question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Every country is trading with other countries around the world, some more than others. I was wondering if there would be any change to the Earth's rotation because of the imbalance of trade between countries. </p> | 52 |
<p>How does <a href="http://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence">$E=mc^2$</a> put a upper limit to velocity of a body? I have read some articles on speed of light and they just tell me that it is the maximum velocity that can be acquired by any particle. How is it so? What is violated if $v>c$ ?</p... | 2,532 |
<p>First post to this site, and I've got at most a high school background in physics - I really appreciate any answer, but I may not be able to follow you if you're too advanced.</p>
<p>I suppose this goes for regular planes too, but I'm especially interested in supersonic planes.</p>
<p>I read some reports in the ne... | 2,533 |
<p>I was told that the total integral of the stress over the surface of a swimmer (i.e. the total force exerted by the swimmer on the fluid) always vanishes, because there are no external forces applied on it. That seems fair by the 3rd Newton Law.</p>
<p>But, how does it take into account the effects of the 2nd Newto... | 2,534 |
<p>I have read that heat pumps are more efficient than generating heat directly for heating homes, until the temperature gets down to a critical value.</p>
<p>I just asked how to calculate temperature of gasses: <a href="http://physics.stackexchange.com/questions/81661/behavior-of-gasses-ideal-and-otherwise">Behavior ... | 2,535 |
<p>I know that electromagnetic waves induce electric currents in conductors and that's the basis for radio, wi-fi etc.</p>
<p>I also know that light is also an electromagnetic wave. So, can light induce a current in a conductor (like a metal wire? or a coil?). And, if the answer is yes, is the same visible for other h... | 2,536 |
<p>My text claims that Gauss's Law has been proven to work for moving charges experimentally, is there a non-experimental way to verify this?</p> | 2,537 |
<p>Suppose we have an ideal gas performing an irreversible cycle composed by:</p>
<ol>
<li>an isothermal transformation at $T_{1}$;</li>
<li>an isobaric transformation at $P_{A}$;</li>
<li>an isothermal transformation at $T_{2}$;</li>
<li>an isobaric transformation at $P_{B}$.</li>
</ol>
<p>with $\frac{T_{1}}{T_{2}}=... | 2,538 |
<p>While waiting for a 3D movie to start, I was playing with the glasses they give you. I understand each lens has different polarized filters, so the left and right superimposed images on the screen go to the correct eyes.</p>
<p>The first thing that tripped me up was that rotating the glasses didn't affect the light... | 2,539 |
<p>If we understand spacetime as a $4$-dimensional manifold $M$, from the point of view of physics what are the consquences of a subset of it being compact? My point here is simple: in math we usually think of compactness as some analogue of finiteness because it shares many properties with finite sets, but what are th... | 2,540 |
<blockquote>
<p>It was found centuries ago that these materials: wool cloth and paraffin wax, glass rod and silk cloth when rubbed against each other attracted one another. While two glass rods when rubbed against their respective silk cloths repelled each other and the same befell two pieces of paraffin wax. These f... | 2,541 |
<p>What is the current status or acceptance of <a href="http://en.wikipedia.org/wiki/Eternalism_%28philosophy_of_time%29" rel="nofollow">block time</a> as it relates to Einstein's theory of relativity? Has quantum mechanics ruled it out or is it still the favored view of the world? Perhaps there can't be any consensus ... | 2,542 |
