question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I'm curious about what happens if an explosive substance detonates in space. On Earth, I guess a good chunk of the energy released is carried away by shock waves in the atmosphere. But in space, the medium that supported the propagation of the shock wave on Earth is much more rarefied, so how does that work? </p> | 5,646 |
<p>Since phase transition is closely connected with symmetry, I am wondering whether it is possible to determine the universality class of phase transitions just by symmetry? </p>
<p>Actually, I found it is quite boring to calculate critical exponent numerically
and I want to find a new method. </p> | 5,647 |
<p>When I asked here why neutrons in nucleus (with protons) don't decay I was told that it would require energy for the neutron to decay, it wouldn't give energy. And since that wasn't really what I wanted to hear, since I already knew that, I'm now asking a similar question.</p>
<p>I know that strong force holds prot... | 5,648 |
<p>A problem in Bohr's day was understanding why an orbiting electron does not continuously radiate an EM field. An orbiting electron is a moving charge and according to Maxwell, this should generate an electric and magnetic field. Bohr said that photons (packets of EM energy) are only emitted when an electron jumps fr... | 132 |
<p>there is some confusion to me in the case of "<strong>motion of block on a frictionless wedge</strong>"</p>
<p>Below is a simple diagram!</p>
<p><img src="http://i.stack.imgur.com/ET6uv.jpg" alt="enter image description here"></p>
<p>Let us consider a situation as above in which there is a block of mass $m$ movin... | 5,649 |
<p>I've been reading about nanotubes lately, and I keep seeing the $ (n,m) $ notation. How does this describe a nanotube's structure? How do I determine which is $n$ and which is $m$ ?</p>
<p>I'm familiar with matrix notation referring to rows and columns, but I couldn't connect it with the nanotube structure which is... | 5,650 |
<p>Because in theory, visible light contains more energy than the microwaves actually used to cook your food. </p>
<p>1) Does it have to do with resonance frequency of the $H_2O$ molecule? <br /></p>
<p>2) How can microwaves be dangerous when they are about the same wavelength as Radio waves? (unless it has to do mor... | 5,651 |
<blockquote>
<p>A sample of $^{24}_{12}\mathrm{Mg}$ is bombarded by a monoenergetic proton. If the resulting nucleus in a $^{24}_{12}\mathrm{Mg}(p,\gamma)$ reaction; $^{24}_{12}\mathrm{Mg}(p,\gamma)$ has its first energy level at 2.5 MeV. What is the minimum energy of the of the proton to excite this level?</p>
</bl... | 5,652 |
<p>Why do same charges repel each other and opposite charges attract each other (please explain the phenomenon using real laws of nature (QED) not with the approximation model)? </p> | 5,653 |
<p>What is a formula for velocity of a spacecraft in a circular orbit? Actually, is there a formula or I can find it from equation of motion?</p> | 5,654 |
<p>I've been told that, from Maxwell's equations, one can find that the propagation of change in the Electromagnetic Field travels at a speed $\frac{1}{\sqrt{\mu_0 \epsilon_0}}$ (the values of which can be empirically found, and, when plugged into the expression, yield the empirically found speed of light)</p>
<p>I'm ... | 5,655 |
<p>Are all elementary particles of the same type EXACTLY the same? Is there some variation in what an electron is, for example, or are they all the same?</p> | 5,656 |
<p>I am trying to find the geometric structure factor and my work here is clearly wrong. I will put my wrong answer and then I will throw up the link to wikipedia for the correct answer, because I cannot tell the difference.</p>
<p>My attempt: BCC has a four atom basis. If x,y,z vectors are taken to be along the edges... | 5,657 |
<p>Cosmic rays can have energies going into the $10^{20}$ eV domain. <a href="http://en.wikipedia.org/wiki/Asteroid">Asteroids</a> and <a href="http://en.wikipedia.org/wiki/Meteoroid">meteoroids</a> originating in the solar system are probably limited in their speed because they all started out from the same lump of ma... | 5,658 |
<p>Can somebody help me in deriving the Hamiltonian of system starting from Euclidean Lagrangian? </p>
<p>Say we are given the Minkowski Lagrangian</p>
<p>$$L_m = \frac{\dot{\phi}^2}{2} - V(\phi).$$</p>
<p>The Hamiltonian can then be found by Legendre transformation</p>
