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": "Suppose we have the following setup, a mass on a spring attached to a wall, as shown in the diagram: <a href=\"https://i.stack.imgur.com/MxC6J.png\" rel=\"nofollow noreferrer\">We are completely ignoring friction between the mass and the ground here, and we have an ideal spring too. The mass start... | Damped Harmonic Oscillator Scenario | physics | 2017-06-22T02:52:26.330 |
[
{
"message": "Why is 24h (angle) equivalent to 360°? The earth does not spin 360° in 24h.When giving astronomical coordinates, my GCSE study guide says right ascension is measured in hours where 24h right ascension = 360°. It also says that 360° of rotation is a sidereal day - 24h 56minutes. So 360° in the cele... | Why is 24h (angle) equivalent to 360°? | physics | 2017-06-22T13:43:44.440 |
[
{
"message": "I believe that for any physical quantity, to know what significance it has in any situation or that it's different from other quantities, we have to first start by assigning a value to it, or some means of comparison. For example, empirical temperature started with a lot of experiments on thermal ... | Definition of mass in Newtonian mechanics | physics | 2017-06-22T15:49:43.707 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/TeutZ.png\" rel=\"nofollow noreferrer\">Each wave front is comprised of an infinite number of point sources, each of which produce wavelets with the same wavelength as the wave itself. The superposition of the wavelets produce a new wave front tangential to the ... | Why are diffracted wave fronts drawn with curved edges in textbook diagrams, when according to Huygen's principle they should be straight lines? | physics | 2017-06-23T10:09:54.837 |
[
{
"message": "I have a solar thermal collector. Its LCD screen shows an output of about 5KWH at the end of the day. How to interpret this number? Is this electrical KW (kilo watt)? If yes, isn't too low for a 1.5x2m (well, I am not sure about its size since it is on the roof) solar panel collector? If no, how ... | What is the energy output of Solar thermal collector? | physics | 2017-06-23T10:19:25.153 |
[
{
"message": "The internal energy $U$ of a given mass of a real gas can be regarded as a function of temperature and volume i.e., $U(T,V)$. Under adiabatic free expansion, the change in the internal energy is zero because $\\delta Q=0$. The workdone $\\delta W=0$ too because the gas expands against vacuum. Henc... | Does the temperature of a real gas decrease in the adiabatic free expansion? | physics | 2017-06-23T17:35:28.717 |
[
{
"message": "I have to solve the radial Schrodinger equation for a particle subjected to the potential:$$V(r)= \\dfrac{A}{r^2}-\\dfrac{B}{r}$$ Where $r$ is the radial component (spherical coordinates) and $A,B>0$While I was uncoupling the equations it was useful to define the following constants/function: $... | Boundary conditions on radial Schrodinger equation for $V(r)=A/r²-B/r$ potential | physics | 2017-06-24T13:30:57.230 |
[
{
"message": "This question is same as the question <a href=\"https://physics.stackexchange.com/questions/106538/why-greens-function-will-diverge-at-the-same-spacetime-point\">here which is not answered yet. By Poincare invariance, the propagator of any field theory $G(x,y)$ must be a function of $|x-y|$ and by... | Is the divergence of the propagator between same two spacetime points a pathology? | physics | 2017-06-24T15:15:32.587 |
[
{
"message": "In Dysons Book \"Quantum Field Theory\", In the Section on Schwinger's action principle, he introduces Feynman's path integral method to obtain transition amplitudes:$$\\langle \\phi_2, t_2 | \\phi_1, t_1 \\rangle = \\Sigma_H N e^{\\frac{i}{\\hbar}I_H}$$H is a classic path of $\\phi(t)$ beginning... | Definition of matrix elements of an operator in the path integral formalism wrong? | physics | 2017-06-24T16:40:47.677 |
[
{
"message": "I studied in textbooks that the boiling point of water is the temperature at which the vapor pressure is equal to the atmospheric presssure. My doubt is since the vapor mixes with atmosphere, how can we say vapor pressure is equal to the atmospheric pressure. Please explain this concept.What are t... | Boiling of Water | physics | 2017-06-25T06:07:50.717 |
[
{
"message": "If elementary particles (specifically, those with mass, such as the electron or other leptons) are pointlike particles, wouldn't that mean they are naked singularities? But these particles have spin- wouldn't that make them naked ring singularities, thus giving them an observed radius, making them... | Are pointlike massive particles naked singularities? | physics | 2017-06-25T12:31:52.000 |
[
{
"message": "The inner product of two vectors in space-time is:$$(x_1, y_1, z_1, t_1) \\cdot (x_2, y_2, z_2, t_2) = x_1 x_2 + y_1 y_2 + z_1 z_2 - t_1 t_2$$So $$(\\frac{\\partial }{\\partial x}, \\frac{\\partial }{\\partial y}, \\frac{\\partial }{\\partial z}, \\frac 1c \\frac{\\partial }{\\partial t}) \\cdot (... | The definition of the Lorenz gauge condition | physics | 2017-06-25T12:40:31.137 |
[
{
