question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>The generalized 2-qubit state is given as:
$$ \rho = \frac{1}{4}[ I\otimes I + (m_x\sigma_x + m_y\sigma_y + m_z\sigma_z)\otimes I + I \otimes (n_x\sigma_x + n_y\sigma_y + n_z\sigma_z) + \sum_{ij}t_{ij}\sigma_i\otimes\sigma_j] $$</p>
<p>Then, is there a method to map a given density matrix:
$$ \rho_g = \pmatrix{... | g7500 | [
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<p>Recently, some experiments show that the supersymmetry is not realised by Nature according to the simple models that we currently have. Nevertheless, it is far from saying that the "game is over" as SUSY might be realised at an unknown energy. I would like to ask what are the experiments that could give us a clue wh... | g7501 | [
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<p>I need two formulas in dealing with ice and water. </p>
<p>First:<br>
If I have 2 x 2 x 2 (cm) ice cube, after it melts, how much water will there be ?</p>
<p>Second:<br>
If I have 2 x 2 x 2 (cm) ice cube, after how much time will it melt ?</p>
<p>I know that there are many variables: temperature, density and so... | g7502 | [
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<p>I would like to pick the correct doping of silicon to get 1 Mohm cm resistivity at liquid helium temperature of 4.2 K. The metal insulator transition implies that I need a very accurate doping. Are there any other effects and is there a way to calculate the correct doping?</p> | g7503 | [
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<p>My question is even though photons have no (rest) mass, do they emit a external force due to EM radiation causing electrons to be excited and jump to higher energy shells which electrons have mass thus photons can emit a kinetic force? I am new so I would like to get the record straight on this issue. </p> | g7504 | [
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<p>Understanding on <a href="http://en.wikipedia.org/wiki/Quantum_entanglement" rel="nofollow">quantum entanglement</a>? I am very vague on this topic and would appreciate a detailed explanation on this phenomenon.
Also what are the possible applied uses for quantum entanglement? What are the problems of putting this p... | g250 | [
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<p>I just tried to calculate the magnetic moment of a proton. I took the </p>
<p>proton <a href="http://en.wikipedia.org/wiki/G-factor_%28physics%29" rel="nofollow">g-Factor</a> of $g=5.585694$ <br>
<a href="http://en.wikipedia.org/wiki/Nuclear_magneton" rel="nofollow">nuclear magneton</a> of $\mu_k = 5.050783 * 10^{−... | g7505 | [
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<p>Given two identical microphones arranged in an ideal XY pattern, recording a single sound source at equal distance from both capsules, the two signals obtained are equal in amplitude, perfectly in phase with each other, and distorted identically by microphone frequency response. Therefore, other than small differenc... | g7506 | [
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<p>I know <a href="http://en.wikipedia.org/wiki/Quantum_computer" rel="nofollow">quantum computers</a> are very complicated and my question is is there any way in "Principle" to create one? Are there already quantum computers being created?</p> | g7507 | [
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<p>Google has no results found for "energy not proportional to frequency" and many results for E=hf. Is there an example of an energy that is not proportional to frequency?</p> | g7508 | [
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<p>It was established by Dennis, Kitaev et al. that the 2D Toric Code
can be mapped to a 2D Random Bond Ising Model. The original derivation
was given in the paper "Topological quantum memory" which can be found in
J. Math. Phys. 43, 4452 (2002); doi: 10.1063/1.1499754 or online at <a href="http://dx.doi.org/10.1063/... | g7509 | [
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<p>What would the calculation look like when computing the wind pressure of a moving vehilce versus compressed air pressure pushing against the the moving vehicle, how much compressed air pressure would be needed to combat the wind of the moving vehicle.?</p> | g7510 | [
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<p>I've read a classbook on the field theory (including EM): it perfectly describes quantitive patterns in EM-theory, but I have no luck understanding how and why it works.</p>
