question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p><strong>EDIT</strong> - I have included the context of the quote I am interested in, as people seem to be as baffled by Einstein's quote as I am:</p>
<hr>
<p>In a 1920 address Einstein says this: </p>
<blockquote>
<p>Think of waves on the surface of water. Here we can describe two entirely different things. Eit... | 4,816 |
<blockquote>
<p>Problem: The marble rolls down the track and around a loop-the-loop of radius R. The marble has mass $m$ and radius $r$. What minimum height $h$ must the track have for the marble to make it around the loop-the-loop without falling off?<br>
Express your answer in terms of the variables $R$ and $r$.<... | 4,817 |
<p>From what I've (hopefully) understood from the AdS/CFT correspondence, physical quantities have a dual version. For example, the position in the bulk is the scale size (in renormalization), and waves in a curved gravitational background are the dynamics of quantum criticality. </p>
<p>But the partition functions of... | 4,818 |
<p>I am not sure if this question is too naive for this site, but here it goes. In QFT calculations, it seems that everything is rooted in formal power series expansions, i.e. , what dynamical systems people would call <a href="http://en.wikipedia.org/wiki/Poincar%C3%A9%E2%80%93Lindstedt_method" rel="nofollow">Lindsted... | 4,819 |
<p>In Ryder Page141, it is written "<em>the electromagnetic field, like any massless field, possesses only two independent components, but is covariantly described by a 4-vector $A_{\mu}$</em>". </p>
<p>Why are there only two independent components? Shouldn't all four components be independent from one another?</p> | 4,820 |
<p>Is there any experiment that would show that radio waves (I am talking about macroscopic wavelength, say between 0.01m - 2m) are made out of individual photons? Sort of an equivalent of the photo-electric effect? Or maybe a photon-multiplier for radio waves? Can a single photon of radio waves be picked up by 2 anten... | 4,821 |
<p>As a grad student, I have a single publication, a conference proceeding, to my name. So, my question is what do I need to do to obtain a post-doc position? Obviously, my references are going to be important. But, what other methods are available to me to demonstrate my competence? As I am US based, is it worth my t... | 4,822 |
<p>Rather surprised I haven't seen many questions or discussion regarding the <a href="http://www.wired.com/wiredscience/2011/12/higgs-lhc-anticipated/" rel="nofollow">rumored confirmation of the Higgs field</a>. As I understand it, the energies where they saw things were actually quite a bit higher than they had pred... | 4,823 |
<p>The focus point is an interesting region of the cMSSM parameter space at high $m_0$ and low $m_{1/2}$. Features are high scalar masses (> 1-2 TeV), light charginos / neutralinos (which are higgsino-like), and fairly low fine-tuning. One can also achieve correct dark matter relic densities and the correct higgs mass.... | 4,824 |
<p>Modelling the diffusion of a gas dissolved in water in a vertical column of water, several meters deep. Also assuming the water is completely still, so only diffusion plays a role. (Actually a model of methane and oxygen diffusion in the water in peatlands.)</p>
<p><a href="http://en.wikipedia.org/wiki/Fick%27s_law... | 4,825 |
<p>just a quick question on $F_{\mu\nu}^a$. I'm correct to think $F_{\mu}^{\mu,a}$ vanishes, aren't I? (Just want to make sure...) My reasoning is as follows:</p>
<p>The derivative terms cancel anyways - that's obvious - so the only "critical" term of $F_{\mu}^{\mu,a}$ is $f^{abc}A_{\mu}^b A^{\mu,c}$ but this vanishes... | 4,826 |
<p>Consider an expanding universe with the following metric in conformal time/co-moving coordinates:</p>
<p>$$ds^2=a^2\left[-c^2\left(1+\frac{2\phi}{c^2}\right)d\eta^2+\left(1-\frac{2\phi}{c^2}\right)\left(dx^2+dy^2+dz^2\right)\right]$$</p>
<p>What would be the formula to compute the redshift $1+z=\frac{\nu_S}{\nu_O}... | 4,827 |
<p>I hope lab / experimental physics is fair game for this web-site. If not, sorry!</p>
<p>I'm designing a sensor system to perform specialized [astronomy and space-sciences] experiments, and need a "reality check" to support or adjust my theoretical calculations.</p>
<p>What I need is the "counts per second" produc... | 4,828 |
<p>Consider a simplest 3D solution of Maxwell's equations:
$$\vec B=\vec e_z \cos\left(\frac{2\pi}{\lambda}(ct-x)\right),$$
$$\vec E=\vec e_y\cos\left(\frac{2\pi}{\lambda}(ct-x)\right),$$</p>
<p>and propagation is in direction of $\vec e_x$.</p>
<p>I'd like to find some vector potential $\vec A$ and scalar potential ... | 4,829 |
<p>Given the Steane code
$$
\left|0\right\rangle_L \equiv \frac{1}{\sqrt{8}}(\left|0000000\right\rangle + \left|1010101\right\rangle + \left|0110011\right\rangle + \left|1100110\right\rangle + \left|0001111\right\rangle + \left|1011010\right\rangle + \left|0111100\right\rangle + \left|1101001\right\rangle)
$$
$$
\left|... | 4,830 |
<p>A long time ago I learned that the electrical resistance of a metallic conductor, when surrounded by a gas, varies with the pressure of said gas.