"message": "If you weighed an object at mid day and then again at midnight, would the objects weight change ( ever so slightly ) due to the centrifugal effect of the earth travelling around the sun ?What I am trying to understand is if the object is weighed at mid-day the centrifugal effect however slight wou... | Would the centrifugal effect of the Earth orbiting around the sun cause the weight of an object to change? | physics | 2017-06-25T22:29:38.167 |
[
{
"message": "What are the quark contents of <a href=\"https://en.wikipedia.org/wiki/D_meson\" rel=\"nofollow noreferrer\">$D^{0 \\ast}$ meson? How to distinguish between $D^{0 \\ast}$ meson and $D^{0}$ meson as I guess both have same quark content.",
"role": "user"
},
{
"message": "The <a href=\"ht... | What is a $D^{0 \ast}$ meson? | physics | 2017-06-25T22:51:35.147 |
[
{
"message": "Does the negative terminal of a battery have greater electron concentration then the positive terminal?Else how would charge start flowing once a conducting wire is connected?",
"role": "user"
},
{
"message": "Starting with a cell with zero net charge the electrochemical reactions with... | Does the negative terminal of a battery have greater electron concentration then the positive terminal? | physics | 2017-06-26T07:50:01.463 |
[
{
"message": "Potassium atoms in the electronic ground state absorb laser light at 769.9, 766.5, 404.7, 404.4, 344.7 and 344.6 nm. Obviously, these absorption lines exist because an electron is excited from the ground state by the laser light. What I would like to know is how the excited states correspondig to ... | Electronic transitions in potassium | physics | 2017-06-26T12:43:16.547 |
[
{
"message": "In classical waveguide analysis (e.g. for optical fibers, as in the notes <a href=\"http://ecee.colorado.edu/~mcleod/pdfs/GWO/lecturenotes/fibers.pdf\" rel=\"nofollow noreferrer\">Modal analysis of step-index fibers, ECE 4006/5166 Guided Wave Optics, Robert R. McLeod, University of Colorado), one ... | Meaning of imaginary part of complex field amplitude for waveguide modes (e.g. TE, TM, HE, EH) | physics | 2017-06-26T12:46:04.673 |
[
{
"message": "I understand how a Faraday cage works. The charges within the conductor rearrange to cancel the applied electric field, etc. However, if you look at the following gif from Wikipedia, the field continues after the cage.<a href=\"https://i.stack.imgur.com/7xn99.gif\" rel=\"nofollow noreferrer\">Say ... | Why do electric fields continue "after" a Faraday cage? | physics | 2017-06-26T14:39:40.950 |
[
{
"message": "An exciton is a bound state of an electron and a hole, much like a hydrogen atom is a bound state of a proton and an electron. Can a \"helium\" exciton be created, such that two electrons are bound to two holes? How about other exciton \"elements\"?If these elements can be created (and momentarily... | Exciton elements and exciton chemistry | physics | 2017-06-26T16:06:22.167 |
[
{
"message": "When looking at the 3D phase diagram of water I felt unsure whether the only physical points were the ones on the surface of the plot. If it is unphysical to move outside the surface of the phase diagram (\"on shell\"?) the question might be moot, but I guess there are conditions for when the phas... | Phase diagram surfaces | physics | 2017-06-26T23:06:40.377 |
[
{
"message": "If there is a block that is placed at the rim of a turntable, and we start rotating this turntable, I know that while the turntable is rotating, a centripetal force is acting on the block. This force is static friction. If we increase the angular speed of the turntable, the static friction must in... | How will "a block on a turntable" move when the turntable move very fast? | physics | 2017-06-27T14:54:31.803 |
[
{
"message": "Why can't you extract heat from your attic and use it to supplement charge to a Tesla wall battery, while also making your house cooler?",
"role": "user"
},
{
"message": "Turning heat into work requires a heat engine. Unfortunately, the efficiency of a heat engine is determined by the... | Removal of thermal energy | physics | 2017-06-27T16:31:28.100 |
[
{
"message": "I learned recently that if you have the Dirac spinor represented in the Weyl (chiral) basis $\\Psi = \\begin{pmatrix} \\psi_L \\\\ \\psi_R \\end{pmatrix}$, then given a Lorentz Transformation $\\Lambda = exp[\\frac{1}{2}\\Omega_{\\rho \\sigma}M^{\\rho\\sigma}]$, the corresponding transformation $S... | Is there a bi-4-vector representation of the Dirac gamma matrices and the spinor? | physics | 2017-06-27T18:04:02.607 |
[
{
"message": "In a particle accelerator, if the force applied to the particles is constant, what approximate values do $F$, $m$ and $a$ have, in $F = ma$?Or if not, is $F = \\dfrac{dp}{dt}$ tested? Either way, to what accuracy is Newton's second law (of acceleration) tested by the accelerations involved?This of... | How accurately is Newton's second law tested in a particle accelerator? | physics | 2017-06-27T19:41:09.073 |
[
{
"message": "since blackholes thermally create and emit sub-atomic particles, does spacetime govern the characteristics that particles display or does a particles characteristics form independently of spacetime?",
"role": "user"
},
{
"message": "We describe the elementary particles using quantum fi... | The nature of particles | physics | 2017-06-28T07:22:48.377 |
