question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>In PADMANABHAN, Gravitation (Foundations and Frontiers), Cambridge, p
$304$, exercice $7.6$, an example of the Schwarzschild metric in a
different coordinate system is given : </p>
<p>$$\mbox{d}s^2= -c^2\mbox{d}T^2 +
\dfrac{4}{9}\left(\frac{9GM}{2(R-cT)}\right)^ {\large \frac{2}{3}}
\mbox{d} R^2+\left(\frac{9... | 3,999 |
<p>From my limited classical interpretation of the universe, i've always found it convenient to think of energy as what happens when an object isnt in its equilibrium position in the universe, and thus has some combination of the 4 fundamental forces acting on it to cause it to move to an equilibrium state.</p>
<p>So ... | 4,000 |
<p>In the gravity well-like 2d surfaces that are used in documentaries to illustrate the fact Earth orbits the Sun, I don't seem to find any kind of geodesic that will at least resemble an ellipse... What am I doing wrong? Is spacetime curved entirely different from what the animators show us? Any mathematical argument... | 4,001 |
<p>For generators of the Lorentz group we have the following algebra:
$$
[\hat {R}_{i}, \hat {R}_{j} ] = -\varepsilon_{ijk}\hat {R}_{k}, \quad [\hat {R}_{i}, \hat {L}_{j} ] = -\varepsilon_{ijk}\hat {L}_{k}, \quad [\hat {L}_{i}, \hat {L}_{j} ] = \varepsilon_{ijk}\hat {R}_{k}.
$$
For the splitting of algebra, we can int... | 4,002 |
<p>It just occurred to me that almost all images I've seen of the (in)famous mushroom cloud show a vertical column rising perpendicular to the ground and a horizontal planar ring parallel to the ground. </p>
<p><img src="http://i.stack.imgur.com/yqTdB.jpg" alt="enter image description here"></p>
<p>Not that I'm an ex... | 4,003 |
<p>Can anyone explain to me the meaning of this picture? I Know that the argument is Quantum Physics and that cat is the Schrödinger's cat, but I don't know how to interpret the bra–ket notation and also the two numerical coefficients...</p>
<p><img src="http://i.stack.imgur.com/Of40B.jpg" alt="enter image description... | 4,004 |
<p>I was watching a show on discovery and according to it, in a nebula the dust and gases slowly come together and as the gravity increases and the pressure rises in the core the gases fuse together and a star is born and the rest of the left over dust and gases come together and form planets and moons.</p>
<p>So my q... | 4,005 |
<p>We all know (or maybe know) that to move, we need to spend energy. If you want to drive a car, you gotta spend gasoline.</p>
<p>We also know that energy can't be created (<a href="http://en.wikipedia.org/wiki/First_law_of_thermodynamics" rel="nofollow">first law of thermodynamics</a>, and <a href="http://en.wikiped... | 202 |
<p>I noticed an unusually fast moving cloud this morning.</p>
<p>My questions:</p>
<ul>
<li><p>What is the average velocity of a cloud on Earth?</p></li>
<li><p>What is the greatest ever recorded cloud velocity?</p></li>
<li><p>What factors affect the velocity of a cloud? (e.g. do they experience inertia?)</p></li>
<... | 4,006 |
<p>Let $H= \frac{p^2}{2m}$, then I am supposed to calculate $[x,e^{-iHt}]$.</p>
<p>My idea was to use $[x,p^n]=i \hbar n p^{n-1}$ and so I ended up by using the series for the exponential function with $-\frac{t \hbar}{m} e^{-iHt}$.</p>
<p>Could anybody tell me, whether this result is correct? </p> | 4,007 |
<p>Let's consider a single-particle(boson or fermion) with $n$ states $\phi_1,\cdots,\phi_n$(normalized orthogonal basis of the single-particle Hilbert space), and let $h$ be the single-particle Hamiltonian. As we all know, the second quantization Hamiltonian $H=\sum\left \langle \phi_i \mid h \phi_j \right \rangle c_i... | 4,008 |
