question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>A plane is flying southeast at 215 km/h. Suddenly there is a wind from the north at 75 km/h. What is the plane's new velocity with respect to the ground in standard position? </p> | g18673 | [
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<p>I have a problem, I have a bi-vector that define like: </p>
<p>$\omega^{\mu \nu}=a^{\mu}b^{\nu}-a^{\nu}b^{\mu}$</p>
<p>where,</p>
<p>$a^{\mu}=(a^0,a^1,a^2,a^3)$
and
$b^{\nu}=(b^0,b^1,b^2,b^3)$</p>
<p>I need show that $\Lambda^{\mu}{}_{\nu}=\exp(\alpha \omega^{\mu}{}_{\nu})$ and the explicit form like a matrix.</... | g18674 | [
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<p>"There is nowhere in the universe where the laws of physics are violated." Considering this general to be true,can i conclude that everything is pre-decided? I can explain this in the following manner: consider a photon or nerve impulse travelling in our brain at this exact moment,in accordance with the above theory... | g18675 | [
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<p>The maximum tension in the string of the pendulum is three time the minimum tension.If x(angle) is the amplitude of the pendulum then find cos(x)</p> | g18676 | [
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<p>I can't seem to find any information about how parallel capacitors or capacitors in a series affect how much a capacitor can charge, not in my textbook or online. Here is the question I am trying to answer: </p>
<blockquote>
<p>You have a capacitor that you will connect across a battery. If you wish to increase t... | g18677 | [
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<p>I have been going through the Preskill lecture notes on quantum computation, and there is a question on Quantum Bit Commitment:</p>
<blockquote>
<p>Alice wants to make a prediction, either $0$ or $1$, before an event. She doesn't want Bob to know her prediction beforehand, but wants to be able to prove to him aft... | g18678 | [
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<p>What is the physical explanation for the dependence for the freeze-out temperature $T_\text{F0}$ of the neutrons as a function of the number of degrees of freedom $g^\star$?</p>
<p>$$T_\text{F0}=\left(\frac{1.66}{G_F^2m_\text{PL}}\right)^{1/3} g_\star^{1/6} $$</p>
<p>Why does the temperature rise, implying that th... | g18679 | [
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<p>OK so I'm trying to understand why the angle of a pendulum as a function of time is a sine wave.</p>
<p>I can't really find an explanation online and when I do find something partial there are certain symbols I don't understand.</p>
<p>$$\frac{d^2\theta}{dt^2} + \frac{g}{l}\sin\theta = 0$$</p>
<p>This is the equa... | g18680 | [
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<p>I understand that the Bernoulli effect is a flawed explanation for the cause of lift, and does not cause much at all, but <em>how much</em>? </p>
<p>Is there any experimental data on the force caused by the Bernoulli effect? Maybe implicitly through data of the pressure difference between the top and underside of a... | g18681 | [
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<p>I was doing a physics experiment, and i encountered a question which i couldnt answer. The experiment was about using a radar technique to measure the speed of sound. The apparatus was a plastic tube 90cm long and the sound source was a speaker connected to a function generator. The generator was sending a square wa... | g18682 | [
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<p>In a superconductor I have read that the energy gap can be defined as the energy difference between the ground state and the virtual excitations of the system. Is this the energy required to form a cooper pair?</p> | g18683 | [
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<p>What is the difference between <em>quantum mechanics</em> and <em>quantum physics</em>?</p> | g18684 | [
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<p>I am receiving unknown units of speed from another system. I must divide the value by 32 to get meters per second. What units do I use to refer to the values I'm receiving? Is there any such unit? Is this just random malice from the previous developers? Google give me nothing.</p> | g18685 | [
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<p>I encountered this in the context of using squid microscopy to test for d-wave pairing in an iron arsenide superconductor where the goal of the experiment was to detect half integer flux quantum transitions to indirectly observe a change in the order parameter.</p> | g18686 | [
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<p>From my limited physics knowledge i know that gravity when compared to Electromagnetic forces is very weak... So if every object is polarized (positive and negative separation), then on a bigger level shouldn't galaxy's have this too?<br>
So then this could explain why galaxy's are repealing away from each other wit... | g18687 | [
