question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>In the pilot's introductory book "Stick and Rudder" it claims that a nose-up glide is possible. It doesn't state how, why or when. It implies it's possible to do and maintain a constant forward velocity.</p>
<p>Is this possible? I really don't see how, unless the aircraft has what I assume would be an extremely unu... | g12495 | [
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<p>The party line of the anthropic camp goes something like this. There are at least $10^{500}$ flux compactifications breaking SUSY out there with all sorts of values for the cosmological constant. Life takes a lot of time to evolve, and this is incompatible with a universe which dilutes away into de Sitter space too ... | g12496 | [
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<p>Ok, I've stumbled onto what I think is a bit of a paradox. </p>
<p>First off, say you had some computer in a very fast(near light speed) centrifuge. You provide power to this computer via a metal plate on the "wall" of the centrifuge's container, so it works similar to how subways and streetcars are powered.</p>
<... | g12497 | [
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<p>Okay, I'm asking a question similar to this one here: <a href="http://physics.stackexchange.com/q/4404/2330">Time Dilation - what happens when you bring the observers back together?</a>. Specifically, I am curious about a specific angle on the second part of his question, regarding when two moving frames of referenc... | g968 | [
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<p>How to do this?</p>
<p>Show that if the tension $F$ in a string is changed by a small amount $\mathrm dF$, the fractional change in frequency of a standing wave, $\frac{\mathrm df}{f}$ is given by:</p>
<p>$$\frac{\mathrm df}{f}~=~0.5\frac{\mathrm dF}{F}.$$</p> | g12498 | [
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<p>This question is raised because of the recent incident in a London subway station involving a stroller falling onto the tracks. The stroller was probably 10 feet (or 3 m) from the edge of the platform but was moved by the wind as the train departed and went into the tunnel.</p>
<p>Assume the weight will likely be ... | g12499 | [
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<p>So I have the potential energy defined as:
$$U(x)=U_0[2(\frac xa)^2-(\frac xa)^4]$$
And I want to find the angular frequency of oscillations about the point of stable equilibrium. I found the point of stable equilibrium to be 0, but now I do not know how to find the angular frequency. Normally I would look to use... | g12500 | [
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<p>Look at any Kruskal–Szekeres coordinate plot of the Schwarzschild solution. It shows the same mass everywhere. Yet the two sides cannot talk to each other, in that no information, particles, etc can cross the wormhole throat. So how do the sides 'know' to be the same mass?</p>
<p>So is there a way to draw a Kruska... | g12501 | [
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<p>Of course it should have dimension $2n$.</p>
<p>But any more conditions?</p>
<p>For example, can a genus-2 surface be the phase space of a Hamiltonian system? </p> | g12502 | [
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<p>How dense does a gas (Argon in particular ) have to be to in order to ionize it using electron bombardment and weak magnetic fields. Is there a correlation with the density of a gas and the easiness to ionize the gas ?</p> | g12503 | [
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<p>I was studying for my exam and looking at the chapter which talks about Potential-energy graphs.</p>
<p>Let's take this as an example:<br>
<img src="http://i.stack.imgur.com/F0iVj.jpg" alt="Potential-Energy Graph"></p>
<p>My book states that: "If the object is in $B$ and has a total energy of $0$ then it can only ... | g12504 | [
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<p>I am trying to derive Feynman rules from a given Lagrangian and I got stuck on some vertex factors. What for example is the vertex factor that corresponds to the four-scalar interaction that is decribed by the following Lagrangian?</p>
<p>\begin{equation}
L = -\frac{1}{4} g_3^2 \phi^\dagger \lambda^a \phi \chi^\dag... | g12505 | [
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<p>I recently asked a <a href="http://physics.stackexchange.com/questions/128471/how-to-simulate-rotational-instability">question</a> about modeling instability in a rotating rigid body. I now realize that I was mentally confounding two different effects:</p>
<ol>
<li><p>The "Dzhanibekov effect" in which a rigid obje... | g12506 | [
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<p>I need to plot the time evolution of the total angular momentum in an accretion disk. This confuses me because I thought this should be constant, since angular momentum has to be conserved?</p>
<p>I'm given the angular velocity $\Omega=(GM/R^3)^\frac{1}{2}$ where $M$ is the mass of the central object, and that the ... | g12507 | [
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<p>The missile plume can be considered a cold plasma. If a radio signal passes across the plume it's attenuated. Obviously the attenuation depends on the frequency of the signal. Where can I find some information about the behaviour of the RF across the cold plasma? Thanks</p> | g12508 | [
