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<p>Just a simple question. Why is it, that when a material becomes superconducting, and by that gets zero resistivity, the electrons don't hit impurities in the material?
For the material to have zero resistivity, that means that the electrons can just flow without any disturbance at all?</p>
<p>Is it because of the C... | 1,684 |
<p>Why is the <a href="http://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29" rel="nofollow">cosmological scale factor</a> (expansion rate of the universe) not simply the time $t$, i.e. the age of the universe?</p> | 1,685 |
<p>My question boils down to this. If the Universe was contracting the stars closer to the center would move faster to the middle than stars that were further away from the center. </p>
<p>That would also produce a red doppler shift. So why is it that the red shift is always linked to expansion? Human optimism? <... | 1,686 |
<p>I recently got into a lengthy debate about the exact nature of boundary layer separation. In common parlance, we have a tendency to talk about certain geometries as being too "sharp" for a viscous flow to remain attached to them. The flow can't "turn the corner" so to speak, and so it separates from the body. While ... | 1,687 |
<p><a href="http://physics.stackexchange.com/questions/55686/gravitational-redshift-around-a-schwarzschild-black-hole">Another question</a> about the Schwarzschild solution of General Relativity:</p>
<p>In the derivation (shown below) of the Schwarzschild metric from the vacuum Einstein Equation, at the step marked "H... | 1,688 |
<p>Intuitively it's easy to accept that the usual variables like temperature, internal energy, etc. are 'macroscopic', but does there exist a formal definition of a macroscopic variable? </p>
<p>In other words, is there a clear way to separate the set of all observables (and functions of observables) on a system into ... | 1,689 |
<p>I'm reading Arnold's "Mathematical Methods of Classical Mechanics" but I failed to find rigorous development for the allowed forms of Hamiltonian.</p>
<p>Space-time structure dictates the form of Hamiltonian. Indeed, we know how the free particle should move in inertial frame of references (straight line) so Hamilt... | 1,690 |
<p>I'm interested in knowing whether sigma models with an $n$-sheeted Riemann surface as the target space have been considered in the literature. To be explicit, these would have the action \begin{align*}
S=\frac{1}{2}\int d^2x\, \left(\partial_a R\partial^a R+R^2\partial_a \theta {\partial}^a\theta\right),
\end{align*... | 1,691 |
<ul>
<li>Is it possible to measure or calculate the total entropy of the Sun?</li>
<li>Assuming it changes over time, what are its current first and second derivatives w.r.t. time? </li>
<li>What is our prediction on its asymptotic behavior (barring possible collisions with other bodies)?</li>
</ul> | 1,692 |
<p>The <a href="http://en.wikipedia.org/wiki/Mathematical_universe_hypothesis" rel="nofollow">Mathematical universe hypothesis</a>, mainly by Max Tegmark and <a href="http://en.wikipedia.org/wiki/A_New_Kind_of_Science" rel="nofollow">A new Kind of Science</a>, mainly by Stephen Wolfram both claim (as least as I underst... | 1,693 |
<p>When using two component notation people often prefer to refrain from using arrows in Feynman diagrams to denote charge flow as is done in four-component notation. Instead, if understand correctly, they use arrows to denote chirality. I'd like to know what is the prescription to draw out the diagrams. I have read <a... | 1,694 |
<p><img src="http://i.stack.imgur.com/6UfAY.jpg" alt="enter image description here">
Laminar flow is a streamlined steady flow with a uniform gradient of velocity across the diameter of the pipe. I am familiar with the elementary treatment of laminar flow, like basic velocity profile, shear stresses etc. But my questio... | 1,695 |
<p>I'm currently studying field theory and I'm having some trouble with conserved charge given in field components. If we have a complex scalar action of a field $\phi=(\phi_1,\phi_2)^T$ that is</p>
<p>$$S[\phi]={\int}\left[ \partial^\mu\phi^\dagger\partial_\mu\phi-m^2\phi^\dagger\phi-\frac{1}{2}\lambda(\phi^\dagger\p... | 1,696 |