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<p>Suppose a satellite is orbiting the Earth. The gravitational and centripetal force supposedly point towards the Earth. Therefore, the net force is towards the Earth. Since the satellite doesn't fall immediately towards the earth, what's the third force holding the satellite in orbit? First impression tells me its th... | g18688 | [
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<p>So I am given a 2-dimensional harmonic oscillator with $H=H_1+H_2$ where
$$H_i=\frac{p_i^2}{2m}+\frac{1}{2}m\omega^2x_i^2$$
Additionally,
$$L=x_1p_2-x_2p_1$$
If we define
$$A=\frac{1}{2\omega}[H_1-H_2]$$
$$B=\frac{1}{2}L$$
$$C=\frac{-i}{\hbar}[A,B]$$
Where [A,B] is the commuatator of A with B. We are asked for the... | g18689 | [
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<p>In the <a href="http://books.google.com.ua/books?id=Tpk-lqyr3GoC&pg=PA99&lpg=PA99&dq=charge%20conjugation%20majorana%20%20lifshitz&source=bl&ots=yokDyfOAxC&sig=oqSfh2MAyTAGaj3Pj1pg9J6ikJs&hl=ru&sa=X&ei=P8zyUr-yO5HIswbG0oCACg&ved=0CGoQ6AEwBQ#v=onepage&q=charge%20conjugation... | g18690 | [
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<p>I know one associates to each symmetry transformation a unitary/antiunitary operater...etc. </p>
<p>But equation 3.123 in Peskin and Schroeder (PS) says that parity is implemented as $(\mathbf{p}$ is the three momentum)</p>
<p>$$P a_{\mathbf{p}}^sP = \eta_a a_{\mathbf{-p}}^s \tag{1}, $$
where $P$ is the operator i... | g18691 | [
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<p>This is a purely speculative question:</p>
<p>Has there been any work that describes non-locality/entanglement in QM by using exotic topologies in configuration space?</p>
<p>The 'conceptual' picture that I have in mind is of two particles that are distant in the usual topology, but when entangled, being somehow p... | g18692 | [
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<p>Naive reasoning suggests that a string theory vacuum with cosmological constant Lambda1 is always unstable as long as there is a string theory vacuum with cosmological constant Lambda2 < Lambda1 since the later is a state with lower energy density. If it's true, there should be very few stable vacua since these w... | g18693 | [
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<p>Given a completely positive and trace preserving map $\Phi : \textrm{L}(\mathcal{H})\to\textrm{L}(\mathcal{G})$, it is clear by the Kraus representation theorem that there exist $A_k \in \text{L}(\mathcal{H}, \mathcal{G})$ such that $\Phi(\rho) = \sum_k A_k \rho A_k^\dagger$ for all density operators $\rho$ on $\mat... | g18694 | [
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<p>One may find on the web a lot of different computational packages to perform "ab-initio" calculations of electron structure of the solids. Usually, the documentation is not quite transparent about the disadvantages of the methods used. It takes some time to find out whether given package is suitable for you needs. A... | g18695 | [
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<p>Consider $\mathcal{N}=1,d=4$ SUSY with $n$ chiral superfields $\Phi^i,$ Kaehler potential $K,$ superpotential $W$ and action ($\overline{\Phi}_i$ is complex conjugate of $\Phi^i$)
$$ S= \int d^4x \left[ \int d^2\theta d^2\overline{\theta} K(\Phi,\overline{\Phi})+ \int d^2\theta W(\Phi) + \int d^2\overline{\theta} \o... | g18696 | [
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<p>If you heat up water in a tank to boiling point, some of the water will turn to steam. Gas bubbles are created in the water. According to Archimedes principle, the gas bubbles will have a force equal to the weight of what they are occupying. Let's denote this force $F_g$.</p>
<p>$$F_g = \text{Bouyant force of a gas... | g18697 | [
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<p>Does an atom moving towards the light that is falling on it, absorb more energy than when it is stationary?</p>
<p>The atom should a see blue shift due to Doppler effect so the atom will see a light of greater frequency, causing it to absorb a greater amount of energy (or, equivalently, it will absorb less energy w... | g18698 | [
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<p>The following paragraph has been extracted from the Wikipedia (<a href="http://en.wikipedia.org/wiki/Atomic_orbital" rel="nofollow">Atomic orbitals</a>): </p>
<blockquote>
<p>Simple pictures showing orbital shapes are intended to describe the angular forms of regions in space where the electrons occupying the orb... | g18699 | [
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<p>If I have two spheres of the same size and one sphere has a small amount of charge compared to the other that has a lot more charge, then clearly the sphere with the larger charge has a larger voltage (relative to the ground). My question is do high voltage power lines have a lot more charge that is placed on them? ... | g18700 | [
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<p>If an object is at rest on a flat surface I remember my school teacher would say, "By Newton's 1st law the normal reaction, R, is mg (mass x g)". Ok, sure this is fine because the object is at constant velocity (velocity=zero) and so there are no net forces and so the two forces must balance.
