question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>In the context of Renormalized Pertubation Theory Peskin Schröder says:<br />
The Lagrangian
$$
\mathcal{L}=\frac{1}{2} (\partial_\mu\phi_r)^2-\frac{1}{2}m^2\phi_r^2-\frac{\lambda}{4!}\phi_r^4 + \frac{1}{2} \delta_Z(\partial_\mu\phi_r)^2 -\frac{1}{2}\delta_m^2\phi_r^2-\frac{\delta_\lambda}{4!}\phi_r^4
$$
gives the f... | g10104 | [
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<p>Burning wood emits smoke and black. Provided more oxygen or whatever required, can wood be practically burnt fully like petroleum gasses that emits a blue flame and little smoke and little black.</p> | g10105 | [
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<p>Over the past hour or so I've been following one of my standard physics-based, wanders-through-the-internet. Specifically, I began by reviewing some details of dark energy theory but soon found myself pondering a totally unassociated topic..</p>
<p>One of today's tweets by #arxivblog concerns a speculative (IMO) pa... | g10106 | [
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<p>I learned programming as a child, for fun. Now I am working as a programmer, even though I got a business major degree.</p>
<p>I wonder if there are career paths for doing physics <em>other</em> than becoming a researcher in a University or a professor, that are not <em>all</em> about credentials?</p> | g10107 | [
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<p>Are photons <a href="http://en.wikipedia.org/wiki/Electromagnetic_radiation" rel="nofollow">electromagnetic waves</a>, quantum waves, or both?</p>
<p>If I subdivide an electromagnetic field into smaller <a href="http://en.wikipedia.org/wiki/Electromagnetic_field" rel="nofollow">electromagnetic fields</a>, should I ... | g304 | [
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<p>You buy one of those remote control toy helicopters. You bring it into an elevator. The elevator goes up. Does the helicopter hit the floor or does the floor of the elevator push the air up into the bottom of the helicopter so that it maintains altitude relative to the elevator? The same question can be reversed. If... | g743 | [
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<p>This question is an attempt to complement <a href="http://physics.stackexchange.com/questions/9421/strange-modulation-of-radiactive-decay-rates-with-solar-activity">this other question</a> about fluctuations in radiactive decay.</p>
<p>This question is completely experimental though: in general, suppose i have cert... | g10108 | [
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<p>Yesterday I was standing by the campfire. I used to think that campfire heat carried to me only by air. It was heating my face too much, so I blocked it with my hand just like blocking the sun. Then area on face which is shadowed by my hand stopped getting heat from campfire. Then I thought if it were getting transf... | g10109 | [
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<p>Howdy, I'm building a simulation for looking at the light field underwater. In order to verify my simulation, I'm looking for some data showing the far-field intensity that comes from single scattering from many small particles in suspension. I suspect Mie theory plays a part here, but I'm having a hard time finding... | g10110 | [
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<p>The chemical potential is defined as:
$$
\mu = -T\frac{\partial{S(N,V,E)}}{\partial{N}}
$$
It seems to me that this is completely independent of where I put the reference point of energy, because only the difference of entropy is relevant (and also temperature is defined as a difference in entropy). </p>
<p>However... | g10111 | [
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<p>Looking through this AP Physics question, I was struck by how the 'collision' between a photon and electron looks so much like a macroscopic collision. Is this even physically possible?</p>
<p>Look at the last page of this pdf: <a href="http://lodischool.tripod.com/dovesol/DOVE02SOL.pdf" rel="nofollow">http://lodis... | g10112 | [
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<p>Consider the dimensional regularized integral</p>
<p>$$ \int d^{d}k (k^{2}-m^{2}+i\epsilon)^{-\lambda} $$</p>
<p>For positive $ \lambda $ this integral has a pole at $ k=m $. Is this the reason we we insert the $ i \epsilon $ part?</p>
<p>Using Shotkhotsky's theorem
$$(k^{2}-m^{2}+i\epsilon)^{-\lambda}= -i\pi \d... | g10113 | [
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<p>As we know time began with the big bang. Before that there was no time, no laws, nothing. Mathematically how can an event take place when no time passes by? How did the big bang took place when there was no time?</p>
<p>Note my question is not about weather big bang took place or not, my question is about is this a... | g10114 | [
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<p>An acquaintance of mine, while being home alone, saw that the light bulb in the room which was hanging from the ceiling with wires having a pendulum motion which was more than noticeable. He says that that was a ghost but i know better than that. </p>
<p>I just can't find an explanation. Maybe you can help.</p>
<p... | g10115 | [
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<p>It's logical to think that the time it takes a microwave to heat the food would be proportional to the mass heated. But since a microwave is based on dielectric heating, I think that if you increase the mass of food there will be more water, which will heat the food faster (due to thermalization). Is this reasoning... | g10116 | [