<p>Previously, on <a href="http://physics.stackexchange.com/q/86509/33806">Save us from swallowing baby universes, please!</a>, I pointed out the dangers associated with false vacuum decay.</p>
<p>I wish to be more specific here. Suppose the Standard Model remains a good description of our universe even at higher ener... | 4,009 |
<p>How do you derive the solution to Poisson's equation with a point charge source? Without using Coulomb's law or the electric field! To be more explicit, we have a point charge at $(0,0)$ of charge $q$ and we want to solve Poisson's equation to find the potential. </p> | 4,010 |
<p>I'm familiar with gravitational lensing but still I'm wondering if there is experiments (conducted here on Earth) which show that light bends due to gravity. For example mirrors setup to hold the light or something like that.</p>
<p>My question is inspired by this <a href="http://physics.stackexchange.com/questions... | 4,011 |
<p>Is it true that a Mach-Zehnder interferometer with two polarizing beam splitters (PBS) is nothing but a bit flip for the polarisation degree of freedom?</p>
<p>Say the PBSs reflect vertical polarized light and transmit horizontal polarized light. If we send in a state like $|+\rangle = \frac{1}{\sqrt 2}(|H\rangle+|... | 4,012 |
<p>Would it be possible for a neutron to lose a positron and become an antiproton? Or would would it need to be the decay of a antineutron to antiproton instead? </p> | 4,013 |
<p>What factors determine whether or not wind resistance will have an
important effect on the trajectory of a projectile? </p> | 4,014 |
<p>I'm trying to understand precession for a gyroscope or top.</p>
<p>I do understand why precession occurs using the vectors for the weight force and torque and angular momentum. But what I don't understand is why precession only occurs at high angular speeds. Looking at the different vectors, there should still be a... | 4,015 |
<p>In scattering theory, P wave means $l=1$, where $l$ is the azimuthal quantum number. However, what does P wave mean when referring to particle states? For example, in <a href="http://arxiv.org/abs/hep-ph/9208254" rel="nofollow">this paper</a> (arXiv link), the authors are talking about <em>P-wave charmonia states</e... | 4,016 |
<p>Following Kepler's publication of his <a href="http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion#Third_law">3rd law of planetary motion</a><sup>1</sup>, </p>
<p>$$p^2 / r^3 = 1$$</p>
<p>in 1619, it would have been possible to use telescopic observations to arrive at an estimate of the orbital radii ... | 4,017 |
<p>I don't know how to solve question like this: </p>
<p>A transverse wave is propagated in a string stretched along the x-axis. The equation of the wave, in SI units, is given by:y = 0.006 cos π(46t - 12x). The frequency of the wave, in SI units, is closest to ...</p>
<p>Will appreciate your help!</p> | 4,018 |
<p>Here is one task below.
How to solve equation
$$
m\ddot {x} + ax = F(t), x(0) = \dot x (0) = 0
$$
in quadratures by using two methods?</p>
<p>I tried to create a system of equations</p>
<p>$$
\begin{matrix} \dot v = F(t) - w_{0}^{2}x \\ \dot x = v \\ \end{matrix},
$$</p>
<p>but I don't know, what to do next with... | 4,019 |
<p>So I was wondering, with all this Higgs talk going on, they just detected a particle with a mass of 125 GeV (CMS) or 126.5 GeV (ATLAS). But they still don't know what it is, since there is tons of data to go through.</p>
<p>How do you determine spin of a particle from such experiments? Measuring the magnetic moment... | 211 |
<p>What's a physical meaning of, for example, complex part of the solution for coordinate change of the anharmonic oscillator?