But what's wrong with s... | g18701 | [
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<p><a href="http://electronics.stackexchange.com/questions/79447">This popular question</a> about "whether an AC circuit with one end grounded to Earth and the other end grounded to Mars would work <em>(ignoring resistance/inductance of the wire)</em>" was recently asked on the Electronics SE.</p>
<p><img src="http://... | g18702 | [
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<p>Layman here, but EE and BS physics. I know that light is affected by gravity. But are neutrinos? During the collapse of a star into a neutron star, as the electrons join protons to form neutrons (e.g., or the collapse of a star to a black hole?), I read that the only things that can get "out" instantaneously are ... | g18703 | [
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... |
<p>I'm a student trying to understand electricity. As I learned from school, electricity is the flow of electrons, but I'm confused about the measurement of electricity. </p>
<ul>
<li><p>As I learned, voltage is the "pressure" of the electricity, but it's a bit abstract while I try to understand the particle world and... | g18704 | [
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<p>So I'm having trouble understanding velocity gradients conceptually, I have little physics training passed physics 101 (I'm a biologist), but I'm currently working in an endothelium research lab with a lot of fluid physics. I came up with an example in my kitchen and I tried to work it out based on youtube videos of... | g18705 | [
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<p>I guess visible light is visible, because it has the right wavelength to be absorbed (or not) and emitted (or not) by many different molecules. Now visible light has a wavelength in the order of a few hundreds nanometers, while the typical size of a molecule is rather in the order of a few angstrom.</p>
<p>I guess ... | g18706 | [
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<p>This is a question following on from my previous post <a href="http://physics.stackexchange.com/questions/120085/time-like-killing-vector-in-frw-metric">Time-like Killing vector in FRW metric?</a></p>
<p>For simplicity I take the spatially flat FRW metric in cartesian co-ordinates given by:
$$ds^2 = -dt^2 + a^2(t)(... | g18707 | [
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<p>If an object that enters a black hole has its information content frozen at the event horizon, in what sense is it frozen? The usual analogy is of a hologram encoded in 2d which can be decoded into a 3d representation. The same analogy is used in describing the 3d universe we see as a representation of the holograph... | g18708 | [
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-... |
<p>While studying the heat equation, I ran into a few equalities that I cannot understand.</p>
<p>For example, <strong>Fourier's law of heat conduction</strong> claims that</p>
<p>$$\varphi(x,t)=-K_0\frac{\partial u}{\partial x},$$</p>
<p>where $\varphi$ is the heat flux (the amount of thermal energy per unit time f... | g18709 | [
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<p>I need to calculate the surface tension of a liquid with the ring-method of du Nouy and the correct formula to use is: </p>
<blockquote>
<p>$\gamma = \frac{F}{4\pi R}$</p>
</blockquote>
<p>I understand that the surface tension is the force that acts on a certain length which, in this case, is the circumference ... | g18710 | [
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<p>This is a followup question to <a href="http://physics.stackexchange.com/a/69296">this pretty good answer</a> regarding deriving the Boltzmann equation.</p>
<p>What if the center of the target particle is actually not the same with the scattering center (or may not have a scattering center)? For example, see the cl... | g18711 | [
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<p>For example, should we write the dimension of mass, e.g. $\mathrm{kg}$ as $[M]$ or is it enough to write it as $M$? </p> | g942 | [
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<p>Consider a simple circuit with a battery of $\theta\ \text V$s, and two resistors of $R_1 \ \Omega$s and $R_2\ \Omega$s connected in series. Let us assume that $R_1$ is connected nearer to the positive terminal of the battery. We are required to find the power $P_1$ and $P_2$, dissipated in these resistors. </p>
