question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I'm guessing that, this would be someone in a rocket or something... When they hit their top speed, at what fraction of $c$ are they traveling?</p> | g7592 | [
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<p>I want to study SUSY QM. I found some excellent physically motivated articles on Arxiv. Despite, I am especially interested in the mathematical structure behind SUSY QM.
Does anybody know whether there is a particularly good reference to start studying SUSY QM from a rigorous mathematical point of view. The referenc... | g7593 | [
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<p>For N non interacting spinless particles in a volume, we have 3N degrees of freedom and we can divide the phase space into 6N dimensional cells of volume h raised to power 3N. </p>
<p>And each cell represents a state of the system. That means the system can be in any of those cells. </p>
<p>How can a cell be visua... | g7594 | [
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<p>Why is the criteria for fusion represented as a triple product nτT instead of the n,τ,T individually? i.e saying the density has to be above this value, temperature above this value? What are the advantage we gain from representing it this way? </p> | g7595 | [
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<p>It strikes me that the recent announcement of data from BICEP2 contains two really Big Deals:</p>
<ul>
<li>the first evidence of gravitational waves</li>
<li>the first evidence of inflation.</li>
</ul>
<p>Is there also a third?</p>
<ul>
<li>the first observation that will require quantum gravity to explain?</li>
... | g7596 | [
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<p>Hi I wanted to know what is spin half in lattice site means? Is it electron or atom or total spins half of electrons in a atomic 1d chain or 2d? </p> | g7597 | [
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<p>Surely someone has found the solutions to the hard sphere collisions (in $n$ dimensions) of two bodies of mass $m_1$ and $m_2$, respectively--that is the resultant velocities (or momenta) of the two bodies after a hard sphere collision given $\vec{p}_1$ and $\vec{p}_2$. I have a solution (both for elastic and inela... | g7598 | [
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<p>Being a grad student in math, and a rather pedantic one indeed, I was unable to accept many of the things taught to me in undergrad physics courses. I am now trying to learn the applications of geometry to string theory and the applications of probability theory, my main field, to statistical physics. Are there ot... | g185 | [
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<p>I am reading the first few pages of Nakahara and refreshing my memory on physics I learned a while ago as a physics math undergrad. Nakahara defines a field $F$ to be conservative if it's the gradient of some potential $V(x)$. (standard) Then he defines the total energy as $1/2mv^2+V(x)$. He then states that $E$ is... | g7599 | [
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<p>From Griffith's <em>Introduction to Electrodynamics</em></p>
<blockquote>
<p>The principle of superposition may seem obvious to you, but it did not have to be so simple: if the electromagnetic force were proportional to the <em>square</em> of the total source charge, for instance, the principle of superposition w... | g7600 | [
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<p>I know it does not because it emerges out of denser medium at 300,000 KM per second, but according to E=MC square and given that speed of light decreases inside denser medium with refractive index greater than 1, does not it suggest that energy of light inside denser medium is less?</p> | g7601 | [
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<p>According to Landau's symmetry breaking theory, there is a symmetry breaking when phase transition occurs. </p>
<ol>
<li><p>What is the symmetry breaking of superfluid-Mott insulator transition in <a href="http://en.wikipedia.org/wiki/Bose%E2%80%93Hubbard_model" rel="nofollow">Bose-Hubbard model</a>? </p></li>
<li>... | g7602 | [
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<p>As you know, impedance is defined as a complex number.</p>
<p>Ideal capacitors:
$$
\frac {1} {j \omega C} \hspace{0.5 pc} \mathrm{or} \hspace{0.5 pc} \frac {1} {sC}
$$</p>
<p>Ideal inductors:
$$
j \omega L \hspace{0.5 pc} \mathrm{or} \hspace{0.5 pc} sL
$$</p>
<p>I know that the reason why they 'invented' the conc... | g7603 | [
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<p>How has CMBR temperature dropped as function of time? A graph would be nice, but I'd be happy with times (age of universe) when it cooled enough to not be visible to human eye, became room temperature equivalent, or reached some interesting temperatures regarding matter in the universe.</p>
<p>If there is a nice fo... | g7604 | [
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<p>I know G.R. change our vision of space and time as a unique surface than can bend.