<p>I mean, magnetic substances are described mainly by magnetic moments of electrons, but all explanations of the phenomenon I've found are ra... | g7511 | [
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<p>I've been working through the derivation of quantities like Gibb's free energy and internal energy, and I realised that I couldn't easily justify one of the final steps in the derivation. </p>
<p>For instance, in deriving the formula for Gibb's Free Energy, we first found the differential equation:</p>
<p>$$dG = d... | g7512 | [
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<p><a href="http://en.wikipedia.org/wiki/Fermi_energy" rel="nofollow">Wikipedia</a> states the definition of Fermi energy as for "a system of non-interacting fermions". If we have to assume free electrons in a solid behave this way before we are able to calculate Fermi energy, how can Pauli exclusion be justified (beca... | g7513 | [
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<p>Is Helmholtz's 1870 paper "<a href="https://www.degruyter.com/view/j/crll.1870.issue-72/crll.1870.72.57/crll.1870.72.57.xml" rel="nofollow">Ueber die Bewegungsgleichungen der Elektricität für ruhende leitende Körper</a>," <em>Journal für die reine und angewandte Mathematik</em> <strong>72</strong>:57-129 translated... | g7514 | [
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0.067709207534790... |
<p>Related to <a href="http://physics.stackexchange.com/questions/83633/how-trustworthy-are-numerically-obtained-periodic-solutions-to-the-three-body-pr?rq=1">this post</a></p>
<p>Just out of curiosity, I have a question about the current status of classical (Newtonian) three-body gravitional numerical simulation. I f... | g7515 | [
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<p>For industrial furnaces, in order to improve radiation heat transfer and save energy, some people say applying a high emissivity coating on to the interior surface of a furnace will do, while some people say applying a high reflectivity coating will do. we all know that at given wavelength and for an opaque object s... | g7516 | [
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<p>I'm puzzled about what should be the normal ordering of the identity operator (or any proportional operator):</p>
<ul>
<li>looking at it from the "Fock space operators POV",the prescription is to move all the creation operators to the left and the annihilators to the right, but the identity by definition as non of ... | g7517 | [
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<p>On page 237 in PS we have (the unnumbered equation after eq. 7.58)</p>
<p>$$\mathcal{P} \sim \frac{iZ}{p^2-m^2-iZ\,\mathrm{Im}M^2(p^2)}$$</p>
<p>but after deriving it myself I obtained</p>
<p>$$\mathcal{P} \sim \frac{iZ}{p^2-m^2-iZ\,\mathrm{Im}M^2(p^2)-iZ\frac{\mathrm{d}\,\mathrm{Im}\, M^2}{\mathrm{d}\,p^2}\cdot(... | g7518 | [
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<p>We have electric charge density $\rho(r) = kr$ in a cylinder of infinite height and radius $a$.</p>
<p>I'm asked to find the electric field.</p>
<p>I'm doing it using two methods and I don't undesrtand why then don't yield the same result</p>
<p><strong>Method 1</strong></p>
<p>Gauss' theorem applied to a cylind... | g7519 | [
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<p>What is the cause of <a href="http://en.wikipedia.org/wiki/Centripetal_force">centripetal</a>/<a href="http://en.wikipedia.org/wiki/Centrifugal_force">centrifugal</a> force? When an object of mass $m$ is moved in a circular orbit, it experiences a centrifugal force radially away from the center. What is the cause of... | g7520 | [
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<p>I learned $F = iLB$ recently. However, I don't understand why $L$ is marked as a vector but $i$ is not.<br>
For a normal rod, how should I define the direction of length vector $L$? And if I reverse the current in it, the force exerted on it by the magnetic field would reverse direction, correct?<br>
So I think in t... | g7521 | [
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<p>A guy <a href="http://stackoverflow.com/a/4888033/56541">suggested to me</a> that getting speed from an accelerometer required the use of this equation:</p>
<p>$\text{speed} = \sqrt{x^2 + y^2 + z^2}$</p>
<p>This does not make any sense to me, all that you would get from this equation would be the magnitude in $m/s... | g7522 | [
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<p>I have a question regarding the $E$ vs $k$ curve in the first Brillouin zone. Why does the curve have an inflection point at some value of $k$ in the curve?
