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": "While frying some chicken I was wondering why the fat becomes transparent when melting.As far as I know, transparency is caused by the fact that the substance can't absorb photons of visible light (due to band gap or other excitation mechanisms)Is this the reason for liquid/solid fat as well? How ... | Why is liquid fat transparent and solid fat opaque? | physics | 2017-12-29T13:21:51.410 |
[
{
"message": "I'm reading polchinski's book and I was asking if I've made a wrong calculation or I didn't understand sth.Well, basically. $$Z[p]=\\int [DX^{\\mu}]e^{-S[X]}e^{ipX}$$$$=(2\\pi)^{d}\\delta^{d}(p_{0})\\det{}^{\\prime}\\left(\\frac{-\\nabla^{2}}{4\\pi^{2}\\alpha'}\\right)^{-d/2}\\exp(-\\frac{1}{2}\\i... | Polchinski book, doubt related to $X_{0}$ | physics | 2017-12-29T16:07:49.987 |
[
{
"message": "Reading Tomas Lee's very interesting historic account of Semiconductor's used in the Electronic industry:<a href=\"https://web.stanford.edu/class/archive/ee/ee214/ee214.1032/Handouts/HO2.pdf\" rel=\"nofollow noreferrer\">https://web.stanford.edu/class/archive/ee/ee214/ee214.1032/Handouts/HO2.pdfI ... | Why did Shockley's Copper Oxide Field Effect Transistor fail and has anybody succeed in creating a Copper as appose to Silicon based FET? | physics | 2017-12-29T16:25:03.147 |
[
{
"message": "Is my understanding correct, that all objects emit a perfect black body spectrum only dependent on its temperature, but we cant measure this perfect spectrum because all objects will reflect some of the radiation distorting the reading for the wavelength of radiation reflected.Since no object is a... | Why are there no perfect black bodies? | physics | 2017-12-29T17:05:22.790 |
[
{
"message": "In SO(3) the methods of parameterizing rotations in terms of sequential simple rotations are categorized as Euler angles or Tait—Bryan angles, with Euler angles often taken as the canonical way of writing rotations in physics. Is there a set of angles for N-dimensional rotations that has a similar... | Is there a "canonical" way to parameterize elements of $\operatorname{SO}(N)$? | physics | 2017-12-29T20:48:35.410 |
[
{
"message": "Compare to the path integral for bosons, how can we formulate the Fermion path integral mathematically? For the boson path integral, the integration means the Lebesgue integral with respect to a measure on $(\\mathbb{R}^T, \\mathcal{B}(\\mathbb{R}^T))$ when we consider the Euclidean action.($T$ he... | Mathematical formulation for Fermion path integrals? | physics | 2017-12-30T07:53:24.967 |
[
{
"message": "I have a question regarding Solid Mechanics and Mohr's circle. In my test today, we had a plane stress state represented in a Mohr circle which was not centered at the origin. The question asked to find the orientation of the planes subjected to a pure shear stress state. However, I thought that w... | Solid Mechanics -- how to find pure shear stress state? | physics | 2017-12-30T08:18:21.830 |
[
{
"message": "If space contains mostly ions (whether positive or negative), then why cant a spacecraft “absorb” them with simple anodes/cathodes, separate them, and repurpose the ions for spacecraft electricity (e-) or propulsion (p+)?",
"role": "user"
},
{
"message": "Ions are indeed used to provid... | Can we use ions in space to propel and power spacecraft? | physics | 2017-12-30T08:45:01.347 |
[
{
"message": "Context 1 The spin $s$ of a relativistic particle of mass $m$ can be read off from the eigenvalue $s(s+1)$ of the operator $-\\frac{W_\\mu W^\\mu}{m^2}$ in the rest frame of the particle where $W^\\mu=\\frac{1}{2}\\epsilon^{\\mu\\nu\\sigma\\rho}J_{\\nu\\sigma}p_{\\rho}$ where $J_{\\mu\\nu}$ and $p... | Connection between the 'spin' and 'polarization' of relativistic and non-relativistic particles | physics | 2017-12-30T10:39:20.890 |
[
{
"message": "I am an older student returning to the field, trying to reteach myself the basics and have run into a problem interpreting a pattern I see.In an introductory book explaining atomic orbitals of a hydrogen atom, it shows the radial probability functions for the 1s, 2s, and 3s subshells. Each one pea... | Radial Probability Function of 3s Orbital | physics | 2017-12-30T13:38:19.073 |
[
{
"message": "What are destructive measurements or incomplete measurements, and what is the (conceptual) difference between them and a usual measurement?I read somewhere that destructive measurements consume their qubit.reference: <a href=\"https://arxiv.org/pdf/0704.1263\" rel=\"nofollow noreferrer\">measure... | What is a destructive measurement? | physics | 2017-12-30T21:19:01.633 |
[
{
"message": "Is it possible that prior to our current universe's Big Bang, there was a universe made up of Dark Matter/Energy created from a prior Big Bang? Its physics/matter could have been different than what our current universe experiences, yet could share, for instance, gravitation. So our current univ... | Could Dark Matter/Energy be explained by a second universe? | physics | 2017-12-31T22:15:02.740 |
[
{
