question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I was watching a few sci-fi movies and was wondering the real science explaining what would happen if you were to be subject to the conditions of outerspace.</p>
<p>I read the <a href="http://en.wikipedia.org/wiki/Space_exposure" rel="nofollow">wikipedia article on space exposure</a>, but was still confused. If a p... | g11390 | [
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<p>Given a metric </p>
<p>$$ ds^{2}~=~ g_{a,b}dx^{a}dx^{b}. $$ </p>
<p>Here Einstein's summation convention is assumed for $a$ and $b$.</p>
<p>Then given the Laplacian over that metric, can then we find a metric $ g_{a,b} $ so</p>
<p>$$ \Delta _{g}f ~=~ - \nabla^2 f +V(x)f. $$</p>
<ul>
<li><p>the first term on th... | g11391 | [
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<p>I have next to no knowledge of any physics, but would be happy if you could answer my question...</p>
<p>I want to know an equation for two astronomical entities such as the star Sirius (2.02 solar mass) colliding. </p> | g134 | [
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<p>Although the motivation of this question comes from the AdS/CFT correspondence, it actually is related to a more general principle of gauge/gravity duality. We know from Maldacena's conjecture that a $\mathcal{N}=4$ SYM theory is dual to a Type IIB String Theory on an $AdS_5 \times S^5$ background.
Mathematically, ... | g11392 | [
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<p>I have two images taken within 30 minutes of each other in the same part of the sky. They are very similar but are slightly offset due to the Earth's rotation and other factors.</p>
<p>I know: the X, Y coordinates and RA/dec of the center of each image, and the pixel scale of both images (eg. 1.3 arcsec/pixel).</... | g11393 | [
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<p>given a radial potential in 3 dimension and its Schroedinguer equation</p>
<p>$ -D^{2}U(r) + \frac{l(l+1)}{r^{2}}+V(r) $ here D means derivative with respect to 'r'</p>
<p>then if we apply quantum scattering how can we calculate the PHASE SHIFT ?? $\delta $ , for a general potential ?? .. for example with the cond... | g11394 | [
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<p>In 2D the entanglement entropy of a simply connected region goes like
\begin{align}
S_L \to \alpha L - \gamma + \cdots,
\end{align}
where $\gamma$ is the topological entanglement entropy.</p>
<p>$\gamma$ is apparently
\begin{align}
\gamma = \log \mathcal{D},
\end{align}
where $\mathcal{D}$ is the total quantum dim... | g11395 | [
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<p>I read a textbook today on quantum mechanics regarding the Pauli spin matrices for two particles, it gives the Hamiltonian as
$$
H = \alpha[\sigma_z^1 + \sigma_z^2] + \gamma\vec{\sigma}^1\cdot\vec{\sigma}^2
$$
where $\vec{\sigma}^1$ and $\vec{\sigma}^2$ are the Pauli spin matrices for two particles separately. I t... | g11396 | [
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<p>Viscous fluid mechanics starts with the assumption that shear stress is
linearly related to velocity by $$\tau = \mu\frac{du}{dy},$$ but it later
turns out that some forces in high speed situations go as the square of the
speed. This is really a reference request: are there critical discussions about
the correctness... | g11397 | [
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<p>Among common household appliances, things one can make from stuff in the garage or hardware store, and reasonably safe, e.g. within reach of hobbyists and high school kids entering a science fair, what is the highest speed of motion of any bit of matter one can obtain?</p>
<p>The bit of matter, or surface points ... | g11398 | [
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<p>This question has been bothering me for a while. I have a crude hypothesis...</p>
<p>As I understand it, an observer falling into a black hole will cross the event horizon at some specific future (proper) time in, and that it will not be a traumatic event if the black hole is big enough (e.g. tidal forces will be q... | g11399 | [
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<p>On page 89 of Griffith's QM book, an exact solution to the time-dependent SE equation for the harmonic oscillator is mentioned:</p>
<p>$$ \Psi(x,t)=\left(\frac{m\omega}{\pi\hbar}\right)^{1/4}\exp\left[-\frac{m\omega}{2\hbar}\left(x^2+\frac{a^2}{2}(1+e^{-2i\omega t})+\frac{i\hbar t}{m}-2axe^{-i\omega t} \right)\righ... | g11400 | [
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<p>I'd like to approximate the force from a solenoid, or at the very least find a formula which is proportional to the force so that I can experimentally find the constant for my particular case. Apparently an exact answer to this is hard and involves quantum physics that is a bit beyond me; something about the Ising m... | g11401 | [
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<p>If an electric current is flowing through an electric wire, can we consider that wire charged?</p>
<p>The answer is required with a proof. Can we consider the wire to be charged positively or negatively?</p> | g11402 | [
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<p><img src="http://i.stack.imgur.com/X7ogH.png" alt=" "></p>
<p>There's already the solution for the problem but I still don't understand why the velocity can't be calculated by just
$$ a = (v(t))'= -B_0 + B_1t \Rightarrow v(t) = -B_0t + 1/2B_1t^2$$</p>
<p>Also, both my solution and given solution tell that at t=0,... | g11403 | [
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<blockquote>
<p>Two balls of mass $m$ each one are connected with mass-less rope with
the same length as the radius of earth. The system is in free fall.
