question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Suppose I have a weightless spring connected perpendicularly to the ground, and it has on top of it some weightless surface. Now, I release some sticky object from height $h$ above the system of light spring-surface. The object eventually hits the surface and the spring is starting to contract till all the kinetic e... | 6,192 |
<p>(I found this related Phys.SE post: <a href="http://physics.stackexchange.com/q/30948/2451">Why is GR renormalizable to one loop?</a>)</p>
<p>I want to know explicitly how it comes that Einstein-Hilbert action in 3+1 dimensions is not renormalizable at two loops or more from a QFT point of view, i.e., by counting ... | 6,193 |
<p>I find <a href="http://en.wikipedia.org/wiki/Fredholm_theory" rel="nofollow">Fredholm theory</a> beautiful, especially the <a href="http://en.wikipedia.org/wiki/Liouville-Neumann_series" rel="nofollow">Liouville-Neumann series</a> for solving <a href="http://en.wikipedia.org/wiki/Fredholm_integral_equation" rel="nof... | 6,194 |
<p>My question relates to the third MIT's video lecture about Electricity
and Magnetism, specifically from $21:18-22:00$ : <a href="http://youtu.be/XaaP1bWFjDA?t=21m18s" rel="nofollow">http://youtu.be/XaaP1bWFjDA?t=21m18s</a></p>
<p>I have watched the development of Gauss's law, but I still don't quite
understand the ... | 6,195 |
<p>While working on physics simulation software, I noticed that I had implemented discrete time (the only type possible on computers).</p>
<p>By that I mean that I had an update mechanism that advanced the simulation for a fixed amount of time repeatedly, emulating a changing system.</p>
<p>I was a bit intrigued by t... | 114 |
<p>A solid disk of mass m is rolling along a surface its center has velocity v what is the kinetic energy of disk?I cannot solve the problem,</p> | 6,196 |
<p>a deSitter space is a maximally symmetric solution of Einstein equations, I have some problem picturing one thing: this space is past and future (time) infinite but spatial slices have finite size, how can we have finite size in slicing at constant time, and infinite time size when slicing at constant radial coordin... | 6,197 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/31247/why-do-we-need-higgs-field-to-re-explain-mass-but-not-charge">Why do we need Higgs field to re-explain mass, but not charge?</a> </p>
</blockquote>
<p>Why have scientists been looking for something... | 217 |
<p>The Helmholtz equation is expressed as $$\nabla^2 \psi + \lambda \psi = 0$$. This equation occurs, for eg., after taking the Fourier transform (with respect to the time coordinate) of the wave equation in free space. While this equation for the case of $\lambda$ real is reasonably well discussed in the literature, t... | 6,198 |
<p>I am learning about electricity and magnetism by watching MIT video
lectures.</p>
<p>In the lecture about Gauss's law, while trying to calculate the flux through a sphere with charge in it, the lecturer states that the direction of the electrical field is radial, since it is the only preferred direction that there ... | 6,199 |
<p>The usual definition given for a greenhouse gas is that it absorbs infrared radiation. Of course, then the gas emits its own thermal radiation, and it does so without preference for direction (assuming homogeneity).</p>
<p>I was looking at the <a href="http://en.wikipedia.org/wiki/File%3aGreenhouse_Effect.svg">gre... | 6,200 |
<p>A two-qubit system was originally in the state $ \frac{3}{4}|00\rangle-\frac{\sqrt{5}}{4}|01\rangle+\frac{1}{4}|10\rangle-\frac{1}{4}|11\rangle $ , and then we measured the first qubit to be 0 . Now, if we measure the second qubit in the standard basis, what is the probability that the outcome is 0 ? </... | 6,201 |
<p>Due to some recent "discoveries" (yet to be completely confirmed), we have hinted the existence of tetraquark particles. </p>
<p><strong>Why QCD exotics like multiquark states beyond n=2,3 (mesons, protons,neutrons,...) like tetraquarks, pentaquarks,...or even glueballs could be useful for new physics? And more gen... | 6,202 |
<p>Suppose that I put in the outer space (where gravity from other bodies is negligible) a large, perfectly round sphere totally filled with water. At the bottom (even though "bottom" doesn't make much sense in the deep space) of the sphere there are several marbles, all touching each other.</p>
<p>If I make rotate th... | 6,203 |
<p>The height of a string in a gravitational field in 2-dimensions is bounded by $h(x_0)=h(x_l)=0$ (nails in the wall) and also $\int_0^l ds= l$. ($h(0)=h(l)=0$, if you take $h$ as a function of arc length)
.</p>
<p><strong>What shape does it take?</strong></p>
<p>My try so far: minimise potential energy of the whol... | 6,204 |
<p><img src="http://i.stack.imgur.com/R70Fu.png" alt="enter image description here"></p>
<p>The question then asks for the potential difference between $X$ and $Y$, which is claimed to be $3.6\text{ volts}%$.</p>
<p>Why would there be a potential difference in this case? If I connect a lightbulb on $X$, and another o... | 6,205 |
<p>How much harder would it have been for Felix to use some powered sled and head for the ISS when he stepped out of his capsule? He was already above most of the atmosphere.