"message": "It is said it makes the cooking more efficient to surround the fuel canister and fire with rocks. How to explain it with physics?<a href=\"https://i.stack.imgur.com/DAqQ3.jpg\" rel=\"nofollow noreferrer\">PS.How does rocks compare with wood blocks in efficiency? Is the heat capacity of rocks relat... | Why it is heat efficient to surround fire with rocks when cooking in the wild? | physics | 2018-01-01T01:01:57.103 |
[
{
"message": "Or do they have exactly the same characteristics?I.e. if I observe them in a place where it’s dark 24 hours.",
"role": "user"
},
{
"message": "<blockquote> Should there be a difference in strength or otherwise between daytime and nighttime auroras?</blockquote>The <a href=\"https://en... | Should there be a difference in strength or otherwise between daytime and nighttime auroras? | physics | 2018-01-01T13:11:41.943 |
[
{
"message": "I have some object (300g) that I want to keep above the water. I could run experiments to figure out how much foam I need but I'd have to do this for every object with a different mass. What equation should I use that will get me close to what I need without trial and error?",
"role": "user"
... | How to calculate how much foam is needed to float something of a certain mass? | physics | 2018-01-02T00:46:55.533 |
[
{
"message": "What naturally occurred radiations or waves that don't produce any sound at all regardless of frequency and medium? In the video below, this person, Donald Gurnett and some other people at University of Iowa claimed to have recorded \"sounds\" from space. What producing those \"sounds\", they said... | What naturally occurred radiations or waves that don't produce any sound at all regardless of frequency and medium? | physics | 2018-01-02T03:43:47.767 |
[
{
"message": "I am just slightly confused about how initial time is chosen in mechanics. I keep thinking I have understood it but some doubts come up later.Basically when I derived the constant acceleration equations in a general way I ended up with $v(t)=v(0)+at$ and $x(t)=x(0)+v(0)t+\\frac{1}{2} at^2$. Howeve... | Can the initial time be non-zero? | physics | 2018-01-02T06:53:43.987 |
[
{
"message": "I'm following this derivation from the NASA website explaining the design of converging/diverging nozzles in rocket design, specifically the derivation in image form at the top of the page:<a href=\"https://www.grc.nasa.gov/www/k-12/airplane/nozzled.html\" rel=\"nofollow noreferrer\">https://www.g... | Density and area in 1D conservation of momentum and nozzle design | physics | 2018-01-02T17:07:30.403 |
[
{
"message": "In <a href=\"https://arxiv.org/abs/hep-th/9804058\" rel=\"nofollow noreferrer\">this paper the scalar 3-point function in AdS/CFT is obtained by performing the following integral:<a href=\"https://i.stack.imgur.com/PbW3Z.png\" rel=\"nofollow noreferrer\">The authors comment that they obtain the re... | AdS/CFT scalar 3-point function integral from Feynman parametrization? | physics | 2018-01-02T22:00:43.263 |
[
{
"message": "I doubt about formula (28.3) from <a href=\"http://www.feynmanlectures.caltech.edu/I_28.html\" rel=\"nofollow noreferrer\">this Feynman's lecture. $$\\textbf{E} = - \\frac{q}{4 \\pi \\epsilon_0 } \\Big{[} \\ \\frac{e_{r'}}{r'^2}+ \\frac{r'}{c} \\frac{d}{dt} \\Big( \\frac{e_{r'}}{r'^2} \\Big) + \\f... | Electric field of uniformly moving charge ; misprint in Feynman textbook? (28.3) | physics | 2018-01-03T11:35:56.400 |
[
{
"message": "This book for example: <blockquote> Theory of Electromagnetic Waves: A Coordinate-free Approach, by Hollis C. Chen (McGraw-Hill, 1983); <a href=\"https://rads.stackoverflow.com/amzn/click/0070106886\" rel=\"nofollow noreferrer\">Amazon link,</blockquote>only I can't find it online without a regis... | Is there a formalism on EM waves that uses only coordinate free calculations? | physics | 2018-01-03T14:04:11.300 |
[
{
"message": "What is <a href=\"https://en.wikipedia.org/wiki/Enstrophy\" rel=\"nofollow noreferrer\">enstrophy and how can we generalize that notion to higher dimensions?Comment: a formulation using differential forms (and/or tensors/multivectors) is preferred!",
"role": "user"
},
{
"message": "If ... | What is enstrophy and how to understand it in higher dimensions? | physics | 2018-01-04T17:00:47.370 |
[
{
"message": "Consider $$\\int \\frac{d^4k}{(2\\pi)^4} \\frac{1}{k^2}\\frac{1}{k^2}\\frac{1}{k^2}.\\tag{1}$$We can Wick rotate $k_0 \\to i k_0$: $$ i \\int \\frac{d^4k_E}{(2\\pi)^4} \\frac{1}{k_E^2}\\frac{1}{k_E^2}\\frac{1}{k_E^2}\\tag{2}$$and switch to spherical coordinates$$ = 2\\pi^2i \\int \\frac{dk_E}{(2\\... | Help understanding loops with negative superficial degree of divergence | physics | 2018-01-04T17:12:23.120 |
[
{
"message": "Take this phase diagram :<a href=\"https://i.stack.imgur.com/xwpmQ.png\" rel=\"nofollow noreferrer\">At the point \"A\" I will have a liquid, at point B a gas.But what I want to know is : which phase do I have at point C. I know that this is precisely where the phase transition occurs, but imagine... | Phase diagram. When will I have a phase transition? | physics | 2018-01-05T00:00:18.317 |
[
{
"message": "You'll have to forgive me if this question is either extremely elementary or does not make sense — I am a civil engineer with little E/M physics background beyond high school education.I am working on a project that involves the harvesting of energy from what is effectively a huge Faraday flashlig... | Amount of energy that can be stored from Faraday flashlight / linear alternator? | physics | 2018-01-05T00:23:44.767 |
