question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I need something like a summary of existing results, including the treatment of BCS Hamiltonian and Hubbard model. Auerbach's book is a good one but I still hope to get more comprehensive review. My purpose is to compare the methods and give an outline of the mathematical framework behind this. Currently I am workin... | g10464 | [
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<p>Take a look at this diagram: <a href="http://www.chegg.com/homework-help/questions-and-answers/7-pipe-assembly-supports-vertical-loads-shown-determine-components-reaction-ball-socket-jo-q2260091" rel="nofollow">http://www.chegg.com/homework-help/questions-and-answers/7-pipe-assembly-supports-vertical-loads-shown-det... | g10465 | [
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<p>How would the non-interacting electron orbitals from a perfect <a href="http://en.wikipedia.org/wiki/Density_functional_theory" rel="nofollow">DFT</a> solution for a given potential shape differ from the 'true' electron wavefunctions? Or can you only really talk about the total wavefunction? Would they be less local... | g10466 | [
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<p>I am interested in the vibrations of a thin, flexible rod that would only be clamped at one point, properly I'd like to calculate its eigenvalue. But the way I learned it in wave mechanics doesn't seem to apply here. The equation is: </p>
<p>$$ \frac{1}{c^2}\frac{\partial^2 u}{\partial t^2} = \frac{\partial^2 u}{\p... | g10467 | [
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<p>I have some questions about Nanotechnologies. I'm not physicist and my knowledges about the topic are limited by the "Engines of Creation" book by Eric Drexler. So I think that my questions are related mostely to popular science.</p>
<ol>
<li><p>As far as I know the molecular mechanisms like nanoassemblers and nano... | g10468 | [
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<p>Let $O$ be an observable on a Hilbert space $\mathcal{H}$, and let $B$ be a subset of the spins composing $\mathcal{H}$, and let $\bar{B}$ be its complement. Now define</p>
<p>$\displaystyle O_B = \frac{1}{\operatorname{Tr}_{\bar{B}}\mathbf{1}_{\bar{B}}} \operatorname{Tr}_{\bar{B}}(O) \otimes \mathbf{1}_{\bar{B}}$.... | g10469 | [
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<p>From <a href="http://en.wikipedia.org/wiki/Kelvin">Wikipedia</a>:</p>
<blockquote>
<p><em>The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water.</em> </p>
</blockquote>
<p>That presupposes that we can take a fraction of temperature.</p>
<p>Now, taking a fr... | g10470 | [
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<p>At what depth in the water atmospheric pressure is 100 times greater than on the ground?
This question comes from the fact that average pressure in Earth( 1000 mbar) is 100 times greater than in Mars( 7 mbar).</p> | g10471 | [
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<p>Numerical Aperture (NA) (for fiber optics) is usually used to denote the acceptance cone for a multi-mode fiber. </p>
<p><strong>Does NA also describe the expansion of light emitted from the end of a fiber?</strong></p>
<p>I have a 1mm core 0.22 NA PMMA fiber, I would like to collimate the light once it's reached ... | g10472 | [
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<p>Does it make sense to say, "The speed of light varies?" Some may say right off the bat "Yes, it changes as a wave passes through a different medium." However, I'd like to say no, because when I hear someone say the speed of light, I always think of the constant $c$ (unless the medium is specified to not be a vacuu... | g1028 | [
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<p>There's this question that has been bugging me most of my life: how is it that wet clothes left hanging to dry, get actually dry?
If I get it right, the clothes are a mesh of fibers (we could assume synthetic fibers to make it simpler) that capture droplets of water in the mesh.
