question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Given the <a href="http://en.wikipedia.org/wiki/Camera_matrix#The_camera_focal_point" rel="nofollow">camera matrix</a>, can I find the focal length of this camera ?</p> | g7221 | [
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<p>What is the role of the resistor in e.g. an AND gate like this one? :</p>
<p><img src="http://i.stack.imgur.com/LirVA.png" alt="AND Gate"></p>
<p>One often sees lots of resistors in electric circuits, but I haven't really understood their role.</p> | g7222 | [
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<p><strong>How are qubits entangled?</strong> </p>
<p>I understand the basics of entanglement but what I do not get is how it occurs in nature or in the lab. What causes entanglement to occur or what is done to the particle to make it occur.</p> | g7223 | [
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<p>I really should know this off by heart (this is my field...) but I never really grasped the difference between the total wavefunction of a system and the wavefunctions of particles within it, so it only just dawned on me that perhaps the total energy of a system was simply the sum of the energies of the individual p... | g7224 | [
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<p>I have been referring to a paper
<a href="http://arxiv.org/abs/physics/0405135" rel="nofollow">http://arxiv.org/abs/physics/0405135</a> to determine the effective resistance using random walks for an infinite square resistive lattice</p>
<p>Though the author seems to indicate this as a simple problem
(maybe i am mi... | g7225 | [
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<p>I heard from my GSI that the commutator of momentum with a position dependent quantity is always $-i\hbar$ times the derivative of the position dependent quantity. Can someone point me towards a derivation, or provide one here?</p> | g7226 | [
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<p>Consider the Klein–Gordon equation and its propagator:
$$G(x,y) = \frac{1}{(2\pi)^4}\int d^4 p \frac{e^{-i p.(x-y)}}{p^2 - m^2} \; .$$</p>
<p>I'd like to see a method of evaluating explicit form of $G$ which does not involve avoiding singularities by the $\varepsilon$ trick. Can you provide such a method?</p> | g7227 | [
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<p>Would it be possible to develop oculars that would enhance the vibrancy of color? I know there are many digital filters to improve vibrancy, but are there physical devices able to produce the same effect? Would it ever be physically possible to produce a device small enough to be worn like a contact lens?</p>
<p>Th... | g7228 | [
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<p>What are some interesting classical systems for which the dynamics can be reduced to a many-body Schrodinger equation, at least in some useful regions of phase space, and in particular, with many variables.</p> | g7229 | [
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<p>I recently read "An Introduction to Supersymmetry in Quantum Mechanical Systems" by T. Wellman (amongst other sources) in an effort to find out what a superpotential actually is and how it relates to the potentials of particles/fields). Here's the link: <a href="http://www.google.co.uk/url?sa=t&rct=j&q=&... | g7230 | [
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<p>I am a physics groupie, so please excuse me if this question is stupid, but I am trying to better understand the particle/wave duality in quantum physics. It would seem that, in the double slit experiment or any similar experiment, there should be some method to tell the difference between two actual waves interferi... | g7231 | [
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<p>In the book <em>The Norton History of Astronomy and Cosmology</em> by the late John North I have found the following statement (page 514):</p>
<p>"The German mathematician Lejeune Dirichlet studied the law of gravitation in non-Euclidean space towards the end of 1850."</p>
<p>Does anyone perhaps know more about th... | g7232 | [
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<p>The part of the Einstein equations of general relativity referred to vacuum energy, introduce a repulsive term in gravity. This means that as the space become bigger and bigger, vacuum part become more and more important, leading to an undefined accelerated growth of the universe. Why vacuum energy does not violate ... | g7233 | [
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<p>I understand all the concepts of what voltage is using all the analogies but some things related to the drop of voltage across a circuit confuses me.</p>
<ol>
