question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Are there any results in classical mechanics that are easier to show by deriving a corresponding result in quantum mechanics and then taking the limit as $\hbar\rightarrow0$?</p>
<p>(Are there classical results that were first discovered through taking the classical limit of quantum mechanics even if they are now e... | g16943 | [
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<p>I recently read that the Great Red Spot arises from the shear instability of zonal flow from zonal jets travelling in opposite directions. </p>
<p>Is there any reason why such zonal jets travel in opposite directions anyway? I thought it would be more intuitive if such zonal jets, over their billions of years of ex... | g16944 | [
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<p>I have a sum of the form</p>
<p>$$\sum_{n,m=-N}^N e^{-\alpha (n-m)^2}$$</p>
<p>where $α>0$ is some constant, and I don't mind if the limit $N\rightarrow\infty$ is taken. I know there is a possibility of exchanging the "variable of summation" by introducing some "relative coordinates" $\tau=n−m$ and $\eta=m+n$, ... | g16945 | [
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<p>In QFT Vol2 written by Weinberg(Chap 16-17), or very much similarly in <a href="http://www.solvayinstitutes.be/events/doctoral/Bilal.pdf">Adel Bilal's notes</a>(Chap 7), a powerful way of proving renormalizability is presented: Analyze the symmetries of the quantum effective action (QEA), and since QEA generates all... | g16946 | [
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<p>if there are two identically equal resistance paths, and you have a large group of electrons, will half of the electrons travel lets say left and half right?
because I've been thinking that maybe the electrons travel down lets say the left one till there is a large enough amount of electrons that causes the resista... | g510 | [
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<p>Suppose that the hypersurface orthogonal co-vector $W$ us perpendicular to the family of hypersurface defined by a function $\varphi$ with $\varphi=constant$. If we choose a coordinate in which $x^0=\varphi$, how to prove that the metric components $g_{0i}=0$ for $i=1,2,3$?</p>
<p>My try is as follows. Because $W$ ... | g16947 | [
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<p>I was watching a documentary where the residents didn't want to have a wind turbine erected nearby. One of the comments from the company was that an ice throw would have very little importance since it would not travel far from the tower.</p>
<pre><code>Description of turbine:
400 foot tower
150 ft length of blade
... | g16948 | [
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<p>If i have a cube (either hollow, or an insulating solid) and i want its surface have a potential such that it looks like a point particle outside of the box does that mean the exact potential on the cube itself is the same as the potential of a point particle?</p> | g16949 | [
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<p>I need to calculate the following integral (which is divergent):</p>
<p>\begin{equation}
I(m,C)=\int_{-\infty}^\infty {\rm d}\omega\int_{\rm space}{\rm d^3 k}\ln\left(\omega-\frac{k^2}{2m}+C+i\epsilon\right)
\end{equation}
where $m$ and $C$ are constants, and $\epsilon$ is an infinitesimal positive number. </p>
<p... | g16950 | [
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<p>If a new Earth came and orbit our Earth within 300,000 km to Earth?
I just did not know.
