question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I have thought up a situation that I cannot understand with my understanding of special relativity. I don't know general relativity, but as the situation doesn't involve gravity or acceleration, I'm not sure if it is needed.</p>
<hr>
<p>Imagine there are 2 digital count up timers, A and B, separated by 100 light d... | g13228 | [
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<p>I want to understand the derivation of the equations 8.3.11 in Polchinski Vol 1. </p>
<p>I can understand that at the self-dual point the Kaluza-Klein momentum index $n$, the winding number $w$, and the left and the right oscillator number $N$ and $\tilde{N}$ are related as,</p>
<p>$$(n+w)^2 + 4N = (n-w)^2 + 4\ti... | g13229 | [
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<p>Sorry for such a vague question but I could have sworn I read somewhere that Hawking proposed the reason we might see a classically appearing universe is due to the possible role of black holes in quantum decoherence. Is there such an idea by him or another physicist? If so, can anyone point me to some names where I... | g13230 | [
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<p>How does a "hammer thrower" that we see in the Olympics, build so much momentum into the club?</p>
<p>It's sort of like the golf swing, the more momentum, primarily in the club head, the further the ball will fly, not accounting for the "Magnus effect".</p>
<p>So, how does a strong hammer thrower, create so much p... | g13231 | [
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<p>For an interacting quantum system, Hubbard-Stratonovich transformation and mean-field field approximation are methods often used to decouple interaction terms in the Hamiltonian. In the first method, auxiliary fields are introduced via an integral identity, and then approximated by their saddle-point values. In the ... | g13232 | [
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<p>I haven't been able to understand what are does someone mean by length and time scales, while talking about <a href="http://en.wikipedia.org/wiki/Turbulence" rel="nofollow">turbulence</a>. Can someone explain it to me or give me a link where i can find a good explanation.</p> | g13233 | [
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<p>Kinetic energy of an object $mc^2$. I want to evaluate the momentum.
We know Kinetic energy,
$$E_k = \frac{p^2}{2m}$$
$$mc^2 = \frac{p^2}{2m}$$
$$ p = \sqrt{2}mc$$</p>
<p>Note that the momentum is the relativistic mometum. Is there anything I did worng? </p> | g13234 | [
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<p>I'm having trouble reconciling two different versions of the <a href="http://en.wikipedia.org/wiki/Ladder_paradox" rel="nofollow">Pole and Barn paradox</a>.</p>
<p>Version 1: Consider a pole 10 m long and a barn 5 m long with a front and rear door. A runner carrying the pole (frame S') moving with respect to the ba... | g13235 | [
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<p>Is the total mass of the universe constant in time?</p> | g27 | [
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<p>We can achieve a simplified version of the Lorentz force by
$$F=q\bigg[-\nabla(\phi-\mathbf{A}\cdot\mathbf{v})-\frac{d\mathbf{A}}{dt}\bigg],$$
where $\mathbf{A}$ is the magnetic vector potential and the scalar $\phi$ the electrostatic potential.</p>
<p>How is this derivable from a velocity-dependent potential
$$U=... | g13236 | [
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<p>As we know, in condensed matter theory, especially in dealing with strongly correlated systems, physicists have constructed various "peculiar" slave-fermion and <a href="http://en.wikipedia.org/wiki/Slave_boson">slave-boson</a> theories. For example,</p>
<p><strong>For Heisenberg model,</strong> we have Schwinger-f... | g13237 | [
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<p>In quantum mechanics, we generally take about "expectation values of dynamical variables". However, by the postulates of quantum mechanics, every dynamical variable in quantum theory is represented by its corresponding operator.</p>
<p>Is it therefore, incorrect to talk about "expectation value of an operator" (rat... | g13238 | [