<li><p>If I had a short circuit and attached a voltmeter I would get a potential difference reading of 0 volts. How is current then going through the wire if... | g7234 | [
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<p>Ok, so theoretically, is it possible to build a spaceship like the ones we see off of Star Trek or Prometheus or will physics not allow it? What are some challenge faces such an task. Also, is there other ways we can use to launch heavier payload from earth or are we just stuck with using tons of fuel to launch smal... | g7235 | [
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<p>I have seen many answers like: because we don't have infinite energy, because of gravity, because it is impossible, because of physics.</p>
<p>But they don't really answer my question.. I mean if there is no friction and at some points, even if just in theory, you could be so far away from other objects or at the r... | g7236 | [
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<p>When a probe like Voyager 1 is sent into deep space they are able to point the camera at the planet and its moons and take pictures. </p>
<ul>
<li>How is the camera pointed at the object?</li>
<li>Is the camera fixed to the probe or do motors orient the camera independently?</li>
<li>Do they know the exact position... | g7237 | [
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<p>I am interested in modelling the trajectory of a rocket from the Earth to the Moon by solving a differential equation numerically. Below are some key facts and assumptions I am using. I want to make sure that I have not made any serious mistakes, nor disregarded any necessary facts.</p>
<p>We will consider the foll... | g7238 | [
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<p>In the setting of general relativity, I came across a source term of the wave equation of the following form:</p>
<p>$$
\frac{1}{\sqrt{q}}\,\delta^{(3)}(p-\gamma(t))
$$</p>
<p>where $p\in M$ is a point in our 4d spacetime and $\gamma(t)$ is a trajectory that the source takes in the 4d spacetime. $\sqrt{q}$ is the ... | g7239 | [
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<p>If it is impossible for matter to accelerate to $c$ (because doing so would take infinite energy), and if light can be deemed matter (because of wave-particle duality, photons are matter, right? And photons clearly have mass per solar radiation pressure), how does light manage to travel at $c$?</p> | g195 | [
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<p>I've been talking to a friend, and he said that it's impossible to travel at exactly the same speed as the speed of sound is. He argued that it's only possible to break through the sound barrier using enough acceleration, but it's impossible to maintain speed exactly equal to that of sound. Is it true? And if it's t... | g7240 | [
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<p>My field of study is computer science, and I recently had some readings on quantum physics and computation.</p>
<p>This is surely a basic question for the physics researcher, but the answer helps me a lot to get a better understanding of the formulas, rather than regarding them "as is."</p>
<hr>
<p>Whenever I rea... | g7241 | [
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<p>What kind of global and causal structures does a Penrose diagram reveal?</p>
<p>How do I see (using a Penrose diagram) that two different spacetimes have a similar global and causal structure?</p>
<p>Also,</p>
<p>I have the following metric </p>
<p>$$ds^2 ~=~ Tdv^2 + 2dTdv,$$ </p>
<p>defined for </p>
<p>$$(v,T... | g7242 | [
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<p>In Chapters 34-36 of the Srednicki QFT book, 2 component spinors and their combinations in Dirac and Majorana spinors are carefully constructed. Specifically, in equations 36.14 and 36.15 the following left-handed spinors are defined:</p>
<p>$$
\begin{equation}
\begin{split}
&\chi = \frac{1}{\sqrt{2}}(\psi_1... | g7243 | [
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<p>Assume an observer sent a beam of photons close to an event horizon, say at some distance x (a distance far enough to avoid the photons falling in.) This light would still be observable, albeit red shifted and with it's path curved appropriately. Now assume the black hole absorbs enough mass to expand it's event hor... | g7244 | [
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<p>If particles are simply regions of space where certain quantum fields have non-zero divergence, are anti-particles simply the corresponding regions of opposite divergence?</p>
<p>This seems like the intuitive answer, especially when considering the process of annihilation. I have heard before that anti-particles ar... | g245 | [