thanks.</p> | g511 | [
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<p>If you see a bolide, is there any way to judge whether it's worthwhile to try to find an impact? (I mean, short of a big "bang" and a debris cloud rising from the remains of your car...) </p>
<p>I imagine it's a once-in-a-lifetime thing at best, but it seems like the meteor hounds have a few leads per year.</p> | g16951 | [
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<p>In this example of a Neutrino jet, it seems that the <strong>supermassive black hole</strong> moves around the space and meets up with a interstellar object sometimes.</p>
<p><img src="http://i.stack.imgur.com/AinGR.jpg" alt="enter image description here"></p>
<p><a href="http://www.nasa.gov/mission_pages/swift/bu... | g16952 | [
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<p>If we observe two galaxies from the Earth that are diametrically opposed and each 10,000 light-years from the Earth, will the separation distance between the galaxies be 20,000 light-years? </p>
<p>Really, the question is: if the galaxies instead were separated from Earth by 10 billion light-years, w... | g16953 | [
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<p>I am doing research with my teacher on photometry of the <a href="http://en.wikipedia.org/wiki/Open_cluster" rel="nofollow">open star cluster</a> <a href="http://www.astro.ex.ac.uk/people/timn/Catalogues/Clusters/cepheus-ob3.html" rel="nofollow">Cepheus OB3</a>, and we are trying to find research papers so we can ta... | g16954 | [
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<p>If the big bang was the birth of everything, and the big bang was an event in the sense that it had a location and a time (time 0), wouldn't that mean that our universe has a center?</p>
<p><em>Where</em> was the big bang? <em>What</em> is there now? Are we moving away from the center still? Are these even valid qu... | g10 | [
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<p>In a lot of the descriptions of the moon <a href="http://en.wikipedia.org/wiki/Io_%28moon%29" rel="nofollow">Io</a> it frequently states that the moon, because of volcanic activity, has been literally "Turned inside out". What exactly is meant by "Turned inside out" and why does this not destroy the moon, or have an... | g16955 | [
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<p>Has <a href="http://physics.stackexchange.com/questions/22876/does-a-photon-exert-a-gravitational-pull">radiation or energy bending spacetime</a> ever been observed?</p>
<p>If not, is it likely that it ever will, assuming current technology?</p>
<hr>
<p><strong>Note:</strong> This is not a question of <em>space</... | g512 | [
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<p>Are telescopes with a concave lens (instead of convex ones) ever useful for astronomy?</p>
<p>And if so, where are they used? Do they ever affect resolving power?</p> | g16956 | [
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<p>Whether you can get the first couple of Maxwell equations from a variational principle? In the second volume of the Landau theoretical physics said that it is impossible.</p> | g16957 | [
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<p>Will changing the amplitude change the frequency of a wave, or is it possible for a specific frequency (50 Hz. for example) to generate from shifting amplitude patterns?</p> | g16958 | [
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<p>I am confusing between non linear dynamics and chaos. Chaos is also a non-linear dynamics right? then what is the difference between <a href="http://en.wikipedia.org/wiki/Chaos_theory" rel="nofollow">chaos</a> and <a href="http://en.wikipedia.org/wiki/Nonlinear_system" rel="nofollow">non-linear dynamics</a>?</p>
<p... | g16959 | [
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<p>Could anyone clarify to me the following:</p>
<ol>
<li>Lightning gives off high current when it hits a car/vehicle, and since the electrical components of the car is grounded on the chassis, are there possibilities that these high currents can destroy or damage the electrical components,battery, antenna etc through... | g16960 | [
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<p>Are there variations of double slit experiment with their results to look up? for example besided the two parallel slits, having two holes or two slits at 90 degree angles?</p> | g16961 | [
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<p>A useful way of thinking (not only) oceanic waves is to consider them as a superimposition of linear modes: the elevation η of the sea surface is given by:</p>
<p>1: $\eta({\bf x}, t) = \int_{-\infty}^{\infty} \hat{\eta}({\bf k}) e^{i({\bf k \cdot x} - \omega t)} d{\bf k}$</p>
<p>where $\omega$ and ${\bf k}$ are r... | g16962 | [
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<p>I am currently trying to carry out the construction of the generalised Hamiltonian, constraints and constraint algebra, etc for a particular field theory following the procedure in Dirac's "Lectures on quantum mechanics". My question is the following: </p>
