question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Suppose Bruce Banner goes back in time, convinced that the Hulk is a stupid menace. Let's say he also borrows Quicksilver's speed abilities (maybe the Flash is more appropriate, but based on the recent X-Men movie Quicksilver is plenty fast enough).</p>
<p>Anyway he decides to run away from the burst of gamma rays ... | 1,781 |
<p>I'm trying to understand a concept spin in QM. I've read some explainations, and it seems that the idea is <em>very</em> easy and straighforward, however I didn't find these exact wordings in my books.<br>
My question: is the following explaination <strong>fully correct and strict</strong>, or I'm missing something?... | 1,782 |
<p>From basic airfoil theory the following free body diagram can be determined for a two dimensional asymmetric airfoil: </p>
<p><img src="http://i.stack.imgur.com/MlDJx.png" alt="enter image description here"></p>
<p>Here the direction of the resultant force is governed by the geometry of the airfoil section.</p>
... | 1,783 |
<p>Is information propagated in any other way than waves? Please distinguish "propagation across a medium" from information "storage within stable states of matter", which might difuse or interact chemically.</p>
<p>Information might be stored in stable configurations of matter, which might diffuse, or interact chemic... | 1,784 |
<p>The <a href="https://en.wikipedia.org/wiki/Drude_model" rel="nofollow">Drude model</a> of electric conduction in solids deals with independent free electrons subject to <em>random</em> collisions with the crystal lattice (the direction where the electrons are scattered after a collision is random). </p>
<p>A simpli... | 1,785 |
<p>Perhaps more of an engineering question, but with the subject recently in the news about hyperspeed maglev tunnels I'll chance it here. Say you set up a network of line of sight underground tunnels for your maglev transportation system operating roughly 50' above sea level through the American continent. These tunn... | 1,786 |
<p>Is there a fundamental difference between the statistical methods of science, comparing medicine/biology with small sample sizes(n < 10^2 or 10^3) to the statistics applied in Quantum Mechanics (h: order 10^34) or statistical mechanics (N: order 10^23)</p> | 1,787 |
<p>It's folklore dating back to von Neumann and Wigner that <a href="http://en.wikipedia.org/wiki/Avoided_crossing" rel="nofollow">time-dependent Hamiltonian systems tend not to have level crossings of their energy eigenvalues</a>. However, we can of course consider smoothly varying Hamiltonians which have been enginee... | 1,788 |
<p>Does a person get electrified when his feet are on the floor, his right hand is holding $220~V$ and his left hand holding a piece of wood or any other insulator?</p> | 1,789 |
<p>Like in title, how small can diffraction grating be? And, of course be "fully operational".
I mean, littles diffraction grating possible that still works as full-sized one.</p> | 1,790 |
<p>Suppose that two spheres, $S1$ and $S2$, with radii $R1$ and $R2$ resp. have the same charge uniform charge $Q$ and $R1 > R2$. After they are forced to come in contact, why does $S1$ gain more charge? Why don't they both continue to have equal charges?</p> | 1,791 |
<p><strong>Background:</strong><br>
This reminds situation reminds be of an episode from the <em>The Big Bang Theory</em>, although it is quite different from it. My roommate and I have similar temperature preferences and also share the objective of saving money on electricity. The optimal solution towards this objecti... | 1,792 |
<p>If we could build a neutrino telescope capable of viewing relic neutrinos that decoupled after the big bang, with a similar angular and spectral resolution that is possible now for the CMB, what would we see? (And I know this will be technically incredibly difficult.)</p>
<p>How would the C$\nu$B differ because of ... | 1,793 |
