question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>If the Gibbs free energy equation is defined as:</p>
<p><code>∆G = ∆H - T∆S</code></p>
<p>And the amount of energy/work released from a reaction is:</p>
<p><code>-∆G = w_max</code></p>
<p>Living organisms use exergonic reactions to metabolize fuel where the Gibbs free energy is negative and they (can) occur spon... | g16756 | [
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<p>I wish to obtain the refractive index of a smooth surface using only a laser of given wavelength and a light sensor. I thought of using the Pfund method (attached), but I can't understand how the light sensor would fit in instead of the paper. I <em>must</em> use the sensor by the way. Can this be done on a horizont... | g16757 | [
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<p>I am studying some basic idea of diffraction and there mention in far field, the diffraction pattern could be understood by Fourier transform. But I just don't understand what's the physical fact for that. And why cannot use Fourier transform for the the near-field case? </p>
<p>Also, when I am trying to understand... | g16758 | [
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<p>Fields in classical mechanics are observables. For example, I can measure the value of the electric field at some (x,t).</p>
<p>In quantum field theory, the classical field is promoted to an operator-valued function of space-time. But no one talks about eigenvectors of the quantum field! If I try to measure the fie... | g16759 | [
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<p>Let $X^\mu (t,\sigma ^1,\ldots ,\sigma ^p)$ be a $p$-brane in space-time and let $g$ be the metric on $X^\mu$ induced from the ambient space-time metric. Then, the Nambu-Goto action on $X^\mu$ is defined to be
$$
S:=-T\int dt\, d\sigma \sqrt{-\det (g)}.
$$
(We use the convention of space-time signature $(-,+,+,+)$.... | g16760 | [
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<p>While the microscopic mechanism leading to type II superconductivity is still debated, do scientists at least have a handle on the phenomonology?</p>
<p>Specifically, are the experimental properties of type II superconductivity understood well enough that it is possible in principle for the properties of a newly di... | g16761 | [
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<p>Consider a pendulum, consisting of a string of length $l$ tied to a ball of negligible mass and radius $r$. The bob is filled with water, which has density $d$, and the pendulum is given a small push and left to oscillate. There is no friction or damping.</p>
<p>This is an analysis I've heard during a high school c... | g595 | [
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<p>Since strings are extended objects, is all angular momentum in string theory essentially "orbital" angular momentum? Or is there still a kind of intrinsic angular momentum assigned to a string? </p>
<p>Either way, is there anything that prevents the "intrinsic spin" of a particle represented by a string from bein... | g16762 | [
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<p>What are the major recent findings and their corresponding contributions to an overall picture?
How well explained are the various regions of the dome, is there any thing that is pretty well understood?</p>
<p>What is left and how are people trying to figure it out?</p> | g16763 | [
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<p>Can the effect of gravity in spacetime be thought of as if nearby particles have a tendency to "align" their four velocity direction? I.e. "to point in the same direction".</p> | g16764 | [
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<p>When I look at pictures taken by a modern spacecraft (like that one showing the surface of Titan: </p>
<p><img src="http://upload.wikimedia.org/wikipedia/commons/b/bc/Huygens_surface_color.jpg" alt="Titan"> </p>
<p>and taken by <a href="http://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens" rel="nofollow">Cassini</... | g16765 | [
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<p>Does Einstein's theory of special or general relativity incorporate volume?</p>
<p>In a particle accelerator two particles smash together at relativistic speeds and "create" new particles (quarks etc) due to $E=mc^2$. In our space-time, the volume needed for these new clumps of mass already exists in local space-ti... | g16766 | [
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<p>Jackson writes,</p>
<blockquote>
<p>The function $1/|\mathbf{x} - \mathbf{x}'|$ is only one of a class of functions depending on the variables $\mathbf{x}$ and $\mathbf{x}'$, and called <em>Green functions</em>, which satisfy (1.31). In general,</p>
<p>$\nabla'^2 G(\mathbf{x}, \mathbf{x}') = -4\pi \delta(\ma... | g16767 | [
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<p>Where to find experimental/theoretical value of (charge) radius of particles like proton, neutron, $pi^+$, etc. ?</p> | g16768 | [