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<p><a href="http://www.nasa.gov/centers/goddard/news/topstory/2007/antimatter_binary.html" rel="nofollow">Being said</a> that the antimatter - matter reaction is faster than that of a fission and fusion, what if the antimatter cloud found at the center of our galaxy could really able to react with matter from the stars... | g10117 | [
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<p>The Einstein-Cartan theory is a generalisation of General Relativity insofar as the condition that the metric affine connection is torsion-free is dropped. In other words, the space time is a Riemannian manifold together with the datum of a metric affine connection (which may differ from the Levi-Civita connection b... | g10118 | [
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<p>Batteries have a circuit which looks like this : </p>
<p><img src="http://i.stack.imgur.com/1DJrq.png" alt="enter image description here"></p>
<p>The electrons go around the circuit and then return through the battery where they get charged again and flow around. </p>
<p>My issue is, what about alternating curren... | g10119 | [
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<p>How would pressure of an ideal gas be distributed over the inside of a capsule (a cylinder with semi-spheres on the ends)? What about the strain on the material? Is there a general formula for how much?</p> | g10120 | [
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<p><img src="http://i.stack.imgur.com/qJfUU.png" alt="enter image description here">
"Fermi level" is the term used to describe the top of the collection of electron energy levels at absolute zero temperature. Why does the <a href="http://en.wikipedia.org/wiki/Topological_insulator" rel="nofollow">Fermi level for the b... | g10121 | [
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<p>What is the meaning of the electron probability cloud? </p>
<p>I understood it to mean that the electron has a probability to be found in a certain postion before measurement, but now after reading experiments involving Schrödinger's cat type states (with bonding and antibonding gaps in $\mathrm{H_2}$ and molecule ... | g10122 | [
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<p>This is a physics/calculus/computer science problem, but I think I'll get better results in the Physics SE.</p>
<p>I have a fun little project I've been working on (hobby, not homework/production), that models the flight of a projectile in various environments (2 Dimensional). Everything is nice and shiny with gra... | g10123 | [
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<p>I know a photon has zero rest mass, but it does have plenty of energy. Since energy and mass are equivalent does this mean that a photon (or more practically, a light beam) exerts a gravitational pull on other objects? If so, does it depend on the frequency of the photon?</p> | g143 | [
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<p>A example of amplitude in Relativistic Quantum Mechanics or specifically in QFT is the amplitude of a field configuration on a space-like hyper-surface of space-time to "lead" to another field configuration on another space-like hyper-surface of space-time. In the path-integral picture one simply integrates over all... | g10124 | [
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<p><em>I know that all planets and stars have a gravitational pull but does a simple much smaller object have a gravitational pull for example a pebble?</em></p> | g10125 | [
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<p>I was studying the <a href="http://www.scholarpedia.org/article/Center_manifold" rel="nofollow">centre manifold theory</a>. It says (see Kuznetsov page 155, theorem 5.2) that the system on the left side of the picture is topologically equivalent to the one on the right. </p>
<p>$
\begin{equation}
\label{}
... | g10126 | [
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<p>Is it possible that from the same initial mass different black hole radius will be created due to different mass distribution during black hole creation? If mass is concentrated more on the outside bigger event horizon will be created? If mass is concentrated more in the center smaller black hole will be created? </... | g10127 | [
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<p>Apparently there has been a paper in nature claiming the finding of a new particle?
<a href="http://www.sciencedaily.com/releases/2012/04/120413160004.htm" rel="nofollow">http://www.sciencedaily.com/releases/2012/04/120413160004.htm</a></p>
<p>Does that mean a new fundamental particle has been found with a special ... | g10128 | [
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<p>We are supposed to give a matrix representation of $L\cdot S$ for an electron with $l=1$ and $s=\frac{1}{2}$. </p>
<p>I read $L\cdot S$ as $L \otimes S$. Is this correct? Then we would have e.g. for </p>
<p>$L\otimes S (|1,1\rangle \otimes |1/2,1/2\rangle) = L |1,1\rangle \otimes S|1/2,1/2\rangle $
$= \sqrt{2} \hb... | g10129 | [
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<blockquote>
<p>Rubbing a glass rod with silk causes charges to be exchanged and consequently both objects get charged.</p>
</blockquote>
<p>Why do the objects have to be "rubbed"? I get that one has a stronger pull on the electrons than the other, but shouldn't just allowing the objects to make contact be enough.?
