question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/6646/physics-of-simple-collisions">Physics of simple collisions</a> </p>
</blockquote>
<p>Let the unit vector along the positive x- axis be i and that along the Y-axis be j. Let us consider a rigid wall... | g287 | [
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<p>Continuing from the my previous <a href="http://physics.stackexchange.com/questions/14272/two-state-system-problem">2-state system problem</a>, I am told that the observable corresponding to the linear operator $\hat{L}$ is measured and we get the +1 state. Then it asks for the probability that +1 is measured again ... | g17123 | [
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<p>Kaku Michio says in <a href="http://www.youtube.com/watch?v=-FqLCLooayM">an interview</a> that we've teleported photons, cesium atoms and beryllium atoms. Having watched a lot of Kaku as well as way too many astrophysics documentaries in general, I know he's exaggerating. From what I understand, some <em>state</em> ... | g17124 | [
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<p>Sound is usually referred to as just "sound waves" - we do not talk about a "sound particle" and only as a wave or "matter wave."</p>
<p>Could something similar apply to light i.e. that there really is no "light particle" (photon) and that the wave respresentation is what applies both to sound and light?</p>
<p>We... | g17125 | [
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<p>in QED the corrections to electron propagator change the bare electron mass from $m_0$ to $m=m_0+δm=m_0+∑(\not{p}=m)$ (Peskin, formula 7.27). This is the consequence of the fact, that the quantum corrections change the propagator from $i/(\not{p}−m0)$ to $i/(\not{p}−m_0−∑(\not{p})))$. This part is written very well... | g17126 | [
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<p>Source: Krane and Weisskopf page 95 (the tensor force).</p> | g17127 | [
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<p>Consider two tiny plane(flat) surfaces A and B meeting at a straight line L.We have a preassigned vector on A at some point P on it.Is it always possible to have a vector parallel to the first one and lying on B at some point on it(say Q)?</p>
<p>[The first vector(that on A) is assumed as <em>not</em> parallel to... | g17128 | [
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<p>Say I record something with a sound recording program like Audacity (e.g. plucking a guitar string). How could I use that recording to plot a dB vs Frequency graph? </p> | g17129 | [
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<p>Consider the image below:</p>
<blockquote>
<p><img src="http://i.stack.imgur.com/HoQET.png" alt="enter image description here"></p>
</blockquote>
<p>Let $\theta_2$ be the angle between the axes of transmission of Polarizer 2 and Polarizer 3 and $\theta_3$ be the angle between the axes of transmission of Polarize... | g17130 | [
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<p>I will copy a little bit of what my textbook says. By the way, we're talking about sound here.</p>
<p>$$Intensity = (0.5)BwkA^2$$</p>
<p>The textbook claims that by using the relationships $w=vk$ and $v^2=\frac{B}{\rho}$, we can transform the previous equation into</p>
<p>$$I = (0.5)(\rho)(B)^{0.5} w^2 A^2$$</p>
... | g17131 | [
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<p>Power spectra, coherence spectra, and linear transfer functions are ubiquitous tools of experimental physics. However, our instruments often retain small nonlinear effects which can contaminate measurements. It appears that higher order spectra, in particular the <a href="http://en.wikipedia.org/wiki/Bispectrum" re... | g17132 | [
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<p>I am reading a text about gas nuclei I encountered the following formula:</p>
<p>$$r = \alpha + \beta \left( \frac{T}{P} \right)^\frac{1}{3} + \kappa \left( \frac{T}{P} \right)^\frac{2}{3}$$</p>
<p>$r$ is the critical radius of the nucleus, while $T$ and $P$ are the current temperature and pressure respectively.</... | g17133 | [
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<p>Today Voyager 1 is approximately 122 AU distance from the Sun. What does the sun look like from this distance? How much brighter does the sun appear to the naked eye compared to other stars in the same field of view? Are any of the other planets from our solar system visible to the naked eye at this distance? Wo... | g17134 | [
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<p>In the $AdS_3/CFT_2$ correspondence, the central charge of the dual CFT2 is universally given by
$$
c = \frac{3\ell}{2G}
$$
This is independent of the matter in the bulk of AdS3. Is it also universal in the higher dimensional analogues $AdS_d/CFT_{d-1}$ or does it depend on details of the matter in the bulk, etc.?</... | g17135 | [
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<p>A particle is projected vertically upwards from point $A$ on the ground. It takes $T_1$ time to reach point $B$ but it still continues to move up. If it takes further $T_2$ time to reach ground from point $B$ then height of point $B$ would be? </p> | g17136 | [
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<p>I was thinking about fluctuations in energy for a system in thermal equilibrium. I think that the Boltzmann distribution itself has an standard deviation approximately equal to the mean, as it is approximately an exponential distribution.</p>