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<p>I have two objects here which are made of the same plastic. When I hold them together, they remain separate objects: I can pull them apart with no resistance.</p>
<p>How does each atom/molecule “know” which object it belongs to? Why do the objects not fuse?</p> | g13239 | [
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<p>By using an optical lattice, how can one change the interaction term $U$? And how is the superfluid phase achieved in the hard-core boson regime?</p>
<p>Why are these phases identified as superfluid or mott insulator?</p> | g13240 | [
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<p>Thanks in advance to anyone who takes the time to answer this, and apologies in advance for what is probably (yet another) question here due to unfamiliarity with The Math.</p>
<p>I had a chance recently to visit the CMS detector at CERN (sheer luck) and it's made me curious to better understand how the Higgs field... | g13241 | [
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<p>Is there any real process in which $PV^n=C$ where $P,V$ stands for pressure, volume respectively. $C$ is a constant and $n$ is a positive integer?</p>
<p>I am familiar with Boyle's law that states that $P\propto\frac{1}{V}$ when the temperature is constant. But according to the first equation, since $n$ is any posi... | g13242 | [
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<p>For some time now I have been wondering if you could not derive any sort of equations of motion from the Standard Model:</p>
<p>$$\mathscr{L}=-\frac{1}{4}F^{\mu\nu}F_{\mu\nu}+i\bar{\psi}D\psi+\bar{\psi}\phi\psi+h.c.+\vert D\phi\vert^2-V(\phi).$$</p>
<p>Since it is a Lagrangian shouldn't we be able to use the Euler... | g13243 | [
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<p>I cannot completely understand what is a <em>regular</em> method to solve Einstein's equations in GR when there are no handy hints like spherical symmetry or time-independence.</p>
<p>E.g. how can one derive Schwarzschild metric starting from arbitrary coordinates $x^0, x^1, x^2, x^3$? I don't even understand the s... | g13244 | [
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<p>I think everybody here knows the equation that gives the potential of a point like dipole, but how does the field look like if you have e.g. a metal sphere with radius $R$ and a certain dipol moment, how does this potential look like?</p> | g13245 | [
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<p>The Bekenstein bound is a limit to the amount of entropy a thermodynamical system can have. The bound is given by the following expression:
\begin{equation}
S \leq \frac{2 \pi k R E}{\hbar c}
\end{equation}
where $k$ is Boltzmann's constant, $R$ is the radius of a sphere that can enclose the given system, $E$ is t... | g13246 | [
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<p>I know that it often occurs that we need to take a derivitive with respect to $\beta$ in statistical mechanics. However, I think it is poor style to use equations with both T and $\beta$ in them especially since in most of the theory we take $\beta = \frac{1}{T}$. I see this abuse of notation frequently in textbooks... | g13247 | [
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<p>Can cosmic radiation (alpha radiation) transmute the material of a space craft, particular carbon, titanium and aluminum?</p>
<p>Where can i find transmutation tables or formulas to calculate the possibility of a transmutation and the outcome?</p> | g13248 | [
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<p>Is there a proof that time is a 4th dimension?</p>
<p>If it is, then why not measure it in units of the previous three?
Logical right?</p>
<p>How many seconds is a temporal meter?</p> | g13249 | [
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<p>The ideal gas law (aka the equation of state) is given by</p>
<p>$$
p/\rho_N = k_BT,
$$
where $\rho_N$ is number density. When am I allowed to use this to describe a fluid?</p> | g13250 | [
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<p>I am having a difficulty solving my homework so I was hoping
I could get some help, so here it is.