[
{
"message": "I read it in my school book that due to symmetry reasons the electric field lines formed by varying magnetic field are circular but my doubt is where the centre of that circle in space is I mean if we consider a circle of radius r and consider another similar circle with its centre somewhere on th... | How to consider centre for induced electric field circle in a flux varying space? | physics | 2018-01-05T09:29:37.673 |
[
{
"message": "I am a mathematician and I am taking a mathematical physics course. In the part of reaction-diffusion equations, there is something that I do not understand. I have been defined the <a href=\"https://en.wikipedia.org/wiki/Allen%E2%80%93Cahn_equation\" rel=\"nofollow noreferrer\">Allen-Cahn equatio... | Free energy in Allen-Cahn PDE | physics | 2018-01-05T16:13:09.503 |
[
{
"message": "I’ve been thinking about the electroweak phase transition in the early universe, and I have some questions about the form of Coulomb’s law during that epoch. As I understand it, before the electroweak phase transition, the electromagnetic and weak forces were still united as one force. The Higgs h... | Form of Coulomb’s law before the electroweak phase transition | physics | 2018-01-05T16:39:52.110 |
[
{
"message": "We can obtain the classical equations of motion for electromagnetism by considering the vector potential $A^\\mu$ and the electric $\\mathbf E$ and magnetic $\\mathbf B$ fields as independent degrees of freedom.$$\\mathcal L = j^\\mu A_\\mu - A^0 (\\nabla \\cdot \\mathbf E) - \\mathbf A \\cdot (\\... | Can QED be formulated in terms of independent vector potential and bivector fields? | physics | 2018-01-06T01:11:57.083 |
[
{
"message": "Kinetic energy is defined in my textbook to be the work required to reduce an object's speed to zero.If a object is moving with some speed and has a mass then we need some force to brake it. Is the total amount of work (not force) needed the same as the kinetic energy it possesses?",
"role": "... | About kinetic energy | physics | 2018-01-06T08:07:52.643 |
[
{
"message": "If you have a transverse wave traveling with a fixed wavelength and speed (such as light) and that wave changes direction, then it seems as if the wavelength will be distorted while it is moving, as seen in the red bracket in my picture. Does this actually happen, or is this model of a wave not ap... | Does the wavelength of a wave change in the moment it changes direction? | physics | 2018-01-06T15:26:17.527 |
[
{
"message": "In my electromagnetic fields course, we discussed Stokes' theorem and how to unterstand the rotation of a vector field. Therefore, my professor showed us the following image (I stole it from the script and you can see it below, sorry prof). <a href=\"https://i.stack.imgur.com/nfcm2.jpg\" rel=\"nof... | How to understand rotation and Stokes' theorem? | physics | 2018-01-06T16:16:50.877 |
[
{
"message": "What's wrong with the following argument to \"produce\" <a href=\"https://en.wikipedia.org/wiki/Negative_mass\" rel=\"nofollow noreferrer\">negative mass?:Consider two charged bodys of weight $m,M$ of distance $r$ with the electric charge $Q$ and $-Q$. Then the energy of this system is:$$E = (m+M)... | Negative mass effect? | physics | 2018-01-06T16:24:28.547 |
[
{
"message": "Given some coordinates $(x_1,\\dots, x_N)$ and $h$ holonomic constraints, it should always be possible to reduce the coordinates to $n=N-h$ generalized coordinates $(q_1,\\dots, q_n)$. This is guaranteed by the <a href=\"https://en.wikipedia.org/wiki/Implicit_function_theorem\" rel=\"noreferrer\">... | Finding generalized coordinates when the implicit function theorem fails | physics | 2018-01-06T20:52:31.977 |
[
{
"message": "Please See this video <a href=\"https://www.youtube.com/watch?v=j_6JxoL8qD4\" rel=\"nofollow noreferrer\">https://www.youtube.com/watch?v=j_6JxoL8qD4Firstly, at 1:13 in the video, is the work done here by the system or on the system?Secondly, are V final(s) in both cases equal? Are both cases adia... | Why is the work done by the system equal P external x (V final - V initial)? | physics | 2018-01-07T05:07:49.830 |
[
{
"message": "Take a look at these three pictures I made of one of our lightbulbs:<a href=\"https://i.stack.imgur.com/x3YUi.jpg\" rel=\"nofollow noreferrer\"><a href=\"https://i.stack.imgur.com/LHKxl.jpg\" rel=\"nofollow noreferrer\"><a href=\"https://i.stack.imgur.com/bX7Wn.jpg\" rel=\"nofollow noreferrer\">Th... | Why does this lightbulb glow faintly when I thouch it with my hand though it's not connected to the AC-source? | physics | 2018-01-08T12:11:32.533 |
[
{
"message": "<blockquote> At $t=0$, the wave function of a particle with Hamiltonian $$\\mathcal{H}=\\mu B L_y \\equiv \\omega L_y$$ is given by $$\\left \\langle \\mathbf{r}|\\alpha \\right \\rangle \\equiv \\psi\\left ( \\mathbf{r} \\right )= f\\left ( r \\right )\\left ( r+z \\right ).$$ Write the time e... | Time evolution with rotation Hamiltonian | physics | 2018-01-08T18:46:30.223 |
[
{