<p>$$H = \dot{\phi}\frac{\partial L_m}{\parti... | 5,659 |
<p>In gamma-gamma physics, what could be some way of either minimising the mass of the intermediary fermions or minimising the time for which those intermediary fermions could exist?</p> | 5,660 |
<p>Let's have Pauli-Lubanski operator:</p>
<p>$$
\hat {W}^{\alpha} = \frac{1}{2}\varepsilon^{\alpha \beta \gamma \delta}\hat {J}_{\beta \gamma}\hat {P}_{\delta} = \frac{1}{2}\varepsilon^{\alpha \beta \gamma \delta}\hat {S}_{\beta \gamma}\hat {P}_{\delta},
$$</p>
<p>where $\hat {J}_{\beta \gamma} = \hat {L}_{\beta \ga... | 5,661 |
<p>In momentum and energy is low enough, we end up with the same number of neutrons, protons and electrons after a collision as before it. This can be considered an approximate conservation law. Shouldn't there be a corresponding (approximate) symmetry corresponding to each of these particle groups?</p> | 5,662 |
<ol>
<li>Most images you see of the solar system are 2D and all planets orbit in the same plane. In a 3D view, are really all planets orbiting in similar planes? Is there a reason for this? I'd expect that the orbits distributed all around the sun, in 3D.</li>
<li>Has an object made by man (a probe) ever left the Solar... | 5,663 |
<p><a href="http://en.wikipedia.org/wiki/Plasma_%28physics%29" rel="nofollow">Plasma</a> is ionized gas which as far as I know only occurs at high temperatures. When plasma cools down it tends to recombine with the electrons present and turn back into gas. But what if the disassociated electrons in the plasma were remo... | 5,664 |
<p>I'm studying the Method of Images and I seemed to have come to a conundrum. Method of Images takes advantage of grounded objects, (I am currently studying spheres), to set boundary conditions. However, how would one use the idea of MoI to set the potential of a conducting sphere as constant?</p>
<p>Since $E = \nabl... | 5,665 |
<p>In equation 6.2.7, Polchinski defines his reduced Green's functions $G'$ on the 2-manifold to satisfy the equation,</p>
<p>$$ \frac{-1}{2\pi \alpha '}\nabla ^2 G'(\sigma_1, \sigma_2) = \frac{1}{\sqrt{g}}\delta ^2 (\sigma_1 - \sigma_2) - X_0^2 $$</p>
<p>(..where $\sigma_1$ and $\sigma_2$ are two points on the mani... | 5,666 |
<p>I know that when there are excess positive charges in a conductor, for example, a metal sphere, the positive charges will spread out over its surface. However, I am confused about how this excess charge spreads out over the surface, if protons cannot move and only electrons can move.<br>
Can someone please inform me... | 5,667 |
<p>I just finished watching Into the Universe with Stephen Hawking (2010). Specifically the third episode titled 'The Story of Everything.'</p>
<p>In the episode Hawking is explaining the mainstream theories of the events just after the Big Bang. What confuses me is that he just said at the beginning that the laws of ... | 5,668 |
<p>I know that water expands in the freezer, but I'm curious about which materials <em>contract</em> in response to cold temperatures --- and most importantly, which ones undergo the most drastic changes?</p> | 5,669 |
<p>Was one of Hilbert questions regarding physics to make an axiomatic foundation for physics? Regardless of Godels work could some Physics principles that are 'basic' and 'presently verifiable' be treated as axioms in a logic system along with Math axioms and Set theory or maybe with Category theory as a basis. If 'a... | 203 |
<p>I am a non-expert in this field, just have a layman's interest in the subject. Has anyone ever considered the possibility of magnetic monopoles (one positive and one negative charge) being confined together like quarks, and hence that could be the reason monopoles have never been observed? At the macro level the to... | 5,670 |
<p><img src="http://imgur.com/KwER0d8" alt="Diagram"></p>
<p>I have a 5 mm (diameter) solid ball lens that I intend to place in front of a 36mm X 24mm camera sensor (I have already made preparations for the image to be focused and for the sensor to not be flooded with light). I want to calculate the resulting horizont... | 5,671 |
<p>When some photon detector detects a photon, is it an instantaneous process (because a photon can be thought of as a point particle), or does the detection require a finite amount of time depending on the wavelength of the photon?</p>
<p>EDIT: I guess what I am wondering is if a photon has a wavelength and travels a... | 5,672 |