<p... | g18712 | [
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<p>Theoretical <a href="http://en.wikipedia.org/wiki/Cellular_automaton" rel="nofollow">cellular automata</a> have been proposed as models for many physical phenomena from music to quantum mechanics. My question concerns the reverse:</p>
<p><strong>Is there a <em>simple</em> physical system that emulates a theoretical... | g18713 | [
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<p>In <em>F. Schwabl</em>, <strong>Quantum Mechanics</strong> p.148 it is explained that if we have a particle in an electromagnetic field given by potentials $\varphi$ and $\mathbf{A}$ with wave function $\psi$, then a gauge transformation
$$\mathbf{A}'=\mathbf{A} + \nabla\chi\ \ \ \ \ \ \varphi'=\varphi - \frac{1}{c}... | g18714 | [
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<p>I want to ask about the connection for massive and massless representation of the Poincare group. Sorry for the awkwardness.</p>
<p>First I must to represent the formalism for both of cases.</p>
<p><strong>Massive representation</strong>.</p>
<p>There is the formalism for an arbitrary spin-$s$ and massive represe... | g18715 | [
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<p>The unit <strong>bar</strong> for pressure is clearly a metric unit, but its order of magnitude is a bit strange. In the centimeter–gram–second system of units we have:</p>
<pre><code>1 bar = 1 000 000 baryes = 1 000 000 dyn/cm²
</code></pre>
<p>so the bar is not "coherent" with this system (the factor is not one)... | g18716 | [
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0.02054914832115173... |
<p>$\text P$ vs $\text {BQP}$ is an open question. That is, "can systems which require a polynomial number of qubits in the size of an input be described with only a polynomial number of bits?" If the answer is "yes", then the device you're reading this with can factor quickly and do other fun things, whoopee! Most qua... | g18717 | [
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0.... |
<p>Are they spinning around the nucleus? If so what makes them move? I just do not understand how they move or if they are "attracted" to something is it another particle that makes it move.</p> | g579 | [
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<p>We have an action: $$S[\boldsymbol{u}] = \frac{1}{2} \int dt \int d^3x \left\{ \mu (\frac{\partial u_{i}}{\partial t})^{2} - \nu (u_{ii})^{2} - \rho(u_{ij})^{2}\right\} $$</p>
<p>Where $u_{ij} = (\partial_{i}u_{j} + \partial_{j} u_{i} )/2$.</p>
<p>Where index $i = 1,2,3$ denotes the $x$ $y$ and $z$ axis and there... | g18718 | [
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<p>I am fascinated with magnets, and specifically the idea of magnetic levitation. I recently purchased a Levitron toy <a href="http://en.wikipedia.org/wiki/Maglev" rel="nofollow">maglev train</a> and have enjoyed finding the perfect sweet spot at which it levitates, and I understand that the Levitron does not violate ... | g18719 | [
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<p>I am puzzling about an exercise in the book "Electromagnetic Theory" by Ferraro (p.543).</p>
<p>An electron (mass $m$, charge $-e$) in a monopole magnetic field $\vec{B}\left(\vec{r}\right)=g\frac{\vec{r}}{r^3}$ has due to the Lorentz force $\vec{F}_L=-e\vec{v}\times\vec{B}$ the following equation of motion:</p>
<... | g18720 | [
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<p>I just saw a formula in my book for relative error in equivalent resistance of two resistors connected in parallel. </p>
<blockquote>
<p>$\frac{\Delta R}{R^2} = \frac{\Delta R_1}{R_1^2}+\frac{\Delta R_2}{R_2^2}$ </p>
</blockquote>
<p>How do I get derive this formula?</p> | g18721 | [
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0.041... |
<p>My physics background goes as "far" as reading popsci books on QM, Particle Physics, and Cosmology so pardon my ignorance in the below questions.</p>
<p>I've read that the photon is the particle (quanta in QFT) exchanged between electrons, and that is how the electromagnetic force is explained in QFT.</p>
<ol>
<li... | g18722 | [
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-0.02424474... |
<p>In <a href="http://www.youtube.com/watch?v=ZMByI4s-D-Y" rel="nofollow">this video</a>, the woman says that a sphere is a <em>pretty simple object</em>. What intrigues me is the use of a sphere for such a calculation. First of all, the sphere wouldn't be perfect as a perfect sphere doesn't exist in nature (first sour... | g18723 | [