When one hangs the cloth gravity make... | g10473 | [
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<p>The Yukawa coupling of the top quark is Dirac-natural in a too excellent way, it is within one sigma experimentally, and within 99.5% in absolute value, of being equal to one. Without some symmetry, it seems too much for a quantity that is supposed to come down from GUT/Planck scale via the renormalization group. Is... | g10474 | [
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<p>While determining the electric field in a Non-Conducting Sphere using Gauss's law,why the positive charges are considered inside the surface,but in determining the electric field in a conducting Sphere,why the positive charges are considered outside the surface? </p>
<p>And,why if any point charge is inside a spher... | g10475 | [
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<p>Can someone explain nuclear isomers to me, and in particular what the energy involved is? I understand generally that we're talking about moving from a less to more stable configuration of nuclear particles, but that's about as far as my understanding goes.</p> | g10476 | [
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<p><a href="http://en.wikipedia.org/wiki/Mechanical_advantage" rel="nofollow">Mechanical advantage</a> is defined as Force Output/Force Input</p>
<p>For a symmetrical wedge with the length of the slopes being equal and the width being the distance between the end points, </p>
<p>articles quote the Mechanical advantag... | g10477 | [
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<p>In studying rotational dynamics of a rigid body , I can't seem to understand why you can solve the problem correctly only using certain points in a body and not all ? Means angular momentum and torque leads to correct answer only in some cases</p> | g10478 | [
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<p>How is the boxed step , physically as well as mathematically justified and correct ?</p>
<p>Source:Wiki <a href="http://en.wikipedia.org/wiki/Electric_potential_energy" rel="nofollow">http://en.wikipedia.org/wiki/Electric_potential_energy</a></p>
<p>As work done = $- \Delta U $. for Conservative force and it shoul... | g10479 | [
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<p>This is just a curiosity and you need to bear with me as my math skills were always sub-par and so is my English academic language. My specialty is Electronics but I have always been a programmer.
Years ago I was working on my diploma paper that dealt with locating leaks using auto-correlation.<BR>
Basically you hav... | g10480 | [
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<p>Light is a transverse wave. Therefore, light in the optical range (i.e. visible light) couples to transverse collective excitations of a material when measuring the optical conductivity for instance. Likewise, X-rays are also transverse waves, but somehow couple to longitudinal collective excitations of a material. ... | g10481 | [
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<p>I am still very new to many physics theories, however while sat in class today, a thought came to mind that I have not been able to answer from simple googling. </p>
<p>What is so specific about our sun that we orbit it? It is by no means the largest star and it's mass is apparently around average for a star. So wh... | g10482 | [
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<p>I just met with a very basic question.(Might even sound silly!) My textbook kinda says(not exactly), 'Whatever flows is a fluid'. That got me wondering because we are creating a whole category of matter just because they flow! So there must be some significance to 'flowing'. That further led me to ask why in the fir... | g10483 | [
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<p>I know this question is probably not adequate to this SE either, but let me explain my situation: I'm civil engineering's college, so, there isn't a SE for civil engineering, and my doubts about integration in engineering are pratically pure physics. So, as I said, I'm graduating, but I'm from Brazil, education here... | g10484 | [
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<p>So I am studying the laws of Newton and I'm wondering, are there any deficiencies related to the laws? I mean, somewhere where I can't use them or anything?</p> | g10485 | [
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<p>Feynman suggested that there is an infinity of trajectories for a single electron travelling from the source to the phosphorescent screen. He said that one electron goes through both holes (Fig 4.10, page 110, The Elegant Universe, Brian Greene).</p>
<p>Is it possible that there is a simpler explanation? </p>
<p>T... | g10486 | [
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<p>The following decay is possible according to the PDG and according to my notes it is a strong decay:</p>
<p>$$\omega(1420) \to \rho^0 + \pi^0$$ </p>
<p>The JPC values are:</p>
<p>$\omega(1420)$ 1-- </p>
<p>$\rho$ 1--</p>
<p>$\pi$ 0-+</p>
<p>So, all three particles have, for themselves, a parity... | g10487 | [
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<p>I'm a physics graduate now working with computers. I study GR in my spare time to keep the material fresh. In the Wikipedia article about <a href="http://en.wikipedia.org/wiki/Mathematics_of_general_relativity" rel="nofollow">the mathematics of GR</a>, one can read the following:</p>