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<p><a href="http://en.wikipedia.org/wiki/Work_%28physics%29" rel="nofollow">Work done</a> is defined as the dot product of force and displacement. </p>
<p>However, intuitively, should it not be the product of force and the time for which the body is acted upon by the force (force * time) because while time is independ... | g12509 | [
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<p>Let's consider a spring which is subjected to forced vibrations:
$$
F = F_0 \cos(\omega t)
$$
Is the resonance frequancy $\omega_0$ of the spring dependent on the amplitude $F_0$? </p>
<p>I ask this because I am currently conducting tests with a plate which is forced to vibrate in the Z-direction orthogonally to i... | g12510 | [
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<p>Redhead claims in his paper "More ado about nothing" (<a href="http://link.springer.com/article/10.1007%2FBF02054660" rel="nofollow">http://link.springer.com/article/10.1007%2FBF02054660</a>) that number operators associated with different space points (at fixed time) fail to commute, and hence are not physically me... | g12511 | [
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<p>When a system is expressed in terms of creation and annihilation operators for bosonic/fermionic modes, what exactly is the physical meaning of the order in which the operators act?</p>
<p>For example, for a fermionic system with states $i$ and $j$, $c_i c_j^\dagger$ is different from $c_j^\dagger c_i$ by a sign ch... | g12512 | [
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<p>I face some trouble solving Maxwell's equations inside a cylinder with perfect conductor boundaries (in 3D) ?
We work with cylindrical coordinates $(r, \phi, z)$ and we make the assumption that fields have a sinusoidal "$e^{i\omega t}$" time dependence. Note that we have a $\phi$ symmetry.
First, and in any coordina... | g12513 | [
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<p>Book: Classical mechanics (textbook) by Douglas Gregory (cambridge publications)</p>
<p>Law of mutual interaction states that when two particle (let it be P1 and P2) interacts, the particle (P1) induces an instantaneous acceleration (a21) on particle P2 and the particle P2 induces an instantaneous acceleration (a12... | g12514 | [
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<p>I saw somewhere about being able to measure the velocity, period and radius of a binary star orbit by looking at red shift and blue shift. </p>
<p>I understand it but can someone give me an example of calculations etc done to calculate the velocity, period and radius of a binary stars in orbit?</p> | g246 | [
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<p>I have read about <a href="http://en.wikipedia.org/wiki/Zeno%27s_paradoxes" rel="nofollow">Zeno's arrow paradox</a> that tells us there is no motion of the arrow at a particular instant of its flight. It can be inferred that there can be no velocity at any instant. Moreover we cannot calculate velocity at any instan... | g12515 | [
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<p>We know that after the big bang the temperature was about 10^32 K.<br>
But now the average temperature of the universe is about 4 K. What happened to the temperature at that time? Where did it go?</p> | g12516 | [
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<p>A teacher has recommended me to read this book in order to prepare for a project I am doing. Anyway, I feel that I should need a book in order to prepare for this one. Any suggestions?</p> | g89 | [
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<p>The wave equation can be solved using Fourier transform, by assuming a solution of the form of
$$\mathbf{E}(x,y,z,t)~=~\mathbf{E}(x,y,z)e^{j\omega t}$$
and then reducing the equation to the <a href="http://en.wikipedia.org/wiki/Helmholtz_equation" rel="nofollow">Helmholtz equation</a>.</p>
<ul>
<li><p>What are the... | g12517 | [
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<p>Assume that you are holding a cage containing a bird. Do you have to make less effort if the bird flies from its position in the cage and manages to stay in the middle without touching the walls of the cage?<br>
Does it make a difference whether the cage is completely closed or it has rods to let air pass? </p> | g792 | [
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<p>I simulate scenario of two contacting elastic spheres, where their radii and the distance of their centers is known, and repulsive force should be computed. Material parameters are also given. Most contact mechanics references (also the Wikipedia page on <a href="http://en.wikipedia.org/wiki/Contact_mechanics" rel="... | g12518 | [
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<p>I'm having trouble understanding just what the hyperbolas on a space-time diagram actually signify. From what I understand, these hyperbolas trace out the equation $S^2=x^2-(ct)^2$, which is the equation for a hyperbola. Fine so far. Furthermore, the plot is supposed to represent the value of $S$, which is the in... | g12519 | [
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<p>Suppose you had 80% up quarks, and only 20% down quarks. How would this affect stellar formation?</p> | g12520 | [
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<p>Using Special relativity theory, of course. Can Lorentz transformations to "tell" something about it?
