question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>In one of tasks I met the concept of unitarily similar matrices: in particular, I need to prove that sets $\gamma_{\mu}, -\gamma_{\mu}$ (Dirac gamma matrices) are unitarily similar. I don't know what does it mean, so can someone tell me? Maybe, I need to find some unitary transformation that connects first and secon... | g7029 | [
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<p>We consider that the force acting on a current carrying wire placed in a uniform magnetic field perpendicular to the length of the wire is given by $IBl$. If the wire moves by a distance $x$ in a direction perpendicular to its length the raise in its kinetic energy is $IBlx$</p>
<p>Now basically the magnetic forces... | g7030 | [
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<p>In a recent question <a href="http://physics.stackexchange.com/questions/31686/can-colliders-detect-b-violation">Can colliders detect B violation?</a> I asked about detecting B violation in collisions. Here I am interested in the theory aspect. (I asked both questions originally in the same question, but I got one a... | g7031 | [
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<p>I am learning how to install water pipes and I was told that to check if a pipe is leaking water I need to check the water pressure. But I don't understanding how water pressure works inside the pipe.</p>
<p>For example, a water pump is connected to a valve and to a tap like this:</p>
<p>pump ----> valve ---->tap... | g7032 | [
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<p>What is the time dilation formula by constant velocity?</p>
<p>Is the right formula
$$t'=t\times \sqrt{1-v^2/c^2}$$ or is it
$$t'=\frac{t}{\sqrt{1-v^2/c^2}}$$ ?</p>
<p>And can someone show me a computational example regarding the time dilation formula?</p>
<p>Thank you in advance.</p> | g7033 | [
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<p>If it is true that particles are in different potential locations until an observer comes along and collapses the wave function, then how can a blind man throw a ball and hit a wall if the particles are spread out?</p> | g7034 | [
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<p>In softly broken SUSY, the bare mass parameters may be specified at e.g. the GUT scale, and then we can run these down to another scale using RGEs, similar in form to the RGEs for gauge couplings, with a 1-loop and 2-loop differential beta function. Once these parameters have been run to the desired scale, tree-leve... | g7035 | [
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<p>Why isn't Newtonian mechanics valid in Quantum world? Suppose you isolate an alpha particle and accelerate it in absolute vacuum. Why it doesn't follow the equation $F=ma$? If Newtonian mechanics is invalid in quantum world, what is the guarantee that Quantum mechanics is valid in macroscopic world?</p> | g7036 | [
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<p>I have a question related to the interference (thought)experiment with water waves given in the book Feynman Lectures on Physics Vol.3. When only one hole (hole 1) is open the measured wave intensity at the second wall varies with the distance from the center. It is shown in the figure as $I_1$ which has a peak righ... | g7037 | [
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<p>From most graph, when the tire doesn't slip, then the friction is zero, for example see the below image</p>
<p>Why there is no friction when there is no slip? As the car stand still on slope, there is no slip but still there is friction holding the car against gravity</p>
<p><img src="http://i.stack.imgur.com/mbyP... | g7038 | [
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<p>How will an electric fields affect the formation of plasma sheaths?</p> | g7039 | [
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<p>When taking the EH action, $$S_{EH} = \frac{1}{16\pi G}\int_M d^4x \sqrt{-g}R$$ and making a small variation in the metric while ignoring boundary terms, we obtain</p>
<p>$$\delta S_{EH} = \frac{1}{16\pi G}\int_M d^4x \sqrt{-g}\left(\frac{1}{2} g^{\mu \nu}R -R^{\mu \nu}\right)\delta g_{\mu \nu} $$.</p>
<p>When loo... | g7040 | [
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<p>The Hamiltonian of the spin $S$ quantum Heisenberg model is
$$H = J\sum_{<i,j>}\mathbf{S}_{i}\cdot\mathbf{S}_{j}$$
I have read that when the spin quantum number $S\to\infty$, quantum fluctuation vanishes, and then the model is identical to the classical Heisenberg model where the spins are treated classically,... | g7041 | [
