question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>The decay mode of Carbon-8 is listed as 'XP' in this <a href="http://ie.lbl.gov/education/parent/C_iso.htm" rel="nofollow">table</a>. None of the references I looked at listed XP as a decay mode. What is it></p> | 4,187 |
<p>What complications arise when examining the statistical mechanics of a system under the influence of gravity? Is it significantly different from the classical treatment of statistical mechanics?</p> | 4,188 |
<p>As far I as I know, and from naturalness considerations, a 125 GeV Higgs mass is rather large for the MSSM. This is because in the MSSM $$m_h^2 \lesssim M_z^2 \cos^22\beta + \Delta$$ where $\Delta$ represents top/stop loop corrections to the Higgs. It takes the form $$\Delta \sim \ln(\frac{m_\text{stop}}{m_\text{top... | 4,189 |
<p>I have a wet teabag in an empty cup. If I will hold the teabag and touch the wall of cup with it, it will stick to the cup, like there would be glue or some magnetic field, but there's just water.</p>
<p><img src="http://i.stack.imgur.com/HaBZ4.jpg" alt="enter image description here"></p>
<p>So, why does it happen... | 4,190 |
<p>Say you have a chemical compound made up of one or more radioactive nuclei. If the nucleus decays, does the compound? </p>
<p>Possible outcomes I can think of:</p>
<ol>
<li><p>the compounds continues to exist if a bonding is still possible between the decay product and the rest of the original compound.</p></li>
<... | 739 |
<p>(little background: I'm trying to develop a small, quick 'n dirty static physics engine to determine whether a stacking of boxes is stable).</p>
<p>If I have a 3D rigid box (with the bottom in the horizontal plane), resting on n points (at [xn, yn]), and we apply a downward force F at [xF, yF], how can I calculate ... | 4,191 |
<p>I was reading today about the birth of the Universe and the conjectures about the matter that was supposed to exist at the moment of the Big Bang and what can be measured now.</p>
<p>There seems to be some sort of discrepancy between the calculated amount of matter in the Big Bang and the amount that can be measure... | 4,192 |
<p>Cepheids are used to evaluate distances. What is the math and physics behind their use?</p> | 4,193 |
<p>I was wondering if it were possible to calculate the drag coefficient by allowing an object to reach terminal velocity. Can you rearrange the terminal velocity formula to give the drag coefficient?</p> | 4,194 |
<p>Why nature made conjugates?
such as momentum and position, time and energy? Why not energy and position even both do not commute. .</p>
<p>thanks in advance</p> | 128 |
<p>I understand that the larger the mass the greater gravity is and the slower time is, as well the faster an object is traveling the slower time passes. My question is that since the faster an object travels the more mass it has, is the increase in mass the reason for the change in time, or is it the velocity?</p> | 4,195 |
<p>Why did nature decide to make conjugate of position to be momentum? Since energy and position do not commute, why not energy? What determines the pairing of time with energy and momentum with position?</p> | 128 |
<p>A satellite is in a circular orbit when its engines turn on to exert a small force in the direction of the velocity for a short time interval. Is the new orbit further or closer to the Earth?</p>
<p>The solution is that the new orbit is further away (which is also intuitive) and is justified by stating that there i... | 4,196 |
<p>can be a theory with an infinite number of divergent integrals of the form</p>
<p>$$ \int \frac{d^{p}k}{k^{m}} $$</p>
<p>for m=1 , 2 , 3 , 4 ,...... so the theory would be IR non renormalizable and you would need and infinite set of operations to cure all the IR divergences </p>
<p>thanks.</p> | 4,197 |
<p>Forgetting Hooke's law for a minute why, from a microscopic perspective (preferably quantum) on up to a macroscopic one, does a spring under tension exert a force?</p>
<p>I was thinking that there might be an analogy between the high and low pressure states of an air wave and the density of the mass distribution of... | 4,198 |
<p>How much energy in form of heat does a human body emit at rest level?</p> | 4,199 |
<p>As I understand it, black holes have an absolute event horizon and an apparent horizon specific an observer. In addition to black holes, an apparent horizon can come from any sustained acceleration. Firstly, there is the <a href="http://en.wikipedia.org/wiki/Event_horizon">"particle horizon" of the universe</a>, w... | 4,200 |
<p>Recently, I read about dipole and multipole bound anions. Dipole bound anions are those, if I understood correctly, when an electron is attached electrostatically on a neutral molecule which is polar. If the molecule is having a quadrupole moment, the anion is said to be a quadrupole bound anion. These bound electro... | 4,201 |
<p>This is probably a really silly confusion I have about the definition of “coordinate differentials”, which I thought were things like $dx,dy,dz$
etc. The Minkowski line element $$ds^{2}=c^{2}dt^{2}-dx^{2}-dy^{2}-dz^{2}$$
defines the Minkowski metric $$\left[\eta_{\mu\nu}\right]=\left(\begin{array}{cccc}
c^2 &... | 4,202 |
<p>The Poisson - Boltzmann equation is to find the potential whose charge density obey the Boltzmann distribution. If the potential is not large compare to $k_BT$, the PBE can lead to the Debye–Hückel equation. However if the potential is large and the system is high density, its result is <a href="http://pubs.acs.org/... | 4,203 |
<p>I'm looking for a treatment of the original basic <a href="http://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory" rel="nofollow">Kaluza-Klein theory</a>.
