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": "This example is given in my book as I know voltage of the source in an RLC circuit can be obtained using following formula $$u=U_m*sin (wt+Φ)$$But in this example the voltage of source is given in the form of $$u=U_m*sinwt$$Why is this so?",
"role": "user"
},
{
"message": "It is often ... | Voltage of source in RLC circuit | physics | 2018-02-27T05:57:33.110 |
[
{
"message": "$$Z=\\sum_i e^{-\\beta E_i}$$I am relatively new to statistical mechanics, and I am wondering if the individual energies ($E_i$) in the equation above are free energies associated with each microstate? If it is, would it be Gibb's Free Energy or Helmholtz's Free Energy?",
"role": "user"
},
... | Partition Function- Are the energies of the individual microstates, free energies? | physics | 2018-02-27T15:20:03.880 |
[
{
"message": "I'm trying to show, for the Hamiltonian $H = \\vec{P}^2/2m + V(\\vec{X})$, that $[\\vec{L}^2,H]=0$ if $V(\\vec{X}) = V(|\\vec{X}|)$, and I pretty much almost have it, there's just one thing I'm getting messed up on.So what I did was:$$ [\\vec{L}^2,H] = [L_x^2 + L_y^2 + L_z^2, \\frac{\\vec{P}^2}{2m... | Angular momentum squared and Hamiltonian? | physics | 2018-02-27T15:43:37.503 |
[
{
"message": "I am reading about lenses and I came across a post: <a href=\"https://physics.stackexchange.com/questions/241348/what-is-exactly-an-virtual-object-from-the-point-of-view-of-lens-maker-s-f\">What is exactly an ‘virtual object’ ? ( From the point of view of lens maker’s formula ) , which defines vir... | Can a virtual object be on the same side of the image? | physics | 2018-02-28T06:43:57.830 |
[
{
"message": "The question of how a receiving antenna works has been asked on this site before, such as here <a href=\"https://physics.stackexchange.com/q/19653/\">How does a receiving antenna get an induced electric current? and here <a href=\"https://physics.stackexchange.com/q/285460/\">How does a receiving ... | How does a receiving antenna work given that the electric field is 0 in conductors? | physics | 2018-02-28T07:32:53.317 |
[
{
"message": "I am working on the Zeeman Effect lab experiment. It involves diffraction and splitting of circular fringes due to magnetic fields.I have taken pictures of the interference pattern, described by a set of bright fringes. Now, I need to measure radii of the fringes from the center.However, I am tryi... | How to find bright fringe peaks from an image? | physics | 2018-02-28T07:33:10.853 |
[
{
"message": "If you measure the sound pressure level from a certain distance, you can recalculate them to another distance. But what is, if a noise is generated directly on your membrane (microphone membrane or eardrum for example). How is the sound pressure calculated in this situation? Because the distance f... | Acoustics; Distance Law | physics | 2018-02-28T10:29:43.187 |
[
{
"message": "Why isn't the graph a straight line but is rather curved ?",
"role": "user"
},
{
"message": "The graph you posted is of the <a href=\"https://en.wikipedia.org/wiki/Barometric_formula\" rel=\"noreferrer\">barometric formula. Compared to the link I posted, your axes are swapped, but neve... | Line graph of altitude and pressure | physics | 2018-02-28T14:16:35.660 |
[
{
"message": "Basically I am trying to plot $H/H_0$ versus $a(t)$ for the Lambda CDM Model. In a paper I am referring to $H/H_0$ decreases with increasing $a(t)$ until a point ($a[t]\\sim 0.7$) and then it starts increasing again until today ($a[t]=1$).When I try doing the same plot using Wikipedia's page on th... | Hubble Parameter as a function of the scale factor in Lambda CDM Model | physics | 2018-02-28T19:16:46.060 |
[
{
"message": "I am struggling to understand the nature of the components of the Dirac matrices.If we view the four components of a Dirac spinor as $\\psi^a$ with $a$ being a 'spinor' index, then if a gamma matrix acts on this to give another spinor, then it's indices would be ... ?? $\\gamma^{\\mu b}{}_{a}$ whe... | spinor vs vector indices of Dirac gamma matrices | physics | 2018-03-01T04:32:34.350 |
[
{
"message": "Lorentz transformations help us transform coordinates of one frame to that of another.For example, let the coordinates of an event in an inertial frame $S$ be $(x, t)$, then the coordinates in frame $S'$ is got as $(x', t')$ using Lorentz transformations.This means that there is some kind of equiv... | What is an event in Special Relativity? | physics | 2018-03-01T13:11:06.400 |
[
{
"message": "Lorentz transformations help us transform coordinates of one frame to that of another.For example, let the coordinates of an event in an inertial frame $S$ be $(x, t)$, then the coordinates in frame $S'$ is got as $(x', t')$ using Lorentz transformations.This means that there is some kind of equiv... | What is an event in Special Relativity? | physics | 2018-03-01T13:11:06.400 |
[
{
"message": "This may seem like a stupid question, and maybe it is, but it is not meant to be. In Einsteins relativity theory we live in 4 dimensional spacetime. Though the way we normally \"imagine\" the world, we tend to believe that we live in a 3 dimensional newtonian space with a separate absolute time di... | What shape is the Earth in relativity theory | physics | 2018-03-01T19:01:15.237 |
