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 |
|---|---|---|---|
[
{
"message": "If the answer to the question is no, I am wondering how we can be sure that the absorption did not alter the \"actual\" wave features.",
"role": "user"
},
{
"message": "It depends what you mean by \"an elementary particle\". If you mean the same elementary particle, as \"this specific ... | Is it possible to measure the wave features of an elementary particle without absorbing it? | physics | 2017-05-26T16:13:36.987 |
[
{
"message": "Consider a positive lens and spherical aberration, which causes the formation of that region of intersection of different rays as in picture.<a href=\"https://i.stack.imgur.com/GBtuQ.jpg\" rel=\"nofollow noreferrer\">Named $q$ the distance of the image from the (idealized) lens, how do the dimensi... | Spherical aberration entity vs. distance from the lens? | physics | 2017-05-27T02:23:33.740 |
[
{
"message": "Hi I'm trying to derive the Compton scattering formula and I don't understand where I'm going wrong. I keep getting that the momentum of the outgoing photon is equal to the momentum of the incoming photon (and thus their wavelengths are the same) which I know (intuitively and from the actual formu... | Derivation of Compton scattering | physics | 2017-05-27T14:38:17.627 |
[
{
"message": "Where does this expression come from? Why is the $N$ an exponent? $J(\\Delta x' \\hat x) = lim_{N \\to \\infty} (1-\\frac{ip_x\\Delta x'}{N\\hbar})^N $",
"role": "user"
},
{
"message": "First, consider the expression$$e^{\\alpha D}f(t) = f(t + \\alpha) \\tag{1}$$where $D$ is the deriva... | Mathematical Representation of the Generator of Translation | physics | 2017-05-27T19:53:24.563 |
[
{
"message": "Say, for example, I am looking at a distant star. I record the different intensities of light of different wavelengths and observe some spectrum lines. Now, since there are three factors affecting what I see - the temperature of the star, the speed at which the star is receding away from me, and t... | Temperature, redshift or true colour of a star? | physics | 2017-05-28T20:47:56.750 |
[
{
"message": "I understand that a BEC of atoms causes all the component atoms to have a single shared state. This affects the position/momentum of the atoms, and even excited states of the electrons.But what about states of the atomic nucleus? Are they all shared as one uniform description, too? Processes inv... | Bose-Einstein Condensate and nuclear states | physics | 2017-05-29T04:58:49.943 |
[
{
"message": "This is my first question and I am just a 14 year old so excuse me for my mistakes. Please simplify your answer a little only. Using terms thinking I won't understand is a mistake.",
"role": "user"
},
{
"message": "If you release the potential energy stored in a piece of water that is ... | In an atom, when an electron loses energy, why is a photon released? If photons are massless, how are they created in this process and why? | physics | 2017-05-29T06:20:14.563 |
[
{
"message": "This is my first question and I am just a 14 year old so excuse me for my mistakes. Please simplify your answer a little only. Using terms thinking I won't understand is a mistake.",
"role": "user"
},
{
"message": "One shouldn't think of a field as a surface, a field is a mathematical ... | In an atom, when an electron loses energy, why is a photon released? If photons are massless, how are they created in this process and why? | physics | 2017-05-29T06:20:14.563 |
[
{
"message": "The photon, which has a fixed wavelength should also have a fixed total length...is the total length of a light wave fixed???",
"role": "user"
},
{
"message": "If the photon has a wave fuction with a fixed wavelength extending to infinity then according to the <a href=\"https://en.wiki... | What is the Total length(not wavelength) of an electromagnetic wave? | physics | 2017-05-29T12:40:55.407 |
[
{
"message": "We know an elastic medium is necessary for the propagation of any kind of wave like sound.But air is not necessarily an elastic medium at all.For the compression and rarefaction which is extremely necessary for the wave to flow a dragging force is highly required to bring the particle to equilibri... | Wave motion in air | physics | 2017-05-29T13:59:38.533 |
[
{
"message": "Assuming constant fan power, how would atmospheric pressure/density affect the cooling rate of objects being cooled by a fan? Like in a lower pressure atmosphere, would a fan be able to cool objects more quickly because it could blow less dense air at a faster speed, would it cancel out and be th... | Can a fan cool objects better in a less dense atmosphere? | physics | 2017-05-29T23:50:34.103 |
[
{
"message": "I know how to find the magnetic field of a current carrying loop along its axis. The result is the following :$$B=\\frac{μ_0IR^2}{2(R^2+z^2)^{3/2}}$$ z is the axis, R the distance of the loop from the axisCan I turn this into an integral and find the total B along a solenoid if its loops are very ... | Magnetic field along the axis of a solenoid - Can I find it this way? | physics | 2017-05-30T00:51:51.397 |
[
{