Why after substitute (for diff. equation solve) for real x we can earn $x = Re(z) + iIm(z)$? It's because of substitute?</p> | 4,020 |
<p>As Wikipedia explains, one photon passing through a crystal sometimes down-converts to two
photons. Wikipedia says total energy and momentum are conserved by just considering the
three photon states; is Wikipedia wrong here?</p>
<p>It seems a phonon (or something else) is needed too. If Wikipedia is right, can yo... | 4,021 |
<p>My sister asked me this question and I keep thinking that water would conduct heat much faster than sand. Hence the energy transfer of heat across the lake does not allow it to heat up soon. Sand on the other hand is probably a bad conductor of heat and hence more heat energy is held up by each grain of sand. </p>
... | 4,022 |
<p>Consider the following action with a fermionic field $\psi$ and a scalar field $\sigma$, </p>
<p>$S = \int d^dx \{ -\bar{\psi}(\gamma^\mu \partial_\mu +\sigma )\psi + \Lambda^{d-4}[ \frac{(\partial_\mu \sigma )^2 + m^2\sigma^2 }{2g^2 } + \frac{\lambda \sigma^4 }{4!g^4 } ] \} - (N'-1)Trln(\gamma^\mu \partial_\mu +... | 4,023 |
<p>Suppose we have a quantum state $\rho$ and let's denote the photon number operator $\hat{n}=\hat{a}^\dagger\hat{a}$ where $\hat{a}$ is the annihilation operator. Let mean photon number $\bar{n}=\operatorname{Tr}(\rho\hat{n})<\infty$ obviously be finite. Can $\rho$ have infinite photon number <em>variance</em>, ... | 4,024 |
<p>Assuming there is an incident beam(i.e. $p$ or $\alpha$) and a target. How can I be sure if a rutherford backscattering will take place?</p>
<p>I know that for high $Z$ it more likely to happen as well as for higher beam energies. Is there a boundary/formula/criterion to tell me that at that beam, for that energy, ... | 4,025 |
<p>I'm trying to develop an inertial navigation system.</p>
<p>I can access data from an accelerometer sensor (acceleration on three axes) and gyroscope sensor (angular velocity on three axes).</p>
<p>First of all, I integrate my angular velocity data with respect of time, and get angles on all three axes at every mo... | 4,026 |
<p>Consider a liquid solid interface $z =\zeta(x,t)$ moving at constant speed $v$, for a two dimensional problem. Due to solidification interface
is changing it position. For simplicity heat conductivities, heat capacity of liquid and solid are assumed to be the same. Heat conduction equation in the liquid and solid re... | 4,027 |
<p>Nuclei spontaneously decay according to a certain decay rate. There are however different kinds of decay, alpha, beta, gamma... What causes then the nuclei, when they decay, to do so in one way of another? Is there a different decay rate for each kind of decay? </p> | 4,028 |
<blockquote>
<p>Is there any reason the universe has matter not being able to exceed the speed of light, or why there is a speed limit in the first place?</p>
</blockquote>
<p>I know why it can't, meaning the basic physics of it. I am just wondering if the reason why the universe is like this is or the benefit of ... | 122 |
<p>Given an electromagnetic wave in resonance mode in a vacuum cavity inside a perfect conductor, on the boundary, the parallel component of $E$ field vanishes, and the perpendicular of component of $B$ field vanishes. How does one derive, through solving Maxwell equation boundary value problem, say by the way of stres... | 4,029 |
<p>I am an undergrad intern at a national lab currently working with a basic proton NMR device. The device consists of two big coils which provide the static magnetic field, and a smaller coil, which sends both the "excitation" signal and receives the NMR signal. A week or so ago, my supervisor asked me to calculate th... | 4,030 |
<blockquote>
<p>A closed calorimeter of negligible water equivalent contains 1kg ice at 0 degree Celsius. 1kg of steam at 100 degrees Celsius is pumped into it. Find the resultant temperature of the mixture. </p>