[
{
"message": "I'm currently reading K. Becker, M. Becker and John. H. Schwartz book on string theory. I have a question about Calabi-Yau compactifications of IIB string theory. In chapter 9 page 403, Why do we don't consider self-dual four-form with two fundamental index and two antifundamental index $C_{ij\\b... | Effective action of IIB Calabi-Yau compactification | physics | 2018-03-02T13:37:23.660 |
[
{
"message": "<br>I have the following definition of star product,\\begin{equation}\\star=\\exp\\left[\\frac{i\\hbar}{2}\\left(\\frac{\\overleftarrow{\\partial}}{\\partial Q^{I}}\\frac{\\overrightarrow{\\partial}}{\\partial P_{I}}-\\frac{\\overleftarrow{\\partial}}{\\partial P_{I}}\\frac{\\overrightarrow{\\part... | Star Product and Poisson Brackets | physics | 2018-03-02T18:13:12.223 |
[
{
"message": "Given the following electrical circuit:<a href=\"https://i.stack.imgur.com/KaQaT.png\" rel=\"nofollow noreferrer\">How to explain that L and K are equipotential?More generic question: why given any electrical circuit with axial symmetry, points that belong to the axis are equipotential:<a href=\"h... | Why are points on the axis of a circuit with axial symmetry equipotential? | physics | 2018-03-02T20:26:20.047 |
[
{
"message": "For lack of a better image, I am searching for the moment of inertia of this<a href=\"https://i.stack.imgur.com/HV4Vv.jpg\" rel=\"nofollow noreferrer\">where$\\ r_1 = r_2$ (negligible thickness), and where the object would be rotating around its central diameter, which is perpendicular to the z-ax... | How to derive the moment of inertia of a thin hoop about its central diameter? | physics | 2018-03-02T23:51:50.623 |
[
{
"message": "For a medical experiment I am doing, I need an equation to find the angle at which someone will lean before falling. I am not mathematically inclined in terms of advanced stuff, I am more so of a trigonometry person.I assume factors that will be needed are BMI, including height and weight, but tha... | Human Lean Equation | physics | 2018-03-03T02:05:15.890 |
[
{
"message": "I am working with lattice Boltzmann simulations of multiphase flow. The Reynolds number from experiments is $\\mathcal{O}(10^{-3})$. For stability reasons, the closest match I can get in simulation is $\\mathcal{O}(10^{-1})$. So my question is how important is the match between the two values for ... | Matching Reynolds numbers in microfluidics | physics | 2018-03-03T15:35:50.507 |
[
{
"message": "My textbook states :<blockquote> The extent of polarization of dielectrics depends on the relative strength of two mutually opposite factors - the dipole potential energy tending to align the dipole with the external field and thermal energy tending to disrupt the alignment.</blockquote>I know th... | How is thermal energy and dipole related? | physics | 2018-03-04T05:34:38.617 |
[
{
"message": "I'm trying to understand quantum teleportation and I was wondering if anyone could provide an intuition about it. I have seen the derivation but it still bugs me.You start with an entangled pair of qbits in a Bell state: $$\\frac{|00\\rangle+|11\\rangle}{\\sqrt{2}}$$You want to 'teleport' the qbit... | Intuition on quantum teleportation | physics | 2018-03-04T19:46:51.350 |
[
{
"message": "I am studying Maxwell's equations and their use to derive a wave equation to derive the behaviour of electromagnetic waves in vacuum. In the case of plane waves, EM fields can be described by:$\\vec E_z = \\vec E_0e^{i(kz - wt)}$$\\vec B_z = \\vec B_0e^{i(kz - wt)}$$ \\nabla^2E = \\mu_o\\epsilon_0... | Relationship between the magnetic and electric component of an EM field | physics | 2018-03-04T20:39:07.577 |
[
{
"message": "Is the definition of the adjoint spinor $\\bar{\\psi}=\\psi^\\dagger \\gamma^0$ forcing a particular choice of representation of the Dirac matrices (or a subset of the possible choices)?More precisely, I assume (possibly incorrectly) that the adjoint of $\\psi$ can always be written as $\\psi^\\da... | Choice of Dirac gamma matrix representation and definition of adjoint spinor | physics | 2018-03-05T04:21:49.413 |
[
{
"message": "Even though I’m familiar with quantum mechanics, I’m unfamiliar with general relativity, so I hope for an explanation simple enough that I can understand.As far as I know the following three (contradictory?) statements are correct, how do they coexist?Light is described as a reservoir of photons, ... | Source of Light bending | physics | 2018-03-06T02:04:08.183 |
[
{
"message": "I was looking for the equations that are used by the GPS receiver to calculate its position and time correction (bias). By looking at the <a href=\"https://en.wikipedia.org/wiki/Global_Positioning_System#Navigation_equations\" rel=\"nofollow noreferrer\">Navigation Equations on Wikipedia, I don't ... | How are GPS corrected for special/general relativity? | physics | 2018-03-06T02:49:12.120 |
[
{
"message": "Will the bulb glow in this circuit? Why not? I think the bulb should glow because there's a potential difference.<a href=\"https://i.stack.imgur.com/0PWOS.jpg\" rel=\"nofollow noreferrer\">",