"Wikipedia's" article:
<a href="http://en.wikipedia.org/wiki/One-way_speed_of_light">http://en.wikipedia.org/wiki/One-way_speed_of_light</a> .</p> | g12521 | [
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<p>In Vladimir I. Arnold's <em>Lectures on Partial Differential Equations</em>, Chapter 3 <em>Huygens' Principle in the Theory of Wave Propagation</em>, which is devoted to the proof of Huygens principle (original one by Huygens, maybe not by Fresnel), it's said that</p>
<blockquote>
<p>the contact elements of space... | g12522 | [
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0.0053... |
<p>Can you give a basic explanation of what is crystal field anisotropy ?</p>
<p>What is the reason to arise ?</p>
<p>In spin ice it forces the dipoles to point in the local 111 direction.</p>
<p>For partially filled rare earth atoms hund rule requires S and L max.
This leaves (2s +1)(2l+1) degeneracy which is parti... | g12523 | [
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... |
<p>I'm going to be brief, I just saw a Discovery Channel show that showed a lot of interesting phenomena around lightning (like <a href="http://en.wikipedia.org/wiki/Lightning#Elves" rel="nofollow">elves</a>, how cool is that(!)), and got me wondering.</p>
<p>1) Thinking of lightning as a purely mechanical phenomenon,... | g12524 | [
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<p>I got an integral in solving Schrodinger equation with delta function potential. It looks like </p>
<p>$$\int \frac{y(x)}{x} \frac{\mathrm{d}\delta(x-x_0)}{\mathrm{d}x}$$</p>
<p>I'm trying to solve this by splitting it into two integrals</p>
<p>$$\int_{-\infty}^{x_0 - \epsilon} \frac{y(x)}{x} \frac{\mathrm{d}\del... | g12525 | [
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<p>Yang's theorem states that a massive spin-1 particle cannot decay into a pair of identical massless spin-1 particles. The proof starts by going to the rest frame of the decaying particle, and relies on process of elimination of possible amplitude structures.</p>
<p>Let $\vec\epsilon_V$ be the spin vector of the de... | g12526 | [
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<p>I am interested to know how does <a href="http://en.wikipedia.org/wiki/Center_of_mass" rel="nofollow">CG</a> of vehicle plays role in the Fuel economy and the vehicle performance. Does CG of vehicle has anything to do while accelerating of your vehicle. I am a student, henceforth I would feel glad to know about thes... | g12527 | [
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<p>How do you calculate the Poynting vector for a laser given it's power? I know for a sphere you can just take the power, and divide it by 4$\pi R^2$, but I don't know what I would do for a laser. Would I have to take into account the aperture size?</p> | g12528 | [
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<p>I have a fridge compartment, the lowest temperature can be set to to about 0c. Is it possible I could bring it down to -2c, -3, -4 c etc by simply adding water bottles which were previously frozen in a freezer compartment. Would the temp be similar throughout the entire fridge or would it fluctuate significantly?<... | g12529 | [
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<p>My sister got this homework that she don't understand, me neither. Can anyone help out?