• What is the name (if any) of the law involved?
• Does the resistance increase or decrease with an increase in gas pressure?
• What is the reason for this?
TIA!</p> | 4,831 |
<p>The problem is as follows:</p>
<p>Consider the system consisting of the <em>symmetric</em> dumb-bell (two particles each of mass $m$ connected by a light, inextensible rod of length $l$) moving in the plane. Use as coordinates the angle $\phi$ between the rod and the $x$-direction, and the Cartesian coordinates of ... | 4,832 |
<p>Do <a href="http://en.wikipedia.org/wiki/Black_hole" rel="nofollow">black holes</a> exist from our point of reference? From our point of reference nothing actually goes inside the event horizon right? So is there anything inside the event horizon from our reference? If not then no black holes actually exist but hol... | 165 |
<p><strong>Note</strong>: My question is duplicate of the following </p>
<ol>
<li><p><a href="http://physics.stackexchange.com/q/87976/">Direction of friction when a car turns</a></p></li>
<li><p><a href="http://physics.stackexchange.com/q/79852/">Why does friction cause a car to turn?</a> </p></li>
</ol>
<hr>
<p>I... | 4,833 |
<p>Can magnetic fields be "blocked"?
For example, in the game, TitanFall, a robot stop bullets with ( presumably ) a magnetic shield.</p>
<p>I wish to calculate the magnetic force required to stop a bullet within a few microseconds. But the problem I have is that my entire electronic system or the vehicle ( most like... | 4,834 |
<p>It it known that the massive spin-2 irreducible representation of the Poincare group is the traceless symmetrical transverse 4-tensor $h_{\mu \nu}$ with rank 2:
$$
(\partial^{2} + m^{2})h_{\mu \nu} = 0, \quad \partial_{\mu}h^{\mu \nu} = 0, \quad h = 0.
$$
These conditions may be united into one equation:
$$
\partia... | 4,835 |
<p>I'm struck with two competing ideas on the question in the title.</p>
<p>Listing #1: <a href="http://van.physics.illinois.edu/qa/listing.php?id=2009" rel="nofollow">http://van.physics.illinois.edu/qa/listing.php?id=2009</a></p>
<p>Q: "How far can a magnetic field bend light?"</p>
<p>A: "Unfortunately, the path li... | 4,836 |
<p>I'm doing the variation of a Lagrangian respect to the metric, but I am having problem with a particular terminus. My action is:</p>
<p>$$ S=\int d^4x \sqrt{-g}[ (\nabla_\mu A^\mu)^2]$$</p>
<p>My lagrangian is:</p>
<p>$$\mathcal{L}=(\nabla_\mu A^\mu)^2$$</p>
<p>to get the energy tensor the formula is $$T_{\mu \n... | 4,837 |
<p>I had a very brief introduction to the <a href="http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect" rel="nofollow">Aharonov-Bohm effect</a> in class. The lecturer introduced the notion that $H(\Phi=\Phi_0)$ and $H(\Phi=0)$ gives identical energy spectrum and that the Hamiltonians are related by a the large ga... | 4,838 |
<p>What telescope refractor aperture size would I need to observe Mars's polar caps?