<p>Consider the following situation. A block of mass $M$ is resting on a rough horizontal ground, and a frame is moving towards the right horizontally with an acceleration $a$. Suppose the coefficient of static friction on the ground on which the block is standing is $ \mu > a/g$.</p>
<p>Clearly the block is moving... | 1,794 |
<p>The light would take 93 billion years to reach the edge of universe but nothing can travel faster than the speed of light not even the big bang?</p> | 10 |
<blockquote>
<p>a short linear object of length b lies along the axis of a concave mirror of focal length f at a distance u from the mirror.what is the size of the image?</p>
</blockquote>
<p>what i have done so far:</p>
<p>since the object is of length b, consider the point of the object closest to the mirror A an... | 1,795 |
<p>I know how transform an integral below, </p>
<p>$$
\iint f(\mathbf v_{1})f(\mathbf v_{2})d^3\mathbf v_{1}d^3\mathbf v_{2},
$$ </p>
<p>using relative speed coordinates: we just use
$$
m_{1} \mathbf v_{1} + m_{2}\mathbf v_{2} = M\mathbf V, \quad \mathbf v = \mathbf v_{1} - \mathbf v_{2} ,
$$</p>
<p>and then we ... | 1,796 |
<p>I asked a similar question but the wrong way <a href="http://physics.stackexchange.com/questions/24835/scale-invariance-and-self-organized-criticality">here</a>. Because my intention was to ask about non thermodynamic system, i will be more specific:</p>
<ul>
<li>What is the relation between critical behaviour and ... | 1,797 |
<p>In particle Physics it's usual to write the physical content of a Theory in adjoint representations of the Gauge group. For example:</p>
<p>$24\rightarrow (8,1)_0\oplus (1,3)_0\oplus (1,1)_0\oplus (3,2)_{-\frac{5}{6}}\oplus (\bar{3},2)_{\frac{5}{6}}$
(Source: <a href="http://en.wikipedia.org/wiki/Georgi-Glashow_mod... | 1,798 |
<p>The inverse square law for an electric field is:
<br>
$$
E = \frac{Q}{4\pi\varepsilon_{0}r^2}
$$
Here: $$\frac{Q}{\varepsilon_{0}}$$
is the source strength of the charge. It is the point charge divided by the vacuum permittivity or electric constant, I would like very much to know what is meant by source strength ... | 1,799 |
<p>First off, I swear this is not homework. I'm doing some practice problems because I got an exam coming up. I'm stuck on this one:
<img src="http://i.stack.imgur.com/w7KMz.png" alt="alt text"></p>
<p>I figured I would use energy conservation for this problem. So since the thing is not moving initially, I tried doing... | 1,800 |
<p>In an ideal gas, the Boltzmann distribution predicts a distribution of particle energies $E_i$ proportional to $ge^{-E_i/k_bT}$.</p>
<p>But, doesn't entropy dictate that the system will always progress towards a state of maximum disorder? In other words the system evolves towards a macro-state which contains the m... | 1,801 |
<p>In the current accelerated expansion universe model will the Hubble constant reach zero asymptotically in the far future?</p> | 1,802 |
<p>If a particle of mass $M$ is given an electric charge $Q$, will its mass change?</p> | 1,803 |
<p>Say I have a series of tubes (not the internet) looking like this, where <code>w</code> represents water:</p>
<pre><code>| | | |
| | | |
|wwww| |w|
|wwww| |w|
|wwww+------+w|
|wwwwwwwwwwwww|
+-------------+
</code></pre>
<p>Why is it that if I put some water in either side, the water leve... | 1,804 |
<p>I really hope someone will take a quick look at the following, I would just love to better understand it...</p>
<p>This exercise is from Arnold's "Mathematical Methods of Classical Mechanics", p. 97 in the chapter on d'Alemberts principle:</p>
<p>A rod of weight P, tilted at an angle of 60° to the plane of a table... | 1,805 |
<p>I just came across a line in a paper:</p>
<p>"Assume the probability that a Lagrangian parameter lies between $a$ and $a + da$ is $dP(a) = $ [...]."</p>
<p>This reminded me again of my single biggest qualm I have with the "Bayesian school" - that they assign <em>probabilities</em> to facts of nature, say $P(m_\mat... | 1,806 |
<p>Please explain why static friction is greater than kinetic friction logically.