Prove that the tension of the rope when the nearest (to the earth)
ball's distance from the earth surface is $R_E/2$ is: $T =
\frac{32}{225} mg$</p>
</block... | g11404 | [
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<ol>
<li><p>Has martian sunset same spectra than this earthly bluish-violet sunset? </p></li>
<li><p>What about sunset on Mercury?</p></li>
</ol> | g11405 | [
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<p><img src="http://i.stack.imgur.com/bQYEE.jpg" alt="enter image description here">
let us consider
the two-dimensional configuration shown in Fig. 3.1a. The lengths of the arrows
represent the magnitude of φ, while their directions indicate the orientation in
the $φ_1 -φ_2$ plane. Regardless of the behavior of the fi... | g11406 | [
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<p>For example, I have a mass, m = 0.1kg and I square root it, giving me m = 0.316 (3s.f.) does the unit still stay as kg, or does it change?</p> | g11407 | [
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<p>I was reading <a href="http://physics.stackexchange.com/questions/17362/what-type-of-substances-allows-the-use-of-the-ideal-gas-law">here</a> about how the ideal gas law assumes point masses and non-interaction. Is it fair to say that all chemistry arises from failures of that?</p>
<p>Of course, such a sweeping gen... | g11408 | [
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<p>Let's consider a cicumference that have the center in the origin of axes and rotates around x-axes. Let's stick a bar in a point $A$ of this circumference and at the end of the bar let's stick a mass point $P$.
Let's call $\theta$ the angle that the radius $OA$ formes with z-axes and $\phi$ the angle that $AP$ form... | g11409 | [
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<p>Is there real materials have Lieb lattice structure? </p>
<p>Some examples?</p> | g11410 | [
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<p>Can someone explain the quantum physics-consciousness connection? In the double slit or quantum eraser experiments, the system behaves as a whole, with some apparent time independent traits. Invoking some kind of time independent but still causal physics, the problem could be simplified. But to include consciousnes... | g11411 | [
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<p>This is <a href="http://path-2.narod.ru/design/base_e/nswr.pdf" rel="nofollow">the original paper</a> by R. Zubrin proposing the Nuclear Salt Water Rocket design.</p>
<p>Basically the design is that a capillar set of pipes store a uranium salt-water solution, inside a cadmium matrix, which helps to keep it below cr... | g11412 | [
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<p>I'm watching water with air bubbles flow through transparent plastic tubing. The inner diameter is a few mm. Bubbles typically are the same diameter as the tubing, with length about the same or up to several cm long. I am not sure what kind of plastic the hose is made of, but it's quite flexible. The general wa... | g11413 | [
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<p>Your Mass is NOT from Higgs Boson?</p>
<p><a href="http://www.youtube.com/watch?v=Ztc6QPNUqls">http://www.youtube.com/watch?v=Ztc6QPNUqls</a></p>
<p>This guy can't be correct, right? He argues that because mostly of a nucleus' mass is made out of the space between quarks (the quark-gluon plasma) then this means th... | g229 | [
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<p>I know gamma-ray photon can only give its momentum energy to the electrons of an atom.</p>
<p>My question is: Can a photon give some of its momentum to the atom (including its nucleus) to give it heat or speed?</p>
<p>If yes, can you tell me how much energy can it give?</p> | g11414 | [
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<p>More and more articles pop up on the shortage of helium, and on the importance of it. Its usage in MRI's spring to mind for example. I looked it up and found out that helium is used for its 'low boiling point' and 'electrical superconductivity'. So this gives me a couple of questions:</p>
<ul>
<li><p>How can the am... | g11415 | [
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<p><a href="http://xkcd.com/1145/" rel="nofollow">A recent XKCD comic</a> implies that the sky is blue as opposed to violet due to human physiology, and that animals more sensitive to shorter wavelengths will perceive the Earth's sky as the shortest wavelength that they can comfortably see. </p>
<p>Is this phenomenon ... | g11416 | [
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<p>This is a follow-up to an <a href="http://physics.stackexchange.com/questions/3343/what-is-tension-in-string-theory">intriguing question last year about tension in string theory</a>.</p>
<p>What are the strings in string theory composed of?</p>
<p>I am serious. Strings made of matter are complex objects that requi... | g24 | [
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<p>My physics book has a topic about <a href="http://en.wikipedia.org/wiki/Zener_diode" rel="nofollow">Zener diodes</a> being used as voltage regulators in the reverse bias.</p>