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<p>Consider two entangled photons with two mutally conjugate circular polarization. What happens when one photon which is, say, left hand polarized gets destroyed. Will the other photon retains its right hand polarization or will it assume some random state? There is another possibility that it looses its circular pola... | g7042 | [
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<p>I am developing a sensor calibration capability that compares a telescope lunar observation to a physics-based radiometric model. I'd like to find some high quality lunar images to test our solution against a wide range of data. To be useful, I need several key pieces of metadata:</p>
<ul>
<li>Raw camera data o... | g7043 | [
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<p>Consider a system which is in an equilibrium state. Now, a small perturbation causes it to start oscillating about the equilibrium state, but over time, the momentum with which it overshoots the equilibrium state keeps on increasing. This can be considered as an exact opposite of what can be expected of reaching a n... | g7044 | [
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<p>In the book 'Modern Particle Physics' byM. thomson the Higgs doublet is written as </p>
<p>$$\phi = \left(\begin{matrix} \phi^+ \\ \phi^0 \end{matrix}\right)=\phi = \left(\begin{matrix} \phi_1 +i\phi_2 \\ \phi_3+i\phi_4 \end{matrix}\right) $$</p>
<p>With the comment</p>
<blockquote>
<p>Because the Higgs mechan... | g7045 | [
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<p>I'm a high school physics student, and part of our project requires us to make an electromagnet. We have an iron core, and it will go inside a solenoid. The problem is, we don't know what the relative permeability constant of iron is so we can calculate the magnetic field with the iron. How can we get this constant... | g7046 | [
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<p>$\frac{d}{dt}$$\hat{H}$ = $\frac{i}{\hbar}$$[\hat{H},\hat{H}]$ +$\frac{\partial{\hat{H}}}{\partial{t}}$</p>
<p>That's as far as I've got. I do not know much about the Heisenberg equation or even what it represents. Could someone give me a beginners intro to it ?</p>
<p>I do have one idea : $\hat{H}$ = $i\hbar$$\fr... | g7047 | [
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<p>Why is the critical point for the phase diagram of pure water degrees of freedom equal to 0? Maybe, you know what is the mathematical explanation for the fact that the number of degrees of freedom at the critical point is 0? What else is affected by the lack of degrees of freedom in addition to the Gibbs phase rule?... | g7048 | [
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<p>I am studying the time evolution of a density matrix using the <a href="http://en.wikipedia.org/wiki/Lindblad_equation" rel="nofollow">Lindblad equation</a>.
My initial density matrix is $\rho(0)=|\alpha\rangle\langle\alpha|$, where $|\alpha\rangle$ is a coherent state. Then I have to compute $\mbox{Tr}\rho^2$.
Due... | g7049 | [
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<p>How do we decide whether a quantum circuit can be realized physically or not ? I was wondering for physical realization of Shor's factoring algorithm using NMR ( I mean can we do it? ). </p> | g7050 | [
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<p><strong>SUPERFLUIDITY:</strong></p>
<p>Superfluidity is one of the most amazing quantum phenomena, which we can sit and watch them happening before our eyes! Watch this video, it is only a couple of minutes long, which will bring you face-to-face with quantum mechanics in all its beauty. Then take a look at the qu... | g7051 | [
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<p>Sometimes it happens that when you pour a boiling water into a glass jar, it cracks. Since glass is very hard material and resilient to pressure, the tension must be very high. Is it possible to estimate what forces / pressure / tension occur in such a moment?</p>
<p>Some supplementary questions:</p>
<ul>
<li>Is i... | g7052 | [
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<p>Displacing something against the gravitational field, gains it potential energy. Moving something against the nature requires work. If the electric field of a negative source charge 'Q' points inward, then by definition, it would require some work to displace a negative test charge 'q' against 'Q'. According to the ... | g7053 | [
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<p>If a linear polarized single photon strikes a linear polarizer such that its polarization is at 45 degrees to the polarization axis of the polarizer, what happens?