Can someone recommend a review article or something?</p> | 4,204 |
<p>In aircraft literature, what does cross-track and along-track wind directions mean? Please explain in terms of the aircraft's motion relative to the wind direction. I can hazard a guess: along-track is wind in the direction of the aircraft's velocity, and cross-track would be perpendicular side-to-side (or is it top... | 4,205 |
<p>It has always been claimed decoherence solves the problem of the preferred-basis for observed probability distributions, but why should this be the case? If there is only one world, and there are probabilities for certain outcomes, why should the basis in which the probabilities are observed coincide with the pointe... | 4,206 |
<p>I have seen <a href="http://www.physics.sfsu.edu/~lea/courses/ugrad/460notes5.PDF" rel="nofollow">this derivation</a>: </p>
<p><img src="http://i.stack.imgur.com/goWYX.png" alt="enter image description here"></p>
<ul>
<li><p>I want to estimate what is the intensity of the electrical field as
function of $r$ the di... | 4,207 |
<p>Let's suppose a cellular automaton has a value $b(r,t)$ belongs to $Q$ at site $r$ and time $t$, where $Q$ is the set of possible states at each site. Let $N(r, t)$ be the values of the states of all the sites in some (e.g., Von Neumann or Moore) neighborhood of $r$ at time $t$, taken in some canonical order. </p>
... | 4,208 |
<p>Don't be a $\frac{d^3x}{dt^3}$</p>
<p><img src="http://i.stack.imgur.com/Ptblb.jpg" alt="enter image description here"></p>
<p>What does it all mean?</p> | 4,209 |
<p>A gun has a recoil speed of 2 m/s when firing. If the gun has a mass of 2kg and the bullet has a mass of 10g (0.01 kg) what speed does the bullet come out at? </p>
<p>The gun has zero total momentum before firing and afterwards the gun has negative acceleration. </p>
<p>So far:</p>
<p><strong>Conservation of mome... | 4,210 |
<p>If we have a planar and harmonic EM wave, with $B$ field:</p>
<p>$$B=A\left(\begin{array}{c}
1\\
i\\0
\end{array}
\right)e^{-i(\omega t-\vec k\cdot\vec r)}$$</p>
<p>and with it's corresponding $E$ field. This is a circularly polarised wave, but that field does not have 0 divergence, the three components of it, whe... | 4,211 |
<p>I want to show that the 2-d wave equation is invariant under a boost, so, the starting point is the wave equation</p>
<p>$$\frac{\partial^2\phi}{\partial x^2}=\frac{1}{c^2}\frac{\partial^2\phi}{\partial t^2} $$</p>
<p>and the Lorentz transformation:</p>
<p>$$t'=\gamma(t-\frac{v}{c^2}x) \\ x'=\gamma(x-vt)$$</p>
<... | 4,212 |
<p>The Earth carries a negative electric charge of roughly 500 thousand Coulombs (according to different sources I've seen). If I touch the Earth I should therefore pick up some of this electric charge (through conduction) and become negative charged. Assuming the earth can modeled as a conducting sphere with radius $\... | 4,213 |
<p>I'm wondering about the exact reason why anyons escape the spin-statistic theorem (SST), see <em>e.g.</em> <a href="http://en.wikipedia.org/wiki/Spin%E2%80%93statistics_theorem">http://en.wikipedia.org/wiki/Spin–statistics_theorem</a>. </p>
<p>I've read somewhere (the wikipedia page is sufficient I believe to under... | 4,214 |
<p>As I understand it, when we say that the $SU(2)_{L} \times U(1)_{Y}$ is broken via the Higgs mechanism, this is because the symmetry acts on the Higgs mass in a way that would change it's value. If we want to pick a particular model we need to pick a fixed value of the Higgs mass, and this is only possible if we say... | 4,215 |
<p>If you happen to have the Third Edition of Classical Electrodynamics by John David Jackson, turn to section 11.8, as that's where I'm getting all this from. If not, you should still be able to follow along.</p>
<p>In said section, Jackson gives us this equation that relates any physical vector <strong>G</strong> in... | 4,216 |
<p>Let's say I have a free jet of air leaving a pipe into the atmosphere. I know that the static gauge pressure at the pipe exit is equal to the atmospheric. But what about the static gauge pressure 10 meters away if the air is still traveling as a free jet? Is it still atmospheric?</p> | 4,217 |
<p>Why is gravity such a weak force? </p>
<p>It becomes strong for particles only at the Planck scale, around $10^{19}$ $\text{GeV}$, much above the electroweak scale ($100$ $\text{GeV}$, the energy scale dominating physics at low energies). </p>
<p>Why are these scales so different from each other? What prevents qua... | 4,218 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/10670/what-nonlinear-deformations-will-a-fast-rotating-planet-exhibit">What nonlinear deformations will a fast rotating planet exhibit?</a> </p>
</blockquote>
<p>This is really a basic physics question t... | 129 |
<p>I am studying scattering theory right now in my QM class, and I'm attempting the Griffiths problem 11.4 as an exercise (it's not for homework). The problem is: Consider the case of low-energy scattering from a spherical delta-function shell: $V(r) = \alpha \delta(r-a)$. Calculate the scattering amplitude $f(\theta)$... | 4,219 |
<p>Why galaxies move away from each other in general on the astronomical scale?
Which answer is correct of the following?</p>
<p>It is because of the big bang theory, everything is just moving away from everything else on the astronomical scale, because of the explosion that happened in the past, just by inertia.</p>
... | 4,220 |