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<p>Haliday-Resnick-Walker state that the escape velocity will cause a projectile to move upward forever, theoretically coming to rest only at infinity.</p>
<p>I was wondering what the forces forcing the body to come to rest at infinity are when the authors are using the word"theoretically".Your help is appreciated.</p... | g16769 | [
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<p>Are any of the big-name physicists associated with the time in the same way that Hawking and Penrose are associated with black holes? I'm interested in some good books that focus on the topic.</p> | g16770 | [
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<p>Superman throws a light emitting object away from himself fast enough to notice a red-shift. The object passes through a region in which time runs more slowly. From Superman's perspective, does the red-shift change as the object slows or is the light's appearance unaffected?</p> | g16771 | [
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<p>I know the one-dimensional case in which the force is proportional to $e^{-R}$ and the force is attractive for solitons with opposite charge and repulsive for solitons with same charge. I was calculating in an approximated model in 3+1 dimensions the force between solitons and I obtain repulsive for different charge... | g16772 | [
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<p>... with X = 6 in my particular case.</p>
<p>I was trying to get a phase diagram for air, only got one for nitrogen and was slightly puzzled. Here's why:</p>
<p>I was wondering about a particular detail in industrial air liquification. The original Linde process used 200 bar pressure and cycled the air though seve... | g16773 | [
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<p>I've generated some white noise in Excel by using the formula </p>
<p>$$2*\mathrm{Math.RAND}()-1$$</p>
<p>I would now like to create some pink noise. I believe this is done by applying some sort of filter to the white noise, but I can't figure out how to do this. </p>
<p>P.S. White noise has a flat spectral densi... | g16774 | [
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<p>all! Is there a physical understanding of fractionalization in condensed matter physics? The textbook approach is theoretical, not physical. I'm thinking of spin-charge separation for electrons, the fractional quantum hall effect, and things like that. The theoretical approach is to introduce an auxiliary gauge fiel... | g16775 | [
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<p>I have some trouble understanding exactly what a mole represents. As I understand, one unit mole is 1/12 of the mass of an atom of carbon-12 (thus it is the mass of one nucleon?). What is a mole, then?</p> | g16776 | [
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<p>I was given the attached 3 degree of freedom spring system with the purpose of analyzing it.
<img src="http://i.imgur.com/pK0p9kG.jpg" alt="system"></p>
<p>I came up with the following equation of motion
<img src="http://i.imgur.com/vr2QWQr.jpg" alt="equation"></p>
<p>and then I ran Matlab to calculate the corre... | g16777 | [
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<p>A body is projected vertically upwards from the surface of the earth with a velocity equal to half the escape velocity. If $R$ is the radius of the earth, then find the maximum height attained by the body.</p>
<p>If we use Law of Conservation of Energy,</p>
<p>$$\frac{-GMm}{R}+\frac12mu^2=\frac{-GMm}{R+h}+0$$</p>
... | g16778 | [
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<p>I have a conductive particle moving at a known speed through changing magnetic field (Permanent magnets attached to a rotating drum alternating north/south). These particles will have induced eddy currents and thus a magnetic field, when the next magnet comes along, it will have the same field as the charged particl... | g16779 | [
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<p>I am trying to show that $\nabla\cdot \vec{A}=-\mu_0 \epsilon_0 \frac{\partial V}{\partial t}$</p>
<p>$V=\frac{1}{4\pi\epsilon_0}\int \frac{\rho(\vec{r}',t_r)}{r}d\tau'$</p>
<p>$\vec{A}=\frac{\mu_0}{4\pi}\int \frac{J(\vec{r}',t_r)}{r}d\tau'$</p>
<p>Where $d\tau'=dxdydz$, $t_r=t-\frac{r}{c}$ is the retarded time, ... | g16780 | [
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<p>Point masses are masses who don't have volume. It is said that they are infinitly dense, but I though division by zero is undefined hence you can't define the <a href="http://en.wikipedia.org/wiki/Density" rel="nofollow">density</a> for a point mass because $\rho=m/V$ (and at $V=0$ then $\rho$ is undefined)</p>
<p... | g16781 | [
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<p>I need to show for $$A = \frac{d}{dx} + \tanh x, \qquad A^{\dagger} = - \frac{d}{dx} + \tanh x,$$ that</p>
<blockquote>
<p>$$\int_{-\infty}^{\infty}\psi^* A^{\dagger}A\psi dx = \int_{-\infty}^{\infty}(A\psi)^*(A\psi)dx. $$</p>
</blockquote>