<p>Let the tight-binding Hamiltonian be $\sum\limits_{ij} {{t_{ij}}\left| i \right\rangle \left\langle j \right|}$. Where ${\left| i \right\rangle }$ is the atomic orbit at lattice site $i$.</p>
<p>My question is, is it correct to express the usual operators in this representation like this:</p>
<p>Position operator:... | 2,543 |
<p>I'm currently searching for a good and reliable source where precision measurements on the wavelength of the so called sodium doublet ($D_1$ and $D_2$ lines) at approximately 589.0 nm and 589.6 nm are made.</p> | 2,544 |
<p>The event horizon of a black hole is where gravity is such that not even light can escape. This is also the point I understand that according to Einstein time dilation will be infinite for a far-away-observer.</p>
<p>If this is the case how can anything ever fall into a black hole. In my thought experiment I am in... | 447 |
<p>I'll have to perform some simple experiments, like measuring the period and damping of a pendulum, focal length of a lens, …</p>
<p>As a result I will end up with some X, Y data points and need to calculate derivation, means, kovariance and provide a fit for a liniarized function.</p>
<p>It explicitly says that we... | 2,545 |
<p>In calculating transition amplitude for Klein-Gordon real-scalar field, I encountered the integral,</p>
<p>$$ \frac{-i}{2(2\pi)^2\Delta x} \int^{\infty}_{-\infty} \,dk \frac{ke^{ik\Delta x}}{\sqrt{k^2+m^2}} $$</p>
<p>I can see here the integrand has branch cuts at $ k= \pm im $
However, later they do a change of... | 2,546 |
<p>Either through doping or gating. What are some good terms to search for if I'm looking for some experimentally obtained values for particular materials? I'm particularly interested in what the limit is for graphene, if anyone knows.</p>
<p>For example, the DOS for regular graphene has states between -3t and +3t, bu... | 2,547 |
<p><img src="http://i.stack.imgur.com/7xqyI.png" alt="http://thecuriousastronomer.wordpress.com/"></p>
<p>My doubt is in the equation (1) and (2). Aren't x,y and z also the radiuses?</p>
<p><strong>EDIT</strong>
Thank you guys for trying to give a wonderful explanation but I figured out the answer myself and it was j... | 2,548 |
<p>Why does light have the speed it does? why is it not considerably faster or slower than it is? I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed of light. Just saying "it is what it is" or being satisfied saying it is 1 ($c=1$), does not sound like science.</p> | 283 |
<hr>
<p>What would a transistor level design of an XOR gate look like?</p>
<hr> | 2,549 |
<p>The Thin Shell Formalism (<a href="http://en.wikipedia.org/wiki/Gravitation_%28book%29" rel="nofollow">MTW</a> 1973 p.551ff) is used to properly paste together different vacuum solutions to the Einstein equations. At the junction of the two solutions is a hypersurface of matter – the so-called thin shell. The thin... | 2,550 |
<p>The action for $N=1$ supergravity in an $4$ spacetime dimenions is</p>
<p>$$
S= \int e\left( R + \overline{\psi}_a \gamma^{abc} D_b \psi_c \right)
$$
Here $R$ is the scalar curvature, $e=\det(e_{a\mu})$, and $e_{a\mu}$ is the frame field. $\psi = \psi_{\mu} dx^{\mu}$ is a spinor valued one-form. The indices $a,b\l... | 2,551 |
<p>I understand that <a href="http://en.wikipedia.org/wiki/Rectenna" rel="nofollow">rectifying antenna</a> (rectenna) is supposed to convert electromagnetic energy to electric current however I do not understand how it's really working.</p>
<p>I do get that it's kind of like how transformer works, but beyond that I am... | 2,552 |
<ol>
<li><p>What causes <a href="http://en.wikipedia.org/wiki/Precession" rel="nofollow">precession</a> in a spinning object?</p></li>
<li><p>What causes <a href="http://en.wikipedia.org/wiki/Nutation" rel="nofollow">nutation</a> in a spinning object? </p></li>