</blockquote>
<p>I did the standard approach. Heat absorbed by ice = Heat lost by steam. I took the chan... | 4,031 |
<p>This question is concerned with a thermodynamic paradox for radiating bodies and radiation in a cavity of a specific shape.</p>
<p>Consider two nested shells that are axisymmetric ellipsoids with the same two foci, A and B, as shown in the figure (line AB is the axis of symmetry). Cut the system along the vertical ... | 4,032 |
<p>We all know that when we say A it sounds different than when we say B. I was wondering what exactly can be the difference between saying A and B in terms of physics. I first thought that it may due to difference in the combination of frequencies. Then I realized I can say any alphabet in many different tones. </p>... | 4,033 |
<p>Is it correct that the number of lines originating from vertices on Feynman diagrams is equal to the order of phi in interaction lagrangian for scalar field?</p> | 4,034 |
<p>Apparently to create wormholes you need negative energy/matter. Say you had negative matter/energy, how would it be applied towards making a wormhole?</p> | 4,035 |
<p>I have a pot of vigorously boiling water on a gas stove. There's some steam, but not alot. When I turn off the gas, the boiling immediately subsides, and a huge waft of steam comes out. This is followed by a steady output of steam that's greater than the amount of steam it was producing while it was actually boiling... | 4,036 |
<p>I recently have read about interception of wireless information, however this mentions that people can intercept the information, and then somehow the recipient also gets the information. Regardless of this context, what happens to the actual photon if it is absorbed by one antenna how can another person receive th... | 4,037 |
<p>Can anybody suggest me a good algorithm for the time evolution of the reduced density matrix using Linbald equation. My Hamiltonian is time dependent. I am aware about Qotoolbox and Qutip. I have checked both things but I don't have any clues about the algorithms they are using. I have to find the entanglement dynam... | 4,038 |
<p>In the Metropolis algorithm, the change in the energy given by the hamiltonian is compared for flipping a spin. This is not the free energy, but for systems above absolute zero you are trying to minimize the free energy, not the energy. So how is free energy built into this kind of simulation? How is entropy?</p> | 4,039 |
<p>I've got a homework question. </p>
<blockquote>
<p>Consider a 2 dimensional space with metric $$ ds^{2} = \frac{dr^{2}}{1 -\frac{2}{r} } + r^{2}d\theta^{2} .$$ </p>
<p>I need to show that this is the induced metric (not sure if im translating this correctly) from $\Bbb R ^{3}$ and I need to find the parametr... | 4,040 |
<p>So, there are all kinds of 'standard' explanations that people just 'know' about how things work which are wrong. The sort of explanations a dad may give to their son when he asks the infamous "why" word to explain how the world works. Not all of these answers are entirely true. </p>
<p>I thought, for the sake o... | 4,041 |
<p>First of all I beg your forgiveness as I am not a physicist and the question I am going to ask may sound silly.</p>
<p>I am aware that beyond a certain threshold in the hierarchy of building blocks of matter (electrons, atoms, etc.) the 'standard' laws of physics (e.g. <a href="http://en.wikipedia.org/wiki/Classica... | 4,042 |
<p>I have this problem: They give me, from a satellite that is in orbit in earth, a value for the period, and the closest height to earth surface, the ask me what the eccentricty of the orbit is. I have no idea how to do this. I've tried using Binet's equation, and the equation that comes for these movements ($p/r=1+e\... | 4,043 |
<p>And what happens with the magnetic field of a star that goes supernova? The magnetic radiation is scattered through the cosmos? Each particle will go away with its own magnetic radiation?</p> | 4,044 |