<p>Where $\psi$ is a normalized wavefunction. I thought that this was t... | g16782 | [
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<p>I know for instance that we can interpret the electric field as the one-form that given a vector gives the change in potential in the direction of the vector, however I'm very unsure about how to write this down. My point is, in the usual definition of electric field we have a charge density $\rho : U \subset \mathb... | g16783 | [
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<p>I'm stuck in an equation derivation of Ryder's QFT book.</p>
<p>Starting with Dirac's equation:</p>
<p>$$(i\gamma^\mu\partial_\mu-m)\psi=0$$</p>
<p>If I multiply by $i\gamma^\nu\partial_\nu$, I get:</p>
<p>$$((\gamma^\nu\partial_\nu)(\gamma^\mu\partial_\mu)+i\gamma^\nu\partial_\nu m)\psi=0$$</p>
<p>I should get... | g16784 | [
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<p>I am interested to see/know if there exist analytical solutions for shock/rarefaction interaction. A rarefaction wave catches up from behind to a shock wave. The shock will decay and the motion will no longer be uniform. I know analytical solutions exist assuming weak shocks and ignoring the entropy dependence but i... | g16785 | [
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0.0... |
<p>When reading about the Big Bang, I see phrases like <em>3 trillionths of a second after...</em> So, what was ticking to give a time scale like this? We define time now in terms of atomic oscillations, but these effects occurred before there were any atoms, or anything else, oscillating to give a reference to measur... | g16786 | [
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<p>This is my first question here. Hope it not too dull to you guys :p</p>
<p>I found <a href="http://www.youtube.com/watch?v=DfPeprQ7oGc">this video</a> on youtube. After 3:24 it says if there is an observer detecting which slit the electron goes through, there won't be an interference pattern. Has there ever been an... | g16787 | [
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<p>I was curios about <a href="http://en.wikipedia.org/wiki/Hausdorff_dimension" rel="nofollow">Hausdorff dimensions</a>. They seem to neatly describe rough surfaces. So I was wondering if there are common applications of Hausdorff dimensions in things like complicated friction research? I have a little bit of a desire... | g16788 | [
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<p>First off, I confess I'm no physicist, but I have been asking people with a more extensive knowledge this one question, without a definitive answer so far. <br/>
Basically, I'm playing around with the idea of photons having mass <a href="https://en.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass" rel="n... | g16789 | [
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<p>With Geostationary orbit your limited to the equator and ~36000km. </p>
<p>Would it be possible to orbit the sun at the same speed as Earth, and then in basically the same place so that the distance to the Sun is slightly less or more than Earth, and the inclination is slightly less or more, in order to achieve a g... | g16790 | [
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<p>The wikipedia <a href="http://en.wikipedia.org/wiki/String_theory" rel="nofollow">page</a> for String Theory lists SO(32) and E8×E8 as group symmetries of some of the string theory types, and the <a href="http://en.wikipedia.org/wiki/E8_%28mathematics%29" rel="nofollow">page</a> on E8 says:</p>
<blockquote>
<p>E8... | g16791 | [
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<p>Can someone provide an expanded explanation on the statement that the Higgs field is already 3/4 detected?</p>
<p><a href="http://www.staff.science.uu.nl/~hooft101/" rel="nofollow">Link to ref</a> (@nic, sorry I left it off, do a quick search on Higgs to find the right location on page)</p> | g16792 | [
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<p>When the electrons flow in a circuit, so are those the electrons from the battery or are those the electrons of conductor like copper wire, etc..which are flowing in the circuit? </p> | g16793 | [
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<p>I've been doing an experiment using liquid nitrogen, and am aware that pouring it into different containers gives a chance for other gases to liquify and contaminate it; what's a good estimate for the amount of other gases in the flask in such a situation?</p> | g16794 | [
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<p>I couldn't really think of a suitable question title, I'm not sure if it's completely related or not.</p>
<p>But this is as far as I know (well, I thought it all up last night and it seemed extremely logical so I think it's probably what scientists believe):</p>
<p>There are 11 possible dimensions, the 1st, 2nd, 3... | g16795 | [
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<p>I am trying to understand the energy spectrum difference between the analytical and the approximated solution for a quantum well.