<p>I have momentum variables that depend on the spatial der... | g16963 | [
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<p>Surely group theory is a very handy tool in the problems dealing with symmetry. But is there any application for ring theory in physics? If not, what's this that makes rings not applicable in physics problems?</p> | g16964 | [
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<p>I recall from my undergraduate statistical mechanics and QM classes that Planck's Law may be derived fairly straight-forwardly by considering the density of states of EM radiation in thermal equilibrium with a particle inside a cubic box. Indeed the derivation on <a href="http://en.wikipedia.org/wiki/Planck%27s_law#... | g16965 | [
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<p>Quantum electrodynamics based upon Euler-Heisenberg or Born-Infeld Lagrangians predict photons
to move according to an effective metric which is dependent on the background electromagnetic
field. In other words, photon trajectories are curved in presence of electromagnetic fields,
meaning that an effective gravity i... | g16966 | [
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<p>How is the following classical optics phenomenon explained in quantum electrodynamics?</p>
<ul>
<li>Reflection and Refraction</li>
</ul>
<p>Are they simply due to photons being absorbed and re-emitted? How do we get to Snell's law, for example, in that case?</p>
<p>Split by request: See the other part of this que... | g905 | [
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<p>The following comes from my text and concerns vapor pressure: Consider a liquid in a closed, cylindrical container that is half full. The molecules at the surface of the container and along the edges have the fewest neighbors; therefore, they will evaporate more quickly than other molecules. This intuitively makes s... | g16967 | [
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<p>Why does an armature of a generator rotate?</p>
<p>a) like poles repel </p>
<p>b) unlike poles attract </p>
<p>c) current flows up </p>
<p>d) an outside force turns it </p>
<p>I am thinking that (d) is the correct answer but still not sure of it</p> | g16968 | [
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<p>There are more than one way to view the description of the universe as flat. There is the description of an open, flat or closed universe in terms of it's fate, expansion forever away from gravity, or a big crunch.</p>
<p>Then there is the description of our observable universe being flat in it's geometry, or is it... | g653 | [
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-0.09355231374502182,
0.07339981943368912,
-0.04666784405708313,
0.05924312770366669,
0.070... |
<p>Why does the <a href="http://en.wikipedia.org/wiki/Capacitance" rel="nofollow">capacitance</a> of a capacitor increase if the distance between the two plates of a parallel plate capacitor is decreased? I think, with decreasing distance between the two plates, the force of attraction between the charges on the two pl... | g16969 | [
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0.054129090160131454,
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0.023... |
<p>How would I go about finding the distribution of initial separations (i.e. the lengths between the centres of mass) of stars that make up binary systems. I am interested in neutron stars and stellar black holes.</p>
<p><a href="http://iopscience.iop.org/0004-637X/652/1/540/fulltext/63576.text.html" rel="nofollow">T... | g16970 | [
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0.011883541010320187,
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<p>I was given the following problem:</p>
<blockquote>
<p>Two objects have a temperature difference of 20 degrees C at time 0. Two minutes later, they have a temperature difference of 18 degrees. How long does it take for them to have a difference of 10 degrees.</p>
</blockquote>
<p>Initially, I tried to approach t... | g16971 | [
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<p>In the context of Helium can anyone explain what a superleak is and why it could be useful?</p> | g16972 | [
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<p>For a real vector $\mathbf{r}$, the direction is given by: $\hat{\mathbf{n}}=\mathbf{r}/\left|\mathbf{r}\right|$.</p>
<p>The <a href="http://en.wikipedia.org/wiki/Transition_dipole_moment" rel="nofollow">transition dipole moment</a> is a complex vector. How do you define its direction?</p>
<p>The point of this que... | g16973 | [
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<p>When to parallel wires carrying currents in same direction I1 & I2. </p>
<p><a href="http://www.youtube.com/watch?v=43AeuDvWc0k" rel="nofollow">http://www.youtube.com/watch?v=43AeuDvWc0k</a> this video demonstrates that effect.</p>
<p>My question is, why <strong>exactly</strong> does this happen? </p>