How does it physically support it?</p>
<p><img src="http://i.stack.imgur.com/Y4DGl.jpg" alt="E vs k"></p> | g7523 | [
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<p>I understand the first law-elliptical orbits, and the second-equal area in same time, but I need help with the third one. Note that I am not in an AP course or taking calculus at the moment so simple quadratics/cubics/CP level explanations would suffice.</p> | g7524 | [
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<p>I'm not asking about how we worked backward from an expanding universe to the age of the big bang, but rather what is the meaning of time in a near infinitely dense point in the context of general relativity? Wouldn't time flow infinitely slowly for a theoretical (though physically impossible) observer?</p> | g7525 | [
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<p>What latitude is needed before you can reliably see the globular cluster <a href="http://en.wikipedia.org/wiki/Omega_Centauri" rel="nofollow">Omega Centauri</a>, say it reaches 20 degrees above the horizon? What about if you are up on a hill looking down, what's the theoretical highest latitude where you could have... | g7526 | [
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<p>After reading up on irregular moons in the solar system - moons that are thought to be captured, most seem to be in retrograde orbit around their parent body. That led me to wonder if retrograde orbits are easier to capture objects than prograde orbits - say prograde orbits are more likely to gravitationally slingsh... | g7527 | [
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<p>Millisecond pulsars are supposed to be old neutron stars. However, they are spinning even more rapidly than newly formed pulsars. Since pulsars slow down as they age, something must have caused these older pulsars to "spin up" and be rotating as fast as they are. What is the mechanism for doing so?</p> | g7528 | [
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<p>Where can I find <a href="http://en.wikipedia.org/wiki/Public_domain" rel="nofollow">public domain</a> astronomical pictures of <a href="http://en.wikipedia.org/wiki/Nebula" rel="nofollow">nebulae</a>, <a href="http://en.wikipedia.org/wiki/Star" rel="nofollow">stars</a>, etc. that can be freely used?</p> | g7529 | [
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<p>If I wanted to explore a <a href="http://en.wikipedia.org/wiki/Discrete_mathematics" rel="nofollow">discrete mathematics</a> approach to <a href="http://en.wikipedia.org/wiki/Continuum_mechanics" rel="nofollow">continuum mechanics</a>, what textbooks should I look into? </p>
<p>I suppose a ready answer to the quest... | g38 | [
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<p><strong>tl;dr</strong></p>
<p>Is there any meaningful (physical) way to compare the energy expended in the exercise of doing $x$ pushups in $t_1$ seconds, vs the exercise of doing the plank for $t_2$ seconds?</p>
<hr/>
<p>I'm confused about the concepts of energy, work, and power, in the case where no distance is... | g7530 | [
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<p>For example, could the numbers / letters on a postage stamp in a randomly specified location be clearly visible from space.</p>
<p>This is to settle a discussion with a friend that piqued my curiosity. </p> | g7531 | [
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<p>I was thinking about my answer to <a href="http://physics.stackexchange.com/questions/25431/are-the-inner-planets-on-planar-orbits-because-there-was-more-dust-in-the-inner">Are the inner planets on planar orbits because there was more dust in the inner solar system (early on in planetary accretion)?</a>
- when it oc... | g7532 | [
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<p>As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought of, then it was found.</p>
<p>Einstein's relativity is middle ground to me, he thought of light beams at the speed ... | g7533 | [
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<p>As I understand it, Stars emit visible light, OBAFGKMRNS, in the range of $10^3 - 10^4 K$.
Yet materials such as steel emit similar frequencies at much lower temps; red is around 800K.
Why the difference? I thought black body radiation applies to all materials and environments.
I am an interested amateur. </p> | g7534 | [
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<p><img src="http://i.stack.imgur.com/uCrT3.jpg" alt="enter image description here"></p>
<p>The current I is flowing upward in the wire in this figure. The direction of the magnetic filed due to the current can be determined by the right hand rule.</p>
<p>Can we determine the north and the south of the magnetic field... | g7535 | [
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<p>Quantum phase arises when a spin-j state is sent through a sequence of transitions that return it to its original position. For example with spin-1/2, a state picks up a complex phase of $\pi/4$ when it goes through three perpendicular (not orthogonal!) transitions:</p>
<p>$\frac{<+z|+y><+y|+x><+x|+z... | g7536 | [
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<p>If the universe didn't have the relativity principle, would it be able to support life?</p>
<p>Life consists of very complicated organisms. The operation of these organisms depends on the laws of physics.</p>
<p>If the laws of physics depended on absolute velocity, then it seems that life would have a more difficu... | g7537 | [
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<p>I just finished reading <a href="http://arxiv.org/abs/physics/0507125" rel="nofollow"> this research</a> about antimatter induced fusion and thermonuclear reactions.
