description:$\\Delta^0 = \\frac{1}{\\sqrt{3}} \\big( udd + dud + ... | Difference between particle and state | physics | 2017-11-02T19:16:42.027 |
[
{
"message": "Thrust reversers are commonly used on aeroplane jet engines, to generate backwards thrust. They work by directing the hot, high speed exhaust forwards instead of backwards. At a basic level, the air has a net momentum gain forwards because the incoming air is slow (and dense), but the outgoing air... | How do boat thrust reversers work? | physics | 2017-11-03T06:01:11.200 |
[
{
"message": "i want to plot the precession of mercury's perihelion in MatLaB .(like the image below).Help me out here ,guys. <a href=\"https://en.wikipedia.org/wiki/Apsidal_precession#/media/File:Perihelion_precession.svg\" rel=\"nofollow noreferrer\">https://en.wikipedia.org/wiki/Apsidal_precession#/media/Fi... | Mercury's perihelion precession | physics | 2017-11-03T20:32:11.093 |
[
{
"message": "Earlier questions (e.g. <a href=\"https://physics.stackexchange.com/questions/298814/how-does-dark-matter-form-a-halo\">How does Dark Matter form a halo?) referred to the distribution of dark matter in the galaxy. My question is different (not a duplicate). I wonder why dark matter would form a ha... | Why does dark matter form halos? | physics | 2017-11-04T05:40:05.290 |
[
{
"message": "I'm only beginning to learn the Lagrangian and Hamiltonian formulations (currently in chapter 9 of Goldstein), so please bear with me if my problem is too elementary.I can see the point of going from $n$ generalized coordinates $q_i$ and their velocities $\\dot q_i$ in the Lagrangian formulation t... | What is my state in the context of Hamiltonian mechanics? | physics | 2017-11-04T11:45:10.867 |
[
{
"message": "I have following queries regarding the decay width of Z boson.In this<a href=\"http://www.hep.phy.cam.ac.uk/~thomson/partIIIparticles/handouts/Handout_13_2011.pdf\" rel=\"nofollow noreferrer\">Thomson's lectures, page 479, it says that decay of Z to hadrons have a large cross section because of fa... | Decay of Z boson | physics | 2017-11-04T13:09:12.577 |
[
{
"message": "A ferromagnetic material can enhance the magnetic field passing through it manifold. But why don't they do the same with an electric field? Are there any materials which do so?",
"role": "user"
},
{
"message": "Ferroelectrics can enhance electric field.",
"role": "assistant"
},
... | Why not ferromagnetic cores enhance electric field? | physics | 2017-11-04T18:04:11.813 |
[
{
"message": "I want to hold a small number of free electrons in a container indefinitely. I read about electron \"bottles\" and I am curious how I could replicate this. How low of a vacuum would I need to prevent the electrons from being bound in ions? Also, how much electricity in amps and volts would I nee... | How could I hold free electrons in a container? | physics | 2017-11-04T19:14:37.433 |
[
{
"message": "In the Bogoliuobov theory of superfluidity, the hamiltonian of a system of weakly interacting bosons in second quantized notation is diagonalized with the following result: <br/>$$\\hat H = H_0 \\hat1 + \\sum_k E_k \\hat\\xi_k^+\\hat \\xi_k\\ $$ Where $H_0$ is the ground state energy (a constant)... | Partition function of weakly interacting Bose gas | physics | 2017-11-04T20:25:22.310 |
[
{
"message": "I'm starting a more 'formal' course on quantum mechanics, and we're going through momentum and position space, which I'm kind of confused on. I would just like clarification on this since I'm not understanding my teacher or my textbook very well. I'm just going to list what I think is going on and... | Understanding momentum space and position space | physics | 2017-11-04T23:10:46.217 |
[
{
"message": "I’m totally new to special relativity and am working through some basic derivations and problems with it for an extra credit activity in a 2nd semester general physics class. My question is this: say you have an airplane traveling close to the speed of light. It goes through an airplane hangar wit... | A special relativity conundrum | physics | 2017-11-05T21:23:30.603 |