I have a Levenuhk Strike NG 80mm, and I can see red disk of planet but cannot see any details on the surface.</p> | 4,839 |
<p>We all know that our universe is inflating from what is known as the <a href="http://en.wikipedia.org/wiki/Big_Bang" rel="nofollow">Big Bang</a>. However, will our universe continue to inflate at the current rate? Or after reaching a maximum size, will it collapse in a <a href="http://en.wikipedia.org/wiki/Big_Crunc... | 4,840 |
<p>I mean besides the obvious "it has to have finite mass or it would suck up the universe." A singularity is a dimensionless point in space with infinite density, if I'm not mistaken. If something is infinitely dense, must it not also be infinitely massive? How does a black hole grow if everything that falls into it m... | 73 |
<p>Wikipedia defines Wigner D-matrix as an irreducible representation of groups SU(2) and SO(3). What is a good way to visualize this representation? Is there any physical system which can be kept in mind as a simple example of the same? </p>
<p>A general explanation of the idea of irreps, beyond just the Wigner-D mat... | 4,841 |
<p>We see waves propagate in air, water, through the cristal of a metal and along a rope.
Isn't a wave a wonder of Nature, or is it just a simple phenomenon?
Are homogeneity and isotropy necessary properties for the correct propagation of waves?</p>
<p>Update</p>
<p>are a rope, water and space/EM field elastic in t... | 4,842 |
<p>I am reviewing some concepts in statistical mechanics and am becoming confused with how to calculate probabilities when a system has $N$ non-interacting particles. </p>
<p>For instance, let's say we have $N$ electrons with magnetic moment $\vec{\mu} = (g e/2 m)\vec{S}$. If we apply a strong magnetic field parallel ... | 4,843 |
<p>I initially thought that it had something to do with the number of slip systems in FCC vs. BCC, but they're both the same.</p> | 4,844 |
<blockquote>
<p>Two balls of the same mass $m$ are connected to each other with rope
of length $l$. One of the balls is also connected to the ceiling with
a rope of the same length $l$. The balls are spinning around the axis
which intersects the point of the connection of the rope in the
ceiling. As a result,... | 4,845 |
<p>A system is described as follows:</p>
<blockquote>
<p>Consider a system consisting of two rotating bars of length $l$ and with
uniform mass density and each with total mass $m$. The bars are attached
to a common axis at one end around which the can rotate. The distance
between the bars on the axis of rotati... | 4,846 |
<p>Is <a href="http://en.wikipedia.org/wiki/Brownian_motion" rel="nofollow">Brownian motion</a> a deterministic system? I.e the motion of all particles are completely determined or is there an innate indeterminism like quantum systems?</p> | 4,847 |
<p>Is there the effect of sun rising and sun setting, in terms of Rayleigh scattering and visual spectrum and other factors completely similar and symmetric? I mean can one recognise them from a picture taken from the sky?</p> | 4,848 |
<p>To prevent <a href="http://en.wikipedia.org/wiki/Grain_Boundary_Sliding" rel="nofollow">grain boundary sliding</a> so that <a href="http://en.wikipedia.org/wiki/Diffusion_creep" rel="nofollow">creep</a> is less likely to occur, usually engineers would design components of larger grains or have columnar grain structu... | 4,849 |
<p>If as some people <a href="http://physics.stackexchange.com/questions/72753/what-happens-after-the-collapse-of-a-wavefunction">suggest</a>, there is no collapse of the wave function (is there a standard name for this position), then must one rule out the many-worlds interpretation of QM ?</p> | 4,850 |
<p>Many books on special relativity eventually mention that the geometry of spacetime is special because the metric has a signature $(-,+,+,+)$ which is non-Euclidean. I have encountered many ways this makes it different from normal Euclidean geometry, for example, there is more than one null vector. </p>
<p>I want to... | 4,851 |
<p>In the cases of nonlinear acoustics, why is shock formation unlikely when the dispersion is strong when compared to the nonlinearity of the wave?</p> | 4,852 |
<p>I have a question about deriving variation of metric under Weyl and coordinate transformations in Polchinski's string theory (3.3.16).</p>
<p>Under transformation $$\zeta: g \rightarrow g^{\zeta}, \,\,\, g_{ab}^{\zeta}(\sigma')=\exp[ 2 \omega (\sigma) ] \frac{ \partial \sigma^c }{\partial \sigma'^a} \frac{ \partial... | 4,853 |
<p>Alright, so I've been messing around with turning air pressure into thrust, however I'm only a sophomore in high school, so my physics knowledge is fairly limited. (I've studied higher level physics, but have nothing official.)</p>
<p>So, with that being said, I've been messing around with utilizing thrust from air... | 4,854 |
<p>I have tried to search through the internet about the definition of solar storm or what this term mean but i could found what it means. Also, what is the difference between the geomagnetic storm</p> | 4,855 |
