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<p>Simple question. A system with a uniform electric field everywhere in space has translational invariance in the directions perpendicular to the electric field but no translational invariance parallel to it. This system also has rotational invariance in the plane perpendicular to the electric field.</p>
<p>What ab... | 3,091 |
<p>One of my favourite ever pictures taken from space is a picture of the 2009 eruption of Sarychev Peak (Ostrov Matua island, Japan) taken by an ISS astronaut during a lucky fly-over.</p>
<p><a href="http://earthobservatory.nasa.gov/IOTD/view.php?id=38985"><img src="http://i.stack.imgur.com/O1FfD.jpg" alt="enter imag... | 3,092 |
<p>What are some good examples? For example, chaotic systems where you can show that quantum nondeterminism sets the initial conditions. </p> | 3,093 |
<p>Let us assume one dimensional heat transfer, for example a finite length wire starting at point $0$ and ending at point $\ell$. If the current passes the wire, the Joule heat $I^{2}R$ will be generated and dissipated into the wire and its thermal surroundings. Had the wire had a constant temperature $T$, the half of... | 3,094 |
<p>Suppose there is a space with constant magnetic field, and a charged particle is moving in that space with a constant velocity, ofcourse it experiences a magnetic force and gets deflected. <br>
But the particle it not necessarily moving wrt all frames. There may be some frame for which the particle doesn't move at a... | 70 |
<p>In particular, I am asking if two distinct many-body systems (e.g. system A and system B) separated at some arbitrary distance will necessarily be found to contain entangled particles (such that particle A1 is entangled with particle B1...etc) <strong><em>simply as a consequence of them both being forced into a grou... | 3,095 |
<p>The mass of a neutron is greater than mass of a proton so how is it possible in positron emission for a proton to form a neutron and a positron?</p> | 737 |
<p>We know that current is passed through a circuit if there is a potential difference across the two terminals of the conductor. But, in the case of a short circuit, we say that there is no potential difference between the two terminals and a large amount of current is passed through it. This is a violation of Ohm's l... | 71 |
<p>For small angles $\theta$ the rotation along a particular axis $n$ is given by</p>
<p>$R(n,\theta)(r)=Id+ \theta (n \times r)+ o(\epsilon)$.
Now, the rotation operator in Quantum Mechanics is given by
$R(n,\theta)(r)=r-\frac{i}{\hbar} \theta \langle n , L \rangle r + o(\epsilon)$</p>
<p>But if I check this for $n... | 3,096 |
<p>Having just heard about the asteroid <a href="http://en.wikipedia.org/wiki/2010_TK7" rel="nofollow">2010 TK7</a> in <em><a href="http://www.bbc.co.uk/news/science-environment-14307987" rel="nofollow">Trojan asteroid seen in Earth's orbit by Wise telescope</a></em>, I want to know more about its orbit. The BBC articl... | 3,097 |
<p>Forgive the elementary nature of this question:</p>
<p>Because a new moon occurs when the moon is positioned between the earth and sun, doesn't this also mean that somewhere on the Earth, a solar eclipse (or partial eclipse) is happening?</p>
<p>What, then, is the difference between a solar eclipse and a new moon?... | 3,098 |
<p>I am simulating a waveguide in COMSOL, a FEM solver. My model looks like this (it is similar to a standard Quantum Cascade Laser geometry):</p>
<p><img src="http://i.stack.imgur.com/Ca9Rj.png" alt="geometry"></p>
<p>Therefore there is a very thin (30nm) layer of gold sandwiched by two regions consisting of Gallium... | 3,099 |
<p>It seems that we are <a href="http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation#CMBR_dipole_anisotropy">moving relative to the universe at the speed of ~ 600 km/s</a>.
This is the speed of our galaxy relative to the cosmic microwave background.</p>
<p>Where does this rest frame come from? Is this s... | 3,100 |
<p>This question has come about because of my discussion with Steve B in the link below. </p>
<p>Related: <a href="http://physics.stackexchange.com/questions/72227/why-is-glass-much-more-transparent-than-water">Why is glass much more transparent than water?</a></p>
<p>For conductors, I can clearly see how resistivity... | 3,101 |
<p><strong>The problem statement:</strong> </p>
<blockquote>
<p>Measurement detects a position of a proton with accuracy of $\pm10pm$.
