question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I am studying <a href="http://en.wikipedia.org/wiki/Mesoscopic_physics" rel="nofollow">mesoscopic physics</a>/quantum transport. Now I am wondering (out of interest): how did this field emerge and what made it such a huge field? I couldn't find this somewhere clear on the web and my book lacks an intro in which this... | 2,907 |
<p>I'm solving an exercise about Hamiltonian equations. I have followed the proceeding below. The results given by the book are different to mine because its first result is the half of mine (and the second one linked to the first one is different to mine). I think that my proceeding is correct and so I can't understan... | 2,908 |
<p>If I take a sponge and place it in a shallow dish of water (i.e. water level is lower than height of sponge), it absorbs water until the sponge is wet, including a portion of the sponge above the water level. In other words, it seems the sponge pulls some water from the bath up into itself, doing work, and the water... | 2,909 |
<p>On reading Feynman's lecture on physics, in the geometrical optics section he said that a curve which focuses all the rays coming from a point to another fixed point beyond the refracting surface perfectly is a complicated fourth degree curve which is actually the locus of all point with its distance $Op$ from one ... | 2,910 |
<p>I'm new at classical mechanics but the text book says there is the torque in the spinning top which generated only by gravitation. It is hard to explain the situation, I've add the link.</p>
<p><a href="http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/imgmech/toppre.gif" rel="nofollow">http://hyperphysics.phy-a... | 2,911 |
<p>In hydraulic analogy one compares electrical circuits with water circuits. For the electric case the formula $P = U \cdot I$ for the electric power holds. The analogous formula for water flow would be $P = \Delta p \cdot I_W$ where $\Delta p$ ist the pressure difference and $I_W$ the flow rate of the water through ... | 2,912 |
<p>If an atom is the smallest particle in the universe, does that mean that the spaces in between the atoms in water when being heated (expansion) are vacuum?</p> | 2,913 |
<p>I am studying quantum physics and I have a question: what is the physical explanation for electrons having less energy than photons with the same wavelength?</p>
<p>Energy of a photon : $E = h c/\lambda$.<br>
Energy of an electron: $E = ... | 2,914 |
<p>I am studying a bit granular dynamics and I have seen that two spheres of radius $R$ in contact with a contact area of radius $a$ would need an applied force $F$ on this two spheres that is nonlinear in the depth of deformation $\delta$ as it goes as:</p>
<p>$F \sim \delta^{3/2}$</p>
<p>To be honnest, I am not rea... | 2,915 |
<p>Forgive me if this topic is too much in the realm of philosophy. John Baez has an interesting perspective on the relative importance of dimensionless constants, which he calls fundamental like alpha, versus dimensioned constants like G or c [ <a href="http://math.ucr.edu/home/baez/constants.html">http://math.ucr.edu... | 2,916 |
<p>Today, Korean media is reporting that a team of South Korean researchers solved <a href="http://en.wikipedia.org/wiki/Yang%E2%80%93Mills_existence_and_mass_gap" rel="nofollow">Yang-Mill existence and mass gap problem</a>. Did anyone outside Korea even notice this? I was not able to notice anything in US media. </p>
... | 2,917 |
<p>I have read the paper</p>
<blockquote>
<p>Theoretical Study of Population Inversion in Graphene under Pulse Excitation. A. Satou, T. Otsuji and V. Ryzhii. <a href="http://dx.doi.org/10.1143/JJAP.50.070116" rel="nofollow"><em>Jpn. J. Appl. Phys.</em> <strong>50</strong> no. 7, pp. 070116-070116-4 (2011)</a>.</p>
<... | 2,918 |
<p>I would like to learn the basics about how interstellar matter contracts into stars under the influence of gravity.</p>
<p>Some of my questions:</p>
<p>Let's assume an ideal and infinite large cloud of equally distributed hydrogen atoms of zero K temperature. Will it collapse into a star if there is a small inhomo... | 2,919 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2392/have-the-rowan-university-hydrino-findings-been-replicated-elsewhere">Have the Rowan University “hydrino” findings been replicated elsewhere?</a> </p>
</blockquote>
<p>I came across this... | 60 |
<p>I can't remember what the equation is for the relationship between the force exerted by a coil and the stress in terms of the current density, the radius and the length.</p>
<p>I was thinking just standard F = AB^2 / 2*4*pi*10^-7(Permetivity Of Free Space), but I can't for the life of me figure out how to calculate... | 2,920 |
<p>Can we use entangled particles to transmit information or data such as TCP/UDP packets?</p>