<p>The string theory landscape seems to this outside observer to be an intermediate step in the intellectual progress toward a more robust theory that explains why our one universe has the particular properties that it has. is this the majority opinion or do most string theorists view the landscape as a plausibly bein... | 1,697 |
<p>I'm working through some exam problems, and I came across this one - the solution of which baffles me considerably.</p>
<blockquote>
<p>A two-dimensional jet emerges from a narrow slit in a wall into fluid which is at rest. If the jet is thin, so that velocity $\vec u = (u, v)$ varies much more rapidly across the... | 1,698 |
<p>In quantum mechanics, uncertainty principle states that we can only measure the quantity of spin in one axis but not others.</p>
<p>Then what about in superstring theory? As quantum mechanics is basically three-dimensional world, this does make sense, but superstring theory adopts more than three-dimensional space.... | 1,699 |
<p>If I had a mass of $100\:\rm{kg}$ accelerating due to gravity, using $F=ma$:</p>
<p>$F = 100\:\rm{kg} \times 9.8\:\rm{m/s^2}$</p>
<p>$F = 980 \:\rm N$...</p>
<p>If I increased the mass to 200kg, the force would be 1960 N:</p>
<p>$F = 200\:\rm{kg} \times 9.8\:\rm{m/s^2}$</p>
<p>$F = 1960 \:\rm{N}$</p>
<p>Now, f... | 1,700 |
<p>The usual explanation of spontaneous radiation is that the energy eigenstates are perturbed by QED interaction, so that the eigenstates obtained from single-particle QM are no longer eigenstates of the full Hamiltonian, and in turn different (original) eigenstates can mix after some time-evolution. However I'm not q... | 1,701 |
<p>I believe the answer to be yes, but I realize that sometimes physicists place additional constraints that might not be obvious. If superalgebras are clifford algebras, why make a literary distinction?</p> | 1,702 |
<p>Does wave-function collapse cause the entropy of the atom (ie. the sub-atomic particle system that makes up the atom) to increase? </p> | 1,703 |
<p>I have been searching for a straight forward answer to this question for ages now and it is driving me crazy.</p>
<p>Here is what I know:
If an object is moving at a constant speed the force of friction must equal the applied force (Please assume the applied force is horizontal) and for it to be accelerating or dec... | 1,704 |
<p>In a specific date what law gives us perfect measurements and how will we measure if latitude is given?</p> | 28 |
<p>Say there were 2 objects with certain masses (e.g. $m_1$ and $m_2$). If they were close together gravity would attract the 2 objects. If they were a large distance apart the expansion of the universe (dark energy) would pull them apart. What is the distance apart that they must be (I assume that it is relative to th... | 1,705 |
<p>I read a saying in wiki of asymptotically flat spacetime
<a href="http://en.wikipedia.org/wiki/Asymptotically_flat_spacetime" rel="nofollow">http://en.wikipedia.org/wiki/Asymptotically_flat_spacetime</a></p>
<p>"In general relativity, an asymptotically flat vacuum solution models the exterior gravitational field of... | 1,706 |
<p>I've read somewhere that one does not need to prove Lorentz invariance of the Maxwell
equations
$F_{\mu\nu,\sigma}+F_{\nu\sigma,\mu}+F_{\sigma\mu,\nu}=0$
because it is "manifestly Lorentz invariant" or "because they are tensor equations"? What is meant by that? I've read that this could mean that space and time are... | 1,707 |
<p>I know the wave nature of electrons was evoked to explain why atoms are stable but I thought waves could be put in the same state like photons yet electrons can not exist in the same state.</p> | 1,708 |
<p>My understanding about conservative force is a force that its work is independent of path such that we can construct another form of the work called potential to make our life easier.</p>
<p>For friction, if I start from microscopic point of view, it should be the macroscopic effect of the electric force or gravity... | 1,709 |
<p>In <a href="http://www.if.ufrj.br/~mbr/warp/etc/cqg15_2523.pdf">this paper</a>, D. H. Coule argues that warp drive metrics, like the one proposed by Alcubierre, require the exotic matter to be laid beforehand on the travel path by conventional travel. At section 5 of this paper "Alteration of the light-cone structur... | 1,710 |
<p>Suppose we have a man traveling in an open car (roof open) with speed $v$ towards right (man faces right). He throws a stone (mass $m$) towards right, in his frame-forward with speed $V$. </p>