"message": "Polymers can be modeled as ideal chains and bead-springs (among other various models). However, in an ideal chain, the interactions are entirely entropic, whereas in the bead-spring model, there are also energetic interactions. Does this lead to differences while calculating thermodynamic quantiti... | Understanding roles of energy and entropy in different polymer models | physics | 2018-01-09T15:43:33.247 |
[
{
"message": "If I have a magnetic material that presents a typical hysteresis curve (M vs H), does this observation imply the existence of magnetic domains?Can you have a hysteresis curve in a mono domain material?",
"role": "user"
},
{
"message": "<blockquote> Can you have a hysteresis curve in a... | Hysteresis curves and domains | physics | 2018-01-09T16:18:12.800 |
[
{
"message": "When you take a container with water and begin to heat it, after a while, you will notice that bubbles begin to form. If you wait a bit longer, you will easily (it's so clear) start noticing smudgy heat waves in the water (which I believe is due to change in refractive index of the water). These w... | mysterious waves while boiling water | physics | 2018-01-09T17:24:01.613 |
[
{
"message": "According to <a href=\"https://en.wikipedia.org/wiki/Stone%E2%80%93von_Neumann_theorem\" rel=\"nofollow noreferrer\">Stone-von Neumann theorem, any two canonically conjugate self adjoint operators following the relation: $$[\\hat{q},\\hat{p}]=i\\hbar$$ cannot be both bounded.I am confused about ho... | Stone-von Neumann theorem | physics | 2018-01-09T20:28:36.367 |
[
{
"message": "If we consider a bipartie system that is entangled,$$|\\psi^{AB}\\rangle=\\frac{|{\\uparrow_z\\downarrow_z}\\rangle-|{\\downarrow_z\\uparrow_z}\\rangle}{\\sqrt{2}} $$And we want to know the probability distribution of an experiment that involves only system A, we can use the reduced density matrix... | What is the state of a single electron in an entanglement? | physics | 2018-01-10T08:56:57.507 |
[
{
"message": "Full disclosure, I'm trying to do an exercises but failing to understand it. The course takes for granted some notions I touched many years ago.There's a solid object rotating around a joint. Gyradius and CoM are provided as distances from the joint.Basically the point of the exercise is to calcul... | Gyradius (Radius of gyration) and CoM | physics | 2018-01-10T11:04:53.647 |
[
{
"message": "If we assume that the substance of time is slower in the presence of very high gravity( early years of the universe) then is it not reasonable to assume that as matter gets further apart, that time, due to less gravitational effect will speed up creating the illusion that the velocity of matter is... | Regarding Dark Energy/optical illusion | physics | 2018-01-10T20:05:52.660 |
[
{
"message": "I need to compute the sound velocity of a mixture of different magmas and their gases.Thanks to physics.stackexchange.com I already found the way to compute the sound velocity of the gas, but what about the liquid part?It would be very kind of you to give me an hint on how to compute the sound spe... | sound speed of a liquid mixture | physics | 2018-01-11T13:12:10.683 |
[
{
"message": "<blockquote> The power delivered by a force is given by the relation $$P=\\frac{\\alpha}{\\beta}e^{-\\beta t},$$ where $t$ is time. Find the dimensional formula for $\\alpha$.</blockquote>So, $-\\beta t$ doesn't make sense for the dimensional formula of $P$. But then we have two unknowns and one ... | Find dimensional formula of $\alpha$ | physics | 2018-01-11T15:45:42.317 |
[
{
"message": "Notation$$X \\equiv \\sigma_x \\qquad Z \\equiv \\sigma_z$$IntroductionThe surface code is a quantum error correction code.In the surface code, we have a two-dimensional grid of qubits each coupled to its four nearest neighbors.As shown in Fig. 1, within a row or column, every other qubit is alter... | What are the quiescent states of the surface code? | physics | 2018-01-12T00:40:24.843 |
[
{
"message": "The temperature change in an isothermal process is zero. As a result (if the system is made of an ideal gas) the change in internal energy must also be zero. I don't want to consult the equations. I'm trying to understand this with logic. Temperature change accounts for heat flow. If there's no ch... | In an isothermal process how is the heat change non zero? | physics | 2018-01-12T02:44:46.170 |
[
{
"message": "Given is $$ \\Psi(x,t) = N \\exp \\left(-ax^2 + ibt \\right) $$ On the particle acts a force which is: $$ F = -kx$$ that means that the potential is: $$V = \\frac{1}{2}kx^2$$ the Time-Dependent Schrödinger equation would then look like this: $$i\\hbar\\frac{\\partial}{\\partial x}\\Psi = \\left[... | How to normalize a non-integrable function? | physics | 2018-01-12T03:37:36.907 |
[
{
"message": "Is there any method we can use to convert a photon into a gluon, as they are similar in many respects. For instance, if we pass a $100\\,{\\rm keV}$ photon through a strong electric field, can this photon convert into a gluon?",
"role": "user"
},
{
"message": "To illustrate @knzhou's ... | Can photons be converted to gluons | physics | 2018-01-12T11:57:58.387 |
[
{