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<p>I watched a program of his in which it was claimed that since mass bends space in accordance to General Relativity, then in the case of very large stars it becomes a strong force to the point of being able to crush a star to a single nucleus (Neutron Stars) or less (Black Holes). </p>
<p>His argument is that Gravit... | g7245 | [
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<p>I was looking at pdf file of the presentation of a conference talk. The speaker discusses two types of "mechanisms" for stabilizing the weak scale and calls them "weakly coupled" and "strongly coupled". The examples are:</p>
<p>Weakly coupled: SM with a light Higgs, SUSY, Little Higgs, Twin Higgs, Large extra dimen... | g7246 | [
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<p>Suppose I am trying to formulate a multipoint model of fluid dynamics. I have a procedure for doing so the details of which is not important to this question, but only that it is based on a series expansion, the higher order terms in which series being dependent on larger number of spacial points. The equations for ... | g7247 | [
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<p>This is a confused part ever since I started learning electricity. What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? All of them have the same SI unit of Volt, right? I would appreciate an answer.</p> | g7248 | [
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<p>The graph of nuclear binding energy is relatively smooth going from H to U, except for He4 (alpha particle). Why is He4's binding energy so anomalously high compared to its neighboring isotopes?</p> | g7249 | [
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<p>Consider a lift, which is at rest in an homogeneous gravity field. There is a thin layer(<strong>with thickness</strong> $h$) of water on the floor of the lift. At some moment a single cable, supporting the lift, breaks and the lift begins free falling(forever). It is easy to describe qualitatively what happens with... | g7250 | [
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0.025354474782943726,
0.03876250982284546,
-0.08587779104709625,
0.0061860703863203526,
-0.021930057555437088,
-0.010294518433511257,
-0.04314592480659485,
-0.... |
<p>Sometimes old faulty CRT monitors generate nasty high-frequency squeal sound. What element might be responsible for generating such sound? I have heard that it might be dry electrolytic capacitor; is it? What is the physics of generating this sound (how it is generated)?</p> | g7251 | [
0.05314381793141365,
0.03622312843799591,
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0.010403771884739399,
0.030805088579654694,
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0.09014128148555756,
0.05473894998431206,
0.03989... |
<p>The 2011 Nobel Prize in Physics, as far as I understand, concerns the expanding universe -- galaxies moving away from each other at ever increasing speed (that's what I think I read in newspapers). Now, the idea of expanding universe is not new. What is the novelty in this study? What was unexpected in it?</p> | g7252 | [
0.003941957373172045,
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<p>What are the direct real life applications of general relativity other than nuclear technology? </p>
<p>What I meant was, was there any technology developed based on general relativity that can benefit mankind today? </p>
<p>Secondly, are there any adverse effects quantum technology today?</p> | g7253 | [
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0.04467659071087837,
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0.029348768293857574,
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0.028372978791594505,
0.031... |
<p>The average energy we receive from the Sun is 1,366 w/m^2, and this only varies by 0.1% from the activity peak to trough of its 11 year cycle. About 9% of the energy comes from wavelengths less than 400 nm. The 200-300 nm region varies on the order of a few percent, 150-200 nm by 10-20% and shorter regions by over 5... | g7254 | [
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0.029762785881757736,
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<p>Inspired by this question: <a href="http://physics.stackexchange.com/questions/8049/are-these-two-quantum-systems-distinguishable">Are these two quantum systems distinguishable?</a> and discussion therein.</p>
<p>Given an ensemble of states, the randomness of a measurement outcome can be due to classical reasons (c... | g7255 | [
-0.007410240825265646,
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0.028762992471456528,
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<p>I am a graduate student in a large experimental physics collaboration. Newcomers to the collaboration invariably complain about excessive use of jargon and insufficient documentation as barriers to their understanding and quick integration into the collaboration. Of course, jargon is unavoidable in any technical p... | g7256 | [