<p>From the microcanonical ensemble perspective, I think the reason the f... | g17137 | [
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<p>Are there other equations that we can predict <a href="http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction" rel="nofollow">Faraday's law</a> from? I know that each of Maxwell's equations are 'fundamental', but I feel like Gauss's law and Ampere's Law are very "nice", and for some reason or another I don't feel... | g17138 | [
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<p>In cold atom experiments, what techniques are used to load Bose-Einstein Condensates into an optical lattice??</p> | g17139 | [
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<p>I'm reading <em>An Introduction to Stochastic Processes in Physics</em> by Don S Lemons. Problem 10.2 leads to a pair of equations:</p>
<p>$dV_x = -\gamma V_xdt+V_y\Omega dt-V_y\sqrt{2\gamma dt}N_t(0,1)$</p>
<p>$dV_y = -\gamma V_ydt-V_x\Omega dt+V_x\sqrt{2\gamma dt}N_t(0,1)$</p>
<p>($\gamma$, $\Omega$ constants,... | g17140 | [
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<p>I did an experiment in my home and I was surprised by the results. I heated a pan without anything in it. After some time it became very hot and I took some water (2 drops) and put it into the pan. It started behaving very strangely. The water is forming droplets, and the droplets are jumping here and there and fizz... | g17141 | [
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<p>If there are two twins. such that one of them goes on a space voyage maintaining a constant velocity, and that one never returns to earth, and the twins decide to never meet but send information about their age to each other by some light pulse or any other method.</p>
<p>If then one knows that he is younger, won't... | g17142 | [
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<p>For example, let's consider the electromagnetic interaction between a massless fermion and a electromagnetic externel sourse $A^\mu$, then the lagrangian is
$$\mathcal{L}=\bar{\psi}\gamma^\mu\partial_\mu\psi+ieA_\mu\bar{\psi}\gamma^\mu\psi$$
and how can we calculate the Feynman diagram and $\mathcal{M}$ of it?</p>
... | g17143 | [
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<p>Gauge symmetries do not give rise to conservation laws via Noether's theorem, and they represent redundancies in our description of the system. So why do we want to keep them after quantization? For example:</p>
<blockquote>
<p>But gauge symmetries are not symmetries at all. They are redundancies in our
descrip... | g773 | [
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<p>In my book, it is written that
"An emf is induced in a loop when the number of magnetic field lines that pass through the loop is changing" (Faraday's law)</p>
<p>I understand that whenever there is a change in magnetic flux, there will an emf induced in a loop and this in turn will induce a current.</p>
<p>Howeve... | g17144 | [
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<p>Unitarity of quantum mechanics prohibits information destruction. On the other hand, the second law of thermodynamics claims entropy to be increasing. If entropy is to be thought of as a measure of information content, how can these two principles be compatible?</p> | g17145 | [
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<p>The momentum $m v$ of a particle is formally the same as the <strong>derivative</strong> its translational kinetic energy $\frac{1}{2} m v^2$ with respect to $v$.</p>
<p>Similarly the angular momentum $I \omega$ is the <strong>derivative</strong> of its rotational energy $\frac{1}{2}I \omega^2$ with respect to $\om... | g17146 | [
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<p>Do we have a well defined mathematical expression denoting the size of a fundamental particle with no internal structure (electron for example) ? If we do, how does it fit in with the uncertainty principle ? And if we don't then what exactly do the experiments reveal claiming radius of electron is of the order $10^{... | g329 | [
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<p>Suppose we have a cube of metal inside a room at temperature 27°. If we heat the metal up to 600° using <em>uniform radiation of that energy</em>, <strong>no part</strong> of it should have higher T°, but nevertheless it will start emitting visible light, that is thermal photons with a temperature in the excess of 4... | g17147 | [
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<p>Given a photon dropping from $\lambda_1$ to $\lambda_2$, its energy will drop from $\frac{hc}{(\lambda_1)}$ to $\frac{hc}{(\lambda_2)}$. However, I was wondering if there is any significance in the energy of the change in wavelength itself. For $\Delta \lambda = \lambda_2 - \lambda_1$, this change in wavelength has ... | g17148 | [
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<p>Every physics book I know explains diffraction (e.g. at slits, gratings and circular apertures) in a way which assumes that the light wave impinges perpendicularly on the aperture. Would there be any difference if that was not the case (i.e. if I have a slit and adjust a laser such that it impinges with a certain an... | g17149 | [
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<p>What will be the acceleration of an object $A$ when its released by another object $B$ moving with an upward acceleration $a$? Will the acceleration of the object $A$ be more than the acceleration due to gravity or less than it?