There is a nearly 50% chance that the photon is transmitted, and assuming it is transmitted, it somehow rotates its polarization to match that of the pol... | g7054 | [
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<p>I've noticed a general phenomenon in compactifying on a circle where if you start with, say, an NS field, then the KK fields with an index along the circle will be in the R sector, and those without will of course remain in the NS sector. </p>
<p>I am wondering how to understand this phenomenon. What is the story f... | g7055 | [
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<p>I am an app developer and I am trying to build a physics app to calculate distance based on the quantities the user gives. for example if the user gives initial speed, time and acceleration, using Newton's 2nd equation, my program can calculate distance. So for example if I have six basic formulas which are:-</p>
<... | g7056 | [
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<p>When a car is traveling round a banked track as fast as possible, it has a tendency to slip up the slope.</p>
<p>Opposite in the case when the car travels slowly and has a tendency to slip down.</p>
<p>Can someone please give me an intuitive reason as to why this "tendency to slip up or down" occurs.</p> | g7057 | [
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<p>Suppose we have a pseudo-Riemannian manifold (modeled by $\mathbb R^{p,q}$) with signature</p>
<p>$$(\underbrace{+,+,\cdots,+}_p,\underbrace{-,-,\cdots,-}_q)$$</p>
<p>Meaning we have $q$ spacelike dimensions and $p$ timelike dimensions. For a given observer in this manifold, we can define the position vector $\mat... | g7058 | [
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<p>I want to show that $\delta q$ is not an exact differential.</p>
<p>Starting from $dE = \delta q - pdV$ and because $E := E(V, T)$ is a state function, which allows to express the exact differential as
$$
dE = \left.\frac{\partial E}{\partial V}\right|_T dV +\left.\frac{\partial E}{\partial T}\right|_V dT,
$$
the ... | g7059 | [
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<p>Let's say I'm in a space station, hurtling towards our galaxy nearly close to the speed of light. From my reference frame, I see the galaxy coming towards my ship at the same speed.</p>
<p>I pass the Sun, and am affected by its gravity.</p>
<p>From Earth's point of view, the gravity of the sun deflected my spacesh... | g7060 | [
0.06503051519393921,
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<p>The ISS and other objects in orbit still experience small acceleration outside from the perfect line of orbit (of the system CM). For instance, two objects in the ISS that are let to be at rest will pass by each other twice as the station makes one orbit because the two items are in separate orbits, and all orbits ... | g7061 | [
0.012854753993451595,
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<p>I have prepared a paper that relies on work of Joe Rosen on symmetry (e.g. "Symmetry Rules: How Science and Nature Are Founded on Symmetry"). I am wondering about his influence. For example, when I once asked on Math.SE about status of Curie symmetry principle, the question was closed, being also repelled by physics... | g7062 | [
0.028147593140602112,
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<p>Since the fine structure constant (denoted alpha) is a pure real number, it just occured to me to ask if it is a rational number or not.</p> | g7063 | [
0.041587524116039276,
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0.03964933753013611,
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0.011041155084967613,
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-0.0... |
<p>As far as my knowledge is concerned, a vector quantity should possess magnitude and direction & more over it should also obey the laws of vector addition.</p>
<p>As we all know that the vector sum of 3 newtons in the x direction and 4 newtons in the y direction will acting at a point will produce a resultant of... | g7064 | [
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<p>Imagine you have a stone that is being hit by focused sunlight from a magnifying glass. Later you will place the stone into water to heat it. What type of stone will transfer the most energy into the water and why? </p> | g7065 | [
0.06187720224261284,
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<p>This is an assignment question for online AP physics. As if it isn't already tough. This question is killing me. I even asked my physics teacher from last year and my calculus teacher. It stumped them, too. I would show some kind of attempt at solving the question, but I've got nothing. I don't even understand how t... | g7066 | [
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<p>If you have $N$ 1ohm resistors, how many distinct equivalent resistances can you create?