<blockquote>
<p>The term 'gen... | g10488 | [
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<p>I am curious. If you were to put a solar panel up in high altitude or on the surface of the moon, both of which have much less atmosphere to reflect/refract light, would that solar panel produce more energy?</p>
<p>I am curious because an article comments discussion got me thinking about setting up a low Earth orbi... | g10489 | [
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<p>After finding the eigenfunctions $u_p(x)=Ce^{ipx/\hbar}$ of the <a href="https://en.wikipedia.org/wiki/Momentum_operator" rel="nofollow">momentum operator</a> just like in <a href="http://quantummechanics.ucsd.edu/ph130a/130_notes/node138.html" rel="nofollow">this UCSD lecture notes</a>, one seeks to normalize them,... | g10490 | [
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<p>How would you read the following particles' names in a conversation in English? I am looking for some "proper" way of doing it. Say, imagine you are reading a technical description in a semi-formal occasion that you would like to avoid being lousy or overly simplistic.</p>
<p>$$\Delta(1750)^0 P_{31}$$
$$\bar\Delt... | g10491 | [
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<p>I am having trouble in understanding the following concepts :</p>
<p>Pg 231 Appendix B of the link <a href="http://books.google.ca/books?id=lEu7CTGjdDkC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q=entropy&f=false" rel="nofollow">http://books.google.ca/books?id=lEu7CTGjdDkC&... | g917 | [
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<p>Take a bucket of hot water and the other bucket of cold water. Why does the bucket full of cold water weigh more than bucket full of hot water?</p> | g10492 | [
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-0.05499185621738434,
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0.... |
<p>It seems there are a lot of respected physicists appearing on pop-sci programs (discovery channel, science channel, etc.) these days spreading the gospel of <a href="http://en.wikipedia.org/wiki/Ignoramus_et_ignorabimus#Hilbert.27s_reaction">"we can know, we must know."</a></p>
<p>Three examples, quickly: 1) Many p... | g10493 | [
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0... |
<p><a href="http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Cu&ascii=html&isotype=some" rel="nofollow">This URL</a> lists the mass of Copper-63 as 62.9295975(6) and <a href="http://physics.nist.gov/PhysRefData/Handbook/Tables/coppertable1.htm" rel="nofollow">this other URL</a> lists the mass as ... | g10494 | [
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-0... |
<p>So as far as I know, nuclear fission uses high weight atomic elements to manufacture power. If the risk of runaway reactions are a major reason for not expanding this technology, why don't we use elements with lower atomic weight (eg. less energy) or lower amounts of fuel (eg. less total mass)?</p> | g10495 | [
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<p>I have a question about the gravity probe B experiment.</p>
<p>According to this site:</p>
<p><a href="http://science.nasa.gov/science-news/science-at-nasa/2011/04may_epic/" rel="nofollow">http://science.nasa.gov/science-news/science-at-nasa/2011/04may_epic/</a></p>
<p>The measurements they made confirm Einsteins... | g10496 | [
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<p>First, a quick remark: I'm a mathematician, now working on some problems coming from physics (in particular Ising models on quasiperiodic chains). A few things I find rather mysterious. I would appreciate your help.</p>
<p>For the purpose of generality, let's consider the following Ising model on a chain of $N$ nod... | g10497 | [
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... |
<p>Is it impossible for a universe that only contains particles/fields with no rest mass to develop life/intelligence? Assume there is no mechanism to generate a rest mass (Higgs, symmetry breaking, etc.)</p>
<p>It seems ridiculous, but I can't think of a good reason why it can't happen since the life/intelligence may... | g10498 | [
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<p>I'm not sure if someone's already asked this before, but I was wondering, in field theory, </p>
<ol>
<li><p>when we say that a certain field is gauge invariant but not gauge covariant, what does this mean? In particular, in <a href="http://en.wikipedia.org/wiki/Pauli%E2%80%93Villars_regularization">Wikipedia</a>, t... | g10499 | [
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<p>While travelling by train (travelling West to East), it seems the moon is moving in opposite direction when seen from the window, but then it reverses its direction, after a certain amount of time and moves along the train, but then flips back again. And it kept oscillating, as the train kept moving. Can anyone poin... | g10500 | [
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<p>Why there is always cold at high altitudes. e.g. at peak of mountains. Also as we go high from see level, temperature starts decreasing, so why is it.</p> | g10501 | [
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<p>How can astronomers find the difference between a parabolic and a hyperbolic comet ? What are the criteria that helps them distinguish these ? Can a parabolic comet switch over to become a hyperbolic one and the vice-versa ?</p> | g10502 | [