It is about gravitational waves and first order gravitational perturbation theory,
I have to prove that under the gauge transformation:
$$h_{ab} \rightarrow h_{ab}+ \nabla{a} \xi_b + \nabla_{b} \xi_a$$
the curvature ... | g13251 | [
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<p>My first question is, how is the Fermi Energy for a material actually determined? I know <a href="http://en.wikipedia.org/wiki/Fermi_energy#Three-dimensional_case" rel="nofollow">this derivation</a>, but it seems to say that the Fermi Energy is just based on the electron density (and maybe some effective mass) of th... | g13252 | [
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<p>I'm really confused about the argument in Cardy's book for why there can't be long range order in 1D for discrete models. Let me just copy it out, and hopefully someone can explain it to me. </p>
<p>He takes an Ising-like system as an example. We start with the ground state with all spins up, and we want to see if ... | g13253 | [
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<p>Suppose I have a lab frame that is freely falling in a gravitational field of the Earth -- assume non-homogeneity-- and a uniform constant electric field. There are 2 test particles in the frame -- both of mass $m$, but one is of charge $e$ and the other neutral. They are initially separated by by a vertical distanc... | g13254 | [
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<ol>
<li><p>How could you measure someone's walking speed at a constant rate? </p></li>
<li><p>What types of errors could you potentially come across? </p></li>
<li><p>And what are some different ways of modelling walking motion?</p></li>
</ol> | g13255 | [
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<p>What are <a href="http://en.wikipedia.org/wiki/Coherence_%28physics%29" rel="nofollow">coherence</a> and <a href="http://en.wikipedia.org/wiki/Quantum_entanglement" rel="nofollow">quantum entanglement</a>? Does it mean that two particles are the same? </p>
<p>I read this in a book called <a href="http://www.goodrea... | g13256 | [
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<p>In Fresnel Diffraction at a circular aperture the central image according to 'Optics' by brij lal and subramanyam will be bright if odd number of full half-period zones can be constructed.But(according to me) an odd number of half-period zones would correspond to 0 amplitude i.e. the central spot will be dark as eac... | g13257 | [
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0.02223440818488598,
-0.00... |
<p>As far as I know, vacuum is the only dispersion free medium for electromagnetic waves. This makes me wonder if there are any other dispersion free media for these waves? (Experimentally established or theoreticaly predicted) If there are none for electromagnetic waves, are there any for other kinds of waves?</p> | g13258 | [
0.022655591368675232,
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<p>Is there a list of basic quantum variables/attributes that all quantum particles have? </p>
<p>Ex. An electron has charge, position, speed, momentum, etc. Is there a complete list of these variables? </p>
<p>I would figure not all quantum particles share the same set of variables? A photon has position and an elec... | g13259 | [
0.05281873047351837,
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0.009898710064589977,
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0.031472399830818176,
0.025098033249378204,
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0.024... |
<p>I'm trying to get my head around perspective.
If you look at the animation in <a href="http://en.wikipedia.org/wiki/Perspective_distortion_%28photography%29" rel="nofollow">Wikipedia </a> :</p>
<p><img src="http://i.stack.imgur.com/5jHlj.gif" alt="enter image description here"></p>
<p>You can see that the cube loo... | g13260 | [
0.040169574320316315,
0.04890577122569084,
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0.05144133418798447,
0.034014370292425156,
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-0.04590095952153206,
0.001678113010711968,
0.032777704298496246,
0.03480030968785286,
0.036122... |
<p>This will probably be a very basic question, but looking for a simple answers.</p>
<p>What I know</p>
<ul>
<li>the <em>visible light</em> is a form of electromagnetic radiation with a defined wavelength.</li>
<li>the full spectrum contains radio waves, microwaves, infrared radiation, visible light, ultraviolet ra... | g13261 | [
0.007973503321409225,
0.00220119534060359,
0.0025006358046084642,
0.018233953043818474,
0.07818953692913055,
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0.029591964557766914,
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0.04566992446780205,
0.023823728784918785,
0.05736102536320686,
-0.0038... |
<p>The diagram: a positive plate is on the left of the page and a negative plate is on the right. The velocity of the particle is going down the page. So, with a right hand rule, I would point my thumb in the direction of the velocity (down) and my palm in the direction of the force. But what's the direction of the for... | g13262 | [
0.05898343399167061,
0.03826406970620155,
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0.009273982606828213,
0.03305276110768318,
0.005715515930205584,
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<p>Imagine a SHO with a drive F(t). (or in general a Hamiltonian system)</p>
<p>What is the power delivered to the system and can we talk about the power reflected? is i am imagining say a MW oscillator cavity fed by a transmission line.</p>
<p>My 3 attempts at the question:</p>
<p>1) One definition of power I kno... | g13263 | [
0.018035203218460083,
0.023905610665678978,
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0.03562536463141441,
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0.... |
<p>My physics book says that six colors can be distinctly seen in white light: red, orange, yellow, green, blue, and violet. Does solar light only use these six wavelengths and mix them additively, or does it use a range of colors from red to violet?</p>
<p>And what effect does the scattering of blue light from the sk... | g13264 | [
0.007618822157382965,
0.04596635326743126,
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<p>What is the de Broglie wavelength?