<p>In Steven Weinberg's Lecture on Quantum Mechanics (p. 342), he writes:</p>
<blockquote>
<p>The correlation between the spins of the two particles can be
expressed as the average value of the product of the $\hat{a}$
component of the spin of particle 1 and the $\hat{b}$ component of the
spin of particle 2:</... | 4,221 |
<p>In equation of <a href="http://en.wikipedia.org/wiki/Gibbs_free_energy#Graphical_interpretation" rel="nofollow">Gibbs free energy</a> change $(\Delta G) = (\Delta H)-T(\Delta S)$, is $T$ the system's or surrounding's temperature? </p>
<p>Edit:Oh sorry I am not clear earlier now I get clear question.I know we have t... | 4,222 |
<p>I am a graduate student in pure mathematics, during my study on <a href="http://en.wikipedia.org/wiki/Ricci_flow" rel="nofollow">Ricci Flow</a> I faced some functional known as <a href="http://en.wikipedia.org/wiki/Energy_functional" rel="nofollow">energy functional</a>. For example Einstein-Hilbert functional is ca... | 4,223 |
<p>The Source of Water is Pond where the water level do change randomly. A pipeline of 200mm pipe diameter run for around 2500 m. The Height difference between the level of the inlet pipe and the level of the exit pipe is around 9m. In other word: Water need to run by gravity for 2500 m. Difference in height is 9m. </p... | 4,224 |
<p>Lets say I enter a closed room with the walls and everything in it (including me and my eyes) at thermal equilibrium. Its a very hot room, but my super-eyes still work at 5000 degrees Kelvin.</p>
<p>I have two propositions which are in conflict.</p>
<p>The first is that I should be effectively blind when I am in t... | 4,225 |
<p>Lets say we have a tunelling problem in the picture, where $W_p$ is a finite potential step: </p>
<p><img src="http://i.stack.imgur.com/aFgQ4.png" alt="enter image description here"></p>
<p>If particle is comming from the left a general solutions to the Schrödinger equations for sepparate intervals I, II and II ar... | 4,226 |
<p><a href="http://www.youtube.com/watch?v=UJJuq_pcyIQ" rel="nofollow">http://www.youtube.com/watch?v=UJJuq_pcyIQ</a></p>
<p>What exactly is going on in the video example? I understand the phenomena occurs because of magnetism but I am trying to figure out the mechanics behind this sculpture. There obviously is a magn... | 4,227 |
<p>Lets say we have a particle of mass $m_1$ which has a kinetic energy $W_{k1}$. This particle collides with another same particle. How can i calculate mass $m_2$ and the speed $v_2$ of the particle which is formed out of the colliding two particles? </p>
<p>I know that relativistic preservation of energy $W$ and mom... | 4,228 |
<p>In 2009, Rowan University released a paper claiming to replicate Blacklight Power's results on energy generation using hydrino states of the hydrogen atom. <a href="http://www.blacklightpower.com/pdf/BLPIndependentReport.pdf" rel="nofollow">The paper</a> appears to describe the procedure in every detail as far as my... | 60 |
<p>So when you're looking at B-H curves for ferromagnetic substances, you often see these magnetic hysteresis curves, which occur, I gather, largely because of domain formation which has some reversible and some irreversible components:</p>
<p><img src="http://i.stack.imgur.com/DNjCd.png" alt="A magnetic hysteresis cu... | 4,229 |
<p>I want to calculate the work done by friction if the length $L$ of uniform rope on the table slides off. There is friction between the cord and the table with coefficient of kinetic friction $\mu_k$.</p>
<p>$$ W = \int F \cdot d \vec{s}$$
I think it would be:
$$ W_{fr} = \frac M L g \int_{0}^{L} dx$$</p>
<p>But th... | 4,230 |
<p>For an experiment I will hopefully be soon conducting at Johns Hopkins I need two different lenses.</p>
<p>The first needs to allow all wavelengths above 500 nm to pass (thus a high pass filter) and cut off everything else.<br>
The second needs to allow all wavelengths below 370 nm to pass (thus a low pass filter) ... | 4,231 |
<p>You build a <a href="http://en.wikipedia.org/wiki/Dyson_sphere">Dyson sphere</a> around a star to capture all its energy. The outer surface of the Dyson sphere still radiates heat at much higher temperature than the cold space background, so you're easy to detect.</p>
<p>But you'd like to stay hidden. So you cool t... | 4,232 |
<p>An ideal spring is attached to a wall, and the other end is attached to a mass $m$. The spring is initially compressed a distance $x$. After it is released, the mass collides with another mass $2m$ at a distance $x/2$ to the right of the spring equilibrium. The collision is inelastic and they slide together. How... | 4,233 |
<p>Suppose I have an atom at rest which is at energy level $E_i$. Would it be possible to raise it to the next higher level $E_{i+1}$ by shooting a photon of energy $E_{i+1}-E_i$ at it?</p>
<p>I ask because the photon will impart some momentum to the atom, so the atom will end up with some kinetic energy after the abs... | 130 |
<p>The <a href="https://en.wikipedia.org/wiki/Bekenstein_bound">Bekenstein bound</a> sets the maximum amount of information that can be contained in a region of space/energy, and is usually referred to in the same way as computer storage density:</p>
<blockquote>
<p>For example, a single hydrogen atom, if it were to... | 4,234 |
<p>For an outside observer the time seems to stop at the event horizon. My intuition suggests, that if it stops there, then it must go backwards inside.