Speak about it microscopically and tell what does happen on surfaces of objects by considering electromagnetic force between atoms on surface.</p> | 30 |
<p>I have the equation $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$
Which calculates the force of an electromagnet. I was wondering if anyone knew what plane Area is taken from? I have heard it is the cross sectional area of electromagnet(which doesn't make sense to me because it already uses the number of turns, N and ... | 1,807 |
<p>I had been thinking about the way an air conditioning system moves heat from one place to another. The unit runs and drops the temp. in the building and raises the temp. outside. Also there is mechanical energy that converts to heat (the compressor and fan motors) and is also put outside. If this is the case, is the... | 1,808 |
<p>Suppose we use the metric $(+,-,-,-)$ thus the momentum squared is </p>
<p>$p^2 = p_0^2-\vec{p}^2 = m^2>0$</p>
<p>Defining $p_E:=\mathrm{i}\cdot p_0$ and $\bar{p}:=(\,p_E,\vec{p})$ with Euclidean norm $\bar{p}^2 = p_E^2+\vec{p}^2$. </p>
<p>Here's my question: </p>
<p>If we plug in </p>
<p>$\mathrm{i}\,p_0$ ... | 1,809 |
<p>Operationally, we can only know about the results of experiments and observations. From them, we can conclude our world is one which is complex enough to allow for computers. After all, we're using computers right now. Our universe has the property of Turing completeness, meaning we can embed any possible computer p... | 1,810 |
<p>I am trying to get to grips with Altarelli-Parisi-type equations. In chapter 17 of Peskin/Schroeder, they first develop the equations for a similar problem in QED. Equation $(17.123)$ introduces the sum rule
$$
\int_0^1 dx ( f_e(x,Q) - f_\bar{e}(x,Q)
) = 1
$$
where $f_e$ and $f_\bar{e}$ are the distribution fu... | 1,811 |
<p>Basically, I can't stop wondering why light (the photon) is so special, compared to all the other particles known (and unknown) to modern day physics.</p>
<p>Could it be that there exists an upper limit on speed that is instead a property of another "entity" (particle / wave), other than the photon?</p>
<p>A quest... | 1,812 |
<p>How complicated is it to calculate a surface normal on the spherical approximation of the earths surface pointing towards the sun at a given point in time?</p>
<p>What I try do is to highlight a small area on a world map where the radiation from the sun tangential hits a imaginary sphere around the earth.</p>
<p>T... | 1,813 |
<p>Does adding heat to a material, thereby increasing electrical resistance in the material increase or decrease entropy? </p>
<p>Follow up questions:<br>
Is there a situation were <a href="http://en.wikipedia.org/wiki/Heat_flux" rel="nofollow">Heat flux</a> ie. thermal flux, will change entropy?<br>
Does increasing ... | 1,814 |
<p>Is there a way to calculate, or a reference table I can to look up which provides the average distance a photon travels before it encounters an electron and is absorbed or re-emitted in a fiber optics cable? I asked a fiber manufacturer but all they could come up with is the index of refraction. I'm just looking for... | 1,815 |
<p>I'm working through Mattuck's "A Guide to Feynman Diagrams in the Many-Body Problem", but I'm stuck on a bit which I feel should be trivial.</p>
<p>In section 3.2 (p 43 in the Dover edition) he gives a Hydrogen atom as an example of a system which can be considered to have a p-dependent potential term.</p>
<p>In h... | 1,816 |
<p>What has the reaction been towards the <a href="http://arxiv.org/abs/1309.4095" rel="nofollow">recent paper</a> claiming to have a proof that scale invariance plus unitarity implies conformal invariance in 4d?</p> | 1,817 |
<p>I've been reading through FLP Vol. II, and he has proven that as the flux through a closed surface is: $\ \int_{surface} \mathbf{F} \space \mathrm{d}\mathbf{a} $, according to the divergence theorem, the flux through a surface can be defined as: $\ \int_{volume} \nabla \cdot \mathbf{F} \space \mathrm{d}V $, where $\... | 1,818 |
<p>Is it true that the mass of air in normal atmospheric pressure over 1$m^2$ is 10326 $kg$?