"message": "I can't remember for sure, which is why I ask this question, but is it the case that gravitational waves are produced not by accelerated masses (like e.m. waves are produced by accelerated charges), but only by masses with a change in their acceleration?And if so, is there a connection with the co... | Are gravitational waves produced only by masses which experience a change in acceleration, and if so, is this connected to the spin 2 of the graviton? | physics | 2017-05-30T11:29:59.160 |
[
{
"message": "I have a confusion about in which part of a Hamiltonian an electrostatic interaction energy can be found. Consider a system of electrons interacting through electric field $\\mathbf{E}$ with the Hamiltonian$$H=H_\\mathrm{el}+H_\\mathrm{field},$$where the Hamiltonians of electrons and of the field ... | Electrostatic interaction energy | physics | 2017-05-30T13:19:37.007 |
[
{
"message": "<a href=\"https://en.wikipedia.org/wiki/Bertrand%27s_theorem\" rel=\"noreferrer\">Bertrand's theorem states<blockquote> Among central force potentials with bound orbits, there are only two types of central force potentials with the property that all bound orbits are also closed orbits, the inve... | Is there a connection between Bertrands theorem and Chaos theory? | physics | 2017-05-30T21:24:59.280 |
[
{
"message": "<a href=\"https://i.stack.imgur.com/1mnlU.jpg\" rel=\"nofollow noreferrer\">The reference point was chosen to be at $V_a$. Using Ohm's law at $i_{R1}$, if $V_a$ is the reference point, it is zero voltage. All the nodes are using it as a reference to ground and my understanding is that the voltage ... | Node Analysis with reference point question | physics | 2017-05-31T02:42:53.207 |
[
{
"message": "note: This is a question about relativistic effects. I've included some detail about the spacecraft and its orbit for background, but the question is about relativistic effects and their observability. When the Parker Solar Probe passes within 8.5 solar radii of the Sun, it will be moving really f... | Parker Solar Probe passing extremely close to the Sun; what relativistic effects will it experience and how large will they be? | physics | 2017-05-31T03:53:40.447 |
[
{
"message": "note: This is a question about relativistic effects. I've included some detail about the spacecraft and its orbit for background, but the question is about relativistic effects and their observability. When the Parker Solar Probe passes within 8.5 solar radii of the Sun, it will be moving really f... | Parker Solar Probe passing extremely close to the Sun; what relativistic effects will it experience and how large will they be? | physics | 2017-05-31T03:53:40.447 |
[
{
"message": "When atoms get heated up, they start emitting EM radiation because of accelerating electrons. But why don't the protons emit EM waves which destructively interfere with other emitted EM waves, because they're also accelerating just as the electrons do, because they're both jiggling as one (atom)?"... | Why don't atomic nuclei emit EM radiation which destructively interfere with the radiation emitted by the electrons? | physics | 2017-05-31T06:12:49.133 |
[
{
"message": "I'm working on a question here where I have solved these boundary conditions;$$\\vec{n} \\cdot \\vec{j}= -\\lambda\\vec{n} \\cdot \\nabla u + k(\\rho - \\rho_0)u\\vec{n}\\cdot\\vec{g}=0$$ So my question is, how do I know which of these 2 terms is a Dirichlet/Neumann boundary condition?Edit:$\\rho$... | Neumann or Dirichlet boundary conditions? | physics | 2017-05-31T14:20:06.873 |
[
{
"message": "Heisenberg uncertainty principle, ΔpΔx ≥ ħ/2, where Δp is the uncertainty in the particle's momentum and Δx is the uncertainty in position. This implies that the momentum of a highly compressed particle is extremely uncertain, since the particles are located in a very confined space. Why is that t... | In quantum mechanics, why in a fully degeneracy fermion state pressure increases when momentum also increase? | physics | 2017-05-31T23:07:36.280 |
[
{
"message": "It is common to read that the lifetime of a virtual particle is given by the uncertainty relation:$$\\tau \\sim \\frac{\\hbar}{E}$$on the premise that the virtual particle 'borrows energy'. This statement is infact wrong (at least I think it is) since energy is conserved in Feynmann diagrams and t... | Lifetime of a virtual particle? | physics | 2017-06-01T07:51:15.310 |
[
{
"message": "I'm trying to understand why there are theoretical models predicting that spin and gravity should couple.Specifically, what I'm asking is if such Standard Model extension comes from gauging the Poincaré group as per the Cartan variant of GR, where additionally torsion is sourced by spin instead o... | Gravity-Spin coupling in SME | physics | 2017-06-01T11:29:21.170 |
[
{
"message": "In quantum mechanics, measurement plays a fundamental role and to me, its role is usually described in a rather odd way. The Copenhagen interpretation states thus<blockquote> When that device makes a measurement, the wave function of the systems is said to collapse, or irreversibly reduce to an ... | A non-metaphysical interpretation of measurement in quantum mechanics | physics | 2017-06-01T18:32:01.310 |
[
{