Is this the case?</p>
<p>This question is a followup for the comment I made for this question: <a href="http://physics.stackexchange.com/questions/23118/are-we-insid... | 4,235 |
<p>Some sources say that when a photon hits the PV cell, it breaks apart electron-hole pairs. Other sources say that photons <em>create</em> electron-hole pairs. Can anyone explain which one is right? I've read several explanations of what goes on in the solar cell, but they don't seem very clear. To me, who has little... | 4,236 |
<p><strong>Question:</strong></p>
<blockquote>
<p>consider a long, straight wire of cross-sectional area $A$ carrying a
current $i$. Let there be $n$ free electrons per unit volume. An observer
places himself on a trolley moving in the direction opposite to the
current with a speed $v = \frac{i}{nAe}$ and sepa... | 4,237 |
<p>I'm doing an experiment where I bring a probe very close to a well full of fluid and then very slowly lower it to obtain some force deformation values. The material behaves very much like a fluid and when I bring the probe close to the fluid, it sort of jumps up and grabs the probe and forms like a "column?" that ac... | 4,238 |
<p>The last decades there has been a lot of research going on in the the area of three dimensional gravity. The motivation, I understand, is threefold:</p>
<ol>
<li><p>Whereas gravity is not perturbatively renormalizable in four spacetime dimensions, in three dimensions it is. To make it even more interesting it has b... | 4,239 |
<p>I'm trying to get motivated in learning the Atiyah-Singer index theorem. In most places I read about it, e.g. wikipedia, it is mentioned that the theorem is important in theoretical physics. So my question is, what are some examples of these applications?</p> | 4,240 |
<p>Why is the critical point for the phase diagram of pure water degrees of freedom equal to 0? Maybe, you know what is the mathematical explanation for the fact that the number of degrees of freedom at the critical point is 0? What else is affected by the lack of degrees of freedom in addition to the Gibbs phase rule?... | 4,241 |
<p>Consider two objects presented in the figure below. Objects have equal masses and are separated by a distance of 60 light seconds. </p>
<p>Assume that we move left object by 3 light seconds to the left in 30 seconds. This requires energy input, lets say it's equal to X. Change in potential energy is also equal to X... | 4,242 |
<p>There have been a few <a href="http://www.crunchgear.com/2010/12/10/navys-mach-7-railgun-fires-a-round-at-33000-megajoules/">articles about the Navy's new Mach 7 33 Megajoule railgun.</a> As a physics teacher, I have a couple of questions about this, and was hoping for some help. </p>
<ol>
<li><p>Is the kinetic ene... | 4,243 |
<p>One of the most disturbing aspects of General Relativity is the 'Marble versus Wood' duality of the theory: Matter creates curvature, and curvature doesn't create curvature (at least not directly)</p>
<p>The holographic principle suggests a reason for this division: matter fields and gravity are paired to structure... | 4,244 |
<p>A wire placed in a magnetic field and has current flowing, it will experience the Lorentz force, work is done by the electric field and energy is conserved. Being converted from the power source to KE, and the wire moves.</p>
<p>How can we apply Poynting's theorem to state that this system's energy will always be c... | 4,245 |
<p>I found the following explanation for <a href="http://en.wikipedia.org/wiki/Chirality_%28physics%29">chirality</a> for spin 1/2 particles <a href="http://www.quantumdiaries.org/2011/06/19/helicity-chirality-mass-and-the-higgs/">here</a></p>