<p>How fast is heat transferred by conduction? Is there some simple, but quantitative way that starts from some properties of the material (e.g. its thermal conductivity) and makes rough predictions, for example about how much time is needed for temperature to change at one end of the body when it is placed, at the oth... | 4,856 |
<p>Decoherence explains how a classical state appears once quantum information in a quantum state leaks out. But presumably that environment has its own quantum state which then leaks out to a larger environment.</p>
<p>Does this mean that decoherence can only be understood locally, and not globally? For example if th... | 4,857 |
<p>The centers of black holes and quasars often have jets coming out the two poles of an accretion disk, say north and south. Is it known if the two jets spin in the same direction or opposite directions to each other? </p> | 4,858 |
<p>What is the importance of dimension six operators in the study of physics beyond the Standard Model? Are these operators more relevant than dimension five operators like $HHFF$ or operators with derivative couplings?</p>
<p>I often see lagrangians with dimension six operators in effective studies of the standard mo... | 4,859 |
<p>I have come up with this differential equation for the evolution of $\vert \Psi \vert^2$, the probability density in quantum mechanics.</p>
<p>Is there a name for this equation? Is the logic sound?</p>
<p>So I start from the conservation of the total probability:</p>
<p>$$ \frac{d}{dt} \int _{all space} \vert \Ps... | 4,860 |
<p>I want to simulate a circuit similar to the one below in MATLAB. If you have a state matrix describing the state of 3 qubits, I understand that you could apply a CNOT matrix tensored with and identity matrix to $\psi_{0} $ get $\psi_{1}$, but if you want to apply a controlled operation to the 1st and 3rd qubit to ge... | 4,861 |
<p>I wondered if magnets could be used to hold a drop of molten liquid metal in air (not for any particular reason just because it could be done), but was disappointed when a quick Google search showed the metal would lose its magnetic traits before it melted.</p>
<p>Are there any other forces that could be used to su... | 4,862 |
<p>I may have confused after thinking too much about Faraday's law. If an emf is induced in a circuit due to some changing magnetic field, the induced current will be in a direction such that the "induced magnetic field" opposes the original magnetic field (Lenz's law).</p>
<p>So wouldn't the induced magnetic field al... | 4,863 |
<p>Firstly, not sure if this question ought to be in the space SE site. Please let me know if it should. (Posted in both for now)</p>
<p>Secondly, I don't know a whole lot about physics (I'm just inquisitive). So please try to keep answers simple (or at least dummed down to laymans terms).</p>
<p>Inspired by "A Hitch... | 4,864 |
<p>I'm working on a certain problem in fluid mechanics, which isn't really my strongest area.
The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing in the same direction as the velocity of river. Level of water inside of the pipe is 7cm higher than the level of riv... | 4,865 |
<p>I'm trying to show that the Hamiltonian for a nanowire with proximity-induced superconductivity </p>
<p>$$
\hat{H} = \int dx \text{ } \left[\sum_{\sigma\epsilon\{\uparrow,\downarrow\}}\psi_{\sigma}^{\dagger}\left(\xi_{p} + \alpha p\sigma_{y} + B\sigma_{z}\right)\psi_{\sigma} + \Delta\left(\psi_{\downarrow}^{\dagger... | 4,866 |
<p>I want to apply the Biot-Savart law to calculate the magnetic field at a point created by current flowing through a square/rectangular conductor. More specifically, a trace on a printed circuit board. </p>
<p>To me, a trace on a circuit board is the summation of many infinitesimal rectangular conductors.</p>
<p>I ... | 4,867 |
<p>Under normal lens operation, a beam is sent through the centre of the lens along the optical axis (ie perpendicular to the lens's plane). What happens when a beam is sent through a lens at an angle to the optical axis? Does it simply exit the lens at the same angle?</p> | 4,868 |
<p>According to <a href="http://en.wikipedia.org/wiki/Terminal_velocity" rel="nofollow">Wikipedia</a>:</p>
<blockquote>
<p>[Terminal Velocity] is the velocity of the object when the sum of the
drag force (Fd) and buoyancy equals the downward force of gravity (FG)
acting on the object. Since the net force on the ... | 4,869 |
<p>In a old paper,
<a href="http://arxiv.org/abs/hep-th/9509163" rel="nofollow">http://arxiv.org/abs/hep-th/9509163</a>
Becca Asquith argues that it is possible to prove that if the SU(2)xU(1) sector of the standard model is chiral, then the SU(3)xU(1) sector is vectorial, ie, that at least one of them must be of purel... | 4,870 |
<p>If a quantum system interacts with a "big" quantum system, you have dephasing. </p>
<p>The models of decoherence all have this atog aproach to them, about what is to understood of the interaction of the quantum state with a bath. </p>
