question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Suppose i have an optical lattice with particles loaded onto it, the potential due to the optical lattice is $V_{0}Cos\left(x\right)$. Assume that the particles interact with eachother through contact interaction $C*\left|\Psi\right|^{2}$ where $\Psi$ is the mean field wavefunction. what will be the effective potent... | 4,728 |
<p>I'm doing a basic realtime simulation of two bodies, but the orbits are unstable for some reason.</p>
<p>This code is run at every timestep:</p>
<pre><code>rsq = (a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y)
a.vx = a.vx - (a.x - b.x) * g * b.m * (1/rsq) * dt
a.vy = a.vy - (a.y - b.y) * g * b.m * (1/rsq) * dt... | 4,729 |
<p>I found the following question on an standardized test, and was debating with some friends what the answer would be:</p>
<p>A car of mass <strong>M</strong> is travelling with a constant velocity through a plane in which friction is non-existent. An object of mass <strong>m</strong> (<code>m = M/3)</code> that is f... | 4,730 |
<p>There are numerous pictures, obviously, of the blackness of space from the shuttle, the space station, and even the moon. But they all suffer from being from the perspective of a camera, which is not sensitive enough to pick up the stars in the background when compared to the bright foreground objects (the limb of t... | 4,731 |
<p>I am interested in astronomy/astrophysics, but I am not science major (I am a computer science graduate). Facts and results of the field are presented to the public without showing how these facts/results got known or inferred. And I have that curiosity to know how we know what we know about the universe (either obs... | 4,732 |
<p>Right now, I am considering moving from 1.25" eyepieces to 2". While I'm convinced of the quality of the premium eyepieces, it would take me years to afford a complete set and, if I go that route, I will necessarily pick them up piecemeal. Would I be wise to follow that route, knowing that in a few years time I'll h... | 4,733 |
<p>When talking about the spinor-helicity formalism in his new textbook on quantum field theory, Matthew D. Schwartz claims as a highly nontrivial example, it is quite easy to use the Parke-Taylor formula to calculate the $gg\to ggg$ scattering cross section at tree level by hand, which is also one of the problems in t... | 4,734 |
<p>I was reading Wikipedia article about <a href="http://en.wikipedia.org/wiki/Universe">universe</a> and stumbled upon pie chart which represents what universe contains. <a href="http://upload.wikimedia.org/wikipedia/commons/7/76/Cosmological_Composition_%E2%80%93_Pie_Chart.svg">It says</a> that stars make up 0.5% of ... | 4,735 |
<p>Suppose a point charge $q$ is located at $(x=0,y=0,z=d)$, and that along the $x$-$y$ plane is a infinite plate of potential $V = 0$. Then the method of images solves Laplace's equation for the potential for $z>0$, $$V(x,y,z) = \frac{1}{4\pi\epsilon_0}\left(\frac{q}{\sqrt{x^2+y^2+\left(z-d\right)^2}} - \frac{q}{\... | 4,736 |
<p>The magnetic moment of a closed current loop is $$\mathbf{m} = \frac{I}{2}\int\mathbf{r}\times d\mathbf{r}.$$ Note that $\mathbf{m}$ is independent of any coordinate frame. How, then, does one determine the <em>location</em> of a magnetic moment?</p>
<p>Certainly the vector potential due to a magnetic dipole $$\m... | 4,737 |