[
{
"message": "Edit: as suggested by @Slereah the following explanation of the path integral approach to QED misses gauge fixing and ghost terms to be correct. So, how can this explanation be made correct?What follows is a (hopefully partially correct) description of path integral approach to QED.As per my under... | How to make this short explanation to path integral approach to QED correct? | physics | 2017-06-28T08:00:09.263 |
[
{
"message": "I was reading various reviews on neutrino physics but I couldn't understand the following to complete satisfaction. How is $\\theta_{12}$ identified with the Solar mixing angle and $\\Delta m^2_{21}$ the Solar mass-squared difference? The formulae for three-flavor oscillation probabilities, in gen... | How is $\Delta m^2_{12}$ is identified with the solar mixing angle? | physics | 2017-06-28T13:26:00.960 |
[
{
"message": "If a photon of 475nm strikes my retina, my brain registers it as \"blue,\" whereas a photon of 650nm is \"red.\" If I ask the question \"what is oscillating, and therefore causing the change in wavelength (and thus frequency) that I observe?\" I'll receive an answer invoking alternating orthogonal... | A Photon's wavelength is Color, but an Electron's wavelength is a Probability? | physics | 2017-06-28T18:50:41.327 |
[
{
"message": "If a photon of 475nm strikes my retina, my brain registers it as \"blue,\" whereas a photon of 650nm is \"red.\" If I ask the question \"what is oscillating, and therefore causing the change in wavelength (and thus frequency) that I observe?\" I'll receive an answer invoking alternating orthogonal... | A Photon's wavelength is Color, but an Electron's wavelength is a Probability? | physics | 2017-06-28T18:50:41.327 |
[
{
"message": "The wikipedia page for gravitational waves contains this statement:\"The area enclosed by the test particles does not change and there is no motion along the direction of propagation. citation needed\"Why citation needed? Is it up for debate?In my case, clarification needed.In my own words:It app... | Can a gravitational wave stretch a volume equally in 3 dimensions? | physics | 2017-06-29T00:30:14.967 |
[
{
"message": "The physical picture is a two-stream system of cold electrons and ions (i.e. $T_i=T_e=0$) with realtive velocities $V_i$ and $V_e$. The <a href=\"https://en.wikipedia.org/wiki/Two-stream_instability\" rel=\"nofollow noreferrer\">dispersion relation obtained is$$D(\\omega)=1-\\frac{\\omega_{pi}^2}{... | Smallest relative velocity driving a two-stream instability | physics | 2017-06-29T04:55:33.923 |
[
{
"message": "According to the article cited behind, and to a post in Astronomy SE , there are galaxies moving away from Milky Way faster than light, even at speeds of 2.3c . According to this article <a href=\"http://curious.astro.cornell.edu/the-universe/cosmology-and-the-big-bang/104-the-universe/cosmology-a... | Does the Milky way have relativistic mass against galaxies which are moving away from it at high speeds? | physics | 2017-06-29T11:39:22.793 |
[
{
"message": "I'm studying phase transitions on Callen's book Thermodynamics and an Introduction to Thermostatistics (chapter 9, section 9.1) but I had some problems while trying to understand the role of the presence of multiple minima in the Gibbs free energy.In the first part of the chapter, Callen makes thi... | Gibbs potential and phase transitions | physics | 2017-06-30T14:10:46.400 |
[
{
"message": "In the Cosmology literature, I have often come across the phrases \"primordial density of matter\" and \"primordial density perturbations\"? What do these phrases really mean and which epoch in the Universe do they refer to? What is/are the origin of density perturbations?",
"role": "user"
}... | What is really meant by primordial density perturbations? | physics | 2017-06-30T15:36:40.367 |
[
{
"message": "My understanding of general relativity is that gravitation is equivalent to spacetime curvature and is proportional to localized mass. Traditionally, we conceptualize that massive things attract each other by bending spacetime. Could some mechanism in the early Universe have warped spacetime and t... | Could dark matter be curved pockets of spacetime left over from the big bang? | physics | 2017-06-30T23:53:58.313 |
[
{
"message": "I know from quantum mechanics that any matter particle has both wave and particle properties. So my question is that like in Newtonian mechanics we calculate the force acting on a particle by applying Newton's 2nd law of motion, can we apply it also for waves?",
"role": "user"
},
{
"m... | Force acting on particles/waves | physics | 2017-07-02T03:53:43.373 |
[
{
"message": "Let $U(\\vec{x}, \\vec{v}) = -K \\vec{A}(\\vec{x})*\\vec{v}$ be the generalized potential, where $\\frac{d}{dt}\\vec{x} = \\vec{v}$, $K$ is a constant and $\\frac{\\partial \\vec{A}(\\vec{x})}{\\partial t} = 0$<br>Now I showed that $$F = \\frac{d}{dt} \\frac{\\partial U}{\\partial v} - \\frac{\\pa... | Lagrangian mechanics, generalized coordinates, equations of motion | physics | 2017-07-02T15:20:37.573 |
[
{