<p>I kn... | g16974 | [
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<p>I was assuming the earth's magnetism is similar to a permanent magnet; But below a depth of somewhere near the Mohorovičić discontinuity (Moho) between earth's crust and mantle it should be above curie temperature. That depth is pretty shallow compared to earth's radius, something like 40km deep.<br>
Is earth roughl... | g16975 | [
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<p><strong>A force of 14.0N is applied to a block as shown in the diagram below</strong></p>
<p><img src="http://img14.imageshack.us/img14/9337/diagramzw.jpg" alt="">!</p>
<p>If the coefficient of friction is between the surface and the blocks is 0.35</p>
<p>a) What is the acceleration of the two blocks?</p>
<p>b) ... | g16976 | [
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<p>I want to know the horsepower produced by an engine at certain RPM by knowing another certain RPM point?</p>
<p>Let's suppose that an engine produces 200 hp at 4000 RPM, how many horsepower is produced by that engine at 5000 RPM?</p>
<p>What is the process?, Do I miss another factors?</p> | g16977 | [
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<p>My understanding of dark energy is that it's like hot air bouncing around in a balloon, except the air is tiny subatomic particles that can't be seen or even detected in any way except for their apparent effect on the universe's expansion, and the balloon is gravity.</p>
<p>I question whether they can really tell i... | g16978 | [
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<p>According to <a href="http://www.princeton.edu/~willman/planetary_systems">this site</a> there are 258 know planetary systems and 302 planets. Mostly each of the listed system has only 1 planet of Mercury's or Mars' size, while our system has up to 8 planets. From what I know our sun is not a "big" star, so theoreti... | g16979 | [
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<p>Towards the end of the paragraph with the title <strong>String theory's added value 2: enhanced non-Abelian symmetries at self-dual radii and abstract C with current algebras</strong> of <a href="http://motls.blogspot.com/2012/08/why-stringy-enhanced-symmetries-are.html#disqus_thread" rel="nofollow">this</a> article... | g16980 | [
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<p>Forgive me if this a simple question with an obvious answer I can't see. I was thinking about pressure and air pressure and how we have thousands of pounds of air pressing down on us. What I'm wondering is why I can move through it so easily. Because of all this air, shouldn't the pressure and the compression of all... | g16981 | [
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<p>I am currently preparing for a physics exam and I have troubles understanding how to solve the following exercise:</p>
<blockquote>
<p>A current that has the constant current density $\vec{j}$ flows through a thin, flat conducter of width $w$, height $h$ ($h \ll w$) and very large length. Calculate the magnetic f... | g16982 | [
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<p>In general theory of relativity I've seen several times this factor:</p>
<p>$$(1-\frac{2GM}{rc^2}),$$</p>
<p>e.g. in the <a href="http://en.wikipedia.org/wiki/Schwarzschild_metric" rel="nofollow">Schwarzschild metric</a> for a black hole, but I still don't know in this factor where 2 comes from?</p> | g16983 | [
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<p>I was wondering if there is a general formula for calculating Ricci scalar for any diagonal n by n metric tensor?</p> | g16984 | [
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<p>Is there a method/formula to calculate the refractive index of air at high temperature (e.g. 400 °C - 800 °C)?</p>
<p>I could only find formulas specified up to 100 °C and our physicist at university couldn't help me out, so I bother you now..</p> | g16985 | [
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<p>I'm a philosophy undergraduate student who has an interest in, and respect for (as most people do) what physicists know about the world. </p>
<p>In philosophy, the traditional criterion of physical existence has been extension in some dimension of space (not necessarily the three most familiar dimensions). For exam... | g16986 | [
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<p>So, after having spent the last 9 hours attempting to understand the basic tenets of stress tensors in fluids, I can honestly say that I think I know less now than when I began.</p>
<p>My questions are these: what precisely is a stress tensor in the context of fluid dynamics, and why is it the case that stress tens... | g513 | [
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... |
<p>This is a follow-up of <a href="http://physics.stackexchange.com/q/83822/18778">this question</a>. After that, I picked up some knowledge of FDTD (an algorithm for solving Maxwell's equations) and simulated following scene:</p>