<p>I'm looking to plot the band gap $\Delta(T)$ as a function of temperature between $T = 0$ and $T = T_c$ by numerical evaluation of the band gap equation</p>
<p>$$\frac{1}{\mathcal{N}(0)V} = \int_0^{\hbar\omega_D}{d\xi\frac{\tanh{\frac{\sqrt{\Delta^2+\xi^2}}{2k_BT}}}{\sqrt{\Delta^2+\xi^2}}}$$</p>
<p>where $\omega_D... | 4,738 |
<p>In a phi fourth theory, the Hamiltonian density is:</p>
<p>$$\mathcal{H}=\frac{1}{2}\pi^2+\frac{1}{2}(\nabla \phi)^2+\frac{1}{2}m^2\phi^2+\frac{\lambda}{4!}\phi^4$$</p>
<p>Now I impose the usual equal time canonical commutation relations for fields ($\hbar=1$)</p>
<p>$$[\phi(\vec{x}),\pi(\vec{y})]=i \delta^3(\vec... | 4,739 |
<p>Non-commutative (sometimes called "fuzzy") black holes are solutions of Einstein's equations obtained with a previous basic assumption of non-commutativity of the coordinates $[x^{\mu},x^{\nu}]=i\, \theta^{\mu\nu}$. This assumption is considered helpful in the sense that removes the singularity in $r=0$. See <a href... | 4,740 |
<p>I am building a computational model of ellipsoidal cell network formation and I would like to use a particle order parameter to study my model's behavior. I have come across this article <a href="http://prb.aps.org/abstract/PRB/v28/i2/p784_1" rel="nofollow">Steinhardt, Nelson, Ronchetti, PRB (1983)</a>, that was app... | 4,741 |
<p>Here I cite part from Sidney Coleman's lectures on Quantum Field Theory:</p>
<blockquote>
<p>It is a phenomenal fluke that relativistic kinematic corrections for the Hydrogen atom work. If the Dirac equation is used, without considering multi-particle intermediate states, corrections of $O \big(\frac{v}{c}\big)$ c... | 4,742 |
<p>Suppose there are <strong>two <a href="http://en.wikipedia.org/wiki/Charged_black_hole" rel="nofollow">charged black holes</a></strong> which <strong>collide to form a bigger black hole</strong>. </p>
<p>But when they combine, a lot of potential energy of the system is lost/gained depending on their charges (the o... | 4,743 |
<p>How does the heat energy from the Sun reach us on the Earth? Since the kinetic energy of an atom is the amount of heat energy and there is no matter in space, how does heat from the Sun reach us? </p> | 4,744 |
<p>How do scientists measure the distance between objects in space? For example, <a href="http://en.wikipedia.org/wiki/Alpha_Centauri" rel="nofollow">Alpha Centauri</a> is 4.3 light years away.</p> | 4,745 |
<p>On one hand, in the classical electrodynamics polarization of transparent media yields in lowering the speed of light by the factor of $n=\sqrt{\epsilon_r \mu_r}$ (refractive index).
On the other, in the quantum field theory the vacuum polarization does not decrease the speed of light. The thing it does is increase ... | 4,746 |
<p>It is true for fermions in the same potential that the total wavefunction of two particles must be antisymmetric with respect to exchange of electrons. Which means the spin wavefunction is given by </p>
<p>$\chi=\frac{1}{\sqrt{2}}[\chi_+ (1)\chi_- (2)-\chi_+ (2)\chi_- (1)] $</p>
<p>which looks very much like the b... | 4,747 |
<p>In the Standard Model of Particle physics the $SU(2)_{EW}$ symmetry and the $SU(2)$ isospin symmetry are broken. What about $SU(3)_C$? Is it broken too?</p>
<p>if YES, what breaks the symmetry?</p>
<p>If NO, what are the consequences? Anything like "all baryons have almost the same mass"?</p> | 4,748 |
<p>I'm guessing this isn't a great physics question, but I just can't find an answer with Google.