"message": "I understand that in a configuration as the one showed in the figure below, the value of $Z_T $ is chosen so $Z_{in} = Z_0 $, meaning that there would not be a reflected wave at the interface $Z_0$-Line/Load+Transformer<a href=\"https://i.stack.imgur.com/NViox.png\" rel=\"nofollow noreferrer\">But... | Reflection at the load when matching with quarter-wave impedance transformer | physics | 2017-07-02T16:38:55.893 |
[
{
"message": "I've read up on quantum annealing, and particularly on the way it is done by companies like D-wave. I think I understand how it works and how it harnesses tunneling to find global optimal in a given energy potential.But the elephant in the room is: How can it be of any use? What is the point of lo... | Is quantum annealing of any use? | physics | 2017-07-02T17:02:30.597 |
[
{
"message": "When electromagnetic waves were introduced to me, they were introduced through the use of Maxwell's equations in a vacuum, which are\\begin{align}\\nabla \\cdot E &= 0 \\\\\\nabla \\cdot B &= 0 \\\\\\nabla \\times E &= -\\frac{\\partial B}{\\partial t}\\\\\\nabla \\times B &= \\mu_... | If electromagnetic fields don't actually propagate in plane waves, how do they propagate? | physics | 2017-07-02T17:11:17.640 |
[
{
"message": "To my surprise I couldn't find any estimate on how many amperes of electrical current are flowing in total in the Earth's core to be able to create the magnetic field strength $5\\cdot 10^{-5}$ T on it's surface.How can I estimate this electrical current?<br>How would the current be spatially dist... | How many amperes are flowing in the Earth's core? | physics | 2017-07-02T22:25:44.407 |
[
{
"message": "I read on wiki that gravitational shielding is considered to be a violation of the equivalence principle. Is that so, How? A conceptual description without lot of mathematics will be helpful. I am not sure whether the wiki article refers to shielding only by materials, or it also includes mechanis... | Gravitational shielding and equivalence principle | physics | 2017-07-03T05:10:29.423 |
[
{
"message": "I'm sure there's a good explanation for the issues leading to my question so please read on:Classically, we can represent Electromagnetism using tensorial quantities such as the Faraday tensor $F^{\\alpha\\beta}$ from which (with the help of the metric $g^{\\mu\\nu}$) we can construct the Maxwell ... | Is Electromagnetism Generally Covariant? | physics | 2017-07-03T07:56:57.600 |
[
{
"message": "I've learnt an electromagnetic field is produced by moving charges, i.e. a current. Is it the case, or is it actually the fact that the charge is changing at a given location? I mean: imagine I have a charge $q_1$ located at a given point of the space. Then imagine the charge changes and becomes... | What produces an electromagnetic field? A charge that moves, or a charge that changes over time? | physics | 2017-07-03T10:48:47.207 |
[
{
"message": "If I understand it correctly:given 2 bodies travelling at different relative speeds, time will appear to run faster for the faster moving of the two, from the slower objects perspectivea single light photon will be seen to be moving at the same speed for both because although the 'distance travell... | General Relativity question | physics | 2017-07-03T12:07:13.927 |
[
{
"message": "As much I understand, in a crystal Berry connection and Berry curvature is defined for a particular band. The Hall conductance is given by the total Chern number (integrated Berry curvature over the full Brillouin zone) of all the bands below Fermi level. In this paper [ <a href=\"https://arxiv.or... | Berry curvature for metal and Anomalous Hall Effect | physics | 2017-07-03T13:49:41.733 |
[
{
"message": "When determining the centripetal force on an object on a banked curve, it is stated that the banking angle for a given speed and radius is found by :tanθ = v^2/rg It is found as follows: The normal force on the object is resolved into components. The x-component (the one providing the centripetal ... | Physical reason of difference between normal force in a banked curve and an inclined plane. | physics | 2017-07-03T15:36:19.287 |
[
{
"message": "A canonical pulsar can be described as a ball of mass $M \\approx 1,44 \\, M_{\\odot}$ and radius $R \\approx 10 \\, \\mathrm{km}$, rotating with a period of about $P \\approx 5 \\, \\mathrm{ms}$. It also have a typical magnetic field of around $B_{\\text{pole}} \\sim 10^{6} \\, \\mathrm{tesla} =... | Magnetic decay versus rotation braking of neutron stars | physics | 2017-07-03T15:47:23.547 |
[
{
"message": "Description of Bose-Einstein condensation (BEC) using grand canonical ensemble results in strongly fluctuating distribution $p(N_0)\\sim e^{-N_0(\\epsilon_0-\\mu)/T}$ of a number of condensate particles $N_0$. Such fluctuations are not observed in atomic BEC, so the problem termed grand canonical ... | Grand canonical fluctiation catastrophe in Bose-Einstein condensate of polaritons? | physics | 2017-07-03T17:45:05.460 |
[
{
"message": "I am learning the diffraction these days, and I am quite curious about the energy distribution of the light. We know that for single slit diffraction the monochromatic light will form some bright and dark areas. Where does the energy of the dark place go? Does it just disappear?<a href=\"https://i... | Diffraction of monochromatic light | physics | 2017-07-04T08:36:25.070 |