Also, does the $\lambda$ sign in the de Broglie equation stand for the normal wavelength or the de Broglie wavelength? If $\lambda$ is the normal wavelength of a photon or particle, is $\lambda \propto \frac{1}{m}$ true?</p>
<p>Can a wave to decrease its amplitude or energy with ... | g13265 | [
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<p>Why is a proton assumed to be always at the center while applying the <a href="https://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation" rel="nofollow">Schrödinger equation</a>? Isn't it a quantum particle?</p> | g13266 | [
0.03348984196782112,
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<p>We have a square loop (I believe it's called) in a uniform magnetic field between the 2 poles of a permanent magnetic field (green is N, red is S). P is connected to the positive pole of a voltage source and Q is connected to the negative pole (so there is a current):</p>
<p><img src="http://i.stack.imgur.com/uUi... | g13267 | [
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... |
<p>Statistical mechanics is used to describe systems with large number of particles ~$10^{23}$.</p>
<p>The observable universe contains between <a href="http://en.wikipedia.org/wiki/Observable_universe">$10^{22}$ to $10^{24}$</a> stars. Can we treat those many stars as a statistical mechanical system (for which one ca... | g13268 | [
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<p>In the news it is often mentioned that some countries are going to enrich uranium to "military grade" (i.e. 80%+) and that it is possible to use it for a nuclear bomb.</p>
<p>1) Is that correct that there are no nuclear warheads in service made of U-235, as plutonium ones are much smaller & much more efficient ... | g13269 | [
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<p>I would like to know how to calculate Temperature Humidity Wind Index (THW Index)? I know how to <a href="http://en.wikipedia.org/wiki/Heat_index" rel="nofollow">calculate Heat Index</a> and <a href="http://en.wikipedia.org/wiki/Wind_chill" rel="nofollow">Wind Chill</a>. I am asking this because my weather station <... | g13270 | [
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0.02923... |
<p>We can very well feel the <a href="http://en.wikipedia.org/wiki/Magnetic_field" rel="nofollow">magnetic field</a> around a magnet, but we can't see it. Why is that so?</p>
<p>Also, can we cut a portion of the <a href="http://en.wikipedia.org/wiki/Field_%28physics%29" rel="nofollow">field</a> and use it?</p> | g13271 | [
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<p>I have read <a href="http://www.physicsforums.com/showthread.php?p=1712273#post1712273" rel="nofollow">here</a>, that $\frac{1}{2}mv^2$ must not be applied on a photon ever. </p>
<p>If i want to calculate escape velocity $v_e$ i need to use $\frac{1}{2}mv^2$ because we say that kinetic energy <em>(positive)</em> mu... | g13272 | [
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<p>Find the velocity of the triangular block when the small block reaches the bottom:
<img src="http://i.stack.imgur.com/WXQHF.png" alt="enter image description here"> </p>
<p>Here is what I did:<br>
The final velocity(at the bottom)of the small block of mass m is $\sqrt{2gh}$ along the plane of the incline with resp... | g13273 | [
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0.010914282873272896,
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<p>I need a same help with it. Some books where i can find a real math explanation of this effect will be good help!!