If the galactic plane is perfectly horizontal at what angle and rotation will the ecliptic plane of our Solar System be?</p> | 4,749 |
<ol>
<li><p>Photons, where do they come from?</p></li>
<li><p>What exactly is a photon? </p></li>
<li><p>I've certainly heard how they get produced, but it doesn't seem to make sense that some sort of particle should need to be produced just to mediate the interactions of electrons. I have yet to take quantum mechanics... | 4,750 |
<p>I googled How to calculate the air requirements of pneumatic conveying and found a clue to what might be a correct equation (<a href="http://uk.ask.com/question/pneumatic-conveying-calculation" rel="nofollow">http://uk.ask.com/question/pneumatic-conveying-calculation</a>). </p>
<p>Here is my attempt at running the ... | 4,751 |
<p>I have read many questions which ask whether there can be photons at speed other than the speed of light and all of them are answered no!</p>
<p>But when the photon is created for ex during electron transition from higher to lower energy level, it cannot simply be at initial speed $c$!</p>
<p>Why it cannot be at $... | 159 |
<p>What happens to the deflection of the magnetic compass if it is surrounded by south poles and north poles in alternating direction of a magnet around it in a circular pattern. Will it be deflected in any particular direction ?</p>
<p><img src="http://i.stack.imgur.com/MHqqH.jpg" alt="enter image description here"><... | 4,752 |
<p>I cannot manage to find any journal papers about the applicability of zinc nitride as active layer of an light emitting diode (LED). But certain papers got mention that zinc nitride with a direct bandgap can be fabricated with potential applications in optoelectronics.</p>
<p>Can anyone give me some opinions on thi... | 4,753 |
<p>Friends, this is a numerical homework problem. I tried my best to solve it but my answer is not matching with the one given at the back of the text book. Please help me out:
A motor car moving at a speed of 72 km/h can come to a stop in 3 seconds, while a truck can come to a stop in 5 seconds. On a highway, the car ... | 4,754 |
<p>What is more effective for travel in outer space ignoring all other factors like air radiation etc. I have a 10 kg bag of rice would I travel faster throwing the whole bag at once or throwing a grain at a time compounding my tiny acceleration or would they end up being equal?</p> | 4,755 |
<p>So, I remember in college physics the prof using liquid nitrogen in a demonstration. When he was done, he threw the container of LN at the front row, and of course it evaporated (or whatever) before it got to the students.</p>
<p>I am watching a cooking show now and they are using LN -- if they touched that, what ... | 4,756 |
<p>I must apologize, I was a little bit excited when I began understanding some of this, I can not say I can compete with professionals, and words are still difficult concepts.</p>
<p>In (<a href="http://arxiv.org/abs/gr-qc/9409013" rel="nofollow">1</a>) S.H. et al. it is discussed that in extremal cases of charged bl... | 4,757 |
<p>Lets assume we have a wire that has $10V$ across and $1$ $Amp$ flowing, now if this conductor is introduced to a changing magnetic field, $-EMF$ is induced, can we control our voltage to increase it and allow current to be stable at $1 Amp$?
Thus more power is required correct?</p>
<p>Generally, in any situation w... | 4,758 |
<p>The atmospheric pressure is 101325 Pa,which is good enough to get our bones crushed.But why aren't we crushed due to it?</p> | 160 |
<p>I'm looking for an originally German introduction to quantum mechanics. Is there such a canonical book used in German QM undergraduate courses?</p> | 4,759 |
<p>Given a wavefunction, $\psi(x)$, is it possible for $\psi$ to be singular at a point? Are there any rules against a wavefunctions having any singularities? For instance if </p>
<p>$$\psi(x) =\frac{\gamma(x)}{x},$$</p>
<p>where $\gamma$ is a continuous function of $x$. Is this a valid wave function?</p> | 4,760 |
<p>I wonder which type of kicking may cause the ball to go a larger distance?
One way is kicking the ball when it is at rest and another is kicking a moving ball in the opposite direction.