... | g10130 | [
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<p>Charge is carried by electrons moving. The protons are always stationary.</p>
<p>The answer I found online is the protons are stuck in the nucleus so they can't move ("strong nuclear force").</p>
<p>But why can't the whole positively charged atom move? </p> | g10131 | [
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-0.012744956649839878,
-0.05374189838767052,
0.0... |
<p>I haven't seen this explained clearly anywhere. Solid angles are described usually as a fraction of the surface area of a unit sphere, similar to how angles are the fraction of the circumference of a unit circle. However, I don't know how <a href="http://en.wikipedia.org/wiki/Solid_angle" rel="nofollow">solid angles... | g10132 | [
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<p>We are searching for a software program that simply helps us to visualize in 3D the interference of planar waves of <em>multiple</em> sources (frequencies) and as sepctrum on a wall. Something like a well known visualisation of the famous double split, but instead of the splits just havnig the possibility to have mu... | g10133 | [
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0.... |
<p>If we add 10 spherical bubbles then there will be some change in their area. Is there any way to find out change in temperature of the liquid from the change of its area?</p> | g10134 | [
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<p><strong>Partial measurement and partial trace</strong></p>
<p>There is a connection between a measurement of a part of a system and tracing this subsystem out. Say, we have a system composed of subsystems $A$ and $B$ in a pure state $|\psi\rangle = \sum_{i,j}a_{ij}|i\rangle_A|j\rangle_B$ and do a projective measure... | g10135 | [
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<p>At the end of this nice video, she says that <a href="http://en.wikipedia.org/wiki/Electromagnetic_radiation">electromagnetic wave</a> is a chain reaction of electric and magnetic fields creating each other so the chain of wave moves forward.</p>
<p>I wonder where the <a href="http://en.wikipedia.org/wiki/Photon">p... | g599 | [
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0.018528549000620842,
0.011892... |
<p>My question is about the field theoretic version of Noether's theorem. I am deeply troubled by one of the hypotheses of the theorem.</p>
<p>As it is the standard textbook for Lagrange mechanics, I'll follow Goldstein's account (starting p. 588 in the second edition of "Classical Mechanics").</p>
<p>I have no probl... | g10136 | [
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... |
<p>In the field of fluid mechanics, what is the momentum flux tensor? Is there an easy explanation for how it "works"?</p> | g10137 | [
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<p>So I understand the the Superposition Principle states that all the forced oscillations, as determined by multiple external forces, are to be added up in order to get the entire solution.</p>
<p>However, I'm at a loss as to go about proving this - do I start with the general solution of a simple driven oscillatory ... | g10138 | [
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0.0... |
<p>I'm doing a research for my stats class in high school and I chose quantum mechanics as my subject. I narrowed down to electron localization in an atom and radial probability distribution. However, I can't find any data to support my claims that probability and statistics are very important in quantum mechanics. Is... | g10139 | [
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0.008113324642181396,
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<p>Assume a static metric with (known) components $g_{\mu\nu}$. I'd like to know what is the gravitational pull $g$ of a test particle placed on an arbitrary point $X$.</p>
<p>The gravitational pull being defined as the acceleration the particle suffers as measured by an observer sitting in a reference frame fixed at ... | g587 | [
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<p>We're all familiar with basic tenets such as "information cannot be transmitted faster than light" and ideas such as information conservation in scenarios like Hawking radiation (and in general, obviously). The Holographic Principle says, loosely, that information about a volume of space is encoded on its two-dimens... | g10140 | [
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<p>I'm wondering what some standard, modern references might be for continuum mechanics. I imagine most references are probably more used by mechanical engineers than physicists but it's still a classical mechanics question. </p>
<p>This came up in a conversation with my father (who is a mechanical engineer). I was ... | g907 | [
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0.013654814101755619,
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0.005143820773810148,
-0.... |
<p>Ignoring the quantum zeno effect (if possible?), can we observe in real-time the transformation of one element to another? I'm talking about an amount visible to the naked eye where one could see obvious changes in colour, reflectivity, phase, surface finish etc. occurring in say, seconds or minutes.</p> | g736 | [
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<p><em>I haven't studied much about this, so if I am mistaken about something please correct me.</em></p>
<p>From what I have seen around the Internet, a force applied to a object takes time to propagate through the object because it has to interact with the molecules around the ones that the force was applied to. Tha... | g10141 | [
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<p>I have a s****d question, how to calculate the central charge of $bc$ conformal-field theory in Polchinski's string theory, Eq. (2.5.12)?