"message": "I know that the impact angle is known with the \"traveling vector\" k in respect of the normal vector, let's say z or (0, 0, 1).Doing the math i know it is 45º, but why the reflected wave has the same angle?The EM wave impacts a plane. Another question, what if, instead of a plane, the EM wave imp... | Why the angle of an incident EM wave is the same as the reflected EM wave? | physics | 2018-01-12T18:58:11.660 |
[
{
"message": "As I'm sure folks here know, the principle of equal a priori probabilities, sometimes called the fundamental postulate of statistical mechanics, states the following:<blockquote> For an isolated system with an exactly known energy and exactly known composition, the system can be found with equal ... | Why is the fundamental postulate of statistical mechanics true? | physics | 2018-01-12T20:16:55.803 |
[
{
"message": "As you may probably tell, I am still new to physics and in school, we're learning about waves right now. When I watched how strings vibrate, they looked like transverse wave.So, my initial thought was all waves looked like transverse wave. But then, after learning the chapter about waves, I found ... | How come a string of a musical instrument produces sound when it looks like a transverse wave instead of a longitudinal wave? | physics | 2018-01-13T11:51:27.333 |
[
{
"message": "How do you calculate the moment of inertia of a regular tetrahedron of side a about an axis passing through the center of one of the phases and perpendicular to it?",
"role": "user"
},
{
"message": "The moment of inertia is given by $\\frac{m*s^2}{20}$, where $m$ refers to mass and $s$... | Moment of Inertia of Tetrahedron | physics | 2018-01-13T14:13:30.690 |
[
{
"message": "If we have a rotating object and it's angular velocity is constant, can the angular acceleration ever be different than 0?EDIT : I know it should be $0$, but my book has this formula $$\\frac{d\\vec{\\omega}}{dt}=\\frac{d\\omega\\vec{a}}{dt}= \\frac{d\\omega}{dt}\\vec{a} + \\omega\\frac{d\\vec{a}}... | Angular velocity and acceleration | physics | 2018-01-13T14:33:16.073 |
[
{
"message": "I reorganized the question to clarify exactly what it is that I'm asking.Suppose an experiment is performed where a particle detector records 50 particles per second, on average.Absent any other considerations, it seems easy enough to come up with any number of theories to explain these results. ... | Is it possible to know the efficiency of a particle detector without assuming the truth of Theory (e.g.,, Quantum Theory) | physics | 2018-01-13T23:07:55.990 |
[
{
"message": "I read that in case of liquid the particle in the bulk experiences a negative potential energy due to the force of attraction around it. Particles on the surface, however experiences less potential energy. That is they must have more kinetic energy causing them to move. Is my assessment correct? ... | Is it true that particles on the liquid surface are having high kinetic energy? | physics | 2018-01-14T13:00:03.077 |
[
{
"message": "For example, say you miss a train and therefore meet the love of your life, would this be considered an example of chaos theory?",
"role": "user"
},
{
"message": "No. Life is way more complicated than chaos.The striking point made by chaos theory is that even seemingly simple systems o... | Can chaos theory apply to human interactions? | physics | 2018-01-15T18:15:37.247 |
[
{
"message": "I am using the three rules of Feynman for calculating probabilities (as outlined in <a href=\"http://www.feynmanlectures.caltech.edu/III_03.html\" rel=\"nofollow noreferrer\">http://www.feynmanlectures.caltech.edu/III_03.html)(1) Probability of reaching a state is the square of an amplitude for re... | Applying Feynman rules for calculating quantum amplitudes and probabilities in correct manner | physics | 2018-01-16T16:22:06.807 |
[
{
"message": "I'm following a course about communication technology and the professor said the following multiple times:\"A radio/EW-wave is reflected at an obstacle which is higher/larger than than half of the wave length.\"However, this statement confuses me, as I can not find any similar statement anywhere e... | Reflection of radio waves at an obstacle with size half wavelength | physics | 2018-01-16T19:01:56.370 |
[
{
"message": "When we set the interval(ds) for a given coordinate(i.e. Schwarzschild coordinates) to 0 to calculate for the velocity of light in a gravitational field, we can arrive at an equation such as <a href=\"https://physics.stackexchange.com/questions/77227/speed-of-light-in-a-gravitational-field\">the o... | Is there a difference between what Schwarzschild vs Gullstrand-Painleve predict for c? | physics | 2018-01-17T06:49:39.087 |
[
{
"message": "I didn't had any course on hyperfine interactions and now I am having trouble in solving the Anisotropic Hyperfine Hamiltonian. The problem is of matrix dimensions that have to be considered in the hyperfine term.I have one nucleus of spin $3/2$ and 4 nuclei of spin $1$ and the electron spin is of... | Hyperfine Interaction Hamiltonian | physics | 2018-01-17T10:45:52.923 |
[
{
"message": "After refraction in a prism white light disperses to VIBGYOR colored radiation and made to fall on a flat screen. Are regions immediately below violet rich in ultra-violet radiation and those above red have more infra-red radiation? If so, has any heating been noticed in these edge areas by sensi... | Radiation in color dispersed edge areas | physics | 2018-01-17T15:26:21.593 |