I calculated it from pressure formula </p>
<p>$p=\frac{F}{A}$. </p>
<p>Let $m=?, A=1 m^2 and p=101300 Pa$. </p>
<p>$p=\frac{F}{A} \Leftrightarrow ...\Leftrightarrow
m= \frac{pA}{g}=\frac{101300 \cdot 1 }{9,81} = 10326 kg $. ... | 1,819 |
<p>What happens if we lift a box of ideal gas? Work is done to the box but no heat is getting into it. So does it's internal energy increase by the amount of work done? Or is it that lifting is not counted as work done to the system?</p>
<p>Or is it the case that work turns into heat in a box which quickly flows out t... | 1,820 |
<p>If a box of ideal gas and another box of diatomic gas are in thermal equilibrium, </p>
<ol>
<li><p>does it mean that the average translational energy of ideal gas particle (A) is the same as that of diatomic gas particle (B)? </p></li>
<li><p>or does it mean that A is equal to the sum of the average translational e... | 1,821 |
<p>I am trying to make sense of statements about unitarity in <a href="https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/" rel="nofollow">this popular science article</a> about Nima and Jaroslav's new idea.</p>
<p>My first query is that it is claimed that unitarity is a pillar of... | 1,822 |
<p>As we all know, the stars we see in the night sky might already be dead. I was wondering though, when was this fact or conclusion commonly established? Today, most people (let's assume with an above average education) would probably be aware of this fact.</p>
<p>When is the earliest time when the same could be said... | 1,823 |
<p>Beyond one-loop, the beta function of a QFT is scheme dependent. I would like to understand better this ambiguity. </p>
<p>The easiest thing to say is that you haven't calculated something physical, so of course it does not need to be scheme independent. However, the anomalous dimension of operators is I think an o... | 1,824 |
<p>I need some <a href="http://en.wikipedia.org/wiki/Albert_Einstein" rel="nofollow">Einstein</a>'s papers translated into English. There is one complete collection of his papers but only a few of them have been translated in English. The rest are in their original language -- German, which, unfortunately, I can't read... | 1,825 |
<p>In classical mechanics coordinates are something a bit secondary. Having a configuration space $Q$ (manifold), coordinates enter as a mapping to $\mathbb R^n$, $q_i : Q \to \mathbb R$. The primary thing is the manifold itself and its points.</p>
<p>On the contrary, quantum mechanics for classical coordinates has op... | 1,826 |
<p>I'm attempting a problem from Zwiebach: A First Course in String Theory and am completely stuck. Could anyone give me a hint? The problem is as follows.</p>
<p>Consider $S$, $S'$ two Lorentz frames with $S'$ boosted along the $+x$ axis. In frame $S$ we have a cubic box with sides of length $L$ at rest. The box is f... | 1,827 |
<p>I am just curious as a non-US person:</p>
<p>how does undergraduate physics course progress in U.S. colleges?</p>
<p>Do they go right into classical mechanics books, or do they teach introductory courses first, then specialize on classical mechanics, electrodynamics etc. in the second year?</p>
<p>First-year, sec... | 1,828 |
<p><a href="http://www.cchem.berkeley.edu/gsac/grad_info/prelims/binders/dimensionless_numbers.pdf" rel="nofollow">Most dimensionless numbers</a> (at least the ones easily found) used for dimensional analysis are about fluid dynamics, or transport phenomena, convection and heat transfer - arguably also sort of fluid m... | 1,829 |
<p>We have known for a long time that graphene has in-plane thermal conductivity ranging between 2000 and 4000 $W m^{-1} K^{-1}$. But in order to model heat transport on a sheet of graphene, we need more than the conductivity: we also need specific heat in order to obtain the thermal diffusivity that is used in the equ... | 1,830 |