If the ball goes farther in the second way,then what is the reason despite the fact that a moving ball will exert extra force to t... | 4,761 |
<p>I have recently just begun studying cosmology. I have a background in physics. I would like a link to download video resources on Stephan Hawking's theories on physics and/or cosmology that have not been proved wrong.</p> | 98 |
<p>Let's have the metric for a sphere:
$$
dl^{2} = R^{2}\left(d\psi ^{2} + sin^{2}(\psi )(d \theta ^{2} + sin^{2}(\theta ) d \varphi^{2})\right).
$$
I tried to calculate Riemann or Ricci tensor's components, but I got problems with it. </p>
<p>The Ricci curvature must be
$$
R_{ij}=\frac{2}{R^{2}}g_{ij}.
$$
But when I ... | 4,762 |
<p>Cut, polished and etched iron meteorites have grain size about 1000 times greater than air quenched iron. The reason for the large grain size is the very slow cooling of the core of a planet or protoplanet. Check web for cross section picture Widmanstätten pattern</p>
<p>What methods can be used to grow large iron... | 4,763 |
<p>Say you have a magnet that is used in a brush-less generator. If the brush-less motor was ran (by external force such as water or human interaction) for 400 years, would the magnet that was under use have a weaker magnetic field than a magnet that had not been used at all? In other words, does using a magnet decreas... | 4,764 |
<p>If the uncertainty principle and Copenhagen Interpretation are true, then how can a clock tick? Supposedly particles can do all sorts of things when not measured, then how can they be formed into gears that make the clock tick when not measured? </p> | 4,765 |
<p>I have came across two separate explanations for why atoms have a positive atomic radius (as opposed to electrons "collapsing" into the nucleus). </p>
<ol>
<li><p>The first is via Heisenberg Uncertainty Principle, where decreasing the atomic radius would raise momentum and hence kinetic energy (while potential ener... | 910 |
<p>According to this lecture note <a href="http://www.staff.science.uu.nl/~wit00103/qft05.pdf" rel="nofollow">http://www.staff.science.uu.nl/~wit00103/qft05.pdf</a></p>
<p>page 115. Consider a Lagrangian for a massive vector field</p>
<blockquote>
<p>$$L = -\frac{1}{4} (\partial_{\mu} V_{\nu} - \partial_{\nu} V_{\... | 4,766 |
<p>How does one calculate the capacitance of two bodies <em>with different charges</em>? I was looking at coefficients of potential, but they don't seem helpful.</p> | 161 |
<p>This is a question I found in my old high-school textbook(I'm revising the topics for a course).Two blocks A and B of masses $1kg$ and $2kg$ are placed on a fixed triangular wedge by a massless in-extensible string as shown.
<img src="http://i.stack.imgur.com/vkP06.png" alt="enter image description here"></p>
<p>Th... | 4,767 |
<p>Why doesn't the Moon, or for that matter anything rotating another larger body, ever fall into the larger body?</p> | 931 |
<p>As the earth rotates around itself, does this have any effect on the dynamics of flights?</p>
<p>Or "shouldn't" this have an effect?</p>
<p>Does flying in the direction of the rotation of earth around itself, or against, it take the same time? and if yes, why?</p>
<p>Let me try to make my question clearer one mor... | 162 |
<p><img src="http://i.stack.imgur.com/YMVBx.jpg" alt="Retarded"></p>
<p>Imagine that we have a pair of parallel plates, $A$ and $B$, separated by some distance as in Fig. $1$ above.</p>
<p>At time $t_1$ we simultaneously charge both the plates. This could be done by previously sending a light signal to a charging app... | 4,768 |
<p>In light of the well known fact that <em>magnetic forces do no work</em>,</p>
<p>In every such case that nature presents us, it is possible to find some agent which does the work while magnetic forces just give direction to it. As an example, in the case of an electromagnet lifting weights, it is the potential sour... | 4,769 |
<p>"Field" is a name for associating a value with each point in space. This value can be a scalar, vector or tensor etc. I read the wikipedia article and got that much, but then it goes it into more unfamiliar concepts. </p>
<p>My question is how to interpret a basic field. Lets say there is a field with momentum and ... | 4,770 |
<p>Imposing SU(2) and U(1) local gauge invariance introduces 4 gauge bosons, two of which correspond to $W^{\pm}$ bosons. The other two gauge fields $W^{\mu}_3$ and $B^{\mu}$ however are said not to correspond to $Z$ and $\gamma$ bosons because of the incorrect chiral coupling of the $Z$ boson if this identification is... | 4,771 |
<p>I watched on TV as they where showing gold bars stored in bank vaults and I noticed that they always stack them with the narrow side down and the wide side up. Like this:</p>
<p><img src="http://i.stack.imgur.com/Mvllb.jpg" alt="Gold Bar Stacking"></p>
<p>So there has to be a mechanical reason why is that. Any ide... | 1,024 |
<p>The question is very simple, but complicated to solve. I am looking for a <em>genera</em> form solution to this problem. Thus there will be no numbers, just variables. What I mean by that is often in physics you have equations like $F = ma$. I don't have the numbers to the problem yet, because that will vary based o... | 4,772 |
<p>I'm having problems seeing the global SU(2) invariance of the QED Lagrangian.