<blockquote>
<p>At which point does the bath character of the "bigger" system ... | 4,871 |
<ol>
<li><p>I think <a href="http://en.wikipedia.org/wiki/Many-worlds_interpretation" rel="nofollow">many worlds interpretation</a> is inconsistent with the EPR paradox. Quantum mechanics says that particles are really in more places at the same time and the particle is really only probability wave - otherwise the conc... | 4,872 |
<p>So I'm having a tough time deciding between courses next semester. I'm a rising 3rd year undergrad math major whose goal is to get a solid understanding of theoretical physics through advanced math (laugh all you want). So in that view, which one should I choose from</p>
<ol>
<li><p>Theoretical Mechanics: This is ... | 4,873 |
<p>The Everett interpretation has memory robots. Copenhagen requires observer memory states. Consistent histories has its IGUSes. Decoherence has its existential interpretation. All of them refer to memory states of observers. What counts as an observer, and which parts of the observer count as memory states? Why isn't... | 4,874 |
<p>There is this puzzling thing that is called <a href="http://en.wikipedia.org/wiki/Mpemba_effect">Mpemba effect</a>: paradoxically, warm (35°C) water freezes faster than cold (5°C) water. As a physisist, I've been asked about it several times already. And I have no definite answer to that, apart from the standard: "... | 4,875 |
<p>I am trying to solve for the equations of motion to simulate a pendulum.
I decided to use the spherical coordinates. The Lagrange equation is:</p>
<p><img src="http://i.stack.imgur.com/yXvMs.png" alt="enter image description here"></p>
<p>where </p>
<ul>
<li>L = length of the rope</li>
<li>ϕ= angle of the project... | 4,876 |
<p><img src="http://i.stack.imgur.com/sPwNH.jpg" alt="experiment">
sorry for terrible graphical representation, I did an experiment, i took 6 coins fixed 4 of them in one place by placing some real heavy objects on them , then i took a 5th coin placed it in the final position at the last , all these coins were touching... | 4,877 |
<p>Consider a simple, circular orifice with an upstream, high gas pressure and downstream, normal atmospheric pressure. Consider also a flat circular plate that can be positioned anywhere along the perpendicular axis of the orifice.</p>
<p>At one extreme the plate occludes the orifice and there is no flow of gas. At t... | 4,878 |
<p>In a non-relativistic quantum mechanical system in an <a href="http://en.wikipedia.org/wiki/Particle_in_a_box" rel="nofollow">infinite potential well</a>. I try to measure the energy and the position of the system simultaneously. Since, the respective operators do commute according to Heisenberg's uncertainty relati... | 4,879 |
<p>I have been struggling with this problem:</p>
<blockquote>
<p>The speed of a projectile when it reaches its maximum height is one half of its speed when it is at half its maximum height. What is the initial projection angle of the projectile?</p>
</blockquote>
<p>Please help</p> | 4,880 |
<p>Would gravitons follow the same trajectory as photons through a gravitational lense? would all other particles follow the same trajectory?</p> | 4,881 |
<p>In the derivation of Galilean transformations the only assumption is that the two frames are moving with some uniform relative velocity $u$. </p>
<p>Suppose with respect to some inertial frame $O$ the two frames $S$ and $S'$ are moving with the same uniform acceleration $a$.</p>
<p>Let $V$ be the velocity of $S$ w... | 4,882 |
<p>1, If I understand correctly, people talk about <a href="http://en.wikipedia.org/wiki/BQP" rel="nofollow">BQP</a>, <a href="http://en.wikipedia.org/wiki/QMA" rel="nofollow">QMA</a>, etc are usually referring to digital quantum computer/Turing machine and not about analog quantum computer. Based on the papers <a href... | 4,883 |
<p>Let $G$ be the group of the permutation of $N$ particles, $P\in G$. Therefore, there are $N!$ elements in $G$. For its subgroup, e.g., even permutation, we can calculate $\text{sign}(P)$ and get $\text{sign}(P)=+1$. Could you please explain the meaning of the the function $\text{sign}(P)$ and the formula as follows... | 4,884 |
<p>I am trying to create an exhaustive list of all assumptions which work as the base of the CHSH inequality.</p>
<ol>
<li>Locality - this means an object can be influenced only by its surroundings. So, the events taken place at Alice and Bob's ends cannot influence each other.</li>
<li>Realism - the value of the obse... | 4,885 |
<p>In inelastic collisions, kinetic energy changes, so the velocities of the objects also change.</p>
<p>So how is momentum conserved in inelastic collisions?</p> | 213 |
<p>Do gravitational lenses have a focus point? Could I burn space ants?</p> | 4,886 |
<p>Hello I wanted to know where does the integral of following picture come from and what are the alternatives in it? How and where can i find information i need to know to understand this text?<br>
thank you in advance!