Assume that only parallel and series and mixture of them is allowed and no bridging between two parallel connections is allowed.</p> | g7067 | [
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<p>The free particle solution in stationary state (with definite energy) to the Schrödinger equation is </p>
<p>$$\psi(x,t) =Ae^{i(kx-\omega t)} + Be^{-i(kx+\omega t)}$$</p>
<p>Since the energy is definite, and hence the momentum is definite, the uncertainty in position must be infinite. How is this reflected by the ... | g7068 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Uncertainty_principle" rel="nofollow">Uncertainty principle</a> says that "△x△p>h/2"; we cannot precisely obtain both position $x$ and momentum $p$ simultaneously.</p>
<p>Is this because the uncertainty is the natural characteristic or it is because we do not know additiona... | g7069 | [
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-... |
<p>I am confused by a simple fact about the $\beta^{-}$ decay of ${}^{60}{\rm Co}$ nucleus. According to <a href="http://en.wikipedia.org/wiki/Cobalt-60" rel="nofollow">Wikipedia</a>, the most likely decay branch is to an excited state of ${}^{60}{\rm Ni}$, see the diagram:</p>
<p><img src="http://i.stack.imgur.com/cv... | g7070 | [
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<p>Studying on own quantum mechanics I came across:</p>
<blockquote>
<p><strong>Preceeding text:</strong>
A basic postulate of quantum mechanics tells us how to set up the operator corresponding to a given observable. Observables, $\Omega$, are represented by operators, $\hat\Omega$, built
from the following p... | g7071 | [
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0.03678005933761597,
... |
<p>In Hawking's paper, <a href="http://books.google.com/books?id=aKcJO8CZ1kIC&pg=PA112&lpg=PA112&dq=Breakdown%20of%20predictability%20in%20gravitational%20collapse&source=bl&ots=uFiQcMfhDF&sig=_7fLRLAEeDnL0AbEgyzERRA70iI&hl=en&sa=X&ei=HBxmUPDLDpDm8QS5l4HADw&ved=0CDwQ6AEwAw#v=onep... | g7072 | [
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0.... |
<p>I have to to write an 4000 word research paper for my IB diploma in high school. It is called the extended essay. I was thinking about writing on the physics of breaking eggs. I came up with the idea that their might be some experiments I could do and find the best way to crack an egg. I'm having trouble finding so... | g7073 | [
0.012324406765401363,
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0.001... |
<p>Consider throwing a stone at an object from rest, it travels at Vms-1. Now throw that stone whilst running at Ums-1. It seems in the latter scenario the total speed of stone is V + U. Now imagine Running at Ums-1, throwing a stone at Vms-1 whilst on a moving train with speed Wms-1 - total stone speed would be V+U+W.... | g7074 | [
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<p>In section 4.3 of Griffths' "Introduction to Quantum Mechanics", just below Figure 4.6, the sentence begins </p>
<blockquote>
<p><em>Let $\hbar \ell$ be the eigenvalue of $L_z$ at this top rung...</em> </p>
</blockquote>
<p>Why is this valid? In the previous pages, there is no derivation of this fact. It's no... | g7075 | [
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<p>I'm a bit confused about the equivalence principle in GR.</p>
<p>I'm quoting from <a href="http://en.wikipedia.org/wiki/Introduction_to_general_relativity" rel="nofollow">Wikipedia</a>:</p>
<blockquote>
<p>An observer in an accelerated reference frame must introduce what
physicists call fictitious forces to ac... | g7076 | [
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0.02963... |
<p>(I know whether I understand this or not doesn't matter much to my work & study but am just curious.)</p>
<p>I still can't differentiate in my head <a href="http://en.wikipedia.org/wiki/Kinetics_%28physics%29" rel="nofollow">kinetics</a> and <a href="http://en.wikipedia.org/wiki/Kinematics" rel="nofollow">kinem... | g7077 | [
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<blockquote>
<p>If I consider equations of motion derived from the pinciple of least action for an <em>explicilty time dependend</em> Lagrangian</p>
<p>$$\delta S[L[q(\text{t}),q'(\text{t}),{\bf t}]]=0,$$</p>
<p>under what circumstances (i.e. which explicit functional $t$-dependence) is the force conservati... | g7078 | [
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<p>In a philosophically rather interesting experiment, <a href="http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2294.html" rel="nofollow">Ma et al.</a> show that backward causality exists in quantum physics. An <a href="http://arstechnica.com/science/2012/04/decision-to-entangle-effects-results-of-measureme... | g7079 | [