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<p>Does the Hilbert space of the universe have to be infinite dimensional to make sense of quantum mechanics? Otherwise, decoherence can never become exact. Does interpreting quantum mechanics require exact decoherence and perfect observers of the sort which can only arise from exact superposition sectors in the asymp... | g10503 | [
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<p>I really got to thinking about this. The speed of sound is measured at 761.2 MPH <strong>at sea level</strong>. But how does this number change as air density decreases? The lack of air density is what allowed his terminal velocity to much lower than say a jump at 5k feet high. I am not disputing his maximum ve... | g10504 | [
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<p>How are the comet-hunters able to precisely locate/know about the required comets ? How can they distinguish between comets from such a far distance ? How are they able to estimate the exact time period of these comets like Hale-Bopp's and Halley's comets have orbital time periods 2520-2533 yrs and 75.3 yrs respect... | g10505 | [
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<p>Given a stream of moving charged particles that encounter a uniform magnetic field such that they are trapped in a circular orbit, what effect do these particles have on the net magnetic field over time? Would the magnetic field get stronger or weaker as the number of trapped particles increase?</p> | g10506 | [
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<p>My original question was in an effort to understand the electrical analogy to Markov chains, which is explained in Snell's article. There are some neat parallels that involve taking a Markov chain and considering the edge weights to be wire conductances. Unfortunately, after reading the article, I realize that the... | g10507 | [
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<p>I would like to ask a stupid question here.</p>
<p>If a body 'b' moving downward with a velocity v in a rotating frame of reference with angular velocity w, and w and v not being parallel and anti parallel. We all know that the body 'b' experiences a Coriolis force.</p>
<p>If it gets deflected in its trajectory th... | g10508 | [
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<p>I recently learnt that a suit called <a href="http://en.wikipedia.org/wiki/Pressure_suit" rel="nofollow">pressure suit</a> is worn by fighter plane pilots to prevent red-outs and black-outs. And it seems to be work by -</p>
<blockquote>
<p>"..applying pressure to selective portions of the body."</p>
</blockquote>... | g10509 | [
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<p>If I have an over-damped mechanical system that is excited with a sinusoidal motion. That sinusoidal motion starts with a determined frequency then increases frequency over time.
Of course, it is known that there will be a phase shift between the driving force and the motion of the hanging mass.</p>
<p>My question ... | g10510 | [
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... |
<p>If I throw a ball straight up, it deflects slightly to the west due to Coriolis forces. If instead I watch a bubble float up in water, is the bubble deflected west, east, or neither?</p>
<p>I think the bubble also moves west, but am not sure. My reasoning is that the air in the bubble must feel a Coriolis force t... | g10511 | [
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<p>When a heavy quark hadronizes it has some probability of forming a meson vs forming a baryon. I suspect there is a well known branching ratio for each type of hadron. Does anyone know what the probability is or, even better, a reference that discusses this? An ideal answer (though not necessary) would further give a... | g10512 | [
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<p>I would to know if there is a correlation between isospin and energy. Consider for example the $\eta$ meson ($I =0$) and the pions($I=1$). The $\eta$ turns out to be much heavier then the pions ($m_\pi \approx 150 \mbox{MeV}$,$m_\eta\approx 550\mbox{MeV}$). </p>
<p>A counterexample is the $\Lambda_b$ ($I=0$) and th... | g10513 | [
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<p>I assume the twin paradox from special relativity is well known. I wish to focus on the apparent symmetry of the problem: both observer seems to move away from each other, and then come back. Yet, the outcome is asymmetrical.
That paradox is resolved because the travelling twin has to turn around at some point. Then... | g10514 | [
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<p>So i read this in some article on the net</p>
<blockquote>
<p>Consider a boy is standing at distance of 10 metres from the wall. Boy
holds a rubber ball and cloth ball in his hands. Firstly, the boy
throws rubber ball with force 2N (Newton) on the wall. The rubber ball
after striking the wall rebounds to 10... | g10515 | [
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<p>I've had a question about this topic previously, but the material was inelastic.</p>
<p><a href="http://physics.stackexchange.com/questions/92089/forces-in-a-balloon-popping">Forces in a balloon popping?</a></p>
<p>What happens when a material is non-hookian? </p>
<p>Say rubber,</p>
<p>I've found this pdf on the... | g10516 | [