<li><p>What causes a top, gyroscope, and the earth to wobb... | 2,553 |
<p>This question appeared quite a time ago and was inspired, of course, by all the fuss around "LHC will destroy the Earth". </p>
<p>Consider a small black hole, that is somehow got inside the Earth. Under "small" I mean small enough to not to destroy Earth instantaneously, but large enough to not to evaporate due to ... | 2,554 |
<p>I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying, so here goes:</p>
<p>I am wondering what is known about QCD, or other field theories, i... | 2,555 |
<p>It's been a couple years since I've taken a physics class, and I have been wondering about this basically since I bought my car:</p>
<p>I drive a 2010 Honda Fit, which has a street weight of <a href="http://consumerguideauto.howstuffworks.com/2010-honda-fit-13.htm" rel="nofollow">approximately 2489 pounds</a> (1129... | 2,556 |
<p>I am sending a couple of questions which seem a bit more specific than others on this site, partially to probe if there is a point in doing so. Not sure what is the range of expertise here, and no way to find out without trying. This one is also not terribly focused, but nonetheless here goes:</p>
<p>I am wondering... | 2,557 |
<p><a href="http://en.wikipedia.org/wiki/Cooper_pair" rel="nofollow">Cooper pairs</a> are one of the models how <a href="http://en.wikipedia.org/wiki/Superconductivity" rel="nofollow">superconductivity</a> is explained.</p>
<p>What still baffles me is how a vibration of the crystal lattice (the so-called <a href="http... | 2,558 |
<p>I was revising the harmonic oscillator for my intro to quantum course and realised I'd sort of accepted a change of variable result without actually being able to get to it. It says:</p>
<p>The stationary state Schrodinger equation of energy $E$ is</p>
<p>$$-\frac{\hbar^{2}}{2m}\frac{d^{2}\psi}{dx^{2}}+\frac{1}{2}... | 2,559 |
<p>I would like to see what type of noise I would get if I used just the frequencies in my voice. I created a matlab array using <code>fft</code> to get a <code>[frequency,amplitude,phase]</code> array of my voice. I then to reproduced my vocal signal using $A*\cos(ft+\phi)$</p>
<p>I would like to take this file/data ... | 2,560 |
<p>I know that the direction of torque is along the axis of rotation, but would it be acceptable to say, for example considering a vertical thin rod in the x-y plane with a force acting on the bottom end towards the left, 'it is a clockwise torque about the centre of mass' (even though strictly speaking the torque's di... | 2,561 |
<p>Does anyone know of websites or texts that have an abundance of <a href="http://www.google.com/search?as_q=Wick%27s+theorem+examples" rel="nofollow">examples</a> of computing time-ordered products of fields using <a href="http://en.wikipedia.org/wiki/Wick%27s_theorem" rel="nofollow">Wick's Theorem</a> for both boson... | 2,562 |
<p>I have been thinking is it possible that using a rather strong magnet on the human body's blood stream we could enact a small case of artificial gravity on the human body via the iron in the hemoglobin in the blood stream. </p>
<p>There are 4 Problems currently with this theory:</p>
<ol>
<li>The could be residual ... | 2,563 |
<p>I have specific questions about Lorentz transformations specifically about length contraction.</p>
<ol>
<li><p>Why does length contraction only occur in the direction of travel, (not in all directions) when approaching the speed of light?</p></li>
<li><p>From an outside observer's perspective watching an object tra... | 2,564 |
<p>When you have a drink with an ice cube and twirl the glass, the liquid itself seems to twirl but the ice cube stays roughly in the same place. Why is this?</p> | 2,565 |