"message": "The well known Schwarzschild solution is given by\\begin{equation}(ds)^2 = \\left( 1 - \\frac{2GM}{c^2r} \\right) dt^2 - \\left( 1 - \\frac{2GM}{c^2r} \\right)^{-1} dr^2 - r^2 d\\Omega^2.\\end{equation}It has been on my mind a lot about attempting to represent an aspherical body in general relat... | Expanding Schwarzschild solution using spherical harmonics? | physics | 2017-06-02T02:30:44.380 |
[
{
"message": "As often stated in books, near a phase transition we may express the free energy density as a power series in the order parameter $\\phi(\\mathbf{r})$. Up to quartic contributions, we have $$f=f_{0}-h\\phi(\\mathbf{r})+a_{2}\\phi(\\mathbf{r})^{2}+\\frac{1}{2}|\\mathbf{\\nabla}\\phi(\\mathbf{r})|^{... | Landau Theory of Phase Transitions | physics | 2017-06-02T18:28:54.470 |
[
{
"message": "In nuclear magnetic resonance some current is indeced in the receiving coin by the rotating magnetisation vector. The current is associated with some energy. From where this energy come from since there is no energy transfer between object and the coil? Or maybe there is?",
"role": "user"
},... | How is current induced in the coil in NMR? | physics | 2017-06-03T14:31:01.540 |
[
{
"message": "I am having trouble with a specific assignment. I am supposed to find the electric potential at P. Normally this is no problem, however, there are two voltage sources that output a current that goes in opposite directions. <a href=\"https://i.stack.imgur.com/ZuVAe.png\" rel=\"nofollow noreferrer\"... | Electric potential in point with current going in opposite directions | physics | 2017-06-03T20:01:37.697 |
[
{
"message": "This is for my report and I wanna know what are the theory behind why magnets repel. Why magnetic force decreases as distance increases. I wrote down one of the theory, magnetic field but I'm not sure what are the other theories are behind this. (I did two experiments, one of them is magnetic spri... | What are the physics principles behind magnetic strength and distances | physics | 2017-06-04T05:25:50.580 |
[
{
"message": "When the marble is viewed from with respect to the ground, it experiences a net inward acceleration, and hence force. However, when the marble is displaced slightly, it moves towards the edge. Why? My first answer would be centrifugal force, but isn't it fictitious? EDIT: The marble isn't the cent... | Why does a marble in a merry-go-round move towards the edge? | physics | 2017-06-04T12:58:11.927 |
[
{
"message": "When the marble is viewed from with respect to the ground, it experiences a net inward acceleration, and hence force. However, when the marble is displaced slightly, it moves towards the edge. Why? My first answer would be centrifugal force, but isn't it fictitious? EDIT: The marble isn't the cent... | Why does a marble in a merry-go-round move towards the edge? | physics | 2017-06-04T12:58:11.927 |
[
{
"message": "As stated in the question title, I am trying to prove the relation (pg. 144 of Griffiths' Introduction to Elementary Particle' or pg. 126 on Riazuddin's 'High Energy Physics') concerning the eigenvalues of a multiplet of isospin $I$ and charge conjugation number $C$:$$G=(-1)^IC,$$My problem:I am g... | Proof of the G-Parity Relation $G=(-1)^IC$ | physics | 2017-06-04T16:07:48.110 |
[
{
"message": "An ultrashort laser pulse can usually be written as a product of a time-varying envelope $A(t)$ and a periodic function with angular frequency $\\omega$ $$E(t)=A(t)\\cos(\\omega t+\\phi(t)+\\phi_0)$$Where $\\phi(t)$ is temporal phase and $\\phi_0$ the absolute phase .(I found this kind of expressi... | Explain the mathematical expression of Ultrashort pulses | physics | 2017-06-04T22:17:02.913 |
[
{
"message": "I ask this question because many of the books I'm familiar with assumes a familiarity with the operator formulation and then develops the path-integral formulation partly based on a mixture of operator formulation and path-integrals (as if it is necessary to know the operator formulation). But I t... | What are the minimal postulates to do quantum mechanics in path-integral formulation without knowing the operator formulation? | physics | 2017-06-05T03:36:13.120 |
[
{
"message": "Just before I explain my problem, please note that all I am looking for is for someone to point out where I got it wrong. Don't downvote this post because my reasoning is wrong - I know it is wrong, and I want to know why.So, we have a source and an observer, moving away from each other at velocit... | Deriving Relativistic Doppler Effect through length contraction | physics | 2017-06-05T17:03:56.190 |
[
{
"message": "Consider a 1-D duct. Standing wave in the duct can be represented as $$A(x)e^{i\\omega t}$$ where A(x) is the amplitude( a function of direction) and $\\omega $ is the frequency in Hz and $t$ time in s. Similarly, is there a simple expression to represent a traveling wave in a duct?To visualize st... | Modelling a travelling wave | physics | 2017-06-06T10:43:37.347 |
[
{
"message": "I am currently working through the method of induced representations in order to calculate the unitary irreducible representations of the Poincare group. Conventions/NotationMetric signature $= (-,+,+,+)$$c=\\hbar=1$Indices i,j,k run over 1,2,3 whilst any other latin indice runs over 0,1,2,3.$x^a=... | Unitary irreducible representations of the little group $SO(3)$ | physics | 2017-06-06T10:53:39.987 |
[
{