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0.0030619364697486162,
0.09226422011852264,
0... |
<p>I am working through the derivation of the equation
$$pV=\frac13mNC_{rms}^2,$$
but relating to this formula my textbook states that the kinetic energy of an average molecule of gas is given by
$$KE=\frac12mC_{rms}^2$$
but how is this formula right since the mean squared speed ($C_{rms}^2$) is not the same as the a... | g18724 | [
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0.022699875757098198,
0.07346154749393463,
0.0030300382059067488,
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0.025... |
<p>Can I make a heat pump beat the Carnot efficiency? Why is the <a href="http://en.wikipedia.org/wiki/Carnot_cycle" rel="nofollow">Carnot process</a> the most efficient one?</p>
<p>If I have a heatpump that is sphere shaped, and cascaded in layers like a onion can I beat Carnot efficiency? Heat would be transferred a... | g18725 | [
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-0.012380555272102356,
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0.014498851262032986,
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-... |
<p>Simply hot dark matter is not allowed due to free streaming. So do gravitational waves:
a) free stream if not why not?-Surely they can since they are relativistic an weakly interacting.
b) if they free stream is it allowed because they don't dominate the dark matter content?</p> | g18726 | [
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<p>I was just wandering if a <a href="http://en.wikipedia.org/wiki/Gravitino">gravitino</a> could be in the <a href="http://en.wikipedia.org/wiki/Weakly_interacting_massive_particle">WIMP</a> class, because they are both massive (admittedly WIMP's more so) and are both weakly interacting and predicted by R-parity. i.e ... | g18727 | [
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0.020784225314855576,
0.05882679298520088,
0.014637451618909836,
-0.06... |
<p>I have learned that all spinning objects will continue spinning even if no force is acting on it, and the tendency to do so is called moment of inertia. But I wonder about the fact that a single point mass in a spinning rigid body changes direction, even though no force is acting on it. How this is possible? This vi... | g18728 | [
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0.000039153252146206796,
... |
<p>I just bought a small stirling engine which converts heat flow down a temperature gradient into circular motion of a little wheel. If I turn the wheel with my finger, will the engine generate a temperature gradient? </p> | g18729 | [
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<p>Consider an RC car going off a jump. What angle is optimal to achieve the greatest distance? The height of each jump is the same. The angle of the jump and the related length of the jump changes. This is an experiment my son is doing for his 6th grade science fair.</p>
<p>The RC car used is a hobbyist RC car wi... | g18730 | [
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... |
<p>A very large number of small particles forms a spherical cloud. Initially they are at rest, have uniform mass density per unit volume $\rho_0$, and occupy a region of radius $r_0$. The cloud collapses due to gravitation; the particles do not
interact with each other in any other way.</p>
<p>How much time passes unt... | g18731 | [
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0.0158093124628067,
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0.005454436410218477,
0.034548237919807434,
-0.00... |
<p>This is a branch question (from <a href="http://physics.stackexchange.com/questions/110087/what-are-the-variables-at-play-during-magnetic-induction">this question</a>) related to magnetic induction:</p>
<p>These deal with how different configurations of coiled layers might affect the outcome:</p>
<ul>
<li><p>If on... | g18732 | [
0.02814709022641182,
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0.... |
<p>My question is about Einstein notation. It does not matter the specifics of this example (the del operator could be another random vector), I just want to know if my assumption about notation is correct.</p>
<p>I know that cross product or curl
$$\vec b=\vec\nabla \times \vec V = \nabla_iV_j\epsilon_{ijk}\hat e_k$... | g18733 | [