Here's the problem:</p>
<p>Give the x-component and y component of the following vectors:</p>
<p>a. A = 7.0 cm, E</p>
<p>b. B = 5.7 cm, S</p>
<p>c. C = 5.5 cm, 30 degrees E of N </p>
<p>d. D = 5.5 cm, 60 degrees S of E </p>... | g12530 | [
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<p>recently I have had <a href="http://physics.stackexchange.com/questions/4372/does-entropy-apply-to-newtons-first-law-or-does-acted-upon-always-require-an-e/4380#4380">some exchanges with @Marek</a> regarding entropy of a single classical particle. </p>
<p>I always believed that to define entropy one must have some ... | g12531 | [
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<p>This question is inspired by the following comment:</p>
<blockquote>
<p>the strings in string theory are relativistic and on a large enough piece of world sheet, the internal SO(1,1) Lorentz symmetry is preserved. That's why a string carries not only an energy density ρ but also a negative pressure p=−ρ in the di... | g12532 | [
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<p>I went (on vacation) to the beach, The sea was very calm (just like solar system) There was one person in a fishing boat, Suddenly a huge wave came to shore...</p>
<p>Is it possible that a gravitational wave of space - time hit the solar system in a same way?</p> | g12533 | [
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<p>1) What is the difference between these two momentum operators:
$\frac{\hbar}{i}\frac{\partial}{\partial x}$ and
$-i\hbar\frac{\partial}{\partial x}$?
How are these two operators the same?</p>
<p>My textbook says that $\frac{\hbar}{i}\frac{\partial}{\partial x}$ is the mathematical operator acting on $\Psi$ that pr... | g12534 | [
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<p>I'm going through an introduction to many-body theory and I am getting tripped up on the formalism. I understand quantities such as $\hat {N} = \sum_{i}\hat{n}_{i}=\sum_{i}\hat{a}_{i}^{\dagger}\hat{a}_{i}=\int d^{3}x\psi^{\dagger}(x)\psi(x)$ but struggling with things interpreting things like the kinetic energy of t... | g12535 | [
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<p>First we have Discretization of the Transport Equation
$$
\frac{\partial \rho \phi}{\partial t} + \nabla(\rho U \phi) - \nabla (\rho \Gamma_\phi \nabla \phi) = S_\phi (\phi)
$$</p>
<p>In Finite Volume Method it looks like:
$$
\int_t^{t+\Delta t} \left[ \frac{\partial}{\partial t} \int_{V_p} \rho \phi dV + \int_{V_p... | g12536 | [
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<p>I'm having trouble grokking the relationship between a winch's pull/torque and a spring's potential energy.</p>
<p><strong>I would like to compress a spring using an electric winch and figure out how far it will be able to launch an object.</strong></p>
<ol>
<li><p>If the spring's maximum load is higher than the w... | g12537 | [
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<p>This theorem is number 44 of chapter 14 in Barret O'Neil's book "Semi-Riemannian Geometry (with applications to relativity)". The proof given, in particular the use of another theorem to justify the last passage, does not convince me. Here is it. How do I prove it?</p>
<p><strong>Lemma</strong></p>
<p>Let $S$ be a... | g12538 | [
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0.043130822479724884,
0.049264341592788696,
-0.0090... |
<p>Goldstein's Classical Mechanics has a puzzling few sentences in his discussion of orbits. </p>
<p>Referring to the case of orbit where the energy is low enough for the orbit to be bounded, he says :"This does not necessarily mean that the orbits are closed. All that can be said is that they are bounded, contained b... | g12539 | [
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<p>In my physics textbook, it says that for any pulse, if $\Delta x$ becomes smaller, $\Delta k$ becomes larger where $k$ refers to $2\pi/\lambda$ and $x$ is x-axis displacement, as described by $\Delta x \Delta k \approx 1$. Why is it like this?</p> | g12540 | [
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0.020539605990052223,
0.04882388934493065,
-0.038... |
<p>I have read about anomalies in different contexts and ways. I would like to read an explanation that unified all these statements or point-views:</p>
<ol>
<li><p>Anomalies are due to the fact that quantum field theories (and maybe quantum mechanical theories with singular potential) must be <em>regularized</em> and... | g12541 | [
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<p>I'm reading <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.44.7880&rep=rep1&type=pdf" rel="nofollow">"Symplectic geometry and geometric quantization"</a> by Matthias Blau and he introduces a complete set of observables for the classical case:</p>