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<p>I was helping a friend of mine with the following question from Knight's book and I was not able to answer part (c).</p>
<p><img src="http://i.stack.imgur.com/G2AdB.jpg" alt="enter image description here"></p>
<p>Here is what I think I know:</p>
<p>(a) I expect $V_1 = V_2$; the two spheres are in equilibrium so n... | g7257 | [
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0.05592558905482292,
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0.019483128562569618,
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0.00... |
<p>I've read from many sources that Dyson Air Multipliers are more efficient and quieter than normal fans. Now, with the proof of concept, is it possible to use its principles as a propulsion system for, say, a quieter helicopter? </p> | g7258 | [
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<p>I have a problem with energy conservation in case of interfering waves.</p>
<p>Imagine two harmonic waves with amplitudes $A$. They both carry energy that is proportional to $A^2$, so the total energy is proportional to $2A^2$. When they interfere, the amplitude raises to $2A$, so energy is now proportional to $4A^... | g7259 | [
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<p>There is a known thought experiment, connected to quantum immortality: a duel between physicist and a philosopher. </p>
<p>Each turn physicist and philosopher fire at each other with a pistol. The quantum immortality predicts that each of the participants will find themselves alive and the opponent dead after a num... | g7260 | [
0.01577741652727127,
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<p>Just wondering about the definitions and usage of these three terms.</p>
<p>To my understanding so far, "covariant" and "form-invariant" are used when referring to physical <em>laws</em>, and these words are synonyms?</p>
<p>"Invariant" on the other hand refers to physical <em>quantities</em>?</p>
<p>Would you ev... | g7261 | [
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0.00124201... |
<p>So I've been doing a lot of reading about the twin paradox and have encountered several different explanations that strive to resolve it. First off let me start by saying general relativity <em>is not</em> an adequate explanation and in fact has nothing to do with resolving the paradox. (That much has been made clea... | g249 | [
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<p>This is potentially a very stupid question but I'm going to ask it anyway. With all these huge buildings such as the Abu Dhabi Mosque, where an unbelievable amount of materials such as marble was moved from one side of the earth to the other, is it possible that if we 'shift enough stuff' that we could change the ea... | g7262 | [
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<p>We know that conducting materials can be heated by electromagnetic induction. Is it possible to generate current using a cooling process?</p> | g7263 | [
0.05334533378481865,
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<p>How are <a href="http://en.wikipedia.org/wiki/Fresnel_zone" rel="nofollow">Fresnel Zones</a> formed? What phenomena of light allow ellipsoid areas to be in phase? I've tried reading articles, but they more or less introduce me to characteristics of light, and then tell me that Fresnel Zones exist. How does the circu... | g7264 | [
0.007512077689170837,
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0.03611355274915695,
0.06618570536375046,
0.039... |
<p>For the last few years, My friend worked on figuring out the "theory of everything". She is afraid of sharing her theory with well known physicists, because she doesn't want other people to take credit for her idea. So, my here's what I'm wondering:</p>
<p><strong>1) What is the best way for her to validate her the... | g7265 | [
0.05024168640375137,
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0.02003912441432476,
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0.044179245829582214,
0.03729459643... |
<p>One of the classic stories in the annals of aerospace engineering is the development (and subsequent redesign) of the F-18 and its Leading Edge Extensions (LEX) due to fatigue problems, problems that were ultimately traced to the poorly-understood process of <a href="http://www.aerospaceweb.org/question/planes/q0176... | g7266 | [
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0.012331490404903889,
0.034... |
<p>During the winter we keep the basement door closed so that the cold air from upstairs won't flow into the basement. Then we heat the basement and the upstairs gets heated partially by conduction through the floor. But during the summer, the upstairs is heated while the basement (unfinished) is around 62 degrees F ... | g7267 | [