[
{
"message": "Two parallel plates are kept in such a way that one is earthed and the other one is held at a potential V1.They have a positive charge density P in the volume between the inner faces of the plates. The distance between the parallel plates is d.What will be the distribution of potential inside the ... | Direction of electric field between a pair of parallel plates having a positive charge in the space between them | physics | 2017-11-06T12:40:59.130 |
[
{
"message": "I am unable to clearly understand the meaning of fitting the data. Like in this paper of determination of mass and width of Z boson and number of neutrinos (from ALEPH detector)<a href=\"https://i.stack.imgur.com/SAKDw.png\" rel=\"nofollow noreferrer\"> Does it mean that that we draw the lineshap... | What do we mean by fit of data in particle physics? | physics | 2017-11-06T17:54:16.643 |
[
{
"message": "Let's consider an arbitrary infinitesimal transformation of the fields and their coordinates :$$x'^{\\mu}= x^{\\mu} + \\delta x^{\\mu} = x^{\\mu} + \\frac{\\delta x^{\\mu}}{\\delta{\\omega}^a}{\\omega}^a\\tag{1}$$$${\\Phi}'(x') = {\\Phi}(x) + \\delta\\Phi= {\\Phi}(x) + \\frac{\\delta\\Phi}{\\delta... | Variation of the Action under infinitesimal arbitrary transformations and Noether's Theorem | physics | 2017-11-06T20:38:56.763 |
[
{
"message": "I am unsure as to why the conservation of kinetic energy can't be used to solve this problem:<blockquote> An open-box is moving at $1\\ \\mathrm{m/s}$ on a frictionless surface. If it starts to rain, what happens to the motion of the open box?</blockquote>If the box weighs $2.0\\ \\mathrm{kg}$, i... | Why doesn't energy conservation work for a moving box filling with rain? | physics | 2017-11-06T20:51:12.160 |
[
{
"message": "ContextLet us consider two reference frames: $S$ and $S'$. $S'$ is rotating with respect to $S$ with an angular velocity $\\vec{\\omega}$ about a rotation axis $MOM'$. The origins of $S$ and $S'$ are $O$ and $O'$ and they coincide. Let's say, I want to write a Lagrangian for a free particle of mas... | Lagrangian for Non-inertial Frame | physics | 2017-11-07T03:02:07.647 |
[
{
"message": "Einstein explained the special relativity (roughly) like this:He first assumed the speed of light would not change regardless the speed of its source. Then he described a person on a moving train was tossing a ball up and down. Because the speed of light would not change, the time was slower than ... | Special Relativity Paradox based on Einstein's explaination | physics | 2017-11-07T14:16:01.460 |
[
{
"message": "I'm not a physicist, nor studying physics, so this may be a dumb or a very hard question, I don’t know. I'm not sure if I used correct tags, feel free to correct them if you feel like it is necesary. Forgive me about my English aswell, it’s not my mother language.I'd like to know if there is a kno... | Relation between particle numbers and collisions between gas molecules inside a closed container | physics | 2017-11-08T02:53:36.213 |
[
{
"message": "I'm not a physicist, nor studying physics, so this may be a dumb or a very hard question, I don’t know. I'm not sure if I used correct tags, feel free to correct them if you feel like it is necesary. Forgive me about my English aswell, it’s not my mother language.I'd like to know if there is a kno... | Relation between particle numbers and collisions between gas molecules inside a closed container | physics | 2017-11-08T02:53:36.213 |
[
{
"message": "I'm not a physicist, nor studying physics, so this may be a dumb or a very hard question, I don’t know. I'm not sure if I used correct tags, feel free to correct them if you feel like it is necesary. Forgive me about my English aswell, it’s not my mother language.I'd like to know if there is a kno... | Relation between particle numbers and collisions between gas molecules inside a closed container | physics | 2017-11-08T02:53:36.213 |
[
{