<blockquote>
<p>The functions $q^k$ and... | g12542 | [
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0... |
<p>Reading <a href="http://www.dnr.state.oh.us/Portals/11/bainbridge/DMRM%202%20Chapter%202%20-%20Hydraulic%20Fracturing%20Analysis.pdf" rel="nofollow">this</a>, I can intuitively understand that fractures propagate along the path of least resistance, creating "width in a direction that requires the least force". Howe... | g12543 | [
0.01664593443274498,
0.06868218630552292,
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0.03036154806613922,
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0.04539938643574715,
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<p>I am a second year undergraduate and studying quantum mechanics from sakurai's 'Modern Quantum Mechanics'. Is it a good idea to solve problems from sakurai, which are mostly mathematical in nature? I need a textbook that has physically relevant problems, maybe going even into condensed matter, or field theory in its... | g12 | [
0.019829977303743362,
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0.021591830998659134,
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0.0072413417510688305,... |
<p>I know of events that are happening about 45 KM away from me which are said to be 210 or 213 dB at 75 meters distance from <a href="http://listverse.com/2007/11/30/top-10-loudest-noises/" rel="nofollow">multiple</a> <a href="http://www.makeitlouder.com/Decibel%20Level%20Chart.txt" rel="nofollow">sources</a>. I think... | g12544 | [
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<p>Consider a column of fluid of length $L$, with initial density $\rho_0$ and initial velocity ($u_0 =0$) everywhere. Now at time $t=0$ gravity is switched on. No-slip boundary conditions are assumed at both end of the fluid column.</p>
<p>We know that after a while column will attain a steady state with fluid everyw... | g12545 | [
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... |
<p>I'm studying the book "Classical Mechanics" by Goldstein together with a coursebook my professor provided.</p>
<p>I'm having trouble grasping how to intuitively determine what the rate of change of a vector is affected by.</p>
<p>Earlier on in the book, I saw a body with 3 frames of reference:<br>
$Oxyz$ which is ... | g12546 | [
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0.01470... |
<p><em>Note: I struggled to decide the appropriate site for this question, between <a href="http://physics.stackexchange.com/">http://physics.stackexchange.com/</a>, <a href="http://avp.stackexchange.com/">http://avp.stackexchange.com/</a>, <a href="http://math.stackexchange.com/">http://math.stackexchange.com/</a>, an... | g12547 | [
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... |
<p>So, I was reading about the Casimir effect. Two mirrors facing each other attract to each other in a vacuum. The reason is due to pressure exerted on those mirrors from the multitude of EM waves (like light) outside of them, while in between those mirrors there are less waves present since long waves can't fit. The ... | g12548 | [
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0.026011284440755844,
0.006015360821038485,
0.00977... |
<p><em>Note</em>: I don't know if this is the best place for this question, because it is very specific. However, I'm not sure of a better place to go (apart from one of the other SE's). If you have a recommendation, I'd love to hear it.</p>
<p>Anyway, here goes:</p>
<p>I'm reading a paper (<a href="http://arxiv.org/... | g12549 | [
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0.0... |
<p>If we positioned a mirror 1 light year away from earth and shot a particle of light at the mirror so that it would reflect and come back to earth, how long would it take for us to receive that particle of light back to earth and if I jumped on this particle of light for the trip how would it effect how much time has... | g12550 | [
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0.05979238823056221,
0.04026314988732338,
-0.000... |
<p>So I have an equilibrium phase diagram of steel and I am asked to 'Calculate the proportion of pearlite in the microstructure of 0.4 wt% C steel just below the eutectoid temperature (727 °C).'</p>
<p>I have been using the forumlas</p>
<p>$Wa=\frac{Cb-Co}{Cb-Ca}$%</p>
<p>$Wb=100-Wa$%</p>
<p>$Ca=weight$% of (Carbo... | g12551 | [
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<p><strong>Question:</strong><br>
3 boys push a small car 25 m up a hill inclined at 19° to the horizontal. The car has a weight of 860 N and they push it at a steady speed of 0.5 m s<sup>-1</sup> against an opposing force of friction of 70 N acting down the hill.