[
{
"message": "Context:Griffith's <a href=\"https://rads.stackoverflow.com/amzn/click/1107179866\" rel=\"nofollow noreferrer\">book on Quantum Mechanics (QM), in Section 2.3.1, tries to solve for the stationary states $\\psi(x)$ of a harmonic oscillator by solving the Time-Independent Schrodinger Equation (TISE)... | Uniqueness of quantum ladder for the harmonic oscillator | physics | 2018-01-17T23:00:21.303 |
[
{
"message": "Soap films under gravity have a gradual thickness gradient, as evident in the smooth interference fringes.<a href=\"https://i.stack.imgur.com/qpDmE.jpg\" rel=\"nofollow noreferrer\">But why is there an abrupt transition from \"white\" to transparent 2/3 of the way up? This transparent region grows... | Soap film sudden transition | physics | 2018-01-17T23:18:36.717 |
[
{
"message": "There are three kinds of representations: real, complex, and pseudoreal. A complex representation is not equivalent to its conjugate, and a real one is, which is pretty straightforward. A pseudoreal representation is also equivalent to its conjugate, but the change of basis matrix that relates the... | Physically, what is a pseudoreal representation? | physics | 2018-01-17T23:57:55.523 |
[
{
"message": "In the <a href=\"https://ncatlab.org/nlab/show/causal+perturbation+theory\" rel=\"nofollow noreferrer\">Epstein-Glaser formulation of a QFT, the would-be divergences are taken care of by meticulously splitting the distributions that appear in the construction of the $S$-matrix (or correlation func... | How do anomalies work in the causal formulation of QFT? | physics | 2018-01-18T01:30:15.560 |
[
{
"message": "What is the classical description of a system consisting of two point charges moving under the influence of the fields generated by their presence (no additional external fields are assumed)? In the lab frame, these point-charge particles will in general be moving, so both (relativistically transf... | Complete classical description of two interacting charges | physics | 2018-01-18T12:48:14.637 |
[
{
"message": "Qualitatively, I understand that water can be supercooled when:It is relatively pure.It is in a container that is relatively smooth of defects.The effect of both of these is to reduce nucleation points, which are needed to provide a place for the ice crystals to start growing.Rate of cooling may a... | When can water be supercooled? | physics | 2018-01-18T23:50:07.220 |
[
{
"message": "Considering omni-directional sound source,why doesnt sound decrease by 12db per doubling of distance?I read about sound decreasing with distance and everybody claim that sound decrease 6db per doubling of distance,that is in my opinion impossible and completly wrong becose the soundwave will sprea... | Why doesnt sound decrease by 12db? | physics | 2018-01-19T07:25:18.543 |
[
{
"message": "Using Euler's method I got this graph. I used separation between angles $10^{-10}$, $\\Delta t$ of integration 0.0001s and max time 100s. The initial angles are the same ($\\theta_1=\\theta_2$). I expected the values to be a lot higher at high initial energy positions. Have I made any mistakes?",
... | Max Lyapunov Exponent of a Double Pendulum | physics | 2018-01-19T12:18:11.650 |
[
{
"message": "I have two lasers, both illuminate on a photo diode, i'm not very sure what's physically going on in the photo diode. My understanding is the following: The electric fields of both lasers add up and get destroyed in the photo detectors, the electrons excited by photons in the process generates a p... | Understanding the principle of photo diode signal generation | physics | 2018-01-19T15:48:13.763 |
[
{
"message": "In the following question the OP asked what is meant in chapter 27-4 of Feynman's Lectures on Physics Vol.II by the ambiguity in the location of electromagnetic field energy:<a href=\"https://physics.stackexchange.com/questions/224349/why-is-there-ambiguity-of-the-field-energy\">Why is there ambig... | Why is there ambiguity of the electromagnetic field energy? | physics | 2018-01-20T00:06:00.877 |
[
{
"message": "In the LIGO paper on the first detection of gravitational waves, they have a <a href=\"https://commons.wikimedia.org/wiki/File:Simplified_diagram_of_an_Advanced_LIGO_detector.png\" rel=\"nofollow noreferrer\">diagram of one of the interferometers in which they label the mirrors with the conceptual... | Why is it correct to conceptualize LIGO's mirrors as "test masses?" | physics | 2018-01-20T02:09:11.137 |
[
{
"message": "It is known that $k$-vector is defined up to a reciprocal lattice vector.So we can write, in the one-dimensional case,$$k'=k+ \\frac{n\\pi} {a}.$$But this corresponds to a completely different wavelength and energy! In fact, energy is infinite for $n \\rightarrow \\infty$. Is it normal after all?"... | Ambiguity of $k$-vector in solid state physics | physics | 2018-01-20T19:30:18.643 |
[
{