<p>If so why hasn't this been done yet? Surely the costs of bringing this to market are much cheaper than laying submarine cables?</p> | 61 |
<p>recently i wrote an assignment in one of the questions i got two different answers for the same question by considering a straight line motion</p>
<p><strong>The question was somewhat like this</strong></p>
<p><strong>THIS IS A HOMEWORK QUESTION AND I AM NOT ASKING THE EXACT ANSWER I JUST WANT GUIDANCE</strong></p... | 2,921 |
<p>A squeezed vacuum state is produced by applying a squeezing operator $S$ on the vacuum state $|0 \rangle$:</p>
<p>\begin{eqnarray}
S | 0 \rangle = \sum_n C_n |n \rangle
\end{eqnarray}</p>
<p>My question is, from $|0 \rangle$ (which means we have zero photons) we produce the state $| n \rangle$ which has $n$ number... | 2,922 |
<p>EXAFS (Extended X-Ray Absorption Fine Structure), core electron is excited to the conduction band. The oscillations in the absorption coefficient persist for 100s of eV after the edge. </p>
<p>Taking fourier transform of the exafs function gives the R space peak positions that are related to the bond lengths.
<a hr... | 2,923 |
<p>I am attaching a section from a text book (Conical Intersections Electronic Structure, dynamics and spectroscopy: David R Yarkony & Horst Koppel).</p>
<p><img src="http://i.stack.imgur.com/rZway.jpg" alt="enter image description here"></p>
<p>Here I am not understanding the so called 'Non Adiabatic Coupling Te... | 2,924 |
<p>We have done an experiment heating water with a wire element and have determined it takes 21.5964 watts to heat 200ml of water to a specific temperature in 10 minutes. However the power of the electrical input is 29.9859 watts. It asks for an explaination of why they are different but I'm a bit lost</p> | 2,925 |
<p>If you know that the radioactive source is, for example, Cesium-137, is it possible to extrapolate a relationship between the count rate and radiation intensity? If it is not possible, what is the minimum information you need to determine this, e.g. activity?</p>
<p>Furthermore, are the units for radiation intensit... | 2,926 |
<p>How do we know that virtual-particle's virtual-pressure differences caused the plates to collide in the Casimir Effect Experiments. </p>
<p>What about micro-gravitation-fields produced but the plates themselves pulling each other towards one another?</p>
<p>Or Van Der Waal's Forces or some other forces?</p> | 2,927 |
<p>I know it's a simple and basic question but would someone show me how to evaluate $[\hat{p}_x,\hat{p}_y]$?</p> | 2,928 |
<p>This question is a continuation of "<a href="http://physics.stackexchange.com/questions/132654/can-a-third-type-of-electrical-charge-exist">Can a third type of electrical charge exist?</a>" and specifically <a href="http://physics.stackexchange.com/questions/132654/can-a-third-type-of-electrical-charge-exist#comment... | 2,929 |
<p>I am simulating a disordered ising-like model in 2d whose phase transition is expected to be continuous, whose universality class is as yet unknown. By plotting the Specific heat scaling function, i.e., $C L^{-\alpha/\nu}$ vs $tL^{1/\nu}$, I find that the ratio ($\alpha/\nu$) is $\approx 2.44$. Is there a previously... | 2,930 |
<p>I am working on the Ginzburg-Landau model for Charge density waves, and I am carrying out the sum of Green's functions to calculate the terms in the GL model. I have the following question:</p>
<p>Is the sum's order over $ \vec{k} $ (or eventually $ \vec{r} $) and $\omega_n$ important? Mathematically the question i... | 2,931 |
<p>In quantum field theory, one defines a particle as a unitary irreducible representations of the Poincaré group. The study of these representations allows to define the mass and the spin of the particle. However, the spin is not defined the same way for massive particles (where the eigenvalue of the Pauli-Lubanski ve... | 2,932 |
<p>I'm no knowledgeable pool player, but I've noticed that sometimes when the cue ball hits another pool ball, they roll together; and sometimes the cue ball bounces back. And I have a very, very rough sense that a hard, sharp, and even strike of the cue ball tends to make it bounce back more while a slower or more an... | 2,933 |
<p>So I've heard of meteorites "originating from Mars" (e.g. <a href="http://en.wikipedia.org/wiki/Allan_Hills_84001" rel="nofollow">AH84001</a>), but the phrase confuses me. I'm interested in what this means - have these rocks somehow escaped Mars' gravity and ended up here; or were they part of the material that Mars... | 2,934 |
<p><em>(Warning! Newbie question coming up!)</em></p>
<h2>Background</h2>
<p>As seen on this picture of the cosmic microwave background (take from the <a href="http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation">Wikipedia entry</a> on the very same topic) there exists irregularities in the distributio... | 2,935 |