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<p>Summary: when the Moon is x degrees below the horizon, it interferes
with stargazing the same as astronomical twilight would. What is x (as a
function of the Moon's phase)? </p>
<p>We define civil, nautical, and astronomical twilight as when the sun
is 0-6, 6-12, and 12-18 degrees below the horizon respectively.... | g7080 | [
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... |
<p>People talk about orbital angular momentum (OAM) of photons. Is there some physical example that cannot be explained without assuming that photons have non-zero OAM? Does different photons have different values of OAM? If yes, then what determines the value of the value orbital angular momentum carried by individual... | g7081 | [
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<p>According to maxwell-ampere equation, the curl of magnetic field at that point equals the current density at that point + change of electric field at that point w.r.t. time. Now, the second factor i.e. change of electric field is also caused by some moving charge at some other point.</p>
<p>$$
\nabla \times \vec B ... | g7082 | [
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<p>I'm looking for an intuitive sketch of how one shows the correspondence of string theory to a certain QFT. My best guess is that one calculates the scattering amplitudes in the string theory as a series in some parameter (string length?) and shows that the leading order term is equal to the scattering amplitudes in ... | g7083 | [
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<p>Let be the unitary evolution operator of a quantum system be $U(t)=\exp(itH)$ for $t >0$.</p>
<p>Then what is the meaning of the equation</p>
<p>$$\det\bigl(I-U(t)e^{itE}\bigr)=0$$</p>
<p>where $E$ is a real variable?</p> | g7084 | [
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0.049926139414310455,
0.049050550907850266,
0.00... |
<p>I know this is a rather basic question, but how do you charge an object? Not a battery, an object. I'm guessing it involves static electricity, but I'm not sure. Some resources I've been reading talk about charging two objects with opposing voltages, and I am trying to figure out how you do it. I think you do it wit... | g7085 | [
0.06686417758464813,
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0... |
<p>I'm looking for a filter that lets through as many wavelengths as possible (from 200 to 5000 nm).</p>
<p>Is that even possible?</p> | g7086 | [
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<p>I am reading the book <a href="http://books.google.com/books/about/Computer_Simulation_of_Liquids.html?id=O32VXB9e5P4C" rel="nofollow"><em>Computer Simulation of Liquids</em> by Allen and Tildesley</a> (<a href="http://rads.stackoverflow.com/amzn/click/0198556454" rel="nofollow">here</a> is another link). On page 8... | g7087 | [
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<p>I was thinking about it some time ago, and now that I've discovered this site I would like to ask it here because I couldn't work it out then.</p>
<p>I know that the higher temperature the air in my room has, the more energy the molecules have. But temperature isn't energy because otherwise we'd be measuring temper... | g7088 | [
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... |
<p>Many believe that nothing can travel faster than speed of light, not even information. Personally, i think theoretically information can. Consider this following imaginary experiment:</p>
<p>Imagine we are living on a planet that is big enough for a, let's say, 10-light-seconds-tall tower to erect. We hang a pendul... | g4 | [
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<p>I'm sorry if the answer is obvious for you guys, but why don't we all (including buildings, road, people, the ground) collapse to the center of the earth because of gravity? Is it because we have velocity, just like the earth not falling to the sun (or electrons not falling to the protons)? But that analogy doesn't ... | g7089 | [
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<p>I have three questions to ask:</p>
<ol>
<li><p>Why do electrons (in an atom) specifically move in orbits and not some other type of motion?</p></li>
<li><p>Where does the energy comes from, for the electron to move at much higher speed, enough to create centrifugal force?</p></li>