BTW, Is that capsule still up there? Why don't more missions use balloons for the first stage?</p> | 6,206 |
<p>I have two arbitrary vectors $\vec{x}$ and $\vec{x}'$ given in spherical coordinates $(|\vec{x}|=x,\theta,\phi)$ (as convention I take the "physics notation" given on Wikipedia <a href="http://en.wikipedia.org/wiki/Spherical_coordinate_system" rel="nofollow">http://en.wikipedia.org/wiki/Spherical_coordinate_system</... | 6,207 |
<p>To illustrate discord and its use, <a href="http://arxiv.org/pdf/quant-ph/0105072.pdf" rel="nofollow">Zurek in his paper on discord</a> (NB pdf) gives example of a partially decohered bell state i.e.
$$\rho_{AB}=\frac{1}{2}(|00\rangle\langle 00|+|11\rangle\langle 11|) + \frac{z}{2}(|00\rangle \langle 11|+|11\rangle... | 6,208 |
<p>In the book Young and Freedman 13th edition, the wave equation is <br/> <br/> $y(x, t) = A\,\text{cos}(kx-wt)$ <br/> <br/> The problem is, I find it hard to console with the fact that <br/> <br/> $y(x, t) = A\,\text{sin}(wt-kx)$. <br/> <br/> How to derive $A\,\text{sin}(wt-kx)$ from $A\,\text{cos}(kx-wt)$?</p> | 6,209 |
<p>In particular I'm interested in any algorithms that can separate multiple tracks from one another reliably.</p> | 6,210 |
<p>From what I understand space itself is expanding, and the Big Bang attempts to describe this expansion at the very early stages of the universe.</p>
<p>This is usually described in a visual way as 2 dots on the surface of a balloon as the balloon is being inflated.</p>
<p>We exist in space, so as space expands we ... | 56 |
<p>If I consider one single Dirac electron in momentum representation, I use the wavefunction $u(p)e^{-ipx}$, however if I consider an one-particle state in the Fock space I use $|p\rangle$. Should it not be same? </p>
<p>Obviously the Dirac 1-particle wavefunction is a bispinor, and probably $|p\rangle$ is not a spin... | 6,211 |
<p>I would like to show that a particle orbiting another will follow the trajectory </p>
<p>\begin{equation}
r = \frac{a(1-e^2)}{1 + e \cos(\theta)}.
\end{equation}</p>
<p>I would like to do this with minimal assumptions. Any pointers? I've read that this is nothing but the equation for an ellipse, as defined from th... | 311 |
<p>So <a href="https://www.youtube.com/watch?v=OTcdutIcEJ4" rel="nofollow">this guy</a> was the first to run a loop and in this (german) <a href="http://www.welt.de/vermischtes/article125146560/Erster-Mensch-der-Welt-rennt-einen-Looping.html" rel="nofollow">article</a> (and also in the video) a certain speed (13.8km/h)... | 6,212 |
<p>any text on photonic crystals will highlight the almost perfect analogy between electrons in a periodic potential and photons in a periodic dielectric. The analogies are:</p>
<p>$$V(\vec r + \vec R) = V(\vec r) \Leftrightarrow \epsilon(\vec r + \vec R) = \epsilon(\vec r)$$</p>
<p>$$\psi(\vec r)=e^{i\vec k\cdot \ve... | 6,213 |
<p>I am a little confused as to what the magnitude of <a href="http://en.wikipedia.org/wiki/Acceleration" rel="nofollow">acceleration</a> is and what it means.</p> | 6,214 |
<blockquote>
<p>The voltage of the battery signifies the difference in voltage between the positive and negative terminal</p>
</blockquote>
<p>What does this mean?</p>
<p>The definition of voltage difference I'm familiar with is the amount of potential energy charge one coloumb of charge would undergo from point A ... | 6,215 |
<p>I'm a high school student. The head is hydrophilic, the tail is fatty acid,in other words hydrophobic. Here is the thing I don't understand, all textbooks state that water is repelled by hydrophobic tail, why? The hydrophilic head is composed of polar molecule,and water is polar,so they will attract each other. But ... | 6,216 |
<p>In the Bose-Hubbard model of cold atoms in an optical lattice, we consider only the short-range interaction or on-site interaction. Is it possible to realize long-range interaction similar to Coulomb interaction in the cold atom experiment? </p> | 6,217 |
<p>The increasing water pressure as you go deeper is generally explained in terms of the weight of the water column above the observation point pressing down. The question, then, is what would happen if you had a big blob of water in free fall, say 100m in diameter-- not big enough to produce large gravitational forces... | 6,218 |
<p>This question pertains to EM signals exchanged between an inertial central clock and an orbiting clock i.e. non-inertial frame.