<p>On November 7, 1631 Pierre Gassendi saw the transit of Mercury across the face of the Sun. How did he see it? I mean what instrument was used to reduce the apparent brightness of the Sun?</p> | 2,936 |
<p>I carefully read the Wikipedia article <em><a href="http://en.wikipedia.org/wiki/Discovery_of_Neptune" rel="nofollow">Discovery of Neptune</a></em>, and I don't get what the irregularity of Uranus orbit was that lead to the discovery of Neptune. Years ago, I watched some educational film that schematically showed th... | 2,937 |
<p>If the earth was flat, would the transition between day and night be sudden?</p> | 2,938 |
<p>When I read descriptions of the many-worlds interpretation of quantum mechanics, they say things like "every possible outcome of every event defines or exists in its own <em>history</em> or <em>world</em>", but is this really accurate? This seems to imply that the universe only split at particular moments when "even... | 908 |
<p>When I push a wall with my hand, the wall does the same and because <strike>both forces cancel out</strike> the sum of the forces applied by me on the wall and the wall on me is zero, plus the friction on the ground to keep me from sliding, neither me or the wall is displaced from its position.</p>
<p>Is there a p... | 2,939 |
<p>I am perplexed by recent papers by 't Hooft giving an explicit construction for an underlying deterministic theory based on integers that is indistinguishable from quantum mechanics at experimentally accessible scales. Does it mean that it is deterministic complexity masquerading as quantum randomness?</p>
<p><a hr... | 2,940 |
<p>I like some 'science' in my 'science fiction', so I started crunching out the kinematic equations for some of the scenarios my characters are getting involved in, and ran smack dab into an issue. (Please excuse my formatting, I can't figure out sub/superscript notations)</p>
<p>$v_f = \sqrt{2ad}$, with $v_i$ assum... | 2,941 |
<p>I'm reading a book about string theory, and it tells me in the future it could be possible to detect existence of other bubble universes through cosmic background radiation. Is this true? What could we potentially see?</p> | 2,942 |
<p>Are timelike diffeomorphisms really redundancies in description in quantum gravity? Certainly Yang-Mills gauge transformations can be considered redundancies in description. Ditto for p-form electrodynamics. Even spatial diffeomorphisms too. What about timelike diffeomorphisms? If they are, do the only real degrees ... | 2,943 |
<p>My second grader thought making a <a href="http://en.wikipedia.org/wiki/Homopolar_motor" rel="nofollow">homopolar motor</a> for her science experiment would be fun. And, it was. Now I am trying to explain how it works and the Lorentz force. Please help me by giving me a very simple explanation to what is turning out... | 2,944 |
<p>Imagine a boxcar with a lamp on the left end and a mirror on the right end, so that a light signal can be sent down and back. The boxcar is moving to the right with velocity v. They find the length of the boxcar with respect to the car itself and then with respect to an observer on the ground using time dilation. Th... | 2,945 |
<p>I would like to ask how the result of interference changes with the change of polarisation angle difference? Obviously we get the best results for 2 parallel polarised beams, and no intensity interference effects for orthogonally polarised, however what happens in the middle? I heard it's changing with $cos\Delta\ph... | 2,946 |
<p>I have a particle near two Schwarzschild black holes. Let the black holes remain at rest so that only the particle is moving for the observer. We are in a plane. I calculate the distance travelled by the particle in one frame for each black hole, using Schwarzschild solution. Now the problem is if it is possible to ... | 2,947 |
<p>recently, I stumbled accross a concept which might be very helpful understanding quasiparticles and effective theories (and might shed light on an the question <a href="http://physics.stackexchange.com/questions/2506/how-to-calculate-the-properties-of-photon-quasiparticles">How to calculate the properties of Photon-... | 2,948 |
<p>The question relates to <a href="http://physics.stackexchange.com/questions/23083/why-is-the-higgs-boson-spin-0">this post</a>.</p>
<p>Spontaneous symmetry breaking is somehow a volume effect, that in-principle only happens at infinity large system. Weinberg in the second volume of his QFT used a chair demostrated ... | 2,949 |
<p>Excuse me for long prehistory. Maybe it can be useful for someone.</p>
<p>I was little confused with spinor indices when getting an expression relating the spinor and antisymmetric tensors. An antisymmetric tensor $M_{\mu \nu}$ have an expression (in spinor formalism)</p>
<p>$$
h_{ab\dot {a}\dot {b}} = \left((\sig... | 2,950 |