<p>In the car's frame, the total energy imparted to it was $$E=E_f-E_i=\frac{1}{2}mV^2$$<br>
In the ground frame, the tota... | 1,711 |
<p>In QED, one can relate the two-particle scattering amplitude to a static potential in the non-relativistic limit using the Born approximation. E.g. in Peskin and Schroeder pg. 125, the tree-level scattering amplitude for electron-electron scattering is computed, and in the non-relativistic limit one finds the Coulom... | 1,712 |
<p>This is related to a <a href="http://physics.stackexchange.com/questions/57733/hamiltonian-of-polymer-chain">question about a simple model of a polymer chain</a> that I have asked yesterday. I have a Hamiltonian that is given as:</p>
<p>$H = \sum\limits_{i=1}^N \frac{p_{\alpha_i}^2}{2m} + \frac{1}{2}\sum\limits_{i=... | 1,713 |
<p>In acoustic metamaterials we have simultaneously negative bulk modulus, $\beta$, and effective mass density, $\rho$.</p>
<p>I understand how one can obtain a -ve $\rho$ by constructing a solid-solid system with vastly different speeds of sound, as this can be considered as a mass-in-mass system connected by springs... | 1,714 |
<p>I've been doing some research into the analysis used in particle physics when determining the significance of a finding (e.g. the recent Higgs candidate was announced as a boson in the 125-126 GeV/$c^{2}$ mass range with a $5\sigma$ significance).</p>
<p>I believe this confidence level is determined by estimating t... | 1,715 |
<p>Does someone know the historical reason behind the difference in physical units between nautical and terrestrial miles?</p> | 1,716 |
<p>I have a system of two spin 1/2 particles in a superposition of spin states in the z-direction given by:</p>
<p>$\psi = \frac{1}{2} |+ +\rangle + \frac{1}{2} |+ -\rangle + \frac{1}{\sqrt{2}} |- -\rangle$ </p>
<p>where $+$ designates spin up, $-$ designates spin down and the first particle's state is the first term... | 1,717 |
<p>In a <a href="http://radio.seti.org/episodes/Skeptic_Check_Science_Blunders" rel="nofollow">recent episode</a> of the <em>Big Picture Science</em> podcast, there was an interview with <a href="http://www.columbia.edu/cu/biology/faculty-data/stuart-firestein/faculty.html" rel="nofollow">Stuart Firestein</a> (chair of... | 1,718 |
<p>I have a question please about <a href="http://en.wikipedia.org/wiki/Renormalization" rel="nofollow">renormalization</a> in QFT. Why a renormalizable theory requires only a finite number of counter-terms?</p> | 1,719 |
<p>What is the force between two perpendicular wire carrying current, one to the north and one to the east?</p> | 1,720 |
<p>I'm currently working on a problem which is really giving me some issues.</p>
<p>The problem concerns the force required to expel water from a syringe. We have a 20 ml syringe (which is $2\times10^{-5}$ meters cubed) with a diameter of 1 cm, full of water. The needle of the syringe is 40 mm in length and has a diam... | 1,721 |
<p>Consider Faraday's flux law for the EMF generated in a conductor loop:</p>
<p>$$ \varepsilon = - \frac{d \phi}{dt},$$</p>
<p>where $\varepsilon$ is the EMF, and $\phi$ is the magnetic flux through the loop.<p></p>
<p>There are two possible causes for the flux to variate over time: variations in the magnetic field... | 1,722 |
<p>I'm curious about the radiant intensity distribution of pulsars: what's the general dependence of intensity on angle, and what are typical angular beam widths? How much does the beam width vary between pulsars? (Presumably this is tied to magnetic field strength.)</p>
<p>Even something as simple as a very sketchy p... | 1,723 |
<p>Given enough time, where are the Voyager spacecrafts heading? (Assuming some alien civilization doesn't pick them up.)</p>
<p>Will they pass by any interesting stars on the way to the black hole at the center of our galaxy or will it perhaps leave the galaxy?</p>
<p>What are the highlights on their journey that we... | 1,724 |
<p>Various websites today are reporting with photos and videos of <a href="http://en.wikipedia.org/wiki/C/2011_W3_%28Lovejoy%29" rel="nofollow">Comet Lovejoy</a>. However, I can't seem to find a definition of which direction to look for it tomorrow morning. I'm in <a href="http://en.wikipedia.org/wiki/Christchurch" rel... | 1,725 |