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0.01569833606481552,
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0.015482136979699135,
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0.028... |
<p>What was the density of the universe when it was only the size of our solar system? Did it approach neutron star density? Is it physically correct to even ask such a question? </p> | g7268 | [
0.011518113315105438,
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<p>Now, I understand that when a an electron travels, it creates a magnetic field. If you put two wires with current traveling in the same direction they repel, and current traveling in opposite directions attract. I (somewhat) understand how this is caused by electrostatics and special relativity, but when I tried to ... | g7269 | [
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<p>According to the first and second law for a closed system containing different chemicals we have</p>
<p>\begin{align}
&\delta Q - \delta W = dU = T dS - p dV +\sum_i \mu_i d N_i\\
&\Rightarrow\;\delta W - p dV + \sum_i \mu_i dN_i = \delta Q - T d S \le 0\qquad\because\text{2nd law}\\
&\Rightarrow\;\delt... | g7270 | [
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0... |
<p>Total noob here.</p>
<p>I realize that photons do not have a mass. However, they must somehow occupy space, as I've read that light waves can collide with one another.</p>
<p><strong>Do photons occupy space?</strong> and if so, does that mean there is a theoretically maximum brightness in which no additional amoun... | g7271 | [
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0.024940... |
<p>Imagine I exist at time $t_1$ and my mass is $m$. At time $t_2$ I time travel back to $t_1$. At time $t_1$ there is now a net increase of mass/energy in the universe by $m$.</p>
<p>At time $t_3 = t_2 - x$ where $x < t_2 - t_1$, I travel back to t1 again. The net mass in the universe has now increased by $2 \t... | g7272 | [
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0.05741928145289421,
0.027098698541522026,
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... |
<h1>Scenario description</h1>
<p>Lets assume both containers have a capacity of 300 litres.</p>
<p>One is a vertical tube as shown in pic 1</p>
<p>Other one is more or less a V shaped containers as shown in pic 2</p>
<p>Both are at ground level</p>
<h1>Question</h1>
<p>No doubt that whole weight of 300 litres wi... | g7273 | [
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0.006217196583747864,
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<p>While reading Peskin and Schroeder (page 64) I come across this</p>
<blockquote>
<p><em>Although any relativistic field theory must be invariant under the proper orthocronous Lorentz group, it need not be invariant under P, T, or C. What is the status of these symmetry operations in the real world? From experimen... | g7274 | [
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-... |
<p>I have read somewhere that for <a href="http://en.wikipedia.org/wiki/Particle_in_a_ring" rel="nofollow">particle on a ring</a> problem you don't have to solve eigenvalue equation $H\psi=E\psi$ you can instead solve eigenvalue equation $P\psi=p\psi$ where P is momentum operator. Why?</p> | g7275 | [
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0.0007102271192707121,
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0.... |
<p>This action reads
$$S=-\frac{1}{4g_{D9}^2}\int d^{10}x F_{MN} F^{MN}-\frac{1}{4g_{D5}^2}\int d^{6}x F'_{MN} F'^{MN}- \int d^6 x \left[ D_{\mu} \chi^{\dagger} D^{\mu} \chi + \frac{g_{D5}^2}{2}\sum\limits_{A=1}^{3}(\chi_i^{\dagger}\sigma_{ij}^A \chi_j)^2\right]$$</p>
<p>My question is about the $\chi$. The field con... | g7276 | [
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0.007355156354606152,
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0.05702563375234604,
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-0.... |
<p>Is there anyway to see by inspection that a form like
$$a(x^2 )^{-3} (g _{μσ} x_{\rho} x_{ ν} + g_{μρ} x_{σ} x_{ ν} +g_{νσ} x_{ρ} x_{ μ} + g_{ νρ} x_{ σ} x_{ μ} ) $$
may be equivalent to (i.e reduced down to or reexpressed) $$
b(g _{μν} x_{ ρ} x_{ σ} + g_{ ρσ} x_{ μ} x_{ ν} )(x^2 )^{ −3} ?$$ where $g_{\mu \nu}$ is... | g7277 | [
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0.010538085363805294,
0.002483246149495244,
0.06576421856880188,
0.011936073191463947,
-0... |
<p>According to my book, "tension is the reaction of a rope when it is stressed". Then it also said when the string is massless, tension is same everywhere. However in a,let, pulley-rope system,when there is friction between the pulley & the rope, the tensions are not same. Why the tension is not same in this case... | g7278 | [