<p>I am trying to confirm a conservation law I cam across in a paper (Janssen 1983 "On a fourth-order envelope equation for deep-water waves" Journal Fluid Mechanics), and am having difficulty. </p>
<p>In particular, I'm trying to confirm the conservation of linear momentum $P$, where </p>
<p>$P = \frac{i}{2} \int AA... | 5,673 |
<p>I am learning supersymmetry right now. I am mostly following Bailin and Love. I try to connect all the steps from the book and complete the derivations in order to get comfortable with the calculations but I feel the lack of a problem book with a lot of solved and unsolved problems, something like the Schaum's serie... | 5,674 |
<p>This question has been asked multiple times here and all over the internet yet I can't find a conclusive answer:</p>
<ul>
<li><p>Some claim that heavier objects do fall faster: <a href="http://physics.stackexchange.com/q/3534/">Don't heavier objects actually fall faster because they exert their own gravity?</a> </p... | 134 |
<p>I am reading through Cavagna's <a href="http://arxiv.org/abs/cond-mat/0505032" rel="nofollow">Spin glass theory for pedestrians</a>, but I am stuck at equation (35).</p>
<p>I'll try to provide a little context. Given two spin configurations $\sigma$ and $\tau$, we define their overlap as:</p>
<p>$$q_{\sigma\tau} =... | 5,675 |
<p>What exactly is meant by <em>Lorentz invariance</em>?</p>
<p>Is it just an experimental observation, or is there a theory that postulates it?</p>
<p>What quantities do we expect to be Lorentz invariant?
Charge? Charge densities? Forces? Lagrangians?</p> | 5,676 |
<p>For example, the Lagrangian formulation.
I may be missing something, i.e. not having done it in enough detail, but here is my issue:</p>
<p>from the definition of the lagrangian ($\mathcal{L}$) and from the principle of least action ($S(t)$), we get that $$ S(t) = \int \mathcal{L} \ dt$$ has to be minimised.</p>
... | 5,677 |
<p>In other words, given a magical room with walls that produce no vibration and transmit zero vibration from the outside, and nothing on the inside except room temperature air, what would be the noise level in dB SPL (<a href="http://en.wikipedia.org/wiki/Sound_pressure" rel="nofollow">sound pressure level</a>) from t... | 5,678 |
<p>Where could I find open-source up-to-date cosmological datasets? Are there any available as a data stream with an API?</p>
<p>I already know about these: </p>
<p><a href="http://cas.sdss.org" rel="nofollow">http://cas.sdss.org</a></p>
<p><a href="http://www.ukidss.org/archive/archive.html" rel="nofollow">http://w... | 204 |
<p>I've looked through several papers that talk about the anomalous integer quantum Hall effect of graphene (such as <a href="http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.95.146801" rel="nofollow">http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.95.146801</a>), and they all state that the Hall effect is anoma... | 5,679 |
<p>I am a beginner in electrical engineering. Often times (most cases actually), the underlying physics aren't really explained to us and we are just left to assume that it works "because it works." This is never enough for me in classes etc and I always end up doing a follow up of physics side of the spectrum.</p>
<p... | 5,680 |
<p><strong>This is the question-</strong></p>
<p>Consider a cylinder of mass $M$ resting on a rough horizontal rug that is pulled out from under it with acceleration $a$ perpendicular to the axis of the cylinder. What is $F$ (friction) at a point <em>P</em>? It is assumed that the cylinder does not slip.</p>
<p><img ... | 5,681 |
<p>I am trying to understand 2D electrostatics of $n$ point charges. Roughly, </p>
<p>$$ H = \sum_{i=1}^N n_i \ln |z- z_i|$$</p>
<p>However, I keep bumping across the Gaudin model instead with this Hamiltonian</p>
<p>$$ H_j = \sum_{i \neq j} \frac{n_i}{z_j- z_i}$$</p>
<p>and these are often put into context with o... | 5,682 |
<blockquote>
<p>Are there physical models of spacetimes, which have bounded (four dimensional) holes in them? </p>
</blockquote>
<p>And do the Einstein equations give restrictions to such phenomena? </p>
<p>Here by holes I mean constructions which are bounded in size in spacetime and which for example might be char... | 5,683 |
<p>Elastomeres are "defined" as:</p>
<p>"linear-chain polymers with widely spaced cross-links attaching each molecule to its neighbours" </p>
<p>Now I found sentences (talking about glass transition):</p>
<p>"This means that at room temperature the secondary bonds are melted and the molecules can slide relative to ... | 5,684 |