We can associate the curvature of the space-time as the gravity created by the mass of planets, stars... But how can we measure the <a href="http://en.wikipedia.org/wiki/Curvature">curvature</a> of the space-time for calculate, as an ... | g7605 | [
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<p>In many presentations of statistical mechanics where we have a system of particles having mass, such as the molecules of an ideal gas, the temperature is often equated to the average relative velocity of the particles. However no such velocity can exceed that of light. Is there therefore an absolute upper bound to t... | g7606 | [
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<p>Is photosynthesis more efficient than solar panels? If so, by how much?</p> | g7607 | [
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<p>Is it correct that for a motion in a <a href="http://en.wikipedia.org/wiki/Central_force" rel="nofollow">central force</a> field, e.g. a gravitational field, the absolute value of the total angular momentum of the particle and the component of the perpendicular to the plane of motion are conserved, but the other com... | g7608 | [
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<p>I understand the reason that bicycle pedals are oppositely threaded on either side. What I don't understand is why it works because I'm missing something.</p>
<p>Take the right pedal for example. It's threads are right-handed, so it would be tightened by turning it clockwise (if the pedal were in between you and th... | g7609 | [
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<p>Here is a video of a GoPro falling from a plane: <a href="http://www.youtube.com/watch?v=QrxPuk0JefA" rel="nofollow">http://www.youtube.com/watch?v=QrxPuk0JefA</a></p>
<p>Any idea what is happening when the image "stabilizes" around 0:35? I think it is because the camera's tangential velocity approaches the speed o... | g7610 | [
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<p>Here and on many other forums and blogs people ask the question <a href="http://physics.stackexchange.com/questions/6438/what-if-the-lhc-doesnt-see-susy">"What if LHC does not find SUSY?"</a>. I would like to ask the opposite. What if it finds it? What would the implications be? Is it going to just confirm something... | g7611 | [
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<p>In optics it is widely mentioned real images are projectable onto screens whereas virtual ones can only be seen by a person. Isn't that contradictory? I mean in order to see the virtual image it has to be <em>projected</em> onto the retina (ultimately acting as a screen). </p>
<p>So, why can you see <a href="http... | g209 | [
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<p>Together with colleagues we got this question. Imagine to take small mirrors, the size for example of a dentist mirror, and stick them to a wooden frame with a parabolic shape. Each mirror is flat, and once set of the frame it can be aligned properly with screws so that it redirects its reflection towards the focus ... | g7612 | [
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<p>I have a graph that i drew and i got all the point and a question came up that what is SI Unit for intercept of a graph.</p>
<p>I have no idea what the answer is. (I'm a total newbie in Physics)</p> | g7613 | [
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<p>I've heard from a physics professor that there's no stationary platform to observe and analyze a body in motion.Why did he mention that? Is it because even seemingly stationary objects like a parked car on a road moves along with the earth's rotation? </p>
<p>As per my intuition there is a stationary platform.If yo... | g7614 | [
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<p>Assume that the air pressure and the amount of water in the air stay constant. How can I figure out how much a change in temperature affects the relative humidity?</p> | g7615 | [
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<p>Consider a charge distribution $ρ_1(r)$ and the potential $φ_1(r)$ due to it. Consider another charge distribution $ρ_2(r)$ and $φ_2(r)$ due to it. Both distributions have finite extent, but are otherwise arbitrary and need not have anything to do with each other. Show that the $$∫ρ_1(r) φ_2(r) dv = ∫ρ_2(r) φ_1(r) \... | g7616 | [
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<p>This might be little of the track but my question is more on possibility of application of principle of center of mass.<br><p>
The probability of a vehicle overturning depends more on the level of center of mass of the body above the ground, the higher it is and smaller is the base to support it, the easier it is t... | g7617 | [
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<p>It is well known that a <a href="http://en.wikipedia.org/wiki/SQUID" rel="nofollow">SQUID</a> can detect an extremely small magnetic flux.</p>
<p>What if the flux is time-dependent? E.g. a slow varying sinusoidal magnetic flux</p>
<p>$$\Phi=\Phi_0\sin(\omega t).$$</p>
<p>Can I still perform a real time measuremen... | g7618 | [
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<p>We know that there is a relativistic version of Schrodinger equation called Klein-Gordon equation. However, it has some problems and due to these problems, there is Dirac equation that handles these problems. </p>
<p>So, the question is, if there is a solution that is allowed by Klein-Gordon, but not by Dirac, can ... | g7619 | [
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<p>Every wavefunction of a form $\Psi(x)$ can be described as a superposition of multiple free particle solutions.