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<p>Let $r_{P/Q}$ be the position vector of $\overrightarrow P$ relative to vector $\overrightarrow Q$ and $v_{P/Q}$ the velocity vector of $\overrightarrow P$ relative to $\overrightarrow Q$. </p>
<p>Suppose $|v_Q| > |v_P|$ and you want to set the direction of $v_P$ such that $|r_{P/Q}|$ becomes minimal at some poi... | g10517 | [
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<p>Is it energy?</p>
<p>Is it energy per unit volume?</p>
<p>Is it energy per unit time i.e power?</p>
<p>What is it?</p> | g10518 | [
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<p>So I keep reading all these articles on the <a href="http://en.wikipedia.org/wiki/EPR_paradox" rel="nofollow">EPR paradox</a>, and I follow them pretty easily right up until it gets to the most important matter.</p>
<p>Assuming you are trying to measure x and y spin,</p>
<p>Wikipedia and others say that when you m... | g10519 | [
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<p>This is a quote from Dirac's Principles of Quantum Mechanics:</p>
<blockquote>
<p>"(...) if an atomic system has its equilibrium disturbed in any way
and is then left alone, it will be set in oscillation and the
oscillations will get impressed on the surrounding electromagnetic
field, so that their frequenc... | g10520 | [
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<p>This question has come to me from my friend in fact: he noted that the heating in the pub is painted black. I replied that it's better for heat emission.</p>
<p>I don't know where did I know that from. And he disagreed, asking me: "Why would black emit more heat than white?" I didn't know. We could, however, agree ... | g10521 | [
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<p>Suppose we have a quantum state, well described by its time-independent wave function Psi. And we have a well-defined Hermitian (self-adjoint) operator $A$. We successfully evaluate the expectation value of the operator $A$. Next we derive the general formula for the higher moments of $A$ (i.e. the expectation value... | g10522 | [
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... |
<p><a href="http://www.nature.com/news/simulations-back-up-theory-that-universe-is-a-hologram-1.14328" rel="nofollow">http://www.nature.com/news/simulations-back-up-theory-that-universe-is-a-hologram-1.14328</a></p>
<p><a href="http://guardianlv.com/2013/12/compelling-evidence-says-our-universe-is-a-hologram/" rel="no... | g10523 | [
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<p>Earth's atmosphere is a chaotic system. In such systems arbitrarily small changes the conditions can give rise to very large effects.</p>
<p>There are many rumors about the physical and large scale environmental impacts that global warming will cause in the future. (for example, <a href="https://en.wikipedia.org/wi... | g10524 | [
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<p>I have a particle and a potential $V(x)=\frac{\hbar^2}{2m}k\delta(x)$.</p>
<p>Where $\delta (x)$ is the Delta function, and I am interested in the solutions of the <strong>stationary</strong> Schroedinger equation.</p>
<p>If $\psi_1$ is the solution for $x<0$ and $\psi_2$ for $x>0$, must be that $\psi_1'(0) ... | g10525 | [
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<p>Imagine we have a diffraction grating consisting of N slits (being N very large) with a separation of "d" from slit to slit. Now, we could regard this grating as a diffraction grating constructed by a repeated double slit, in which case the periodicity would be 2d. </p>
<p>I realize this can't be legitimate since ... | g10526 | [
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<p>If it is established that the Earth does have a dark matter disk as this recent discovery suggests.</p>
<p><a href="http://www.newscientist.com/article/mg22129503.100-gps-satellites-suggest-earth-is-heavy-with-dark-matter.html" rel="nofollow">http://www.newscientist.com/article/mg22129503.100-gps-satellites-suggest... | g10527 | [
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<p>I know there exists surfaces that only reflect light (mirrors), but are there surfaces that only refract light? If so, how does that happen?</p> | g10528 | [
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<p>Our professor hasn't explained what <a href="http://en.wikipedia.org/wiki/Bound_state" rel="nofollow">bound states</a> are. Could you give me an idea of what they mean and their importance in quantum-mechanics problems with potential (e.g. a potential described by a delta function)?</p>
<p>And why, when a stable bo... | g10529 | [
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<p>We all know that (visible for human) light essentially is an electromagnetic wave with a frequency around 1/((any value between 380 and 760)*pow(10,9)) Hertz. </p>
<p>So, if we will build (hypothetically) an electromagnet and feed it with such a frequency, would we observe a light beam coming out of it?</p> | g334 | [
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<p>I am studying for my Bachelor thesis (in Mathematics). I and my advisor agreed on the <a href="http://en.wikipedia.org/wiki/Penrose%E2%80%93Hawking_singularity_theorems" rel="nofollow">Penrose-Hawking singularity theorems</a>.</p>
<p>My question is: </p>
<p>1) Which mathematical background should I focus on maste... | g10530 | [