<li><p>And when electrons enter an... | g7090 | [
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<p>I couldn't find on web how can I get the velocity dispersion and velocity maps of galaxies from the 3D data cube I get from integral field spectrograph. </p> | g7091 | [
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<p>I came across a problem in Griffiths where the derivative of the wave function (with respect to position in one dimension) evaluated at $\pm\infty$ is zero. Why is this? Is it true for any function that evaluates to zero at $\pm\infty$ or is there a special constraint on the wave function that I am forgetting?</p> | g7092 | [
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<p>These three questions are phrased as alternative-history questions, but my real intent is to understand better how well different modeling approaches fit the phenomena they are used to describe; see <sup>1</sup> below for more discussion of that point.</p>
<p>Short "informed opinion" answers are fine (better, actua... | g7093 | [
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<p>I am traveling on a train running at a speed of 100mph. If from the train I shoot a ball at a speed of 100mph in opposite direction then what would be the speed of the ball with respect to a person standing outside the train, <strike> given that I shoot the ball as soon as the person standing out comes in parallel t... | g7094 | [
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<p>I'm confused with the latest home lightning bulbs.</p>
<p>Understanding filament bulbs was easy. For example take 220V, 100W filament bulb:</p>
<p>Power = $V^2/R$ Filament gets heated and emits energy in the form of light & heat. Whose sum is 100J per second. I'm getting a light energy of little less than 100J... | g7095 | [
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<p>If we take a light switch to embody an entire category, we could take the light switch to be a set with two elements and the morphisms are all endofunctions. Let's say, for fun, that we define the endofunctor for the monad as: </p>
<blockquote>
<p>flip switch up $\rightarrow$ light turns on</p>
<p>flip swit... | g7096 | [
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<p>If the graph isomorphism problem can't be solved in polynomial time, do spin-networks in loop quantum gravity violate the Church-Turing thesis? To determine whether or not two graphs are isomorphic (labelled in the case of spin networks, but this doesn't change anything essential) is conjectured to be unsolvable in ... | g7097 | [
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<p>So, in the calculation of $ D(t,r) = \left[ \phi(x) , \phi(y) \right] $, where $ t= x^0 - y^0,~ \vec{r} = \vec{x} - \vec{y} $ you need to calculate the following integral
$$
D(t,r) = \frac{1}{2\pi^2 r} \int\limits_0^\infty dp \frac{ p \sin(p r) \sin \left[(p^2 + m^2)^{1/2} t \right]} { (p^2 + m^2 )^{1/2}}
$$
For $m=... | g7098 | [
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<p>Does the transmission medium affect the speed of a signal? For instance does light traveling through a fiber cable get a bit from A => B faster than copper can transmit a bit the over the same distance?</p> | g7099 | [
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<p>I was doing this question about the energy released in a fusion reaction: </p>
<p><img src="http://i.stack.imgur.com/Cogxc.jpg" alt="enter image description here"></p>
<p>In the mark scheme it included the mass of the electrons (for part cii) on the left and just used the mass of protons for the H. Do the H in thi... | g7100 | [
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<p>At university, I was shown the Schrodinger Equation, and how to solve it, including in the $1/r$ potential, modelling the hydrogen atom.</p>
<p>And it was then asserted that the differences between the eigenvalues of the operator were the permitted frequencies of emitted and absorbed photons.</p>
<p>This calculati... | g7101 | [
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<p>According to quantum mechanics each state has a specific shape. So, how does the electron get into that shape of the orbital?</p> | g7102 | [
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<p>A uncharged capacitor $C$ is connected to a battery with potential $V$. It becomes fully charged and has a charge $Q=CV$ stored on it. </p>
<p>Now the polarity of the battery is reversed. The capacitor will have the charge $Q$ still but with polarity reversed too.</p>
<p>My question is: <em>What is the work done b... | g7103 | [