For a $bc$ CFT given by</p>
<p>$$S=\frac{1}{2\pi } \int d^2 z \,\,b \bar{\partial} c $$</p>
<p>where $b$ and $c$ are anticommuting fields,
define normal ordering as
$$:b(z_1) c... | g10142 | [
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0.04020209237933159,
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<p>In a picture or video of a numerical relativity simulation, such as a neutron star merger into a black hole, how do they set up their coordinate system? Lets take the point in a video corresponding to x=10km, y=20km, z=30km, t=1ms. Spacetime itself is distorted, in a very complex way, so how do you make sense of the... | g10143 | [
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<ul>
<li><p>Did <a href="http://en.wikipedia.org/wiki/Charles-Augustin_de_Coulomb" rel="nofollow">Charles-Augustin de Coulomb</a> know:</p>
<ul>
<li><a href="http://en.wikipedia.org/wiki/Coulomb%27s_constant" rel="nofollow">Coulomb's constant</a></li>
<li>Coulomb (as a unit)</li>
</ul></li>
</ul>
<p>if not then what ... | g10144 | [
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<p>It seems to me that there is no such thing as time. There is only movement in the universe and we compare our own movement to a different object to have a sense of time. It can be a clock or a atomic vibration.</p>
<p>Does this view of time work within the current framework of phsics?</p>
<p>Do physicists have an... | g813 | [
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<p>For some time now I've been confused about heat capacity. The way I understand it, if I put in an amount of heat energy into the system, $dQ$, its temperature will change by $CdT$. But now, everywhere I look I only find $C_p$ and $C_V$, the heat capacities in isobaric/isochoric processes. But for an arbitrary proce... | g10145 | [
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<p>Suppose we are given a stick and a stone tied to the stick by a string. Now if we rotate the stone around the stick the stone rises in height (see picture below). My question is which force accounts for this rise in height? </p>
<p><img src="http://i.stack.imgur.com/0oySD.jpg" alt="enter image description here"></p... | g10146 | [
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<p>I'm having a bit of trouble understanding Balmer lines, is this correct, and the questions are in brackets:</p>
<p>1) A star needs to be hot enough such that electrons are in the n=2 state <em>(why does the temperature cause the electrons to be in n=2 state?)</em></p>
<p>2)As light of a specific frequency passes t... | g10147 | [
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<p>I've gotten interested in physics recently due to the many educational channels on YouTube such as sixtysymbols and minutephysics. They talk about quarks sometimes, and I was wondering if there is anything smaller than a quark. I'm not at that stage in school yet, the smallest we have discussed in class have been ne... | g324 | [
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<p>For a homogeneous material of length $L$, we can write the heat equation as $$\rho c\frac{dT}{dt}=k\frac{du^2}{dx^2}, \text{ } x\in (O,L)$$ where $T$ is the temperature, $\rho$ is the thermal conductivity, $c$ is specific heat, and $k$ is the thermal conductivity. </p>
<p>To non-dimensionalize it, I know that I ca... | g10148 | [
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<p>Can you explain me some of the mathematical details of such concept as symmetries?