<img src="http://i.stack.imgur.com/2Hp6Z.png" alt="ente... | g12552 | [
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<p>There are theoretical predictions for SM Higgs decay branching ratios. What about the experimental results on BRs?</p>
<p>All that I found was measurements of signal-strengths $\mu = \frac{(\sigma \cdot BR)_{\text{meas}}}{(\sigma \cdot BR)_{\text{SM}}} $ and coupling strengths $\kappa$. </p>
<p>Why are there no r... | g12553 | [
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<p>In another Physics stack exchange thread here, <a href="http://physics.stackexchange.com/questions/119381/spin-matrix-for-various-spacetime-fields[/url]">Spin matrix for various spacetime fields</a> I obtained the generator of rotations of the SO(2) rotation group for an infinitesimal rotation of 2D vectors. I the... | g12554 | [
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<p>Now I'm trying to give an answer of the question. Satellite rotates about earth by the gravitational force of earth. Now if we place the satellite in such an orbit so that it rotate in opposite to earth rotation and having a greater angular rotational speed. </p>
<p>Now there is an existence of earth magnetic field... | g82 | [
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<p>I don't want to open a debate about whether cell phones can cause cancer,
I read the thread:<br> <a href="http://physics.stackexchange.com/questions/12069/could-cell-phone-radiation-cause-cancer">Could cell-phone radiation cause cancer?</a></p>
<p>For the sake of this question let's assume there's a chance for cell... | g12555 | [
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<p>I heard there were powerful convective movements in clouds which were responsible for increasing the size of water droplets or ice crystals. My question is: do the same movements appear outside of clouds? Or in other words: what's so special about a cloud that makes it host these convective movements? Couldn't warm,... | g12556 | [
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<p>I have been studying solitons theory to make a note on </p>
<blockquote>
<p>dimension analysis for solitons</p>
</blockquote>
<p>At first I have derived one space dimensional kink solution for soliton theory.
I want to go to higher dimension for solitons.</p>
<p>What theories would be fundamental for analyzing... | g12557 | [
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<p>It seems X-ray absorption spectroscopy is usually ascribed to the interation between photons and inner electrons. Does it mean inner electrons are much preferred by X-ray photons to outer electrons? If so, why? Thank you very much!</p> | g12558 | [
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<p>Materials with large coefficients of static friction would be cool and useful. Rubber on rough surfaces typically has $\mu_s\sim1-2$. When people talk about examples with very high friction, often they're actually talking about surfaces that are sticky (so that a force is needed in order to separate them) or wet (li... | g12559 | [
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<p>What makes it a good idea to use RMS rather than peak values of current and voltage when we talk about or compute with AC signals.</p> | g12560 | [
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<p>Thinking about the equivalence principle, is there a nice, simple way to show that a local, freely falling frame in Schwarzschild spacetime is described by the Minkowski metric</p>
<p>$$ds{}^{2}=c^{2}dt^{2}-dr^{2}-r^{2}d\theta^{2}-r^{2}\sin^{2}\theta\left(d\phi\right)^{2}.$$</p>
<p>I thought if I could describe a ... | g12561 | [
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<p>I am trying to calculate lattice parameter of ZnO (wurtzite). I have found out the formula for calculating lattice parameter of this system from a research article.</p>
<p>$\frac{1}{^{d^{2}}}=\frac{H ^{2}+ K^{2}}{a^{2}}+\frac{L^{2}}{c^{2}}$</p>
<p>I have this jcpds data of ZnO for carrying out calculations</p>
<p... | g12562 | [