"role": "user"
},
{
"message": "It will not glow until the circuit is completed. The batterie... | Will the bulb glow in this circuit? | physics | 2018-03-06T16:11:22.270 |
[
{
"message": "What is the relationship between Gravity and Inertia? Einstein told us that gravity and inertia are identical. And from the fact that two different masses fall at the same rate, I believe we can say that gravity and inertia are equal (That is, the inertia of a dropped larger mass is exactly suff... | What is the relationship between gravity and inertia? | physics | 2018-03-06T17:27:39.567 |
[
{
"message": "What is the relationship between Gravity and Inertia? Einstein told us that gravity and inertia are identical. And from the fact that two different masses fall at the same rate, I believe we can say that gravity and inertia are equal (That is, the inertia of a dropped larger mass is exactly suff... | What is the relationship between gravity and inertia? | physics | 2018-03-06T17:27:39.567 |
[
{
"message": "In the equations for time dilation and length contraction, what is a good way of choosing who is the relative time and length and who is the proper time and length so we can get good measurements of the variables? Should the proper time and length be the static observer $t$ and $l$ and the moving ... | Relativity equations | physics | 2018-03-07T01:50:19.463 |
[
{
"message": "I am quite comfortable with the complex wavefunctions for the three p-orbitals ($ p_{0},p_{1},p_{-1}$) and the construction of the real-valued versions ($ p_{z},p_{x},p_{y}$) from the $ \\pm m $ superpositions (there are plenty of questions here relating to that). My question is not regarding the ... | Why exactly is it useful to construct the real-valued p-orbitals? | physics | 2018-03-07T08:58:21.167 |
[
{
"message": "I am a little bit confused about photon particle/wave duality. Do we have to interact with photon to detect it? Or without interacting photon, only by its wave nature, can we detect the existence of a photon. Consider the following image:<a href=\"https://i.stack.imgur.com/QbtGF.jpg\" rel=\"nofoll... | Is it possible to detect a photon without intercepting it? | physics | 2018-03-07T15:23:42.520 |
[
{
"message": "I'm sorry if my question is too classic and basic.As Dirac-Bergmann algorithm for Hamiltonian formalism, I find out that a Hamiltonian system is inconsistent if Poisson bracket of primary constraints and Hamiltonian $$\\{f_{i},H\\}=1\\approx 0$$If the Poisson brackets are equal to $0$ or produce n... | Identify a Hamiltonian system consistent or not? | physics | 2018-03-08T01:59:59.983 |
[
{
"message": "Are eigenfunctions of observables solutions to the time-dependent Schrödinger equation? Or is this not necessarily the case? From what I had been reading they are not necessarily solutions to Schrödinger, but their associated eigenvalues are possible measurements results. Not only that, the eigenf... | Eigenfunctions of observables | physics | 2018-03-08T22:59:11.577 |
[
{
"message": "Naively one might expect the W weak vector bosons to have slightly higher mass than the Z due to EM self-energy, while the opposite is true (80 vs. 91 Gev). Presumably due to the strong interactions and mediated by quarks since that is the only particle coupled to both interactions, but I can't fi... | Calculating $W$ - $Z$ bosons mass difference | physics | 2018-03-09T00:59:37.543 |
[
{
"message": "Consider the shm for a single particle. Then the particle's position is given by (assume zero initial phase):$$x = a \\times \\sin(\\omega t)$$The infinitesimal probability of finding a particle between $x$ and $x + dx$ is:$$dp(x) = \\frac{dt}{T} = \\frac{dt \\times \\omega}{2\\pi} = \\frac{dx}{2\... | Particle ensemble performing shm, calculate amplitude pdf | physics | 2018-03-09T09:12:03.593 |
[
{
"message": "<blockquote> Imagine we want to take the partial derivative of a quantity, we will call it $\\rho_i = f(F(r_{ij}))$ with respect to a particle's position vector, $\\vec{r}_k$. </blockquote>In mathematical terms, this would be expressed as:$$\\frac{\\partial \\rho_i}{\\partial \\vec{r}_k} = \\frac... | Partial Derivative of a scalar (absolute distance) with respect to its position vector | physics | 2018-03-09T10:35:14.847 |
[
{
"message": "Given the wave equation$$u_{xx}(x,t)=\\frac {1}{c^2}u_{tt}(x,t) $$with initial conditions:IC1: $$u(x,0)= f(x)$$IC2: $$u_{t}(x,0)= g(x)$$Why isn't $g(x)$ always equal to $f_t(x)$?<br>For example, if $t=0$ is the time that a snapshot is taken of a freely traveling wave it seems to me that it must ... | Intuition into why the wave equation needs the second initial condition (e.g. velocity) | physics | 2018-03-09T19:38:52.853 |
[
{
"message": "In the Abelian-Higgs model, $$S=\\int d^{3}x\\left\\{-\\frac{1}{4g^{2}}F_{\\mu\\nu}F^{\\mu\\nu}+|D\\phi|^{2}-a|\\phi|^{2}-b|\\phi|^{4}\\right\\}\\tag{5.34}$$there is a $U(1)$ gauge symmetry. In David Tongs' lecture notes <a href=\"http://www.damtp.cam.ac.uk/user/tong/qhe.html\" rel=\"nofollow nore... | Global $U(1)$ symmetry of 2+1D Abelian-Higgs Model | physics | 2018-03-09T23:11:24.793 |