In physics, we have some manifold, and fields are functions on this manifold.</p>
<p><em>On the one hand</em>, we have <strong>symmetries of fields</strong>: for example, in the simplest case of spontaneous symmetry breaking group $\... | g10149 | [
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<p>I'm trying to get to grips with the Schrödinger equation by looking at a free particle. I'm certain at some point I massively misunderstood something.</p>
<p>According to a textbook and a lecture the free particle moving in positive x direction can be described by</p>
<p>$$
\Psi(x,t) = A e^{i(kx - \omega t)} = \... | g10150 | [
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<p>Ok so while there have been many discussions regarding the solution(say using the Fourier transform or the lattice Green's function approach) to the two-point resistance of an infinite-square resistive lattice my doubt is actually related to one thing common to almost all the approaches to the problem i.e how does h... | g10151 | [
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<p>Looking back at my quantum mechanics notes, the angular momentum addition theorem is listed as:</p>
<p>$j=j_1+j_2,j_1+j_2-1, ..., |j_1-j_2| $ (Using conventional notation)</p>
<p>, but I'm a little unsure how to interpret the introduction of the modulus operation ($|...|$) and couldn't easily find any examples. </... | g10152 | [
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<p>Is there any way of achieving effective thrust in space without using conventional fluid or gas propellants such as rocket-fuels or supercooled material? </p>
<p>For instance: gaining thrust through solar energy conversion or pressure pulses? (If that is even possible.)</p> | g10153 | [
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<p>It is common when evaluating the partition function for a $O(N)$ non-linear sigma model to enforce the confinement to the $N$-sphere with a delta functional, so that
$$
Z ~=~ \int d[\pi] d[\sigma] ~ \delta \left[ \pi^2 + \sigma^2 -1 \right]
\exp (i S(\phi)),
$$
where $\pi$ is an $N-1$ component field. Then, one e... | g10154 | [
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<p>In special relativity, I know you can prove that the derivative with respect to a contravariant 4-vector component transforms like a covariant vector operator by using the chain rule, but I can't work out how to prove the inverse, that the derivative with respect to a covariant 4-vector component transforms like a c... | g10155 | [
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... |
<p>Water boils at positive temperatures when put into a vacuum. Is this the case with all liquids, e.g. mercury?</p> | g10156 | [
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0.02994869090616703,
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<p>The Conformal group contains the Poincare group. Typically, if you take a representation of a group and then look at it as a representation of a subgroup, the representation will be reducible. I often hear that CFT's cannot have particles, and I have some understanding of this since $P_\mu P^\mu $ is not a Casimir o... | g10157 | [
0.032896097749471664,
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0.04136095196008682,
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0.03098636120557785,
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0.0... |
<p>I've gone through an intermediate classical mechanics course, and in solving the two-body problem, we reduce it to a one-body between a larger stationary mass, and a smaller reduced mass.</p>
<p>Most solutions I've seen of the hydrogen atom simply neglect the movement of the nucleus. Some solutions replace the elec... | g10158 | [
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... |
<p>I've been asked to study on any phenomena related to Weather and Climate. While thinking about this, I noticed that each day, there was a small difference on sunrise and sunset. Like, at one day it was 5:58 AM and at the second day, it was 5:40 AM etc. Does this have anything to do with weather or harmful/useful eff... | g10159 | [
0.0017795590683817863,
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<p>If I switch on a generator connected to an open circuit, are the charges oscillating along wires? Where has the energy gone in the open circuit?</p> | g10160 | [
0.028318822383880615,
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<p>Motivated by a previous <a href="http://physics.stackexchange.com/q/79296/6316">question</a>, consider bosonic creation/anihilation operators $a, a^+$ such that $[a, a^+]=1$, and $N = a^+a$.</p>
<p>Is there an analytic expression for the following commutators: </p>
<p>$[e^{za}, e^{wN}]$ and $[e^{za^+}, e^{wN}]$</... | g10161 | [
-0.024528203532099724,
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0.038890209048986435,
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0.006299400236457586,
0.05825325474143028,
0.... |
<p>We use <strong>stimulated emission</strong> and not <strong>spontaneous emission</strong> to produce lasers. Why is this? Can't we produce lasers by the spontaneous emission method?</p> | g10162 | [
0.001584799261763692,
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<p><em>Is it necessary for work to be done on a body that the agent of the force remains in contact with the body?</em> For example, if I hit a football with my foot with a small amount of force and it moves a certain distance on the ground, then what could we say about the 'work' in this case if there would be no fric... | g10163 | [
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<p>Why and when do we need to place oil over the sample to achieve higher optical resolution ? Is this idea is valid for the enhancement of all optical microscopy techniques and magnification scales ? </p> | g10164 | [
0.005533952731639147,
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<p>Before anything, I'm sorry for being an outsider coming to opine about your field. This is almost always a stupid decision, but I do have a good justification for this case. I've been reading about <a href="https://en.wikipedia.org/wiki/Superdeterminism">superdeterminism</a> and it bothered me that most of you <a hr... | g10165 | [
0.0489826574921608,
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0.0485... |
<p>I have recently found my copy of Hawkings' <em>A Brief History of Time</em> which I have never finished. This time I'm determined to read it all the way through. However, the book is now almost 25 years old. Is the book still relevant, or has any recent discoveries invalidated parts of it?</p> | g10166 | [
0.034361276775598526,
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0.05008236691355705,
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<p>I am learning how to physically render images in computer graphics. I just saw that the area that gets light is given by the <a href="http://en.wikipedia.org/wiki/Lambert%27s_cosine_law" rel="nofollow">Lambert's cosine law</a>.