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<p>Suppose there are two slopes. Imagine its just small slope and can be placed on your floor. One slope is made of a very smooth material and another which provides a lot of friction for example made of rubber. Now you place a cubical metal block on each of the slopes. Both the blocks are exactly identical. The metal... | g10531 | [
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<p>My professor said that a law was stated and announced as a law because it happens in our everyday life. He gave us an example of Newton's 3 laws. He said that walking possess 3 laws of Newton's. Is it true that all laws really happen in our daily motion?</p> | g10532 | [
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<p>I'm trying to analyze the motion of the particles which exert the gravitational force each other. Let $M_1$, $M_2$ be the masses of the particles, and the equation of motion of particle $M_1$</p>
<p>$$
F=G\frac{M_1M_2}{r^2}=M_1\ddot{r} \\
\ddot{r}r^2-GM_2=0
$$</p>
<p>I find it doubtful that the simple motion has d... | g10533 | [
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<p>I want to know if the following has been done experimentally; after the spin (or any other characteristic with a probability of 50%) of 2 entangled particles has been measured, we change the spin of one and we see the spin of the other changing instantaneously at a distance. </p>
<p>For example, entangled particle ... | g10534 | [
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<p>While playing racquetball, I frequently hear a very prominent "boing" sound (or more formally, a <a href="http://en.wikipedia.org/wiki/Chirp">chirp</a>). For example, you can hear it in <a href="https://www.youtube.com/watch?v=mfWllzz-6YI">this video</a> when the ball hits the front wall.</p>
<p>Does anyone know wh... | g10535 | [
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<p>How do I find the values of $x$ for a given wave function $\Psi(x)$ such that it's probability density function $|\Psi(x)|^2$ will be maximized? </p>
<p>My guess is to to constrain the derivative by the conditions $\frac{d\Psi}{dx} = 0$, and then plug those values into $|\Psi(x)|^2$. Is this the right approach?</p... | g10536 | [
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<p>When it comes to questions of existence of bounds for PDE's and such, one must often make some assumptions regarding the topology of the space-time to use well known theorems. </p>
<p>My question is two-pronged:</p>
<p>i) I've often read, on Wikipedia (<a href="http://en.wikipedia.org/wiki/Spacetime" rel="nofollow... | g10537 | [
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<p>Given potential $V(x) = Asec(x)$ for $x > 0$. I want to calculate the ground-state energy $E_0$ via the Schrödinger equation. </p>
<p>I'm completely stuck on this one. I've set up the time-independent Schrödinger equation, but it can't be solved without using special functions. I don't see how I can calculate th... | g10538 | [
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<p>Why is the topological phase in a <a href="http://en.wikipedia.org/wiki/Gaussian_beam#Laguerre-Gaussian_modes" rel="nofollow">Laguerre-Gaussian transverse mode</a> is the sum of orbital angular momenta per photon, and why is it quantized? </p> | g10539 | [
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<p>A yoyo on a horizontal table is being pulled by a string to the right, the table is not frictionless. If we only know that the object doesn't slip, how do we know if the string is winding up or unwinding? My reasoning is initially the friction is not ever effect so the force pulling the yoyo to the right will act a ... | g10540 | [
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<p>I am a biochemistry and molecular biology major. If photons can be absorbed by electrons, wouldn't that mean light has a charge? Electrons only attract positive charges. Isn't it?</p> | g335 | [
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<p>Like the title say, does quark color matter in counting contributions in a early universe plasma (QGP), as when adding up the total plasma energy density, or is it just spin? The book I have (Pathria) only does one example and doesn't really firmly say one way or the other. I kind of thought it was to account for al... | g10541 | [
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<p>I was reading about the planet <a href="http://www.ras.org.uk/news-and-press/217-news2011/2000-alien-world-is-blacker-than-coal" rel="nofollow">TrES-2b</a> which is less reflective than charcoal. What could possibly be its composition?</p> | g10542 | [
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<p>If we currently can look into some of the furthest stars, actually seeing the past<br>
Isn't it conceivable that given enough distance we should be able to see <br>
Parts of the Big Bang? If the Universe is endless, it means we should be able to see into its beginning. <br>
Has this theory ever been presented ? Is t... | g10543 | [
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<p>So tonight's Quatrantids shower got me thinking. Why does the debris from comets and former comets hang around so long? Each year the earth sweeps through the region of space that the comet went through. However, the comet doesn't come by each year, so the earth must be going through the same cloud numerous times... | g10544 | [