And one conclusion I could make is that very little mass of antimatter (in range of micrograms) is needed to initiate a fusion reaction in lithium-deu... | g7538 | [
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<p>Several posts and my classes in thermodynamics equate increase in entropy with loss of information. Shannon clearly showed that the information content of a message is zero when its entropy is zero and that its information content increases with increasing entropy. So entropy increase leads to more information, wh... | g7539 | [
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<p>In my textbook there are 2 formulas for <a href="http://en.wikipedia.org/wiki/Electric_power" rel="nofollow">electric power</a>:</p>
<p>$$\begin{array}{cccr}
P &=& E/t &\hspace{10pt} (1) \\
P &=& VI. &\hspace{10pt} (2)
\end{array}$$</p>
<p>What is the difference between the 2 formulas? Do t... | g7540 | [
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0.0230... |
<p><img src="http://i.stack.imgur.com/kUyg1.png" alt="enter image description here"></p>
<p>A wheel rolling down a hill has two axis of rotation. One is where the center or mass is and the other is the point of contact with the surface which acts as a fulcrum. I was trying to understand how this happens, how it rotate... | g7541 | [
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<p>Say I do an an experiment 5 times, each of which gives you a list of data points. Do I fit a curve to each one separately and then average the parameters and their uncertainties? Or do I take the average of all the experiments and then do fit a single curve to that?</p> | g7542 | [
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<p>Let's say I have a triangular light source. From that light source I want to calculate a pyramidal frustum (tetrahedron with no apex). How would I calculate the maximum bottom area where light would be visible to the naked eye? And how would I calculate the apparent brightness?</p> | g7543 | [
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<p>In the newly released movie "Gravity" the main character is left alone floating in space in spacesuit, in a fast spin. Assuming there are no external forces (no tether, jet-pack etc) the system is closed and the initial angular momentum has to be preserved. However, can the astronaut change the axis of rotation? Say... | g7544 | [
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... |
<p>In other words, how strong does gravity have to be to cause Hawking radiation to occur?</p> | g7545 | [
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<p>I would like to know if mirrors have a quality of "resolution" to them like a regular photograph might, or like a JPEG does.</p>
<p>For example, if you looked to closely, or magnified a photograph, you would soon come to a point where the image blurs, or that which was too far away when photographed is not discerni... | g7546 | [
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<p>Let's look at the measurement problem in the orthodox interpretation of quantum mechanics as an inconsistency between inner and outer treatment of the measurement apparatus. You can always push your boundaries of treating the evolution of your system as unitary further and further. You can say OK, the universe as a ... | g7547 | [
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<p>Anyone have good mnemonics for remembering standard packets of data in physics?