[
{
"message": "Actually I'm trying to figure out what is time and how it works, imagine there are only 2 photons in the universe (and assuming they are not traveling in parallel). Since photon do not have any inertial frame, so can I safely say that in this particular scenario time do not exist because otherwise... | Only 2 photons in the universe? | physics | 2018-03-10T08:25:39.653 |
[
{
"message": "If you have an object moving at u initial velocity with no acceleration, and a surface with a $$\\mu_k$$ frictional coefficient, how can you calculate its final velocity after having traveled d distance over this surface?Would I also need mass m to figure this out?I've tried looking for a formula ... | How to calculate a change in velocity as a result of friction? | physics | 2018-03-10T08:27:46.903 |
[
{
"message": "I am reading the following article dealing with the properties of Dirac fermion in condensed matter physics : <a href=\"https://arxiv.org/abs/1410.4098\" rel=\"nofollow noreferrer\">https://arxiv.org/abs/1410.4098In the page 5 of this article, the formula for the eigenvector of the Dirac fermion i... | Relation of Berry phase and winding number | physics | 2018-03-10T15:22:43.197 |
[
{
"message": "As far as I've understood, quantum decoherence is the \"loss\" of quantum coherence. To a person who knows almost nothing about quantum mechanics, who studied physics only at high school and who is more or less mathematically educated (i.e. knows the basics of linear algebra, calculus, etc), how w... | What is quantum coherence and decoherence in Layman's terms? | physics | 2018-03-10T17:28:02.820 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/TEhW6.png\" rel=\"nofollow noreferrer\"><a href=\"https://i.stack.imgur.com/mIZb3.png\" rel=\"nofollow noreferrer\">Attached above is an example problem from College Physics by Nicholas Giordano.Of course, the problem is extremely simple - and I solved it too; h... | Oscillation of Two Fluid Interface in a U-tube: The Story before Statics | physics | 2018-03-11T06:45:22.490 |
[
{
"message": "Decoupling of photons from the cosmic plasma or thermal bath is said to be a point of departure from thermal equilibrium. But we know that the cosmic microwave background (CMB), consisting of the decoupled photons, fits a blackbody distribution curve to an astonishing accuracy of $1\\%$. But therm... | If photon decoupling was a departure from equilibrium why does CMB exhibit a blackbody spectrum? | physics | 2018-03-11T10:00:05.517 |
[
{
"message": "Referring to Einstein's train hit by lightning bolts thought experiment.What if, in the middle of the train, together with the moving observer there is a stopwatch, with 2 displays.One display stops counting when the clock is hit by the beam coming from the left, and the other stops with the beam ... | Einstein's train experiment with clocks | physics | 2018-03-11T15:00:06.347 |
[
{
"message": "I recently watched at a talk by Cumrum Vafa in which he stated that the cosmological constant allows us to define a time-scale $T_\\Lambda=1/\\sqrt{E_\\Lambda}$. The time scale of this time is about 10¹¹ years, or about 10 times the current age of the Universe. Can we know what this time scale is ... | Cosmological constant phase transition? | physics | 2018-03-11T19:18:57.133 |
[
{
"message": "Following a talk by Cumrum Vafa, I understood that light branes are important as he quoted the formula:$$m\\sim \\exp(-\\alpha M/M_P)$$and then, he stated that light massive particles AND extended objects (particle/p-brane species) are produced as we get $M>M_P$, where $M_P$ is the Planck mass.... | Light branes and swampland/landscape | physics | 2018-03-11T20:12:26.733 |
[
{
"message": "I don't want a rigorous proof of gauss's law but, I cant understand why only symmetric charge distributions are found their application in Gauss's law. A source says;<blockquote> Now imagine a sphere that is not uniformly charged. Suppose there is more charge on one side of the sphere than the o... | Why is a symmetric charge distribution required for application of gauss's law? | physics | 2018-03-12T14:15:29.660 |
[
{
"message": "In Kolb and Turner's Early Universe, (see <a href=\"https://books.google.co.in/books?id=FwpQDwAAQBAJ&pg=PT15&lpg=PT15&dq=Variation%20in%20the%20CMBR%20temperature%20in%20different%20directions%20is%20expected%20due%20to%20several%20effects:%20the%20motion%20of%20our&source=bl&o... | Effect of local reference frame and rotation of Universe in CMBR anisotropy | physics | 2018-03-12T17:26:49.890 |
[
{
"message": "In the paper <a href=\"https://arxiv.org/abs/1606.01989\" rel=\"nofollow noreferrer\">A Duality Web in 2 + 1 Dimensions and Condensed Matter Physics,on page 34, it talks about the periods of a closed $2$-form. Consider the following path integral,$$\\int\\mathcal{D}B\\;\\exp{\\left\\{-\\frac{i}{8\... | What are periods of field strength? | physics | 2018-03-12T19:11:28.910 |
[
{
"message": "I have thought of this question due to personal experience. I am short-sighted, and over the last three years my short-sightedness has worsened. Taking a lifeguard certificate again now that I did already three years ago, I noticed while diving that I have almost no vision anymore when trying to f... | Refraction: Swimming goggles, short-sightedness, and underwater vision | physics | 2018-03-12T20:37:33.927 |