0.07356096059083939,
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0.010853156447410583,
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0.017184700816869736,
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0.015308300964534283,
-0.009718172252178192,
... |
<p>I'm looking for the pure mathematical definition of <a href="http://en.wikipedia.org/wiki/Work_%28physics%29" rel="nofollow">work</a>, but I haven't yet learned line integrals.</p>
<p>My book says that the work due to a force ${\bf F}$ from point $A$ to point $B$ is
$$
W= |AB|\cdot |{\bf F}|\cdot\cos(\angle AB,{\bf... | g7279 | [
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0.017389945685863495,
0.005778866354376078,
-0.0... |
<p>How would the universe be modified if protons (as we know them) have negative charge and electrons (as de know them) have positive charge.</p> | g7280 | [
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-0.0063209994696080685,
0.027240870520472527,
0.06546001136302948,
0.02472870424389839,
-0.10399030148983002,
0.04969481751322746,
0.030067211017012596,
-0.01092746201902628,
0.02869163639843464,
0.021640144288539886,
0.031371232122182846,
0.05... |
<p>I learned that electron absorbs a photon and goes into higher energy state. But also all electrons are identical. </p>
<p>What is a difference between the electron in low orbital energy state? and the high one?</p> | g7281 | [
0.052150797098875046,
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<p>For quite sometime there has been a claim that the firewall paradox has been resolved (via lasers). For instance, <a href="http://global.ofweek.com/news/Lasers-to-solve-the-black-hole-information-paradox-9867" rel="nofollow">http://global.ofweek.com/news/Lasers-to-solve-the-black-hole-information-paradox-9867</a> . ... | g7282 | [
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<blockquote>
<p>Even if the system is isolated and there is no heat exchange with surroundings, shouldn't the decrease/increase of pressure result in increase/decrease of entropy?</p>
<p>Does this property of an isolated system means that increase of pressure means equivalent decrease in volume, so after the pro... | g7283 | [
0.010833113454282284,
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<p>My textbook explains Newton's Third Law like this:</p>
<blockquote>
<p>If an object A exterts a force on object B, then object B exerts an equal but opposite force on object A</p>
</blockquote>
<p>It then says:</p>
<blockquote>
<p>Newton's 3rd law applies in all situations and to all types of force. But the p... | g7284 | [
0.05233211815357208,
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0.01090330071747303,
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0.004579461645334959,
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<p>If an object is acted on by equal and opposite forces then it will be in equilibrium, and it's acceleration or velocity (and so direction as well) will not be changed.</p>
<p>So when a ball bounces, it exerts a force on the floor, which matches the magnitude of the force in the opposite direction (the ball is bounc... | g7285 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/22700/about-binary-stars-and-calculating-velocity-period-and-radius-of-their-orbit">About binary stars and calculating velocity, period and radius of their orbit</a> </p>
</blockquote>
<p>I am given the ... | g246 | [
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<p>To get from point $A$ to $B$, a river will take a path that is $\pi$ times longer than as the crow flies (I think this result is from Einstein). What is the proof of this, and how well does it hold water against experiment?</p>
<p>What assumptions are made during the proof?</p>
<p><strong>Edit:</strong> I was also... | g7286 | [
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<p>Four questions: (To start off, I know very little about physics it isn't even funny (I probably use a ton of wrong terms here and leave out vital information, if so I will try to edit it in as you point it out!), Anyways, I have been always curious about this scenario though so I finally figured I'd ask some people ... | g7287 | [
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<p>From Wikipedia on how a <a href="http://en.wikipedia.org/wiki/Salisbury_screen" rel="nofollow">Salisbury Screen</a> works:</p>
<blockquote>
<p><em>1. When the radar wave strikes the front surface of the dielectric, it is split into two waves.</em> </p>
<p><em>2. One wave is reflected from the glossy surface ... | g7288 | [
0.08088140934705734,
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<p>I'm trying to calculate the <em>released energy from a reaction</em>.