[
{
"message": "In <a href=\"http://courses.egr.uh.edu/ECE/ECE5317/Class%20Notes/Notes%2013%205317-6351%20Transverse%20resonance%20method.pptx\" rel=\"nofollow noreferrer\">this document, a transmission line terminated at both ends with purely reactive loads is considered as an example for the Transverse Resonanc... | Resonance condition in transmission line | physics | 2017-07-04T13:46:50.383 |
[
{
"message": "In QED, when dealing with the vacuum polarization and the photon propagator, some authors like Peskin & Schroeder introduce the so-called \"1-particle irreducible\" diagrams. These are defined as:<blockquote> Let us define a one-particle irreducible (1PI) diagram to be any diagram that cannot... | How to correctly understand these "1-particle-irreducible insertions"? | physics | 2017-07-04T20:34:30.763 |
[
{
"message": "I know this is related to the mass of the object, so that an ant falling will have a little terminal velocity and won't get much damage, when compared to a human which will reach an higher velocity.<br>I'm trying to explain this to myself: the energy that is \"converted to damage\" is the final ki... | Why falling ants will get less damage than a human? | physics | 2017-07-04T23:03:45.037 |
[
{
"message": "While reading the book <a href=\"http://rads.stackoverflow.com/amzn/click/0521882230\" rel=\"nofollow noreferrer\">Gravitation Foundation and Frontiers by Padmanabhan, I came across the Lagrangian for a scalar theory of gravity. But the coupling term consist of trace of the Energy Momentum Tensor.... | Scalar Field Theory for Gravity | physics | 2017-07-05T14:01:49.940 |
[
{
"message": "In a circuit with just a resistor and a capacitor I'm trying to figure out which voltage is being referred to that is lagging the current(which is the same current throughout the entire SERIES AC circuit). The voltage which leads or lags is the same voltage referred to by $$I(t)=C\\frac{dV(t)}{dt}... | In an AC circuit which voltage lags the current in a capacitor: Source voltage or capacitor voltage? | physics | 2017-07-06T08:16:53.647 |
[
{
"message": "I tried to google it but couldn't found an intuitive explanation (not existing in Wikipedia). I have also tried to read <a href=\"http://science.sciencemag.org/content/303/5663/1490\" rel=\"nofollow noreferrer\">the Science paper by T. Senthil et al, but couldn't fully understand the derivations i... | What is the meaning of "Deconfined Quantum Critical Point"? | physics | 2017-07-06T08:53:55.130 |
[
{
"message": "I am self-studying P. Davies, D. Betts, Quantum Mechanics. Exercise 4 of Chapter 1 says:\"A snooker ball of mass $0.1$kg rests on top of an identical ball and is stabilized by a dent $10^{-4}$m wide on the surface of the lower ball. Use the uncertainty principle to estimate how long the system wil... | Estimate of the effect of quantum disturbances on a macroscopic object | physics | 2017-07-06T14:14:36.667 |
[
{
"message": "Based on <a href=\"https://physics.stackexchange.com/questions/142159/deriving-the-coulomb-force-equation-from-the-idea-of-photon-exchange\">this question and in the answers we see how the tree-level amplitude allows ust to relate the bare photon propagator to the Coulomb potential using basically... | How Coulomb's potential is related to the propagator? | physics | 2017-07-06T16:49:04.920 |
[
{
"message": "Not sure if I should be asking this in maths or physics section so please excuse me if asked in the wrong section. I am trying to numerically integrate the equations obtained in the exponential potential scalar field model of dark energy. The set of equations I have obtained is:\\begin{align}x &am... | Numerically solving scalar field model of dark energy | physics | 2017-07-06T21:50:53.757 |
[
{
"message": "<a href=\"https://en.wikipedia.org/wiki/Machmeter\" rel=\"nofollow noreferrer\">Wikipedia states that for a <a href=\"https://en.wikipedia.org/wiki/Pitot-static_system\" rel=\"nofollow noreferrer\">pitot-static tachometer, the mach number for subsonic flow equates to$$M = \\sqrt{5\\left[\\left(\\f... | How is the equation of Mach number derived? | physics | 2017-07-07T07:12:48.007 |
[
{
"message": "As I understand it, if $S \\gg h$ then we are in the classical realm, whereas if $S \\leq h$ we are in the quantum realm. My question is what happens somewhere in between those 2 limits? Are we quantum and classical at the same time?",
"role": "user"
},
{
"message": "There are two diff... | Transition from quantum to classical mechanics | physics | 2017-07-07T10:54:08.827 |
[
{
"message": "This is a solved example in my text book\"Engineering mechanics dynamics. R.C.Hibbeler\" :The 3 kg disk is attached to the end of a cord. The other end of the cord is attached to a ball and socket joint located at the center of the platform. If the platform rotates rapidly, and the disk is placed ... | Circular motion and friction | physics | 2017-07-07T17:51:14.103 |
[
{
"message": "The SCF HF method is a variational method that calculates the minimal energy of a many-body ground state (actually, it converges to a number which I take as the ground state energy). But what are the second minimum, third minimum, and... energies? do they correspond to the excited states?",