"message": "In my previous <a href=\"https://physics.stackexchange.com/q/364671/\">question, I asked about how to handle Grassmann-number variations of operators. I read a book that uses those variations $\\delta \\Phi = c \\mathbb{1}$, with $c$ being a grassmann number (which, from what I understood, ist me... | Can Grassmann-number variations of operators be represented by operators? | physics | 2017-11-08T12:42:35.047 |
[
{
"message": "I'm a bit confused as to when ordinary and partial derivatives are used in the Dirac formalism.In the Schrödinger equation, for instance, Griffiths [3.85] uses ordinary derivatives:$$ i \\hbar \\frac{\\mathrm{d}}{\\mathrm{d}t} \\lvert \\mathcal{S} \\rangle = H \\lvert \\mathcal{S} \\rangle, $$and ... | Ordinary vs. partial derivatives of kets and observables in Dirac formalism | physics | 2017-11-08T18:13:45.583 |
[
{
"message": "Is the gravitational field stronger in the transverse plane of a mass than along its axis of propagation? I read somewhere that it was but cannot find the reference again. That is, for a mass traveling at very high velocity, or any velocity I suppose, I read that the gravitational force was stro... | Is the gravitational field stronger in the transverse plane of a mass than along its axis of propagation? | physics | 2017-11-09T19:48:33.700 |
[
{
"message": "It is known in Liouville CFT from the crossing symmetry that the four points $s$-channel and 4t$-channel conformal blocks are related to each other via an integral transformation$$\\mathcal{F}\\left[\\begin{matrix}\\theta_1,\\theta_{t}\\\\ \\theta_{\\infty},\\theta_0\\end{matrix};\\sigma,t\\right]... | On fusion transformation in Liouville CFT | physics | 2017-11-10T10:06:06.113 |
[
{
"message": "I just put like half a cup of water in a mason jar and put that in the microwave and accidentally left it in there for to long and it got boiling hot, then when I took it out and let it cool of course the glass cooled much quicker near the top away from the boiling liquid, and there was some very ... | How come I never see cosmic rays in steam like they appear in a cloud chamber? | physics | 2017-11-10T22:31:42.980 |
[
{
"message": "Why are metals malleable and ductile? These two properties seem to be related. Is there a microscopic understanding of these properties possible?",
"role": "user"
},
{
"message": "Let's draw a comparison with ceramics, which—just as metals are generally ductile—are generally brittle. F... | Why are metals malleable and ductile? | physics | 2017-11-11T14:16:50.637 |
[
{
"message": "I did a practical to determine the density of water and oil, the practical succeed but some quesions were arise. So I hope your help for solve these problems.I did this practical using a u shaped tube, and the density was determined by the height of each liquid due to the pressure.When I do this p... | Determine the density using a u shaped tube | physics | 2017-11-12T07:51:06.077 |
[
{
"message": "Let's take a concrete example. One is dealing with a wire through which a DC is running. One measures its voltage and obtain its current by measuring the magnetic field around it in some way such that the standard deviation of the current is $\\sigma_\\text{I, raw}=0.179222... A$. According to sev... | When to round off standard deviations in uncertainty propagation? | physics | 2017-11-12T14:29:19.503 |
[
{
"message": "I read that an incoming photon with a particular frequency can be absorbed by an already excited electron, the electron will then emits 2 similar photons with the same frequency or energy state as the incoming photon. What happens to the photon that was absorbed by the electron earlier and assume ... | Simulated emission of photon, why same energy state? | physics | 2017-11-13T07:05:30.697 |
[
{
"message": "In the treatment of Bosonic or Fermionic systems that I'm familiar with, you start with a state containing at least two particles:$$ \\left| a_{i}, a_{j} \\right\\rangle$$And define a permutation operator, that switches their place. When you apply it twice to any state, you get back the same state... | What is special about the indistinguishability of Boson and Fermions? | physics | 2017-11-14T17:23:25.310 |