<p>Well, I'm curious to know how does a Zener diode maintain the potential across its terminals after it has undergone avalanche breakdown? D... | g11417 | [
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<p>I'm having trouble conceptualizing why the voltage drop between two points of an ideal wire (i.e. no resistance) is $0~V$. Using Ohm's Law, the equation is such:</p>
<p>$$
V = IR \\
V = I(0~\Omega) \\
V = 0$$</p>
<p>However, conceptually I can't see how there is no change in energy between these two points.</p>
<... | g71 | [
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<p>For a little colour: this came from my wondering why fork-lifts are hydraulically driven, rather than electromechanically.</p>
<p>My question is this: why is it that some systems, while in static equilibrium and seeming to do no work, actually are work.</p>
<p>I'm thinking, specifically, of these examples:</p>
<u... | g315 | [
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<p>I am studying General Relativity and am trying to understand the Equivalence Principle more thoroughly. Basically, it is said that if you are in a uniformly accelerated frame of reference in free space away from any gravitational field, let's say an elevator, there is no way for the observer in the elevator to know... | g11418 | [
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<p>I've always assumed that the strong resistance of air is the reason there is no flow of electrons between the terminals of a battery until a wire is connect. However, in a vacuum there is no resistive substance to impede the flow of electrons.</p>
<p>Does this mean that in a vacuum an average AA battery will sponta... | g11419 | [
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<p>As far as I'm aware (please correct me if I'm wrong) quantum fields are simply operators, constructed from a linear combination of creation and annihilation operators, which are defined at every point in space. These then act on the vacuum or existing states. We have one of these fields for every type of particle we... | g11420 | [
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<p>Could someone please explain the trajectory of the ball that is bouncing in this picture...</p>
<p>The vertical component of the velocity of a bouncing ball is shown in the graph below. The positive Y direction is vertically up. The ball deforms slightly when it is in contact with the ground.</p>
<p><img src="http... | g11421 | [
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<p>This is probably not the kind of question you'll often encounter on this forum, but I think a bit of background is needed for this question to make sense and not seem like a duplicate:</p>
<p>2012 has been an annus horribilis in my life. I have lost a lot of close relatives in a sudden surge of cardiovascular disea... | g11422 | [
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<p>It is a well known fact that the location of the pole of a propagator (in QFT) can be interpreted as the physical mass.</p>
<p>Is there an interpretation for the residue of the propagator?</p>
<p><strong>Note:</strong> I´m thinking of generalised propagator, not necessarily a propagator of a fundamental field.</p> | g11423 | [
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<p>Yesterday I randomly started thinking about Newton's Law of Cooling. The problem I realized is that it assumes the ambient temperature stays constant over time, which is obviously not true. So what I tried doing was to modify the differential equation into a system of differential equations, and taking the heat capa... | g11424 | [
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<p>I am aware that electrons are moving in an empty space so basically there is no friction to slow it down and its velocity stays the same. However where did the electron get its energy from in the first place(during the creation of the universe"Big bang"). Plus when we "touch" there is no physical contact.The electro... | g11425 | [
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<p>I believe GPS works because of extremely small time differences between the satellites. Because of how small the time differences are, it needs to take into account gravity's effect on time. Although gravity warping time seems very far fetched in normal life, there are practical applications that we use every day ... | g11426 | [
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<p>I am a budding novelist, and im researching a few things for a fictional narrative. the characters are from other dimensions and i want to present a coherent scientific structure. any suggestions orhelp would be appreciated.</p> | g11427 | [
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<p>String theory has at least $10^{500}$ 6D compactifications. <a href="http://arxiv.org/abs/hep-th/0602072" rel="nofollow">Denef and Douglas</a> proved the computational complexity of finding a compactification which fits the parameters of the low energy effective action like the cosmological constant, the electroweak... | g11428 | [