<p>The electric energy stored in a system of two point charges $Q_1$ and $Q_2$ is simply $$W = \frac{1}{4\pi\epsilon_0}\frac{Q_1Q_2}{a}$$ where $a$ is the distance between them.</p>
<p>However, the total energy can also be calculated through the volume integral of magnitude squared of the electric over all space: $$W ... | 1,831 |
<p>Bernoulli's principle makes sense when you apply it to fluids. If you decrease the diameter of a pipe then the velocity of the fluid increases because it needs to keep the same rate of fluid moving through the pipe. </p>
<p>So my question is:</p>
<p>If Voltage == Diameter of the pipe</p>
<p>and</p>
<p>Current ==... | 1,832 |
<p><img src="http://i.stack.imgur.com/w04j8.jpg" alt="heat exchanger diagram"></p>
<p>I want to design a heat exchanger in a chimney in order to utilize heat from chimney. I have done several experiments, but I could not determine the exact length of tube (carrying water), such that its inlet temp is ambient temperatu... | 1,833 |
<p>A glass mirror (with metal backing layer) will reverse the polarisation of circularly polarised light upon reflection.</p>
<p>A polished piece of metal will also reverse the polarisation of circularly polarised light upon reflection. (I have tested and confirmed this for myself).</p>
<p>wikipedia states the reason... | 1,834 |
<p>So I have been trying to learn about entanglement and quantum teleportation and from what I've been able to gather so far, the <strong>teleportation</strong> part seems to be misleading.</p>
<p>At first I thought that the two particles were of a uniform undetermined state which would collapse probabilistically upon... | 1,835 |
<p>What is Dalitz decay?</p>
<p>I know there are Dalitz $\pi^0 \to e^+ + e^- + \gamma$ <a href="http://www.nikhef.nl/pub/experiments/zeus/theses/wouter_verkerke/latex2html/node60.html" rel="nofollow">decay</a>, $w \to \pi^0 + e^+ + e^-$ decay, may be more. But is there a rule to say which decay is Dalitz and which is... | 1,836 |
<p>In Pockels electro-optic effect, change in Electric field produces change in refractive index/ birefringence. Moreover this effect becomes electric field squared in the case of Kerr effect. If we increase the electric field more for example 3 ,4 , 5 times . we will observe the same phenomenon of Kerr effect or is it... | 1,837 |
<p>I want to determine the potential energy of two equally charged spherical charges by using the equation: $V_{pot}= \int_V \frac{1}{2} \epsilon_0 E^2 dV$ and therefore I was wondering what I has to take as $E$? The sum of the electric fields of both charges? Notice, that I want to use this equation on purpose since i... | 1,838 |
<p>Imagine we live on cylinder(we are 2d creature), put a rope around that cylinder and start pulling both ends of the rope against each another. Will the space get deformed? I guess it will, I have to put some energy to the rope and energy deforms the space. Is it possible to calculate shape of the space based on the ... | 1,839 |
<p>I am trying to calculate B mixing in the Standard Model (in preparation to go beyond the SM). I have no trouble doing the gamma matrix algebra etc. but the loop integral keeps tripping me up. In my calculation I have
$$ \int \frac{d^4 k}{(2\pi)^4} \frac{k^2}{(k^2-m_1^2) (k^2 - m_2^2) (k^2- M_W^2)^2} $$
I know about ... | 1,840 |
<p>I've been told that a vacuum isn't actually empty space, rather that it consists of antiparticle pairs spontaneously materialising then quickly annihilating, which leads me to a few questions.</p>
<p>Firstly, is this true? And secondly, if so, where do these particles come from?... (do the particles even have to co... | 1,841 |
<p>I have a setup where a motor is spinning at a constant (known) RPM, under no load. I know the power going into the motor (voltage * current), and I can find out the rotational kinetic energy of the rotor. </p>