Will the net acceleration reduce or increase?</p> | g17150 | [
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<p>I have created a program, that draws a plane mesh, and allows to me edit or animate all the separate vertices along it. The idea behind it, is for me to be able to create a gridMesh based wave simulation. The common <a href="http://www.google.com/search?as_q=gerstner+wave" rel="nofollow">Gerstner Wave formula</a> do... | g17151 | [
0.0002494790533091873,
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... |
<p>Since a substance emits heat as it transitions from a high energy state (gas) to a lower energy state (solid), is it possible to devise a method to capture this heat and convert it to usable energy?</p>
<p>I'm not sure how economical this would be, but consider the exothermic reaction of water freezing. The heat of... | g17152 | [
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<p>How fast is the rate of "switch" for the domains to align with an exterior field? Possibly in milliseconds?
I assume it won't take much time since domains are very small, and they only turn from a certain degree to another.</p>
<p>I know this would depend on a lot of factors, but if powerful large magnet can attra... | g17153 | [
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<p>I have a basic confusion about how to compute string scattering amplitudes in light cone gauge, using the operator formalism reviewed in GSW. I am familiar with the covariant gauge formalism, where I know how to use the state-operator correspondence to find the vertex operators corresponding to a physical state, but... | g17154 | [
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<p>Please try to answer in layman terms, i am only starting to study thermodynamics (And physics)</p>
<p>In my book one of the curiosity parts gives that fans don't actually cool the room but by hitting the air particles they increase their kinetic energy, these high speed particles hit us and hence evaporate our swea... | g17155 | [
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<p><a href="http://en.wikipedia.org/wiki/Dual_space">Dual spaces</a> are home to bras in quantum mechanics; cotangent spaces are home to linear maps in the tensor formalism of general relativity. After taking courses in these two subjects, I've still never really understood the physical significance of these "dual spac... | g17156 | [
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<p>It is often stated that the Lagrangian formalism and the Hamiltonian formalism are equivalent. </p>
<p>We often hear people talk about eigenvalues of Hamiltonians but I have never ever heard a word about eigenvalues of Lagrangians. </p>
<p>Why is this so? Is it not useful? is it not possible to do it? </p> | g17157 | [
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<p>Does the uncertainty principle imply the non-deterministic universe, or just the fact that our model of the universe, the one based on observation, can be at most non-deterministic, since we will not be able to measure with perfect accuracy, even if such would exist (and therefore we will have to provide probability... | g139 | [
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<p>Since white is our perception of reflection of light, why are mirrors and other metallic objects that are more grey or silvery capable more reflective than a white object?</p>
<p>This is somewhat related: <a href="http://physics.stackexchange.com/questions/1957/what-is-the-difference-between-a-white-object-and-a-mi... | g17158 | [
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<p>According to <a href="http://en.wikipedia.org/wiki/Worldwide_nuclear_testing_counts_and_summary" rel="nofollow">Wikipedia</a> over 2000 nuclear tests have been performed since the Manhattan Project. If nuclear war would bring about a nuclear winter, why didn't testing do? Were they too much spread out in time to cau... | g17159 | [
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<p>I'm currently studying for an exam in thermodynamics/classic statistical mechanics and 2 things came up which are confusing me.</p>
<p>First the ergodic hypothesis states that it is equal to take the mean value of one micro state with respect to time or take the mean of the whole ensemble. In our textbook the state... | g17160 | [
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<p>Can anyone please explain me the process of earthing of a spherical conductor in detail. I am aware about the basic idea of earthing but I am not able to understand and visualize it properly.</p> | g17161 | [