<blockquote>
<p><img src="http://i.stack.imgur.com/mUD0C.png" alt="enter ... | 4,246 |
<p>I was reading <a href="http://www.lightreading.in/document.asp?doc_id=226833&site=lrindia&" rel="nofollow">this article</a>. There is a statement "It is a well-known fact that the telecom towers mounted with antennas in the lower frequency bands can cover far greater areas than those using the 1800 frequen... | 4,247 |
<p>I've recently been reading (at a basic level) about the double slit experiment and how the mere act of observing can cause the "wave function to collapse", as they say. I find this mind-blowingly fascinating, and it naturally sparks some questions.</p>
<p>In particular, consider the following scenario: I perform th... | 4,248 |
<p>Is photon interaction , electrostatic interaction outside the nucleus and gravitational interaction is all due to electromagnetic waves ? and CAN be identified as with the de Broglie waves ?</p>
<p>I thought of a theory in which is assuming that photon interaction , electrostatic interaction outside the nucleus and... | 4,249 |
<p>Let $\mathbf{E}(r,t),\mathbf{B}(r,t)$ be two vector fields (in $\mathbb{R}^3$), s.t. they satisfy fot $t=0$ the equations:</p>
<ol>
<li><p>$\nabla \cdot \mathbf{B}(r,0)=0.$ </p></li>
<li><p>$\nabla \cdot \mathbf{E}(r,0)=\frac{\rho(r,0)}{\epsilon_0}.$</p></li>
</ol>
<p>The question now is:</p>
<p>What properties ... | 4,250 |
<p>Conventional wires become very lossy at high frequencies. </p>
<p><strong>Is this because of the skin effect?</strong></p>
<p>Plasmon based computer chips, since plasmons can support much higher frequencies (~100 THz range). </p>
<p>Aren't free electron oscillations in a metal plasmons. What is the difference and... | 4,251 |
<p>Two equal masses of mass M are glued to a massless hoop of radius R is free to rotate about its center in a vertical plane. The angle between the masses is 2$\theta$. Find the frequency of oscillations.</p>
<p>My attempt at a solution is ($\phi$ is the displaced angle):
$$x_{m1}=-R\sin (\theta -\phi)$$
$$y_{m1}=-R\... | 4,252 |
<p>Everybody has been taught at one point, "oh the universe expands, but that doesn't mean that everything is expanding uniformly, since that means we can't detect the expansion, but only that huge galaxies are moving away from each other".</p>
<p>But I'm rather confused. Can't the expanding universe simply be thought... | 56 |
<p>This is related to this question:<a href="http://physics.stackexchange.com/questions/88826/does-the-weight-of-an-hourglass-change-when-sands-are-falling-inside">Does the weight of an hourglass change when sands are falling inside?</a></p>
<p>At Brigham Young University, there is a display consisting of a sealed off... | 4,253 |
<p>The <a href="http://en.wikipedia.org/wiki/Uncertainty_principle" rel="nofollow">uncertainty principle</a> states that,</p>
<p>$$\sigma _{{x}}\sigma _{{p}}\geq {\frac {\hbar }{2}}.$$</p>
<p>It is mentioned from many sources that the probability distribution of the particle position and momentum would follow a Gauss... | 4,254 |
<p>I read somewhere that the tidal forces between the earth and the moon causes the equality between the 2 periods of the moon and that every planet-satellite system will evolve to this condition (like pluto-charon of you consider pluto a planet). Can somebody give me some references (books, articles) discussing this i... | 4,255 |
<p>The global conformal group in 2D is $SL(2,\mathbb{C})$. It consists of the fractional linear transforms that map the Riemann sphere into itself bijectively and is finite dimensional. </p>
<p>However, when studying $CFT_2$ people always use the full Virasoro algebra, not just the $L_{0,\pm1}$ which actually exponent... | 4,256 |