The particle is inside a box with domain $\Omega=(0,0)$X$(1,1)$. For this I have $\hbar = m = 1$ and the energy is given analytically by $E_{m,n}=\frac{\pi^2}{2}(n^2 + m^2)$</p>
<p>My ap... | g16796 | [
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<blockquote>
<p><em>In quantum mechanics, quantum state refers to the state of a quantum
system. A quantum state is given as a vector in a vector space, called
the state vector. The state vector theoretically contains statistical
information about the quantum system.</em></p>
</blockquote>
<p>The article in Wi... | g16797 | [
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<p>I know that it is somehow related to the parton distribution functions, allowing specific reactions with gluons instead of quarks and anti-quarks, but I would really appreciate more detailed answers !</p>
<p>Thanks</p> | g16798 | [
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<p>Coulomb force and gravitational force has the same governing equation. So they should be same in nature. A moving electric charge creates magnetic field, so a moving mass should create some force which will be analogous to magnetic force. </p> | g16799 | [
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<ol>
<li><p>Suppose we are interested in in string on a specific metric G, is it necessary to include a Dilaton field on back ground in order to preserve the Weyl invariance? suppose the spacetime is not empty, for example consider a cosmological constant term too. </p></li>
<li><p>In Polchinski's book it is shown that... | g16800 | [
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<p>For those who don't know what a steadicam is, I'll explain it in two points to give a <em>basic</em> idea. If you know what a steadicam is, skip to point 3.</p>
<p>1) A <a href="http://en.wikipedia.org/wiki/Steadicam" rel="nofollow">steadicam</a> is a stabilizing mount for a motion picture camera, which mechanicall... | g16801 | [
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<p>At our QM intro our professor said that we derive <em>uncertainty principle</em> using the integral of plane waves $\psi = \psi_0(k) e^{i(kx - \omega t)}$ over wave numbers $k$. We do it at $t=0$ hence $\psi = \psi_0(k) e^{ikx}$ </p>
<p>$$
\psi = \int\limits_{-\infty}^{+\infty} \psi_0\!(k) \cdot e^{ikx} \, \textrm{... | g16802 | [
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<p>I am confused about something. </p>
<p>Group theory books written for physicists say that any reducible representation can be decomposed in terms of irreducible representations (so correct me if I am wrong, to me irreducible representations are like the unit vectors i j k in terms of which any 3D vector can be exp... | g16803 | [
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<p>I am building a control system to levitate a ping pong ball at a given height in a clear plastic tube using an arduino and implementing PID control.</p>
<p>I have to come up with a transfer function... I am using an air pump with pulse width modulation that controls the air speed, the pump is attached to the side o... | g16804 | [
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<p>If we put a solid sphere in space, it will lose some molecules which will
form a sort of an atmosphere around it so that we have the required vapour
pressure for solid-vapour equilibrium (Temp. of body is the average temp
of space ~ 3K) Now, this gas has some velocity distribution profile. A
fraction of the molecule... | g16805 | [
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<p>What is the explanation between equality of proton and electron charges (up to a sign)? This is connected to the gauge invariance and renormalization of charge is connected to the renormalization of photon field, but is this explanation enough? Do we have some experimental evidence that quarks have 2/3 and -1/3 char... | g97 | [
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<p>Suppose a man leaves from Earth to a star which is 1000 light years away. He accelerates to a velocity such that the entire trip lasts a year, from the reference frame of the rocket.</p>
<p>Now lets pretend the person in the rocket wants to have a transmission of the radio to him.</p>