<p>We say the universe is expanding, and by expanding we mean the distance between objects gets larger over time. We call that "Metric Expansion of the Universe". So far so good. I kind of get the idea about of distances getting larger. </p>
<p>Now, I think of a balloon's surface and the distance between two arbitrar... | 62 |
<p>I am trying to investigate the relationship between velocity and drag force of falling object in air. I used video analysis from logger pro to determine the displacement of the falling object at different time, and then differentiation to find velocity and acceleration. Drag force at each time interval is found by s... | 2,951 |
<p>Wave equations take the form:</p>
<p>$$\frac{ \partial^2 f} {\partial t^2} = c^2 \nabla ^2f$$</p>
<p>But the Schroedinger equation takes the form:</p>
<p>$$i \hbar \frac{ \partial f} {\partial t} = - \frac{\hbar ^2}{2m}\nabla ^2f + U(x) f$$</p>
<p>The partials with respect to time are not the same order. How c... | 188 |
<p>In this <a href="http://www.cs.princeton.edu/courses/archive/fall05/frs119/papers/feynman85_optics_letters.pdf" rel="nofollow">paper</a>, Feynman gave the idea of creating a time-independent Hamiltonian from a quantum circuit. Is there anyway to say that these Hamiltonians will always be Hermitian? Moreover, will th... | 2,952 |
<p>I am a beginner to study QFT and confused about path integral for boson or fermion.</p>
<p>I have read about the path integral for single particle, and finished some problems. But I cannot understand the next chapter which is about path integral for boson and fermion. </p>
<p>Here, I am confused for a long time. C... | 2,953 |
<p>Is there a way to view the Airy Pattern as an infinite sum of Fraunhoffer diffraction patterns? I don't know where the 1.22 would come from then. Is there something inherently wrong with collapsing diffraction slits to infinitely small slits?</p> | 2,954 |
<p>There is this thing I got confused:</p>
<p>Microcausality is the statement that spacelike separated local field variables commute so that we can specify field variables on a spatial slice as a complete base. It is usually referred to as a statement about locality---if microcausality is broken then the "local" opera... | 2,955 |
<blockquote>
<blockquote>
<p>Suppose an observer $\mathcal{O}$ uses the coordinates $t$, $x$, and that another observer $\mathcal{O}'$, with coordinates $t'$, $x'$, is moving with velocity $\mathbb{v}$ in the $x$ direction relative to $\mathcal{O}$. Where do the coordinate axes for $t'$ and $x'$ go in the spaceti... | 2,956 |
<p>A guy who has a career in medical physics named Pierre-Marie Robitaille argues in two recently published papers in “Progress in Physics”, that the CMB is not from the big bang but from the oceans. </p>
<p>The first paper is entitled WMAP: A Radiological Analysis. This work analyzes the WMAP images based on accepted... | 355 |
<p>I have heard that the presence of an extremely strong gravitational field possesses the capacity to warp or tear spacetime and to potentially create a wormhole. Is any energy lost when spacetime is ripped, and if so is there a constant energy per volume required to 'rip' a given region of spacetime? Otherwise, is ... | 2,957 |
<p>I would like to compare my result in an order of magnitude. So, How can I estimate the strength of the electric field in a typical Si PN-junction?</p> | 2,958 |
<p>Let's assume we have a capacitor of capacitance $C$ and potential difference $U$. After charging it we disconnect it. Then we put a dielectric between the plates. I know that capacitance will increase by $C * k$, however what happens with the charge and potential difference on it.</p>
<p>Let's say $k = 2$. Will $q$... | 2,959 |
<p>I had very well read that when charge is stored on a rough surface, the leakage is very high from the pointed tips of such surfaces, by a phenomenon called action of points. But now, I've come to know that if a surface is over-polished (or say ideally polished), it becomes very difficult to store charge on it. I'm c... | 2,960 |
<p>I'm reading these <a href="http://www.maths.dur.ac.uk/~dma0saa/lecture_notes.pdf" rel="nofollow">notes</a> - page 8 and 9 - and I'm a bit confused.</p>
<p>If we consider a field $\phi$ (which can be either bosonic or fermionic) transforming as:
\begin{equation}
\phi(x) \rightarrow \phi(x) + \delta \phi (x)
\end{equ... | 2,961 |
<p>Given a general metric, $g_{ab}$ I can select an orthonormal basis $\omega^{a}$ such that,</p>
<p>$$g_{ab} = \eta_{ab}\omega^a \otimes \omega^b$$</p>
<p>where $\eta_{ab}$ = $\mathrm{diag}(1,-1,-1,-1).$ We may conveniently compute the spin connection and curvature form by employing Cartan's equations. The problem I... | 2,962 |
<p>I have read that <strong>Gaussian surface</strong> cannot pass through discrete charges. Why is it so?