(I edited out the variables connected with gravity and separation between bodies)</p>
<p>This is how I found the frequency and wavelength received by clock (orbiting) as sent from clock (... | 6,219 |
<p>Padmanabhan's discussion of dynamics mentions that in general the two dimensional harmonic oscillator fills the surface of a two torus.</p>
<p>He further notes that there will be an extra isolating integral of motion provided that the ratio of frequencies is a rational number.</p>
<blockquote>
<p>$ -\frac{\omega... | 6,220 |
<p>Someone please tell (advice) me some research study problems on Classical Mechanics that can be tackled with Undergraduate level knowledge. </p> | 12 |
<p>As far as I know, a black body is an ideal emitter. So how can it be that a non-ideal emitter emits more radiation than a black body?</p>
<p>This happens only in a very limited area at <strong>around 500nm</strong>, but it still happens: it looks like at the maximum it is around 15% above black body.</p>
<p>This s... | 6,221 |
<p>It is always told as a fact without explaining the reason. Why do two objects get charged by rubbing? Why one object get negative charge and other get positive <a href="http://en.wikipedia.org/wiki/Electric_charge" rel="nofollow">charge</a>?</p> | 363 |
<p>If the fields in QFT are representations of the Poincare group (or generally speaking the symmetry group of interest), then I think it's a straight forward consequence that the matrix elements and therefore the observables, are also invariant.</p>
<p>What about the converse:</p>
<blockquote>
<p>If I want the mat... | 6,222 |
<p>Can anybody elaborate on the implications of the BICEP2 result for string theory?</p>
<p>The discussion here <a href="http://physics.stackexchange.com/questions/15/what-experiment-would-disprove-string-theory">What experiment would disprove string theory?</a> suggests that refuting string theory is rather difficult... | 6,223 |
<p>given the density of states according to Gutzwiller's trace formula</p>
<p>$ g(E)= g_{smooth}(E)+ g_{osc}(E) $</p>
<p>i know that the 'smooth' part comes from $ g_{smooth}(E)= \iint dxdp \delta(E-p^{2}-V(x)) $ for one dimensional system</p>
<p>however how it is the oscillating part of the trace obtained ?? :D i m... | 6,224 |
<p>(Background) In the scenario where a gauge symmetry is spontaneously broken and the gauge field eats the Goldstone boson to acquire a mass, the massive gauge field acquires a longitudinal polarization. I have seen the argument that the massless field has only two physical polarizations, and I have heard the hand-wav... | 6,225 |
<p>I understand that it is more common in GR for the metric to be given a $(-,+,+,+)$ signature and more common in particle physics (or field theory, as Peskin & Schroeder tells me) to use the $(+,-,-,-)$ metric signature. I'm wondering why. Is there any advantage in these disciplines in terms of actual physics to ... | 6,226 |
<p>Right now I'm simply looking for an intuitive explaination of actions that integrate over a 4-volume element, $d^4x$ rather than a parameter say $\lambda$. More specifically I'm well versed in action principles that say have an action as $\int L d\lambda$. But in trying to understand actions such as the Einstein Hi... | 6,227 |
<p>What happens to the energy when waves perfectly cancel each other (destructive interference)? It appears that the energy "disappear" but the law of conservation of energy states that it can't be destructed. My guess is that the kinetic energy is transformed into potential energy. Or maybe it depends on the context o... | 531 |
<p>How accurately can our current technological tools measure the human bio-electromagnetic field emitted by a person? Or, to put it differently, does each person have a different electromagnetic field signature, and can we measure that with enough accuracy to tell two people apart by their frequencies? </p> | 6,228 |
<p>Let $\mathcal{A}$ be the Ashtekar connection. Since $^{(3)}g_{AB}=i\frac{\delta}{\delta\mathcal{A}^{AB}}$ (see R. Penrose, 2004: Road to Reality. Vintage Books, 1136 pp.), the Ashtekar connection, in a way, represents the graviton. Let $\mathcal{Riem}$ denote the configuration space of GR. </p>
<p>If one managed to... | 6,229 |
<p>In <a href="http://www.het.brown.edu/people/danieldf/literary/eric-KKtheories.pdf" rel="nofollow">this</a> review about Kaluza-Klein theories, (page 1115) in order to determine the mass spectrum of the 5 dimensional theory the metric is expanded to first order.</p>
<p>Why this? Why not retain the full metric? Why d... | 6,230 |