"r... | What is the physical interpretation of the "energies" I am getting from the self-consistent field Hartree-Fock (SCF HF) method? | physics | 2017-07-07T22:53:54.677 |
[
{
"message": "Please refer to the figure below. The center of mass of the rod under the net force will accelerate. At the same time, the whole rod will also rotate around its center of mass. In his lectures, Feynman explained mathematically the reason why the center of mass translates according to Newton's law ... | Change in center of rotation of an object | physics | 2017-07-08T02:18:57.547 |
[
{
"message": "If a current carrying conductor is placed inside a solenoid where current passes through both solenoid & conductor, Will an extra emf(potential difference)/current induce in the conductor? [current in conductor is less than that of solenoid]?Let emf already existing in conductor be E1.If emf ... | Will Emf induce in current carrying conductor in solenoid? | physics | 2017-07-08T12:51:19.143 |
[
{
"message": "The book of Dyson \"Quantum-Field-Theory\" states in section 4.4 that one can derive canonical commutation relations from Schwingers quantum action principle. However, doesn't give a calculation for the canonical momenta, which should commute. Is it possible to derive the canonical commutation rel... | Derive canonical commutation relations from Schwingers principle | physics | 2017-07-08T13:57:42.880 |
[
{
"message": "The book of Dyson \"Quantum-Field-Theory\" states in section 4.4 that one can derive canonical commutation relations from Schwingers quantum action principle. However, doesn't give a calculation for the canonical momenta, which should commute. Is it possible to derive the canonical commutation rel... | Derive canonical commutation relations from Schwingers principle | physics | 2017-07-08T13:57:42.880 |
[
{
"message": "What's the difference between formation and production processes, e.q. for p-pbar seen on <a href=\"https://www.google.de/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiRq4_PsPzUAhUPbVAKHavqDR4QjRwIBw&url=http%3A%2F%2Fslideplayer.com%2Fsli... | Difference between formation and production | physics | 2017-07-09T14:18:22.493 |
[
{
"message": "The Earth's acceleration in numbers is $9.8 \\frac{m}{s^2}$ and it stays constant in time.How much is the acceleration of the Universe expansion in numbers? I noticed that the Hubble constant (which is about 74) is measured in $\\frac{m^2}{s}$ instead of $\\frac{m}{s^2}$.And is this acceleration s... | Accelerating expansion of the universe in numbers | physics | 2017-07-10T00:11:53.793 |
[
{
"message": "One way to write an effective Hamiltonian for a Hamiltonian $H$ is via the equation$$\\frac{1}{E-H_{eff}} = P\\frac{1}{E-H}P$$where P projects into the subspace we're interested in, and $H_{eff}$ is the effective Hamiltonian of this subspace. This equation is meant to hold for all $E$. I've heard ... | Self-consistency of Effective Hamiltonian equation | physics | 2017-07-11T00:26:56.580 |
[
{
"message": "I know that two particles are entangled when their Hamiltonian contains an interaction part, but it seems to me that for the ground state of the hydrogen atom $\\frac{1}{\\sqrt{\\pi}}\\left(\\frac{1}{a_0}\\right)^{3/2}e^{-\\frac{r}{a_0}}$, when under different reference frames, can be entangled in... | Why does the separability of the hydrogen wavefunction vary under different reference frames? | physics | 2017-07-11T11:14:40.070 |
[
{
"message": "I recently learned that a beam of light that undergoes total internal reflection leads to the formation of an evanescent surface wave on the reflection surface. What happens if this wave encounters a material with a higher or lower refractive index (the edge of the prism for example)? Will it refr... | Evanescent Wave Refraction | physics | 2017-07-11T22:43:35.380 |
[
{
"message": "Let's consider an infinite solenoid, with $n$ loops per unit length, radius $a$, which carries a current $i$. Using symmetries and Ampère's law, one can find that the magnetic field is ortho-radial, and that$$\\begin{cases}B_{int} = \\mu_0ni + A \\\\B_{ext} = A\\end{cases}$$where $A$ is a constant... | How to find the magnetic field outside an infinite solenoid without Biot-Savart law? | physics | 2017-07-13T09:22:19.533 |
[
{
"message": "If I understand correctly, the electrostatic approximation assumes that all charges are stationary (i.e the charge density is constant in time, and current density is zero). The magnetostatic approximation assumes the current density is constant in time. Are these the correct definitions?I have al... | What does electrostatic/magnetostatic approximation mean, exactly? | physics | 2017-07-13T16:06:19.923 |
[
{
"message": "It seems like whenever we talk about \"released\" energy the assumed form of that energy is electromagnetic radiation. Is it possible for \"energy\" that appears in any theory or process to exist in any form that is not:A photon, orA particle with non-zero mass, orEmbodied in the relationship bet... | What forms can energy take? | physics | 2017-07-13T17:48:37.393 |