We can see the following Fourier transform:
$$ \psi(x) = \int e^{ik\cdot x} \psi(k) dk $$</p>
<p>We can make it time dependent by replacing $e^{ik\cdot x}$ with $e^{ik\cdot x - i E_k t}$ where $E_k = \sq... | g7620 | [
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<p>During a transition of a molecule from one state to another, it pass through a transition state. This transition state, mathematically speaking, is a saddle point. That means, the second derivative along all the coordinates, except one, is greater than zero. I have two questions: </p>
<p>1) Is it possible for a mol... | g7621 | [
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<p>I have been wondering why a fluid in a rotating container has a parabola shape? Is it possible to prove this mathematically? </p> | g7622 | [
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<p>In an analogy to the neutron, which decays rapidly as a free particle, but when bound in a nucleus it is stable, would it be possible to crease a structure that permits the stability of muons - be it muonic atoms, some sort of muonic lattice, etc.?</p>
<p>Granted, the energetic benefit of the neutron $\beta$ decay ... | g7623 | [
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<p>Just a quick question: In high energy experiments, the fundamental forces are thought to merge into a single force. My question is, in very low energy experiments (very low), do the forces we know about split up even more/is this possible or likely?</p>
<p>Thanks</p> | g7624 | [
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<p>Hi all what is the definition of pressure derivative of <a href="http://en.wikipedia.org/wiki/Bulk_modulus" rel="nofollow">bulk modulus</a> if it is a pressure derivative of bulk modulus at zero pressure. if the pressure is zero how it is derivative by pressure? </p> | g7625 | [
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<p>When a sensor registers electromagnetic radiation, such as that used for the transmission of communication like light or radio waves, does this radiation "abrade" or "erode" the material of the sensor?</p>
<p>Are there any traces of the received radiation that can be detected, even if only theoretically?</p>
<p>An... | g7626 | [
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<ol>
<li><p>My question is why are we colliding particles in LHC to produce new ones? </p></li>
<li><p>And these particles that they sometimes say live for a fraction of a second, how in space they exists then? </p></li>
<li><p>In space all these particle exist without smashing to each other, why do we need to smash th... | g7627 | [
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<p>I'm curious about how to calculate the 2-point function of graviton, but there are no textbooks of general relativity covering this problem. </p>
<p>So how to calculate it? In which book can I find the answer?</p> | g7628 | [
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<p>I have a relatively complex (for me anyhow) situation which I would like to capture in bra-ket notation, rather than in words. However, I've not been able to find a source which will help me understand better how to do so, and I was hoping that one of you might help me out. I'll first describe exactly what I want to... | g7629 | [
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<p>I have come to know the electrostatic potential energy in vacuum is given by
$${\frac{1}{2}} \epsilon_0\int d^3x {E^2} $$ and this energy is due to the mutual electrostatic coulomb potential energy.</p>
<p>So only a single point charge in space also contributes to some electrostatic potential energy according to ... | g7630 | [
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<p>What are the results of fusing an electron neutrino and a muon neutrino? If you have an answer, then why? I looked this up and searched for stuff on Google, Wikipedia and a few other sites, but all the results say are stuff on nuclear fusion and neutrinos.</p>
<p><b> BONUS QUESTION: </b>
<br>
What happens if you pu... | g7631 | [
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0.048... |
<p>When an coil rotor is moving around a magnetic field there is -V induced to resist the input V.</p>
<p>Let's take an example, a 12 V DC motor induces -10V, and the actual running voltage is 2V.</p>
<p>If there we're no -V in the process, the motor would preform a lot better?