<p>I am in AMO Physics and work a lot with optics. I just wanted to get an idea of what coupling efficiencies one "should" get in a "reasonable time"* by coupling light into a fiber using different couplers, like collimators, mounting plates, mounted lens systems, etc. I understand that this dependents on a lot of fact... | 5,685 |
<p>The maximum obtainable angular resolution of an optical system with some given aperture is well known, but it seems to me that this isn't a real theoretical limit. The assumption is that you are going to take a picture using the system and no further processing will take place. However, given the known point spread ... | 5,686 |
<p>Can we see any galaxies/stars that are newer than our own galaxy?</p>
<p>As light takes (c) amount of times to reach us - so relatively speaking, light which would have left the newer galaxy (and far enough from us) still would not have reached us. Therefore, can we ever see a galaxy that is newer than our own one.... | 5,687 |
<p>The <a href="http://www.nasa.gov/mission_pages/newhorizons/main/index.html">New Horizons Spacecraft</a> is scheduled to whiz by Pluto around 2015, and my understanding is that it is going to do exactly that — whiz by it.</p>
<p>Where will it go after that? Or what else can it do once that mission is completed?</p> | 5,688 |
<p>In reference to the <a href="http://www.nasa.gov/mission_pages/kepler/news/kepscicon-briefing.html">Kepler 22b news</a>:</p>
<blockquote>
<p>The Kepler team had to wait for three passes of the planet before
upping its status from "candidate" to "confirmed".</p>
</blockquote>
<p>This is possible because the pla... | 5,689 |
<p>Shortly, I will be beginning my third year at University in Computer Science, I am a software developer and I will be required to work on a final year project. </p>
<p>My idea for my final year project is to write a desktop application which would allow the user to specify a date/time and it would return all of th... | 5,690 |
<p>So, here's a diagram with some galaxies.</p>
<p>I realize there are 500 billion galaxies out there (likely many more), but is there are fairly up-to-date diagram of all the galaxies, or a representative sample, at all observable distances?</p>
<p><img src="http://i.stack.imgur.com/uCejG.gif" alt="Hubble Diagram"><... | 5,691 |
<p>It seems there is a term called "center of gravity of a band" in solid state physics or chemistry which I'm confused about. Could anyone give a formal definition of the term or point to some reference that have a clear explanation of it's meaning?</p> | 5,692 |
<p>I was just reading about quantum entanglement and the example was the Double-Slit Quantum Eraser Experiment. Then this was used as a basis for saying that particles might be half a universe apart and still be just as connected.</p>
<p>So I was just wondering if entanglement experiments have been done to show that ... | 5,693 |
<p>Considering that all frames are equivalent, isn't it up to the observer to say "The earth turns around the sun" or "The sun turns around the earth"? Isn't this more or less like arguing about which meridian should be considered the null-meridian, or whether time should be counted according to years before/after Jesu... | 205 |
<p>I've seen the rings from powder diffraction images, and I read that each line is made up of a lot of dots, I was wondering if these dots are reciprocal lattice points of the structure. And if we weren't looking at a powder but just a 2D hexagonal lattice, then the xrd pattern would simply be its reciprocal lattice? ... | 5,694 |
<p>In P. Di Francesco, P. Mathieu, D. Snchal they fix the generators of the conformal group acting on a scalar field by somewhat arbitrarily defining
$$\Phi'(x)=\Phi(x)-i\omega_a G_a\Phi(x)$$
and by arbitrary I mean the sign. The "full" transformation would then be given by the exponentiation
$$\Phi'(x)=e^{-i\omega_a... | 5,695 |
<p>Currently I'm doing Advanced Classical Mechanics courses. I'm finding it hard to understand due to the lack of knowledge in linear algebra, multi variable calculus and other chapters.</p>
<p>Can anyone suggest a mathematical book which is dedicated to teaching all the math that is used in physics?</p> | 185 |
<p>Are earthquakes getting less frequent across the centuries? I know that more seismic stations have register more earthquakes in the last century, but that doesn't imply there were more. I am interested on the geophysical side of it.</p>