<p>If an effective field theory has a chiral anomaly it means that chiral symmetry isn't a symmetry of the underlying theory which has been cut off to make the EFT. My question is whether there's a good example where this can seen explicitly. The kind of thing I'm picturing would be an EFT at cutoff A which has no chir... | 1,726 |
<p>From what I've learned, the more an object travels closer and closer to the speed of light, the more time will slow down for that object.. at least from an outside perspective.. </p>
<p>It was shown that atomic clocks run slower in high speed orbit than clocks on earth.. I assume that the rate of radioactive decay ... | 1,727 |
<p>I'm trying to understand the derivation of the angular momentum commutator relations. How is</p>
<p>$$[zp_y, zp_x] ~=~ 0?$$ </p>
<p>How is</p>
<p>$$[yp_z, zp_x] ~=~ y[p_z, z]p_x?$$ </p> | 1,728 |
<p>My question is: <strong>is there a simple and truly general equation for the resistance between two electrical equipotential surfaces?</strong>. Obviously, if so, what is it, and if not, why? It would be very difficult to solve, granted, but I just want to see a calculus equation that is fully descriptive. I have... | 1,729 |
<p>Suppose I want to launch a rocket from earth to some point $O$ between the center of earth and the center of moon (on a straight line connecting their centers), where the gravitational force of the moon 'cancels out' the gravitational force of the earth (this point is located at $\approx 54 R_E$ from the center of e... | 1,730 |
<p>Are there physical theories in use, which don't fit into the frameworks of either <em>Thermodynamics</em>, <em>Classical Mechanics</em> (including General Relativity and the notion of classical fields) or <em>Quantum Mechanics</em> (including Quantum Field Theory and friends)?</p> | 1,731 |
<p>As the <a href="http://en.wikipedia.org/wiki/Earth_wobble" rel="nofollow">Earth wobbles</a> during rotation, does the higher gravity at the equator tend to pull the moon toward an equatorial orbit even as the earth does that thousands of years wobble cycle? It would seem to me that the higher gravity, due to the la... | 1,732 |
<p>What is the moment of inertia of a pizza slice that has a radius r, an angle (radians) of theta, and a height of h about the center point perpendicular to the cheese plane?</p> | 1,733 |
<p>How do I prove that $$\int \dot{x}^2 dt\geq \int \langle \dot{x}\rangle^2 dt $$</p>
<p>(i.e a free particle not in any external potential field movies with uniform veloctiy)</p> | 1,734 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/21360/cosmic-radiation-cutoff-at-low-energies">Cosmic radiation cutoff at LOW energies?</a> </p>
</blockquote>
<p>The energy spectrum of the cosmic radiation (not CMB) is limited on both sides.</p>
<p>I... | 29 |
<p>I've been solving a problem in quantum mechanics, and I was deriving the standard deviation of $P$, knowing that $\langle P\rangle=0$. Because $\Delta P=\sqrt{\langle P^2 \rangle - \langle P \rangle ^2} = \sqrt{\langle P^2 \rangle}$, I was trying to calculate the expectation value of the square of the momentum. The ... | 1,735 |
<p>There are a bunch of stars orbiting the black hole in the center of <a href="http://en.wikipedia.org/wiki/Milky_Way" rel="nofollow">our galaxy</a>.</p>
<p>These stars move at huge speed. Why do we see this? Why do the black hole not impose any noticeable time dilation on these stars?</p> | 1,736 |
<p>Let's say I light a wall with two spotlights: One red and one green one. Where they overlap, I'll see a yellow area at the wall.</p>
<p>My question is, whether this is caused by an modification of the frequency/wavelength or simply by my eye combining the two incoming lights.</p>
<p>Light is "added", wavelength is... | 1,737 |
<p><a href="http://www.linkedin.com/profile/view?id=14132627&authType=NAME_SEARCH&authToken=Q-WY&locale=en_US&srchid=120ba6d2-2971-4f13-8f93-22815076ab52-0&srchindex=1&srchtotal=10&goback=.fps_PBCK_Jay+Wacker_%2a1_%2a1_%2a1_%2a1_%2a1_%2a1_%2a2_%2a1_Y_%2a1_%2a1_%2a1_false_1_R_%2a1_%2a51_%2a1_... | 1,738 |
<p>My son got an orion starblast 4.5 for Christmas. It comes with orion explorer II 17mm and 6mm eyepieces. We are looking at some additional accessories and wondering what you would recommend as "first accessories" to get the most out of the telescope. Our initial inclination is towards:</p>
<ol>
<li>A barlow lens.... | 1,739 |