"message": "This problem is in reference to Q3.239 in Problems in General Physics by I.E. Irodov.Question: N = $2.5*10^3 $wire turns are uniformly wound on a wooden toroidal core of very small cross-section. A current I flows through the wire. Find the ratio 1 of the magnetic induction inside the core to tha... | Magnetic Induction at the centre of a Toroid | physics | 2018-01-20T22:23:42.070 |
[
{
"message": "Currently, I understand that under the aether model, the two perpendicular light rays (which were created when a monochromatic light was split by a half silvered mirror) will be out of phase when they reach the interferometer. I also understand that the light rays interact in some way at the inter... | Michelson Morley Experiment- how are fringe shifts created? | physics | 2018-01-21T06:39:21.267 |
[
{
"message": "$PHP^{-1}=-H$ (particle-hole symmetry)and $\\Gamma H \\Gamma^{-1}=-H$ (chiral symmetry) I understand why we get the negative signs but im just a bit confused as to why such equalities mean $H$ is particle hole and chiral symmetric. When we say $H$ is symmetric under some operation, like time rever... | Why particle hole symmetry and chiral symmetry are called symmetries? | physics | 2018-01-21T10:23:39.633 |
[
{
"message": "I frequently move dust/salt-like material from one small plastic container to another. I do this with a steel rod about 3x the thickness of a paper clip that has a flattened end. Sometimes the material is statically charged and either sticks to the sides of the parent container and while scooping ... | Can I turn a thin steel rod into an electromagnet and have it collect statically charged dust? | physics | 2018-01-21T16:44:50.560 |
[
{
"message": "Let $\\mathcal L(\\phi,\\partial\\phi)$ be a Lagrangian for a field $\\phi$. It is known that the Lagrangian $\\mathcal L$ and the Lagrangian $\\mathcal L+\\partial_\\mu K^\\mu$ produces the same physics, provided that $K$ depends on spacetime points through $\\phi$ and $x$ only (eg. not through $... | Why is dependence on derivatives not a problem in the definition of canonical energy-momentum tensor? | physics | 2018-01-21T18:33:05.267 |
[
{
"message": "I've been studying information theory, and I'm curious about how many bits of information an elementary particle, like an electron, could have. If we take only the spin, of course it has 1 qubit (2 quantum states), but in the context of QFT, we could give it a qubit by just \"being there\" or not.... | How many bits of information does an elementary particle have? | physics | 2018-01-21T23:51:38.877 |
[
{
"message": "What I am trying to solve right now is that I have a magnetic particle (nanoparticle to be exact) floating in liquid that is viscoelastic and apply sinusoidal magnetic field. The applied magnetic field will create torque that aligns the magnetic moment of the particle to the field. Also, the parti... | Shear stress of a suspended sphere in a viscoelastic fluid | physics | 2018-01-22T12:57:06.320 |
[
{
"message": "Can electron stick ''glue'' with proton if they collide with each other? What will happen if electron collide with pion? Can it glue with it or not?",
"role": "user"
},
{
"message": "<blockquote> Can electron stick ''glue'' with proton if they collide with each other?</blockquote>Dep... | About electron and proton | physics | 2018-01-22T18:25:53.080 |
[
{
"message": "I have learned that due to doppler effect the wavelength of light increases when source is moving away from observer. Also this proves big bang theory and also universe is expanding. Like red shift , is there anything like blue shift that decrease the wavelength of light? Is there any experiment... | Doppler effect and shift in visible region and constant velocity of waves | physics | 2018-01-23T15:41:39.270 |
[
{
"message": "Towels (and coats) are often stored on hooks, like this:<a href=\"https://i.stack.imgur.com/WaSiEl.jpg\" rel=\"noreferrer\">To the untrained eye, it looks like the towel will slide off from its own weight. The hook usually angles upwards slightly, but a towel does not have any \"handle\" to string... | How do towels stay on hooks? | physics | 2018-01-23T21:10:25.330 |
[
{
"message": "I'm trying to understand the time delay induced on each photon when several individual photons travel in an open space from a sender to a receiver for example in the application of Quantum Key Distribution. So what I understand so far is light(photon) travel around 299,792 km (186,282 miles) per s... | Time Delay on Multiple Photons when travelling from one place to another | physics | 2018-01-24T06:01:39.450 |
[
{
"message": "I'm a bit confused over whether the parity operator should always square to one. My impression was that if $W(\\Lambda, a)$ was a representation of the Poincare group, then the parity operator $\\hat{P}$ was defined to be $W(P,0)$ where $P$ is the improper parity Lorentz transformation. Since $P^2... | Does the parity operator always square to 1, in relativistic quantum field theory? | physics | 2018-01-24T10:49:20.820 |
[
{
"message": "Introduction(The idea to this question came from my answer to <a href=\"https://physics.stackexchange.com/questions/380655/uniqueness-of-quantum-ladder-for-the-harmonic-oscillator/381005#381005\">Uniqueness of quantum ladder for the harmonic oscillator)The Hamiltonian $H$ for quantum harmonic osci... | Non-integer powers for the quantum harmonic oscillator ladder operators and spectrum uniqueness | physics | 2018-01-24T17:10:20.673 |