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<p>I'm a little confused as to when to use <a href="http://en.wikipedia.org/wiki/Significant_figures" rel="nofollow">significant figures</a> for my physics class. For example, I'm asked to find the average speed of a race car that travels around a circular track with a radius of $500~\mathrm{m}$ in $50~\mathrm{s}$.</p>... | g941 | [
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<p>Suppose we have a spherical surface with a surface charge density varying as $cos(\theta)$. Apparently one can find the electric field both outside and inside such a spherical surface by superposing the fields of two slightly offset charged spheres with uniform volume charge density.</p>
<p>Tips regarding how one g... | g10545 | [
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<p>The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?</p> | g10 | [
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<p>Let's say I have a spinning steel ball that I have somehow managed to be completely free in all axes of movement. If I fire a BB at it with enough force on a north-south (to the ball) angle, what will happen. Will it start to wobble by a certain amount? Will it change it's orientation and then stay there? I welcome ... | g10546 | [
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<p>If time stops inside a black hole, due to gravitational time dilation, how can it's life end after a very long time? If time doesn't pass inside a black hole, then an event to occur inside a black hole needs infinite time relative to the outside. Thus, it will never age.</p>
<p>Please keep it simple..</p> | g10547 | [
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<p>I have seen someone putting a sandstone in water. With only about 10% of the stone sitting in the water. One could see the stone getting soaked with water. So there must be a force, which lets the water climb up through the stone against gravity.</p>
<p>What is that force? Or is there some other effect present?</p> | g10548 | [
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<p>If $A$ is the vector potential, the London equations imply that:</p>
<p>$$(\nabla^{2}-\mu^{2})A=0$$</p>
<p>if there is no external current. This can be interpreted as an effective photon mass and
so, light cannot propagate indefinitely within a superconductor. Let $\lambda = 1/\mu$ be the
London penetration depth... | g10549 | [
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<p>I have <a href="http://astronomy.stackexchange.com/questions/3649/is-the-expansion-accelerating-or-decelerating">already asked this on Astronomy.SE</a> but I couldn't understand the answer there.</p>
<blockquote>
<p>According to Hubble's Law, the farther a galaxy is, the farther it is moving away. But do we take ... | g336 | [
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0.0174084883... |
<p>Here we have a wire. At both ends there is an equal and opposite field caused by a chemical reaction. So, if we decrease or increase the distance between the two points, the strength of the field increases/decreases with the square of distance. Why then is resistance linearly proportional to distance then?</p> | g10550 | [
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<p>I have a question about the mechanism of Cooper instability. I know the naive picture with two interacting electrons and noninteracting fermi sea wchich leads to the bound state formation. However, if you take all electrons into acount and introduce these effective attractive interaction coming from phonon exchange ... | g10551 | [
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... |
<p>Recently, I was studying about Thomson's experiment with cathode rays. My textbook shows it like this. <img src="http://i.stack.imgur.com/GrPY3.jpg" alt="enter image description here"></p>
<p>It says:</p>
<blockquote>
<p>When only electric field is applied, the
electrons deviate from their path and hit the
c... | g10552 | [
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... |
<p>I'm trying to write with a ball-point ink pen on a plastic<sup>[1]</sup> sandwich bag. When I try to write on some parts of the bag, no ink transfers to the bag: I can continue trying for quite a while in vain. I move to another part of the bag, and the ink transfers just fine. Then in other parts of the bag again, ... | g10553 | [
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<p>In many artistic impressions or movies there are pictures or scenes where the sky is filled with an enormous moon (as seen from a planet) or vice versa.
I wonder if there is an upper limit to the apparent size when viewed with the naked eye (no tele lens). Since the Roche Limit forbids celestial bodies coming too cl... | g10554 | [
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0.... |
<p>Just as circumference of circle will remain $\pi$ for unit diameter, no matter what standard unit we take, are the speeds of light and sound irrational or rational in nature ? </p>
<p>I'm talking about theoretical speeds and not empirical, which of course are rational numbers.</p> | g10555 | [
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<p>I know that there are several questions about the naturalness (or hierarchy or fine-tunning) problem of scalars masses in physics.stackexcange.com, but I have not found answers to any of the following questions. Suppose that we add to the SM Lagrangian the following piece:</p>
<p>$(\partial b)^2-M^2 \, b^2-g\, b^2 ... | g10556 | [
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