<p>What happens with very small spherical objects ($d=1\mu m$, e.g. a bacterium) in air? Do they fall? How quickly? Does it depend on their mass?</p>
<p>We often see objects of little mass e.g. leaves falling from trees, but these object ususally have a very large surface, so their behaviour is very different to spher... | 2,566 |
<p>I have a question with conformal field theory in Polchinski's string theory vol 1 p. 51.</p>
<p>For $bc$ conformal field theory
$$ S=\frac{1}{2\pi} \int d^2 z b \bar{\partial} c $$
$$ T(z)= :(\partial b) c: - \lambda \partial (: bc:) $$
with central charge $c=-3 (2 \lambda-1)^2 +1 =1$. Introducing $\psi$ and $\ba... | 2,567 |
<p><img src="http://i.stack.imgur.com/BB7m9.jpg" alt=""></p>
<p>Hello everyone.</p>
<p>Imagine an object moving around a certain point on a circular orbit. Magnitude of the velocity is constant during the motion ($|v|$). The orbit radius is $r$. (I'd better notice that we're just talking about <strong>kinematic</stro... | 2,568 |
<p>Long before statistical mechanics, entropy was introduced as:</p>
<p>$dS = \frac{dQ}{T}$</p>
<p>At the time when entropy was introduced in this manner, was it known that entropy represents how "disordered" a system is? If so, how can one tell that entropy represents the disorder of a system from the above definit... | 2,569 |
<p>This is based off question 4.30 from Griffith's <em>Introduction to Quanum Mechanics</em>. It asks for the matrix $\textbf{S}_r$ representing the component of spin angular momentum about an axis defined by: $$r = \sin{\theta}\cos{\phi}\hat{i}+\sin\theta\sin\phi\hat{j}+\cos\theta\hat{k}$$</p>
<p>for a spin = $1/2$ p... | 2,570 |
<p>The 2D vector field (x,-y) does not transform like a vector under rotation(Arfken Vol. 1)! Does this mean we cannot have such a vector field physically?</p> | 2,571 |
<p>The EEP is used to justify that if an observer on the ground shoots a beam of light towards a tower, then when the light reaches the tower, it will be red shifted. This is because of what happens in an accelerating spaceship.</p>
<p>The books seem to say this implies time dilation, but I don't completely see why. C... | 2,572 |
<p>When two wavefunctions are orthogonal we can write that</p>
<p>$$\langle\Psi_n|\Psi_m\rangle=\delta_{mn}$$</p>
<p>This means that </p>
<p>$$\langle\Psi_1|\Psi_2\rangle=\langle\Psi_2|\Psi_1\rangle=0$$</p>
<p>But if the two wavefunctions aren't orthogonal but $\langle\Psi_1|\Psi_2\rangle=d \in\mathbb{R}$ is real, ... | 2,573 |
<p>Why do some conductors follow <a href="http://en.wikipedia.org/wiki/Ohm%27s_law" rel="nofollow">Ohm's law</a> and some do not? Isn't there any universal law that can explain the flow of current?</p> | 2,574 |
<p>Wikipedia defines the <a href="http://en.wikipedia.org/wiki/Willmore_energy" rel="nofollow">Willmore energy</a> as: </p>
<p>$$e[{\mathcal{M}}]=\frac{1}{2} \int_{\mathcal{M}} H^2\, \mathrm{d}A,$$</p>
<p>where $H$ stands for the mean curvature of the manifold $\mathcal{M}$.</p>
<p>What is the Willmore energy of the... | 2,575 |
<blockquote>
<p>A ball moving with velocity $1 \hat i \ ms^{-1}$ and collides with a friction less wall, afetr collision the velocity of ball becomes $1/2 \hat j \ ms^{-1}$. Find the coefficient of restitution between wall and ball.</p>
</blockquote>
<p>I approached it like: </p>
<p><img src="http://i.stack.imgur.... | 2,576 |
<p>Calculate the potential and the intensity of the gravitational field at a distance $x> 0$ in the axis of thin homogeneous circular plate of radius $a$ and mass $M$.</p>
<p><img src="http://i.stack.imgur.com/nSXTf.png" alt="enter image description here"></p>
<p>Could anybody describe how to calculate this? Slowl... | 313 |
<p>In the derivation of the Poisson-Boltzmann equation, my <a href="http://rads.stackoverflow.com/amzn/click/0716787598" rel="nofollow">textbook</a> arrives at the expression</p>