The radioactive substance polonium decays according to this formula:
$$^{210}_{84}\mbox{Po} \rightarrow \mbox{X}+^4_{2}\mbox{He} $$
At first I solved X to be: $^{206}_{82} \mbox{Pb}$</p>
<p>Now when I have the whole reaction, what formula should... | g7289 | [
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<p>In the multiverse as it is described by eternal inflation, it is not clear to me what is its causal structure and in particular if the bubble-universes are causally connected. We start from a de-Sitter space-time and a scalar field whose almost constant potential plays the role of a positive cosmological constant, b... | g7290 | [
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<p>Given the definition of unix timestamp as the number of seconds elapsed since January 1st, 1970 as GMT+0, without leap seconds, is it possible to create a universal clock that will generate the correct timestamp?</p>
<p>Is the current definition of a second </p>
<blockquote>
<p>the duration of 9192631770 periods... | g7291 | [
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<p>I'm having problems solving for the electric field and the current that an electric eel generates. Would I use Gauss's law and treat it as a long charged wire? How would I find the charge of the electric eel? I'm really confused about what I can do and where to start. </p>
<p>In the second part of the project I nee... | g7292 | [
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<p>I recently read <a href="http://newsoffice.mit.edu/2013/you-cant-get-entangled-without-a-wormhole-1205" rel="nofollow">this</a> article from MIT News. I then started thinking about how a particle accelerator creates a temporary <a href="http://press.web.cern.ch/backgrounders/safety-lhc" rel="nofollow">microscopic bl... | g7293 | [
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<p>I'm an undergraduate reading up on some quantum physics so that I can help out more in the lab that I'm working in this summer. In the book I'm reading (Shankar's "Principles of Quantum Mechanics") I just came across the term <a href="http://www.google.com/search?as_q=interaction+hamiltonian" rel="nofollow">interact... | g7294 | [
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<p>I haven't yet gotten a good answer to this: If you have two rays of light of the same wavelength and polarization (just to make it simple for now, but it easily generalizes to any range and all polarizations) meet at a point such that they're 180 degrees out of phase (due to path length difference, or whatever), we ... | g7295 | [
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<p>Given a (closed or not) surface and a point emitting a spherical sound wave, how can I calculate the wave amplitude in any point of space, considering reflections on this surface ?</p>
<p>The idea is to determine the response of the cavity to a dirac impulse, for use in <a href="http://en.wikipedia.org/wiki/Convolu... | g7296 | [
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<p>I'm aware of the critical constants for gas-liquid transition but is there such constants for liquid-solid transition? Like the maximum temperature above which a liquid cannot be solidified.</p> | g7297 | [
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... |
<p>As in, if I'm accelerating away from the Earth, then does the Earth <em>also</em> appear to be accelerating away from me at the same rate? Or is there something to "break" this type of symmetry?</p>
<p>My question is inspired by the below discussions:</p>
<p><a href="http://www.quora.com/Special-Relativity/When-I-... | g7298 | [
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<p>Let be a dimensional regularized integral</p>
<p>$$ \int d^{4-\epsilon}kF(k,m,s)= \frac{2}{\epsilon}+\frac{m^{2}}{3}(\gamma +log(4\pi)-\frac{1}{\epsilon}))$$</p>
<p>then formally if we elmiinate the divergent quantities we may have</p>
<p>$$ \int d^{4-\epsilon}kF(k,m,s)_{reg}= \frac{m^{2}}{3}(\gamma +log(4\pi)+lo... | g7299 | [
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<p>Well, the Possion bracket:</p>
<p>$ \{ A(q,p),B(q,p) \} \equiv \sum_{s} \left( \dfrac{\partial A}{\partial q_{s}} \dfrac{\partial B}{\partial p_{s}} - \dfrac{\partial A}{\partial p_{s}} \dfrac{\partial B}{\partial q_{s}} \right) $</p>
<p>is a coordinate transformation according to the words of this Wikipedia page:... | g7300 | [
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<p>I was asking myself if there is a closed formula for the following product of gamma matrices:</p>
<p>$$\gamma_\mu\gamma_\nu \gamma_5.$$</p>
<p>I would like to express this matrix in terms of the basis </p>
<p>$${\mathbb{1}, \gamma_{5}, \gamma_{\mu}, \gamma_{\mu}\gamma_{5},[\gamma_{\nu},\gamma_{\mu}]} .$$</p>
<p>... | g7301 | [
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... |
<p>The <a href="http://www.phys.uconn.edu/~dunne/dunne_schwinger.html">Schwinger effect</a> can be calculated in the world-line formalism by coupling the particle to the target space potential $A$.</p>
<p>My question relates to how this calculation might extend to computing particle creation in an accelerating frame o... | g7302 | [