<img src="http://i.stack.imgur.com/LBBlE.png" alt="Detailed balance formulation"></p> | 4,887 |
<p>After being excited by a photon, an electron of a photoactive molecule jumps to a higher electronic state. When it relaxes, the molecule emits a photon (in simple terms). How is this photon "generated"? Photons are particle/waves, right? So somehow this particle has to form. I picture it in a way similar to when you... | 4,888 |
<p>Heisenberg said that we can't tell precisely both the location of an electron and the momentum of it in the same instant. If we observe one thing, the other is changed. How he concluded this principle? </p>
<p>I want to say if we want to locate an electron we'll send photons to it, but after hitting the electrons, ... | 4,889 |
<p>If $ \lbrace f,g \rbrace $ is Poisson bracket
and $\epsilon_{ijk}$ is Levi-Civita symbol, how to show that</p>
<p>$$ \epsilon_{iab}\epsilon_{jcd}(x_ap_d\lbrace x_c,p_b \rbrace+x_cp_b\lbrace x_a,p_d \rbrace) = x_ip_j-x_jp_i$$</p>
<p>where $x_i$ are generalized coordinates and $p_i$ are momentums ?</p> | 4,890 |
<p>if I transform the time-dependent Schrödinger equation without a potential I get: </p>
<p>$$ - \hbar \omega \psi(\omega,x) = \frac{- \hbar^2}{2m} \frac{\partial^2 \psi(\omega,x)}{\partial x^2}$$</p>
<p>The solutions is clealy: $$\psi(\omega,x)={\it C1}\,{{\rm e}^{{\frac {\sqrt {2\omega m}x}{\sqrt {\hbar}}}}
}+{\it... | 4,891 |
<p>What are some good condensed matter physics books that can fill the gap between Ashcroft & Mermin and research papers? Suggestions for any specialized topics (such as superconductivity, CFT, topological insulators) are welcomed.</p> | 453 |
<p>I have another question on the notation in Shankar. I think it's sloppy, but I also may just be misunderstanding it. Again, this is at the very beginning of the math intro.</p>
<p>He has:</p>
<blockquote>
<p>$$a\left| V \right\rangle \to \left[ {\begin{array}{*{20}{c}}
{a{v_1}}\\ {a{v_2}}\\ \vdots \\ {a{v_... | 4,892 |
<p>BEC cold atoms occupy the same ground state. But what about the electrons or other fermions of the BEC atoms? Are they in the same state? Do electrons of one atom interact with those of another?</p> | 4,893 |
<p>Is the magnetic field propagated by photons or by virtual photons? If it is by photons, then doesn't that mean that magnets lose energy and eventually become non magnets?</p> | 4,894 |
<p>We are all familiar with the version of Quantum Mechanics based on state space, operators, Schrodinger equation etc. This allows us to successfully compute relevant physical quantities such as expectation values of operators in certain states and then compare with experiment.</p>
<p>However, it is often claimed tha... | 4,895 |
<p>If I place a mercury thermometer in hot water, heat energy will transfer from the water to the mercury inside the thermometer. Will this continue until thermal equilibrium is reached and thus the mercury will show the temperature of the water?</p>
<p>However, if this is so, will the thermometer show the right tempe... | 4,896 |
<p>As Weinberg exposited in his QFT Vol1, there are two equivalent ways of arriving at the same quantum field theories:</p>
<p><strong>(1).</strong> Start with single-particle representations of Poincare group, and then make a multiparticle theory out of it, while preserving principles of causality etc. I would call t... | 4,897 |
<h2>[I have updated the below description to clarify that the mechanism does not depend on a truly frictionless implementation. Also, since 2 commenters apparently assumed that I was proposing a mechanism to create energy from nothing, it seems necessary to state that this is <strong>not</strong> what I am proposing.]... | 4,898 |