<p>The assumptions are: </p>
<ul>
<li>Alice and Bob have perfectly synchronized clocks</li>
<li>Alice and Bob have successfully exchanged a pair of entangled photons</li>
</ul>
<p>The idea is simply to have Alice and Bob perform the Quantum Eraser Experiment (doesn't need to be the delayed choice). </p>
<p>Alice and... | 4,045 |
<p>my problem is that I can’t find a way to calculate the power required to drive the shaft and thus decide on a motor, I have tried several times using different methods and calculations but can’t seem to get a power requirement that would seem accurate, most recently I tried using a fluid equation of force on an imme... | 4,046 |
<p>It is well-known that some exotic phases in condensed matter physics are described by <a href="http://en.wikipedia.org/wiki/Topological_quantum_field_theory#Schwarz-type_TQFTs">Schwarz-type TQFT</a>s, such as Chern-Simons theory of quantum Hall states. My question is whether there are condensed matter systems that c... | 4,047 |
<p>Ryder in his QFT book writes in eqn (2.20):</p>
<p>Probability density, $\rho = \frac{i\hbar}{2m}(\phi^*\frac{\partial \phi}{\partial t} - \phi \frac{\partial \phi^*}{\partial t})$</p>
<p>Then in the next paragraph he writes: Since the Klein-Gordon equation is second order, $\phi$ and $\frac{\partial \phi}{\partia... | 4,048 |
<p>I have a question about Eq. (4.3.3) in Polchinski's string theory book volume I, p. 131. It is said</p>
<blockquote>
<p>Replacing the $X^{\mu}$ with a general matter CFT, the BRST transformation of the matter fields is a conformal transformation with $v(z)=c(z)$, while $T^m$ replaces $T^X$ in the transformation o... | 4,049 |
<p>I'm quite familiar with SR, but I have very limited understanding in GR, singularities, and black holes. My friend, which is well-read and is interested in general physics, said that we can "jump" into another universe by entering a black hole.</p>
<p><em>Suppose that we and our equipments can withstand the tidal f... | 4,050 |
<p>If, as I asked in <a href="http://physics.stackexchange.com/questions/19631/question-about-the-perturbative-renormalization-group">this question</a>, a relevant operator in a renormalization group transformation can't be used in a perturbative expansion since it becomes large as the transformations are applied, does... | 4,051 |
<p>I'm currently learning about the renormalization group (RG) in condensed matter physics and just want to clarify a couple of things:</p>
<p>When doing the RG transformation, there's a flow to a fixed point. A coupling constant is a relevant operator (or relevant coupling, depending on which book you look at) if it ... | 4,052 |
<p>Since electromagnetic waves have both electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. How much is that electric charge? Can you possibly get a shock in some way?</p> | 485 |
<p>I'm supposed to derive a relation for the range of wavelengths that's being transmitted by a spectrometer (bandpass) in terms of the dispersion, focal length and exit slit width.</p>
<p>Given grating is $100mm$ wide, slit separation $d=5.6\times 10^{-7} m$, focal length $f=1\space m$, exit slit width $w=100\mu m$ a... | 4,053 |
<p>I've heard a couple of scary stories from experienced accellerator physiscists about something called neutron clouds. Apparently, if you have an experiment like a fixed-target experiment that produces a lot of neutrons with the correct energy, they don't just dissipate or get caught in surrounding matter. Instead, t... | 4,054 |
<p>In an experiment we were given non-homogenous dielectric substances described by functions of coordinate. How can capacitance be determined from this?</p> | 4,055 |
<p>If we have a spherical capacitor with inner radius or r1 and outer radius of r2, with charges (+/-)q on them and there is a dielectric material (with constant e) in between them with. </p>