"message": "Do photons lose energy due to interaction with the particles in a medium? If yes, then does the frequency of the component electromagnetic waves change? ( since energy of light is directly proportional to it's frequency)",
"role": "user"
},
{
"message": "It is possible for light to be ... | Is there dissipation of energy when light through a medium? | physics | 2017-06-06T14:32:19.967 |
[
{
"message": "I have just been introduced to the concept of on/off-shell particles, and to my understanding, on-shell particles are those that verify:$$E^2=(pc)^2+(mc^2)^2$$Free particles verify this equation but, if I am not mistaken, the energy of a bounded state/particle is such that $E^2<(pc)^2+(mc^2)^2$... | Are bounded particles off-shell? | physics | 2017-06-06T17:21:51.827 |
[
{
"message": "I have been trying my best to solve a problem that has been haunting and taunting me for the past couple days. The questions poses a scenario of two inductors wound around the same iron core. One inductor possesses $800$ turns and is connected to power. The other inductor possesses $500$ turns and... | Self Starting Engineer trying to learn Electromechanics, Help with Problem | physics | 2017-06-07T00:39:55.033 |
[
{
"message": "We know, curl of E is zero(this field is conservative). Again E=-grad V. So, we get curl of (-grad V)=0, i.e. curl of gradient of potential is zero. Is there any condition on potential?",
"role": "user"
},
{
"message": "Try to manually compute (i.e. write it out in it's explicit form) ... | Curl of gradient of potential in electrostatic | physics | 2017-06-07T07:23:15.730 |
[
{
"message": "As stated in this <a href=\"https://physics.stackexchange.com/questions/75902/e-times-b-drift-of-a-single-particle-in-vacuum-with-unifiorm-e-and-b\">question, the force on a charged particle in electric field $E$ and magnetic field $B$ is given by:\\begin{equation}m \\dot{v} = q ( E + v \\times B)... | intuitive explanation of $E \times B$ drift with constant and perpendicular $E$ and $B$ | physics | 2017-06-07T08:20:08.583 |
[
{
"message": "I came across this MCQ in my text book, it says:<blockquote> The laser beam is a collimated parallel one, that means its photons have the same...... direction 2. frequency 3. intensity 4. phase </blockquote>I will not pick either frequency or intensity, but I am confused between phase and d... | Why laser is a collimated parallel beam? | physics | 2017-06-07T20:30:26.510 |
[
{
"message": "Just curiosity, as follows: I was trying to explain/illustrate to a non-technical friend that physics is just \"mathematical models\", which may or may not represent/correspond_to some \"underlying reality\". And we can't infer it does just because the calculated numbers work (correspond to observ... | Could epicycles approximate anything to any precision? In what way is QED different? | physics | 2017-06-07T23:19:56.673 |
[
{
"message": "It is well known when two cyclists are driving together, one in front, one on the back, that the second cyclist profits from the slipstream provided by the man (or woman) in front. Does the first cyclist also profit from the situation? I can imagine that the turbulence (the slipstream) behind the ... | Does a cyclist in front of two also profits from the slipstream the second cyclists profits from? | physics | 2017-06-08T04:32:05.930 |
[
{
"message": "In Bence, Hobson, Riley Mathematical Methods for Physics pg 317, a double pendulum consisting of a rod attached to a string is pictured as follows: <a href=\"https://i.stack.imgur.com/z9QOR.jpg\" rel=\"nofollow noreferrer\">I'm trying to understand the formula for the rotational kinetic energy(T o... | Formula for a double pendulum | physics | 2017-06-08T10:09:11.200 |
[
{
"message": "Please forgive my amateur physics knowledge.Say it's Thanksgiving leftover day. You load a plate with turkey, potatoes, cranberry sauce, and salad. Now it's time to heat your food, but oh no! You put the cold foods on your plate before using the microwave!The mesh grate over the microwave windo... | Can a mesh shield keep food cold in a running microwave? | physics | 2017-06-08T21:44:05.650 |
[
{
"message": "Let $\\tau$ be the random variable that describes the lifetime of a given particle. It seems to conform to common-sense that $\\mathbf{P}(\\tau>t+s|\\tau>s)=\\mathbf{P}(\\tau>t)$, as it would be weird if the particle could ``keep track\" of how long it has been around.My question is, do w... | How do we know that radioactive decay is memoryless? | physics | 2017-06-09T05:37:23.440 |
[
{
"message": "Say you have a frequently occurring event and you have measured the intervals between the occurrences in seconds. (so have a dataset that looks like [4, 6, 9, 13] for example).What formula(s) would you use to determine if the event occurrences were accelerating or increasing in frequency?One solut... | Is the occurrence of an event accelerating | physics | 2017-06-09T16:14:15.240 |
[
{
"message": "As khown, <a href=\"https://en.wikipedia.org/wiki/Ernst_Chladni#Chladni_figures\" rel=\"noreferrer\">Chladni figures display nodal lines of eigenfunctions satisfying the equation $\\Delta^2\\psi=k^4\\psi$ with appropriate boundary conditions. One can note these lines don't like to cross each other... | Chladni figures: avoided crossings of nodal lines | physics | 2017-06-09T16:27:03.453 |