[
{
"message": "Admittingly this seems rather simple to be a real problem with the theory so there is problably something I’m not understanding. However I’m very interested on how to overcome this paradox. So here goes. It involves 4 observers A1, A2 (not moving wrt each other) in inertial reference frame A; B1, ... | Special Relativity Paradox at low speed | physics | 2018-03-13T01:18:14.187 |
[
{
"message": "I was reading a wonderful explanation of matrix mechanics on mathpages<a href=\"http://www.mathpages.com/home/kmath698/kmath698.htm\" rel=\"nofollow noreferrer\">1. There we see that $\\hat{q}_{mn}=q_{mn}\\exp(i(E_m-E_n)t/\\hbar )$ and consequently using Hamilton's classical equations we arrive at... | Energy differences and matrix mechanics | physics | 2018-03-13T05:40:50.293 |
[
{
"message": "I know that generally the uncertainty in the mean of a sample should be equal to: $\\frac{V_{max} - V_{min}}{2} $where $V_{max}$ is the maximum value and $V_{min}$ the minimum value of the sample of data.However, what if each value has its own uncertainty? For example, I have to values:$R1 = 12.8 ... | Uncertainty in the average of two measurements (with their respective uncertainty) | physics | 2018-03-13T16:59:38.950 |
[
{
"message": "In between a rainbow, the sky appears much brighter because all the colors can get reflected in the raindrop.<a href=\"https://i.stack.imgur.com/hGtHf.jpg\" rel=\"nofollow noreferrer\">The maximum angles at which red light and blue light get reflected reflected are $42^{\\circ}$ and $40^{\\circ}$... | Why can the blue colour in a rainbow be seen? | physics | 2018-03-13T22:09:30.980 |
[
{
"message": "Can quark theory account for the masses and radiuses of the proton and other elementary particles? What kind of orbits, if any, do the three quarks in a proton follow? Do the two positively charged quarks orbit the third negatively charged quark in the center, or are the orbits of the three quarks... | Does quark theory account for the masses and radiuses of the elementary particles? | physics | 2018-03-13T23:02:39.900 |
[
{
"message": "Consider 3 point masses in 1+1D flat Minkowski spacetime initially at rest w.r.t. each other and equally separated:$A----B----C$Suddenly, $A$ acquires a speed towards $C$ of $0.97c$. This corresponds to a Lorentz factor $\\gamma(v) \\simeq 4$.From $A$'s viewpoint, distances to $B$ and $C$ are cont... | No spatial ordering in 1+1D flat Minkowski spacetime? | physics | 2018-03-14T01:45:05.250 |
[
{
"message": "I am in need to shave a special material (composite much like fiberglass/kevlar) from 30 microns down to 10 microns, on a consistent basis.How would I make something like this? or is there anything out there that already does this?",
"role": "user"
},
{
"message": "it's called a microt... | micron sanding apparatus | physics | 2018-03-14T04:02:40.213 |
[
{
"message": "Can a mathematician with no knowledge in physics understand this proof? Is there a paper that presents in suitable way for me?",
"role": "user"
},
{
"message": "<blockquote> Where can a mathematician read Hawking's proof for the existence of a black hole's radiation?</blockquote>IMHO ... | Where can a mathematician read Hawking's proof for the existence of a black hole's radiation? | physics | 2018-03-15T14:24:28.043 |
[
{
"message": "I would like to make a series RLC circuit which will serve as RF receiver. I would like very high frequency selectivity, i.e. narrow bandwidth, i.e. $\\pm$200 Hz. The sharpness of a resonance is described by $Q$ which itself is equal to $$Q = \\frac{\\omega_{0}L}{R} = \\frac{1}{R \\omega_0 C}$$but... | Designing a high-$Q$ RLC circuit | physics | 2018-03-15T14:32:51.973 |
[
{
"message": "I'm trying to piece together a coherent understanding of the EW symmetry breaking and its effect on early cosmology, from a number of somewhat incomplete sources. Any corrections to the following presumed steps or conclusion would be greatly appreciated. i) In the early universe, before freeze-out... | ElectroWeak symmetry breaking and the early universe | physics | 2018-03-15T17:09:25.043 |
[
{
"message": "I recently got interested in electronic paper.One design that I liked was the one from Mirasol: <a href=\"https://en.wikipedia.org/wiki/Interferometric_modulator_display\" rel=\"nofollow noreferrer\">https://en.wikipedia.org/wiki/Interferometric_modulator_display<a href=\"https://i.stack.imgur.com... | Different Color Intenensities from simple ON/OFF RGB subpixels | physics | 2018-03-16T12:41:05.050 |
[
{
"message": "I have been pondering about the following question:<blockquote> Given a time-dependent function $f(t)$, is it possible to show that its autocorrelation function will generally follow a decaying exponential behavior for some time $\\tau$, i.e. $\\langle f(t)f(t+dt) \\rangle_t \\rightarrow e^{-dt/{... | exponential autocorrelation function by approximation of derivative | physics | 2018-03-16T13:12:57.430 |
[
{