<p>What kind of a potential would this create outside the entire capacitor? in the region with the dielectric? and inside the e... | 4,056 |
<p>This question is based on the description of Longair in his book "Theoretical Concepts in Physics".</p>
<p>He starts by giving some provisions:</p>
<ul>
<li>Conservative force field</li>
<li>Fixed times $t_1$ and $t_2$</li>
<li>Object moves from fixed point at $t_1$ to fixed point at $t_2$</li>
</ul>
<p>Then he d... | 4,057 |
<p>We use ceiling and table fans in home which are can be set to low or high speeds using regulators. I want to ask that does it uses or consumes same amount of electricity at different speeds? Here, "same amount of electricity" means exactly I want to know that, my electricity bill will be different for different spee... | 4,058 |
<p>I am experimenting and playing around with some data, and I'm having trouble seeing how to generate invariant mass plots.</p>
<p>The data I have has a bunch of events, and variables such as $P,P_T,\eta,\phi$ etc.. but no energy. There is a histogram which generates the invariant mass, but no macro provided for this... | 4,059 |
<p>Suppose we are given two conducting, cocentric spheres of radius $a_1$ and $a_2$ respectively. The inner sphere with charge $q$, the outer sphere with charge $-q$.</p>
<p>I can calculate the capacitance of this system by calculating the potential difference $U$ between the plates and then use the definition $C = q ... | 4,060 |
<p>I am trying to do a crude particle identification, using a Bethe Bloch tenchnique. Here is a plot I made from the data that I have
<img src="http://i.stack.imgur.com/SeyLv.png" alt="enter image description here"></p>
<p>From what I've read, the standard method to identify charged particles is by measuring the ioni... | 4,061 |
<p>I've been having trouble with my physics homework. The problem is: </p>
<blockquote>
<p><em>You may have measured the properties of a simple spring-mass system in the lab. Suppose you found ks = 0.9 N/m and m = 0.01 kg, and you observed an oscillation with an amplitude of 0.5 m. What is the approximate value of N... | 4,062 |
<p>What is the advantage/purpose of using $\psi$ for wavefunctions and getting the probability with $|\psi|^2$ as opposed to just defining and using the probability function?</p> | 4,063 |
<p>I am trying to derive the <a href="http://en.wikipedia.org/wiki/Fermi%E2%80%93Dirac_statistics" rel="nofollow">Fermi-Dirac statistics</a> using density matrix formalism.
I know that </p>
<p>$$<A>= Tr \rho A.$$</p>
<p>So I started from</p>
<p>$$<n(\epsilon_i)>= Tr \rho n(\epsilon_i)=\frac {1}{Z} \sum e... | 4,064 |
<p><img src="http://i.stack.imgur.com/hbp7B.jpg" alt="enter image description here"></p>
<p>The mass is released at height $h$ above the spring, how far will the spring move?
$E_i=mgh, E_f= kx^2/2+mgx$...why the second equation isn't $ E_f= kx^2/2-mgx$? Since it is below the "zero".</p> | 4,065 |
<p>In the first term the energies are given by the Wentzel–Kramers–Brillouin (WKB) formula</p>
<p>$$ \oint p dq = 2\pi \left( n+\frac{1}{2} \right) $$</p>
<p>However, can this formula be improved to include further corrections? For example the wave function in the WKB approach can be evaluated to several orders of ... | 4,066 |
<p>There is a large metal container in form of a cube made of stainless steel. It is used for storing water in it for technical uses. The problem is that all joints at the bottom of the container have micro cavities and water leaks through them very slowly. I am thinking of a method to close these micro cavities from i... | 4,067 |
<p>I have a differential operator $L$,</p>
<p>$\displaystyle L = i (t\frac{\partial}{\partial z} - z\frac{\partial}{\partial t})$</p>
<p>I can trivially hit this operator to $x,y,z$ and $t$ as $L x$, $L t$, $L y$, $L z$.</p>