I have even seen in application of Gauss' Law when we imagine a Gaussian Surface passing through a charge distribution, e.g. in case of infinite plane charge carrying sheet .</p>
<p>If it cannot pass through dis... | 2,963 |
<p>Consider the following game show: two friends Tom and Jerry (X and Y) are selected from an audience to compete for a grand prize, a brand new Ferrari. </p>
<p>The game description: </p>
<ol>
<li><p>The two contestants are space-like separated.</p></li>
<li><p>Each contestant will be asked one of three questions {A... | 2,964 |
<p>The contraction in most images looks like a gravity well. Is it that you use negative energy to BOTH contract and expand space or positive and negative to contract (positive energy) and then expand with then negative energy?</p> | 2,965 |
<p>In a different thread, a user stated the following in respect of events preceding or following other events:</p>
<blockquote>
<p>However, if the two events are causally connected ("event A causes event B"), the causal order is preserved (i.e. "event A precedes event B") in all frames of reference.</p>
</blockquot... | 2,966 |
<p>I was wondering the other day about teletransportation (human). And I had the idea that as far as I know, matter is energy. So I was wondering if it's possible to excite matter so it turns into energy, energy which may be could be moved to another physical location and then it would be allowed to return to it's orig... | 2,967 |
<blockquote>
<p>A 1 meter long rod on the ice with mass $m_2=1$ kg is perpendicularly hit on one end by a point particle with mass $m_1=0.1$ kg. The collision is elastic and the point particle is bounced back in the same direction. After the collision the rod's frequency is $\nu =2$ Hz. What was the initial velocity ... | 2,968 |
<p>An air stream is created by a propeller at velocity $\nu = 93.6\frac{m}{s}$</p>
<p>To calculate force applied by the propeller I used this formula:</p>
<p>$$F=\frac{1}{2}\rho\nu^2A$$</p>
<p>where:</p>
<ul>
<li><p>$\rho = 1.29 kg/m^3$ is the air density</p></li>
<li><p>$\nu = 93.6\frac{m}{s}$ is the air velocity<... | 2,969 |
<p>Is there any way in which air can be made to reflect light? By making air denser or by any other way? The task is to project images in air...</p> | 2,970 |
<p>How does a body on the surface of the earth apply a force on the ground? Since neither the body nor the surface of the earth is in motion, there is no acceleration and, hence, there can be no force because force equals mass times acceleration. </p> | 63 |
<p>If <strong>light</strong> is switched ON, only for a second, and the distance between the observer and the light source is 10 million kilometers, can I still see the light spark?</p>
<p>For example, let's assume that the source is the Sun and the observer is a human eye.</p> | 2,971 |
<p>If I understand entropy correctly, then for example two objects orbiting a centre of mass have lower entropy than when said objects eventually crash into each other and form a new one.</p>
<p>So let's say that a typical galaxy spirals around its centre of mass and eventually objects within it will fall into the cen... | 2,972 |
<p>Assume that a coin is placed on circular disk and now a disk is rotated with constant angular velocity.</p>
<p>If there is no friction between the surfaces of a disk and coin, according to theory the coin will move away from centre of disk. But I have confusion here that the centripetal and centrifugal forces are o... | 64 |
<p>Does anyone know, is a model with lagrangian
$\mathcal{L} = \frac{(\partial_{\mu}\phi_a)^2}{2}-\frac{m^2 \phi_a^2}{2}-\frac{\lambda}{8N}(\phi_a \, \phi_a)^2$ renormalizable? I'm using BPHZ scheme and everything is OK in one loop. But it seems to me (may be I'm mistaken) that the scheme breaks down even in two loops.... | 2,973 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/48543/do-some-half-lives-change-over-time">Do some half-lives change over time?</a> </p>