[
{
"message": "I just came to know about barycentre. What exactly is this?",
"role": "user"
},
{
"message": "The Earth's spin is about its geometrical axis - that's the definition of that axis. This passes through the center of mass (barycenter) of the Earth itself.Zooming out a bit, the Earth and th... | Does Earth rotate around its geometrical axis OR the center of mass of Earth-Moon system? | physics | 2017-06-09T20:45:02.283 |
[
{
"message": "Considering the two electrons in <code>2p</code>, is the total wave function of C-12 (anti)symmetric under particle exchanging in it's ground state? What about other states?",
"role": "user"
},
{
"message": "The total wavefunction of any system of electrons is always antisymmetric with... | What's the form of total wavefunction of Carbon-12: symmetric or asymmetric? | physics | 2017-06-09T22:31:53.170 |
[
{
"message": "Recently, me and my dad were discussing the theoretical design of a small homemade submarine. Lets assume that it is a hollow acrylic sphere with a radius of around 25cm. The radius would likely need to be adjusted to meet certain requirements, like a certain depth at which the submarine should fl... | Physics and depth control of a small spherical submarine | physics | 2017-06-09T22:58:04.530 |
[
{
"message": "I was observing the solution to the potential function for a dielectric sphere (dielectric constant= $\\epsilon$) of radius $r=a$ at a constant field $E_0$. The boundary conditions were as follows:[WHERE, $\\phi_1(r,\\theta)$ is the potential inside the sphere and $\\phi_2(r,\\theta)$ outside the ... | Solving the potential function for a Dielectric Sphere in a constant Electric Field | physics | 2017-06-10T16:14:46.197 |
[
{
"message": "The book \"Introduction to quantum mechanics\" by Griffiths starts by introducing the wave function. The squared of the integral of the wave function gives you the probability of measuring the position of a particle between a and b. Later it talks about eigenstates and eigenvalues.The eigenstate d... | Need help with clarification of eigenstates and wavefunctions | physics | 2017-06-10T23:21:58.953 |
[
{
"message": "Pick a Carnot Cycle (being $T_1<T_2$), it is reversible, therefore $\\Delta S_{univ, cycle}=0$.The same result is obtained via the sum of all entropies associated with its transformation, which means:$\\Delta S_{univ, cycle} = \\Delta S_{gas+ambient,AB} + \\Delta S_{gas+ambient,BC}+\\Delta S_{g... | Irreversible processes don't account in entropy calculations? | physics | 2017-06-11T12:31:10.203 |
[
{
"message": "I'm trying to run some calculations on <a href=\"https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric\" rel=\"nofollow noreferrer\">Kerr-Newman black holes, but I'm having two major difficulties. First, most equations I've been able to find are only for <a href=\"https://en.wikipedia.org/wiki... | Explain Kerr-Newmann Black Hole Spins in SI Units | physics | 2017-06-11T23:26:10.493 |
[
{
"message": "What is the physical interpretation of curl of curl of an E-field vector? I know that this gives the expression for an EM wave using the Maxwell equations but, I want to understand what exactly curl of curl signifies?",
"role": "user"
},
{
"message": "Curl actually signifies the rotati... | Physical interpretation of curl of curl of Electric field vector | physics | 2017-06-12T10:16:19.493 |
[
{
"message": "In a hypothetical situation I'm still sitting in a coffee shop but a gravitational wave similar to the three reported by LIGO passes through me from behind. The source is much closer though, so this one is perceptible but (let's hope) not yet destructive. (If a perceptible event would destroy the ... | How would a passing gravitational wave look or feel? | physics | 2017-06-12T11:04:29.830 |
[
{
"message": "In a hypothetical situation I'm still sitting in a coffee shop but a gravitational wave similar to the three reported by LIGO passes through me from behind. The source is much closer though, so this one is perceptible but (let's hope) not yet destructive. (If a perceptible event would destroy the ... | How would a passing gravitational wave look or feel? | physics | 2017-06-12T11:04:29.830 |
[
{
"message": "Since an antiparticle by definition is a particle with the same mass but opposite charge, how is there such a thing as an antineutrino? A neutrino has 0 charge so could not have an opposite. So why does an antineutrino exist and how does it differ from a neutrino?",
"role": "user"
},
{
... | What is the difference between a neutrino and an antineutrino? | physics | 2017-06-12T11:51:21.877 |
[
{
"message": "Mean square velocity= $ C_{rms} = \\frac{\\int_0^\\infty C^2 dn}{n} $ ( where dn= no. density of molecules having velocity between C and C+dC , n= no. density of molecules including all velocities) .<br>Why is the integration taken from 0 to $\\infty$ and not from $-\\infty$ to $\\infty$? The re... | In deriving the expression for mean square velocity of gas molecules why the integration is not taken from negative infinity to infinity? | physics | 2017-06-12T15:12:59.150 |
[
{