<p>But I have a problem with <em>exponential of that operator</em>. I want to hit this opera... | 4,068 |
<p>I'm trying to derive the equation for the cosmological fluid:</p>
<p>$$\dot \rho + 3 \frac{\dot a}{a}(\rho +P)=0$$</p>
<p>by starting from the conservation of the stress-energy tensor:</p>
<p>$$\nabla^\mu T_{\mu \nu} = 0$$</p>
<p>with the stress-energy for a perfect fluid in its own frame being:</p>
<p>$$ T_{\m... | 4,069 |
<p>I am working through Franz Schwabl's book on Statistical Mechanics, and he has a number of derivations of thermodynamic quantities that are different than those I have seen before. I am also having difficulty finding them repeated elsewhere.</p>
<p>In particular, he has a method for calculating $\Omega(E)$, the num... | 4,070 |
<p>This is just a question about terminology that is used in the beginning of a chapter about phonons.</p>
<p>In a simple cubic crystal, we can consider elastic oscillations in f.i. the [100] direction. In this direction there is one longitudinal and two transversal oscillation modes. Now my textbook tells that these ... | 4,071 |
<p>I'm currently a third year undergrad writing about Minimal Surfaces. In particular, trapped surfaces and black holes.</p>
<p>What does the <a href="http://www.google.com/search?as_q=Positive+Mass+Theorem" rel="nofollow">Positive Mass Theorem</a> have to do with this? And does the theorem directly predict the existe... | 256 |
<p>I have a throlabs half- and quarter-wave plate with rotation plate. There shown the angle scales and a line denotes the fast axis. But what does the angle mean? I do some research and someone said the angle reading tells the angle away from the transmission direction and other said that's the angle away from the fas... | 4,072 |
<p>Suppose a warm body moving in an empty space with high speed. </p>
<p>The body emits radiation based on its temperature. The protons emitted forwards of the body will have higher energy due to Doppler shift than those emitted backwards. Thus they will care greater momentum. The body should slowdown due to emitted r... | 4,073 |
<p>If one looks into a mirror, he can see a certain field of view.</p>
<p>If he places a convex lens that magnifies (or a concave lens that does the opposite) in front of the mirror, but so that he can still see the entire mirror, will it affect the field of view shown in the mirror?</p> | 4,074 |
<p>The Problem:</p>
<blockquote>
<p><em>An 8-m-long beam, weighing 14,700 N, is hinged to a wall and supported by a
light rope that is attached 2.0 m from the free end of the beam. If the beam is
supported at an angle of 30.0° above the horizontal, (a) find the tension in the
rope and (b) the reaction force of... | 4,075 |
<p>In David J. Griffiths's <em>Introduction to Electrodynamics,</em> the author gave the following problem in an exercise.</p>
<blockquote>
<p><em>Sketch the vector function</em>
$$ \vec{v} ~=~ \frac{\hat{r}}{r^2}, $$
<em>and compute its divergence, where</em>
$$\hat{r}~:=~ \frac{\vec{r}}{r} , \qquad r~:=~... | 4,076 |
<p>I read that </p>
<blockquote>
<p><em>Halo nuclei could be seen as special Efimov states, depending on the subtle definitions.</em> (The last sentence in the second to last paragraph of <a href="http://en.wikipedia.org/wiki/Efimov_state" rel="nofollow">this</a> Wikipedia article.) </p>
</blockquote>
<p>This does ... | 4,077 |
<p>This question is more about trying to feel the waters in our current abilities to compute (or roughly estimate) the refraction index of vacuum, specifically when high numbers of electromagnetic quanta of a given frequency $\omega$ occupy a spherical symmetric incoming wavefront modes
$$\frac{e^{i k r}}{r^2}$$</p>
... | 4,078 |
<p>What is Curie-Weiss temperature? What is the difference between Curie-Weiss temperature and <a href="http://en.wikipedia.org/wiki/Curie_temperature" rel="nofollow">Curie temperature</a>?</p> | 4,079 |
<p>This is homework and I need some guidance.