</blockquote>
<p>Would it be possible to considerably speed up the decay rate of an isotope?<br>
Considerably mean... | 65 |
<p>At the page 336 of Hawking, Ellis: <em>The Large Scale Structure of Space-Time</em>, the Gauss-Bonnet theorem is stated as</p>
<p>$$\int_H \hat{R}\ d\hat{S} = 2\pi \chi(H) \qquad (1)$$</p>
<p>with</p>
<p>$$\hat{R} = R_{abcd} \hat{h}^{ac} \hat{h}^{bd}$$</p>
<p>and induced metric on the horizon $\hat{h}_{ab}$,</p>... | 2,974 |
<p>Admittedly, Nuclear Physics is not my strength. I'm writing a simulation to model alpha-decay. So far, I have looked up the values of the kinetic energy of the alpha particles that are emitted in a certain decay. Now I have seen this a lot of times, for instance for 212-Polonium:</p>
<p><strong>$^{212}$Po -10.3649 ... | 2,975 |
<p>I am reading Bailin and Love's review on Kaluza Klein theories. On section 4.1 they start talking about infinitesimal isometries generated "with a particular generator $t_a$ of the isometry group".</p>
<p>$I+id\sigma{}t_a$ $y^n\to{}y'^n=y^n+d\sigma{}\xi_a^n(y)$</p>
<p>where the $\xi_a^n(y)$ are just killing ve... | 2,976 |
<p>I'm not sure the Physics StackExchange is the perfect place for this environmental/applied physics question, but as I found no forum more fitting I ask my question here. Otherwise please move my question.</p>
<p><strong>Main Question</strong></p>
<p><strong>In which direction will the fumes move when leaving the e... | 2,977 |
<p>This is a Homework problem so please feel free to not answer and just give pointers.</p>
<p>A localized wavepacket is given as:</p>
<p>$$\Phi(r,t=0 ) = \frac { e^{-\large\frac {r^2}{2s^2}} e^{\large\frac{i\pi x}{4a}} } {(2\pi^{\frac{3}{4}}s^\frac{3}{2})}$$</p>
<p>Find the group velocity (given by: $v_g = \frac{d\... | 2,978 |
<p>I once worked as a kitchen porter over a winter season.<br>
We had fun with thermal temperature guns (like <a href="http://www.amazon.co.uk/tag/infrared%20thermometer/products" rel="nofollow">these</a>) which I learned can be used for measuring the temperature of something a reasonable distance away (aside from the ... | 2,979 |
<p>I usually wonder which thermodynamics first law is better to use ? </p>
<p>The one given by physics : $\Delta U=Q-\Delta W$</p>
<p>or the one by chemistry : $\Delta U=Q+\Delta W$</p>
<hr>
<p>In other words, should I take the gas as my system and take every parameter in its terms?</p> | 2,980 |
<p>Suppose that an asteroid) that moves at a velocity $v$ passes near to a planet: now I know that the gravity force of the planet will curve the trajectory of the asteroid so I tried to make a draw of the asteroid while passing near the planet using vectors but as result the planet <strong>ALWAYS</strong> falls into ... | 2,981 |
<p>How does one know whether, in treating a certain problem, one should consider particles as waves or as point-like objects? Are there certain guidelines regarding this?</p> | 2,982 |
<p>It maybe a stupid question, but from the Ehrenfest's theorem, we have
\begin{eqnarray*}
\frac{d\langle A\rangle}{dt} &=& \left\langle\frac{\partial A}{\partial t}\right\rangle + \frac{1}{i\hbar}\left\langle[A,H]\right\rangle
\end{eqnarray*}
The if we apply it to the Hamiltonian,
\begin{eqnarray*}
\frac{d\lan... | 2,983 |
<blockquote>
<p>This question is part of <a href="http://meta.physics.stackexchange.com/a/5171/8563">this week's Journal Club session</a>.</p>
</blockquote>
<hr>
<p>These systems look ridiculously fun to construct. Could someone explain the particulars? What are the various types of solutions, and what are their dy... | 2,984 |
<p>Thanks if you take the time to read this. Here is the problem statement:
<img src="http://i.stack.imgur.com/Xne8Y.png" alt="problem statement"></p>
<p>The problem I'm getting is that I'm not getting the kinetic energy diagonal when I convert to the coordinates that diagonalize the potential energy. If you scroll al... | 2,985 |
<p>Can the firewall be viewed as the holographic boundary?