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<p>In the cosmic history of the universe, does the dark energy comes before the radiation epoch, or only now, in the 'matter' universe (matter dominated era)? </p>
<p>Because, we now know that like 75% of our visible universe is made up of dark energy, about 20% is dark matter and the rest is the 'ordinary matter', bu... | g7303 | [
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<hr>
<p>Consider a dielectric slab waveguide (lossless, isotropic) illuminated transversally from the vacuum (with coherent, monochromatic light).</p>
<p>We define the <em>base bandwidth</em> of a waveguide (or optical fiber), $AB$, to be the inverse of the time retardation, $\Delta t$, at 1 km of the waveguide betwe... | g7304 | [
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<p><img src="http://i.stack.imgur.com/CvXe0.png" alt="Look at this."></p>
<p>I'm trying to work out a model for the system above, that is, $N$ particles of unitary mass subject to the constraints: $$1=\varphi _i(\mathbf r _1,\mathbf {r}_2,...,\mathbf r _n)=|\mathbf r_i-\mathbf r_{i-1}|^2,\qquad 1\leq i \leq n+1,$$
and... | g7305 | [
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0.0150... |
<p>For a given system, how can you tell which one is kinetic energy for center of mass and which one is internal kientic energy?</p>
<p>K = Kcm + K int</p>
<p>For example, "A 150 g trick baseball is thrown at 63 km/h. It explodes in flight into two pieces, with a 39 g piece continuing straight ahead at 85 km/h. How ... | g7306 | [
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<p>While analysing a problem in quantum Mechanics, I realized that I don't fully understand the physical meanings of certain integrals. I have been interpreting: </p>
<ul>
<li><p>$\int \phi^\dagger \hat A \psi \:\mathrm dx$ as "(square root of) probability that a particle with state $|\psi\rangle$ will collapse to a ... | g7307 | [
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<p>Given two (or more) observables $A, B$ which commute one can construct a third observable $C= A \circ B$. If $\psi$ is a common eigenvector of $A, B$ with eigenvalues $\lambda_1, \lambda_2$ then it is clear that the measurement of $C$ of the state $\psi$ gives the measurement result $\lambda =\lambda_1 \lambda_2$, i... | g7308 | [
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<p>In the movie <a href="http://www.imdb.com/title/tt1454468/" rel="nofollow"><em>Gravity</em></a> the two astronauts (Bullock and Clooney) are hit <em>twice</em> by the fast moving debris that bring havoc to their locations. I think this is a bad scientific mistake in the movie plot.</p>
<p>Indeed, different objects ... | g7309 | [
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<p>Imagine a source of photons at the center of a spherical shell of detectors at radius $R$.</p>
<p>Assume the photons are emitted one at a time.</p>
<p>Now if photons are particles that are highly likely to travel on straight paths at velocity $c$ then one would expect the following behavior:</p>
<p>At time $t=0$ ... | g7310 | [
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<p>Imagine a point process defined by the passage time of purely brownian particles through a given point (in 1D), line (2D) or plane (3D). I'm interested in the variance of the counts (number of particles passing the points) as a function of sampling time.</p>
<p>Unlike brownian motion, I expect my signal to show non... | g7311 | [
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<p>The identification of an electron as a <em>particle</em> and the positron as an <em>antiparticle</em> is a matter of convention. We see lots of electrons around us so they become the normal particle and the rare and unusual positrons become the <a href="http://en.wikipedia.org/wiki/Antiparticle">antiparticle</a>.</p... | g686 | [
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<p>Wikipedia has articles on <a href="https://en.wikipedia.org/wiki/Two-photon_absorption" rel="nofollow">two photon absorption</a>. And a lot of NMR literature refers to <a href="https://www.google.com/search?q=double+quantum+transitions&client=ubuntu&channel=cs&oq=double+quantum+transitions&aqs=chrome... | g7312 | [
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<p>I've done this before, but it's been a long time.</p>
<p>Using trigonometric functions, I've been asked to solve the following problem. However, I'm at a complete loss as to how to do it. I have 5 questions similar that I know I can figure out if given an example.</p>
<p>A plane moving at $180$ mi/hr comes down to... | g7313 | [
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<p>It's a somewhat theoretical question. In special relativity, The energy of a photon is given by $E = pc$. But, my argument is that, since photons have no mass, how can they have a momentum $p$? The energy $E$ turns out to be 0 always. So, why does this equation hold?</p> | g195 | [
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<p>Is the earth's magnetic field strong enough to hold a quantum locked superconductor, or the superconductor wouldn't be able hold its own weight?</p>
<p>How strong should be the earth's magnetic field to hold quantum locked superconductors?</p> | g7314 | [
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