In my head it makes perfect sense the relation but once I see the drawing I just cannot s... | g10167 | [
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0.... |
<p>We have a uranium-236 nucleus that fissions into two equal fragments, and I'm supposed to find the electrical potential energy just as the two fragments split apart. No other information is provided. </p>
<p>I am very confused about this problem for two reasons. First, U-236 is electrically neutral, with exactly 92... | g10168 | [
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... |
<p>Lets have the scalar Klein-Gordon field interacting with EM field:</p>
<p>$$
L = \partial_{\mu}\varphi \partial^{\mu}\varphi - m^2\varphi \varphi^{*} - j_{\mu}A^{\mu} + q^{2} A_{\mu}A^{\mu}\varphi \varphi^{*} - \frac{1}{4}F_{\mu \nu}F^{\mu \nu}. \qquad (1)
$$
I heard that the normalization of Klein-Gordon field in ... | g10169 | [
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<p>What will be the velocity of a comet is falling to the Earth from infinity at the time of impact if Earth had no atmosphere? the comet is falling radially towards the earth.</p>
<p>Will this velocity be different for comets with different masses or same?</p> | g10170 | [
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... |
<p>My question is based on the paper <a href="http://arxiv.org/abs/hep-th/0702146" rel="nofollow">Split states, entropy enigma, holes, halos</a>. </p>
<p>What are the scaling solutions discussed on page 49 of the paper ?</p>
<p>It is stated that the equations ${\sum_{j, i\neq j}\frac{I_{ij}}{r_{ij}} = \theta_{i}}$ al... | g10171 | [
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0.008109823800623417,
-0... |
<p>$$m_i\mathbf{r}_i\times\frac{\mathrm{d}^2\mathbf{r}_i}{\mathrm{d}t^2} = \frac{\mathrm{d}}{\mathrm{d}t}\biggl(m_i\mathbf{r}_i\times\frac{\mathrm{d}\mathbf{r}_i}{\mathrm{d}t}\biggr)$$</p>
<p>I do not understand this. How did the $\mathrm{d}/\mathrm{d}t$ go out?</p> | g10172 | [
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0.04856806620955467,
0.00020... |
<p>Lets say we have a tank with a fixed mass of liquid at atmospheric pressure and room temperature. How do we influence the temperature when we exert pressure (e. g., with a piston) on the liquid? Are pressure-enthalpy diagrams the key for that question?</p>
<p>If it is incompressible, temperature would not change, s... | g10173 | [
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0.01... |
<p>Consider the imaginary time Greens function of a fermion field $\Psi(x,τ)$ at zero temperature</p>
<p>$$ G^τ = -\langle \theta(τ)\Psi(x,τ)\Psi^\dagger(0,0) - \theta(-τ)\Psi^\dagger(0,0)\Psi(x,τ) \rangle $$</p>
<p>It is well known that we can obtain the retarded Greens function by performing Fourier transformation ... | g10174 | [
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0.0009386982419528067,
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0.019962815567851067,
0... |
<p>For a probability distribution $P$, Renyi fractal dimension is defined as</p>
<p>$$D_q = \lim_{\epsilon\rightarrow 0} \frac{R_q(P_\epsilon)}{\log(1/\epsilon)},$$
where $R_q$ is Renyi entropy of order $q$ and $P_\epsilon$ is the coarse-grained probability distribution (i.e. put in boxes of linear size $\epsilon$).</... | g10175 | [
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0.023... |
<p>Essentially I am wanting to evaluate $$\langle j\, m \mid a^\dagger(\mathbf{k}, \lambda) \mid 0 \rangle \,,$$ where $\lambda$ indicates the circular polarization (about $\mathbf{k}$). We have that $\mathbf{J}= \mathbf{L} + \mathbf{S}$. It's straightforward to show that circular polarization corresponds to definite s... | g10176 | [
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<p>I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently.</p>
<p>Attracting something involves energy. If a permanent magnet can do this forever, from where does this energy come from? How can it not run out of energy? Doesn't it contradict with the laws of energy?<... | g325 | [
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<p>I want to calculate the total electrostatic energy of the Cavendish Experiment (two concentric spheres of radii $R_{1,2}$ which are connected, outer one gets charged, then removed, then after removing the outer sphere and measuring the charge of the inner one, it's zero).</p>