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<p>I am wondering: If I have a regular octahedron as my starting point, oriented along the x-y-z axis, and now Jahn-Teller suggest I elongate or compress along the $z$-axis, what happens along the other axis? I expect that these move in the opposite direction, but by how much? Say my displacement in $z$-direction is $\... | g17162 | [
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<p>Here <a href="http://en.wikipedia.org/wiki/Internal_energy" rel="nofollow">http://en.wikipedia.org/wiki/Internal_energy</a> we can read </p>
<p>$$U= TS-PV+\sum_i \mu_i N_i$$</p>
<p>Let's suppose i=1 and a ideal gas. We know:
$$U=N/N_A c_v T$$;</p>
<p>$$PV=NKT$$;</p>
<p>$$\mu=\frac{\partial U}{\partial N}= c_v T/... | g17163 | [
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<p>From my preliminary research I've learned that desiccants are a good (best?) method to absorb water from air. Assuming I'm using silica gel (or kitchen salt, or rice) then what is the best way to extract the water out of the desiccant?</p> | g17164 | [
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<p>There have been a lot of sci-fi shows recently using the "rotating space station" explanation for gravity on space stations.</p>
<p>After watching these videos:</p>
<p><a href="http://www.youtube.com/watch?v=49JwbrXcPjc&NR=1" rel="nofollow">http://www.youtube.com/watch?v=49JwbrXcPjc&NR=1</a><br>
<a href="h... | g17165 | [
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<p>why pumping to the 3rd level in a 4 level laser system will decrease the output PL intensity?</p> | g17166 | [
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<p>Typically, one way of understanding the physics of an interacting quantum system is by diagonalizing the Hamiltonian. In principle, can we always diagonalize a Hamiltonian, such that it is expressed in terms of non-interacting particle states? If so, is the diagonalization unique?</p> | g17167 | [
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<p>As it can be shown, the equations for the irrep with zero mass and helicity 2, -2 respectively can be given in a form
$$
\tag 1 \partial^{\dot {b}a}C_{abcd} = 0, \quad \partial^{\dot{b}a}C_{\dot{a}\dot{b}\dot{c}\dot{d}} = 0.
$$
Here $C_{abcd} = C_{(abcd)}, C_{\dot{a}\dot{b}\dot{c}\dot{d}} = C_{(\dot{a}\dot{b}\dot{c}... | g17168 | [
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<p>I just need a confirmation I've understood this concept and help in a particular problem. </p>
<p>So, what I understand under "voltage" is basically a difference between two electrical potentials (positions) which are actually just ratios of electrical energy per charge; if we knew how strong the probe charge is (h... | g17169 | [
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<p>The block suspended by the spring is hanging freely and its mass is M.
The small block of mass m is dropped on the bigger block from height h. <img src="http://i.stack.imgur.com/XuQaO.png" alt="enter image description here"></p>
<p>After the small block is dropped 》》》
<img src="http://i.stack.imgur.com/lYZ6Q.png" a... | g17170 | [
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0.... |
<p>What if somebody says that <strong>Sun revolves around the Earth</strong> and not Earth revolving around the Sun?</p>
<p>What would be the <em>consequences</em>?</p> | g205 | [
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<p>I've been learning about tensor analysis, and things have been going well so far, but I'm a bit stuck when it comes to the idea of a <a href="http://www.google.com/search?as_epq=cobasis" rel="nofollow">cobasis</a> (by which I mean the <a href="http://www.google.com/search?as_epq=reciprocal+basis" rel="nofollow">reci... | g17171 | [
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<p>I've recently read up about <a href="https://en.wikipedia.org/wiki/Universal_time#Versions" rel="nofollow">time standards</a> and now understand that UTC is a second-corrected version of international atomic time so that it is kept within 0.9s from UT1. And then UT1 is defined as the mean solar time at 0° longitude.... | g17172 | [
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<p>Reading on wikipedia about <a href="http://en.wikipedia.org/wiki/Faddeev_equation" rel="nofollow">Faddeev equations</a>, I've come across the notion of three-body force. The <a href="http://en.wikipedia.org/wiki/Three-body_force" rel="nofollow">article</a> which describes this type of force doesn't give me any under... | g17173 | [