<p>Using a laser setup, I was asked to determine the aperture of a given lens and then use some geometrical arguments and compare the theoretical value from the manufacturer and the experimental value. However, when I did this, the values <em>differed by orders of magnitude</em>.
The way I got the aperture was to let ... | 6,231 |
<p>All the examples of plasma I have come across are visible. Is there any plasma which is not visible? For example, during a dark lightening we don't see the radiation because its gamma radiation. Is plasma formed during a dark lightening?</p> | 6,232 |
<p>When we calculate electric field intensity for a point charge at any point inside electric field the field intensity is $E = F/q$ where $F$ is the force acting on charge $q$. In this case, the charge $q$ should be very small. The practical value of $q$ cannot be so small as needed. In defining electric field by meas... | 6,233 |
<p>I've been trying to derive the relation</p>
<p>$$[\hat L_i,\hat L_j] = i\hbar\epsilon_{ijk} \hat L_k $$</p>
<p>without doing each permutation of ${x,y,z}$ individually, but I'm not really getting anywhere. Can someone help me out please?</p>
<p>I've tried expanding the $\hat L_i = \epsilon_{nmi} \hat x_n \hat... | 6,234 |
<p>For demonstrating basic probability concepts, it would be nice to have a coin-like object that lands heads/tails not in 50/50% ratio, but biased in a way that can be revealed in a short experiment. What I'd like is to make an object satisfying:</p>
<ul>
<li>Thin disk shape, say thickness around 1/10 to 1/20 of dia... | 6,235 |
<p>This is in reference to the argument given towards the end of page $61$ of this <a href="http://arxiv.org/abs/hep-th/9702155" rel="nofollow">review paper</a>. There for the path-integral argument to work the author clearly needed some argument to be able to ignore the kinetic term(Kahler potential). But I can't get ... | 6,236 |
<p>The Heterotic (HO and HE) string is found by tensoring the left movers of the bosonic string theory state and the right movers of the Type II string theory state:
$$|\psi_{\operatorname{H}}\rangle=|\psi_{\operatorname{B}}\rangle\otimes|\psi_{\operatorname {II}}\rangle$$ </p>
<p>The bosonic state is of course based ... | 6,237 |
<p>This question disusses the same concepts as <a href="http://theoreticalphysics.stackexchange.com/questions/848/relativistic-center-of-mass">that question</a> (this time in quantum context). Consider a relativistic system in spacetime dimension $D$. Poincare symmetry yields the conserved charges $M$ (a 2-form associa... | 6,238 |
<p>The answers in this question: <a href="http://physics.stackexchange.com/questions/1/what-is-spin-as-it-relates-to-subatomic-particles">What is spin as it relates to subatomic particles?</a>
do not address some particular questions regarding the concept of spin:</p>
<p>How are some useful ways to <em>imagine</em> a... | 383 |
<p>I was wondering if anyone put together a law to describe the rising temperature of the water coming out of a tap.</p>
<p>The setup is fairly simple: there's a water tank at temperature T, a metal tube of length L connected to it and a tap at the end where temperature is measured. The water flows at P l/s.</p>
<p>G... | 6,239 |
<p>I would like to have a good understanding of what is happening when you add salt to boiling water.</p>
<p>My understanding is that the boiling point will be higher, thus lengthening the process (obtaining boiling water), but at the same time, the dissolved salt reduce the polarization effect of the water molecules ... | 6,240 |
<p>I'm interested in the process that goes from, for example, huge data sets of temperature, pressure, precipitation etc readings to a model of the atmosphere. I'd like to know about how much relies on a priori knowledge of Navier-Stokes, and how much curve fitting is done.</p>
<p>Some sort of general overview of the ... | 6,241 |
<p>The following situation interests me and I was wondering if there is software to model it? </p>
<p>A large set of n spheres of uniform density and discrete sizes, mass proportional to volume, are dropped together on a narrow inclined plane under low gravity (so they are free to bounce and sort themselves) . The sp... | 6,242 |
<p>Magnetic monopole predicted by Dirac nearly a century ago was found in spin ice as quasi-particle(2). My question is Why magnetic monopole found in spin ice don't modify the Maxwell's Equations? (I know they are not elementary particles but quasi-particles.)</p>
<p>(1) Dirac, P. A. M. Quantised singularities in the... | 6,243 |