<p>I understand that a general interpretation of the $1/r^2$ interactions is that virtual particles are exchanged, and to conserve their flux through spheres of different radii, one must assume the inverse-square law. This fundamentally relies on the 3D nature of space.</p>
<p>General relativity does not suppose that ... | 4,257 |
<p>This in the context of the AdS/CFT correspondence. I am reading <a href="http://arxiv.org/abs/hep--th/9905111.pdf" rel="nofollow">this</a> review on AdS/CFT Aharony et. al. (The MAGOO review) The abstract can be found <a href="http://arxiv.org/abs/hep-th/9905111" rel="nofollow">here</a></p>
<p>Equation (2.50) of t... | 4,258 |
<p>Is it possible to quick freeze half of an unopened bottle of water or soda by putting half of the bottle in a subfreezing solution liquid nitrogen or other solution without freezing the whole bottle?</p> | 4,259 |
<p>A hollow cylinder, with no top or bottom, of radius $R$ and length $L$ is uniformly charged with density $\sigma>0$. I have to find the point on space where a point charge $q>0$ has to be drawn from $\infty$ with speed $v\rightarrow0$ so that the work done is maximum, so I have to find the point with maximum p... | 4,260 |
<p>This is about the same paper as this thread: <a href="http://physics.stackexchange.com/questions/11645/some-questions-about-chapter-i-1-by-minahan-of-the-review-of-ads-cft-integrab">Some questions about chapter I.1 (by Minahan) of the "Review of AdS/CFT Integrability"</a> but it was never answered. </p>
... | 4,261 |
<p>Lets say we have a potential step with regions 1 with zero potential $W_p\!=\!0$ (this is a free particle) and region 2 with potential $W_p$. Wave functions in this case are: </p>
<p>\begin{align}
\psi_1&=Ae^{i\mathcal L x} + B e^{-i\mathcal L x} & \mathcal L &\equiv \sqrt{\frac{2mW}{\hbar^2}}\\
\psi_2&... | 4,262 |
<p>I would like to find the equation of motion for the scalar field $\phi$ by varying the following action in General Relativity. </p>
<p>Special Relativity:
$$
S = -\tfrac{1}{2}\int d^4\xi\, \eta^{ab} \partial_a \phi\partial_b\phi
$$</p>
<p>General Relativity:
$$
S = -\tfrac{1}{2}\int d^4x \sqrt{g}\, g^{\mu\nu} \par... | 4,263 |
<p>What would happen if you were to accelerate one end of a material, say a steel rod for instance, at faster per second than the speed of sound in that material? </p>
<p>For example, if the speed of sound in steel is 6100m/s, what would happen if you pushed the end of that piece of steel at more than 6100m/s/s?</p>
... | 4,264 |
<p>I heard that this statement is correct. However, it seems odd to me. The number of possible microstates is still the same, so isn't the entropy constant?</p> | 4,265 |
<p>For a spin 1/2 particle you have two spin states, either up or down which are orthogonal. But what about a spin 1 particle which has 3 spin states, either up, down, not up/not down?</p> | 4,266 |
<p>Red colour bares 430-480THz and Violet bares 670-750THz according to Wikipedia.</p>
<p>What frequencies are the colours between red and violet? Will they be higher than red? or lower than violet?</p>
<p>What physically properties do opposite colours carry? Cyan is the opposite colour of red; yellow is the opposite... | 4,267 |
<p>Basically, What is the difference <a href="http://en.wikipedia.org/wiki/Diamagnetism" rel="nofollow">diamagnetism</a> and <a href="http://en.wikipedia.org/wiki/Superconductivity" rel="nofollow">superconductivity</a>?</p>
<p>As far as I understand, diamagnetism comes from the fact, that all electrons in a solid, whe... | 4,268 |
<p>I recently studied that NASA has planned to tow and place it in the orbit of the moon.