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<p>If the Moon rotates then we should see the dark side right? But as far as I know the Moon only shows one side to Earth, how can this be if it is rotating? </p> | g263 | [
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<p>What's wrong with this general solution of the <a href="http://en.wikipedia.org/wiki/Lippmann%E2%80%93Schwinger_equation" rel="nofollow">Lippmann-Schwinger equation</a>:
$$
|\psi_k \rangle=|\phi_k \rangle+G_k V|\psi_k \rangle
$$
Taking the inner product with $\langle\phi_{k'}|$
\begin{align}
\langle \phi_{k'}|\psi_... | g18734 | [
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<p>More turns -> stronger field<br>
more turns -> longer copper wire<br>
longer copper wire -> more resistance(ohm)<br>
<br>
at what turn does the resistance make the electromagnet weaker? - I want to make an ideal electromagnet.
<br><br>
(Sorry for being vague but I'm looking for some kind of formula or an example) <... | g18735 | [
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<p>Which of these two equations of state are valid?</p>
<p>$$S_1 = L_0 \gamma (\theta E/L_0)^{1/2} - L_0\gamma\left[\frac{1}{2} \left(\frac{L}{L_0}\right)^2 + \frac{L_0}{L} - \frac{3}{2}\right]$$</p>
<p>$$S_2 = L_0 \gamma e^{\theta n E/L_0} - L_0\gamma\left[\frac{1}{2} \left(\frac{L}{L_0}\right)^2 + \frac{L_0}{L} - \... | g18736 | [
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<p>I was reading about the seesaw mechanism in my Lecture notes and got a technical question. See for example
<a href="http://www.lhep.unibe.ch/img/lectureslides/9_2007-11-30_SeeSawMechanism.pdf" rel="nofollow">http://www.lhep.unibe.ch/img/lectureslides/9_2007-11-30_SeeSawMechanism.pdf</a>
page 13.</p>
<p>There it say... | g18737 | [
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<p>Someone told me that units for $G$ and $\epsilon_0$ (<a href="http://en.wikipedia.org/wiki/Gravitational_constant" rel="nofollow">gravitational constant</a> and <a href="http://en.wikipedia.org/wiki/Coulomb%27s_constant" rel="nofollow">Coulomb's constant</a>) are placed there simply to make equations work dimensiona... | g18738 | [
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<p>Recently, there was a <a href="http://www.mit.edu/newsoffice/2011/optical-computing-diode-1123.html" rel="nofollow">publication</a> regarding some new materials that would let thru light in one direction and either absorb it or reflect it in the other direction; the publication does not clarify on which one. It does... | g18739 | [
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<p>From what little I know of general relativity, the equality of inertial and gravitational mass is an axiom of the theory. I suspect that this precludes GR from unifying them in the same sense as electric, magnetic and weak interactions are unified as the electroweak force.</p>
<p>But since the two appear to be equa... | g18740 | [
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<p>There is a nice result that in 3+1 space time, a Yukawa coupling leads to an inverse square law force as the mass of the scalar field goes to zero. I was wondering what the corresponding force in a 2+1 dimensional Universe would be? Geometrically, I would guess that it should be $1/r$ rather than $1/r^2$, but my exp... | g18741 | [
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<p>I'm writing a short story set in an artificial planet-sized sphere with an ecosystem in its inner surface, whose "gravity" is created through spinning.</p>
<p>Energy sources aside, what other interesting physical characteristics should I take into consideration, apart from varying force levels as one moves relative... | g18742 | [
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<p>Suppose there is a DC $1.5\mathrm{V}$ battery connected with $1.5\times10^{-3}\mathrm{\Omega}$ resistor.</p>
<p>Then the amount of circuit current is $I=V/R=10^3\mathrm{A}$. (according to Ohm's law)</p>
<p>I know the formula $P=IV$ which is electrical power.</p>
<p>Finally I got the electrical power of $1500 \mat... | g18743 | [
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<p>In short: Do bouncing balls keep bouncing forever? If not, does it have to do more with energy than velocity?</p>
<blockquote>
<p>Learner.org: Energy</p>
<blockquote>
<p>If energy is conserved, why do bouncing balls, pendulums, and other cyclic systems eventually stop moving? The energy doesn’t disappear... | g18744 | [