What is the advantages and disadvantage... | g7632 | [
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<p>The question relates to <a href="http://physics.stackexchange.com/questions/53148/in-qft-why-does-a-vanishing-commutator-ensure-causality">this post</a>.</p>
<p>As shown in Peskin and Schroeder's introduction to quantum field theory p. 28.,</p>
<p>$$[\phi(x),\phi(y)] = 0 \;\;\mathrm{if}\;\; (x-y)^2<0$$,</p>
<p... | g7633 | [
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... |
<p>If something crossed the horizon of the observable Universe, does this mean that all information about it is lost forever? If yes (or no), how this fits with the information-cannot-be-lost law? </p>
<p>Also, does it mean that the energy of our observable Universe is constantly decreasing? If yes, what are the conse... | g7634 | [
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0.03... |
<p>There is a surprising number of papers seriously discussing the "<a href="http://focus.aps.org/story/v13/st3" rel="nofollow">feigel effect</a>" This has been linked to the <a href="http://peter.mapledesign.co.uk/writings/physics/2005_dissertation_The_Abraham-Minkowski_Controversy.pdf" rel="nofollow">Abraham-Minkows... | g7635 | [
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0.0... |
<p>We learn that the quantum wave function $\Psi$ <a href="http://en.wikipedia.org/wiki/Wave_function_collapse" rel="nofollow">collapses</a> when it interacts with a classic object (measurement). </p>
<p><strong>My question is:</strong><br> Why are there <em>classic</em> objects after all, how did it all start? In a <... | g7636 | [
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<p>A <a href="http://prl.aps.org/abstract/PRL/v104/i7/e070401" rel="nofollow">paper</a> was published in 2010 claiming to resolve the <a href="http://en.wikipedia.org/wiki/Abraham%E2%80%93Minkowski_controversy" rel="nofollow">Abraham-Minkowski controversy</a>. Is this paper viewed as definitive by physicists?</p> | g7637 | [
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<p>This was my engineering viva question and I couldn't think of any example, for I am totally convinced that there cannot be drag in a inviscid flow. It also bothers me whether it is possible, a tricky scenario in fluid mechanics or gas dynamics. </p> | g7638 | [
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<p>How can one make sense of the idea of extremizing a Hamilton-Jacobi equation?</p>
<p>In Schrödinger's paper "Quantisation as a Problem of Proper Values I" (<em>Annalen der Physik</em> (4), vol. 79, 1926, p. 1, available e.g. in <a href="http://einstein.drexel.edu/~bob/Quantum_Papers/Schr_1.pdf" rel="nofollow"><em>C... | g7639 | [
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<p>The ability to manipulate light spectra (as in mercury lamps, sodium lamps, infra red) is within the ambit of contemporary technology. Stars are said to be unique in the spectrum they emit ; </p>
<p><a href="http://skyserver.sdss.org/dr1/en/proj/basic/spectraltypes/" rel="nofollow">http://skyserver.sdss.org/dr1/en/... | g7640 | [
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<p>I am trying to get a clear picture of the valence band, conduction band, and the band gap. Now I've been researching it for a little while now and understand most of what's going on. I'm still a little confused about some specifics though, so if you could please address the following, that would be great!</p>
<p>My... | g7641 | [
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<p>I'm having a problem following a derivation of <a href="http://en.wikipedia.org/wiki/Bloch_wave" rel="nofollow">Bloch's theorem</a>, looking at a one dimensional lattice with $N$ nodes and spacing a, we impose periodic boundary conditions, meaning that the wave-function of a single electron $\psi(x)$ can be decompos... | g7642 | [
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... |
<p>Here's the conundrum I have been facing. Yesterday I asked the question: how can batteries constantly motivate electrons to complete a circuit? (<a href="http://physics.stackexchange.com/questions/126971/what-maintains-constant-voltage-in-a-battery">What maintains constant voltage in a battery?</a>)
After some thoug... | g7643 | [
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<p>I have been given this formula from optics here, with no background:
$$\vec\nabla{n} = \frac{d(n\hat{u})}{ds}$$</p>
<p>Where $n$ is the refractive index and $\hat{u}$ is a unit vector tangent to the path $s$ that light takes inside a medium.</p>
<p>Does anyone know if this formula has a name? I am looking specifi... | g7644 | [
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<p>Yesterday I looked underwater with my eyes open (and no goggles) and I realized I can't see anything clearly. Everything looks very, very blurry. My guess is that the eye needs direct contact with air in order to work properly. With water, the refraction index is different, and the eye lens are not able to compensat... | g7645 | [
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0.0010... |
<p>Consider a theory of one complex scalar field with the following Lagrangian.
$$
\mathcal{L}=\partial _\mu \phi ^*\partial ^\mu \phi +\mu ^2\phi ^*\phi -\frac{\lambda}{2}(\phi ^*\phi )^2.
$$
The potential is
$$
V(\phi )=-\mu ^2|\phi |^2+\frac{\lambda}{2}|\phi|^4.