<p><strong><em>Pic 1</em></strong></p>
<p><img src="http://i.stack.imgur.com/6hJ0C.jpg"... | g16987 | [
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<p>What is the reaction, or reactions that make anti-matter? I don't understand how anti-matter is created by CERN if interaction with normal matter causes annihilation. </p> | g16988 | [
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<p>I'm just starting to learn about special relativity, and I'm a little bit confused about something. Take the example of an observer in $S$ on the ground observing a train move at constant velocity $v$ relative to $S$, an observer in $S'$ is on the train, and this observer in $S'$ flashes a light that reflects from t... | g16989 | [
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0.01932... |
<p>From Young & Freedman, <em>Univ. Phys.</em> p. 1394 about <a href="http://en.wikipedia.org/wiki/Moseley%27s_law" rel="nofollow">Moseley's law</a>:</p>
<blockquote>
<p><em>Suppose one electron is knocked out of the K shell. This process leaves a vacancy, which we’ll call a hole. (One electron remains in the K ... | g16990 | [
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... |
<p>I am planning to design a scrubber system to separate CO2 and some other gases
from a gas mixture. For this purpose, I thought to cool the gas below CO2's boiling point which is -57 Celsius. There are some other gases which is below this and going to about -90 Celsius. By doing so, the actual gas I want which has mu... | g16991 | [
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0.... |
<p>I am interested in the math/physics behind the simple bell siphon. In <a href="http://www.youtube.com/watch?v=gFokOynqOqQ" rel="nofollow">this YouTube video</a>, the presenter says that the space in the top of the bell becomes a vacuum when the water flow eventually fills the entire downpipe. </p>
<p>Right after th... | g16992 | [
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<p>I am looking for both a mathematical and a physical reason for energy band gap in metals. For Physical reason, I was told that at each reciprocal lattice, you could have Bragg scattering, that would cause the band gap, but this does not really make full sense to me.</p>
<p>For a mathematical reason, do we have to s... | g16993 | [
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<p>I'm a little confused, for the twentieth time, on what tensors are. I thought they were a generalization of matrices-but then they have special transformation rules. I'm looking for a concise definition of what a tensor is. In Griffiths, he says that an $n$ rank tensor transforms with $n$ components of a rotation ma... | g514 | [
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0.02668277733027935,
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-0.... |
<p>Magnets will attract or repel over a distance before physically touching each other. </p>
<p>What makes this effect possible? My best guess is that the forces generated by the angular momentum of the electrons in the outer shell produce a "wind" of force that is similar to the draft you feel when a fast moving o... | g16994 | [
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-0.009... |
<p>This might be a simple problem for many of you. However, please help me understand it too. I have been looking trough a lot of materials online, and I still have the following questions, that would help me a lot.</p>
<p>I saw this video on youtube: <a href="https://www.youtube.com/watch?v=NeXIV-wMVUk" rel="nofollow... | g16995 | [
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<p><img src="http://i.stack.imgur.com/3Dwfj.png" alt="pulley"></p>
<p>Why does gravity do more work on the block going down?</p>
<p>The total work done (by gravity) on the $8kg$ block is more than the work done (by gravity) on the lighter block. How?</p> | g16996 | [
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<p>How would you go about showing that in the quantum canonical ensemble (that is, in the density matrix and operator formulation), the energy fluctuations, namely $\langle H^2\rangle - \langle H\rangle^2$ is the same as in the classical case, i.e. $k_b T^2 C_V$?</p>
<p>I've seen a lot of books asserting this, but can... | g16997 | [
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0.037... |
<p>Consider there is a box of mass $m$ at rest on the floor. Most books give an example that we need to do a work of $mgh$ to lift the box $h$ upward.</p>
<p>If we analyze this work done, the external force acting on the box by us should be equal to the weight of the box. Therefore the net force is zero which in turn ... | g16998 | [
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<p>It seems that $\textrm{eV}\!/c^2$ (and its multiples) is commonly used as <em>the</em> unit of mass in particle physics. For example, David Griffiths uses it quite naturally in <a href="http://rads.stackoverflow.com/amzn/click/3527406018" rel="nofollow"><em>Introduction to Elementary Particles</em></a>, so does <a h... | g16999 | [