"message": "I'm currently studying for a physics exam, and I'm coming up with some trouble on a particle physics question. I'd probably be able to get it, but I'm not actually sure if the content was taught and as far as I can tell there's no practice material (with worked answers that might help me understan... | Particle interaction selection rules | physics | 2017-06-13T04:04:07.280 |
[
{
"message": "Einstein: \"Energy cannot be created or destroyed, it can only be changed from one form to another.\" Is a human thought merely energy that is changed from one form to another?",
"role": "user"
},
{
"message": "An analogue to your question:Is this answer you are reading merely a chang... | Is a human thought merely energy that is changed from one form to another? | physics | 2017-06-13T07:33:44.207 |
[
{
"message": "Snell's Law:$$\\frac{\\sin(\\theta_1)}{\\sin(\\theta_2)}=\\frac{n_2}{n_1}$$I have read some explanation on understanding complex Snell's Law like <a href=\"https://physics.stackexchange.com/q/312895/\">Explanation of sin(theta) > 1 for total internal reflection, but still have questions on conc... | Example on Snell's Law with complex solution | physics | 2017-06-13T08:58:03.067 |
[
{
"message": "I am following Carroll, he states that the geodesic equation is the the generalization to curved spacetime $\\vec f = m \\vec a$, for $\\vec f = \\vec 0$. This leads me to wonder what is the correct to generalize this further to:Paths that are not geodesicsCases where $\\vec f \\neq 0$Suppose for ... | GR: What is the curved spacetime analogue of Newton 2nd law? | physics | 2017-06-13T14:37:55.687 |
[
{
"message": "The question is:Taking into account as obstacle only <a href=\"http://www.atnf.csiro.au/outreach/education/senior/cosmicengine/stars_luminosity.html\" rel=\"nofollow noreferrer\">inverse-square relationship. Does there exist border distance below which we can see a star and above which we can not?... | Inverse-square relationship and seeing stars from far away: Is there maximum distance from which we can see a star? | physics | 2017-06-13T21:45:27.120 |
[
{
"message": "I know that in fluid dynamics, we use <a href=\"https://en.wikipedia.org/wiki/Lagrangian_and_Eulerian_specification_of_the_flow_field\" rel=\"nofollow noreferrer\">Lagrangian description of acceleration. That is, a <a href=\"https://en.wikipedia.org/wiki/Material_derivative\" rel=\"nofollow norefe... | Formulation of acceleration in general | physics | 2017-06-14T10:26:31.350 |
[
{
"message": "This is claimed by Jared Kaplan in his <a href=\"http://sites.krieger.jhu.edu/jared-kaplan/files/2016/05/AdSCFTCourseNotesCurrentPublic.pdf\" rel=\"noreferrer\">Lectures on AdS/CFT from the Bottom Up.He writes:<blockquote> It seems that all QFTs can be viewed as points along an Renormalization Fl... | Why can consistent QFTs only arise from CFTs? | physics | 2017-06-14T11:20:12.290 |
[
{
"message": "The Dirac delta function can be defined as $$\\delta(x)=\\frac{1}{2\\pi}\\int_{-\\infty}^\\infty e^{itx}dt$$From this we see that the dirac function has units of $x^{-1}$.<blockquote> How do we represent the units in cases like the momentum eigenvectors which, when units are included, is represen... | Representing dimensions in Dirac delta function results | physics | 2017-06-14T16:29:53.177 |
[
{
"message": "Can we detect any two electrons at the exact same time?Lets say all electrons are actually just one electron, and that is why they have exactly the same in spin, charge and so on.Lets say there is only one electron in the Universe.Can we detect any two electrons at the exact same time?",
"role... | Can we detect any two electrons at the exact same time? | physics | 2017-06-14T18:47:14.977 |
[
{
"message": "Consider a scientist who is accelerating at a constant rate along the x direction, in flat minkovski space. The relevant coordinate transformations are $$\\begin{cases}t'=t \\\\ x'=x+\\frac{1}{2}at^2 && a=\\text{const} \\\\ y'=y \\\\ z'=z\\end{cases}$$The question is, do you expect the cu... | Applying the principle of equivalence to an accelerated frame | physics | 2017-06-15T01:31:04.417 |
[
{
"message": "Can first law of thermodynamics defined for a closed system be applied to the steady flow energy equation? Why?I came across the derivation of $Vdp$ work and Every book applied the first law defined for closed system to steady flow energy equation.<a href=\"https://i.stack.imgur.com/DI90N.jpg\" re... | First law of thermodynamics, steady flow energy equation (SFEE) and $Vdp$ work | physics | 2017-06-15T06:54:45.793 |
[
{
"message": "I've been having a discussion with a friend about nuclear materials and whether bringing two bits of subcritical fissile material together at a decent enough speed would cause a spontaneous explosion.I'm aware that there have been several nuclear accidents involving fissile material over the years... | Could you cause a small "nuclear" explosion manually | physics | 2017-06-15T11:55:25.133 |
[
{
"message": "ContextFrom what I understand about the Cosmic Microwave Background Radiation is that it was from the big bang, and since space has streched and become bigger since then the wavelength of the CMBR has increased over time, which means that when the universe stopped being opaque it wasn't microwaves... | If the CMB was emitted at the ionization energy of hydrogen, why is it a blackbody spectrum instead of a line spectrum? | physics | 2017-06-15T12:19:59.937 |