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<p>When the sun is out after a rain, I can see what appears to be steam rising off a wooden bridge nearby. I'm pretty sure this is water turning into a gas.</p>
<p>However, I thought water had to reach 100 degrees C to be able to turn into a gas.</p>
<p>Is there an edge case, for small amounts of water perhaps, that ... | g685 | [
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<p>I am a PhD student in mathematics who knows little more about physics than what one learns in high school. For my research on tilings of space and aperiodic order, every now and then I have to skim a physics research article on solid state physics. And it would be good for me to know more about the basic principles ... | g365 | [
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<p>Classically, probability distributions are nonnegative real measures over the space of all possible outcomes which add up to 1. What they mean is open to debate between Bayesians, frequentists and ensemble interpretations. A degenerate distribution is the least random distribution with a probability of 1 for a given... | g11429 | [
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<p>I am looking for a textbook that treats the subject of Special Relativity from a geometric point of view, i.e. a textbook that introduces the theory right from the start in terms of 4-vectors and Minkowski tensors, instead of the more traditional "beginners" approach. Would anyone have a recommendation for such a te... | g328 | [
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<blockquote>
<p>1) First of all, let us consider a particle of light, also known as a photon. One of the interesting properties of photons is that they have momentum and yet have no mass. This was established in the 1850s by James Clerk Maxwell. However, if we recall our basic physics, we know that momentum is made u... | g11430 | [
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<p>I've found many definitions of Lorentz generators that satisfy the Lorentz algebra: $$[L_{\mu\nu},L_{\rho\sigma}]=i(\eta_{\mu\sigma}L_{\nu\rho}-\eta_{\mu\rho}L_{\nu\sigma}-\eta_{\nu\sigma}L_{\mu\rho}+\eta_{\nu\rho}L_{\mu\sigma}),$$ but I don't know the difference between them.</p>
<p>Firstly, there is the straightf... | g11431 | [
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<p>Consider a bath of Brownian particles at temperature $T$. If we sprinkle some larger particles in this (eg: pollen grains in water or dust motes in air), they'll diffuse with diffusion constant $D$ due to bombardments by the Brownian particles. For the same bombardments, any acceleration of these bigger particles du... | g11432 | [
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<p>I am using <a href="http://home.rzg.mpg.de/~mam/" rel="nofollow">SimNRA</a> to simulate the classical Rutherford Scattering. Playing around with it, I came across some spectra that I cannot explain...</p>
<p>First of all, if someone plots the spectrum of scattering angle $\theta=0$ will get one! I expected that I w... | g11433 | [
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<p>If an object is say thrown down (vertically) at an initial speed that is faster than its terminal velocity, what would happen to that objects speed? Would it slow down?</p> | g11434 | [
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<p>I am referring to the use of specific particle types such as an antiproton beam, positron beam, meson beam or muon beam for example in the likes of shows like star trek. I was curious if a beam of a certain particle would produce specific effects or is this purely wishful thinking. </p>
<p>I am by no means a physic... | g11435 | [
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<p>I'm interested in getting a basic physical understanding of how Earth's magnetic field is generated. I understand that it's a "dynamo" type of effect, driven by convection currents in the molten outer core. These currents cause charges to move, and this generates the field.</p>
<p>However, what I can't find a good ... | g11436 | [
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<p>Will <a href="http://en.wikipedia.org/wiki/Relative_density" rel="nofollow">Relative density</a> of water change based on the state it is in? Ie solid, liquid, gas.</p>
<p>What causes this change(if any) in Rd?</p> | g11437 | [
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<p>While going from a given Lagrangian to Hamiltonian for a fermionic field, we use the following formula. $$ H = \Sigma_{i} \pi_i \dot{\phi_i} - L$$ where $\pi_i = \dfrac{\partial L}{\partial \dot{\phi_i}} $
In a Lagrangian involving fermionic fields given by, $$ L = \dfrac{1}{2}(\bar{\psi_i} \dot{\psi_j} - \dot{\bar... | g11438 | [
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<p>Are there general conditions (preservation of symmetries for example) under which after regularization and renormalization in a given renormalizable QFT, results obtained for physical quantities are regulator-scheme-independent? </p> | g11439 | [