Any field within physics would be welcomed. Examples of such "packets":</p>
<ul>
<li><p>data in the standard model of particle physics</p></li>
<li><p>charges/masses of common subatomic particles and light atoms</p></li>
<li><p>cosmolo... | g7548 | [
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<p>Would an object like a wooden bed interfere or block the signal coming from a 802.11 wireless router?</p> | g7549 | [
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... |
<p>We found that water with salt, sugar, or baking soda dissolved in it cools faster than pure water.<br>
Water has a very high specific heat; how do these solutes lower it?</p>
<p>We heated a beaker (300ml) of water to 90° C and let it cool, checking the temperature every 5 minutes. We repeated the experiment adding... | g266 | [
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<p>I've just come across Krasinsky and Brumberg's <a href="http://iau-comm4.jpl.nasa.gov/GAKVAB.pdf" rel="nofollow">paper</a> that claims, from an analysis of radiometric measurements, that the astronomical unit (earth-sun distance) is increasing at the rate:</p>
<p>$$\frac{d}{dt}AU = 15 \pm 4 \ m/yr.$$</p>
<p>If on... | g251 | [
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<p>I can find the energy of a spring using $F = -kx$, or by using the formula $e = 1/2mv^2 + 1/2I\omega^2 + mgh + 1/2kx^2$. The first way, I get $mg/k = x$, but the second way, I get $2mg/k = x$. Which one is correct to use and why?</p>
<p>This is assuming that there is no angular velocity or linear velocity. </p> | g7550 | [
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<p>Let $\hat{x} = x$ and $\hat{p} = -i \hbar \frac {\partial} {\partial x}$ be the position and momentum operators, respectively, and $|\psi_p\rangle$ be the eigenfunction of $\hat{p}$ and therefore $$\hat{p} |\psi_p\rangle = p |\psi_p\rangle,$$ where $p$ is the eigenvalue of $\hat{p}$. Then, we have $$ [\hat{x},\hat{p... | g7551 | [
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-... |
<blockquote>
<p>Is there any case of potential $V$, such that the continuity of the operator
$H=c\ \Delta+V$
is not spoiled? </p>
</blockquote>
<p>And I don't know any non-differnetial operator examples for continous spectra. I guess I don't know the full spectrum of operators (ba dum tss!).</p>
<p>My question ... | g7552 | [
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<p>There is the idea that there is no time in a completely closed (thus unobservable) system. Within such a system, a subsystem may be imagined to be split off by some virtual boundary. However, one wants to continue to consider the remaining system as if it was the complete system (which of course is not correct). In ... | g7553 | [
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<p>For a pure species, the equlibrium between liquid phase and vapour phase is given by the equality of molar Gibbs energy in both phase:</p>
<p>$$\underline{G}^l=\underline{G}^v$$</p>
<p>Where $\underline{G}$ with an underline represents molar Gibbs energy.</p>
<p>In a multicomponent system, the equilibrium criteri... | g7554 | [
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... |
<p>Noether's Theorem states that if a Lagrangian is symmetric for a certain transformation, this leads to an invariant: Symmetry of translation gives momentum conservation, Symmetry of time gives Energy conservation etc.</p>
<p>The Galilean principle stating that all reference frames that move with constant speed rel... | g252 | [
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<p>I have a volume which is deforming (using explicit time-integration scheme) uniformly with velocity gradient $L$ and stress tensor $\sigma$. I would like to determine work done by the volume deformation during one timestep $\Delta t$, knowing both current and previous values of $L$, $\sigma$ and volume $V$.</p>
<p>... | g7555 | [
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0.0... |
<p>I listen to the radio via my iPad with wifi. When I switch the microwave oven on, the radio cuts out. When the microwave oven is finished, the radio comes back on. (This is 100% reproducible!)</p>
<p>So - is it (as I suspect) the microwave oven affecting the wifi? If so, how can that happen (I thought microwaves co... | g7556 | [
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<p>Since low-energy, non-relativistic thermal field theories are defined in Euclidean spacetime, while high-energy relativistic theories are define in Minkowski spacetime, I was wondering if there are renormalization methods that can show such a change in metric signature.</p> | g7557 | [
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<p>I am interested in the pratical method and I like to discover
if it is cheap enough to be done as an experiment in a high school.