[
{
"message": "Faraday's law says that the change in magnetic flux through the area enclosed by a wire loop induced an emf in the circuit. What exactly is this induced emf?If I understand correctly, it is the amount of work done on a unit charge which makes 1 full turn around the loop by the induced electric fie... | Confusion about induced emf vs motional emf | physics | 2017-06-15T14:49:03.010 |
[
{
"message": "This question is based on page 68 of Thomas Hartman's notes on <a href=\"http://www.hartmanhep.net/topics2015/gravity-lectures.pdf\" rel=\"nofollow noreferrer\">Quantum Gravity and Black Holes.To evaluate a path integral in ordinary quantum field theory, we integrate over fields defined on a fixed... | Boundary conditions for the gravitational path integral | physics | 2017-06-15T17:17:17.180 |
[
{
"message": "I've faced this question when trying to solve a test problem I had. The test, of course, did not require those functions to be expressed, but I just had to know what's going on.<blockquote> We're given a body falling in the air. Air friction is defined so $|\\vec f|=kv^2$, when $k$ is a constant,... | Acceleration-Velocity function to Velocity-time function with non-constant acceleration | physics | 2017-06-16T20:41:48.533 |
[
{
"message": "As no information is allowed from inside event horizon, how did we figure out that all matter/energy in a black hole is concentrated at a point like singularity.Say for example how it was ruled out that all the matter was compacted in half, or a third, or a tenth of the volume that is enclosed by ... | How do we know black hole is empty (except singularity)? | physics | 2017-06-17T08:09:52.363 |
[
{
"message": "The famous <a href=\"https://en.wikipedia.org/wiki/Thomas%E2%80%93Fermi_model\" rel=\"nofollow noreferrer\">Thomas Fermi theory says that we can express the total energy of a atomic system with $N$ electrons orbiting around a charged nucleus of atomic number $Z$ in terms of radial density of elect... | The energy difference between $H$ atom and $H^+$ ion in Thomas Fermi Theory | physics | 2017-06-17T13:08:52.930 |
[
{
"message": "Today was one of the rare clear sunny days in my city, and I was watching the Sun for several hours. When looking with naked eyes at the sky very near the Sun, standing on the border of a shadow of a building, I noticed that, despite there were no clouds anywhere near the Sun, the light-blue sky h... | Is the Sun disk always surrounded by a rainbow? | physics | 2017-06-17T15:49:54.393 |
[
{
"message": "I'm having some difficulty with understanding why KVL (Kirchhoff voltage law) is valid when considering an AC circuit. I mean, the system is by definition not in steady state, right? That in turn means that the change in current causes a change in the magnetic field, which is manifested within the... | Kirchhoff's Voltage Law for AC circuits | physics | 2017-06-17T16:06:58.237 |
[
{
"message": "<blockquote> A particle moves along $x$-axis such that each position is given by $x(t)=2t^3-15t^2+36t+5$, $x$ is expressed in metres. Find the total distance within the time interval $t=0$ second to $t=4$ seconds.</blockquote>My method: I integrated the equation $x(t)=2t^3-15t^2+36t+5$ to get $11... | A basic question in kinematics | physics | 2017-06-17T16:34:51.817 |
[
{
"message": "What the question really amount to asking is, if (as LIGO said) the gravitational waves emitted from the black hole collision were emitted as 'pure energy' this surely means that they were emitted as photons. If this is the right interpretation does it therefore mean that when the waves interacted... | Can gravitational waves be explained by the interactions between photons? | physics | 2017-06-17T16:41:27.113 |
[
{
"message": "I understand that more temperature means more molecules hitting each other and therefore more noise. But why is the ratio between the two roughly constant? If the temperature doubles, why would its Gaussian distribution also double?",
"role": "user"
},
{
"message": "Consider a particle... | Why is the ratio thermal noise/temperature constant? | physics | 2017-06-17T18:11:45.787 |
[
{
"message": "An example of a pair of anti-commutative Hermitian operators in a finite Hilbert space is $\\sigma_x$ with $\\sigma_z.$Indeed $\\sigma_z\\sigma_x=i\\sigma_y$, whereas $\\sigma_x\\sigma_z=-i\\sigma_y$.My question is, do there exist pairs of anti-commutative Hermitian operators in an infinite dimens... | Anti-commutative Hermitian operators in an infinite dimensional Hilbert space | physics | 2017-06-18T02:32:42.523 |
[
{
"message": "As current(DC) flows from positive to negative terminal which is actually flow of electrons which in turn flow from negative to positive terminal. So the question is which side of battery starts conducting current first? According to me it should be negative side as current is flow of electrons w... | In which terminal does current starts to flow first i.e. positive or negative? | physics | 2017-06-18T13:54:27.000 |
[
{
"message": "Lets say we have a gyroscope that has a flywheel spinning with constant angular velocity. The gyroscope is held in place in a position where the massless metal rod connecting to the flywheel is parallel to the ground. We now let go and are asked to predict the gyroscoped motion. When researching g... | Reasoning behind predicting a gyroscopes motion | physics | 2017-06-18T20:26:18.180 |