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<p>Nuclear fusion research appears to promise sustainable, practically unlimited energy, and according to <a href="http://www.iter.org/environment">ITER</a> it will be a perfectly safe, non-polluting source of energy.</p>
<p>My question is if there are any plausible scenarios under which operating a thermonuclear reac... | g17174 | [
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<p>I was interested in learning more about the status of our scientific understanding and technological instruments regarding extra solar spectroscopy.</p>
<p>I am motivated by <a href="http://physics.stackexchange.com/questions/26459/how-do-we-determine-what-distant-planets-stars-etc-are-made-of">this</a> almost 3 ye... | g17175 | [
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... |
<p>What is the difference between:</p>
<p>$\nabla _{\sigma} $ and $ \nabla^{\sigma}$? </p>
<p>I've been told that the first is the covariant derivative, however I'm just starting a course on spacetime geometry and am still a bit unsure of the notation.</p> | g17176 | [
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<p>The famous equation for mass energy equivalence: $E=mc^2$</p>
<p>It cannot conserve energy or momentum without some loss in one way or another. To elaborate further if I take $1kg$ of mass and I also take electromagnetic radiation with same energy as the $1kg$ mass and ensuring its accuracy using the above equatio... | g17177 | [
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<p>How different would the effects of gravity be if the planet we're on is in the shape of a torus (doughnut-shaped)?</p>
<p>For an (approximately) spherical planet, it's slightly clear that objects would tend to be gravitationally attracted towards the center. However a torus would have a hole in its center, and I'm ... | g17178 | [
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<p>Some food or medical items, like rasberry juice concentrate I just bought, have a "protect from light" warning on the label. How can light influence products like milk and what does this warning mean in practice?</p> | g17179 | [
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0.007087109610438347,
0.040478549897670746,
0... |
<p>Due to certain reasons, I don't have the chance for going to college for under-graduation, but that doesn't mean I can't choose to walk the hard path and learn. Over the past month or so a lot of people have asked about resources for physics online or offline, but what I want isn't just the resources, but advice on ... | g17180 | [
0.0007227311725728214,
0.030896160751581192,
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0.0014229061780497432,
0.004113169852644205,
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0.004668488632887602,
-0.10768016427755356,
0.03915544971823692,
0.0028311703354120255,
0.06072369962930679,
... |
<p>Take the following gedankenexperiment in which two astronauts meet each other again and again in a perfectly symmetrical setting - a hyperspherical (3-manifold) universe in which the 3 dimensions are curved into the 4. dimension so that they can travel without acceleration in straight opposite directions and yet mee... | g503 | [
0.04774852469563484,
0.01744437962770462,
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0.0027043018490076065,
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0.00838386733084917,
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-0.0038844591472297907,
0.036515865474939346,
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0.03248682990670204,
0.02... |
<p>I'm watching some Physics lectures on the internet by Leonard Susskind:<br>
<a href="http://www.youtube.com/watch?v=pyX8kQ-JzHI&feature=BFa&list=PL189C0DCE90CB6D81&lf=plpp_video" rel="nofollow">http://www.youtube.com/watch?v=pyX8kQ-JzHI&feature=BFa&list=PL189C0DCE90CB6D81&lf=plpp_video</a></p... | g17181 | [
0.038207586854696274,
0.05998751521110535,
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0.07460556924343109,
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0.04149607941508293,
0.06588628888130188,
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0.004054189193993807,
-0.02869296632707119,
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-0.00... |
<p>$C$ is a 3x3x3x3 tensor. How should the expression $C_{ijkl}u_{i,j}u_{k,l}$ be interpreted? This is my guess:</p>
<p>$$
\sum_{i=1}^3\sum_{j=1}^3
\sum_{k=1}^3\sum_{l=1}^3
C_{ijkl}u_{i,j}u_{k,l}
$$</p> | g17182 | [
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0.0313662551343441,
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<p><strong>Why is there no proper time without inertial frame?</strong></p>