$$
The classic stable minimum of this potential is gi... | g7646 | [
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0.034... |
<p>My question is the following. Are there solutions to the Einstein field equations, which have the property that there is a hypersurface of constant time and to the past of that surface space is empty (Minkowski space-time) and to the future it is not (non-vanishing stress-energy tensor)? At first thought it seems st... | g7647 | [
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<p>In <a href="http://en.wikipedia.org/wiki/The_Adventures_of_Tintin_%28film%29" rel="nofollow"><em>The Adventures of Tintin</em></a>, an opera singer (the Milanese Nightingale) broke a bulletproof glass case using her voice. Is that scientifically possible?</p>
<p>From the <em><a href="http://en.wikipedia.org/wiki/Bu... | g7648 | [
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0.013313849456608295,
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... |
<p>The Super-Symmetry operators reduce or increase helicity by a half unit. And this result in an algebra that where the fermions and bosons vacuum energy sums to zero. And it seems to generate gravity, when the upgraded to a local symmetry. But as yet, physicist seem to have found no good way to break super-symmetry, ... | g7649 | [
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... |
<p>I want to ask if anyone has gone through the derivation of the second equality in the following formula </p>
<p><img src="http://i.stack.imgur.com/okF7P.jpg" alt="enter image description here"></p>
<p>which comes from <a href="http://journals.aps.org/prb/abstract/10.1103/PhysRevB.80.165102" rel="nofollow">http://j... | g7650 | [
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0.... |
<p>The uncertainty principle is listed in most textbooks and articles as
$$ \Delta E \Delta t \geq \frac{\hbar}{2}.$$
This can be derived in many ways in many different settings, most of them involving commutation relations with appropriate operators.</p>
<p>This is often interpreted such that $\Delta E$ is the amount... | g7651 | [
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<p>Does anyone have an intuitive explanation of why this is the case? </p> | g7652 | [
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<p>I have arm wrestled people with less strength than me who win simply because they have thicker wrists, or larger hands. It has nary to do with having better technique either, because their wrist size alone seems to be a big advantage.</p>
<p>I want to know why, as explained by physics, why the torque they produce i... | g7653 | [
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<p>It's easy to find the "magic" numbers of neutrons on the diagrams of alpha-decay energy: 82, 126, 152, 162. Such "magic" nuclei should be more stable than their neighbors.</p>
<p><IMG src="http://elementy.ru/blogs/u/i/2598.gif">
<IMG src="http://elementy.ru/blogs/u/i/2599.gif"></p>
<p>But why some nuclei with "m... | g7654 | [
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<p>For example, let's assume a chair here: It can be "slid" across the force if we use minimal upwards force, but not enough to actually "lift" the chair. Why should it move?</p>
<p>Here's a better example: I have seen some strong people lift and slide the back of cars, however, the back tires of the car never elevate... | g7655 | [
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<p>Is my understanding of this <a href="http://en.wikipedia.org/wiki/Mechanical_equivalent_of_heat" rel="nofollow">experiment</a> correct?
There is the quantity $MC\delta \theta$ associated to the heat which I think is not an absolute value to be compared with $mgh$ since the $\delta \theta$ could be defined arbitraril... | g7656 | [
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<p>I know they have accurate means of measuring the distance of the planets in the Solar System from the Sun. I'm skeptical how can they use the same tools or techniques for other systems so far away as 22 light years.</p>
<p>According to this <a href="http://www.dailygalaxy.com/my_weblog/2012/02/newsflash-habitable-z... | g7657 | [
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<p><img src="http://i.stack.imgur.com/0dOhU.jpg" alt="enter image description here"></p>
<p>In this picture if the only parts of an object in contact with a surface are the lines AB and CD am I right in saying that the centre of mass has to be in the area enclosed by ABCD (as shown). I think this is correct as if the ... | g7658 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2175/is-it-possible-for-information-to-be-transmitted-faster-than-light">Is it possible for information to be transmitted faster than light?</a> </p>
</blockquote>
<p>I mean by using a perfect solid stic... | g4 | [
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<p>In a recent answer (here: <a href="http://physics.stackexchange.com/questions/20944/the-equipartition-theorem-in-momentum-space/20981#20981">The equipartition theorem in momentum space</a> ), I suggested that if you have an appropriate first order equation (in the answer I used a second order equation, but it is mor... | g7659 | [
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<p>Higher velocity implies low pressure. So in whirlpool the velocity of water have to decrease with radius in order to have force towards its center.</p>
<p>My question is how is explained whirlpool formation in simple words.</p> | g7660 | [
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<blockquote>
<p>A man pulling sled of his daughter by a massless rope, climbing a snowy hill whose slope is equal to 15 °. Considering that the mass of the sled is $4Kg$, the girl's $26Kg$ and $\mu _c = 0,25$, calculate the work done by the tension of the string after walking with constant speed a distance of $130m \... | g7661 | [
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<p>how to define electric charge ? How to explain this term ? As learned by me
electric charge is an intrinsic property of atoms like mass of different atoms. </p> | g253 | [
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<p>Let's have the spherical spinors:
$$
\mathbf {Y}_{j, m, l = j \pm \frac{1}{2}} = \frac{1}{\sqrt{2l + 1}}\begin{pmatrix} \pm \sqrt{l \pm m +\frac{1}{2}}Y_{l, m - \frac{1}{2}} \\ \sqrt{l \mp m +\frac{1}{2}}Y_{l, m + \frac{1}{2}} \end{pmatrix}.