How much is the position uncertainty $1s$ later? Assume the speed of a
proton $v\ll c$.</p>
</blockquote>
<p><strong>What i understand:</strong></p>
<p>I know that in general i... | 3,102 |
<p>If we placed <code>p-type</code> and <code>n-type</code> semiconductors close enough to be touching (see fig. 1), would this arrangement work as a diode? Please explain.</p>
<p><img src="http://i.stack.imgur.com/n5UzB.jpg" alt="connecting p-type and n-type semiconductors"></p>
<p><sup>Fig. 1 - Connecting p-type a... | 3,103 |
<p>I live in a tall building (20 floors) on a mountain. Because the water pressure from the water company is not enough, there is a water pump at the last floor which is activated each time someone is using fresh water in his apartment.</p>
<p>To me, that's a big waste of energy, and I think that in theory it would be... | 3,104 |
<p>I remember from introductory Quantum Mechanics, that hydrogen atom is one of those systems that we can solve without too much ( embarrassing ) approximations.</p>
<p>After a number of postulates, QM succeeds at giving right numbers about energy levels, which is very good news.</p>
<p>We got rid of the orbit that e... | 3,105 |
<p>Using zeta regularization one can get a formula for regularizing the integral $ \int_{a}^{\infty}x^{m-s}\text dx $ for any $m$. </p>
<p>However, I have not seen anywhere. For example, I do not know why in physics you can use zeta regularization to define infinite products $ \prod _{n=0}^{\infty}a_{n} $, but they do... | 3,106 |
<p>The <a href="http://en.wikipedia.org/wiki/Husimi_Q_representation" rel="nofollow">Husimi $Q$ function</a> of a quantum state $\rho $ is defined as
$ Q (\alpha)=\langle \alpha \vert \rho \vert \alpha \rangle $, where $\alpha = (x, p) $ is a phase space coordinate and $\vert \alpha \rangle$ is a coherent state.</p>
<... | 3,107 |
<p>Heat is to be transfer from $CO_2$ gas to fluid.
$CO_2$ is being heated by solar energy.</p>
<p>How can we calculate heat transfer from the hot $CO_2$ gas to the moving fluid?</p> | 3,108 |
<p>Suppose I have a charge moving back and forth above an infinite, grounded, conducting plane. Can I calculate the total radiated power by using image charges? That is, are the scalar and vector potentials the same in the upper-half space for all time for both the image charge "picture" and the standard picture?</p> | 3,109 |
<p>I'd want to know the basic rules to apply the conservation laws in nuclear reactions (nuclear fusion, nuclear fission, radioactive decays, etc.) to determine parity and angular momentum of the products. I know that these principles lay deep in quantum mechanics, but I don't need a very thorough explanation, just th... | 3,110 |
<p>In this discussion: <a href="http://chat.stackexchange.com/rooms/4243/discussion-between-arnold-neumaier-and-ron-maimon">http://chat.stackexchange.com/rooms/4243/discussion-between-arnold-neumaier-and-ron-maimon</a> Arnold Neumaier suggested that there might be a close link between classical and quantum integrabilit... | 3,111 |
<p>A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #$1$). At a time of $60$ s later the friend catches a bus (event #$2$)
If the distance separating the events is 126 m in the frame of the girl on the bicycle, what is the bicycle's speed?</p>
<p>$$u... | 3,112 |
<p>Quantum interpretations like <a href="http://physics.stackexchange.com/q/34074/36915%5C">superdeterminism</a>, nonlocal hidden variables, etc. are regularly dismissed by the vast majority of physicists because they require "cosmic conspiracies" which can potentially involve anything and everything within the univers... | 3,113 |
<p>As the cone cells are different in numbers in people, how can we say that everyone is seeing the color as same? for example the color you are saying as red may be not the one i see as red..</p> | 72 |
<p>The range of electromagnetic radiation is indefinite.</p>
<p>When was that established? Doesn't Hubble's limit have an effect?</p> | 3,114 |
<p>I am working on a physics problem, but my issue is math-related. My professor skips some steps based on 'intuition' that I lack:</p>
<p>In a conservative system, to find out the nature of equilibrium points, we are looking at the potential energy functional, in general form given by $P[f(s)] = \int F(f(s)) ds$. (Th... | 3,115 |
<p>This might be a naive question, but how can an object such as a black hole singularity have infinite density but finite mass? (For example, we can approximate the mass of a black hole based on Kepler's Laws and use info from surrounding movements of stars to determine the central mass, but the black hole, excluding ... | 73 |
<p>This <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydr.html" rel="nofollow">link</a> describes a method for determining the most probable radius of an electron for a Hydrogen atom in the ground state.</p>
<p>It states that :</p>
<blockquote>
<p><em>The radial probability density for the hydrogen g... | 3,116 |
<p>In a <a href="http://en.wikipedia.org/wiki/Metric_expansion_of_space" rel="nofollow">Wikipedia article</a> I read that the "Metric Expansion of Space" exceeds the speed of light.