Thank you.</p> | g7558 | [
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<p>Perhaps someone can suggest the right terms for the following mathematical objects related to moment of inertia?</p>
<ol>
<li>A <em>inertia tensor</em> $I$. $$I \equiv \begin{bmatrix} I_{1,1} & I_{1,2} & I_{1,3} \\ I_{2,1} & I_{2,2} & I_{2,3} \\ I_{3,1} & I_{3,2} & I_{3,3} \\\end{bmatrix}$$<... | g7559 | [
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<p>I am an undergraduate physics student. I have a question in approximation methods for time-dependent problems in quantum mechanics. I read the proof of the <a href="http://en.wikipedia.org/wiki/Adiabatic_theorem" rel="nofollow">adiabatic theorem</a> but I didn't understand it. This theorem states:</p>
<blockquote>
... | g7560 | [
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0.04... |
<p><img src="http://i.stack.imgur.com/Z1Sko.jpg" alt="enter image description here"></p>
<p>How do you from 2.8 to 2.10 ? I'm confused :/</p> | g7561 | [
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<p>We often find bathroom mirrors get fogged while hot water is used. Looking this up on the internet, we find several easy solutions:</p>
<ul>
<li>use a hot air blower</li>
<li>use a heater behind the mirror</li>
<li>vinegar + water mixture</li>
<li>thin film shaving cream/foam lather</li>
<li>thin film of regular(an... | g7562 | [
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<p>If we accept $E=\hbar \omega$, $p=\hbar k$, and $E^2-(pc)^2=(m_0 c^2)^2$, then we find $$(m_0 c^2)^2 = (\hbar \omega)^2-(\hbar kc)^2 = \hbar (\omega^2 - (kc)^2)=0$$i.e. the rest mass of any particle is $0$. Therefore every particle is a photon. What is wrong with this?</p> | g7563 | [
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<p>why is SUSY QM important ? i mean for each one DImensional Hamiltonian , can we write 'H' as</p>
<p>$ H= A.A^{+}+C$ (or similar constant)</p>
<p>here $ A= \frac{d}{dt}+A(x)$ and $ A^{+}= -\frac{d}{dt}+A(x)$</p>
<p>1) can we always express 'x' and 'p' as a combination of A and its adjoint?</p>
<p>2) does SUSY QM ... | g7564 | [
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<p>Gravity is the weakest of the fundamental forces, so what is so special about gravity that it can form an inescapably strong field while a force like the EM force cannot? It seems to me that if there were some extremely strong electric field, that it would only have an influence on particles that carry a charge, an... | g7565 | [
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<p>It follows from special relativity that nothing can travel faster than light. Einstein believed this would have to hold so generally that he assumed the <a href="http://en.wikipedia.org/wiki/EPR_paradox" rel="nofollow">Einstein-Podolsky-Rosen paradox</a> to indicate a contradiction in quantum physics. Nowadays we kn... | g7566 | [
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<p>It seems that the entropy for AdS$_2$ black hole is independent of the temperature $s=s_0$. While for near extremal AdS RN black brane, $s=s_0+ s(T/\mu)$. Should not these two entropies be the same since the AdS$_2$ black hole can be thought of a near horizon geometry of near extremal AdS RN black brane? </p> | g7567 | [
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<p>What is the approximate mass density of dark matter in our solar system at the radius of the Earth's orbit?</p>
<p>I would like some idea of the mass of dark matter going through each cubic meter of material on earth. </p> | g7568 | [
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<p>I am trying to solve a time dependent perturbation theory problem, and it involves the Hamiltonian
$$H=-\mu B\sigma_z$$
And a perturbation
$$V=-\mu B_1\sigma\cdot(\cos(\omega t)\hat x-\sin(\omega t)\hat y)$$
I want to find the probability that the spin will go from the Ground state of $H_0$ at t=0 to the excited sta... | g7569 | [
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0.001... |
<p>You can use a vacuum cleaner to vacuum the floor but if you tried to vacuum the the air in a small room would this work or will the laws of physics stop this from working in any way?