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<p>Even though dust particles are neutral, they tend to be attracted to a charged surface. I am guessing this is due to charge induction. </p>
<p>Is there a way I can compute the attraction? how will it vary based on: </p>
<ul>
<li><p><strong>separation distance.</strong>
I think the distance will affect as inverse s... | g7104 | [
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<p>Take the state vector for a single photon as </p>
<p>$\psi = \int \gamma_{\omega} | \omega \rangle \otimes (\alpha |H \rangle + \beta | V \rangle )d \omega$</p>
<p>$H, V, \omega$ are the horizontal polarization, vertical polarization and frequency components of the photon. We have a nice, big tensor product space... | g7105 | [
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<p>Are non-associative operators (or other kind of elements) used in Physics?</p>
<p>For example, in QM I'm looking for something like this: $A(BC)|\psi\rangle \ne (AB)C|\psi\rangle$</p>
<p>NOTE: I think that this question does not make much sense, in that case I will close it.</p> | g7106 | [
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<p>I'm trying to understand how people actually measure decay constants that are discussed in meson decays. As a concrete example lets consider the pion decay constant. The amplitude for $\pi ^-$ decay is given by,
\begin{equation}
\big\langle 0 | T \exp \big[ i \int \,d^4x {\cal H} \big] | \pi ^- ( p _\pi ) \big\... | g7107 | [
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<p><img src="http://i.stack.imgur.com/vlpOb.jpg" alt="enter image description here"><img src="http://i.stack.imgur.com/SOeju.jpg" alt="enter image description here"></p>
<p>i'm solved this question, I'm sure that solution is right, but my instructor says that V1=116V, and also he said that he will not show how he get ... | g7108 | [
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<p><img src="http://i.stack.imgur.com/qlOgY.png" alt="this equatio was just randomly given without any description "></p>
<p>i would greatly appreciate it if someone could provide me with the concept to learn about this equation</p> | g7109 | [
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<p>There have been a number of intriguing ideas over the years hinting at the possibility that a black hole might not have an inside, that it might consist of nothing but a surface and an external gravitational field.</p>
<p>Here are some of the ideas that lead me to ask the question, in no particular order:</p>
<ul>... | g7110 | [
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<p>I have recently been reading <em>Intro to Lie algebras and representation theory</em> by Humphreys, and when I am finished I am interested in reading about Lie groups and Lie algebras and their applications to particle physics.</p>
<blockquote>
<p>Is there a book that assumes basic knowledge of Lie algebras, and ... | g177 | [
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<p>I am able to explicitly verify to one-loop order that pole masses are independent of the choice of gauge paramter.</p>
<p>But how do I use the Ward-Identity/Taylor-Slavnov identity show that the position of the poles in Greens functions are gauge-independent to all orders?</p>
<p>The difficulty I'm running into is... | g7111 | [
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<p>This is a common assumption in the study of quantum computation to assume that the quantum systems involved are finite-dimensional, since qubits lives in the two-dimensional Hilbert space. </p>
<p>According to <a href="http://arxiv.org/abs/0710.5239" rel="nofollow">Roman Gielerak and Marek Sawerwain</a>, the quantu... | g7112 | [
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<p>A 2500.0kg car is going at a constant velocity of 14.0 m/s and hits the breaks to stop. It skids 25m. What is the coefficient of friction of the tires to the ground? </p>
<p>So I have acceleration = -4.0 m/s^2
Normal force = 24525 N</p>
<p>I got Fnet = -100,000 N</p>
<p>And I don't know what to do now because nor... | g7113 | [
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<p>How would I show the acceleration vector</p>
<p>$
a^\mu = u^\nu \bigtriangledown_\nu u^\mu = \bigtriangledown^\mu lnV
$</p>
<p>for an observer instantaneously 'at rest,' where $u^\mu = dx^\mu/d\tau$ and $V^2 = -\xi_\mu \xi^\mu$ ($\xi^\mu$ is timelike killing vector field). I guess we're assuming that we have a sta... | g7114 | [