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<p>Suppose we perform a double-slit experiment with a detector placed at a position of minimum intensity (maximum destructive interference), off-center where the path lengths differ by half a wavelength. The light source is alternately turned on and off (or blocked and unblocked near the source) and the intensity over... | g12563 | [
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<p>Between 1947 and 1962 the US conducted 105 tests of nuclear weapons in the <a href="http://en.wikipedia.org/wiki/Pacific_Proving_Grounds" rel="nofollow">"Pacific Proving Grounds"</a>. I'm wondering how much radiation exposure resulted on the west coast of the US. These were part of the <a href="http://en.wikipedia.o... | g12564 | [
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<p>A recent experimental paper measures a difference between the top quark and anti-top quark masses:</p>
<p>Fermilab-Pub-11-062-E, CDF Collaboration, <em>Measurement of the mass difference between $t$ and $\bar{t}$ quarks</em></p>
<blockquote>
<p>We present a direct measurement of the
mass difference between $t$... | g12565 | [
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<p>I can't seem to find any info on connected rigid bodies by a joint. Can someone explain the basics to me? I'm trying to do a little research to find out how feasible it would be to implement 3d ragdoll physics for my first person shooter game. </p> | g12566 | [
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<p>I'm trying to understand what would really happen when large quantities (e.g., 10g) of anti-matter collide with matter. The normal response is that they'd annihilate each other and generate an expanding sphere of gamma ray photons. </p>
<p>However, thinking about it in more detail, what I see is that the anti-elect... | g487 | [
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<p>So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light having a lower frequency which equates to lowering its energy.</p>
<p>My question is, where does the energy of the ... | g12567 | [
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<p>From what we know now about Quantum Mechanics and Elements, could we simulate <strike>life</strike> <em>the Universe</em> at a Quantum to Element level? </p>
<p>If we can't assume enough to create a sim, what fundamentals are we missing? (Gravity?Knowing the limit of Elements? Knowing the limit of Molecules? String... | g12568 | [
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<p>the Lienard-Wiechert green functions have future and past null cones of radiation. Maxwell equations allow for a continuous range of mixtures between the retarded and advanced components, but we have observed so far only the retarded emission components</p>
<p>or so it goes the story, but is that really accurate? I... | g12569 | [
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<p>Okay, I've got a little bit of a layman's question here.<br>
We're doing a bit of spring cleaning in our office and we've found a cabinet with boxes upon boxes of stored wires, so naturally, this discussion arose...</p>
<p>Picture a normal, bog-standard wire, with a plastic outer coating. Now, quite often when thes... | g12570 | [
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<p>I think this question has its place here because I am sure some of you are "self-taught experts" and can guide me a little through this process.</p>
<p>Considering that :</p>
<ul>
<li>I don't have any physics scholar background at all.</li>
<li>I have a little math background but nothing too complicated like calcu... | g40 | [
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<p>The task is to draw the two 4th-order Feynman diagrams of:</p>
<p>$$e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu $$</p>
<p>I drew the first one as (time left->right):</p>
<pre><code> mu^+ \bar{\nu}_\mu \nu_\mu
--<---------<----------<-----
/ /
/W^- /Z^0
/ /... | g12571 | [
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0.06350130587816238,
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<p>Consider the hamiltonian $H=\frac{p_x^2}{2m}$ in 1-D. It is invariant under $p_x \rightarrow -p_x$.