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<p>Suppose Saturn simply vanished. How would that affect the rest of the Solar System, specifically Earth?</p> | g18745 | [
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<p>How do I find the date of next crescent moon on wolframalpha or any other site which tells the appearance date time of next crescent on a specific location?</p>
<p><em>I am searching for it to look for 1st of Ramadan</em></p> | g18746 | [
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<p>In other words, what is the proper technique (star-hopping or other?) in order to find and properly point a telescope to this target? Would a star atlas or other tool/reference help? Can I use the R.A. and Dec. coordinates to find such deep-space objects?</p>
<p>I can recognize the constellations around which M31 i... | g18747 | [
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<p>Since the Sun is a gravitational lens with as focal length of 550 AU for visible light, with an immense amplification factor, shouldn't it light up objects hanging out there?</p>
<p>We should get solar sails up there to finally boost them somewhere interesting, opposite to the star that is emitting the light.<... | g18748 | [
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<p>On Earth the Milky Way appears very ghostly when looked at with the naked eye, somewhat easier to see when NOT looking directly at it. Is it substantially easier to see by astronauts in space or is it largely the same?</p> | g18749 | [
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<p>Do we know any neutron stars just below the Tolman–Oppenheimer–Volkoff limit?</p>
<p>And how are they different from most other neutron stars?</p> | g18750 | [
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<p>I was reading about <a href="http://en.wikipedia.org/wiki/Stirling_radioisotope_generator" rel="nofollow">Stirling Generators</a> having potential applications for power generation in outer space. Have Stirling engines ever been sent into space?</p> | g18751 | [
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<p>At night, I can look up and see the Milky Way across the sky. My question is, supposing our solar system was, instead of way out on an 'arm' of the galaxy, if we were near the galactic center. Would the night sky be much brighter?? If so, how close would we have to be to never have darkness of night??</p>
<p>Thanks... | g18752 | [
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... |
<p><strong>Wikipedia article:</strong> <a href="http://en.wikipedia.org/wiki/Rietdijk%E2%80%93Putnam_argument">http://en.wikipedia.org/wiki/Rietdijk–Putnam_argument</a></p>
<p><strong>Abstract of 1966 Rietdijk paper:</strong></p>
<blockquote>
<p>A proof is given that there does not exist an event, that is not alrea... | g18753 | [
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<p><strong>Harmonic Oscillator</strong> </p>
<ul>
<li>$\displaystyle \Delta x\Delta p_x = \hbar (n+\frac{1}{2})$</li>
</ul>
<p><strong>Particle in a box</strong></p>
<ul>
<li>$\displaystyle \Delta x\Delta p_x = \frac{\hbar}{2} \sqrt{(\frac{n^2\pi^2}{3}-2)}$</li>
</ul>
<p>We notice that for small n the product is ... | g18754 | [
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<p>the scattering integrals for fermions involves both momentum ($k$) and energy ($k^2$) conservation and a nonlinear phase space factor of a distribution function $f(k)$.</p>
<p>$$\begin{multline}I(k) = \sum_{k_1, k_2, k_3} \delta(k^2+k_1^2+k_2^2+k_3^2) \delta(k+k_1+k_2+k_3)\times \\
\Bigl[f(k)f(k_1)\bigl(1-f(k_2)\b... | g18755 | [
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<p>I was wondering if say I use an magnet which is facing positive and then I expel an another magnet above it which is facing the positive with its positive side and I ensure the magnet does not rotate or change its face via say and small string so its always facing positive will face positive. As a result (I hypothes... | g18756 | [
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<p>Ordinarily we consider the path of a charged particle under the influence of a magnetic field to be curved. However, in order for the trajectory of the particle to change, it must emit a photon. Therefore, in principle, if we were able to view the path of the particle at sufficiently high resolution, would its path ... | g18757 | [
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<p>Is any percentage of the regular solar wind charged ions able to penetrate the earth atmosphere?