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<p>I see that it appears as a constant in the relation for the running of the strong coupling constant. What is its significance? Does it have to be established by experiment? Is it somehow a scale for quark confinement? If yes, how? I ask because I saw this in Perkins' <em>Particle Astrophysics</em> </p>
<blockquote>... | g11440 | [
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<p>Sorry if this is a silly question.</p>
<p>If I understand correctly, for two atoms "having the same number of protons" is equivalent to "being of the same element", while "having the same number of protons and the same number of neutrons" equates to "being of the same isotope (of the same element)".</p>
<p>But doe... | g11441 | [
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<p>Astronomical telescopes are now mega projects and cost $1Bn and although they are pitched to solve the current interest of the day they are general purpose machines and with upgrades and new instruments have a life of perhaps 50years.</p>
<p>It seems that large accelerator projects are built to answer one question,... | g11442 | [
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<p>The Hamiltonian of <a href="http://en.wikipedia.org/wiki/Helium_atom" rel="nofollow">helium</a> can be expressed as the sum of two hydrogen Hamiltonians and that of the Coulomb interaction of two electrons. </p>
<p>$$\hat H = \hat H_1 + \hat H_2 + \hat H_{1,2}.$$</p>
<p>The wave function for parahelium (spin = 0) ... | g11443 | [
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0.01... |
<p>The question is:</p>
<blockquote>
<p>A student performs an experiment to determine the Young's modulus of a wire, exactly 2m long, by <a href="http://www.google.com/search?hl=en&as_q=searle+method+young+modulus" rel="nofollow">Searle's method</a>. In a particular reading, the student measures the extension in... | g11444 | [
0.011773113161325455,
0.04919981211423874,
0.012343219481408596,
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0.03710630536079407,
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0.01... |
<p>Black holes are caused by massive curvature of the fabric of space-time. Is it right in believing theoretically that forces of electromagnetic origin could also lead to distortion of the fabric of space-time, (though it may not be as tremendous as the extent to which distortion is brought about by gravitational forc... | g366 | [
0.04200071096420288,
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0.013807754963636398,
0.07629561424255371,
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0.012527518905699253,
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<p>Is there a theory for why the charge of an electron is precisely 50% larger (magnitude) than a quark's? I have usually thought of this the other way around: the charge of a quark being 2/3 (or -2/3) that of an electron. Is there something fundamental in space/time/mass/etc that makes it a nice proportion?
(I unders... | g11445 | [
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<p>I study Power Engineering in University. Today I asked my lecturer to explain me exactly how atom's electrons act under spinning rotor's magnetic field, that generated dynamic electricity. But he even didn't gave me to finish my question and said : "Explaining it to you is useless, you are not capable of understandi... | g11446 | [
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<p>I'm trying to design a parachute that minimizes the descent velocity, but I'm not sure what shape I should use.</p>
<p>From what I've read, ellipse-shaped parachutes are too aerodynamic and minimize drag, while squares are good enough to maximize drag, but I've read this from very unreliable sources and unfortunate... | g11447 | [
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<p>I took my son to a science museum where they had a gadget that many of us probably saw in movies involving a mad scientist. The gadget had two metal rods about two inches apart at the bottom. The rods were about six feet long, and four inches apart at the top. An electric spark would start at the bottom where the ro... | g11448 | [
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<p>I took my son to a science museum where they had a solenoid oriented vertically with a plastic cylinder passing through the solenoid. An employee dropped an aluminum ring over the top of the cylinder when there was no current going through the solenoid. Then they turned on the current going through the solenoid and... | g11449 | [
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<p>I would like clarification on an equation in the paper "Free matter wave packet teleportation via cold-molecule dynamics", L. Fisch and G. Kurizki, <em>Europhysics Letters</em> <strong>75</strong> (2006), pp. 847-853, DOI: <a href="http://dx.doi.org/10.1209/epl/i2006-10205-7" rel="nofollow">10.1209/epl/i2006-10205-7... | g11450 | [
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<p>I'm thinking of writing a short story set on a version of Earth that is tidally locked to the Sun. I'm not exactly sure how to research the topic. Here's a number of questions about what would happen:</p>
<ul>
<li><p>How hot would the light side get? Are we talking ocean-boiling levels? I imagine that life would ev... | g11451 | [