[
{
"message": "In all the measurements taken over the years, has anyone ever observed any effect of gravitational lensing on red shift?So: if we would look at 2 galaxies at, say, 250 million lightyears away, where the light of one travels directly towards us while the light of the other passes another galaxy on ... | (How) does gravitational lensing affect red shift? | physics | 2017-11-15T00:12:11.863 |
[
{
"message": "I am trying to prove that the covariant derivative is a tensor (ie it transforms well under a change of coordinates) but I can't succeed to it.Here is the definition of the covariant derivative :$$ \\nabla_XV= X^{\\mu}(\\partial_{\\mu} V^{\\rho}+V^{\\nu}\\Gamma_{\\mu \\nu}^{\\rho})\\partial_{\\rho... | Why is covariant derivative a tensor? | physics | 2017-11-15T19:12:54.130 |
[
{
"message": "I have a few questions here-Why do you need an increase in static pressure, why not total pressure?The rotor vane increase total energy, is this energy converted into kinetic energy or total pressure or both? And then the stator vanes increase the static pressure.",
"role": "user"
},
{
... | I'm confused about the aerodynamics of a gas turbine compressor blade of a jet engine? | physics | 2017-11-15T19:21:03.110 |
[
{
"message": "This problem is from Introduction to Classical Mechanics With Problems and Solutions by David Morin. The solution is also given in the book for this particular problem. <blockquote> Problem #6.6.1 A particle moves in a potential $V(r) = -V_0 \\exp(-\\lambda^2 x^2)$. (a) Given angular momen... | Central force - stable/unstable circular orbit for $V = -V_0 \exp(-\lambda^2 r^2)$ | physics | 2017-11-15T19:58:52.913 |
[
{
"message": "One person took experiment from Montenegro and with distance 201 km he saw clearly montains that are 1521 meters high. He was on 189 meters above the sea level. Official calculator says you cannot see less than 1811 meters from that distance. My question is: Why he saw the mountain? Is there any r... | Why we see things on distances we shouldn't see? | physics | 2017-11-16T04:14:23.983 |
[
{
"message": "That's probably a plain question but I wonder: Which <a href=\"https://en.wikipedia.org/wiki/Meson\" rel=\"nofollow noreferrer\">mesons can exist? The only limitation I'm aware of is the charge (antiparticle+particle). Ok, finally also the color (anticolor+color) but I assume this is not really re... | Which mesons are possible? | physics | 2017-11-16T07:57:38.080 |
[
{
"message": "Imagine a particular potential that allows a superposition of eigenstates such that in space basis the probability density $|\\psi(x)|^2$ is a lorentzian (Cauchy) distribution.The properties of the lorentzian imply that there is no defined expected value for x, $\\langle x\\rangle$. What does this... | Is there a condition of quantum mechanics that forbids Lorentzian distributions? | physics | 2017-11-16T09:14:59.263 |
[
{
"message": "Can someone please explain to me how the wave function of a Cooper pair is spherically symmetric?",
"role": "user"
},
{
"message": "Summary: There's an attraction, mediated by the material lattice vibrations (phonons), between electrons. Considering that this attractive potential depen... | Spherical symmetry of Cooper pair wave function | physics | 2017-11-16T15:34:26.913 |
[
{
"message": "I am aware that similar questions have been answered earlier. But still I am not able to convince myself on following question:If mass(/energy) eigenstates are eigenstates of the Hamiltonian operator, which operator is connected to weak eigenstates and what is its eigenvalue.",
"role": "user"
... | Mass eigenstates and weak eigenstates of neutrinos | physics | 2017-11-17T06:15:21.867 |
[
{
"message": "In the gravitational wave calculation for binary systems: what is the effect of rotation of two BH (or neutron stars, BH-NS,...) on the usual calculations? Is there any EXACT result known?",
"role": "user"
},
{
"message": "There are two questions; I will first answer the simpler one <c... | Kerr BH effects on inspiral binaries | physics | 2017-11-17T16:53:47.557 |