<p>$$
\rho_i = c_+ z_+ F + c_-z_-F = c_+^oz_+^oFe^{-z_+e\phi_i/kT} + c_-^oz_-Fe^{-z_-e\phi_i/kT}
$$</p>
<p>where $c_\pm$ is the concentrati... | 2,577 |
<p>I have came across this equation for <a href="http://en.wikipedia.org/wiki/Quantum_harmonic_oscillator" rel="nofollow">quantum harmonic oscillator</a></p>
<p>$$
W \psi = - \frac{\hbar^2}{2m}\frac{d^2\psi}{dx^2} + \frac{1}{2} m \omega^2 x^2 \psi
$$</p>
<p>which is often remodelled by defining a new variable $\varep... | 2,578 |
<p>Ok, let me make myself clear. I saw all the other questions related to the question, but none of them actually asks the question the way I would put it and therefore no one answers it the way I want it answered, so here it is, I'll try to formulate it.</p>
<p>I perfectly understand that every single point in the Un... | 2,579 |
<p>If two black holes collide and then evaporate, do they leave behind two naked sigularities ore? If there are two, can we know how they interact?</p> | 2,580 |
<p>How to calculate number of exchanged virtual pohotons per unit of time between two electromagnetically interacting objects?</p> | 2,581 |
<p>This <a href="http://arxiv.org/abs/1302.6165" rel="nofollow">paper</a> proposes a microscopic mechanism for generating the values of $c, \epsilon_0, \mu_0$. They state that their vacuum is assumed to contain ephemeral (meaning existing within the limits of the HUP) fermion/antifermion pairs. This affects the mecha... | 2,582 |
<p>VEVs of Wilson loops in Chern-Simons theory with compact gauge groups give us colored Jones, HOMFLY and Kauffman polynomials. I have not seen the computation for Wilson loops in Chern-Simons theory with non-compact gauge groups. I think that what keep us from computing them is due to infinite dimensional representat... | 2,583 |
<p>How do I derive the General Linear Wave Equation $$d^2y/dx^2=(1/v^2)d^2y/dt^2?$$ </p>
<p>My teacher differentiated the general wave function $f(x + vt)+g(x - vt)$ twice with respect to both variables to get $d^2y/dx^2$ and $v^2d^2y/dt^2$, and then somehow combined them to get $$d^2y/dx^2=(1/v^2)d^2y/dt^2,$$ but I d... | 2,584 |
<p>The RPP note on quarks masses has traditionally carried, and it is still there, the comment that</p>
<blockquote>
<p>It is particularly important to determine the quark mass ratio mu/md,
since there is no strong CP problem if $m_u$ =
0.</p>
</blockquote>
<p>But in <a href="http://pdg.lbl.gov/2011/reviews/rpp... | 2,585 |
<p>I guess I never had a proper physical intuition on, for example, the "<a href="http://en.wikipedia.org/wiki/KMS_state" rel="nofollow">KMS condition</a>". I have an undergraduate student who studies calculation of Hawking temperature using the Euclidean path integral technique, and shamefully his teacher is not able ... | 2,586 |
<p>Suppose we try to apply supersymmetry in quantum mechanics to a particular potential. If you come up with two partner potentials, and two partner Hamiltonians, and then look at the energy of the ground state, is it true that at most one of them can be zero?</p>
<p>If they are both zero, does that mean that supersym... | 2,587 |
<p>It seems most books about QM only talk about position and momentum operators. But isn't it also possible to define a acceleration operator? </p>
<p>I thought about doing it in the following way, starting from the definition of the momentum operator:</p>
<p>$\hat{p} = -i\hbar \frac{\partial }{\partial x}$</p>
<p>T... | 2,588 |
<blockquote>
<p>A particle travels with speed $50 m/s$ from the point $(3,-7)$ in the
direction $7i-24j$ . Find its positional vector after 3 seconds.</p>
</blockquote>
<p><strong>My approach</strong>:
It has travelled a distance of 150m in the direction given by the unit vector $\frac{7\hat i - 24 \hat j}{25} $