<p>How can I determine whether the mass of an object is evenly distributed without doing any permanent damage? Suppose I got all the typical lab equipment. I guess I can calculate its center of mass and compare with experiment result or measure its moment of inertia among other things, but is there a way to be 99.9% su... | 1,740 |
<p>Let us only consider classical field theories in this discussion.</p>
<p>Noether's theorem states that for every global symmetry, there exists a conserved current and a conserved charge. The charge is the generator of the symmetry transformation. Concretely, if $\phi \to \phi + \varepsilon^a\delta_a \phi$ is a symm... | 1,741 |
<p>Consider the following question:</p>
<blockquote>
<p>In which of the following situations would a force be exerted on an object and no work be done on the object? </p>
<p>I. a centripetal force is exerted on a moving object</p>
<p>II. a force in the opposite direction as the object is moving</p>
<p... | 1,742 |
<p>At the mean-field level, the dynamics of a polariton condensate can be described by a type of nonlinear Schrodinger equation (Gross-Pitaevskii-type), for a classical (complex-number) wavefunction $\psi_{LP}$. Its form in momentum space reads:</p>
<p>\begin{multline}
i \frac{d}{dt}\psi_{LP}(k) =\left[\epsilon(k)
-i... | 1,743 |
<p>Most universities provide an experiment about the photoelectric effect to determine $h$ by measuring the stop voltage against the light frequency and calculating the slope $h/e$.</p>
<p>But mostly they also talk about the contact voltage, which just changes the offset, but not the slope.</p>
<p>I have several rela... | 1,744 |
<p>There are a lot of supersymmetric theories, and, sometimes,in the Lagrangian, there are interacting terms between bosonic and fermionic degrees of freedom, and sometimes not. Why ?</p>
<p>For instance, for the basic chiral superfield without superpotential, there is no interaction, while for 11-D supergravity, ther... | 1,745 |
<p>I have a very simple question with regard to numerical methods in physics.</p>
<p>I want to solve the eigenvalue problem for a particle moving in an arbitrary potential. Let's take 1D to be concrete. I.e. I want to find $(E,\psi(x))$ satisfying</p>
<p>\begin{align}
\left[-\frac{1}{2}\partial_x^2 + V(x) \right]\psi... | 1,746 |
<p>For example, imagine an object of a certain mass which is attached to a rope and is dangling in the air. The rope needs to have a certain tension to be able to hold the object up, that is, negate the effects of gravity pulling it down. I'm wondering, if you took the other end of the rope and started pulling it upwar... | 1,747 |
<p>What would be an experimental test of AdS/CFT correspondence? Or it's extensions?</p>
<p>I've heard that people are studying AdS/CMT (condensed matter) correspondence, but I don't know the details of it?</p>
<p>But in general, how would you test it?</p> | 1,748 |
<p>I am doing a simple project for a self-learn class with a friend to understand physics better over the summer.</p>
<p>We slide down a hill on a tarp on an ice-block and then half way down, we hit grass and we want to compare the friction between the grass and the tarp.</p>
<p>We calculated the angle of the hill as... | 1,749 |
<p>In a forward-biased PN junction, the potential barrier decreases, allowing more majority carriers from one side to diffuse to the other side where they are minority carriers. After they cross the potential barrier, they form a diffusion current, the drift current of minority carriers is insignificant, then they reco... | 1,750 |
<p>How was it discovered that the electric field of a negative charge points towards the charge itself? Is it true? </p>
<p><img src="http://i.stack.imgur.com/bh9uO.png" alt="field of a negative point charge"></p>
<p>(Courtesy of wikipedia)</p> | 1,751 |
<p>As we all know the speed of light is the limit at which energy/matter can travel through our universe. </p>
<p>My question being: is there a similar limit for acceleration? Is there a limit to how quickly we can speed something up and if so why is this the case?</p>
<p>Short question, not sure what else I can elab... | 1,752 |
<p>I am searching for not too old literature on the quantum description of unstable particles. I am referring to something beyond the ad-hoc S-matrix description based on the optical theorem common to textbooks such as those given by Peskin and Schröder or Weinberg etc. The book "Open Quantum Systems and Feynman Integr... | 1,753 |