<p>My question is, how do I calculate the efficiency of the motor from this? Is it even possible? I unders... | 1,842 |
<p>Consider the image below. It shows a double slit experiment but with a single photon at a time. <strong>My question is as follows</strong>:</p>
<p>Why is it that the photons always take a different path when shot at the same target? Where does the uncertainty lie? If we shoot it in exactly the middle of the two sli... | 1,843 |
<p>The macroscopic Maxwell's equations can be put in terms of differential forms as
$$\mathrm{d}\mathrm{F}=0,\quad\delta \mathrm{D}=j\implies \delta j=0,\quad \mathrm{D}=\mathrm{F}+\mathrm{P}.$$
$\mathrm{F}$, $\mathrm{D}$, and $\mathrm{P}$ are 2-forms; $j$ is a 1-form. $\mathrm{F}$ is the $electromagnetic\ field$, whic... | 1,844 |
<p>Explained at the level of a 5$^{\text {th}}$ semester physics student (i.e. pre QFT, but far beyond the level of a news article for non-physicists, which avoids all details and only deals in analogies) ...</p>
<ul>
<li>What has been measured at CERN some days ago?</li>
<li>What are the essential ingredients of the ... | 1,845 |
<p>Why do we need neutrino to explain neutron <a href="http://en.wikipedia.org/wiki/Beta_decay" rel="nofollow">decay</a>?
Is there any evidence regarding existence neutrinos in the context of
$n\to p + e + \bar{\nu}_e$?</p> | 1,846 |
<p>What is the maximum voltage that can be put on a metal sphere before electrons fly off it or the metal itself explodes due to electrostatic forces?</p> | 31 |
<p>We have the the five <a href="http://en.wikipedia.org/wiki/Lagrangian_point" rel="nofollow">Lagrange points</a> (let consider Earth and Sun):</p>
<ul>
<li>$L_1$ - lie between Sun and Earth;</li>
<li>$L_2$ - beyond the Earth;</li>
<li>$L_3$ - beyond the Sun;</li>
</ul>
<p>And what's the difference between $L_4$ and... | 1,847 |
<p>Why does the nature always prefer low energy and maximum entropy?</p>
<p>I've just learned electrostatics and I still have no idea why like charges repel each other.
<a href="http://in.answers.yahoo.com/question/index?qid=20061106060503AAkbIfa">http://in.answers.yahoo.com/question/index?qid=20061106060503AAkbIfa</a... | 1,848 |
<p>I'm a student and I had to give a talk on seminar about <a href="http://en.wikipedia.org/wiki/Quantum_Zeno_effect">Quantum Zeno effect</a> and Anti-Zeno effect to my colleagues (all listeners have had a course in quantum physics, but not a heavy one with all the bra and ket stuff).</p>
<p>My first idea to give a si... | 1,849 |
<p>How can we compute the integral $\int_{-\infty}^\infty t^n e^{-t^2/2} dt$ when $n=-1$ or $-2$? It is a problem (1.11) in Prof James Nearing's course <em>Mathematical Tools for Physics.</em> Can a situation arise in physics where this type of integral with negative power can be used?</p> | 1,850 |
<p>By my understanding, if everything doubled in size, such as the Sun and the Earth, and because the space in between them (which is nothing) can't expand, would the gravities greatly change and the Earth be pulled into the Sun? </p> | 454 |
<p>Suppose we have a system of bosons represented by their occupation numbers
$$\tag{1} | n_1, n_2, ..., n_\alpha, ... \rangle$$
Then we can define creation and annihilation operators
$$\tag{2} a_\alpha^\dagger| n_1, n_2, ..., n_\alpha, ... \rangle = \sqrt{n_\alpha+1} | n_1, n_2, ..., n_\alpha+1, ... \rangle$$
$$\tag{3... | 1,851 |
<p>I would like to construct a 2-local Hamiltonian that acts on a 1D spin chain where each spin transforms as the 3D irrep of $A_4$ which is a subgroup of $SO(3)$. I know that an $SO(3)$ invariant Hamiltonian can be constructed using the Casimir operator like $H = \sum_i \vec{S_i} . \vec{S_{i+1}}$. Is there a similar t... | 1,852 |
<p>Is there some optimal layout of items, or types of items (characterized by size, shape, density, solid/liquid, etc) that will allow a common household refrigerator to function with optimal energy efficiency?</p>