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<p>Does one exist, or do you think it would be possible to design a tracking magnetic field distortion detector to detect fast moving magnetic anomalies in our air space. ie; track a stealth aircraft or unidentified flying object at some distance by detecting the disturbance of the ambient magnetic fields?</p> | g7115 | [
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<p>I'm doing a mobile/wireless networking subject and the physics aspect is giving me some trouble. I'm mainly confused about the conversion of dB, dBm and dBW and how to calculate the gain/loss from an input. </p>
<p>The problem I'm trying to solve is what the resulting power (in milliwatts) is at certain points in a... | g7116 | [
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<p>If photons are emitted at intervals a, from the top of a tower of height $h$, down to earth, is this formula correct for the intervals b in which they are received at earth? $b=a(1-gh/c^2)$
If so, how does it not lead to a paradox, if say we wait a long time N, then at the top of the tower, N/a photons have been emi... | g7117 | [
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<p>So I am studying CP violation in SM. Experimentalists are trying to study B meson decays now a days. B meson systems involve quarks from the third generation and hence B physics gives more information than the Kaon system. Is there any other reason?</p> | g7118 | [
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<p>Is it possible to write down a Lagrangian for a string theory with a critical dimension different than the familiar 10 or 26? How could one find a string theory Lagrangian for a given dimension? Could you prove that no string theory exists for a given critical dimension?</p> | g7119 | [
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... |
<p>Assume a very simplified model without Corolis effect, the falloff of the local gravitational field and the like. My answer is <em>no</em>. It is sufficient to look at the vertical velocity of the projectile, because only that determines the time. The periods do not equal, because it is possible to vertically accele... | g7120 | [
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<p>My apologies in advance if this question is poorly worded or doesn't make any sense, however I have just finished reading into this theory and it seems as though Hawkings No Boundary Universe is basically emergent from a Universal Wave Function that is timeless. So no time took place before the big bang.</p>
<p>How... | g7121 | [
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<p>I've been playing around with some <a href="http://en.wikipedia.org/wiki/Contactless_payment" rel="nofollow">contactless bank cards</a> and an <a href="https://github.com/nadam/nfc-reader" rel="nofollow">RFID reader app</a> on my phone. As expected, if I wrap the card in foil, the reader no longer detects it. But I ... | g7122 | [
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<p>Suppose we have some very imprecise knowledge of classical particle's coordinates and momentum: what we can only tell is the probability density to find it in some point of phase space. This is (almost?) all what is usually known by quantum state function.</p>
<p>For quantum particle, there's an equation, which gov... | g7123 | [
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<p>Pardon my ignorance but I just can seem to find an Answer to my question and I hope that you can help me.</p>
<p>What is the equation for calculating how long a Lithium Battery can supply a device?</p>
<p>For instance a Lithium battery has a capacity of 5600mAh, and an Output of 5V 2A. The drawing device requires ... | g7124 | [
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<p>Stephen Wolfram's <em>A New Kind of Science</em> (NKS) hit the bookstores in 2002 with maximum hype.
His thesis is that the laws of physics can be generated by various cellular automata--simple programs producing complexity. Occasionally (meaning rarely) I look at the NKS blog and look for any new applications. I s... | g7125 | [
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... |
<p>I have read Sean Carrol's book. I have listened to Roger Penrose talk on "Before the Big Bang". Both are offering to explain the mystery of low entropy, highly ordered state, at the Big Bang.
Since the second law of thermodynamics is considered a fundamental law of nature, and since it states that in a closed system... | g7126 | [
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0.055215612053871155,
... |
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