<p>I am confused on few topics...</p>
<p>What is meant by "Frequency of Light"? Does the Photon(s) vibrate, that is known as its frequency? If the Photons vibrate, then they have a specific frequency, then What is meant by "Higher frequency light" as used in Photo-electric Effect? In which directions/axis do they vibr... | 1,754 |
<p>I have a simple question. I hope I don't get a stupid answer. Where does the magnetic field of a permanent magnet comes from AND why is it permanent (are we dealing with perpetual motion)?</p>
<p>This is what wiki is saying:
"The spin of the electrons in atoms is the main source of ferromagnetism, although there is... | 1,755 |
<p>I know that this isn't the place for such basic questions, but I didn't find the answer to this anywhere else. It's pretty simple: some particle moves in straight line under constant acceleration from one point $x_0$ to another point $x_1$ during the time interval $\Delta t_1$. When the particle reaches the point $x... | 1,756 |
<p>When sitting in a gravity well, as we do on earth, does our effective mass become smaller than our rest mass due to having negative potential energy? Correspondingly, does a free falling mass (from infinity, radial path) have an effective mass equal to its rest mass, as here potential and kinetic energies are ballan... | 1,757 |
<p>I have a very simple mental picture that earthquake waves travel like shear (transverse) waves through the earth.</p>
<p>a. Does the speed of this wave give any valuable information about the mechanical properties of the geological medium?</p>
<p>b. Can this data be used to characterize mechanical properties of th... | 1,758 |
<p>I have been trying to understand "wave-particle duality" and other cases related to it. I am currently a college level student. I have few question which I am not getting answers clearly. </p>
<p>In double slit experiment, A particle behave like a wave, then how is "wave-particle duality" explained? I mean, If the ... | 1,759 |
<p>I'm writing up a lab report and have a question about the following formula</p>
<p>$$N = N_0e^{-\lambda t}$$</p>
<p>$N$ indicates the number of nuclei left after a time $t$ and $N_0$ indicates how much there was to begin with. In the experiment, we used a scintillation counter (consists of a crystal and a photomul... | 1,760 |
<p>How does free electrons moving through a wire cause random vibrational motion of the positive ions?</p> | 1,761 |
<p>Can a laser powerful enough to cut(100w for example) be redirected using fiber optics ?
What issues need to be considered?</p>
<p>To be clear it should retain the ability to cut after exiting the fiber.</p> | 1,762 |
<p>Alice and Bob are moving in opposite direction around a circular ring of Radius $R$, which is at rest in an inertial frame. Both move with constant speed $V$ as measured in that frame. Each carries a clock, which they synchronize to zero time at a moment when they are at the same position on the ring. Bob predicts t... | 1,763 |
<p>Temperature is disordered kinetic energy, with 0K being 0 Joules disordered kinetic energy, if I"m not mistaken. So, given required parameters(temperature, number of particles, mass of each particle, whatever is required) can you find the disordered kinetic energy of each particle?</p> | 1,764 |
<p>Are there any handy exercises about nuclear weapon design that are suitable for advanced undergrads in a nuclear physics or similar level physics course? I'm most curious about questions that actually appeared in textbooks or course homeworks.</p>
<p>It doesn't matter if it's about gun weapon design or implosion w... | 1,765 |
<p>I have a couple of conceptual questions that I have always been asking myself.</p>
<p>Suppose we have an electron and a proton at very large distance apart, with nothing in their way. They would feel each the other particle's field - however weak - and start accelerating towards each other.</p>
<p>Now:</p>
<p>1) ... | 1,766 |
<p>If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere (according to <a href="http://www.youtube.com/watch?v=iBsywDWmwyA" rel="nofollow">this</a> documentary). </p>
<p>Therefore, if we accept that the universe is infinite and it's possible to trave... | 1,767 |