Again, this hamiltonian also has translational symmetry. Which one of these two is responsible for doubly degenerate energy eigenfunctions for a given energy $E$? I think it is the first one (Should I call it parity s... | g12572 | [
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<p>What are the units for <a href="http://en.wikipedia.org/wiki/Thermal_conductivity" rel="nofollow">thermal conductivity</a> and why?</p> | g12573 | [
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<p>As the title states, can a <a href="http://en.wikipedia.org/wiki/Miller_index" rel="nofollow">Miller index</a> for a cubic structure have 4 digits? If I have a structure with intercepts (2,8,3) on the x-y-z axes respectively, the following Miller index would be (12,3,8), which is not 3 digits.</p> | g12574 | [
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<p>If centripetal acceleration is towards the center, then why - when you spin a bucket of water (a classic demonstration) - does the water not get pushed out but rather stays in the bucket without spilling?</p> | g12575 | [
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<p>Carbon detonation is a characteristic event of Type 1a Supernova (EDIT: where an accreting white dwarf near the Chandrashankar limit of 1.4 solar masses explodes), an extremely important standard candle for cosmology. An area of active research is designing computer simulations to model supernova spectra and light c... | g12576 | [
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<p>The Earth turns with a very high velocity, around its own axis and around the Sun.
So why can't we feel that it's turning, but we can still feel earthquake.</p> | g12577 | [
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<p>Cosmological Inflation was proposed by Alan Guth to explain the flatness problem, the horizon problem and the magnetic monopole problem. I think I pretty much understand the first two, however I don't quite understand how a period of exponential expansion fully explains monopole problem. </p>
<p>From Weinburg's Cos... | g12578 | [
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0.057219650596380234,
0.0065... |
<p>I know what an Hilbert Space is, but I'm not sure what exactly is the single particle hilbert space; I understand it as the space of all possible states of the particle; does it matter if you're talking about an electron, a neutron or a quark, or is it a particle in the 'abstract'? How does one construct it?</p> | g12579 | [
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<p>I live at roughly 52.4,-2.1. On a sunny evenings I've often looked at the moon and the sun and noticed that the light part of the moon does not appear to line up with the sun. For example, at about 17:00 GMT on 13 Mar 2011, I noticed the half moon was facing toward a point roughly 10-20 degrees above where the sun a... | g12580 | [
0.0010539935901761055,
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... |
<p>We don't normally consider the possibility that massless particles could undergo radioactive decay. There are elementary arguments that make it sound implausible. (A bunch of the following is summarized from Fiore 1996. Most of the rest, except as noted, is my ideas, many of which are probably wrong.)</p>
<ul>
<li>... | g12581 | [
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<p>I had the intuition that, in classical mechanics, when the trajectory
of a body is known, then analysis of its motion can be done in the
linear space of that trajectory, if all forces are projected on the
tangent of the trajectory.</p>
<p>My original idea was to bypass the consideration of angular momentum,
and wor... | g12582 | [
0.0667916014790535,
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0.0070949094370007515,
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-0.007... |
<p>A flop transition changes the second homotopy group of a Calabi-Yau compactifation, but not the fundamental group or the number of connected components. Can the number of connected spatial components change in string theory? Can a part of space pinch off never to interact with the rest of space?</p> | g12583 | [
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... |
<p>In mathematics, we talk about tangent vectors and cotangent vectors on a manifold at each point, and vector fields and cotangent vector fields (also known as differential one-forms). When we talk about tensor fields, we mean differentiable sections of some tensor power of the tangent or cotangent bundle (or a combin... | g12584 | [
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-... |
<p>If we apply the Friedmann Lemaître equation to the Universe, we find a critical density $\rho_c$ : if the actual density $\rho$ is under it, the Universe will continue to expand, if it is higher than it, it will end in a Big-crunch.</p>
<p>For what reason (mathematically or physically), can't we apply Friedmann-Lem... | g12585 | [
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0.... |
<p>What is the parametric equation guiding the geometry of a <a href="http://en.wikipedia.org/wiki/File%3aFerrofluid_Magnet_under_glass_edit.jpg" rel="nofollow">ferrofluid</a> under a magnetic field? See also <a href="http://en.wikipedia.org/wiki/Ferrofluid" rel="nofollow">this</a> Wikipedia page.</p>
<p>From previous... | g12586 | [
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0.02436487004160881,
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0.03584135323762894,
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-0.014794638380408287,
-0.01557242963463068,
0.006032786797732115,
0.07647040486335754,
-0.0354... |
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