If this is true then we must be being disconnected from very remote parts of the universe since gravity can only travel at the speed of li... | 3,117 |
<p>As I understand lasers, you start off with a few photons that are in an identical state, and other photons that are created later tend to have the same quantum numbers due to Einstein-Bose statistics. Isn't each photon that "joins" the group of preexisting ones a clone of the previous ones? Why doesn't this violate ... | 3,118 |
<p>In terms of the different light phenomenon (reflection, diffraction, rectilinear propagation and dispersion), what are some problems with Huygen's wave model of light?</p> | 3,119 |
<p>How can I derive the Einstein's relation $D=k_{b}TB$, where $D$ is the diffusion coefficient and B is the mobility coefficient, from the concept of osmotic pressure?</p> | 3,120 |
<p>I have a question. Is it possible to perform computer simulations based on the M-Theory?</p>
<p>I was looking for such simulators or source codes but I have not found anything.</p>
<p>However, M-theory must have a mathematical model that can be saved as a code to be executed by the computer.</p>
<p>Something like... | 3,121 |
<p>How can you calculate the work done by a force (of unknown quantity) exerted on a 10kg block on an inclined plane. The force is pointing upwards and parallel to the incline (which is inclined 30 degrees with respect to the horizontal).</p>
<p>a. frctionless plane
b. coefficient of friction = 0.12</p>
<p>So the for... | 3,122 |
<p>The <a href="http://www.celestrak.com/NORAD/documentation/tle-fmt.asp" rel="nofollow">Celestrak website</a> provides information on reading the TLE ( Two-Line Element Set ) format. In <code>Line 1, Column 34-43 & 45-52</code> give information about <code>First Time Derivative of the Mean Motion</code> and <code>... | 3,123 |
<p>How to calculate the quasiparticle current density starting from bogoliubov - de gennes equation:
$$\left( \begin{array}{cc}H_{0} - E_{F} & -i\sigma_{y}\Delta \\ i\sigma_{y}\Delta^{*} & E_{F} - H_{0}^{*}\end{array}\right)\Psi = \mathcal{E}\Psi$$
I am not assuming that the single particle hamiltonian $H_{0}$ ... | 3,124 |
<p>I am attempting to design a obstacle avoidance system with the <a href="http://en.wikipedia.org/wiki/Arduino" rel="nofollow">Arduino</a>. My position (for now) is going to be stationary. I will be detecting an incoming object and I want to use the below known variables to predict if it will hit me or not. Unfortunat... | 3,125 |
<p>My question has 2 parts:</p>
<ol>
<li><p>I just followed the derivation of Navier Stokes (for Control Volume CFD analysis) and was able to understand most parts. However, the book I use (by <a href="http://rads.stackoverflow.com/amzn/click/0131274988" rel="nofollow">Versteeg</a>) does not derive it in its entirety.... | 3,126 |
<blockquote>
<p>Find the electric potential in the middle of a square with side length $a$ and charge $Q$.</p>
</blockquote>
<p>If I put the origin in the middle of the square, for the potential I get: $$4\frac{1}{4\pi\epsilon_0}\int_0^\frac{a}{2}\int_0^\frac{a}{2}\frac{\sigma}{\sqrt{x^2 + y^2}}dxdy$$</p>
<p>,where... | 3,127 |
<p>How are contact forces electromagnetic? What are they: Coulombic forces between polarized molecules in contact? Or they are the magnetic forces due to the motion of subatomic particles? I also would like to know what the feeling of 'Mechanical Contact' means? First I thought that it only means normal reaction force,... | 3,128 |
<p>The are several ways, in which one can write the Klein-Gordon equation, the most straightforward being probably the following:</p>
<p>$$
\hbar^2 \partial_t^2 \psi(x) = (\hbar^2 c^2 \Delta + m^2c^4) \psi(x)
$$</p>
<p>However it is possible to use the d'Alembert operator $\square$ and write KG equation like this:</p... | 3,129 |
<p>A virtual creation with total mass-energy = $E$ is allowed as long as that virtual creation doesn’t last longer than $E/h$. Can the uncertainty principle also be used to estimate the mass-energy in the spontaneous creation of a universe - a spontaneous creation that has now lasted $13.6$ billion years? If so, the p... | 27 |
<p>Kind of an odd, random question that popped into my head. Tidal energy - earth's ocean movement, volcanism on some of Jupiter's moons, etc. - obviously comes from the gravitational interaction between large bodies. On earth the interactions with the moon are pulling water around the surface, creating some amount of ... | 3,130 |
<p><strong>Problem/Solution</strong></p>
<p><img src="http://img215.imageshack.us/img215/6696/problem2f.jpg" alt="">!