"message": "This will sound like a philosophical question (i.e. a question with no actual theoretical content), but I dont intend it as such. Admittedly, my question is based on a very vague intuition.Also note, I'm a beginner at QM.When two particles X, Y are perfectly entangled in quantum mechanics, then th... | When two particles are maximally entangled, can we decompose the combined system arbitrarily? | physics | 2018-03-16T20:03:19.377 |
[
{
"message": "Many physics textbooks and websites state that electric current is the source of all magnetism. They go on to support this statement by saying that electrons move around nuclei AND they have spin. Later, and almost without exception, the book or site will warn us that the term spin is not to be ta... | On the accuracy of the statement "Current is the source of all magnetism" | physics | 2018-03-16T20:47:57.847 |
[
{
"message": "In <a href=\"http://www.feynmanlectures.caltech.edu/I_39.html\" rel=\"nofollow noreferrer\">The Feynman Lectures on Physics, Volume I 39-2 The pressureof a gas, the followingis presented:<blockquote> If $v$ is the velocity of an atom, and $v_{x}$ is the $x$-component of $v$, then $mv_{x}$ is the... | Understanding Feynman's development of the ideal gas law: Vol I 39-2 of The Feynman Lectures on Physics | physics | 2018-03-17T16:40:25.557 |
[
{
"message": "I’m trying to calculate the burn rate of a theoretical sugar rocket (for a computer game).The equation I have is $r = aP^n$ . Where $r$ is the burn rate, $a$ is the burn rate coefficient, $n$ is the burn rate pressure exponent and $P$ is the pressure.I am struggling to use use equation in general ... | How to calculate rocket Burn Rate? | physics | 2018-03-18T08:40:35.420 |
[
{
"message": "What is the magnetic field due to current carrying wire at a point on the wire itself?",
"role": "user"
},
{
"message": "Complementing <a href=\"https://physics.stackexchange.com/a/394018/75633\">jim's answer in order to explicitly address the questions that possibly motivated the orig... | Magnetic field due to current carrying wire at the wire | physics | 2018-03-18T09:42:56.673 |
[
{
"message": "The decay constant $f$ of a hadron with momentum $P$ or its in-hadron condensate $\\kappa$ (See <a href=\"https://arxiv.org/abs/1109.2903\" rel=\"nofollow noreferrer\">this paper, Eq. (8)) are given by terms like$\\begin{align*}f_\\pi P^\\mu &\\sim \\langle 0|J_\\text{axial}^\\mu (0) |\\pi(P)\... | How to interpret $\langle\pi|J|\pi\rangle$? | physics | 2018-03-18T09:50:29.210 |
[
{
"message": "This is a repost of a question I saw here:<a href=\"https://physics.stackexchange.com/q/81732/\">Could the spacetime manifold itself end at the event horizon?which was closed because it apparently didn't seem clear as to what the poster there was asking. However when I saw it I think I had a fairl... | Is it possible the space-time manifold itself could stop at a black hole's event horizon? | physics | 2018-03-18T14:30:36.003 |
[
{
"message": "This may be a stupid question, but it seems to me that we could calculate the value of the scale factor at any stage in the history of the universe by analysing the relationship between recessional velocity and distance in faraway galaxy clusters. Basically, use the same method Hubble used to get ... | Can't we obtain observational values for scale factor at different periods in the history of the universe? | physics | 2018-03-18T22:46:28.317 |
[
{
"message": "first of all, is the universse infinite or finite? If finite, then the universe is itself expanding, so if you assume the farthest star in the farthest galaxy emits light. The photon would be able to reach the edge of universe and then what would happen to it would it? Would it travel out and be ... | Can light be one of the causes for the expansion of universe? | physics | 2018-03-19T07:16:11.733 |
[
{
"message": "We known that the potential generated by a charge pointwise $q$ is $V(r) = kq/r $ and the equipotential surfaces (in 3D) are spheres centered in the charge with $r\\geq 0$ where $r=d(O,P)$, i.e. the distance between the origin and a generic point $P$.In fact if we are in space, where an orthonorm... | Laplace operator to find a bundle of parallel planes (equipotential surfaces) to two plates | physics | 2018-03-19T11:46:50.517 |
[
{
"message": "This question is about the role complex number have in quantum mechanics.In a two state system, by definition you can take a measurement and will find the system to be in either of two states. Taking this measurement again yields the same result. Quantum theory states that you can take a different... | How many 'independent ways' can you measure a quantum 2-state system | physics | 2018-03-19T20:39:24.877 |
[
{
"message": "Consider a current-carrying loop of radius R, and we want to find the field at the center of the loop on the same plane as the loop.Biot-Savart law tells me that it is $B_{center}=\\frac{\\mu_0I}{2R}$.With Ampere's Law, I tried to consider the loop as a superposition of many infinitesimal arc segm... | Ampere's Law vs Biot-Savart Law on the field of the center of a current-carrying loop | physics | 2018-03-20T03:58:06.157 |
[
{