[
{
"message": "Green's Functions can be used to solve boundary value problems. In particular, there is a textbook standard recipe for dealing with von Neumann boundary conditions.But how can I find a particular Green's function?Example:A cuboid width=a, length=b and height=c, defining a simple surface.According ... | How is Neumann's green function found for a particular surface? | physics | 2018-01-25T13:13:03.687 |
[
{
"message": "I have an MD simulation that I'm pretty confident it works correctly. One of my tests was to check if the velocity distribution follows a Maxwell Boltzmann distribution. I printed out the velocity of just one atom to file, and when I histogrammed it, I obtained the following plot. The solid curve ... | Maxwell Boltzmann Distribution in Molecular Dynamics Simulation | physics | 2018-01-25T20:11:12.437 |
[
{
"message": "Strongly-correlated metals often become insulators due to the repulsive Coulomb interaction, and the basic model here is the Mott-Hubbard Model:$$H=-t\\sum(\\hat{c}_{i,\\sigma}^{\\dagger}\\hat{c}_{j,\\sigma}+\\hat{c}_{j,\\sigma}^{\\dagger}\\hat{c}_{i,\\sigma})+U\\sum\\hat{n}_i^{\\uparrow}\\hat{n}_... | Why is the distinction between Mott Insulators and Charge Transfer Insulators important? | physics | 2018-01-25T21:18:50.200 |
[
{
"message": "I was watching a video on \"<a href=\"https://youtu.be/g_IaVepNDT4?t=4m17s\" rel=\"nofollow noreferrer\">How Does a Quantum Computer Work?\". I'm confused about what they mean by: \"Although the qubits can exist in any combination of states, when they are measured they must fall into one of the ba... | Which set of basis states can a quantum system of qubits actually collapse to? | physics | 2018-01-26T06:51:05.470 |
[
{
"message": "I have a wheel spinning away from me in the vertical plane. The angular momentum is pointing to the left. The axis of rotation is horizontal, and it is supported on either side by a bearing and the whole mount is on a turntable constrained to rotate about the Z-axis. Think of a free spinning bike ... | Where does the energy used to rotate the axis of a flywheel orthogonally go? | physics | 2018-01-26T20:12:25.877 |
[
{
"message": "Before us are two half-integer-spin particles. Their spin directions are parallel, aligned with the line connecting their locations. They are indistinguishable but for the fact we have affixed the label \"A\" to the one on the left and \"B\" to the one on the right. Both spins point to the right. ... | particle exchange versus spin | physics | 2018-01-27T20:05:11.733 |
[
{
"message": "Before us are two half-integer-spin particles. Their spin directions are parallel, aligned with the line connecting their locations. They are indistinguishable but for the fact we have affixed the label \"A\" to the one on the left and \"B\" to the one on the right. Both spins point to the right. ... | particle exchange versus spin | physics | 2018-01-27T20:05:11.733 |
[
{
"message": "So, we all know the world famous equations$$E^2=\\left(mc^2\\right)^2+(pc)^2\\tag{1}$$$$E=hf={hc\\over{\\lambda}}{\\rm\\ (for\\ light)}\\tag{2}$$$$p={h\\over{\\lambda}}\\tag{3}$$We can realise in eq.2 and 3. The $hc\\over{\\lambda}$ can be replaced by $pc$And the $E=pc$ can be used in eq.1 to obta... | Light cannot be at rest. Can this be proven mathematically? | physics | 2018-01-28T01:36:14.577 |
[
{
"message": "wikipedia says:<blockquote> The CMB has a thermal black body spectrum at a temperature of (T=) 2.72548±0.00057 °K. The spectral radiance dEν/dν peaks at 160.23 GHz</blockquote>Could you explain how is T= 2.72 K obtained? is it an average, is it an integral or what? Is the thermal spectrum fixed ... | How is temperature of space calculated? | physics | 2018-01-28T07:50:45.797 |
[
{
"message": "Firstly, I know that the equation for the <a href=\"https://en.wikipedia.org/wiki/Escape_velocity\" rel=\"nofollow noreferrer\">escape velocity is $$v_{\\text{escape}}=\\sqrt{\\frac{2\\,GM}{r}}\\tag{1}$$ and understand it's derivation.The following is such a simple derivation; for a test body of m... | Why is $v=\sqrt{\frac{GM}{r}}$ not a valid equation for escape velocity? | physics | 2018-01-28T08:20:16.123 |
[
{
"message": "I am thinking of the thermocouple as just two wires twisted together and the twisted section being heated (hot junction). If one of the wires has a larger amount of the wire heated, but the same temperature difference, the voltage reading is the same for a smaller area.From my understanding of a t... | Why does changing the size of a hot junction not affect the voltage output of a thermocouple? | physics | 2018-01-28T10:22:01.903 |
[
{
"message": "Updated Preface (in response to comments).Per the title, this question is focused on understanding \"the specific photon-particle interaction by which momentum is transferred in radiation pressure\".In the original question I included a preface which gave an example of what I meant by \"radiation ... | What is the specific photon-particle interaction by which momentum is transferred in radiation pressure? | physics | 2018-01-28T18:58:40.377 |
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