In what way would attempting to vacuum clean the air be different from using an air scrubber(in terms of physics). </p>
<p>Thanks</p> | g7570 | [
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<p>Would not speed of the light emitted from the front of the fast moving object be the speed of light + the speed of the fast moving object? </p> | g109 | [
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<p><img src="http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/imgmag/sol.gif" alt="solenoid"></p>
<p>To calculate the magnetic field, a rectangle amperian loop was drawn, and since the sides of the rectangle are perpendicular to the magnetic field, and the top is too far away to have any field lines cross it, only ... | g7571 | [
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<p>I was considering <a href="http://xkcd.com/1366/" rel="nofollow">this</a> xkcd comic from 5/10/14, with the alt-text "Trains rotate the Earth around various axes while elevators shift its position in space." I'm wondering about its accuracy.</p>
<p><img src="http://i.stack.imgur.com/EvUsH.png" alt="http://xkcd.com/... | g7572 | [
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<p>Alright, so David Griffiths in his "Introduction to Electrodynamics" states that the Twin Paradox is not a paradox at all since the traveling twin returns to Earth. By returning to Earth, the twin had to reverse direction, thus undergoes acceleration, and therefore cannot claim to be a stationary observer. </p>
<p>... | g7573 | [
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<p>From this <a href="http://physics.stackexchange.com/questions/11940/if-you-view-the-earth-from-far-enough-away-can-you-observe-its-past?rq=1">Stack Exchange Physics Post</a>, I am certain that it is possible to view the past. </p>
<p>But then this interesting question came to me.</p>
<p>Is it possible to hear the ... | g7574 | [
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<p>I want to know why different colours appear when viewed with a different angle. Can anyone tell me why?</p> | g7575 | [
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<p>What is the origin of electromagnetic interaction between molecules? Anyway, it should have some relation with atoms. Also, These electromagnetic interactions are playing a major role in different properties of matter including the transition between solid-liquid-gas. Hence, what would be the <strong>source</strong>... | g7576 | [
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<p>How does quantum electrodynamics actually explain HOW reflection occurs on a microscopic scale? </p>
<p>Note that Feynman's QED lecture series/book is not sufficient, as he only assumes that light DOES reflect ('turn around and go back') in order to expound his path integral theory. My question is why does light ha... | g92 | [
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<p>I've on many occasions that there are various numbers of 'extra' dimensions above the 4th. However, I've heard that they are 'compacted' or 'folded' tightly and unimaginably small. Now, as I understand, we live in 3 dimensional space coupled with time. So, by extension, those four dimensions should be present all ar... | g7577 | [
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<p>Recently I was made aware of the following arXiv preprint by Maxim Raykin: <a href="http://arxiv.org/abs/1204.1540">Analytical Quantum Dynamics in Infinite Phase Space</a>. As far as I understand it, Raykin's idea is to reinterpret quantum mechanics as a theory of ordinary classical particles moving around in R<sup... | g7578 | [
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0... |
<p>We could use either the current configuration $x$ or the displacement $u$ as unknown while solving for the deformation, for example, of a solid object. I want to know what's the difference between them? Is it that there is no difference, or one is numerically better than the other?</p> | g7579 | [
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<p>I need a full explantation for this concept.</p>
<p>Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.</p> | g7580 | [
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<p>Consider a scalar field $\phi$ described by the Klein-Gordon Lagrangian density
$L = \frac{1}{2}\partial_\mu \phi^\ast\partial^\mu \phi - \frac{1}{2} m^2 \phi^\ast\phi$.</p>
<p>As written in every graduate QM textbook, the corresponding conserved 4-current $j^\mu = \phi^\ast i \overset{\leftrightarrow}{\partial^\mu... | g7581 | [
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<p>The common argument for vanishing Goldstone boson is like, if there is some massless particle generated from the spontaneous symmetry breaking, it should be detected. Since we never saw that, it is not possible.</p>
<p>However, if there is some particle which has not been found, it could be (a) very heavy; (b) very... | g7582 | [
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<p>Assume that we got a Lagrangian of a classical wave $\phi(x,t)$ and a classical particle $q(t)$. The interaction term in the lagrangian is </p>
<p>$$ L_{int}=\frac g 2 \dot{\phi}(x=q(t),t)$$</p>
<p>It is very likely that this interaction has already been investigated, but I find it hard to search for such a lagran... | g7583 | [
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0.0... |