<p>Due to time dilation, when... | g16806 | [
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<p>Can someone please explain me what is a <a href="http://en.wikipedia.org/wiki/Moyal_product" rel="nofollow">Moyal product</a>?</p>
<p>Also, how does putting $$X_a(\psi) ~=~ x_a\star\psi$$ realise $$[X_a,X_b]=i\theta_{ab}{\bf 1}?$$ <br/></p>
<p>Ref: <a href="http://arxiv.org/abs/hep-th/0102050" rel="nofollow">Quant... | g16807 | [
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<p>Is this somehow a consequence of the second law of thermodynamics? </p> | g16808 | [
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<p>Consider a theory in D spatial dimensions involving one or more scalar fields $\phi_a$, with a Lagrangian density of the form $$L= \frac{1}{2} G_{ab}(\phi) \partial_\mu \phi_a \partial^\mu \phi_b- V(\phi)$$
where the eigenvalues of G are all positive definite for any value of $\phi$, and V = 0
at its minima.
Any fi... | g16809 | [
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<p>Okay, odd question popped up in my physics class today. If a rocket ship is traveling at .99c for 1 year, and is streaming a video at 30 frames/sec to earth, how would the earth feed be affected? Would it show the video at a much slower rate, would it remain constant, or would it be sped up?</p>
<p>Also, what if yo... | g16810 | [
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<p>I guess by now most people have heard about the new paper (<a href="http://arxiv.org/abs/1109.4897" rel="nofollow">arXiv:1109.4897</a>) by the OPERA collaboration which claims to have observed superluminal neutrinos with 6$\sigma$ significance. Obviously this has been greeted with a great deal of skepticism, and the... | g16811 | [
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<p>Similar to this <a href="http://cstheory.stackexchange.com/questions/1198/what-videos-should-everybody-watch">cstheory question</a> "What videos should everyone watch?" What conferences, workshops or lectures have recordings that researchers in theoretical physics should watch?</p> | g16812 | [
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<p>I know that when a system is in its lowest level of energy, it is stablest. However, what if system 1 has lower energy than system 2, does it keep meaning so? Or do we need to examine their binding energies of them? If the systems have only two bodies, easy: the one which has lower binding energy is stabler because ... | g16813 | [
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... |
<p>What is the explicit form of the Lorentz transformation changing the light cone coordinates in the light cone gauge in string theory? The extended nature of the strings complicate matters, especially with interactions turned on. String modes tend to be mixed up.</p> | g16814 | [
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... |
<p>$$
\DeclareMathOperator{\dif}{d \!}
\newcommand{\ramuno}{\mathrm{i}}
\newcommand{\exponent}{\mathrm{e}}
\newcommand{\ket}[1]{|{#1}\rangle}
\newcommand{\bra}[1]{\langle{#1}|}
\newcommand{\braket}[2]{\langle{#1}|{#2}\rangle}
\newcommand{\bracket}[3]{\langle{#1}|{#2}|{#3}\rangle}
\newcommand{\linop}[1]{\hat{#1}}
\newco... | g16815 | [
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0.055254850536584854,
-0.000424581317929551,
0.012547995895147324,
0.025656787678599358,
-0.04003745689988136,
0.023531537503004074,
-0.030066855251789093,
... |
<p>I'm confused about fermion zero modes in relation to instantons. I understand that instantons can create fermion zero modes, but it's not clear to me when a fermion has a zero mode.</p>
<p>For example, consider QCD with nonzero fermion masses: i.e. there are explicit mass terms in the Lagrangian. Do these fermions ... | g16816 | [
0.024017807096242905,
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0.047... |
<p>Slightly biological, hopefully physical enough to be answered.</p>
<p>Suppose a magenta hue is represented by a mix of red and blue pigment. This is all very well for a creature with red and blue photoreceptors, but suppose it was seen by a creature which had a magenta-sensitive receptor, but no red or blue. Would ... | g825 | [