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<p>Assuming gaussian error distributions, how to calculate the discrepancy between the two values in units of sigmas?</p> | g11452 | [
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<p>I just watched a BBC Horizon episode where they talked about the Hawking Paradox. They mentioned a controversy about information being lost but I couldn't get my head around this.</p>
<p><a href="http://nrumiano.free.fr/Estars/bh_thermo.html" rel="nofollow">Black hole thermodynamics</a> gives us the formula $$S ~=~... | g11453 | [
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... |
<p>What does it precisely mean the often repeated statement that the electric charges of all leptons are the same. </p>
<p>Let's consider QED with two leptons: electron and muon. The interaction part of the bare lagrangian contains two electron-electron-photon and muon-muon-photon vertices with some coupling constants... | g11454 | [
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<p>What physical quantity has SI unit $\mathrm{kg}/\mathrm{m}$?</p>
<p>For example, the physical quantity with SI unit $\mathrm{kg}\cdot\mathrm{m}/\mathrm{s}^2$ is force $F$ and the physical quantity with SI unit $\mathrm{m}/\mathrm{s}^2$ is acceleration $a$.</p> | g11455 | [
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<p>Assuming no sliding and that the shoulder is 1.2m from the feet, what force is required to topple a person weighing 70 Kg standing with his feet spread 0.9 m? If possible, please include an explanation about your answer.</p> | g11456 | [
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<p>A while back in my Dynamics & Relativity lectures my lecturer mentioned that an object need not be accelerating relative to anything - he said it makes sense for an object to just be accelerating. Now, to me (and to my supervisor for this course), this sounds a little weird. An object's velocity is relative to t... | g695 | [
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<p>Excerpt from an essay of mine:</p>
<blockquote>
<p>Let $\Psi(\varsigma)$ be the wavefunction in the loop representation, where $\varsigma:[0,1]\to\mathcal{M}$, where $\mathcal{M}$ is spacetime. Then, let $\mathcal{A}$ be the Ashtekar connection and $\mathcal{W}_\varsigma[\mathcal{A}]$ be the Wilson loop of the co... | g11457 | [
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<p>CIE defined color matching functions (CMF) for XYZ and thus RGB colors. But of course, each camera has its own color sensitivities for visible spectrum. Is there any way to estimate this function (or a series of values by wavelengths) for a given camera? </p> | g11458 | [
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<p>The interpretation of the double slit experiment is very strange and i want to understand how they did it before I give up my concept of reality. With the double slit experiment a interference pattern is created even when you emit just one photon. However, when you use photon detectors to find out which slit the pho... | g11459 | [
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<p>I did an experiment involve how R scales with q (the other variables are constant), and I got a relationship like $R\ \propto \sqrt q$</p>
<p>I have been told to evaluate my findings with those in literature, and I found an equation in literature to compare it to. I have been told that the equation $$R=\dfrac{4q^2}... | g11460 | [
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<p>Let's say there is a charged tube(a cylinder with no top and bottom) with radius r and length l, charge q1 which also made out of insulating material. And also if there is an object with charge q2 along the axis of the surface of the tube, how can I calculate the force applied on this object?(the distance between tu... | g11461 | [
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<p>I wonder if time and movement can be translated into a simulation of an extra spatial dimension. At least in one point at a time. I'll try to explain.</p>
<p>Imagine a fixed probe which measures the distance to one point on the surface of a cube. As the cube rotates around its center, the probe will measure differe... | g11462 | [
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<p>I'm trying to calculate the probability of finding $n$ particles in a certain volume $v$ in a system with a total of $N$ particles and total volume of $V$. My problem is that I've tried two approaches which both seem valid to me, but give differing answers.</p>
<p>One approach is to use binomial probability, where ... | g11463 | [
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<p>With accelerated expansion of universe which is same in all direction we know that dark energy increase with time because space between any two point in space time increases with time. So after some finite time we can not see nearby galaxy cluster which we can see now. So doesn't that violate conservation of energy ... | g166 | [
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<p>FLEX method was invented by N.E.Bickers and D.J.Scalapino in 1989 (PRL 62,961; Ann. Phys. 193,206). Later it was extended to multi-orbital system (T.Takimoto,PRB,69,104504). </p>