<p>I've seen OPEs commonly used in 2d CFT, it's quite apparent to me that, in that case, it dresses a bridge between the algebraic and the operator formalism especially when combined with radial ordering and the use of contour integral. Even more powerful in the minimal models where it leads to the bootstrap equations ... | 4,899 |
<p>I am trying to learn Hamiltonian mechanics. While many textbooks treat closed systems, I have a hard time finding references for forced systems.</p>
<p>For example, if I consider simple systems of masses ($m_i$ connected to $m_{i+1}$ with a spring) it is easy to write down the Hamiltonian. But I'm not so sure how ... | 4,900 |
<p>I came across and interesting effect today, I have a dozen of Neodymium magnets around my house. And, they are very strong. Anyhow, one of them got attracted to my large steel plate table(use for cutting and building). It was almost impossible to take it apart, till I contacted the manufactured of those magnets and ... | 4,901 |
<p>The compression spring equations are generally given for helical coil. What are the equivalent equations for alternative coil shapes, like oval?</p> | 4,902 |
<p>Spin, position, and velocity are observables which are QM for quantum particles. My question is, what determines whether an observable is QM or not?</p>
<p>For example, why is electric charge not QM? That is, why don't (or can't) particles exist in a superposition of being positive and negative?</p>
<p>What is the... | 4,903 |
<p>Does the Higgs Mechanism contradict <a href="http://en.wikipedia.org/wiki/Entropic_gravity" rel="nofollow">Entropic Gravity</a>?</p>
<p>It seems like it probably does. But then again, one is a microscopic theory and the other is macroscopic. Can they live together in harmony? or is the recent CERN stuff empirical e... | 4,904 |
<p>Is the dimensionality of spacetime in all usual models constant?</p> | 4,905 |
<p>Can somebody explain a detailed procedure, of producing orientation maps? I need to implement this into a software. Right now im able to transform EBSD pattern to probabilistic Hough space, get lines parameters - unfortunetly with some noised/wrong parameters too (any advices?), and autoindex this lines. What is the... | 4,906 |
<p>I had a question regarding cosmic event horizon. Let's say that a far away solar system has just crossed the cosmic event horizon due to the expansion of the universe. In that solar system let us say there is a planet orbiting the solar system's star, for half of the planet's orbit, it will be traveling towards us... | 4,907 |
<blockquote>
<p><em>How long does it take a baseball with velocity $(30, 20, 25) m/s$ to
travel from location $r_1 = (3, 7,−9) m$ to location $r_2 = (18, 17, 3.5)m$?</em></p>
</blockquote>
<p>I am thinking that it should be the displacement vector divided by velocity. but velocity is a vector and my text is adaman... | 4,908 |
<p>Pretend you are throwing darts at a dart board. You throw dart $d_1$ at time $t_1$. After you throw your first dart, you throw your second dart $d_2$ at time $t_2$. Given that $t_2 > t_1$ in a stationary frame of reference, is it possible for a frame of reference to exist that will make an observer $O_1$ in that ... | 4,909 |
<p>Most string theory compactifications analyzed so far have as backgrounds a conformal field theory corresponding to a nonlinear sigma model with a Calabi-Yau target space, or some relatively classical background, possibly with orbifolding. But as long as the central charge of the Virasoro algebra is right, and worlds... | 4,910 |
<p>For <strong>S</strong> and <strong>S'</strong> in standard configuration, the Galilean transformations are:</p>
<p><strong>x' = x - vt, y' = y, z' = z, t' = t</strong></p>
<p>From the Lorentz transformations for v << c:</p>
<p><strong>x' = x - vt, y' = y, z' = z, t' = t - vx/c^2</strong></p>
<p>So it looks... | 4,911 |
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