simple exp of this effect will be good too)</p> | g13274 | [
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<p>I would like to provide a more thorough answer to this question here</p>
<p><a href="http://aviation.stackexchange.com/q/3709">http://aviation.stackexchange.com/q/3709</a></p>
<p>but I realized I don't know enough about angular momentum. If an airplane wheel is rotating at 100 rpm, and the wheel weighs 10kg, with ... | g13275 | [
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<p>I have some difficulty understanding the concept of pure thermal radiation, as described in Hawking and Page's paper on the Hawking-Page phase transition.</p>
<p>The four-dimensional thermal AdS solution (with cosmological constant $\Lambda<0$) is given by</p>
<p>$ds^2=f(r)d\tau^2+\frac{1}{f(r)}dr^2+r^2d\Omega^... | g13276 | [
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<p>So my problem is that i am working on an art instalation that needs to float. The idea is that i need to find a formula between the volume (V) of the buoy and the total weight of the whole instalation. </p> | g13277 | [
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<p>For example, just consider a 1D atom chain with $N$ sites and lattice constant $a=2\pi$, under periodic boundary conditions, the crystal momentum reads as $k=\frac{n}{N}\frac{2\pi}{a}=\frac{n}{N}$, with $n=0,1,2,...,N-1$. In the thermodynamic limit $N\rightarrow \infty$, there would be infinitely dense $k$ points wi... | g13278 | [
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<p>I would like to know, what are the simplest/starting/basic examples that are typically used to introduce students to how AdS/CFT really works? (not the <a href="http://arxiv.org/abs/hep-th/9905111" rel="nofollow">MAGOO paper</a>, as I am not sure it has concrete examples that a beginning student can work through) </... | g13279 | [
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<p>As the title says, I have a rigid rotor with a perturbation given below
$$H=\frac{L^2}{2I}-\alpha B L_z.$$</p>
<p>So I know that the eigenvalues of $H$ will be $\ell(\ell+1)/2I -\alpha B m$ where $m$ is our projection component. </p>
<p>I am then asked to find the probability that the system will be in the $\ell$... | g13280 | [
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0.0410... |
<p>According to the the definition of anti-particles, they are particles with same mass but opposite charge. Neutrinos by definition have no charge. So, how can it have an anti-particle?</p> | g13281 | [
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<p>Assume there is a rainstorm, and the rain falling over the entire subject area is perfectly, uniformly distributed. Now assume there are two identical cars in this area. One is standing still, and one is traveling (at any rate, it doesn't matter).</p>
<p>In theory, does one get struck by more water than the other... | g416 | [
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<p>I apologise in advance that my knowledge of differential geometry and GR is very limited. In general relativity the equation of motion for a particle moving only under the influence of gravity is given by the geodesic equation:</p>
<p>$$
\ddot{x}^\lambda + \Gamma^\lambda_{\mu\nu}\dot{x}^\mu\dot{x}^\nu =0.
$$</p>
<... | g13282 | [
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0.011... |
<p>Ok, this question is more a result of my lack of knowledge of how to manipulate equations involving index notation rather than about physics...</p>
<p>I have the geodesic equation with $U^\lambda\equiv\dot{x}^\lambda$:-</p>
<p>$$
\dot{U^\lambda} + \Gamma^\lambda_{\mu\nu} U^\mu U^\nu
$$</p>
<p>And I want to transf... | g13283 | [
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... |
<p><img src="http://i.stack.imgur.com/DOu2r.png" alt="enter image description here"></p>
<p>While i was studying about chaos theory, i stumbled upon this, When a ball confined in a square, and at the center is located a circle, is to bounce elastically, the path of the object deviates significantly. thereby causing ch... | g13284 | [
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<p>A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be?</p>
<p>Logically, to me the answer seems to be infinity, as always a fraction of velocity will get reduced. But in my book the answer is n^2/(2n-1) (that comes from energy balanc... | g849 | [
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0.059787... |
<p>I'm reading <a href="http://eu.wiley.com/WileyCDA/WileyTitle/productCd-3527617361.html" rel="nofollow">Gauge Field Theories: An Introduction with Applications by Mike Guidry</a> and this particular remark is not obvious to me:</p>
<blockquote>
<p><em>A tempting avenue is suggested by the QED paradigm, for if a lo... | g13285 | [
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... |
<p>Does there exist a mathematical model for determining the electron configuration of an atom? I mean the theory which would generalize the notion behind the informal elements of the <a href="http://en.wikipedia.org/wiki/Aufbau_principle" rel="nofollow">Aufbau principle</a>.</p> | g13286 | [