.... | 2,589 |
<p>When placing ice cubes in a fizzy drink such as Prosecco, ice makes a cracking sound, after which the fizzy bubbles more than usual. What is the physics of this phenomenon?</p>
<p><img src="http://i.stack.imgur.com/hKlxy.jpg" alt="enter image description here"></p> | 2,590 |
<p>Consider 3 particles. All 3 particles travel along the x-axis.</p>
<ul>
<li>The 1st particle possesses some mass, m, and its initial position is somewhere on the negative x-axis. It has some (positive) velocity v.</li>
<li>The 2nd particle possesses some mass, A*m, and its initial position is at the origin of the x... | 2,591 |
<p>So I gather the way you (and Vera Rubin) calculate a galaxy's mass is by measuring a star's orbital velocity $v$ and its distance $R$ from the galactic center, and then plugging them into this equation derived from Newton's second law:</p>
<p>$$M_{gal}=Rv^2/G$$</p>
<p>($G=6.67\times10^{-11}$. Units of $v$ and $R$ ... | 2,592 |
<p>Noether's theorem says that if the following transformation is a symmetry of the Lagrangian</p>
<p>$t \to t + \epsilon T$</p>
<p>$q \to q + \epsilon Q$</p>
<p>Then the following quantity is conserved</p>
<p>$\left( \frac{\partial L}{\partial \dot{q}}\dot{q} - L \right) T - \frac{\partial L}{\partial \dot{q}} Q$.... | 2,593 |
<p>I am trying to obtain the polchinski's equation 4.3.16
which is following</p>
<p>$ Q_B^2 = \frac{1}{2}\{ Q_B, Q_B \} = -\frac{1}{2}g^{K}_{IJ}g^{M}_{KL}c^Ic^Jc^L b_M =0$</p>
<p>Where
$ Q_B = C^I(G_I^m +\frac{1}{2}G_I^g)$
and $C^I$, $b^J$ are anticommuting(ghosts)</p>
<p>and
$[G_I, G_J]=ig^K_{IJ} G_K$,<br>
$G_... | 2,594 |
<p>I have a series of number theoretic phenomena (mathematics) that I can describe exactly by the superpositions or linear combination of the below function (I know it is an inverse Fourier type). Does anybody knows from parallels in physics (quantum, particle, waves) where exactly this function is applied? Are there p... | 2,595 |
<p>My friend and I had a little discussion about <a href="http://en.wikipedia.org/wiki/Added_mass" rel="nofollow">added mass forces</a>. </p>
<p>I always interpreted $F=ma$ as a cause-effect relationship, so I find rather uneasy to accept that the cause can instantaneously depend on the effect.</p>
<p>Is it fine to h... | 2,596 |
<p>I'm confused about the Kronecker delta. In the context of four-dimensional spacetime, multiplying the metric tensor by its inverse, I've seen (where the upstairs and downstairs indices are the same):</p>
<p>$$g^{\mu\nu}g_{\mu\nu}=\delta_{\nu}^{\nu}=\delta_{0}^{0}+\delta_{1}^{1}+\delta_{2}^{2}+\delta_{3}^{3}=1+1+1+1... | 2,597 |
<p>Triangle defined by points <strong>OA</strong>, <strong>OB</strong> and <strong>OC</strong> : (-<strong>i</strong>,3 <strong>j</strong>,-4 <strong>k</strong>), (<strong>i</strong>,2 <strong>j</strong>,2 <strong>k</strong>) and (3 <strong>i</strong>,7 <strong>j</strong>,- <strong>k</strong>) where <strong>i</strong>,... | 2,598 |
<p>While looking through the questions, a came across a section about black holes. I immediately though; what would happen if an atom is orbiting a black hole and emitted a photon perpendicular to the event horizon, going away from the black hole. </p>
<p>How would light going away from a black hole react to the gravi... | 2,599 |
<p>Consider a cube of ice in a flat based container(the base is very broad).The temperature of the system is at first fixed at a minus Celsius temperature, but then the system is left on a table with the top open to atmosphere.<br>
The ice starts melting, and finally there is only water, spread over the container's bas... | 2,600 |
<p>I am reading some lecture notes which demonstrate how various models in <strong>SUSY QM</strong> can be used to obtain topological invariants such as the Euler characteristic from the Witten Index. </p>