if so, can it be detected or measured on the surface of earth at sea level?</p> | g18758 | [
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<p>Testing a capacitive screen, it's clear that it can tell the difference between a celery touching it (human holding it with an isolating material) and a human touching it. Touching it holding a celery, but no isolating material works too.</p>
<p>So, what is the range of 'normal' capacitive potential of a human body... | g18759 | [
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<p>Are there any libraries available for solving problems at the level of college physics?</p>
<p>In particular, I'm interested in libraries for general purpose programming languages that can calculate results both numerically <em>and</em> symbolically.</p>
<p>Libraries which could be used for implementing something ... | g18760 | [
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<p>My question is: when a electromagnet is activated, the field must take time to form at both ends and stabilize. What is this time? Or, to put it differently, what is the speed at which the magnetic field forms?</p> | g18761 | [
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<p>1) Can a state be entangled without also being a superposition? (Please give an example.) </p>
<p>2) Can a state be a superposition without being entangled? (Again, an example please.) </p>
<p>3) And what about a cat state? </p>
<p>I am royally confused, and a little bit of googling didn't help.<br>
This quest... | g18762 | [
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<p>I am not a professional physicist, so I may say something rubbish in here, but this question has always popped in my mind every time I read or hear anyone speak of particles hitting singularities and "weird things happen". </p>
<p>Now to the question at hand, please follow my slow reasoning... As far as I've learne... | g18763 | [
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<p>A boson field can be understood as a collection of stationary modes (e.g. plane waves of various polarizations), and for each mode there is a quantum harmonic oscillator. If the QHO for some mode is in an energy eigenstate $|n\rangle$, we interpret this as meaning that the field constains $n$ particles in that mode... | g18764 | [
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<p>Just a simple question. Does a muon detector on Earth's surface correctly measure the mean lifetime of a muon? I would think the answer is no because most muons detected are created about 15 km above Earth's surface, so on average they will have survived for some amount of time calculated using special relativity be... | g18765 | [
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<p>I have a bottle filled with a fluid A, and a tube of volume $V_0$ filled with a fluid B leading away from it.
When I now start pumping fluid A out of the bottle, I am interested in the concentration $c(V)$ of fluid A in fluid B at the end of the tube after the volume $V$ exited the tube.</p>
<p>In my second situati... | g18766 | [
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<p>Okay, so I just read through huge sections of <a href="http://gordonwatts.wordpress.com" rel="nofollow">http://gordonwatts.wordpress.com</a>, which I found quite interesting. There are some questions that really came to my mind.</p>
<p>Do a lot of particle physicists use windows computers? (relative to other physic... | g18767 | [
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<p>There are well-documented methods of calculating the impulse response of a room (ex. <a href="http://home.tiscali.nl/ehabets/rir_generator/rir_generator.pdf" rel="nofollow">image method</a>, ray-tracing method); however, I have not been able to find anything similar for the impulse response of an arbitrary solid giv... | g18768 | [
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0... |
<ul>
<li><p>I would like to know how does Polchinski in his book "derive" what is the "tachyon vertex operator" (..as say stated in equation 3.6.25, 6.2.11..) I can't locate a "derivation" of the fact that $:e^{ikX}:$ is the tachyon vertex operator. </p>
<p>(..I understand that it follows from some application of the ... | g18769 | [
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0... |
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