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<p>I have this question:</p>
<blockquote>
<p>An electron with Energy $E = 40 eV$ hits a potential barrier with $E_0 = 30 eV$. What is the wavelength of the electron after hitting the potential barrier?</p>
</blockquote>
<p>I worked from the energy $E = p\cdot v \Rightarrow m_e \cdot E = p^2$ and combined it with th... | g17000 | [
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<p>Knowing the per kWh price of electricity, what other factors are needed to calculate how much would one pay per km traveled on electric power compared to gasoline power?<br>
EDIT: For example, the <a href="http://en.wikipedia.org/wiki/Chevrolet_Volt" rel="nofollow">Chevrolet Volt</a> reports a 35 kWh per 100 miles. ... | g17001 | [
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<p>How come when I spin a cup with water in it, the water does not spin, but the moment I stop spinning the cup, the water starts spinning the other way?</p> | g17002 | [
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<p>In the detection of weakly interacting massive particles (WIMPs), which is the basis of dark matter, what is the use of the tank filled with liquid xenon? I mean, how does the releasing of photons contribute in the detection of WIMPs?<br>
To relate to what I'm talking about, you can follow this link:<br>
<a href="ht... | g17003 | [
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<p>Just a little background before I present my question - I am a Psychology graduate looking to move into Neuroscience so I'm going through some Physics to learn more about this topic as it is relevant for some Neuroscience courses. As such I lack some background knowledge of Physics and have last studied it at GCSE a... | g17004 | [
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<p>A friend of mine, based on casual observation, believes that coffee will cool faster than ordinary hot tap water. Being curious about this I have tried to investigate it myself, but I'm not well versed in physics and thermodnamics. Also, I know that there are many variables to this, so I will attempt to ask the ques... | g17005 | [
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<p>Causality is generally accepted to be a fundamental physical principle. But quantum mechanics is acausal (e.g. there is no 'why' as to the result of a measurement of the position of a particle in an infinite 1D square potential well). In which case what is a distinction between causality and determinism, that has a ... | g17006 | [
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<p>If it's really hot inside, but cooler outside; what is the best way to place a single fan to try and cool a room down?</p>
<p>I always assumed it would be better pointing inwards (and <a href="http://boards.straightdope.com/sdmb/showthread.php?t=518543">this thread</a> suggests the same).</p>
<p>However; today I h... | g515 | [
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<p>I was wondering whether there is a simple formula in order to calculate the ground velocity (the velocity with which the satellite is moving along the planet's surface) on basis of the orbital velocity.</p>
<p>So for instance, a GEO satellite at Earth has an orbital velocity of around 3.07 km/s, while its ground ve... | g17007 | [
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<p>When reports state that Voyager is traveling at ~17kmps or that a comet is traveling at 600kmps, what are these numbers relative to? Given that the Earth travels at ~30kmps and orbits the Sun which is traveling at ~25kmps (and so on), is there an implicit qualifier attached to them?</p>
<p>Similarly, when a spacecr... | g17008 | [
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<p>This thought came from researching a <a href="http://physics.stackexchange.com/questions/71618/hollow-gold-bar">previous question</a>. In the spirit of our get-rich-quick scheming I looked up element densities and <a href="http://en.wikipedia.org/wiki/Prices_of_elements_and_their_compounds">prices</a> near gold.</p... | g17009 | [
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<p>I'm applying for a position that is interested in studying crack growth using peridynamics. I have experience with MD on polymeric systems, but I had never knew of this method before. It seems very well suited for at least qualitative description of cracks. </p>
<p>My concern is: can it also provide quantitative re... | g17010 | [
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<p>In the discussion of "Landau Straggling", the following expression comes up for the energy loss $\xi$ in Landau's original paper:</p>
<p>$$\xi = x\frac{2\pi N e^4\varrho\sum Z}{mv^2\sum A}$$</p>
<p>Here $N$ is avogadro's number, $e$ is the electron charge, $\varrho$ is the density, $m$ the electron's mass and $v$ ... | g17011 | [
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<p>My friends and I are debating over the correct answer for this particular physics problem.</p>