<img src="http://img59.imageshack.us/img59/4281/sol2pp.jpg" alt="">!</p>
<p>In the third FBD, they made the whole system as one object. What happens if I <em>don't</em> want to do that? What if I jsut... | 3,131 |
<h2>Why are quasicrystals projections from higher dimensional regular crystal lattices?</h2>
<p>See for example <a href="http://en.wikipedia.org/wiki/Quasi_crystal#History" rel="nofollow">wikipedia</a>: </p>
<blockquote>
<p>»Mathematically, quasicrystals have been shown to be derivable from a
general method, whic... | 3,132 |
<p>I <a href="http://physics.stackexchange.com/q/21851/2451">read</a> some <a href="http://physics.stackexchange.com/q/48292/2451">answers</a> regarding <a href="http://en.wikipedia.org/wiki/Negative_temperature" rel="nofollow">negative temperatures</a> but I think my question is new. I want to know that what is the ph... | 3,133 |
<p>I have always been told that the geomagnetic field acts "as if" there were a bar magnet inside the Earth. I now this is not true, but I feel that knowing what is actually going on would help me understand the answer to the question that I'm about to ask:</p>
<p>Why does geomagnetic reversal happen? Is it something ... | 3,134 |
<p>In stat mech we calculated the <a href="https://en.wikipedia.org/wiki/Radial_distribution_function">radial distribution function</a> (a.k.a. pair correlation function) for a classical gas by using perturbation theory for the <a href="https://en.wikipedia.org/wiki/BBGKY_hierarchy">BBGKY hierarchy</a>. (I could post m... | 3,135 |
<p>I did some maths and physics up to the age of 18, and hold an amateur radio licence. This thing has puzzled me for a while - does reception of an electromagnetic wave imply an interaction with the transmitter? Does it drain some of the transmitter's energy?</p> | 3,136 |
<p>What is degenerate in degenerate electron gas state? Why is it called degenerate?</p> | 3,137 |
<p>I'm looking for an equation to find the tension on the ends of a cable suspended between two poles (one higher than the other) with no load but the cable itself.</p>
<p><img src="http://i.stack.imgur.com/1rkOa.png" alt="catenary curve section"></p>
<p>I determined that the tension would be different on each end, t... | 3,138 |
<p>Almost all uncertainties (for example the position-momentum uncertainty or time-energy uncertainty) are greater than ${\hbar}/{2} $. But what is the derivation of this <a href="http://en.wikipedia.org/wiki/Uncertainty_principle" rel="nofollow">uncertainty</a> by Heisenberg? Is there any sort of intuitive explanation... | 74 |
<p>With a hypothetical system, where the moon would be always on the opposite side of the planet than the sun, in a way that the moon would only be visible at night on the planet.</p>
<p>I don't know if this is possible, but if it was possible how they would behave. For example, I think that if this being possible, ma... | 3,139 |
<p>I have a homework assignment about rigid body dynamics. Take a disc of radius $r=2m$ with uniform mass density $\rho=1$ $kg/m^2$ in the x-y plane, resting in an inertial frame. At some instant, a force of $F = (0,0,1)kN$ is applied at the point $A=(0,r,0)$. What's the acceleration of the point $A$ at that instant?</... | 3,140 |
<p>It's not difficult to see that the graviton in $D$ spacetime dimensions has $(D-3)D/2$ polarizations. In $D=4$ there are two $\epsilon^{\pm}_{\mu\nu}$. What I find curious is that in $D=4$ I can actually pick $\epsilon^{\pm}_{\mu\nu}=\epsilon^{\pm}_{\mu}\epsilon^{\pm}_{\mu}$ where $\epsilon^{\pm}_{\mu}$ are the two ... | 3,141 |
<p>It's often stated that the central charge c of a CFT counts the degrees of freedom: it adds up when stacking different fields, decreases as you integrate out UV dof from one fixed point to another, etc...