<p>The logic is that things settle down, so there is less stuff to shuttle. Add... | 5,696 |
<p>It is well known that scattering cross-sections computed at tree level correspond to cross-sections in the classical theory. For example the tree level cross-section for electron-electron scaterring in QED corresponds to scattering of classical point charges. The naive explanation for this is that the power of hbar ... | 5,697 |
<p>An elementary example to explain what I mean. Consider introducing a classical point particle with a Lagrangian $L(\mathbf{q} ,\dot{\mathbf{q}}, t)$. The most general gauge transformation is $L \mapsto L + \frac{d}{dt} \Lambda(\mathbf{q},t)$ which implies the usual transformations of the canonical momentum $p \to p... | 5,698 |
<p>For instance, given a theory and a formulation thereof in terms of a principal bundle with a Lie group $G$ as its fiber and spacetime as its base manifold, would a principle bundle with the Poincaré group as its fiber and $\mathcal{M}$ as its base manifold, where $\mathcal{M}$ is a manifold the group of whose isomet... | 5,699 |
<p>Many recent papers study entanglement in eigenstates of fermionic free hamiltonians (normally on a lattice) using the basic assumption that the reduced density matrices are <em>thermal</em> (e.g. <a href="http://arxiv.org/abs/cond-mat/0212631">Peschel 2003</a>). As I understand it, the theorem that we need in order ... | 5,700 |
<p>I'm sure many of us are familiar with the following plot showing the running of the inverse of the fine-structure constants of the SM.</p>
<p><img src="http://i.stack.imgur.com/1PZin.png" alt="running of SM couplings">
(I got the picture from google)</p>
<p>At one-loop, the expressions for the fine-structure cons... | 5,701 |
<p>This is a question about terminology.</p>
<p>Given two vertex algebras $V_1$ and $V_2$ (= chiral CFTs), there are two kinds of maps $V_1\to V_2$ that one might want to consider.</p>
<p>1) Morphisms of VOAs that send the conformal vector of $V_1$ to the conformal vector of $V_2$. In other words, morphisms that send... | 5,702 |
<p>I am reading Cheng and Li. On page 9, it is written that the coefficient $\frac{1}{2 \cdot (4!)^2}$ for the second order term of the four point function becomes just $\frac{1}{2}$ for the following diagram:</p>
<p><img src="http://i.stack.imgur.com/hzbgJ.png" alt="enter image description here"></p>
<p>I am not get... | 5,703 |
<p>Consider an adiabatic system as follows. It consists of a gas in a container and a piston.
Initially, the system is at equilibrium and the gas inside it occupies a volume $V_i$ at a pressure $p_i$ which is equal to the outside pressure. Suddenly, the outside pressure changes and reduces to $p_{atm}$. The piston mov... | 5,704 |
<p>Does there exist a single plate capacitor(conductor)? <em>if yes</em></p>
<p>How will you define the <strong>capacitance</strong> and potential(difference)
of such conductor?</p> | 5,705 |
<p>Due to the <a href="https://en.wikipedia.org/wiki/Propagator" rel="nofollow">Wiki article</a>, "...In quantum mechanics and quantum field theory, the propagator gives the probability amplitude for a particle to travel from one place to another in a given time, or to travel with a certain energy and momentum...".</p>... | 5,706 |
<p>Consider a particle raised to height $h$ by applying a constant force of $F$ vertically opposite to the direction of force of gravity on it. The potential energy of the particle is</p>
<p>$$W = mgh$$</p>
<p>But, according to the definition of work, the work done on the particle is </p>
<p>$$W' = Fh$$</p>
<p>Acco... | 5,707 |
<p>In equation 7 of the paper, <a href="http://arxiv.org/abs/1301.2326" rel="nofollow">Feynman's clock, a new variational principle, and parallel-in-time quantum dynamics</a>, the clock register is different from Feynman's <a href="http://www.cs.princeton.edu/courses/archive/fall05/frs119/papers/feynman85_optics_letter... | 5,708 |
<p>I am creating a data acquisition software, based on <a href="http://www.sparrowcorp.com/products/software" rel="nofollow">Sparrow's Kmax</a>. There I would like to add a feature that will show the system's dead time.</p>
<p>I have already a text field that shows the real time and live. My question has to do, with t... | 5,709 |
<ol>
<li><p>According to theory of time dilation, flow of time slows down significantly at the speed of light.Is there any conditions practically or theoretically when flow of time is reduced to zero means it comes to still?</p></li>