<p>But I don't find FLEX including the SOC term. More generally, can FLEX method be applied to the $SU(2)$ spin-rotation symmetry <em>bro... | g11464 | [
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<p>I want to get the density of a fluid going through a pipe. I can measure the flow and pressure with a flowmeter and the temperature using a thermometer. With this information, I want to calculate (or approximate) the instantaneous density of the fluid passing through my instruments.</p>
<p>How would I go about do... | g11465 | [
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<p>I recently attended a talk in which the speaker defined a topological phase as "A phase which has a gap above the ground state for bulk excitations in the thermodynamic limit." I am interested in what sense then can we think of confinement in non-Abelian Yang-Mills theories as topological phases. </p>
<p>What I'm l... | g11466 | [
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<p>I happened to hear people saying that the nuclear fusion bomb tests could set the atmosphere on fire. I have some serious doubts about that - but I have no facts.<br>
Nuclear fusion reaction requires $15*10^{6}$ kelvins to start. If we produce such temperature in "<em>open air</em>" would the atmosphere become a fue... | g11467 | [
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<p>Consider a space ship, undergoing constant acceleration (which for our purposes means that the same amount of energy is being used per second to increase its speed). According to special relativity the ship will accelerate but in such a way that it will approach the speed of light $c$, but never reach the speed itse... | g11468 | [
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<p>Why are we taking 2$\theta$ instead of $\theta$ in X-ray <a href="http://en.wikipedia.org/wiki/Powder_diffraction" rel="nofollow">powder diffraction</a> (XRD). I have found the forum post <em><a href="http://www.chemicalforums.com/index.php?topic=7411.0" rel="nofollow">2 theta in X-ray Powder Diffraction (XRD)</a></... | g11469 | [
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<p>How does wireless signal strength correspond to distance? RSSI lies between -100 and 0 (at least, on my computer). Let's say I walk a distance x towards the router, and my RSSI goes from -60 to -50. Now, lets say instead I walk a distance 2x towards the router. Would this imply that RSSI would go from -60 to -40? I'... | g11470 | [
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<p>So I was given the following vector field:</p>
<p>$\vec{A}(t)=\{A_{0x}cos(\omega t + \phi_x), A_{0y}cos(\omega t + \phi_y), A_{0z}cos(\omega t + \phi_z)\}$</p>
<p>Where the amplitudes $A_{0i}$ and phase shifts \phi_i are constants. An electron is moving through this field with the constant initial velocity:</p>
... | g11471 | [
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<p>I'm quoting a passage from my notes:</p>
<blockquote>
<p>The development of clocks based on atomic oscillations allowed measures of timing with accuracy on the order of $1$ part in $10^{14}$, corresponding to errors of less than one microsecond (one millionth of a second) per year.</p>
</blockquote>
<p>I do not ... | g11472 | [
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<p>Is there any example of explicit one loop computation for Witten diagrams?
It seems like it will be hard to compute for even for a simple $\phi^4$ theory in the bulk.</p> | g11473 | [
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<p>In the case of stimulated emission we always see that one photon goes into the gain medium and two photons come out. How can this conserve energy?</p> | g11474 | [
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<p>I've always read that all matter has gravity. But, can we observe it? I mean, The Earth pulls us but what about small daily objects?</p>
<p>For example, if we release 2 small objects in space, do they get closer?</p>
<p>My point of asking this question is that, maybe the gravity comes from the rotation of the Eart... | g11475 | [
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<p>This question is a follow up to <a href="http://physics.stackexchange.com/questions/19378/what-was-missing-in-diracs-argument-to-come-up-with-the-modern-interpretation-o">What was missing in Dirac's argument to come up with the modern interpretation of the positron?</a></p>
<p>There still is some confusion in m... | g11476 | [
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<p>If a baseball is dropped on a trampoline, the point under the object will move a certain distance downward before starting to travel upward again. If a bowling ball is dropped, it will deform further downwards. What is the nature of the relationship between the magnitude of this deformation and the object's mass? ... | g11477 | [
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<p>what is the relation between mass density $\rho$ and pressure $P$ for a perfect fluid ? </p> | g11478 | [
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