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0... |
<p>I am self studying for upcoming exams and I am stuck on the end of a problem related to perturbation theory. Here is the problem</p>
<p><img src="http://i.stack.imgur.com/CrBoC.png" alt="enter image description here"></p>
<p>I can't manage to do the very last part -- showing the exact change in all of the energy l... | g13287 | [
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<p>It is known that - When a star collapses during the formation of the black hole, the black hole obtains the spin of the star which it collapsed from...</p>
<p>What I'd like to know is, If this spin <em>accelerates</em> as a result of angular momentum (if any), What effects could this <em>rapid</em> rotation have on... | g13288 | [
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<p><a href="http://pegasus.udea.edu.co/~undheim/Classical-Theory-of-Rayleigh-and-Raman-Scattering-18p.pdf" rel="nofollow">So from the classical theory</a>, you find a formula for a dipole in a planar electromagnetic wave, where there will be two cosine terms with a frequency (actually angular velocity in $[rad/s]$, as ... | g13289 | [
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<p>I was struggling today with this question: does a free photon have a continuous energy spectra?</p>
<p>Free means in no context of any energy system (eg. an atom, em field). Although I'm asking myself if the quantization of the electromagnetic field is omnipresent and will always make the energy discrete?</p>
<p>E... | g13290 | [
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<p>I find it hard to believe that photons always travel with 3 x 10^8 m/s just from the start. But there must be some acceleration of light. Maybe huge or taking place in picoseconds. So what maybe the acceleration of light or photons?</p> | g159 | [
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<p><a href="http://www.dailygalaxy.com/my_weblog/2011/08/blackholes-glow-like-a-hot-body-stephen-hawking.html" rel="nofollow">Here's the reference</a>:</p>
<blockquote>
<p>The researchers showed that a magnetic field-pulsed microwave transmission line containing an array of superconducting quantum interference devic... | g13291 | [
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<p>I have asked a question at <a href="http://math.stackexchange.com/questions/356142/existance-of-inverse-operators-for-hermitian-adjoint-operators?noredirect=1">math.stackexchange </a> that have a physical meaning.</p>
<blockquote>
<p><em>My assumption: Suppose $a$ and $a^\dagger$ is Hermitian adjoint operators an... | g13292 | [
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<p>I know what <a href="http://en.wikipedia.org/wiki/Paramagnetism" rel="nofollow">paramagnetism</a> is. But first I want to know about the paramagnetic current and then the above-mentioned correlation?</p>
<p>Actually, I am working on a paper on superconductivity where I have seen the term:
<a href="http://prb.aps.or... | g13293 | [
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<p>Today in physics class we were talking about angular momentum and rotational kinetic energy. My teacher used the classic example of a figure skater spinning on ice - when she pulls her arms in, her angular momentum is conserved and her angular velocity increases, meaning that her rotational kinetic energy also incre... | g13294 | [
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<p>I know that <a href="http://en.wikipedia.org/wiki/Tide#Physics" rel="nofollow">tide</a> is caused by the gravitational pull of moon but what I don't know is how it effects on water. I have actually these doubts.</p>
<ol>
<li><p>Why does gravity of the moon creates tides only in water?</p></li>
<li><p>Are there othe... | g13295 | [
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<p>Consider a thin metal rod placed in a magnetic field whose direction is constant but whose magnitude is changing with time, with the length of the rod perpendicular to the direction of the magnetic field. The rod is stationary, so there is no motional emf. If the rod were part of a conducting loop, there would be an... | g13296 | [
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<p>I found this image :<img src="http://i.stack.imgur.com/2ua1x.jpg" alt="enter image description here"> on the internet and I traced it back to <a href="http://iopscience.iop.org/0953-4075/labtalk-article/47053" rel="nofollow">this article</a> ,I wanted to use it as part of an architectural visualization for my projec... | g13297 | [
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<p>If an object is rotating in space, then there has to be a centripetal force acting upon it to constantly change its direction. I thought if an object begins to rotate in space, it would slow down since there is no centripetal force that keeps it changing direction, but that is contradictory to the conservation of an... | g13298 | [
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<p>The strength of Hamilton's principle is obvious to me and I see the advantage.