<p>In question n°95054 I learned that there is no proper time zero and no proper distance zero for photons because they are no inertial frames.</p>
<p>That means, in my observer's spacetime Minkowski diagram with movements of objects (incl. p... | g17183 | [
0.03760366141796112,
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/3795/why-are-snowflakes-symmetrical">Why are snowflakes symmetrical?</a> </p>
</blockquote>
<p>Under ideal situations, a snowflake forms into near perfect hexagonal symmetry. How? For instance, when a wa... | g521 | [
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<p>I believe to have understood that some physical experiments suggest finite values to divergent series (please correct me if I'm wrong, my understanding of these matters is limited). </p>
<p>I heard, for example, that the "equality"
$$ \sum_{n=1}^{ \infty} n = - \frac{1}{12} $$ was suggested by some experiment cond... | g17184 | [
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-0.05482293665409088,
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0.01464154664427042,
0.0834... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/16626/are-there-any-good-audio-recordings-of-educational-physics-material">Are there any good audio recordings of educational physics material?</a> </p>
</blockquote>
<p>In the same way that was already ... | g522 | [
0.03219062089920044,
0.03536897152662277,
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0.04404199495911598,
0.05952415242791176,
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0.00... |
<p>Can the following be true?</p>
<ol>
<li>$g^{\sigma\rho}\nabla_{\rho}\nabla_{\mu} = \nabla^{\sigma}\nabla_{\mu}$</li>
<li>$g^{\sigma\rho}\nabla_{\nu}\nabla_{\sigma} = \nabla_{\nu}\nabla^{\rho}$</li>
<li>$g^{\sigma\rho}\nabla_{\nu}\nabla_{\mu}T_{\sigma\rho} = \nabla_{\nu}\nabla_{\mu}T$</li>
</ol> | g17185 | [
-0.005177473649382591,
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0.012590428814291954,
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0.029952319338917732,
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0.07554935663938522,
0.008879244327545166,
-... |
<p>Water, at room temperature is poured into a hole made of a block of melting ice(kept at room temperature).I was wondering if the water will ever freeze?</p>
<p>Thank you.</p> | g17186 | [
0.019364632666110992,
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0.01978491060435772,
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0.004021813627332449,
0.037662241607904434,
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<p>To calculate pressure at a given altitude, the following formula is used:</p>
<p>$p = p_0 \cdot \left(1 - \frac{L \cdot h}{T_0} \right)^\frac{g \cdot M}{R \cdot L}$</p>
<p><em>(the values can be found <a href="http://en.wikipedia.org/wiki/Density_of_air#Altitude" rel="nofollow">here</a>)</em></p>
<p>This formula ... | g17187 | [
0.031466223299503326,
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0.018844198435544968,
0.0050488426350057125,
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0.03445945307612419,
0.02158859372138977,
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0.0393701046705246,
0.029909541830420494,
0.016340360045433044,
0.06336332112550735,
-0.04... |
<p>So i've been a bit confused, looking at PN junction, semiconductors and the like (trying to nail down <em>how exactly</em> semiconductors work, transistors and such). I've read the wiki on <a href="http://en.wikipedia.org/wiki/Carrier_generation_and_recombination" rel="nofollow">band structure</a> (“holes” and free ... | g17188 | [
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0.008370758034288883,
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-0.026430916041135788,
0.005070576444268227,
0.035828541964292526,
0.03367780148983002,
-0.04... |
<p>Consider the following problem:</p>
<p><em>Robby wants to put a light in the shed so he puts a cable between his house and the shed. In the cable there are 2 wires with a combined resistance of $0,92 \space \Omega$. Robby connects his transformator at his house on an electricity grid of $230 V$. He connects the sec... | g17189 | [
-0.006867824587970972,
-0.017264563590288162,
-0.028566230088472366,
-0.03847425803542137,
0.027423352003097534,
-0.08824903517961502,
0.06552556157112122,
0.018270699307322502,
-0.04019909352064133,
-0.016581321135163307,
-0.046408217400312424,
0.061399802565574646,
0.0032892196904867887,
... |
<p>I see the prices of Nd:YAG rods for lasers, and could someone explain why they are so expensive? </p>
<p>Do they need to be mono-crystalline or something?