[
{
"message": "Define a physical system when Aristotelian mechanics $F=mv$ instead of Newtonian mechanics $F=ma$.Then we could have action $I=\\int L(q,t)dx$ rather than $\\int L(q',q,t)dx$.Is there an action principle? Will the formula $I=\\int p d q$ still hold?What will be the Hamiltonian and conservation la... | Action principle, Lagrangian mechanics, Hamiltonian mechanics, and conservation laws when assuming Aristotelian mechanics $F=mv$ | physics | 2017-06-18T20:54:40.097 |
[
{
"message": "What is meant by <a href=\"https://www.google.com/search?as_epq=projected+hilbert+space\" rel=\"nofollow noreferrer\">Projected Hilbert space? I know almost everything about coherent states. But I don't know the use of projected coherent states. I googled, but I can't find any source.",
"role"... | What is meant by Projected Hilbert space? | physics | 2017-06-19T06:51:21.427 |
[
{
"message": "In summer, that is when it's warmer outside the house than inside, one want to prevent the air in the house to warm up too much. Let's consider that all the windows are kept closed, that they are double panes and made of \"Low-E\" glass. During the day, does closing the curtains on the windows red... | In summer, should I close curtains during the day? | physics | 2017-06-19T14:51:16.707 |
[
{
"message": "I am self-studying Statistical Mechanics from J. Sethna's book <a href=\"http://pages.physics.cornell.edu/~sethna/StatMech/EntropyOrderParametersComplexity.pdf\" rel=\"nofollow noreferrer\" title=\"Entropy, Order parameters and complexity\">Entropy, Order parameters, complexity. In one of the exer... | What does it mean to Taylor expand free energy density "in gradients"? | physics | 2017-06-19T16:19:31.860 |
[
{
"message": "In special relativity, is it silently assumed that the observer is only a “measuring machine” without an innate conception of space and time, so what he thinks about motion is exactly what he measures, only this, and nothing more?So i’m also asking whether the other option is silenty assumed: that... | The nature of the observer in special relativity | physics | 2017-06-19T22:08:34.390 |
[
{
"message": "An <a href=\"https://www.livescience.com/25959-atoms-colder-than-absolute-zero.html\" rel=\"nofollow noreferrer\">article claims >100% efficiency engines possible using \"negative temperatures\":<blockquote> Negative temperatures could be used to create heat engines — engines that convert heat en... | Can "negative temperatures" be used for >100% efficiency engines? | physics | 2017-06-19T22:47:55.463 |
[
{
"message": "Could you kindly tell me where I could find the rudiments and simple applications of symmetries like particle-hole, chiral etc. in the context of condensed matter physics?",
"role": "user"
},
{
"message": "Here are some of my favorite resources on the subject of symmetries in condensed... | Resource recommendation for symmetries in condensed matter physics | physics | 2017-06-20T01:19:43.757 |
[
{
"message": "So I know the Boltzmann distribution is:$$P\\propto \\exp \\left(-E / k_BT \\right)$$where $E$ is energy, $k_B$ is the Boltzmann constant and $T$ is the temperature. However, when we replace $E$ for the kinetic energy $1/2 mv^2$ and we get$$P \\propto \\exp \\left(-mv^2 / 2k_BT \\right) \\, .$$Th... | Why do velocities obey the Boltzmann distribution? | physics | 2017-06-20T16:13:48.777 |
[
{
"message": "Consider the usual commutation relations of two scalar fields$$\\left[\\phi_{m}\\left(t,\\boldsymbol{x}\\right),\\pi_{n}\\left(t,\\boldsymbol{y}\\right)\\right]=\\boldsymbol{i}\\delta_{mn}\\delta\\left(\\boldsymbol{x}-\\boldsymbol{y}\\right),$$$$\\left[\\phi_{m}\\left(t,\\boldsymbol{x}\\right),\\p... | Commutator of scalar field and its spatial derivative | physics | 2017-06-20T18:38:28.320 |
[
{
"message": "is that right to say metal has positive charge in normal position?if not, so why does electricity pass through my body when I touch the doorknob?why does some stuff have extra electron or some others have positive charge? like when I put my foot on rug it conducts electron to my foot, and my foot ... | why does metal have positive charge in normal position? | physics | 2017-06-20T20:17:58.290 |
[
{
"message": "Say, we have an alternating current source of max voltage V, and frequency v= 1 GHz connected to 2 plates as in a capacitor with an air gap of distance d, thus we get an oscillating electric field E, inside the capacitor plates, Emax = Vmax/d;, if atomised water is sprayed in between the capacitor... | What is the effect of water molecules in an oscillating electric field? | physics | 2017-06-21T04:51:22.630 |
[
{
"message": "Consider a black hole of some radius $R$. Now, suppose a cosmohiker (with her extremely powerful rockets and a glass bowl) enters the black hole. The mass of the cosmohiker along with her belongings is $m$. As they cross the horizon (according to a good choice of coordinates in which this happens)... | Laws of Thermodynamics Breakdown Immediately Inside the Event Horizon? | physics | 2017-06-21T16:24:41.020 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.