<p>There's a pendulum with a $2kg.$ mass and a $5m.$ string attached to a ceiling at $53^{\circ}$ to the vertical. It's released. At point B, $37^{\circ}$ from the vertical, we are asked to find the tension in the string.... | g17012 | [
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<p>The spatial part of the positive curvature FRW metric has the form
\begin{equation}
ds^2=\frac{dr^2}{1-(r/R)^2}+r^2d\Omega^2
\end{equation}
or
\begin{equation}
ds^2=R^2(d\chi^2+\sin{\chi}^2d\Omega^2)
\end{equation}</p>
<p>This is described as "closed", as it has the metric of a three-sphere, but I want to know what... | g17013 | [
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<p>What is the current "consensus" on Max Tegmark's Mathematical Universe Hypothesis (MUH) which claims every concievable mathematical structure exists, including infinite different Universes etc.</p>
<p>I realize it's more metaphysics than physics and that it is not falsifiable, yet a lot of people seem to be taking ... | g17014 | [
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<p>Batteries generate fields in wires that essentially cause the movement of electrons. I think of batteries as two charged plates that essentially contain a mechanism between them to move electrons from the positive to negative plate.</p>
<p>If you have two charged plates they would essentially create a field everywh... | g17015 | [
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<p>In a slide wire generator, when the slide wire attains a final constant velocity, is the current in the circuit 0?</p>
<p>It does not make sense if it is 0 as the area keeps increasing, allowing more flux to pass, meaning more current would need to be generated to counteract the increasing flux.</p> | g17016 | [
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<p>I am a non-physics person trying to wrap my head around some EM radiation facts. Please help me with this.</p>
<p>I have read about <a href="http://en.wikipedia.org/wiki/Dielectric_heating" rel="nofollow">Dielectric Heating on Wikipedia</a>. And watched <a href="https://www.youtube.com/results?search_query=how%20mi... | g17017 | [
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<p>In my physics textbook, it says that a qualitative way to envision pressure from EM waves is as follows: the electric field drives charges in the $x$ direction, and the magnetic field then exerts on them a force $q\vec{v}\times\vec{B}$ in the $z$ direction. The net force on all the charges in the surface produces th... | g17018 | [
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<p><img src="http://i.stack.imgur.com/Vy9SB.jpg" alt="Chemical potential of Bose-Einstein condensation"></p>
<p>This is a problem in <a href="http://physics.weber.edu/thermal/" rel="nofollow">An Introduction to Thermal Physics</a>.</p>
<p>(a)(b) is easy to work out. In (c), I use the formula $N_{excited}=(\frac{T}{T_... | g17019 | [
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<p>Just what the title states.
The gain medium in a gas/fluid laser works by shedding stimulant energy. </p>
<p>My elementary knowledge of physics tells me a photon is mass-less. Ergo, photon emission would continue ad infinitum in the presence of stimulant energy - no need to replenish the medium.</p>
<p>Is this co... | g17020 | [
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<p>Why is it that after pouring a delicious beer from a bottle, I can hold it upside down for several seconds without reward, but if I wait a bit, the remainder presumably settles at the bottom and immediately pours out on demand?</p> | g17021 | [
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<p>On a Bragg <em>reflection</em> with incomming angle Theta the total diffraction angle of the incomming wave is 2*Theta, of course.</p>
<p>But I have Bragg <em>transmission</em> with electrons on a graphite crystal (experiment about de-Broglie-wavelength and wave-particle-duality). The Bragg interference condition i... | g17022 | [
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<p>I'm afraid this question could sound a little too vague. I don't even know if dark matter (DM) can be genuinely described by quantum field theory, or if quantum field theory should be somehow "modified" in order to include dark matter.</p>
<p>Assuming that ordinary QFT describes DM, what can be said (or what is kno... | g17023 | [
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<p>Since a quantum information lecture today I have been wondering what does it really mean for a state to be in superposition? Is this something that is answerable? </p>
<p>This is what we learnt (or what I gathered :) )</p>
<p>A classical bit is always in a state 0 or 1. Sometimes there exists a degree of uncertain... | g17024 | [
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<p>Is there a way to express $\cos(x(t))$ (or $\sin(x(t))$) as the solution to the Euler-Lagrange equation, in other words is there a sense in which this function is the path of stationary action?</p> | g17025 | [