Now, for conservative systems we also have <a href="http://en.wikipedia.org/wiki/Maupertuis%27_principle">Maupertuis' principle</a> that says:</p>
<p>$$ \delta \int p dq =0$$</p>
<p>and I am not sure how to derive an equation of motion ... | g13299 | [
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<p>I have a 2 compartment simulation. The first compartment simulates reactions using <a href="http://en.wikipedia.org/wiki/Ordinary_differential_equation" rel="nofollow">ODE</a>s. The second compartment uses Brownian motion. I want to be able to have molecules from the ODE compartment diffuse into the Brownian compart... | g13300 | [
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<p>Is it possible to use <a href="http://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_principle" rel="nofollow">band-limited double-step Fresnel diffraction</a> to assemble a <a href="http://www.opticsinfobase.org/oe/viewmedia.cfm?uri=oe-21-7-9192&seq=0" rel="nofollow">holographic image with radio waves</a>? If no... | g13301 | [
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<p>I have a question on the article</p>
<p><code>J. S. Bell, On the Einstein Podolsky Rosen paradox, Physics 1, 195, 1964.</code> (<a href="http://philoscience.unibe.ch/documents/TexteHS10/bell1964epr.pdf" rel="nofollow">link</a>)</p>
<p>My question concerns the expression (3) of the article, at page 196. I don't und... | g13302 | [
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<p>I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work on the box. So, if work occurs when a force causes displacement, how does negative work happen? Are my hands displaci... | g13303 | [
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<p>It is well known that a <a href="http://en.wikipedia.org/wiki/Prism_%28optics%29">prism</a> can "split light" by separating different frequencies of light:</p>
<p><img src="http://i.stack.imgur.com/ZfYPs.gif" alt="prism diagram"></p>
<p>Many sources state that the reason this happens is that the <a href="http://en... | g298 | [
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<p>The scalar fields $X^\mu$ in bosonic string theory have a clear physical interpretation - they describe the embedding of the string in spacetime.</p>
<p>Adding fermionic fields on the worldsheet is a generalization for sure, gives fermions in the spectrum, has a smaller critical dimension and no tachyons, that's al... | g13304 | [
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<p>Asymptotic completeness is a strong constraint on quantum field theories that rules out generalized free fields, which otherwise satisfy the Wightman axioms. If we were to take a limit of a list of continuous mass distributions $\rho_n(k^2)$ that approaches a distribution in some topological sense, however, is there... | g13305 | [
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<p>Given a symmetric (densely defined) operator in a Hilbert space, there might be quite a lot of selfadjoint extensions to it. This might be the case for a Schrödinger operator with a "bad" potential. There is a "smallest" one (Friedrichs) and a largest one (Krein), and all others are in some sense in between.
Conside... | g13306 | [
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<p>At the end of section 9 on page 49 of Dirac's 1966 "Lectures on Quantum Field Theory" he says that if we quantize a real scalar field according to Fermi statistics [i.e., if we impose Canonical Anticommutation Relations (<a href="http://en.wikipedia.org/wiki/CCR_and_CAR_algebras" rel="nofollow">CAR</a>)], the quantu... | g13307 | [
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<p>Sorry for this very simple question but I am still very new to the laws of <a href="http://en.wikipedia.org/wiki/Kinematics" rel="nofollow">motion</a>.</p>
<p>I am dealing with 2-dimensional vectors in my programming environment and I'm following <a href="http://www.richardlord.net/presentations/physics-for-flash-g... | g13308 | [
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... |
<p>How to apply a Hadamard gate to 3 qubits? by example how to apply $H$ to $(1/\sqrt{2})(\left|000\right> + \left|111\right>)$?</p> | g13309 | [
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<p>I'm interested in calculating scattering processes (e.g. Coulomb scattering of an electron beam by a single ion) in the context of lattice quantum field theory, and wonder if there is something like the expansion of a plane wave in spherical harmonics on the lattice? (I mean in discrete space modeled by a three dime... | g13310 | [
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<p>Is imaginary time an extra dimension?