Will Nd:YAG laser work with amorphous/poly-crystalline rod?</p> | g17190 | [
0.0071993316523730755,
0.03010268695652485,
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0.003802964696660638,
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0.031587302684783936,
0.017201555892825127,
-0.018885880708694458,
0.04129046946763992,
0.045839425176382065,
0.007628853432834148,
-... |
<p>Antimatter is like matter on opposite day: it has the same properties as the stuff that makes up planets, stars and galaxies, but one vital piece is different—its charge. The universe supposedly started off with equal parts matter and antimatter, but somehow, matter won out. Most of both substances annihilated each ... | g17191 | [
0.08336520940065384,
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0.021438414230942726,
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0.054916951805353165,
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0.08557755500078201,
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0.026604721322655678,
0... |
<p>Is it possible to fully define a system, then be incapable of simulating or calculating its future states due to the <a href="http://en.wikipedia.org/wiki/Uncertainty_principle" rel="nofollow">Uncertainty Principle</a>? If it can be done, how?</p> | g17192 | [
-0.015489000827074051,
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0.00009909000800689682,
-0.02423364296555519,
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-0.001023013726808130... |
<p>I've been reading about string theory, and as I understand it, it proposes that matter is nothing more than a vibration of a membrane of space-time. Is my understanding correct?</p> | g523 | [
0.023189179599285126,
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0.00863944087177515,
-0.00... |
<p>I have a problem where, basically, in part (a) I correctly found a fundamental equation $$TdS = dE - 2\sigma l dx$$</p>
<p>Then the problem goes on to say that the only parameters of interest are $x$ and $T$, so I would assume we can write the relation $$dS =
\frac{\partial S}{\partial x} dx + \frac{\partial S}{\p... | g17193 | [
0.031633418053388596,
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0.003935681190341711,
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0.0036483872681856155,
0.00645796675235033,
0.027558691799640656,
-... |
<p>I was looking into orbitals and found something I haven't been able to understand.</p>
<p><a href="http://www.math.ubc.ca/~cass/courses/m309-01a/hunter/satelliteOrbits.html" rel="nofollow">http://www.math.ubc.ca/~cass/courses/m309-01a/hunter/satelliteOrbits.html</a></p>
<p>There is a part on the page which states ... | g17194 | [
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0.004159163683652878,
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-0.00936526246368885,
0.0017893480835482478,
0.029657695442438126,
0.046453677117824554,
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0.004131223075091839,
0.00791169423609972,
0.07455503940582275,
0.023848049342632294,
0.034... |
<p>If $\vec{\mathbf B}=B\vec{\mathbf a}_z$, compute the magnetic flux passing through a hemisphere of radius $R$ centered at the origin and bounded by the plane $z=0$.</p>
<p><img src="http://i.stack.imgur.com/WavK2.png" alt="Figure"></p>
<hr>
<p><strong>Solution</strong>
The hemisphere and the circular disc of radi... | g17195 | [
0.033490702509880066,
0.01204658579081297,
-0.006775352172553539,
-0.024010300636291504,
0.02596518211066723,
0.08881412446498871,
0.10769764333963394,
0.04324295371770859,
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-0.021588297560811043,
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0.040900398045778275,
0.0062611522153019905,
-0.0... |
<p><strong>Q1:</strong></p>
<p>Ok so i have come to a point where i know that $\Psi(r,t)$ which we denote only by $\Psi$ can be represented in a Hilbert space by a vector which we denote $\left|\Psi\right\rangle$. Does this mean $\left| \Psi(r,t) \right\rangle$? </p>
<p><strong>Q2:</strong></p>
<p>I know that equati... | g17196 | [
0.017754293978214264,
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0.06135693937540054,
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0.007217162288725376,
0.05684996768832207,
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0.015022790990769863,
-0.0072980644181370735,
-0.0137096606194973,
-0.031439825892448425,
0.... |
<p>If you have two entangled quantum states, One state falls into a black hole and you measure the other state, What can you say about the state that has fallen into the black hole?</p>
<p>If you have billions of these entangled pairs and one partner of each falls into the black hole, If you don't measure the states o... | g17197 | [
-0.051879845559597015,
0.05495506152510643,
0.012444962747395039,
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0.... |
<p>This might sound like the silliest question ever, but can someone shed some light on what is actually happening in the following situation:</p>
<p><strong>There is an asteroid in outer space what is rotating with high speed. There is an astronaut standing on its surface.</strong></p>
<ol>
<li><p>Does the astronaut... | g17198 | [
0.02919795550405979,
0.050457149744033813,
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0.000043159314373042434,
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0.04519888386130333,
... |
<p>Please can someone help me with a equation for how much energy a person generates when swinging on a swing?</p> | g17199 | [
0.005758436396718025,
0.06779499351978302,
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0.011888071894645691,
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... |