<p>Why don't the stars in a star cluster attract each other gravitationally, forming one big star? What causes a cluster to disperse the stars in it? </p> | 6,244 |
<p>Today in my Physics lecture I suddenly thought of something. We all know that gravitational force is proportional to the two masses and inversely proportional to the square of the distance between them. So, naturally, there exists a system of natural units which equates the proportionality by setting $G=1$. Here I'm... | 6,245 |
<p>I'm really stuck. I need to figure out the mass/light ratio of a galaxy in solar units. I know its mass is 5.7 x 10<sup>10</sup> solar masses. I know its absolute magnitude (-17.3) and distance (29 Mpc). I'm feeling dumb here because I think this ought to be clear to me, but I'm getting hung up at the magnitude - lu... | 6,246 |
<p>If you put a object in contact with a heat reservoir that is infinitesimally higher in temperature than the object and allow equilibrium to be reached the entropy change is zero right?</p> | 6,247 |
<p>Can someone send me pointers to work (either theoretical or simulations)
showing (in)stability of satellite orbits around tidally locked exoplanets?
I want to know firstly if satellite orbits can survive the inward migration
and secondly if once the planet becomes tidally locked if that has any
implications for the ... | 6,248 |
<p>The twinkling of stars, or scintillation, occurs because the optical path length of the atmosphere varies in both space and time due to turbulence.</p>
<p>This means that when the wavefront from a distant star enters a telescope, it is distorted from the flat wavefront expected for an object at infinity.</p>
<p>Be... | 6,249 |
<p>A question came up on Outdoors StackExchange, <a href="http://outdoors.stackexchange.com/questions/1093/how-to-tell-the-time-at-night">How to tell time at night</a>. I wrote an answer to that question, and in my answer I said that a standard sundial wouldn't work without some fiddling, but that an astronomer would ... | 6,250 |
<p>Josh Hill, 9, Oakdale Elementary has always talked Theory of Relativity and Astrophysics etc., I can answer most but lately he has stumped me and has been begging me to ask a pro, so here it is....</p>
<p>"What happens when Dark Matter comes in contact with the event horizon of a large Black Hole?”</p>
<p>Josh Hil... | 6,251 |
<p>Every object at a non-zero temperature radiates light, i.e. it glows.
(Is that called <em>blackbody radiation</em>?)</p>
<p>What is the physical reason to this?</p>
<p>Is it because more heat implies that the atoms vibrate, and vibrating charges (the electrons or the nuclei) generate electromagnetic radiation?</p> | 218 |
<p>The question is available <a href="http://puu.sh/42HC2.png" rel="nofollow">here</a>:</p>
<p><img src="http://i.stack.imgur.com/MLall.png" alt="enter image description here"></p>
<p>I've modeled the building as a rod on a torsional spring (with a pendulum hanging from the top).</p>
<p>$\phi$ is the angle from the ... | 6,252 |
<p>Why <a href="http://en.wikipedia.org/wiki/Gauss%27s_law" rel="nofollow">Gauss' law</a> is applied? Why is there a need of finding electric field by Gauss' law if we can find the electric field through Coulomb's law?</p>
<p>or has it got more applications than Coulomb's law?</p> | 6,253 |
<p>Who proposed the <a href="http://www.google.de/search?q=bulk+edge+correspondence" rel="nofollow">bulk-edge correspondence principle</a>?</p>
<p>The principle is often quoted in counting the number of zero energy states localized on the interface between two insulators with distinct band topology. However, I could n... | 6,254 |
<p>It seems to me that diffraction gratings are completely described by the double slit experiment-why then is it called a diffraction grating?</p> | 6,255 |
<p>Since the medium in which light propagates is spacetime, would light be able to exist if spacetime did not exist? Is this like one of those chicken/egg problems, or can light be thought of as a legitimately independent entity? This might be bordering on an philosophical question, so if it is, let me know and I'll ... | 6,256 |
<p>I am trying to follow <a href="http://arxiv.org/abs/cond-mat/0503717" rel="nofollow">this paper</a> and track the dynamics of vortex motion on a discrete (square) lattice. The idea is to simulate the time evolution of the Gross-Pitaevskii (GP) equation, which reads (in rescaled units)</p>
<p>$$i \partial_t \psi = -... | 6,257 |
<p>The intensity of particles come to sea level depend to the zenith angle $I=Iv (\cos(z))^n$, where $z$ is the zenith angle and $n$ depend to the particle.