<p>The following lagrangian has been used directly, said to be the supersymmetric generalization of the bosonic $... | 2,601 |
<p>I've observed many times that if you drop a lot of a 'granular' substance in one place and keep the nozzle out of which the substance flows, that the shape of the pile created very much resembles a bell curve. The situation is a bit hard to explain so for example image somebody holding a small pipe vertically above ... | 2,602 |
<p>Calculate the probability current density vector $\vec{j}$ for the wave function : $$\psi = Ae^{-i(wt-kx)}.$$</p>
<p>From my very poor and beginner's understanding of probability density current it is :</p>
<p>$$\frac{d(\psi \psi^{*})}{dt}=\frac{i\hbar}{2m}[\frac{d\psi}{dx}\psi^{*}-\frac{d\psi^{*}}{dx}\psi]$$</p>
... | 2,603 |
<p>Consider a single isolated rotating mass (for example planet), is it possible to extract energy out of its rotation? If yes, how could that theoretically be achieved?</p> | 2,604 |
<p>Consider you have a quantum field theory that undergoes spontaneous symmetry breaking at some critical temperature. It doesn't necessarily have to be a continuous symmetry that's broken, I don't think that matters for my question. For simplicity, think of the field being a scalar field.</p>
<p>I (think I) do unders... | 2,605 |
<p>This may look like a philosophical question, but I'm looking for physical explanations (if there's any), that's is why I'm asking it here.</p>
<p>What is the ability of thinking? We are all creatures consist of flesh and bones. Our brains are also nothing but flesh and water? Why are we thinking? What happens to th... | 2,606 |
<p>Are there any known potentially useful, nontrivial, irreducible representations of the Lorentz Group $O(3,1)$ of dimension more than $4$? Examples? A $5$-dimensional representation? EDIT: Is there some deep reason why higher-dimensional representations (other than infinite-dimensional representations) are less usefu... | 2,607 |
<p>I don't understand how the zeroth order intensity maximum works. The intensity of a transmission diffraction grating is:</p>
<p>$$I=I_0\sin^2(β/2)/(β/2)^2\sin^2(Nγ/2)/\sin^2(γ/2)$$</p>
<p>Where $γ =kd\sin(θ)$, $β=kb\sin(θ)$, $d$ is the grating constant and $b$ is slit width. For the zeroth order intensity maximum,... | 2,608 |
<p>So based on the topic, this is the question.</p>
<p>"A particle with mass $m$ is moving along x-axis with $v_0$ at $t=0$ and $x=0$. The particle is acted by an opposing force with magnitude proportional to the square of velocity. Find out the a) velocity b) position and c) acceleration of particle at any time ($t&g... | 2,609 |
<p>What kinds of inconsistencies would one get if one starts with Lorentz noninvariant Lagrangian of QFT? The question is motivated by <a href="http://arxiv.org/abs/1203.0609" rel="nofollow">this preprint arXiv:1203.0609</a> by Murayama and Watanabe. </p>
<p>Also, what is the basic difference between </p>
<ul>
<li><p... | 2,610 |
<p>While searching, i found this page: <a href="http://timesofindia.indiatimes.com/home/stoi/Why-does-a-magnet-attract-iron/articleshow/4298171.cms" rel="nofollow">http://timesofindia.indiatimes.com/home/stoi/Why-does-a-magnet-attract-iron/articleshow/4298171.cms</a> but it does not have full explanation. So Please tel... | 2,611 |
<p>Is there any formulated lagrangian (density) for M-theory? If not, why is there no lagrangian?</p>
<p>If not, is this related to many vacua existing?</p>
<p>Thnx.</p> | 2,612 |
<p>Why are ceramic containers used for hot beverages? For example, is it dangerous to use plastic? Are there any other reasons other than to protect hands from heat?</p> | 2,613 |
<p>I'm reading the book "Fundamental Physics 2: Electromagnetism" by Alonso and Finn.