"message": "I'm currently writing something that explores the phenomenon of inside jokes, in which I use an astrophysicist joke that is meant to be undecipherable to the average reader. It was recommended to me by someone who, as it turns out, has as little understanding of physics as I do. After finishing a ... | A joke on the Doppler effect: does this make sense? | physics | 2018-03-20T08:39:22.773 |
[
{
"message": "My question is simple: is it possible to create radiation with the same shape of spectrum as black body radiation, isotropic, but with greater density (number of photons with given frequency in unit volume) than black body radiation, which is (energy per unit volume per unit frequency):$$S_\\nu = ... | "Super dense" black body radiation | physics | 2018-03-20T10:48:50.083 |
[
{
"message": "I came across the following proposition while reading Goldstein, in chapter 10, page 430, on Hamilton Jacobi theory. Here he performs a canonical transformation and he asserts that,<blockquote> We can automatically ensure that the new variables are constant in time by requiring that the transform... | Canonical Transformation View Of Hamilton-Jacobi Theory | physics | 2018-03-20T11:37:16.283 |
[
{
"message": "I read that when the stellar aberration of light is measured with the help of a telescope filled with water, the value of the aberration is equal as in the case of a telescope filled with air.Just to draw your attention: note that it were the problems concerning aberration that led to SRT.Report o... | Stellar aberration in a water-filled telescope | physics | 2018-03-20T20:28:41.380 |
[
{
"message": "For example, the <a href=\"https://physics.nist.gov/cgi-bin/cuu/Value?bg|search_for=g\" rel=\"nofollow noreferrer\">NIST reference value for Newton's gravitational constant is$$G = 6.674 08(31) \\times 10^{-11}\\,\\mathrm{m^{3} kg^{-1} s^{-2}}.$$What is meant by the $(31)$?I have generally underst... | What is the meaning of the bracketed numbers in reference values for constants? | physics | 2018-03-20T23:35:45.120 |
[
{
"message": "I am fascinated by the relationship between entropy and life. From the Wikipedia article of that name, to the science fiction series \"Three Body Problem\" characterizing human-like lifeforms across the universe as simply 'low entropy beings'. However, entropy can be a tricky concept to grasp my m... | Does the act of organizing information (e.g. categorization) reduce entropy? | physics | 2018-03-21T02:04:00.280 |
[
{
"message": "My question is different but based on the same quote from Wikipedia as <a href=\"https://physics.stackexchange.com/questions/350895/scale-invariance-at-phase-transitions\">here. According to <a href=\"https://en.wikipedia.org/wiki/Scale_invariance\" rel=\"nofollow noreferrer\">Wikipedia, <blockquo... | Is the Landau free energy scale-invariant at the critical point? | physics | 2018-03-21T15:48:11.893 |
[
{
"message": "In analogy to a compressed gas allowed to reversibly expand and do work, I've been thinking about the behavior of a compressed spring that is very slowly and incrementally relieved of its pressure. At each incremental removal of a delta mass, the spring will expand to a new equilibrium length by ... | Why doesn't reversible adiabatic expansion generate heat? | physics | 2018-03-22T05:57:50.347 |
[
{
"message": "<blockquote> Tritter is a generalisation of the fifty-fifty beam-splitter to situations where photons can propagate along three paths. It has the following matrix representation: $$T\\equiv\\left(\\begin{array}{ccc} 1 & 1 & 1 \\\\ 1 & \\alpha & \\alpha^2 \\\\ 1 & \\alpha^2 &a... | How do I write an operator in Dirac notation? | physics | 2018-03-22T08:05:59.247 |
[
{
"message": "I am new here and I got a question that I never read in any textbook. Are Feynman rules actually unique or can one derive different rules, which are equivalent?Of course, we have a freedom to choose a gauge. So my question concerns whether or not Feynman rules are unique after we have chosen such ... | Are Feynman rules unique? | physics | 2018-03-22T10:15:45.433 |
[
{
"message": "Torque about a point = rate of change of angular momentum about that point.Say we're in an inertial frame and see a body accelerating and rotating and another point(either a part of this body or an external point) accelerating. Can we apply T = dL/dt for that body about that accelerating point if ... | Can the reference point in an inertial frame be accelerated when applying torque equation? | physics | 2018-03-22T13:34:14.690 |
[
{
"message": "In <a href=\"https://bicycles.stackexchange.com/a/53685/33564\">this answer on the cycling SE, the claim is made that adding more mass to a bicycle increases the stopping distance. I was under the impression that mass should not affect the stopping distance so long as all the other factors remain ... | Does the mass of a bicycle directly affect stopping distance? | physics | 2018-03-22T15:24:39.493 |
[
{
"message": "There is one thing about Young's modulus that I find unexpected and confusing.When certain solid materials, pure metal, steel or an alloy of a certain composition, gets strengthened by cold working or by heat treating, the Young's modulus stays exactly the same as before even though the yield stre... | Why doesn't the Young's modulus change when an alloy is strengthened? | physics | 2018-03-23T03:14:01.020 |