<p>I know this is a very broad and any answer will have to make several assumptions, not the least of wh... | 1,853 |
<p>I thought that modern 3d glasses work by having one lens filter horizontally polarized light, and the other filter vertically polarized light.</p>
<p>However, I found this pair of 3d glasses at my parents' house, and looked at the reflection from the floor at different angles:</p>
<p><img src="http://i.stack.imgur... | 1,854 |
<p>In the lecture, the professor said something along the lines of:</p>
<p>"After a suitable gauge transformation, the standard model higgs field can be expanded as</p>
<p>$$\phi =\left(\begin{array}{c}
0 \\
v+H(x)
\end{array}\right)$$
".</p>
<p>Now, the argument I have been able to scramble from different source... | 1,855 |
<p>This is a bit quirky: For a very long time I've found Stephen Hawking's evaporating small black holes a lot more reasonable and intuitive than large black holes.</p>
<p>The main reason is that gravity is relative only if your gravity vectors are all parallel. When that is true, you can simply accelerate along with ... | 1,856 |
<p>I'm puzzled about how to derive the equations of motion for certain classical systems where some entity is controlling some of the DOFs.</p>
<p>For example, consider a double-pendulum, with lengths $l_1$ and $l_2$, masses $m_1$ and $m_2$, and which deviate from the vertical by $\theta_1$ and $\theta_2$. Let's say ... | 1,857 |
<p>From Lagrangian I got two primary constraint $\phi_i$ and $\phi$. And my Hamiltonian in presence of the constraints becomes- $$H_p=p\dot q-L+\lambda_i\phi_i+\lambda\phi$$ here the $\lambda_i$ and $\lambda$ are Lagrange undetermined multiplier. Now from $\dot \phi_i=[\phi_i,H_p]$ I got secondary constraint $\Sigma_k$... | 1,858 |
<p>I am trying to find the following:</p>
<p><strong>How many pieces of toast would you need to make a black hole?</strong></p>
<p>From what I've learnt so far I need to find an equation for the compression force the massive amount of the intergalactic pile of pieces of toast would exert on itself to be able to compr... | 1,859 |
<p>I know this question sounds silly, as if there was a potential difference a current would be created when the terminals are connected together and this would mean energy has come from somewhere.</p>
<p>The reason I ask this though is that from my understanding of the depletion region and built in potential of a dio... | 1,860 |
<p>For example, a harmonic oscillator can have an algebraic solution, and hydrogen potential can<br>
also have an algebraic solution. Here the algebraic method of solution means that we can use the similar methods like $a$ and $a^\dagger$ to solve QM problem. So in general what kind of problem in QM can have an algebr... | 1,861 |
<p>Can anyone please explain why: $$a_1=a_2\tan\alpha $$
<img src="http://i.stack.imgur.com/9IPBy.jpg" alt="enter image description here"></p>
<p>We have 2 <strong>same</strong> cubes placed on a platform, between them there is a wedge which is pushing the cubes in opposite directions. The hard part of the question is... | 1,862 |
<p>In open-closed string duality, we can reinterpret the one-loop open string diagram (an annulus or cylinder) as a propagating closed string, depending on the direction in which we take time to be. This duality is reflected in the amplitudes we attach to these two different interpretations of the cylinder diagram. My... | 1,863 |
<p>I am trying to understand the electronic structure of the negatively charged <a href="http://en.wikipedia.org/wiki/Nitrogen-vacancy_center" rel="nofollow">NV centre in diamond</a>, where there is a so-called <a href="http://en.wikipedia.org/wiki/Zero-phonon_line_and_phonon_sideband" rel="nofollow">Zero-Phonon Line</... | 1,864 |