I know the vertical intensity depend to the energy or momentum of the particle, for exemple, to muons, $n$ is about 2 and vertical intensity is $0.0094\, \mathrm{... | 6,258 |
<p>A simple question about notation of <a href="http://arxiv.org/abs/hep-th/9803265" rel="nofollow">Moore Nekrasov and Shatashvili</a> which makes me confused. Page 3, the authors rearranged the action into a novel form.</p>
<p>For D=3+1,5+1,9+1 respectively, the path integral is
$$
I_D=(\frac{\pi}{g})^{\frac{(N^2-1)(... | 6,259 |
<p>What is the importance of deriving the results of perturbation theory in condensed matter physics in terms of spectral functions ?</p> | 6,260 |
<p>I would like to understand better the role of Higgs mass in the gravitational interaction. I read here in some posts, that the Higgs mass has nothing to do with gravitation. Is it justified to say that? Gravitation acts on "energy" rather than mass but it is only mass, among the physical observables, which provides ... | 6,261 |
<p>As a physics bsc student, I have a very limited knowledge of QM:</p>
<p>Dirac formalism, Schrodinger equation and simple solutions (oscillators, particle in a given potential, hydrogen-like atom etc). There are more advanced QM courses I can take, but I find more interest in QFT.</p>
<p>What are the prerequisite s... | 443 |
<p>It is well known that the negative cosmological constant of AdS spacetime can act like a confining potential. That is, in contrast to asymptotically flat spacetime, in an asymptotically AdS spacetime <em>massive particles cannot escape to infinity</em>. However, massless particles can escape to infinity and actually... | 6,262 |
<ol>
<li><p>Recently I am studying electromagnetic waves, and I am wondering why it is formed by acceleration of electric charges? </p></li>
<li><p>Can the EM waves be formed by other movements of electric charges, such as at a constant velocity? </p></li>
<li><p>And also, is there a way to visualize the formation of E... | 219 |
<p>Special relativity was well established by the time the schrodinger equation came out. Using the correspondence of classical energy with frequency and momentum with wave number, this is the equation that comes out, and looks sensible because this is of the form of a wave equation, like the one for sound etc, except ... | 6,263 |
<p>I would like to clarify something that mixes cosmology and relativistic effects. Maybe I'm not understanding something or maybe there a difference of vocabulary between the cosmological and the relativistic people. </p>
<p>If you ask a cosmologist at which scale the relativistic effects appears (for example in N-bo... | 6,264 |
<p>I couldn't find anything about the parity of an electron. Neither in the german, nor in the spanish and nor in the english version of Wikipedia. </p>
<p>I only found one sentence in the parity article of Wiki:</p>
<blockquote>
<p>One way to fix a standard parity operator is to assign the parities of three partic... | 6,265 |
<p>I want to transmit sunlight over a distance of approx 4 m via optical fiber. Ideally I want to light up the whole house with sunlight.</p>
<p>I was reading that the largest diameter for an optical fiber may not be the right way to solve this issue. I was wondering if there some sort of equation where I can insert t... | 6,266 |
<p>I was reading through the first chapter of Polyakov's book "Gauge-fields and Strings" and couldn't understand a hand-wavy argument he makes to explain why in systems with discrete gauge-symmetry only gauge-invariant quantities can have finite expectation value. This is known as <a href="http://en.wikipedia.org/wiki/... | 6,267 |
<p>In the derivation of <a href="http://en.wikipedia.org/wiki/Lorentz_transformation" rel="nofollow">Lorentz transformations</a>, the <a href="http://en.wikipedia.org/wiki/Derivations_of_the_Lorentz_transformations" rel="nofollow">Wikipedia article</a> mentions a couple of times that the linearity comes from the <a hre... | 6,268 |