[
{
"message": "Q: Why does physics express formulas with a single unit vector when a linear combination of basis vectors is needed?So, instead of: $\\vec{v} = v_x \\cdot \\hat{x} + v_y \\cdot \\hat{y} + v_z \\cdot \\hat{z}$ , which we learn in linear algebra, physics uses: $\\vec{v} = ||\\vec{v}|| \\cdot \\hat{v... | Newton's Second Law with unit vectors | physics | 2017-07-13T18:17:54.423 |
[
{
"message": "There are various more or less formal ways of expressing the foundational principles of nonrelativistic quantum mechanics, including both nonmathmatical statements and more rigorous axiomatizations. Recently there have been various people who have treated this from a quantum-computing point of vie... | Differences between principles of QM and QFT | physics | 2017-07-13T20:56:29.327 |
[
{
"message": "The Einstein-Rosen bridge describes a short cut between two point by \"connecting\" the two destinations in a folded 2-dimensional representation of the three dimensional universe, but if the universe is actually a multiverse wouldn't the short cut have to \"tunnel\" through multiple universes for... | Einstein-Rosen bridge through multiverse? | physics | 2017-07-13T22:04:06.820 |
[
{
"message": "Similarly to steady electric or magnetic fields for example?",
"role": "user"
},
{
"message": "Lets clear up terminology:<a href=\"http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/expar.html\" rel=\"noreferrer\">Virtual particles are mathematical entities in Feynman diagrams, used ... | Can the gravitational force be described just with virtual particles of its own field? | physics | 2017-07-14T06:44:06.313 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/aEv16.png\" rel=\"nofollow noreferrer\">The way I see it, when I push a block across a table, taking care to push in line with its centre of mass or just below, the object should topple over because the friction should create a (clockwise, in the case of the dia... | Why is the net torque 0 when pushing a block across a table? | physics | 2017-07-15T13:52:22.830 |
[
{
"message": "The Wikipedia definition of a geodesic is,<blockquote> the worldline of a particle free from all external, non-gravitational forces</blockquote>Now for a binary system like Hulse-Taylor I have heard it described as a free-falling oscillating mass quadrupole and so the worldlines are perturbed fro... | Do the stars of the Hulse-Taylor binary follow geodesics? | physics | 2017-07-15T17:15:58.423 |
[
{
"message": "If space is infinite, it's it also possible that energy is infinite? Given that we can't really conceptualize infinite space, could we say with certainty that energy is not infinite? How?",
"role": "user"
},
{
"message": "This is a reasonable question. Here are some more about the same... | Infinite Space && Infinite Energy? | physics | 2017-07-16T01:05:40.180 |
[
{
"message": "According to my book, the magnetic field in any location inside the toroid (the empty region inside the toroid circumference) is zero because if we consider a circular loop passing through that point, the magnetic field would be zero as there is no current inside that loop. If we use this logic fo... | Why can't we consider Amperean loop inside solenoid just like a toroid? | physics | 2017-07-16T07:55:54.527 |
[
{
"message": "If I move a magnet towards the coil then the magnet will experience a restive force because of <a href=\"https://en.wikipedia.org/wiki/Lenz%27s_law\" rel=\"nofollow noreferrer\">Lenz's law. This way mechanical energy will convert into electrical energy.But what if the magnet and the coil are a suf... | Violation of energy conservation in retarded interaction of magnet and coil | physics | 2017-07-16T11:59:31.347 |
[
{
"message": "In school, I've been taught that waves follow the path/shape of a <a href=\"https://en.wikipedia.org/wiki/Sine\" rel=\"nofollow noreferrer\">Sine. Often demonstrated by either a projection of a circle or by a swinging pendulum or shaking string.I guess those are simple models with great academic v... | Internal speed of light | physics | 2017-07-16T19:43:14.460 |
[
{
"message": "As a light source in the universe (e.g. sun) emits light in different directions, some of the light emitted reaches places like Earth, and some doesn't. So does the light that reaches the Earth disappear or it is reflected in other directions? And for the light that doesn't reach any place, does i... | About light in the universe | physics | 2017-07-17T01:06:01.637 |
[
{
"message": "As a light source in the universe (e.g. sun) emits light in different directions, some of the light emitted reaches places like Earth, and some doesn't. So does the light that reaches the Earth disappear or it is reflected in other directions? And for the light that doesn't reach any place, does i... | About light in the universe | physics | 2017-07-17T01:06:01.637 |
[
{
"message": "Work by definition is given by,$W=\\vec{F}.\\vec{dx}$.If $\\theta=0$, we can obtain:$dW=PdV$So, according to me, it should hold for all the processes be it quasistatic or non-quasistatic.But I have read that $dW=PdV$ is only valid for quasistatic processes. Why isn't it valid for non-quasistatic p... | Intuitive understanding of work done in quasistatic and non-quasistatic process | physics | 2017-07-17T15:06:26.420 |