But now I am puzzled by the fact that certain fields have negative central charge, for example a b/c system has ... | 3,142 |
<p>On a similar note: when using Gauss' Law, do you even begin with Coulomb's law, or does one take it as given that flux is the surface integral of the Electric field in the direction of the normal to the surface at a point?</p> | 327 |
<p>Einstein was able to make some predictions before GR was fully formulated. e.g. gravitational time dilation.</p>
<p>Such predictions before the full theory are referred to as "semi-heuristic derivations" here: <a href="http://motls.blogspot.cz/2012/09/albert-einstein-1911-12-1922-23.html" rel="nofollow">http://motl... | 3,143 |
<p>Is it true to say Space time <a href="http://en.wikipedia.org/wiki/Curvature" rel="nofollow">curvature</a> and <a href="http://en.wikipedia.org/wiki/Matter" rel="nofollow">Matter</a> are just the same thing, part of the same coin and that therefore <em>Space time curvature</em> $\Leftrightarrow$ <em>Matter</em>? In ... | 3,144 |
<p>this is simple.</p>
<p>what i actually want to ask is, when they do the subatomic particle collision experiments, how do they produce one single subatomic particle, e.g proton, neutron? how do they rip one single electron or photon off something? where do they store the single particle?</p>
<p>still, how do they k... | 3,145 |
<p>I am looking at <a href="http://www.mcgrating.com/references/ref02.pdf" rel="nofollow">this paper</a> (Multicoated gratings, J. Opt. Soc. Am., 1981) and I am getting confused around equation 22. I do not completely understand where he comes up with the equation </p>
<p>$$\xi^j_q=b_q^j(R^{-1}V_q^j)\qquad \text{(22... | 3,146 |
<p>We know that if Single Line to Fault occurs, then fault current flows to the earth. I want to know whether the current will return to the source or not. For the current to flow we need a closed path.</p>
<p>How it is possible for current to flow in a open circuit if you say that current does not return to the sourc... | 3,147 |
<p>The planetary orbits have been studied as ellipses but the solar system is in motion in relation to the distant stars. Their path is along the tip of an <strong>helix</strong> and the ecliptic plane is a convenient plane of projection. I think that the studies were never conducted under this viewpoint. </p>
<p>The... | 3,148 |
<p>Sorry I have a stupid question in Polchinski's string theory book vol 1, p46.
For a holomorphic function $T(z)$ with a general operator $\mathcal{A}$, there is a Laurent expansion
$$T(z) A(0,0) \sim \sum_{n=0}^{\infty} \frac{1}{z^{n+1}} \mathcal{A}^{(n)}(0,0). \tag{2.4.11}$$
Under transformation $\delta \mathcal{A}=... | 3,149 |
<p>My question relates to something that I´ve seen in many books and appears in all its glory here: <a href="http://books.google.com.br/books?id=nnuW_kVJ500C&pg=PA198&lpg=PA198&dq=the%20left-hand%20side%20of%20%286.72%29&source=bl&ots=vpxrfzRO2V&sig=ZdPtvv_zqoLv8MTvE5Brc87zhOs&hl=pt-BR&s... | 3,150 |
<p>I am familiar with the tools that appear in (linear) perturbation theory for general relativity, that is namely that one writes:</p>
<p>$$g_{\mu \nu} = g^{(0)}_{\mu \nu} + \epsilon g^{(1)}_{\mu \nu} + \mathcal{O}(\epsilon^2) \tag{*}$$</p>
<p>Where $g^{(0)}_{\mu \nu}$ is typically assumed, and then one assumes a pe... | 3,151 |
<p>I have very basic question regarding sound I tried to search it over google but couldn’t find the right answer, my question:</p>
<pre><code>What are those characteristics by which every sound can identified uniquely?