<li><p>Whether time & space are infinite?</p></li>
</ol> | 5,710 |
<p>Executive summary: "Collapse of the wave function" is inherently supraluminal.</p>
<p>I suggest an easier thought experiment to demonstrate the apparently supraluminal (or FTL) aspect of a quantum mechanical measurement, without spin and polarizers.</p>
<p>A photon is sent through a beam splitter. The photon trave... | 5,711 |
<p>We know that there is Adler and Bell-Jackiw(ABJ) type anomalies for fermions. In some case, the ABJ anomaly affecs particle physics pheonomelogy, such as pion decays or kaon decays(in the case of pion, we still have a calculation on left/right chiral fermions running on the 1-loop triangle diagram). In some other ca... | 5,712 |
<p>In condensed matter, one usually considers Bloch states inside the first Brilliouin zone, which, for 1d system with lattice constant $a$, is $-\pi/a<k<\pi/a$.</p>
<p>But the basis of this, Bloch theorem, is based on periodic boundary condition, which implies $k=\frac{2\pi n}{Na}$ with $n=0,1,\cdots N-1$ and $... | 5,713 |
<p>The colloquial explanation is that the spacetime in front of a ship contracts and the spacetime behind expands. I see how one could <em>think</em> that this would bring you closer, but I don't see that it actually does.</p>
<p>Let's look at the front of the bubble. So spacetime "contracts". If you look at a diff... | 5,714 |
<p><img src="http://i.stack.imgur.com/7NVNH.png" alt="enter image description here"></p>
<blockquote>
<p>A rod of mass $m$ and length $l$ is pivoted at one end to ceiling and free to rotate in the vertical plane. A disc of radius $R$, which is less than $l$, can be fixed at its other end in 2 ways :</p>
<p>$1$ ... | 5,715 |
<p>i read Landau's book recently. In this book p.43</p>
<p>Landau says from (16.1) (16.2)</p>
<p>can be write down $T_10$= $p_0^2$/2$m_1$=($M-m_1$)($E_i-E_1i-E_i'$)/$M$</p>
<p>For me, it is hard to understand the factor ($M-m_1$)/$M$.</p>
<p>Can someone give me a hand to let me understanding master's idea?</p>
<p>... | 5,716 |
<p>Minecraft is a game of mining where one digs and finds ore (to put it simply). the world is composed of "blocks" 3 dimensional cubes that have different "pictures" on them, that make them appear like grass or rock or Steele or diamonds...ect. In minecraft there is also TNT which is a block just like all others excep... | 5,717 |
<p>I assume that the reason water freezes is because as you decrease the temperature, the kinetic energy of the water molecules decreases and the dipole bonding potential eventually over comes the escape velocity of the molecules and they form a crystal structure. What would happen if you attempted to freeze water in t... | 5,718 |
<p>Despite the fact that zinc is more electronegative than copper,why it will lose electrons more readily than copper in the voltaic cell due to sulphate ions.</p> | 5,719 |
<p>If quarks and leptons carried flavor charges that differed across generations (as they do in some theories), then could mixing take place?</p> | 5,720 |
<p>I have solved the following problem from Griffiths "Introduction to Quantum Mechanics". </p>
<p>Consider the wavefunction:
$\Psi (x,t) = A e^{-\lambda |x|} e^{-i\omega t} $</p>
<p>Normalize $\Psi$. </p>
<p>Now, we want $ \int_{-\infty}^\infty |\Psi (x,t)|^2 dx = 1$</p>
<p>It is fairly straightforward, where the... | 5,721 |
<p>I understand that the concept of an average of a data list means finding a certain value 'x', which ensures that the sum of the deviations of the numbers on the left of 'x' and on the right of 'x' yields the value 0. Assume we are given the values 2,6,9 and 12. I label these values from left to right in the sequence... | 5,722 |
<p>I want to check whether my result for the invariant amplitude of the electron-electron scattering (to lowest order in $\alpha$; t+u channels) is correct or not. </p>
<p>I can't find any reference that has the result explicitly. Can someone point out some kind of database of scattering amplitudes? </p>
<p><strong>E... | 5,723 |
<p>I'm slightly confused as to answer this question, someone please help:</p>
<p>Consider a free particle in one dimension, described by the initial wave function
$$\psi(x,0) = e^{ip_{0}x/\hbar}e^{-x^{2}/2\Delta^{2}}(\pi\Delta^2)^{-1/4}.$$</p>
<p>Find the time-evolved wavefunctions $\psi(x,t)$.</p>
<p>Now I know tha... | 5,724 |