$$
How to prove the relation
$$
(\hat {\sigma} \cdot \mathbf r )\mathbf {Y}... | g7662 | [
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<p>I have searched around the web and looked at Wiki entries and I am overcome by the number of catalogs available. What I want is a catalog that includes all objects you might conceivably see with equipment under $500k (I hope that captures all backyard astronomers).</p>
<p>Apart from that the main requirements are t... | g7663 | [
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<p>(Rest) mass of proton = (rest) mass of neutron (approximately) = $1.67 \times 10^{-27}$ kg.</p>
<p>let $m$ be the mass of nitrogen atom then $m = 2.32 \times 10^{-26}$ kg.</p>
<p>$c = 3 \times 10^8$ m/s (approx).</p>
<p>Energy $E = mc^2$.</p>
<p>$E = 2.32 \times 10^{-26} \times 3 \times 10^8 \times 3 \times 10^8... | g7664 | [
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<p>I have a question regarding the <a href="http://en.wikipedia.org/wiki/Holstein%E2%80%93Primakoff_transformation" rel="nofollow">Holstein-Primakoff representation</a>.</p>
<p>In the HP-representation we define the spin operators in terms of bosonic creation and annihilation operators.</p>
<p>$$
S_j^+ = \sqrt{2S - n... | g7665 | [
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<p>One of the quantities appearing in the integral form of Maxwell's Equations is the line integral of the magnetic field around a closed loop. (The relevant equation states that this is equal to the current through any surface bounded by that loop, plus the displacement current in the case of changing electric fields... | g7666 | [
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<p>I guess that everything that happens to me (or I do), happens before my shadow "records" the information. Is that right? Is it the same for any observer?</p> | g7667 | [
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<p>Does someone know simple model of energy loss in solid materials for a solid bullet?</p>
<p>For example: I want to estimate momentum transferred to a thin plastic plate given by a small bullet. No matter how difficult model is. But it should depend only on plate/projectile parameters?</p>
<p><strong>EDIT:</strong>... | g7668 | [
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<p>It is well known that you can trap water in a drinking straw by placing the tip of your finger over the top while the straw is in the water, and then lifting it out. The inner diameter of the straw is 0.5 cm; the height of the trapped water column inside the straw is 5.0 cm. Find the pressure in the air pocket betwe... | g7669 | [
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<p>I read couple of similar question on this forum and few blogs on web, though I am still confused,I am determined to calculate object displacement using accelerometer data.</p>
<p>So, I tried using www.freescale.com/files/sensors/doc/app_note/AN3397.pdf , which gives nearly 20-50% error.</p>
<p>I also tried this eq... | g7670 | [
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<p>I need to know the consumption of a water tap in Liters. </p>
<p>I'm able to know the cross-sectional area of the pipe and how long the tap is open. With these data, how can I know the consumption/volume of water that pass through the water tap?</p>
<p>It can be rough estimation. I can assume a maximum volume of w... | g7671 | [
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<p>Are the stars in our galaxy spiraling inwards towards the center, or are they in a permanent orbit?</p>
<p>And if we are heading towards the center then what is the rate of this process?</p>
<p>I started wondering this while watching this documentary: <a href="http://www.youtube.com/watch?v=zKE4Bt8ylhM" rel="nofol... | g1017 | [
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<p>While hiking through the Grand Canyon, I started wondering. Say we have a pipe for the purpose of transporting water across a canyon, with the bottom submerged in a pool of water. Like the blue line in this terribly drawn image:</p>
<p><img src="http://i.stack.imgur.com/7iVLE.png" alt="enter image description here"... | g7672 | [
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<p>Theorem 5.1 on page 80 of <a href="http://arxiv.org/abs/hep-th/0307199" rel="nofollow">this</a> paper says that </p>
<p><em>Assuming that the matter fields satisfy their equations of motion, the matter field action is locally Weyl invariant if and only if the corresponding energy-momentum tensor is traceless.</em><... | g7673 | [
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<p>I was reading about <a href="http://it.wikipedia.org/wiki/Mulinello_di_Joule" rel="nofollow">the experiment of Joule</a> (Italian wiki page). I'm not sure how it's called in English, since there is only an Italian and French version. In any case, in the page it is stated that (my translation):</p>