<p>In 4-D flat metric E&M context, given a rank $p$ tensor, one can construct dual of $4-p$ rank tensor by Levi-Civita tensor. Here dual is not in the same sense of mathematical dual. I do not know where it comes from. The followings are my questions:</p>
<ol>
<li><p>Is it necessarily true for arbitrary dimension ... | g17200 | [
0.01829591579735279,
0.0024594489950686693,
0.004241498187184334,
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0.018794488161802292,
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0.04183657839894295,
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-0.016907833516597748,
-0.02014830894768238,
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0.09206845611333847,
-0... |
<p>This is obviously a follow on question to the Phys.SE post <a href="http://physics.stackexchange.com/q/64869/">Hilbert space of harmonic oscillator: Countable vs uncountable?</a></p>
<p>So I thought that the Hilbert space of a bound electron is countable, but the Hilbert space of a free electron is uncountable. Bu... | g42 | [
0.05460008606314659,
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0.02948940172791481,
0.04787640646100044,
0.030... |
<p>I took a basic quantum chemistry course (McQuarrie's "Quantum Chemistry"), but it never dealt with <a href="http://en.wikipedia.org/wiki/Quantum_state#Mixed_states" rel="nofollow">mixed states</a> -- only pure states (or if it did, we never got to it in class).</p>
<p>So I'm trying to understand them on my own. Co... | g17201 | [
-0.03442040830850601,
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0.0011095176450908184,
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-0.... |
<blockquote>
<p><em>A beam of particles each having mass $m$ and velocity $v$ in the incident on a circular hole of radius $b$ located on a screen. If another screen is placed at a distance $D$ from the hole, determine the minimum size of the pattern formed on the screen by the beam.</em></p>
</blockquote> | g17202 | [
0.01706882379949093,
0.01836349442601204,
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0.024644527584314346,
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0.03618137910962105,
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0.042... |
<p>The classical description of <a href="http://en.wikipedia.org/wiki/Electro-optic_modulator" rel="nofollow">electro-optic modulators</a> is an index of refraction that depends on the applied voltage. For example, for a sine modulation $\sin(\Omega t)$, a monochromatic laser of frequency $\omega$ would get an addition... | g17203 | [
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0.006895816884934902,
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0.04973757639527321,
0.011961215175688267,
0.033... |
<p>classical computers store information in bits which can either be 0 or 1, but in quantum computer the qubit can store 0 , 1 or a state that is the superposition of these two states
so how this superposition help to use less qubit to stor information for example:
how many qubit we are need to store "16"?
I know a lit... | g17204 | [
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<p>I was watching a special on divers who dove down hundreds of feet without tanks or gear. The show referred to a depth at which the diver was no longer buoyant and would actually sink, even with lungs full of air. Is there such a point and if so, why? What is happening there?</p> | g17205 | [
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<p>Roughly speaking, <a href="http://en.wikipedia.org/wiki/Mermin%E2%80%93Wagner_theorem">Mermin-Wagner theorem</a> states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions $d\leq 2$.</p>
<p>What is the precise statement ... | g17206 | [
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<p>Does that is even possible? I have almost zero knowledge in quantum physics, it is just a curiosity that popped in my mind.</p> | g17207 | [
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<p>It seems very clear, that because atoms and ion compounds are electrically neutral, our world seems to consist of an equal amount of positive and negative charge resulting in a zero net charge.</p>
<p>What would be the consequence of (small) non-zero net charges on cosmological scales?</p>
<h2>Planetary</h2>
<p>W... | g17208 | [
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<p>(I am not exactly sure if this question is supposed to go here, but it seems like the appropriate place for it.)</p>
<p>Hello Scientific Community,</p>
<p>I am soon graduating from high school and, as everyone does, I am searching for something to study at college. I have always wanted to study straight forward ph... | g17209 | [
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<p>I was wondering why water freezes from up to bottom and not the other way around. The reason I question this is because in a Video I came across, I discovered water freezes from top but surely with the current knowledge I would say it should be opposite because we know cool air drifts down while hot air drifts up so... | g17210 | [
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<p>What do we mean by the following statement?</p>
<blockquote>
<p>The SV $\lambda$ 786.46 line is detected with a equivalent width of $W = 22.7\pm10.2$ corresponding to a significance of $2.2\sigma$</p>
</blockquote>
<p>How does one calculate $\sigma$?</p> | g17211 | [
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<p>How big could an array of space telescopes acting as an interferometer be ?</p>
<p>How big would it have to be to resolve exoplanet surface detail the size of Iceland at a distance of 100 light years ?</p> | g17212 | [
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