My specific problem is seeing why
\begin{equation}
e^{-i a_i \sigma_i} \gamma_\mu e^{i a_i \sigma_i} = \gamma_\mu
\end{equation}</p>
<p>In every book i looked it up, it was written this is trivial and i couldn't find a computation, so i... | 4,773 |
<p>Well for example we put a ball filled with water, with a density of $1\cdot 10^3 kg/m^3$, in space.</p>
<p>How to calculate the pressure the water is exposed to?</p> | 4,774 |
<p>It is possible to calculate the time dilation with Lorentz transformation? So with the equation $$t'=\gamma(t-\frac{x v}{c^2}) \tag{1}$$ in which $\gamma$ is the Lorentz-Factor?</p>
<p>In an exercise I have succeeded.</p>
<p>So why can be calculated with the equation $(1)$ the time dilation? What is the reason? </... | 117 |
<p>Looking for suggestions on how to approach calculating the capacitance of a capacitor where the plates have an arbitrary shape. I've seen derivations of capacitance for a few highly symmetric arrangement (eg coaxial cylinders) but nothing like a general approach to predicting the measurable capacitance of arbitrary ... | 4,775 |
<p>Does anyone know where I can find the solution for a spherically symmetric thin shell of timelike matter falling into a Schwarzschild black hole? The matter should be pressureless, so that each particle on the shell follows a radial geodesic. I am interested in the case where the shell is released from rest at a giv... | 4,776 |
<p>My question is little bit philosophical.
I would like to explain my ideas with a 2 dimensional universe model. </p>
<p>If we had lived in 2 dimensional universe like a plane, What could we observe when seeing a 3d object? </p>
<p>For example:
If a square pyramid that is inside full of material comes to the plane... | 4,777 |
<p>I would like to estimate the Maximum power/ tension that can be, between the sky diving guider and the "tourist".</p>
<p>In this <a href="http://skykef.co.il/upload2/Image/Edit%202.jpg" rel="nofollow">picture</a> what the max tenstion will be, I think it is maximum when the parachute is opened.</p> | 4,778 |
<p>I did an exercise which probably is quite popular,<br>
in which you draw an electromagnetic wave and prove that it should
propagate at the speed of light $1 \over \sqrt {\mu_0\epsilon_0}$ using Farday's law and Ampere's law.</p>
<p>Basically if this is the wave: </p>
<p><br>
<img src="http://i.stack.imgur.com/SqAz... | 4,779 |
<p>I've constructed such table from many different sources for my thesis introduction:
<img src="http://i.stack.imgur.com/zixNi.jpg" alt="enter image description here"></p>
<p>I'm trying to make a bit of philosophy it the thesis first chapter.</p>
<p>Are they realistic or not? Could you make any comments on the range... | 4,780 |
<p><strong>Problem statement:</strong></p>
<p>A cylinder rolls without slipping down a hill. It is released from height h. What is its speed when it come down? The cylinder mass may be completely concentrated on the radius R, which is the radius of the cylinder.</p>
<p><strong>My thoughts:</strong></p>
<p>At the top... | 4,781 |
<blockquote>
<p><em>A block of mass $200$kg is connected to a horizontal ceiling by four identical light elastic ropes, each having natural length $7$m and stiffness $180$N/m. It is also connected to the floor by a single light elastic rope having stiffness $80$N/m. All five ropes are stretched and vertical, and air ... | 4,782 |
<p>I want to find out how to predict Iridium flares, but I don't know where to start. If I know Solar position, Iridium satelites' TLE and it's shape, I need a magnitude(time) function for some place on Earth. As I see now, main question is in satellite orientation (it's panels).</p>
<p>Any ideas?</p> | 4,783 |