</code></pre>
<p>For e.g. pitch is one of the characteristics of sound but let’s say a note C# can... | 819 |
<p>I wonder if it is possible to generate electric energy from the radiation of radioactive materials like nuclear waste? If it is then wouldn't that also mean that it could be used as an energy source for a very long time since the radiation takes a long time to decay?</p> | 3,152 |
<p>I've been teaching myself DC electronics as a hobby and, although I have a feeling i'm "missing something obvious", I was wondering if someone could help me out. If two components of differing resistance are wired in series, they likewise drop different voltages; yet when they are wired in parallel they apparently s... | 3,153 |
<p>This is a difficult question to phrase, so please bear with me. I found some cheap sunglasses and pulled out the plastic lenses which are polarized. For clarity, I have labeled them as lens-1 and -2 with faces A and B. </p>
<p><img src="http://i.stack.imgur.com/iKSi9.jpg" alt="enter image description here">
There a... | 3,154 |
<p>Assume an alternate universe with same physical laws as here. In this universe nothing exists except 3 observers, each in a transparent box with a clock. Observer A is travelling at .5c. Observer C is travelling in the opposite direction at .5c. Observer B is at rest. </p>
<p>In the absence of outside landmarks eac... | 3,155 |
<p>everyone. I got a bit stuck on 2(iii), this is supposed to be a easy question, but i don't know how you get the square term? I thought you just do the Fourier transform, but then I got some exponential out of it and I don't know what to do? Can anyone suggest or shed some light on the problem? THANKS
If you just plu... | 3,156 |
<p>I've heard this in many quantum mechanics talks and lectures, nevertheless I don't seem to grasp the idea behind it.</p>
<p>What I mean is, at which point is that our modern understanding of quantum mechanics led to a technological development so fundamental for today's computers that we could not have got it worki... | 3,157 |
<p>Given a nail, and a magnet it is possible to magnetize the nail by patiently rubbing the nail until it is magnetized; albeit the field strength may be less than that of the source. </p>
<p>With several score kilograms of space debris in orbit, all ferromagnetic material up there may each well have been subjected to... | 3,158 |
<p>I place $N$ Brownian particles in $V$ liters of solution, shake until I assume that the particles are "well-mixed", and sample and randomly sample an $S$ liter volume. What is the probability distribution for the number of particles in my sample of $S$ liters? </p> | 3,159 |
<p>What happens at the zone boundaries of the brillouin zones in the tight binding model?
How does the band gap originate in the TB model?</p> | 3,160 |
<p>I have read some articles such as <a href="http://sinnott.mse.ufl.edu/Backgrounds/theo01_CNT.html" rel="nofollow">http://sinnott.mse.ufl.edu/Backgrounds/theo01_CNT.html</a> and <a href="https://www.rose-hulman.edu/math/seminar/seminarfiles/2006-07/abstract2006-11-01.pdf" rel="nofollow">https://www.rose-hulman.edu/ma... | 3,161 |
<p>In Chemistry, I was taught that there are three main states of matter: solid, liquid, and gas, and that heat and pressure determine that state. For some substances, the line is blurry between them.</p>
<p>Some materials don't seem intuitively to do this--nor have I been able to find data on them. For example, wha... | 3,162 |
<p>Why does the vacuum polarization in 2D massless Fermion QED, </p>
<p>$$ i\Pi^{\mu\nu}(q) = i(\eta^{\mu\nu}-\frac{q^\mu q^\nu}{q^2})\frac{e^2}{\pi}, $$</p>
<p>have the structure of a photon mass term, as is claimed on Peskin chapter 19 page 653?</p> | 3,163 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/9857/nature-of-an-observer">nature of an observer</a> </p>
</blockquote>
<p>For instance, in the double slit experiment, what is exactly defined as an observer?