[
{
"message": "Is it theoretically possible that the $G$ constant in Einstein's equation be a functional of all fields present in a given spacetime ?\\begin{equation}\\tag{1}G_{\\mu \\nu} + \\Lambda \\, g_{\\mu \\nu} = -\\, \\frac{8 \\pi}{c^4} \\, G[g, \\phi] \\, T_{\\mu \\nu}.\\end{equation}Since it's by hypoth... | May the gravitational constant $G$ be a *functional* of all fields on spacetime? | physics | 2017-07-17T17:34:43.540 |
[
{
"message": "In a science fiction movie some aliens come to earth and when asked why, they say they received our radio transmission and came to investigate, the radio transmission being the first television broadcast (the Berlin Olympiad in 1936). So, the idea is that it took decades for the signal to reach th... | Attenuation of radio frequency transmissions in space | physics | 2017-07-17T18:35:19.787 |
[
{
"message": "What is the significance behind defining normal to any surface? Why we do it?",
"role": "user"
},
{
"message": "Geometrically, it's only the component normal to the surface that \"pushes the stuff through\" the surface. As illustrated below, the \"stuff\" that \"moves\" parallel to the... | Why surface normal is used while defining flux through an open surface? | physics | 2017-07-17T18:50:09.633 |
[
{
"message": "I am trying to figure out why in a conductor, lets for example say a uniform sheet of metal (infinitely large to neglect edge effects) that has a net positive charge, at all points inside the conductor the electric field is zero. I understand the Gauss's law explanation that there is no net free c... | Electric Field inside a Conductor--- not Gauss's Law Explanation Please | physics | 2017-07-17T22:40:04.913 |
[
{
"message": "While squeezing a wiffle ball earlier today, I wondered what was causing it to \"push back\" and oppose the squeezing. If it was a pressurized ball, I would assume it was the air pressure causing it. If it was a solid ball, I would assume it was something due to the Young's modulus of the material... | What forces respond to the compression of a ball? | physics | 2017-07-18T01:14:33.150 |
[
{
"message": "$\\mathbf{Background}$:In my research I am studying the Ising model, expressed in terms of Jordan-Wigner fermions:$$H = \\sum_{j=1}^n(c_j - c_j^\\dagger)(c_{j+1} + c_{j+1}^\\dagger) + \\lambda c_jc_j^\\dagger - \\lambda c_j^\\dagger c_j$$where the operators $\\{c_j, c_j^\\dagger\\}_{j=1}^n$ obey t... | Why must the Bogoliubov transform preserve anticommutation relations? | physics | 2017-07-18T07:50:13.113 |
[
{
"message": "Like my topic, I'd like to know why we need to analyze the forward-backward asymmetry:$$A_{FB}=\\frac{\\int_0^1dz\\frac{d\\sigma}{dz}-\\int_{-1}^0dz\\frac{d\\sigma}{dz}}{\\int_{-1}^1dz\\frac{d\\sigma}{dz}}$$in particle physics. What physical concept does it relates to?",
"role": "user"
},
... | Physical Interpretation of Forward-Backward Asymmetry | physics | 2017-07-18T14:09:41.707 |
[
{
"message": "Say I have 3 closed containers of 1L each. By volume, the 1st one is 50/50 air and water, the 2nd is 20% water and 80% air, and the third is 80% water and 20% air. If I heat all of them to the same temperature of 120 C. Are they all under the same internal pressure?EDIT: They all start at atmosphe... | Is the pressure the same if I heat to the same temperature different closed containers with distinct ratios of water to air? | physics | 2017-07-18T21:17:21.527 |
[
{
"message": "I am trying (as an exercise) to determine the force between two wires, in a similar nature to this question <a href=\"https://physics.stackexchange.com/questions/293097/average-force-between-two-parallel-finite-wires-with-ac\">here. This suggests a solution based on the wavelength of the wave. H... | What is the wavelength of electrical current? | physics | 2017-07-19T01:32:44.517 |
[
{
"message": "My assumption is that stars have significantly larger volume than black holes. And if they spiraled they would would merge before they had the chance to reach high enough velocities to generate gravitational waves detectable by the current LIGO.Is this the main reason why we know LIGO detected bla... | How do we know LIGO didn't detect stars but Black holes? | physics | 2017-07-19T06:44:10.620 |
[
{
"message": "There are a few things in car Physics that keep confusing me and I hope you can help me improve my understanding. The first thing I would like to discuss is braking. <br>I understand that when a car is accelerating, the wheels are pushing backwards on the asphalt which results in a towing force sp... | Braking car and the force of friction - front-wheel-drive | physics | 2017-07-19T09:25:32.903 |
[
{
"message": "So in quantum mechanics, most of the people uses exponential equation to handle the problem and present the relationship.Another word, we often handle the classical wave function in trigonometric way by utilizing sine and cosine.How can these two be correlated?Using Euler's formula the exponential... | Problems with function transforming | physics | 2017-07-20T15:46:23.313 |
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