The question I struggle with is:</p>
<p>Place a particle with $m=2$ , $q=3$ in a constant electric field $\vec{E}=(5,0,0)$
Choose $\vec{r}(0)=(0,0,0)$ and $\vec{v}(0)=(0,0,0)$ and time steps $dt=1*10^{-4}$</p>
<p>I've nummerically found a solution using Euler-Cromer metho... | 4,080 |
<p>I understand the nature of light can be complex and has extensive theories/experimental data. We hear light can be both a wave and particle, so why can't it be both, a wave of particles?</p> | 4,081 |
<p>It is well known that the speed of light $c$ can be interpreted as the speed limit for information propagation. Similarly, the Planck's constant $h$ is interpreted as the minimum quantum package of action/entropy. Is there a similar interpretation for the Newton's constant $G$?</p> | 4,082 |
<p>I'm reading <a href="http://www.tcm.phy.cam.ac.uk/~bds10/aqp/handout_operator.pdf" rel="nofollow">this tutorial</a> by Ben Simons entitled <em>Operator methods in
quantum mechanics</em> in connection with his course in advanced QM, and I'm a bit puzzled by an identity in page 25, a bit above relation (3.3):</p>
<p>... | 4,083 |
<p>I am in a serious doubt about it.</p>
<p>Consider a battery of emf E and we connect it to an inductor. Initially the switch is open, now we close the switch. My question is: What mechanism happens just after closing the switch?</p>
<p>When we close the switch, the electric field produced in the conductor by the ba... | 4,084 |
<p>I got given this question and im just lost.</p>
<blockquote>
<p>An object that weighs 25 kg experiences two perpendicular
forces of 80N and 50N respectively. </p>
<p>What's the acceleration that object gets?</p>
</blockquote>
<p>What i don't understand is how i would use that information to work out the a... | 4,085 |
<p>Is the flow of time regular? How would we come to know if the <strong>our</strong> galaxy along with everything in it stops for a while(may be a century) <strong>w.r.t to the galaxies far beyond our reach</strong>. Is there a way to know if flow of time is smooth,or irregular?</p>
<p>PS I would describe myself as a... | 4,086 |
<p>In this <a href="http://physics.stackexchange.com/questions/26617/how-to-determine-day-night-based-on-latitude-longitude-and-a-date-time">question about how to calculate sunrise</a>,
there is a link to a page that describes a <a href="http://williams.best.vwh.net/sunrise_sunset_algorithm.htm">algorithm to calculate... | 4,087 |
<p>The all-electron code Wien2K will optionally calculate the character tables for a specified list of $k$-points. I'd like to know the parity eigenvalue for a given $k$-point and band index. Is there some way to compute the parity eigenvalue from the irreducible representation of the group given that $\{i\}$ is a symm... | 4,088 |
<p>Consider a block sliding down an incline plane at an angle $\theta$ with the horizontal. For the acceleration as a function of $\theta$ I find $$\ddot{x}=g \ \sin\theta $$ My text then claims we can find the block's velocity after it moves a distance $x_0$ from rest by multiplying both sides by $2\dot{x}$ and doing ... | 4,089 |
<p>As far as my knowledge goes, Higgs field is only currently formulated in term of classical gauge theory. What is the importance of Higgs field being formulated in term of quantum gauge theory? In other words, why do we need to formulate Higgs field in term of quantum gauge theory?</p>
<p><a href="http://en.wikipedi... | 4,090 |
<p>My layman understanding of the Uncertainty Principle is that you can't determine the both the position and momentum of a particle at the same point in time, because measuring one variable changes the other, and both cannot be measured at once.</p>
<p>But what happens if I measure a charged particle with any number ... | 4,091 |
<p>I am trying to figure out if Snell's Law for refraction can be derived from <a href="http://www.google.com/search?q=scalar+diffraction+theory" rel="nofollow">Scalar Diffraction Theory</a>.</p>
<p>The setup is this: light (plane wave, with wave vector $\vec k_i = (k_x, k_y, k_z)$ ) falls on a flat interface which i... | 4,092 |
<p>There are a number of factors that I can think of:</p>
<ul>
<li><strong>The larger mass of the hammer</strong> would cause more force to be applied due to
F=MA.</li>
<li><strong>The larger surface area of the pillow</strong> would spread out the force of the impact, applying less pressure at any given point.</li>
<... | 4,093 |
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