[
{
"message": "What would append if a human jumped while in a rotating ring ? From what I can imagine, the jump would induce a force that would propel the ring in one direction, but as the human has now both a vertical and forward speed (from an external reference point), he would land ahead of it's original pos... | Jumping in Artificial Gravity equals Thrust? | physics | 2017-11-18T02:16:15.537 |
[
{
"message": "I wanted to ask about an idea I got about the Double Slit Experiment.As you may know, you can use the Double Slit Experiment to have particles form an interference pattern with themselves, however, observation of what slit they went through causes this pattern do disappear, even if that observatio... | Idea for the Double Slit Experiment/Quantum Eraser | physics | 2017-11-18T03:41:34.547 |
[
{
"message": "A toilet roll with mass m and outer radius R and inner radius r is held by its first piece and is released from a certain height such that it unfurls. The equations of motion, taking downward as positive is given by$mg - T = ma$ (Translational)$TR = \\frac{a}{2R}(R^2 + r^2)$ (Rotational)If I want ... | Toilet paper roll falling | physics | 2017-11-18T04:46:01.760 |
[
{
"message": "I just asked this <a href=\"https://physics.stackexchange.com/q/369729/\">question concerning the application of Noether's theory. Think about this got me wondering about the following. In the usual derivation of the Noether current the assumption is made that:$$\\mathcal{L}(\\phi'(x'),\\partial_\... | Expansion of $\mathcal{L}(\phi'(x'),\partial_\mu'\phi'(x'),x')$ when looking at Noether's current | physics | 2017-11-19T16:17:52.043 |
[
{
"message": "I'm working on a project at work. We pump different media into a 45L bottle through a 3/16\" tube. The has a 3/16\" vent line that is 13\" long with a 0.2um filter. The project is to reduce the length of the vent line to 2\".I've been challenged on it with the question \"Does reducing the vent ... | Airflow Out of a Container when a Liquid is pumped in | physics | 2017-11-19T20:31:42.557 |
[
{
"message": "A big result from vector calculus is the <a href=\"https://en.wikipedia.org/wiki/Helmholtz_decomposition\" rel=\"noreferrer\">Helmholtz Decomposition: for any vector-valued function $\\mathbf{F} : \\mathbb{R}^{3} \\to \\mathbb{R}^3$ that is well-behaved enough, we can always decompose it as follow... | Helmholtz Decomposition for a four-vector field | physics | 2017-11-19T20:47:35.170 |
[
{
"message": "An example are the anomalies in abelian and non-abelian gauge quantum field theories. For example, the abelian anomaly is $\\tilde {F}_{\\mu\\nu}F^{\\mu\\nu}$ and the integral over this quantity is a topological invariant which measures a topological characteristic of the gauge field $A_\\mu$.All ... | Why are topological properties described by surface terms? | physics | 2017-11-20T10:30:10.497 |
[
{
"message": "An example are the anomalies in abelian and non-abelian gauge quantum field theories. For example, the abelian anomaly is $\\tilde {F}_{\\mu\\nu}F^{\\mu\\nu}$ and the integral over this quantity is a topological invariant which measures a topological characteristic of the gauge field $A_\\mu$.All ... | Why are topological properties described by surface terms? | physics | 2017-11-20T10:30:10.497 |
[
{
"message": "When solving the Schrödinger equation for finite potential well, the solution outside of the well is $$\\psi _{1}=Fe^{{-\\alpha x}}+Ge^{{\\alpha x}}\\,\\!$$ and $$\\psi _{3}=He^{{-\\alpha x}}+Ie^{{\\alpha x}}\\,\\!$$However, when solving the Schrödinger equation for the quantum barrier, the soluti... | Question regarding the solution of Schrödinger equation for finite potential well and quantum barrier | physics | 2017-11-20T15:37:25.573 |
[
{
"message": "A u-pipe is filled with liquid $A$ (density: $1.2\\ \\mathrm{g/cm^3}$. When the left leg of the pipe is filled with liquid $B$ $3.75\\ \\mathrm{cm}$ high, the liquid’s level in the left leg falls $2.5\\ \\mathrm{cm}$.So is the height of liquid $A$ $2.5\\ \\mathrm{cm}$ or $5\\ \\mathrm{cm}$ ($2.5 \... | How to calculate the height of liquid in a communicating vessel after another liquid is added | physics | 2017-11-20T18:56:26.270 |