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<p>Consider an elevator moving down with uniform velocity. A person standing inside watches an object fall from the ceiling of the elevator to the floor. Say the height of the elevator is $h$. Then the work done by gravity in that frame of reference should be $mgh$. But consider this same event being watched by someone... | g17026 | [
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0.00179954688064754,
0.017354898154735565,
0.004342682659626007,
-0.009... |
<p>I've confused myself about the following scenario: </p>
<p>Suppose you make a black hole out of states with spin aligned into one direction, say the positive x-direction, and let's call this "up". Then the so-created black hole has an non-zero angular momentum because the expectation value of the spin is nonzero. ... | g17027 | [
-0.0015332546317949891,
-0.0509335957467556,
0.01912737637758255,
-0.04707254841923714,
0.049931369721889496,
0.012827816419303417,
0.08766766637563705,
0.06124220788478851,
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-0.02458576112985611,
-0.017014015465974808,
0.0056014955043792725,
0.01387406699359417,
-0.0... |
<p>In the <a href="http://arxiv.org/abs/hep-th/0703281" rel="nofollow">paper</a> of Intriligator, Seiberg, and Shih from 2007, they give an expression for the effective potential on the pseudo-moduli space $X$, estimated at large $X$ (equation 1.3).</p>
<p>In this equation, "$\gamma$ is the anomalous dimension of a pa... | g17028 | [
0.0019264932489022613,
0.035316262394189835,
0.0036973797250539064,
-0.031384363770484924,
-0.005692005157470703,
0.008724404498934746,
-0.018860625103116035,
0.028896933421492577,
-0.049120012670755386,
0.06012605503201485,
-0.048725955188274384,
0.025411520153284073,
-0.020502015948295593,... |
<p>In Steven Weinberg's book "The Quantum Theory of Fields" vol. I, Section 12.1, page 500, it writes: </p>
<p><em>"We will write the asymptotic behavior of the propagator $\Delta_f(k)$ of a field of type $f$ in the form</em> </p>
<p>$$\Delta_f(k)\sim k^{-2+2s_f}$$</p>
<p><em>Looking back at Chapter 6, we see that $... | g17029 | [
0.02144007198512554,
0.020432408899068832,
-0.01294591836631298,
0.027914639562368393,
0.048661451786756516,
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0.08725075423717499,
0.03589412569999695,
0.017378000542521477,
-0.00031371836666949093,
-0.07012172043323517,
0.03659985587000847,
0.02340725250542164,
-0.006... |
<p>My question is about the reduction of a representation of a group $SU(5)$ to irreps of the subgroup $SU(3)\times SU(2) \times U(1)$.</p>
<p>For example the weights of the 10 dimensional representation of SU(5) are</p>
<p><img src="http://i.stack.imgur.com/SlEAK.png" alt="enter image description here"></p>
<p>One ... | g17030 | [
-0.011189587414264679,
-0.020757941529154778,
-0.03748496249318123,
-0.06048010289669037,
0.11154614388942719,
-0.036063119769096375,
0.02377886138856411,
0.02937667816877365,
-0.06098146364092827,
0.038828812539577484,
-0.01311434991657734,
0.033918775618076324,
-0.022676870226860046,
0.0... |
<p>I'm reviewing David Tong's excellent QFT lecture notes <a href="http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf">here</a> and am a little confused by something he writes on page 94.</p>
<p>We've considered the standard chiral representation of the Clifford Algebra, and he is now generalising to a different represe... | g17031 | [
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-0.02555055171251297,
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0.03673985227942467,
0.01629374548792839,
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0.029468730092048645,
-0.036264777183532715,
0.06098037585616112,
-0.038658998906612396,
-0.... |
<p>I need to measure the atoms spin along a direction perpendicular to the z-axis but at an angle
$$
\phi
$$
with the x-axis.</p>
<p>They then get the output of the spin measured is + with probability
$$
\cos^2(\phi/2)
$$
Is there a general formula I can use to compute the + spin state and then form that determine t... | g17032 | [
-0.03955288976430893,
0.02288276143372059,
-0.00882488302886486,
-0.03839470073580742,
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0.03163038566708565,
0.026129338890314102,
0.013895517215132713,
0.01864718832075596,
0.059002239257097244,
0.039200227707624435,
-0.0197... |
<p>I faced the following sentences:</p>
<blockquote>
<p>We consider a gravitational collapse
taking place in this spacetime. The singularity theorems assure us that a singularity will
form. The assumption that the cosmic censorship conjecture is valid will then imply that
the collapse must produce a black hole... | g17033 | [
0.04631078988313675,
0.010385220870375633,
0.034988511353731155,
0.0008487907471135259,
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0.02621200680732727,
0.03215404972434044,
0.01252731867134571,
0.029809175059199333,
0.00475890... |
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