<p>I am reading Gelfand's Calculus of Variations & mathematically everything makes sense to me, it makes perfect sense to me to set up the mathematics of extremization of functionals & show that in extremizing a certain functional you can end up with Newton's laws (i.e. you could extremize some arbitrary functi... | 4,784 |
<p><strong>Problem statement</strong></p>
<p>A straight and homogenous stick with mass m is pressed against a wall with the force F. The stick is horizontal perpendicular against the wall. Given that the friction between the wall and the stick is μ, determine the horizontal component of F in order for the stick to not... | 4,785 |
<p>Is it possible to see <a href="http://en.wikipedia.org/wiki/Fraunhofer_lines" rel="nofollow">Fraunhofer lines</a> with amateur equipment?</p>
<p>Would it be possible (with reasonable effort) to identify elements or is this hard?</p> | 4,786 |
<p>I cannot find the answer to the above question.
I know that para-positronium is created with a probability of $25\%$ and decays into 2 photons, while ortho-positronium is created with a probability of $75\%$ and decays into 3 photons.
I also know that ortho-positronium has a way longer life time than para-positron... | 4,787 |
<p>According to classical electromagnetic theory, accelerated charges should emit radiation and lose energy. The reason given in my book why atoms don't emit radiation (say, when the atom moves along a circle) is because the atom is neutral. I can understand how this works for a neutral particle like a neutron but the... | 4,788 |
<p>I have read that adiabatic process is isentropic because there is no heat exchange in an adiabatic process and thus no change in entropy.</p>
<p>But my question is - Even in adiabatic process, work can be done. Let's take an example of an adiabatic vessel with a piston attached. That vessel does not exchange heat b... | 4,789 |
<p>Momentum measures how hard it is to stop an object. While Photons are massless they still have relativistic mass and energy. My question is can something stop photons other than being absorbed by something?</p>
<p>What does momentum mean when talking about massless particles?</p> | 4,790 |
<h1>Question</h1>
<p>This is from my textbook:</p>
<blockquote>
<p>There are 2 balls of the same size made of rubber and iron respectively kept on the smooth surface of a moving train. Which ball will move faster when the train brakes suddenly?</p>
</blockquote>
<h1>My Answer</h1>
<p>In that start it seems simple... | 4,791 |
<p>I am going through the <a href="http://www.staff.science.uu.nl/~aruty101/lecture1.pdf" rel="nofollow">lecture note</a> by Gleb Arutyunov on the derivation of critical dimension for bosonic string theory. I was able to reproduce all the results till the last step given on page 62. </p>
<p>For $[S^{i-},S^{j-}]$, the ... | 4,792 |
<p>We see light as having travelled in a straight line from stars or galaxies light years away from us. However it's path is more likely of multiple curves as a result of gravity along the journey (gravitational lensing) . How can we be sure that the accelerations thus experienced have not produced braking radiation (<... | 4,793 |
<p>I'm a high school senior and I have to write a paper about <a href="http://en.wikipedia.org/wiki/Resonance" rel="nofollow">resonance</a> and differential equations. I've been searching the Internet for a long time, but I haven't found an equation that is properly explained. Could anyone explain whether there is an e... | 4,794 |
<p>I am looking for some more information about how to obtain electricity from heat directly. This e.g. involves the Seebeck effect, as I have found it is called, where a material produces a voltage across when heated in one end and having the other end slightly cooler. This should be the princip in measuring instrumen... | 163 |