<p>It is well known fundamental behaviour that, <em>oppositely charged bodies attract each other</em> (I don't know whether it applies also for charges of equal magnitude or not), and identical charges repel each other. </p>
<p>It is also well known that, a system of oppositely charged bodies with equal charge in mag... | g7584 | [
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... |
<p>Let's say a clothespin is modeled as a simple torsion spring as follows.</p>
<p><strong>Given:</strong></p>
<ul>
<li>$p_1,\ p_2,\ p_3$: point-like objects of equal mass in 2-D space.</li>
<li>All objects float in space, i.e. the center of mass will not change.</li>
<li>At time $t_0$ a torsion spring is inserted at... | g7585 | [
0.041692111641168594,
0.00011620439909165725,
-0.007971641607582569,
0.008650322444736958,
0.06735391169786453,
0.04357040673494339,
0.014869780279695988,
0.034668032079935074,
-0.05349235609173775,
0.019128210842609406,
-0.052006132900714874,
0.009741703048348427,
0.008355713449418545,
-0... |
<p>Imagine two parallel conductive plates. Charge up both to have the same amount of positive charge. Then put positive test particle between the two.</p>
<p>The Coulomb's law is an inverse square law, so one might think the positive test particle is repelled from the nearby plane and accelerated towards the middle be... | g7586 | [
0.10657810419797897,
0.040237907320261,
0.01008081715553999,
0.0537605844438076,
0.11915857344865799,
0.05781862512230873,
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0.040158990770578384,
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0.02097749523818493,
0.01677563786506653,
0.048658858984708786,
-0.070431187748909,
-0.0173374637961... |
<p>If I have a drum floating in water, how do I find the equivalent spring constant?</p>
<p>I know that the water has density $\rho$, the drum has diameter $d$ and height $\ell$, and the positive direction is in the downward direction. Therefore, the buoyancy pushing up on the barrel is my spring.</p>
<p>I have been... | g7587 | [
0.0924602821469307,
-0.00155813863966614,
0.0030096140690147877,
-0.008026677183806896,
0.012078743427991867,
0.05237457528710365,
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-0.03427140414714813,
-0.07586260885000229,
0.012908698990941048,
0.02941390499472618,
0.0106... |
<blockquote>
<p>Quantum mechanics (QM; also known as quantum physics, or quantum theory) is a branch of physics which deals with physical phenomena at nanoscopic scales where the action is on the order of the Planck constant.</p>
</blockquote>
<p>-wiki</p>
<p>Time is much less finite than matter. Matter can be spli... | g7588 | [
0.06552325189113617,
0.05713224411010742,
0.0038634154479950666,
-0.04104231670498848,
0.018924569711089134,
0.030316080898046494,
-0.00049129209946841,
-0.006545660551637411,
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-0.013161558657884598,
0.02213491126894951,
-0.028457244858145714,
-0.04809727892279625,
0.... |
<p>Normal <a href="http://en.wikipedia.org/wiki/Surface_wave">surface water waves</a>, as generated by <a href="http://en.wikipedia.org/wiki/Ocean_surface_wave">wind</a>, do not have sine form but wave peak is higher and shorter than wave trough with different wave steepness. What parameters characterize such a surface... | g7589 | [
0.05710418522357941,
0.005170278716832399,
-0.040756870061159134,
-0.014133057557046413,
0.040425077080726624,
0.04577629268169403,
0.07020361721515656,
0.0017793376464396715,
0.020532673224806786,
-0.04874859377741814,
-0.05090736597776413,
0.0587252676486969,
0.05853969231247902,
0.06199... |
<p>I know that the <a href="http://en.wikipedia.org/wiki/Generalized_coordinates" rel="nofollow">generalized coordinates</a> obtained after taking into account the constraint forces are independent. How can I prove this?</p> | g7590 | [
0.013937070034444332,
0.06912824511528015,
-0.017148200422525406,
-0.01820690557360649,
0.042844440788030624,
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-0.0006970968679524958,
-0.032804932445287704,
-0.008172896690666676,
-0.029013361781835556,
... |
<p>Given that a worldline, worldsheet, worldvolume, are representation in a 4D-spacetime of a point particle, a string or a <a href="http://en.wikipedia.org/wiki/Membrane_%28M-theory%29" rel="nofollow">brane</a>, respectively, I was wondering if those objects necessarily have to be static in spacetime, or if they are a... | g7591 | [
-0.012269620783627033,
0.029199229553341866,
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-0.03123936615884304,
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-0.0043139467015862465,
-0.026903893798589706,
0.015600563026964664,
0.03305049240589142,
... |
<p>I'm tutoring senior high school students. So far I've explained them the concepts of atomic structure (Bohr's model & Quantum mechanical model) very clearly. Now the next topic to be taught is semiconductors.</p>
<p>I myself am not conviced with the concept of electron holes. If there is no electron then there ... | g834 | [
-0.02636556699872017,
0.01084538921713829,
-0.002268978161737323,
-0.07489605993032455,
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-0.006222454831004143,
0.018051695078611374,
0.021324314177036285,
0.01277625560760498,
0.01139... |
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