<p>Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with respect to relative rest observer would become stopped ..if. it means light travels with respect to all frame of referen... | 5,725 |
<p><a href="http://physics.stackexchange.com/q/98189/">Here</a> is a question about the canonical momentum that I had asked some days ago, but I still have one point that I am not understand.</p>
<p>Considering a particle moves in a magnetic field with charge $q$ and mass $m$, its hamiltonian is $$H=\frac{\vec{P}^2}{2... | 5,726 |
<p>I understand fresnel lenses are manufactured using CNC machines. I was wondering, if it would be possible to use sound to vibrate liquid silicon and then fast cool it into the standard form of a fresnel lens? This occurred to me when I noticed that ripples on a pond resemble the lenses in question, and that certain ... | 5,727 |
<p>Does string theory contradict the theory of <a href="http://en.wikipedia.org/wiki/Preon" rel="nofollow">preons</a>, especially the <a href="http://en.wikipedia.org/wiki/Rishon_model" rel="nofollow">Harari-Shupe</a> one?</p> | 5,728 |
<p>I am trying to understand how to combine uncertainties when they are dependent and independent from each other.</p>
<p>Using this formula :</p>
<p>$$\delta z = \sqrt {\Biggl(\dfrac{\partial f}{\partial x} \delta x\Biggr)^2+\Biggl(\dfrac{\partial f}{\partial y} \delta y\Biggr)^2+2\Biggl(\dfrac{\partial f}{\partial ... | 5,729 |
<p>I have googled for the "meaning of universe" where I found the following:
"all existing <strong>matter and space</strong> considered as a whole; the cosmos. The universe is believed to be at least 10 billion light years in diameter and contains a vast number of galaxies; it has been expanding since its creation in t... | 62 |
<p><a href="http://physics.stackexchange.com/a/88984/7665">In this answer to a question about viscosity of water in the presence of solutes</a>, the Falkenhagen relation is given:</p>
<blockquote>
<p>$$\frac{\eta_s}{\eta_0}=1+A\sqrt{c}$$ where $\eta_s$ is the solution
viscosity, $\eta_0$ the solvent viscosity, $A$... | 5,730 |
<p>According to my understanding of black hole thermodynamics, if I observe a black hole from a safe distance I should observe black body radiation emanating from it, with a temperature determined by its mass. The energy from this radiation comes from the black hole's mass itself.</p>
<p>But where (in space-time) doe... | 5,731 |
<p>How large in the night sky would Saturn look from Titan's surface? I believe they are tidally locked.</p> | 5,732 |
<p>Why 1 <a href="http://en.wikipedia.org/wiki/Astronomical_unit" rel="nofollow">AU</a> is defined as the distance between the Sun and the Earth? (approximately if you like to be precise) </p>
<blockquote>
<p>An astronomical unit (abbreviated as AU, au, a.u., or ua) is a unit of length equal to about 149,597,87... | 5,733 |
<p>With the recent lunar eclipse, for some reason this question came to me: The reason the Moon turns red is that the only appreciable sunlight hitting it when it's in Earth's umbra is refracted through Earth's atmosphere and shorter wavelengths are scattered out. I couldn't think of any reason why this shouldn't hap... | 5,734 |
<p>The effect of gravitational waves in transverse traceless gauge on matter is represented by the expansion and contraction of a ring of test particles in the direction of polarization of the wave. </p>
<p>This result is obtained by choosing a gauge which in GR is a choice of a coordinates.</p>
<p>Does that mean tha... | 5,735 |
<p>I'm programming a game where different types of objects will be sliding over different types of terrains (Top-down in two dimensions). At my current level of physics education we are given the coefficient of friction between any pairing of surfaces, but that's not practical for the amount of objects and terrains thi... | 5,736 |
<p>Can a photon/EM-field-excitation redshifted by spatial expansion be completely dissipated? Does the energy reach a minimum value (Planck's constant) and continue on as normal? Does expansion also cause energy to be lost from travelling massive particles, as they too have a "wavy" aspect? From an informational point ... | 5,737 |
<p>A conductor is placed in a magnetic field, current starts to flow, and the wire experiences the Lorentz force of $x$ Newtons. However, what confuses me is that $x$ is a <strong>value</strong> that is calculated from $F = IL \times B$. If $-EMF$ is induced due to the change in exterior magnetic field(due to the curre... | 5,738 |
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