My doubt is when asteroid is placed in the orbit near moon.since the gravitational field of earth is very high.what will it revolve around the moon or the earth.
Can anyone clarify my doubt ??</p> | 4,269 |
<p>I am trying to prove the following equivalent form for long-range-order in superconductivity (Annett's book states something like this) : </p>
<p>\begin{equation}\lim_{|R-R'|\to \infty}<\psi^{\dagger}(R')\psi(R)> = <\psi^{\dagger}(R)\psi(R)> \end{equation}</p>
<p>where the brackets are evaluated on the... | 4,270 |
<p>I am trying to solve this problem:</p>
<blockquote>
<p><em>Consider a rocket moving relative to an inertial frame $\mathcal{F}$ , such that its worldline is given by $$x^{\mu}=c^2/g(\sinh(g\tau/c),\cosh(g\tau/c)-1,0,0).$$ What are the components of four acceleration relative to the instantaneous rest frame of the... | 4,271 |
<p>Apologies in advance for the long question.</p>
<p>My understanding is that in GR, massive observers move along timelike curves $x^\mu(\lambda)$, and if an observer moves from point $x^\mu(\lambda_a)$ to $x^\mu(\lambda_b)$, then his clock will measure that an amount of time $t_{ba}$ given by the curve's arc length;... | 4,272 |
<p>An object with a density of $x$ inside a liquid with a density greater than $x$ would float.
If we assume that both of these are positively charged and the object is in the middle of the liquid:</p>
<ol>
<li><p>Would the liquid touch the object?</p></li>
<li><p>Would the object still float up because of buoyancy?</... | 4,273 |
<p>Usually what helps me understand a concept better in physics is to write a simulation of it. I've got to the point where I'm competent in the basics of special relativity, but, I can't figure out how to write a relativistic simulation! My normal approach in Newtonian mechanics is just to attach two objects together ... | 4,274 |
<p>In one of his lecture,Prof. Susskind mentioned that the event horizon "bulges" forward to meet any incoming radiation or matter; and it is a property of Einstein field equations. I have not come across any such property, and if it exists, shouldn't it belong to the Schwarzchild metric rather?
Please explain me that ... | 4,275 |
<p>I notice a $2\pi$ term in the $\delta$-function when trying to construct an amplitude using the Feynman Rules. The $2\pi$ also appears as an integration measure to enforce normalisation in the phase space, what is the origin of this $2\pi$ term? Where does it come from? </p> | 4,276 |
<p>I've heard two different descriptions of gravity, and I'm wondering how they work together.</p>
<p>The first is Gravitons:</p>
<blockquote>
<p>"The three other known forces of nature are mediated by elementary
particles: electromagnetism by the photon, the strong interaction by
the gluons, and the weak inter... | 131 |
<p>What sort of mode-locked laser systems allow for the production of single isolated pulse of light (as opposed to a train of more than one pulse), where the individual pulse duration is on order picoseconds ($\approx 10^{-12}$ seconds) to femtoseconds ($\approx 10^{-15}$ seconds)? Is there any reason I couldn't use ... | 4,277 |
<p>Malcolm Gladwell made a claim in a <a href="https://www.youtube.com/watch?feature=player_embedded&v=5L0GGfQblrc" rel="nofollow">recent talk</a> that a sling with a stone going at 30m/s has the same stopping power as a .45 calibre handgun.</p>
<p>How would I verify whether or not this claim is true - even given ... | 4,278 |
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