<blockquote>
<p... | g7674 | [
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<p>In 2008, NASA astronaut Clayton Anderson <a href="http://www.space.com/6056-space-station-trash-burns-south-pacific.html" rel="nofollow">tossed a 635-kg tank of ammonia coolant</a> overboard from the International Space Station (ISS). Subsequently the tank burned up in earth atmosphere as planned.</p>
<p>Obviously ... | g7675 | [
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<p>Please note that I am very new on this website so have some difficulties in writings as required here but trying really hard to learn quickly. La-Tex is the main problem but please understand me that I am serious.</p>
<p>How do Vectors transform from one inertial reference frame to another inertial reference frame ... | g7676 | [
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<p>What common household liquids / foodstuffs show Herschel-Bulkley fluid behavior?
I assume tomato soup to be one, since when sloshing it around lightly on a spoon the visible surface moves as one (as can be seen by following the dots of black pepper that don't change relative position) - is this observation basically... | g7677 | [
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<p>When we derive Ohm's Law using the Drude Model, we assume at one point of time that $E=V/L$, when is fact, $E=dV/dL$, unless $E$ is constant, in which case the assumption $E=V/L$ is true. But I don't understand why the electric field in a conductor must be constant as current flows. Is there a convincing explanation... | g7678 | [
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<p>To preface my question, I ask this as a mathematics student, so I don't have a very good sense of how physicists think.</p>
<p>Here is the historical context I'm imagining (in particular taking into account the development of differential geometry in the 19th century):</p>
<p>Classical mechanics is about Lagrangia... | g7679 | [
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<p>Many of the most brilliant ideas of modern physics are very much unpopperian. In view of this, it has become more and more difficult to hold an orthodox Popperian attitude in physics. It simply looks like more of a philosophical dogma nowadays. My question is, should physicists abandon this criterion at least partia... | g7680 | [
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<p>So, one thing has been annoying me ever since I learned about <a href="http://en.wikipedia.org/wiki/Orbital_hybridisation">orbital hybridization</a>: you explain the shape of molecules by postulating that the orbitals of multi-electron atoms are linear combinations of the orbitals of the hydrogen atom. Fine.</p>
<... | g7681 | [
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<p>If our universe comes from a flux compactification of string theory over 6 dimensions with a nonzero flux, then it can't be continually deformed to another compactification with zero flux as the total flux is a topological invariant. The cosmological constant of our universe is positive, which in string theory means... | g7682 | [
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<p>The WIKI Higgs boson site has an interesting diagram illustrating likely Higgs mass intervals that experiments (LEP & Tevatron) or indirect measurements have determined with a 95% confidence level. It posits that the feasible mass ranges are in the intervals of about 115-158 GeV or 175-185 GeV. The Tevatron conf... | g7683 | [
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<p>It can be shown the sum over all Feynman diagrams in quantum field theory leads to a unitary S-matrix. Where can I find a proof that the sum over string worldsheets with varying genuses also leads to a unitary S-matrix?</p> | g7684 | [
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<p>The current zeitgeist here is on interpretations of quantum mechanics, so let me add my own two cents here. As you may know, consistent histories is an alternative interpretation proposed in a series of papers 1990-1994 by Gell-Mann and Hartle. In a shocking article, <a href="http://arxiv.org/abs/gr-qc/9412067" rel=... | g7685 | [
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<p>There're some easy concepts which I don't get exactly in my mind. I've been studying these things for two years of my engineering but they still bother me. Battery is one of them. Can someone explain?</p>
<ul>
<li>Whether a battery store energy or simply it makes energy?</li>
</ul>
<p>I have searched it on Google ... | g7686 | [
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... |
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