<p>In my readings of Mirman (1995), "Group Theory: An Intuitive Approach", on p.35 he asks me to consider a so-called "water group" that has 4 transformations. I'll list them for completeness, but I'm only concerned about two of them. </p>
<ol>
<li>The identity element</li>
<li>Reflection in the plane element</li>
<li... | 6,269 |
<p>This is a follow up of this <a href="http://physics.stackexchange.com/questions/119886/how-to-calculate-roll-yaw-and-pitch-angles-from-3d-co-ordinates-euler-angles">question</a> :</p>
<p>I have the rotation matrix </p>
<p>$$
\left( \begin{matrix}
a_{11} & a_{12} & a_{13}\\
a_{21} & a_{22} & a_{23... | 6,270 |
<p>This is a question with a philosophical, as well as physical, flavor.</p>
<p>Why should a physical principle (or a description of one), be applicable to different systems that can be in different positions in space and time?</p>
<p>In other words why should there be such (<em>modulo</em>) equivalence classes (with... | 179 |
<p>Given a hot air balloon of radius 10 meters and negligible mass, calculate the maximum weight it can carry if the density of outside air is 1.2 $\frac{kg}{m^3}$ and the density of inside air is 0.9 $\frac{kg}{m^3}$. </p>
<p>Edit:
My attempt:
Since the maximum weight the balloon can carry is determined by the relati... | 6,271 |
<p>If the moon was alone in space and covered in X feet of water and it began to rotate would it displace to a bias along the equator? </p> | 6,272 |
<p>Let's have <a href="https://en.wikipedia.org/wiki/K%C3%A4ll%C3%A9n%E2%80%93Lehmann_spectral_representation" rel="nofollow">Kallen–Lehmann spectral representation</a> for the scalar theory:
$$
\tag 1 D(p) = \int \limits_{0}^{\infty} d(\mu^{2})\frac{\rho (\mu^{2})}{p^{2} - \mu^{2} + i\varepsilon}.
$$
We can represent ... | 6,273 |
<p>Which mass of the particle is the source of gravitational field? If we define mass as a pole of the propagator, and calculate loop corrections to the pole we get infinities. Now the way we get rid of these infinities defines what is our renormalized propagator and what is its pole. What is the mass of the particle i... | 6,274 |
<p>Not sure if this is a physics or chemistry question. But if the motion of atoms and it's particles can be described by quantum mechanics, then is there a software that simulate full atoms and it's boundings, in a way you can visualize them, and that can be used, for instance, to throw 2 molecules together and watch ... | 6,275 |
<p>This is thought experiment. I couldn't get a good answer because I keep getting negative mass.</p>
<p>Gauss's Law say that eletric field is proportional to charge, how much charged is enclosed. Newton's gravitational pretty much says the same thing. More mass, strong gravitational strength.</p>
<p>So to put it mat... | 6,276 |
<p><strong>Problem/Solution</strong></p>
<p><img src="http://img221.imageshack.us/img221/4285/20841428g.jpg" alt="">!</p>
<p>I am deeply confused. </p>
<p>B) We know that </p>
<p>$x = 2\sin(3\pi t)$.</p>
<p>$x' = 6\pi\cos(3\pi t)$</p>
<p>So max <em>speed</em> is $6\pi$</p>
<p>$6\pi = 6\pi \cos(3\pi t)$</p>
... | 6,277 |
<p>I've seen the post on mathoverflow.SE asking almost the same question, and I have indeed flipped through said answers, but most are in a more general context ie quantum mechanics and do not provide a conceptual answer with physical interpretation. Anyone able to offer any insight, or even an example in the aforement... | 6,278 |
<blockquote>
<p>A ball is thrown vertically upwards at $5\text{ m/s}$ from a roof top of $100\text{ m}$. The ball B is thrown down from the same point $2\text{ s}$ later at $20\text{ m/s}$. Where and when will they meet?</p>
</blockquote>
<p>Well at first I separated the fact that while ball B falls at say $t$ secon... | 6,279 |
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