In other words, are time and imaginary time considered two separate dimensions?
If so, does imaginary time appear (as a separate dimension) in string theory (thus contributing to the 11 dimensions in M-theory)?</p> | g13311 | [
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<p><strong>Note: I have already tried googling. Although similar questions have been asked on different forums, I couldn't find a detailed explanation, which I could really understand.</strong> </p>
<p><img src="http://i.stack.imgur.com/6JTCp.png" alt="Circuit Diagram"></p>
<p>Circuit diagram courtesy of Wikipedia.</... | g697 | [
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<p>I am in my last year of high school and am struggling with some homework. I'm sorry if this question is incredibly stupid, but I simply can't find the answer in my notes.</p>
<p>If I have an object with a velocity of 10ms-1 travelling at a bearing of 090 degrees (to the right) with no acceleration, and then all of... | g13312 | [
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<p>How are <a href="http://en.wikipedia.org/wiki/Symmetry_%28physics%29">symmetries</a> precisely defined?</p>
<p>In basic physics courses it is usual to see arguments on symmetry to derive some equations. This, however, is done in a kind of sloppy way: "we are calculating the electric field on a semicircle wire on th... | g984 | [
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0.011... |
<p>In the quantization of the Klein-Gordon field (for example) we interpret the quanta of the fields with definite momentum and energy as particles but are they also localized in space? Shouldn't a physical particle in quantum mechanics be represented by a wave-packet in the peaked about some point is space? Is the sce... | g13313 | [
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<p>How do derive the following transformation rule (J.D. Jackson third Edition 11.10) for electric and magnetic field?
$$\vec E' = \gamma \left( \vec E + \vec \beta \times \vec B\right) - \frac{\gamma^2}{\gamma +1} \vec \beta \left( \vec\beta \cdot \vec E \right ) \tag{1}$$
$$\vec B' = \gamma \left( \vec B - \vec \beta... | g13314 | [
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<p>What are the facts that one should consider and incorporate in going from non-relativistic <a href="http://en.wikipedia.org/wiki/Fermi%27s_interaction" rel="nofollow">Fermi theory of beta decay</a> to its relativistic generalization? In other words, how would the Lagrangian or Hamiltonian of the interaction be modif... | g13315 | [
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<p>I have an object that is orbit around a point mass in a 2D environment with a known speed, radius and zenith. I calculate the following orbital parameters as such and can confirm that these values are correct (where $R_{p}$ is the periapsis, $R_{a}$ is the apoapsis, $e$ is the eccentricity, $a$ is the semimajor axis... | g13316 | [
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<p>Well you know how it's said that things can't travel at or past the speed of light? However, can't they move at speeds greater than the speed of light relative to another object? </p>
<p>For example: What if two rocket ships that are travelling at 60% the speed of light fly past each other? Won't people on both shi... | g417 | [
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<p><img src="http://i.stack.imgur.com/I5qBu.jpg" alt="This is the question"></p>
<p>This is the problem, basically. Now my question is about the approach. Mine, and my teacher's. I would like some help as to which one is correct...</p>
<p>Mine: </p>
<p>As the whole chain is in equilibrium, the horizontal forces must... | g13317 | [
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<p>In the complex Klein-Gordon field we regard as dynamical variables the field $\phi$, the complex conjugate of the field $\phi^*$, and the momenta $\pi$, $\pi^*$. I can't see how should arise the (equal time) canonical commutation relations, in particular:</p>
<p>$$ \left[\phi\left(t, {\bf x}\right),\ \pi\left(t,{\b... | g13318 | [
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<p>There are a couple of interesting lectures by Leonard Susskind online, and in the <a href="https://www.youtube.com/watch?v=W6srShxBCrk" rel="nofollow">first lecture on Supersymmetry & Grand Unification</a> he explains renormalization. His example is the mass renormalization of a scalar field, and he uses a coupl... | g13319 | [
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0... |
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