<p>The formula for this is: </p>
<p>$E... | g10177 | [
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0.03653331473469734,
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0.029186194762587547,
0.018375080078840256,
-0.03... |
<p>A book which I referenced for Electrical Machinery states that the voltage induced in a conductor inside a magnetic field is given by</p>
<p>$$ \mathcal{E}=(\mathbf{v} \times \mathbf{B})\cdot \mathbf{l}$$</p>
<p>Since all three are vectors, and the cross multiplication inside the brackets results in another vector... | g10178 | [
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0.03592748939990997,
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... |
<p>Sean Carroll has a new popularization about the Higgs, The Particle at the End of the Universe. Carroll is a relativist, and I enjoyed seeing how he presented the four forces of nature synoptically, without a lot of math. One thing I'm having trouble puzzling out, however, is his treatment of gravity as just another... | g10179 | [
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<p>I am a physicist. I always heard physicists used the terminology "<a href="http://www.encyclopediaofmath.org/index.php/Symmetric_operator" rel="nofollow">symmetric</a>", "Hermitian", "<a href="http://en.wikipedia.org/wiki/Self-adjoint_operator" rel="nofollow">self-adjoint</a>", and "essentially self-adjoint" operato... | g10180 | [
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0.04006550461053848,
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0.020... |
<p>I'm trying to wrap my head around how geodesics describe trajectories at the moment.</p>
<p>I get that for events to be causally connected, they must be connected by a timelike curve, so free objects must move along a timelike geodesic. And a timelike geodesic can be defined as a geodesic that lies within the light... | g10181 | [
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0.04397840052843094,
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0.12172487378120422,
0.026213... |
<p>I always heard the eigenfunctions of a <a href="http://en.wikipedia.org/wiki/Self-adjoint_operator">self-adjoint operator</a> form a complete basis. Where can I find a proof in infinite dimension space? Presumably readable for physicists.</p> | g10182 | [
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0.07... |
<p>Can anyone tell me how to solve this problem: </p>
<blockquote>
<p>Alpha Centauri is $4.4$ light years away from Earth. What speed $u$
would a spaceship headed towards Alpha centauri had to have in order
to last $t' = 10 \text{ years}$ for a passanger onboard?</p>
</blockquote>
<p>The only thing i know how t... | g10183 | [
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0.011640120297670364,
0.01942473277449608,
0.05029692500829697,
0.007309973239898682,
0.040... |
<p>Is <a href="http://en.wikipedia.org/wiki/Potential_energy" rel="nofollow">potential energy</a> and "<a href="http://en.wikipedia.org/wiki/Work_%28physics%29" rel="nofollow">work</a> done" the same thing?</p>
<p>If they are not one and the same thing then why is potential energy always associated with "work done"?</... | g10184 | [
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0.01348800491541624,
0.00... |
<p>Suppose I want to write down an interaction term for an action for spin 1/2 fermions that is $SU(2)$-symmetric. </p>
<p>I start from the most naive general form of such an action:
$$S_{int} ~=~ \int_{4321} \sum_{\alpha \beta \gamma \delta} \bar \psi(4)_\alpha \bar \psi(3)_\beta \psi(2)_\gamma \psi(1)_\delta V(4,3,2... | g10185 | [
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0.0066673243418335915,
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0.029328035190701485,
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... |
<p>Is there a fundamental difference in the definition of entropy when considering the classical thermodynamic picture vs. the quantum mechanical picture, or are they both fundamentally equivalent?</p> | g10186 | [
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0.02043718285858631,
0.03618174046278,
0.006585093680769205,
-0.014089136384427547,
-0.02... |
<p>I am trying to find the following dipole moment matrix element $(|n,\ell,m\rangle)$.</p>
<p>$$e\langle1,0,0|\vec r|2,0,0\rangle$$