I understand everything up to the point where everything is "unified".</p>
<p>The following example is given in the book:</p>
<blockquote>
<p><em>Take 2 observers $O$ and $O'$ that are moving with a constant velocity $v$ relative ... | 2,614 |
<p>I have an object in free space (no gravity) with angular momentum $ = \omega_i $, and some velocity vector $=\vec{V_i}$. To simplify we will say it has a mass-less rigid rod length $ = \ell $, connecting two small masses both of mass $ = M $. The masses are small in the sense of a radius equal to the rod radius both... | 2,615 |
<p>I came across a method for writing the constraint equations known as "The Virtual Work Method".I am quoting the exact language of the text(well,not exactly the exact)-</p>
<blockquote>
<p>Consider the atwood machine shown.When one holds both the masses such that the string is slack,there is no tension.Once releas... | 2,616 |
<p>In high-school level books (for example the german standard text: "Dorn-Bader") I have often seen an explanation of the Lorentz force as on the following picture:</p>
<p><img src="http://i.stack.imgur.com/eHiQk.gif" alt="enter image description here"></p>
<p>The textbooks consider the superposition of the circular... | 2,617 |
<p>It's interesting because we don't normally consider the "vaccuum of space" as a fluid, but it's becoming more apparent that it's an ocean of subatomic stuff.</p>
<p>Here's a link to a book: <a href="http://rads.stackoverflow.com/amzn/click/1463441541" rel="nofollow">Unified Fluid Dynamic Theory Of Physics</a></p>
... | 2,618 |
<ol>
<li><p>Can anyone outline the theory of plane wave <a href="http://en.wikipedia.org/wiki/Born_approximation" rel="nofollow">Born approximation</a> for direct nuclear reactions in detail?</p></li>
<li><p>Also What are the modification introduced in the distorted wave Born approximation?</p></li>
</ol>
<p>I was una... | 2,619 |
<p>I personally cringe when people talk about scientific theories in the same way we talk about everyday theories. </p>
<p>I was under the impression a scientific theory is similar to a mathematical proof; however a friend of mine disagreed. </p>
<p>He said that you can never be absolutely certain and a scientific <a... | 2,620 |
<p>Why are all observable <a href="http://en.wikipedia.org/wiki/Gauge_theory" rel="nofollow">gauge theories</a> not vector-like? </p>
<p>Will this imply that the electron and/or fermions do not have mass? </p>
<p>How is this issue resolved? </p>
<p>Background: </p>
<p><a href="http://en.wikipedia.org/wiki/The_S... | 2,621 |
<p>I'm studying the oscillations of systems with more than one degree of freedom from Landau & Lifshitz's <em>Mechanics</em> Third Edition (for those who have the book, my question corresponds roughly to explaining the last paragraph before equation 23.9).</p>
<p>First I give a brief background to my problem to sh... | 2,622 |
<p>This is a question about the negative energy solutions to the free particle Dirac Equation in the first quantized picture. We need both the positive and negative energy solutions to have a complete set of states.</p>
<p>For example, the bound states of the hydrogen atom consists of superpositions of positive and n... | 2,623 |
<p>A DIY fractal antenna project is described at <a href="http://www.htpc-diy.com/2012/04/diy-flexible-fractal-window-hdtv.html" rel="nofollow">http://www.htpc-diy.com/2012/04/diy-flexible-fractal-window-hdtv.html</a></p>
<p>Mainly idle curiosity, but I was wondering what the principles behind these might be, and if t... | 2,624 |
<p>A question is given as </p>
<blockquote>
<p>Consider a fluid of density $ \rho(x, y, z, t) $ which moves with velocity $v(x, y, z, t) $ without sources or sink. Show that $ \nabla \cdot \vec J + \frac{\partial \rho }{\partial t} = 0 ;$ where $ \vec J = \rho \vec v \hspace{0.5 cm}$ ( $\vec v$ being velocity of fl... | 2,625 |
<p>I'm familiar with the equations for friction for a static object and an object moving at steady speed over a surface from high school physics. But we never learned how an object moving only due to momentum experiences friction. This is something I've modeled several times while building simple 2D games, but I have n... | 2,626 |
<p>Does the <a href="http://en.wikipedia.org/wiki/Casimir_effect" rel="nofollow">Casimir Effect</a> violate the <a href="http://en.wikipedia.org/wiki/Quantum_inequalities" rel="nofollow">Quantum Inequalities</a>? From what I understand, the Casimir Effect is able to produce negative energy densities for an indefinite a... | 2,627 |
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