Naively a hologram 3d image can not cross the hologram 2d surface that produces that image. According to the metaphor the boundary - 2d field quantum theory without gravity - could act as a firewall for the enclosed space - 3d string theory with gravity and bla... | 2,986 |
<p>When talking about gamma ray or x-ray propagation in media, we usually talk about the mass attenuation coefficient, and we desire high density materials for shielding. This seems probabilistic: we increase the shielding to maximize the chance of EM radiation interacting with the media.</p>
<p>However, conductivity ... | 2,987 |
<p>In about 7 Billion years our planed will be consumed by the ever-growing sun, life would have become extinct long before that. That means that in several hundred thousand years we have a deadline to either:</p>
<p>1) Move earth to a higher orbit to keep it from heating up<br>
2) Move our civilization to Mars and be... | 2,988 |
<p>I am solving a CLASSICAL an-harmonic oscillator problem with Hamiltonian given by
$H= (1/2)\dot{x}^2+(1/2)x^2-(1/2)x^4$ with all the constants (k's) and mass being taken as 1 (one).</p>
<p>I find that $x= \tanh(t/\sqrt{2})$ is satisfying the equation of motion. </p>
<p>But my question is how to incorporate the Ha... | 2,989 |
<p>Please consider the circuit diagram below, in particular, look at the capacitors enclosed by the green loop.</p>
<p><img src="http://i.stack.imgur.com/dybm1.jpg" alt="enter image description here"></p>
<p>*Note that the green loop and the (+) and (-) charges on the plates were drawn by me, the original circuit has... | 2,990 |
<p>In classical mechanics, if I want to view the Earth as the fixed center of the solar system, I must accelerate my reference frame to keep it centered on the Earth. That accelerated reference frame causes all sorts of messy fictitious forces that push the stars and planets around(<a href="http://physics.stackexchang... | 205 |
<p>I'm trying to solve this elementary problem. I'm studying mathematics, but there is a compulsory course in physics that has to be passed. I'm having an exam in 5 days and I have some doubts on problems like this:</p>
<blockquote>
<p><img src="http://i.stack.imgur.com/Y72Td.jpg" alt="enter image description here">... | 2,991 |
<p>As per Newton objects with mass attract each other, and per Einstein this is further explained by saying that mass warps space-time. So a massive object makes a "dent" into space-time,
a gravity well. I have taken to visualizing this as placing a object on a rubber sheet and the
resulting dent, being the gravity fie... | 2,992 |
<p>I'm using CERN library's libmathlib.a and libkernlib.a, downloaded from <a href="http://cernlib.web.cern.ch/cernlib/version.html" rel="nofollow">this site</a>, and running on Ubuntu linux to do <a href="http://mbtools.hepforge.org/" rel="nofollow">Mellin-Barnes integrals</a> with f77 fortran code in i386 mode (hence... | 2,993 |
<p>Is the concept of inertia still used? When is it useful as a <em>fictitious force</em>?</p>
<p>Can you list a few situations in which, if we didn't use this tool we might be in difficulty?</p> | 2,994 |
<p>Reading a <a href="http://physics.stackexchange.com/questions/2460/time-travel-and-random-events-closed">previous closed question</a> an interesting variation has come to my mind.</p>
<p>Suppose that time travel to the past was possible:</p>
<ul>
<li>I wait for an atom to decay and measure the time, $t_{1a}$ </li>... | 2,995 |
<p>Some friends and I were at Disneyland this past week. We spent an hour arguing back and forth whether it is possible for someone to throw an NFL football over the Matterhorn? I think it is, but no one else really thought it was possible.</p>
<p>What do you guys think? Is this humanly possible?</p>
<p>The Matter... | 2,996 |
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