I believe that I can say this matrix element is zero because of parity. The wavefunctions have parity $(-1)^\ell$ and seeing as each has $\ell =0$, they are even parity. Then r is odd,... | g10187 | [
-0.02736433409154415,
-0.0030834334902465343,
0.002346606459468603,
-0.04140687361359596,
0.10264666378498077,
-0.03785138577222824,
0.013326713815331459,
0.023135129362344742,
-0.00106517830863595,
-0.004710318520665169,
-0.039343200623989105,
-0.0006213287124410272,
-0.03048139251768589,
... |
<p>Do all forms of energy have a mass? We know by $E=mc^2$ that mass and energy are directly proportional, but there are massless forms of energy such as electro-magnetic waves. I am also told that there are different forms of mass, such as invariant mass, virtual mass, and relativistic mass. This electro-magnetic wave... | g10188 | [
0.04782091826200485,
-0.017254527658224106,
0.014461001381278038,
-0.008381946943700314,
0.04553713649511337,
0.04015561565756798,
0.0016670838231220841,
0.06997503340244293,
-0.044237468391656876,
-0.04845709353685379,
-0.021198954433202744,
-0.03079637512564659,
0.03746659681200981,
0.00... |
<p>Consider a point-mass $m$ having constant velocity but undergoing influence from two forces, $F_1$, $F_2$, having equal magnitude but opposite directions. Because the forces' magnitudes are equal, I would expect no net acceleration of $m$, but if $m$ is moving, the forces are doing work on $m$ ($F_1$'s work being th... | g10189 | [
0.06545572727918625,
0.024662727490067482,
0.007389967795461416,
0.0015332496259361506,
0.054245349019765854,
0.04244221746921539,
0.03930329903960228,
-0.0023421673104166985,
-0.11323045939207077,
-0.03280101343989372,
0.005352917592972517,
-0.017700212076306343,
0.0005778286722488701,
0.... |
<p>I know that matter can be converted to energy through E=mc^2.</p>
<p>I also know that engery can be and has been converted to information through Landauer's principle (with Maxwell's demons).</p>
<p>Does this mean that I can take a brick and covert it into information? (It is irrelivent if there is no known proces... | g10190 | [
0.03872576728463173,
0.027894534170627594,
-0.0006117980810813606,
-0.014500818215310574,
0.05493045225739479,
-0.0351254977285862,
-0.0068613579496741295,
0.04635664448142052,
-0.031377654522657394,
0.011005832813680172,
-0.02536552958190441,
0.0011096431408077478,
-0.011908633634448051,
... |
<p>A Cessna 150 aircraft has a lift-off speed of approximately 125 $kmh^{-1}$.
What minimum constant acceleration does this require if the aircraft is to be airborne after a take-off run of 129 m?</p>
<p>So I wanted to use the formula that $x=\cfrac{(v_{final}^2 - v_{initial}^2)}{2a}$</p>
<p>To solve for the constant... | g10191 | [
0.0375029481947422,
0.025606809183955193,
0.00791784655302763,
0.01753641478717327,
-0.02728634513914585,
-0.008861535228788853,
-0.0020953721832484007,
0.05619310960173607,
-0.06081213429570198,
-0.004627054091542959,
-0.005068502388894558,
-0.001989198150113225,
-0.056385587900877,
0.052... |
<p>I have done a physics experiment (setup below). And was asked to determine the experimental and theoretical acceleration. </p>
<p><img src="http://i.stack.imgur.com/xW1il.png" alt="enter image description here"></p>
<p>The data I've got </p>
<p><img src="http://i.stack.imgur.com/oqn75.png" alt="enter image descri... | g10192 | [
0.08183413743972778,
0.01914677768945694,
0.0018938962602987885,
0.03723422437906265,
0.0795150175690651,
-0.05339996516704559,
0.025744689628481865,
0.010880043730139732,
-0.053254906088113785,
-0.0034968219697475433,
0.019537728279829025,
0.01426661480218172,
-0.01746031828224659,
0.0250... |
<p>I had asked a similar question about a calculation involving the winding number <a href="http://physics.stackexchange.com/questions/30997/winding-number-in-the-topology-of-magnetic-monopoles">here</a>. But i haven't got a satisfactory response. So, I am rephrasing this question in a slightly different manner. What i... | g10193 | [
-0.004242460243403912,
0.01705031469464302,
-0.004390735179185867,
-0.004944111220538616,
0.08289278298616409,
0.016791123896837234,
0.052448272705078125,
0.06979281455278397,
0.01186384167522192,
0.030120695009827614,
-0.052408620715141296,
0.02935013733804226,
0.059338025748729706,
0.014... |
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