<p>I am currently trying to learn some basic quantum mechanics and I am a bit confused. Wikipedia defines a <a href="http://en.wikipedia.org/wiki/Photon" rel="nofollow">photon</a> as a quantum of light, which it further explains as some kind of a <a href="https://en.wikipedia.org/wiki/Wave_packet" rel="nofollow">wave-p... | 562 |
<p>Specifically: What are empirically well-understood examples of (integrable) Hamiltonian systems whose Hamiltonians include polynomial expressions, in the canonical coordinates $\{q^i,p_i\mid i=1,\ldots,n\}$, having degree greater than 2?</p>
<p>Below are follow up questions/replies in response to the comments/quest... | 1,768 |
<p>I`ve just learned that electrically charged particles and magnetically charged monopoles in QED are S-dual to each other such that it depends on the value of the fine structure constant which of the two is the ligher (and more fundamental) one and which is heavier (and more complicated).</p>
<p>Whereas I think I un... | 1,769 |
<p>As a thought experiment let us assume that we have isolated a magnetic domain. This domain is of finite size and we know its dimensions. Assuming that we can measure an infinitesimal field, will there be a certain region beyond which the field won't be applicable?</p>
<p>The instinctive answer to this question is n... | 1,770 |
<p>I have a bunch of magnets (one of those game-board thingies) given to me when I was a school-going lad over 20 years ago, and the magnets feel just as strong as it was the day it was given. </p>
<p>As a corollary to this question <a href="http://physics.stackexchange.com/questions/8036/do-magnets-lose-their-magneti... | 1,771 |
<p>If one covers up one eye, then he loses depth perception (two dimensional perspective). When we uncover that eye, we can now see depth (three dimensional perspective). My question is if we had four eyes, would we be able to see from a four dimensional perspective?</p> | 1,772 |
<p>When someone performs Young's Double Slit experiment, the person sees an interference pattern on the screen. What is the time taken to for the pattern to appear on the screen? Is it distance between slit and the screen divided by speed of light? Another way to put the question is when photons are converted to waves ... | 1,773 |
<p>This thought has completely changed my perspective towards matter. If the matter in a star can collapse to a point to form a Black hole, surely the true nature of matter should be able explain this behavior. I find this collapse easy to imagine if I visualize Matter as something which lies in space, but which <em>it... | 1,774 |
<p>So I'm using the following definition for the Reflection coefficient :</p>
<p>$$\frac{\vec{j}_{reflected}}{\vec{j}_{incident}}$$</p>
<p>Hence, since :</p>
<p>$$\psi_{reflected}=Be^{-ikx}$$ and $$\psi^{*}_{reflected}=B^{*}e^{ikx}$$</p>
<p>We can perform the usual to obtain the incident probability density current... | 1,775 |
<p>What if I take a laser pen and direct it towards the middle of two wide slits? Will I get interference pattern or just two lines? Do I need to scatter photons before they hit the slits to observe interference pattern?</p> | 1,776 |
<p>I saw a claim in <a href="http://arxiv.org/abs/0902.2790" rel="nofollow">this paper</a> that holomorphic boundary CFT$_2$ primary operators correspond to massless states in the AdS$_3$ bulk. Specifically,</p>
<blockquote>
<p>As always, we simplify the situation by assuming the absence of holomorphic primary opera... | 1,777 |
<p>More specifically, I want to understand why a <a href="http://en.wikipedia.org/wiki/Wave" rel="nofollow">wave</a> is a wave but a <a href="http://en.wikipedia.org/wiki/Wave_packet" rel="nofollow">wave packet</a> is not considered a wave (<a href="http://physics.stackexchange.com/questions/37891/what-is-the-mass-of-a... | 1,778 |
<p>I know that a capacitor with a dielectric can operate normally up till a certain voltage (AFAIK called breakdown voltage) which depends on the strength of the dielectric placed between the plates. After this voltage, the circuit becomes short and current flows between the plates and thus the capacitor breaks down. B... | 1,779 |
<p>This may be anecdotal.
Playing in the kitchen I realized the frying pan comes with both a flat, and a concave bottom. So here's the question - </p>
<p>Given two pans made of brass, one has a concave base & the other a flat base, which of the two would use heat more efficiently? I would believe the latter becau... | 1,780 |
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