I remember from somewhere, light is also ... | 75 |
<p>What exactly is a <a href="http://en.wikipedia.org/wiki/Boson" rel="nofollow">boson</a>?</p>
<p>Is the <a href="http://en.wikipedia.org/wiki/Higgs_boson" rel="nofollow">Higgs boson</a> the cause of gravity or a result of it? Does the collision of particles at the LHC create a gravity field or waves or somehow inter... | 3,164 |
<p>To me this is very confusing, but I hope we can discuss it and find a solid answer to the question.</p>
<p>If you were somewhere where there was absolutely nothing, what colour would your eyes see?</p> | 3,165 |
<p>I'm studying quantum field theory and I encountered some problems of diffusion of particles by an external potential. Until now I have to do with diffusion of the type particle-particle obtaining the Feynman rules from the Lagrangian of the theory and I don't know how to implement the presence of an external potenti... | 3,166 |
<p>Let me base the discussion on the <a href="http://en.wikipedia.org/wiki/File%3aKim_EtAl_Quantum_Eraser.svg">pictorial description of the delayed choice quantum eraser experiment on wikipedia</a>.</p>
<p><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Kim_EtAl_Quantum_Eraser.svg/1000px-Kim_EtAl_Qu... | 3,167 |
<p>I am trying to understand the structure of the fermions in non-abelian gauge theories. Disclaimer: my question might be very trivial (I suspect the answer could simply be "a change of basis"), but I would be grateful is someone could shed some light if there's something deeper lurking around the corner.</p>
<p>Let'... | 3,168 |
<p>Given a 4-dimensional compact manifold (torsion free), the Euler characteristic is defined as:</p>
<p>$$E_4 ~=~ \int \epsilon_{abcd}R^{ab} \wedge R^{cd}$$</p>
<p>with $R^{ab}$ is the curvature 2-form. Perturb the connection 1-form (represent by $\delta \omega^{ab}$), $E_4$ should be unchanged. How can I proof that... | 3,169 |
<p>I have been reading up on the production methods of graphene, and one that I found interesting in particular was the thermal exfoliation of graphite oxide. From what I gather the basic idea is that the oxides are located in between the graphene layers of graphite, and that you then heat the material up, causing gass... | 3,170 |
<p>From Peskin & Schroeder <em>QFT</em> page 35:</p>
<blockquote>
<p><em>The Lagrangian formulation of field theory makes it especially easy to discuss Lorentz invariance. And equation of motion is automatically Lorentz invariant by the above definition if it follows from a Lagrangian that is a Lorentz scalar. T... | 3,171 |
<p><em>I realise that this might be conventially very difficult to answer because there's no KG or Newtons in space, only particles.</em></p>
<p>As far as I understand, every object creates a 'pull' due to the forces of gravity, that'll be felt noticeably by smaller objects (as well as the larger object being attracte... | 3,172 |
<p>Assuming you have a flat poster with no curvature, why is it that when you pin it to the wall (with thumbtacks) it gains curvature as seen in the picture below. When I put the poster up it was entirely flat to the wall with no curvature, but over time it somehow curls and develops this sort of curvature (it looks li... | 3,173 |
<p>The charge and current density fields in classical electromagnetism are scalar real number fields on space time manifold. But these fields diverge/become infinite in case of point charges, how is this justified and mathematically consistent ?</p> | 3,174 |
<p>In Neil DeGrass Tyson's epic video, at 2:26:50</p>
<p><a href="https://www.youtube.com/watch?v=AdHlVY8pEk0&list=PL1L9zQimONkUOxXJyM0xcJja9ItQu1P8l&src_vid=AdHlVY8pEk0&feature=iv&annotation_id=annotation_4179310099#t=12s" rel="nofollow">https://www.youtube.com/watch?v=AdHlVY8pEk0&list=PL1L9zQimON... | 3,175 |
<p>How is <a href="http://en.wikipedia.org/wiki/Graphene" rel="nofollow">graphene</a> a 2D substance? It has length, width and some thickness to it, else it would be invisible. Why is it considered a 2D substance?</p> | 3,176 |
<p>Are they equivalent?</p>
<p>I came up this question because they both explain states beyond Loughlin state.</p> | 3,177 |
<p>Please bear in mind that I'm neither a physics guy nor particularly a math guy. So I will probably need a bit more hand-holding than just a complex equation.</p>
<p>For a game, I'm trying to calculate a <em>reasonable</em> simulation of a human body on a trampoline. It seems to me that there are two phases to consi... | 3,178 |
<p><strong>Imagine if there was a hole between two earth poles, let's say 100 meters wide, as deep as the Earth's height between north and south poles - what would happen if we threw an object from the North Pole, weighing 100 kg?</strong></p>
<p>Would it lose speed as it approached Earth's center/core, would it speed... | 76 |
<p>I have a homework question based on the following diagram:</p>
<p><img src="http://gyazo.com/f0de3827222c4c5651df70ae25b657e9.png" alt="velocity diagram"></p>
<p>I need to find the <strong>angular velocity of the object as seen by an observer at the origin</strong> of the frame. The question says that the observed... | 3,179 |
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