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0.030191699042916298,
-0.012991491705179214,
0.020311474800109863,
0.011290669441223145,
0.026219891384243965... |
<p><strong>Consider this example:</strong> </p>
<p><img src="http://i.stack.imgur.com/uDk0d.png" alt="images"></p>
<ul>
<li>Treat G as 10.</li>
<li>The blue blocks provide lift of 10N, or -1KG.</li>
<li>The red block has a weight of 20N, or 2KG.</li>
<li>The black bar has no weight.</li>
<li>All have their center of... | g16817 | [
0.009630345739424229,
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0.014191731810569763,
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... |
<p>What is terminal velocity? I've heard the term especially when the Discovery Channel is covering something about sky diving. Also, it is commonly known that HALO (Hi-Altitude, Lo-Opening) infantry reach <em>terminal velocity</em> before their chutes open. </p>
<p>Can the terminal velocity be different for one indi... | g16818 | [
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<p>Time taken to occur a direct nuclear reaction is very low $10^{-22}$sec . I want to know the Importance of direct nuclear reactions. </p> | g16819 | [
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<p>Reading <a href="http://www.physics.umd.edu/grt/taj/776b/fleming.pdf">this paper</a> which is itself an exposition of <a href="http://arxiv.org/abs/hep-th/9907001">Parikh and Wilczek's paper</a>, I get to a point where I fail to be able to follow the calculation. Now this is undoubtably because my calculational ski... | g16820 | [
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<p>I happened to notice the shadow of my legs in the sunlight on the floor and I noticed that I could see the shadow of the hairs on my legs only when I moved my leg slowly (slowly moving onto my toes etc.) As soon as the movement stopped the shadow of the hair seemed to diffuse. Why? Many Thanks, Terry</p> | g16821 | [
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<p>This is the relationship between density operator and Bloch vector:
$$\rho= \frac{1}{2}({\bf{\hat{1}}}+{\bf{b}}.\boldsymbol{\hat{\sigma}})$$</p>
<p>We define the NOT Universal Operator in the following way:</p>
<p>$$U: {\bf{b}}\to -{\bf{b}}/3$$</p>
<p>My question is - How does NOT Universal Operator act on the el... | g16822 | [
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0.0... |
<p>I came across a paper that claims to prove that the Many Worlds interpretation is invalid by applying weak measurements.</p>
<p>The paper can be found here: <a href="http://philsci-archive.pitt.edu/9494/1/aa-mwi_further_v9.pdf" rel="nofollow">http://philsci-archive.pitt.edu/9494/1/aa-mwi_further_v9.pdf</a></p>
<p>... | g16823 | [
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0.0535... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/47669/black-hole-formation-as-seen-by-a-distant-observer">Black hole formation as seen by a distant observer</a> </p>
</blockquote>
<p>Given that matter can never cross the event horizon of a black hole ... | g447 | [
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0.002579936059191823,
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-0.006426340434700251,
0... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/19388/radial-fall-in-a-newtonian-gravitational-field">Radial fall in a Newtonian gravitational field</a> </p>
</blockquote>
<p>My math and physics are rusty. I am trying to calculate the time an object t... | g134 | [
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0.02016296796500683,
0.049459002912044525,
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0.016101906076073647,
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-0.... |
<p>How can I get from a photograph of a liquid surface to a value for the surface tension.</p> | g16824 | [
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... |
<p>For my physics class we were just given an exam that asked the following:</p>
<p><img src="http://dev.tinyclark.com/files/problem.png" alt="See This Image For Reference"></p>
<p>A 12Kg lawnmower is pushed with a constant force along the 30* handle with 80N.