<p>The hotter something is glowing the more white/blue it appears. A dying medium sized star expands, cools and becomes a red giant for a while, but eventually it is going to gravitationally collapse (once enough Iron (Fe) is accumulated in the core). Then it blows the outer layers away and what is left collapses into ... | 1,865 |
<p>We distinguish between the states of matter: gas, liquid and solid. Possibly we could add the plasma state and/or the superconductive state as new states of matter. Phase transistions at certain temperature perhaps with some other conditions should have to exist. What do you think, does it make sense?</p> | 1,866 |
<p>I'm just going over a few past exams for tomorrow, and I've come across a question that I'm having quite a bit of difficulty with.</p>
<blockquote>
<p>Let $\left|0\right\rangle$ denote the Fock vacuum state so that $b_j \left|0\right\rangle = 0$, for all $j$. For any positive integer $N$, show that the state $(b_... | 1,867 |
<p>In <a href="http://en.wikipedia.org/wiki/Quantum_entanglement" rel="nofollow">Wikipedia</a> it is mentioned that position and momentum can be entangled as well as spin and polarization etc. I assume etc. is charge etc.
I understand how if you measure spin up on one of a pair you get spin down on the second of the pa... | 1,868 |
<p>I may be totally off with this quite abstract (?) question(s).</p>
<p>But still, here are some closely related sub-questions:</p>
<ul>
<li>Is there a list of currently "known" intrinsic properties of nature?</li>
<li>How exactly is an intrinsic property of nature defined? Is it defined as "<em>it is so, because it... | 1,869 |
<p>If we designate the origin (the reference point from which all displacement vectors are measured) $\vec{0}$, and If we consider a sphere $\mathbb{B}\left(\vec{0},\mathcal{R}\right)$ of radius $\mathcal{R}$ and centered at $\vec{0}$, and say that outside this sphere the charge density $\rho$ and current density $\vec... | 1,870 |
<p>I am to solve the following:</p>
<blockquote>
<p>A jet engine of mass $m$ is fastened to the fuselage of a passenger jet by a bolt. During flight, the plane encounters turbulence, which suddenly imparts an upward vertical acceleration of $2.60\mathrm{~m/s^2}$ to the plane. Calculate the force on the bolt.</p>
</b... | 1,871 |
<p><img src="http://i.stack.imgur.com/eHV8x.png" alt="BICEP2 B-mode Signal"></p>
<p>The first image of <a href="http://bicepkeck.org/visuals.html">BICEP2 visuals</a> shows the "BICEP2 B-mode Signal", described as follows:</p>
<blockquote>
<p>Gravitational waves from inflation generate a faint but distinctive
twis... | 1,872 |
<p>The observed Higgs boson mass is at an interesting place in parameter space, placing the standard model electroweak vacuum right at the edge of metastability. Among the proposed explanations of this value is the existence of a <a href="http://arxiv.org/abs/1204.2551">"shift symmetry" in the Higgs sector</a>. </p>
<... | 1,873 |
<p>When light refracts from a medium to a second one, its frequency stays the same, and its wavelength changes. If this is true, why we see the refracted light ray's colour is the same as the incident light ray in the second medium? The colors should not be the same. If the wavelength changes, colour should change too.... | 32 |
<p>Not sure where to ask this question - thought you guys would probably have the best idea!</p>
<p>Today a single key on my keychain in my pocket heated up so that it was too hot to handle and scalded my leg. Any ideas what could possibly have done this?</p>
<p>I always keep a prison guard style set of keys attached... | 1,874 |
<p>I am studying a field theory where the field is a matrix. The problem is that I have to calculate some functional derivative. How could we define functional derivative when the field is a matrix ?</p> | 1,875 |
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