[
{
"message": "80's SF novel, not by a big name. Set in a feudal interstellar empire of perhaps a hundred worlds. From the point of view of an aristocratic fleet captain who falls in love with his commoner mistress and starts to question the social system. Simultaneously a space cloud/amoeba appears at the fring... | 80s SF Novel, Space Cloud vs Interstellar Feudal Kingdom | scifi | 2017-01-20T04:09:03.930 |
[
{
"message": "In the episode the Joker is Wild, the Joker is in a museum and four henchmen come out from behind the busts of four famous comedians. I was wondering if anyone knew the four actors that appear next to the busts of the four comedians. Two are pretty easy. Gil Perkins is Oliver Hardy and Roger Cree... | Batman 1966 - The Joker is Wild - who are the actors behind the busts? | scifi | 2017-01-20T19:31:18.497 |
[
{
"message": "From what I understood, Bodhi Rook was tortured and left starving by Saw Gerrera for several days in the Catacombs of Cadera. The movie also doesn't indicate how much time passes between the moment when Cassian hears from Tivik that an Imperial defector on Jedha has a message from Galen Erso for S... | How much time passes in Rogue One? | scifi | 2017-01-21T01:03:36.360 |
[
{
"message": "I want to know if Luke and Leia being Vader's kids becomes public knowledge? Presumably people would be more suspicious of them if they knew the truth.Does Poe know his General is connected to the Empire?",
"role": "user"
},
{
"message": "I don’t have any quotes, but I’ll try to give a... | Do other planets and their government learn who Princess Leia of Alderaan's biological father is? | scifi | 2017-01-21T02:03:35.973 |
[
{
"message": "I remember a novel about the Earth's landmass going from roughly a third of the total surface area to almost a half so that mankind had more room. I thought it was called \"Cataclysm\" and would have been written sometime in the 70's I believe. Trying to find the author's name and the official tit... | Looking for a novel about an expansion in the Earth's landmass - Possibly "Cataclysm" | scifi | 2017-01-21T19:49:32.373 |
[
{
"message": "We know that Doctor's character is changed with every regeneration, but we don't know where is the borderline. He eats different (sometimes very strange) things. He is in different ages and looks. Sometimes he doesn't like soldiers, sometimes he is nearly one of them. Sometimes he gets in love or... | How much can regeneration change the Doctor (any timelord)? | scifi | 2017-01-22T08:54:31.767 |
[
{
"message": "It is a science fiction/fantasy novel set on some world that isn't earth. I think it is either in the future or an alternate universe. I read it in high school or college so, 10-17 years ago. There is a female mercenary who is part of a mercenary guild. I feel like I recall she was being pursued b... | Story identification female mercenary who was able to grow iron nails | scifi | 2017-01-27T01:28:20.743 |
[
{
"message": "Are there any aliens that actively participate in field work in the Men In Black movies?I know that there are aliens that work at the organization - that is shoved down our throats - but are there any aliens that are active field agents like K or J, or are all of the agents humans only?",
"rol... | Aliens In Black? | scifi | 2017-01-29T22:55:20.090 |
[
{
"message": "I remember from the movie that the crew was suspended in a liquid that fills their lungs to protect them from the high acceleration of the ship (I think 20 or 40 g were mentioned?)This made me curious. Given that the problem with space drives normally is that the more effective ones give only poor... | In Event Horizon, how did the Lewis & Clark accelerate? | scifi | 2017-01-30T12:14:41.603 |
[
{
"message": "<blockquote> \"All right, guys, uh, listen. This is a blues riff in B, watch me for the changes, and try and keep up, okay?\"</blockquote> When asked for \"another one\", \"something that really cooks\", Marty McFly busts out \"Johnny B Goode\". He gets a bit carried aw... | Which guitarists does Marty imitate? | scifi | 2017-01-30T14:13:46.307 |
[
{
"message": "In Episode II we see the early plans for the Death Star (<a href=\"http://starwars.wikia.com/wiki/Death_Star_plans#Clone_Wars\" rel=\"nofollow noreferrer\">initially developed by the Separatist Geonosians, led by <a href=\"http://starwars.wikia.com/wiki/Poggle_the_Lesser\" rel=\"nofollow noreferre... | Why did the Separatists start planning the Death Star before the Clone Wars broke out? | scifi | 2017-01-30T21:15:51.653 |
[
{
"message": "In the question '<a href=\"https://scifi.stackexchange.com/questions/151503/why-does-one-at-at-have-a-hole-in-it-in-rogue-one\">Why does one AT-AT have a hole in it in “Rogue One”?' I learned about the AT-ACT, and also that the orange doors open and close.As we can see in the following picture the... | Where does the AT-ACT door go? | scifi | 2017-01-31T09:39:35.977 |
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