Break the Forces into its vector components. (Assume 0 Fr... | g16825 | [
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<p>Cut a narrow slit in a thin sheet of opaque material. Immerse the sheet in a liquid,
such as water. After removing the sheet from the liquid, you will see a liquid film in
the slit. The question is: why does water make a liquid film and not stay where it was originally?</p> | g16826 | [
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0.0... |
<p>I am familiar with the fact that Magnetars have a really strong magnetic field and an ordinary star such as the Sun has a very strong gravitational field. But what about the opposite? What is the strength of the <em>gravitational field</em> of a Magnetar and how strong is the <em>magnetic field</em> of an ordinary s... | g16827 | [
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<p>In physics, <a href="http://en.wikipedia.org/wiki/Quantum" rel="nofollow">a quantum</a> (plural: quanta) is the minimum amount of any physical entity involved in an interaction.
In Quantum Mechanics There is no difference between one Quantum to another one.</p>
<p>According to <a href="http://en.wikipedia.org/wiki/... | g507 | [
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0.024227555841207504,
... |
<p>Quantum Copenhagenists will tell you if there is a stop sign, it only manifests itself by the act of observation. When no one is looking, there is nothing there. This is like the cognitive process of a baby before learning object constancy. But if nothing is there, how does the stop sign know how to appear at the sa... | g16828 | [
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0.... |
<p>Can someone describe a simple experiment to convince a person thinking about physics classically (called Claus) that quantum mechanics has something weird, entangled?</p>
<p>I mean an experiment that he wouldn't been able to explain classically. It should <em>not</em> be one of these proofs that introduces abstract... | g16829 | [
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0.007222974207252264,
0.05377260968089104,
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0.002... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2166/is-it-possible-to-go-back-in-time">Is it possible to go back in time?</a> </p>
</blockquote>
<p>I believe that everything is possible in this world.
If that can be done then why aren't we receiving ... | g104 | [
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0.025... |
<p>I need to check units in this equation, I know, that there's Pa in the numerator, but what about the denominator?</p>
<p>$p_1$ - pressure in [Pa]<br>
$T_1$, $T_2$ - temperature in [K]<br>
$\rho_w$ - density<br>
$g$ - acceleration </p>
<p><img src="http://i.stack.imgur.com/2crz0.png" alt="Units"></p> | g16830 | [
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-0.02... |
<p>why is the magnitude of the basis vector at the point differ by a scale factor when considering the tangent as compared to the normal to the coordinate surface?</p>
<p>what exactly is the coordinate surface in 1D?</p>
<p>what about the coordinate surface normal in 2D?</p>
<p>this whole thing is throwing me off a ... | g16831 | [
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0.011327548883855343,
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<p>My knowledge of quantum mechanics is rather limited, but what I always understood was that Bosons have integer spins and Fermions have half-integer spins.</p>
<p>My question is very simple: the Majorana particle has no spin according to <a href="http://arxiv.org/abs/1209.5115" rel="nofollow">this paper</a> and <a h... | g16832 | [
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<p>So I know that two particles can be entangled in a quantum way, but is it possible that more than two particles be entangled in a quantum way? Most descriptions provide with two-particles cases, so I wonder. (It's hard to think of three particles entangled in spin, or so.)</p> | g16833 | [
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0.007842163555324078,
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<p>The propagation of high frequencies sound waves is more directional (specular), and they don't diffract as much as low frequencies. Low-frequencies diffract and thus propagate in a more omni-spherical fashion. This, to my knowledge, applies to all waves, not only sound ones.</p>
<p>Now trying to imagine the air par... | g16834 | [
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-0.06075283885002136,
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0.038904231041669846,
0.031584154814481735,
0.052... |
<p>How do physicists know that mass of possible <a href="http://en.wikipedia.org/wiki/Higgs_boson">Higgs particle</a> is limited between two values 90 GeV/c$^2$ and 145 GeV/c$^2$?</p> | g16835 | [