<p>As I was reading about the experimental arrangement for photoelectric effect, I saw a diagram that puzzled my knowledge of electrodes. I found that in the experimental setup the cathode of the photoelectric plate or emitter was connected to the positive terminal of the cell. Why is it so? How can a negative electrod... | 164 |
<p>Regarding conservation of mass-energy <a href="http://en.wikipedia.org/wiki/Conservation_law" rel="nofollow">Wikipedia</a> says: <strong>"this is an exact law, or more precisely, has never been shown to be violated."</strong></p>
<p>However, regarding quantum fluctuations, Wikipedia says <a href="http://en.wikipedi... | 4,795 |
<p>My elementary school playground was made of asphalt and had a track painted on with white lines. While walking on the track, I noticed that cracks in the asphalt often followed the paint.</p>
<p>The conclusion I came to and that I still hold is that the white tape on the black asphalt causes a temperature differenc... | 4,796 |
<p>The <a href="http://en.wikipedia.org/wiki/Gibbons%E2%80%93Hawking%E2%80%93York_boundary_term" rel="nofollow">Gibbons-Hawking-York term</a> which supplements the Einstein-Hilbert action is,</p>
<p>$$S_{GH} = \frac{1}{8\pi G} \int_{\partial M} d^3 x\sqrt{-h} \, K$$</p>
<p>where $\partial M$ is the boundary of the ma... | 4,797 |
<p>In 2006 the radius for a possible internal structure of the electron has been pinned down to $10^{-18} m$. This validates the approximation of electrons as point particles at long distances, e.g. in an atom. The upper bound on the internal electron radius has been derived from a very precise measurement of the $g$-f... | 4,798 |
<p>I have a tube with a length "L" and diameter "d" that is open on 1 side .
At a certain point ( say "x" ) from the closed end of the tube, I have a gas with a high pressure.</p>
<p>At this point, "x", there is also a weight of mass "m".
It is also known what the velocity of the weight is at point "L".</p>
<p>Initia... | 4,799 |
<p>The electron contains finite negative charge.The same charges repel each other.What makes electron stable and why does it not burst? Is it a law of nature that the electron charge is the smallest possible charge that can exist independently? What is a charge after all? Is it like space and time or we can explain it ... | 329 |
<p>In Chiral representation, a Majorana spinor looks like:</p>
<p>$$\psi=\begin{pmatrix}
\psi_L\\
-i\sigma^2\psi_L^*\end{pmatrix}$$ </p>
<p>In this representation the Right handed field is the charge-conjugate of the left handed field. i.e., $(\psi_R)^c=\psi_L$, where $$\psi_R=\begin{pmatrix}
0\\
-i\sigma^2\psi_L^*\e... | 4,800 |
<p>In the context of asymptotic symmetry groups, what is a boundary current? Why is it called a "current"? </p>
<p>Context: I'm reading Strominger's recent paper on Asymptotic symmetry group of Yang-Mills (link <a href="http://arxiv.org/abs/1308.0589">here</a>) and he has a section on the boundary current (section 2.3... | 4,801 |
<p>The Higgs is not detected in the asymptotic data, so it is possible that there is no particle interpretation for the Higgs quantum field. Indeed, the Higgs potential is only positive definite if the quartic term is included --- the quadratic term corresponds to a negative mass term. It would seem, therefore, that th... | 4,802 |
<p>What is the principle behind <a href="http://en.wikipedia.org/wiki/Centrifugation" rel="nofollow">centrifugation</a>?</p>
<p>I understand the idea that you spin something around the centripetal force will cause an apparent force on the spinning system.