[
{
"message": "I had been thinking about how much energy would be needed to actually accelerate a spaceship to a speed that is a significant fraction of the speed of light. Because of the huge energies involved, I resorted to matter-anti matter conversion as the fuel needed in the ship. I have made a formula for... | Some calculations on the energy consumption of a relativistic rocket | physics | 2017-11-20T23:17:41.860 |
[
{
"message": "Conducting a little hypothetical experiment here that I do not have all of the equipment to physically conduct, let's say that one uses a toy plastic solider like this<a href=\"https://i.stack.imgur.com/RZcZN.jpg\" rel=\"nofollow noreferrer\">... as well as a sealable acrylic tube that was more th... | How does terminal velocity affect the weight of a closed system? | physics | 2017-11-21T16:00:00.350 |
[
{
"message": "Let us consider a theory defined by an action on a flat space $S[\\phi]$ where $\\phi$ denotes collectively the fields of the theory. We will study the theory on a general background $g_{\\mu\\nu}$ and then we will set the metric to be flat.The Euclidean partition function of the theory in the pre... | Identically vanishing trace of $T^{\mu\nu}$ and trace anomaly | physics | 2017-11-22T09:31:41.840 |
[
{
"message": "<a href=\"https://youtu.be/wZzHnZzm_58?t=5m50s\" rel=\"nofollow noreferrer\">https://youtu.be/wZzHnZzm_58?t=5m50sHis words seem contradictory when explaining entanglement.When the two entangled particles ( red and white ) are taken apart. He describe them as pink.Then he states, if you measure on... | This lecture on entanglement seems awesome but are the words correct? | physics | 2017-11-22T18:28:46.660 |
[
{
"message": "I deal with this action but i really do not know how differential forms can be expressed in terms of tensor components.$$S\\stackrel{\\text{def}}{=} M_{pl}^2\\int_{M}\\epsilon_{abcd}\\left(e^a\\wedge e^{b}\\wedge\\Omega^{cd}\\right)=M_{pl}^2\\int_{M}d^4x\\, \\epsilon^{\\mu\\nu\\rho\\sigma}\\epsilo... | Converting gravity action from differential forms to tensor component | physics | 2017-11-22T18:57:55.530 |
[
{
"message": "My teacher gave me this exercise:Consider a billiard table with balls of radius $r$. How high should be the edge of the table to not allow undesirable pressures (and thus slips of the ball)? I.e. if there was no gravity, the billiard ball would still bounce off parallelly to the table plane.Howeve... | How high should be the edge of a billiard table to not allow undesirable pressures on balls when bouncing off? | physics | 2017-11-22T21:56:45.897 |
[
{
"message": "Is Bell inequality always violated by a quantum system? Can it ever be violated by a classical system?",
"role": "user"
},
{
"message": "Bell's inequality is not always violated. For particular orientations of your detectors you will find that your system follows the inequality (classi... | Is Bells inequality always violated? | physics | 2017-11-23T05:54:31.903 |
[
{
"message": "In the system of up-spin and down-spin states of an electron, we can write a general state of electron at time $t$ as$$\\left|\\psi(t)\\right>=a\\left|\\uparrow\\right>+b\\left|\\downarrow\\right>,$$where $\\left|\\uparrow\\right>$ is up-spin state and $\\left|\\downarrow\\right>$ i... | Comparison between two flavor neutrino oscillation and a system of up-spin and down-spin states of an electron? | physics | 2017-11-23T15:39:35.540 |
[
{
"message": "Is it possible to bend a magnetic field away from an area with a laser, after all, photons are electromagnetic, so couldn't they disrupt the magnetic field, bending it away from a area? If so, how could I do this? I need to block a refrigerator magnet's magnetic field repeatedly.",
"role": "us... | Is it possible to use a laser to prevent a magnetic field from entering a given area? | physics | 2017-11-24T04:12:37.073 |
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