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<p>With aeroplane flight, the wings are shaped so that the air that goes over the top of the wing has to travel faster than the air that goes below the wing. This means that the air below the wing has higher pressure than the air above it (as the air above is moving much faster), keeping it in the air.</p>
<p>Why is i... | g16836 | [
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0.... |
<p>I always wondered what the description of Big Bang would be like in string theory.</p>
<p>How is it different from QFT version of Big Bang?</p>
<p>Thanks.</p> | g16837 | [
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<p>In my electricity and magnetism course, we used a Thompson tube to produce an electron beam. There is a heating element at the back of the tube and the lab manual claims that "electrons are boiled off." Can someone explain what is meant by this? Boiled off seems an odd term to use but maybe if I understand it meanin... | g16838 | [
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-0.0... |
<p>Having a brick lying on a table, I can exert horizontal force equal to $\mu m g$ to a middle of it's side, and it will start moving (assume $\mu$ is the friction coefficient). However, can I make the brick moving with less horizontal force? May be, applying it not to a middle of a side can help? I have no idea of ho... | g16839 | [
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0.0216010... |
<p>I ran an experiment using translucent single crystal solids. I modified the solids along the way using different chemical/temperature environments. After every stage, I ran the samples through a UV-VIS spectrometer (maybe it was technically a spectrophotometer, I'm a bit confused by the distinctions.</p>
<p>This ... | g16840 | [
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0.0077701229602098465,
0.037751711905002594,
0... |
<p><strong>Background</strong></p>
<p>Last night, I was reading the <a href="http://www.globalsecurity.org/military/library/policy/army/fm/23-10/index.html" rel="nofollow">FM 23-10</a> (The U.S. army official field manual for sniper training), and I've noticed that they're potentially teaching snipers incorrect inform... | g16841 | [
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<p><a href="http://www.space.com/25691-dark-matter-black-hole-atoms.html" rel="nofollow">This article</a> talks about a potential explanation of dark matter based on something called the "friedmon." I have no interest in the dark matter question, but the article has made me curious about this friedmon thing. Googling... | g16842 | [
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<p>I've been trying to grok General Relativity for a while now, and I've been having some trouble. Many physics textbooks gloss over the subject with an "it's too advanced for this medium", and many other resources start out with something like "well space is just a non-euclidean manifold with a Ricci tensor defined as... | g16843 | [
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<p>Also would a spring under tension greater than the force of gravity pulling the spring downward shrink in both directions until it has depleted it's stored energy while in free fall?</p> | g16844 | [
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<p>A beam of particles pass through a target made of thin foil of a very
small thickness $\Delta x$ having $N$ particles per unit volume. Let the collision cross section be $\sigma$ . If the intensity of the beam ( number of particles per unit area per unit time) is I to start with what would be the decrease in the int... | g16845 | [
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<p>This is stated as an obvious example of a <a href="http://en.wikipedia.org/wiki/Exterior_algebra" rel="nofollow">Grassmann algebra</a> on page 32 in <a href="http://arxiv.org/abs/hep-th/0201124/" rel="nofollow">this</a> tutorial I am trying to read, but to me it is unfortunately not so obvious.</p>
<p>So can somebo... | g16846 | [
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<p>Almost in every book on physics, there's an example of conservation of momentum when the ball that is moving horizontally in the air, hits some massive wall. They claim that the return speed of the ball when it bounces off is the same as it was before the hit. If there were no external forces acting on the system (o... | g16847 | [
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<p>Deterministic models. Clarification of the question:</p>
<p>The problem with these blogs is that people are inclined to start yelling at each other. (I admit, I got infected and it's difficult not to raise one's electronic voice.) I want to ask my question without an entourage of polemics.</p>
<p>My recent papers ... | g16848 | [
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