However I don't quite grasp how particles (in the non subatomic... | 4,803 |
<blockquote>
<p>Could life on earth survive a large pole shift caused by an asteroid collision?</p>
</blockquote>
<p>I became aware that there are people who believe that the earth's pole suddenly shifts. That is, its rotational axis changes rather than its magnetic axis. This is listed in wikipedia as follows:</p>
... | 4,804 |
<p>For example, when we meassure Higgs boson mass to be 125 GeV, do we think about renormalized or pole mass? Should the mass of the Higgs change if it is produced at higher energies?</p> | 4,805 |
<p>I couldn't find one but assumed it must exist. Tried to find it on the back of an envelope, but got to an ugly differential equation I can't solve.</p>
<p>I'm assuming a square duct of infinite length, incompressible fluid, constant pressure gradient. The flow is steady. I'm also assuming there's only flow down the... | 4,806 |
<p>If the S-Matrix is the only observable, that rules out both generalized free fields and Wick-ordered polynomials of generalized free fields as interesting Physical models, because both result in a unit S-matrix. Neither possibility has been developed since the 1960s when these results were proved, and when the S-Mat... | 4,807 |
<p>Let's say there is two tubes(cylinders with no tops or bottoms) with charges $q_1$ and $q_2$, radii $b_1$ and $b_2$, lengths $l_1$ and $l_2$. These tubes are located along the axis of each other's surfaces like in this figure:
<img src="http://i.stack.imgur.com/stO7E.png" alt="two cylinders along the same axis, sepa... | 4,808 |
<p>As I have understood it, the Standard Model includes particles that carry the different forces, e.g. the electromagnetic (EM) force, the gravitational (G) force. When talking about EM fields such as visible light or microwaves, the associated particle is said to be the photon. But what about a static EM field withou... | 4,809 |
<p>Referring particularly to </p>
<p><a href="http://arxiv.org/abs/hep-th/9909056" rel="nofollow">http://arxiv.org/abs/hep-th/9909056</a></p>
<p>in regard to the wave equation for Schwarzschild-AdS black holes (p.4), I'm trying to understand tortoise coordinates. </p>
<p>So starting with the 4-dimensionalSchwarzschi... | 4,810 |
<p>Two friends, $A$ and $B$ are part of an experiment. $A$ is placed in a closed box and made to accelerate in free space at an acceleration $g$. $B$ is also placed in a closed box, but is made to rotate in a circle at uniform speed, such that the radial acceleration is also $g$. Can $A$ and $B$ perform some experiment... | 4,811 |
<p>When water freezes in a pipe it can crack the pipe open. I assume this takes quite a lot of energy as when I try to crack a pipe it can be hard work!</p>
<p>I think water freezing is a result of energy (heat) being lost from the water and out of the pipe into the freezing environment around it. </p>
<p>So what ene... | 4,812 |
<p>I'm reading <a href="http://arxiv.org/abs/gr-qc/9804087" rel="nofollow">an article</a> which includes the following equation involving a perturbed metric:</p>
<p>$$G_{AB} = \eta_{AB} + \overset{1}{\gamma}_{AB} + 2\overset{1}{\chi}_{(A,B)}\tag{4.1}$$</p>
<p>I don't understand how this equation was obtained; in part... | 4,813 |
<blockquote>
<p>Given a delta function $\alpha\delta(x+a)$ and an infinite energy potential barrier at $[0,\infty)$, calculate the scattered state, calculate the probability of reflection as a function of $\alpha$, momentum of the packet and energy. Also calculate the probability of finding the particle between the t... | 4,814 |
<p>I am looking at a spin 1/2 particle in a magnetic field. This has Hamiltonian
$$H=-\mu s\cdot B_0$$
For simplicity, assume $B_0=B_0\hat z$ so $H=-\mu B_0$. I then apply a perturbative magnetic field such that
$$V'=-\mu B_1 s_x$$
First I wanted to compute $E^{(1)}$
$$E^{(1)}_n=\langle\psi_n^{(0)}|-\mu B_1s_x|\psi_... | 4,815 |
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