question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I have read on several sites that this is a theory that cannot be tested. Why is this a theory that can not be tested? It seems to me that if the mass of particles is continually increasing, then the wavelength of a spectral line emitted by an atom would also be continually changing. This means that over a length ... | g9259 | [
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<p>It is often stated, particularly in popular physics articles and videos, that if one measures a particle A that is entangled with some other particle B, then this measurement will immediately affect the state of the entangled partner.</p>
<p>For example, if Alice and Bob share an entangled pair of electrons and Ali... | g61 | [
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<p>When you attach a bolt to something using a nut, it is clear what the roles of the nut and bold are. </p>
<p><img src="http://i.stack.imgur.com/JC94D.jpg" alt="enter image description here"></p>
<p>The more you tighten the bolt the more secure your fastening. However, you are often also told to use a washer as wel... | g9260 | [
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<p>Let there be two objects that have zero relative velocity with respect to each other in an inertial frame. If they both undergo identical accelerations, but one starts the acceleration at t = T1 and the other starts the acceleration at t = T2, then per special relativity the maximum distance that rest frame can mea... | g9261 | [
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<p>$xp$ is not a hermitian operator and hence doesn't represent an observable. Then, how can we interpret the expression</p>
<p>$$
\langle x p \rangle \text{,}
$$</p>
<p>the expectation value of position times momentum?</p>
<p>How to interpret the expectation value of a hermitian operator, say $p$, is clear: make se... | g9262 | [
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<p>I was hoping someone could help me with understanding why a row of polarizes reflects a light wave when the whole row is the same length as the wavelength of the light.</p>
<p><img src="http://i.stack.imgur.com/kdcDG.gif" alt="Liquid crystals"></p>
<p>I pretty much get the physics behind the rest, just don't under... | g9263 | [
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<p>Which is the smallest particle that has been actually seen by the scientists? When I say "actually seen", (may be using some ultra advanced microscope or any other man made eye, using any wavelength or phenomena) I really mean it; just like we have seen the <a href="http://www.wellcome.ac.uk/stellent/groups/corpor... | g9264 | [
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<p>If there was a standing sound wave tube and a flammable gas was introduced then ignited, would the combustion be more forceful and more efficient since its following a standing wave, than just a gas ignited within a tube?</p> | g9265 | [
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<p>This question is refered to those who are familiar with the concept of weak measurement.</p>
<p><strong>In short:</strong></p>
<p>How can the polarization of a photon be coupled to the position of a pointer state? What is the pointer state? The position of some particle? How to realise that in a lab?</p>
<p><stro... | g9266 | [
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<p>I have been study about Veneziano amplitude and Virasoro Shapiro amplitude.
I want to summarize this two amplitude in the following way, please check that i am understand them properly.</p>
<p>Veneziano amplitude : they are open string amplitude for disk.
Usually we called four-open string tachyon on disk as Vene... | g9267 | [
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<p>Let $V_1$, $I_1$, $R_1$ and $V_2$, $I_2$, $R_2$ be voltages, currents, resistance in first, second circuit.</p>
<p>And we assume $R_1=R_2$, $I_1\neq I_2$.</p>
<p>The conservation of electrical power $P=V_1I_1=V_2I_2$ holds in the transformer circuits.</p>
<p>Hence $I_1^2R_1=I_2^2R_2$, $R_2=(I_1^2/I_2^2)R_1$ which... | g9268 | [
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<p>Is entanglement necessary for quantum computation?
If there was no error in the computation,superposition of states would be sufficient for quantum computation to be carried out.Is this right?</p> | g9269 | [
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<p>I live in Seattle and am thinking of purchasing a telescope. Is fall/winter a decent time of year for viewing (aside from summer)? Are there any major viewings/events during that this of year?</p>
<p>I know I live in a city of rain, but there are some nice nights. </p> | g9270 | [
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<p>Is this photo "real"? Are the stars not super-imposed in the image?</p>
<p> <img src="http://i.stack.imgur.com/BvJZ0.jpg" alt="galaxy"></p> | g9271 | [
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<p>Quarks and leptons are considered elementary particles, while phonons, holes, and solitons are quasiparticles. </p>
<p>In light of emergent phenomena, such as fractionally charged particles in fractional quantum Hall effect and spinon and chargon in spin-charge separation, are elementary particles actually more <em... | g9272 | [
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<p>Consider this penny on my desc. It is a particular piece of metal,
well described by statistical mechanics, which assigns to it a state,
namely the density matrix $\rho_0=\frac{1}{Z}e^{-\beta H}$ (in the
simplest model). This is an operator in a space of functions depending
on the coordinates of a huge number $N... | g9273 | [
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<p>It's obvious that as you increase the payload of a rocket, you need to also increase the amount of rocket fuel. Yet, as you increase the amount of rocket fuel, you are also increasing the overall mass of the rocket and, therefore, require even more fuel to get the rocket off the ground.</p>
<p>From this observation... | g305 | [
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<p>In both string theory and soliton theory, moduli spaces are frequently used. </p>
<p>As far as I known, for soliton theory, moduli spaces are something like collective coordinates for solitons, and for string theory, moduli spaces is the spaces of all metrices divided by all conformal rescalings and diffeomorphisms... | g9274 | [
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<p>A conductor that passes a magnetic field, decreases its velocity due to the opposing magnetic forces created by the Eddy Currents.</p>
<p>This "magnetic breaking" effect can be reduced if we change the shape of the conductor from a bar, to a this conductor like this:</p>
<p><img src="http://i.stack.imgur.com/0NFr5... | g9275 | [
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<p>It is one of the axioms of special relativity that the <a href="http://physics.stackexchange.com/q/16018/2451">photon has no rest frame</a>; light travels at speed c when measured in any inertial frame of reference. As a corollary, it is often said that if one <em>were</em> in a photon's rest frame, infinite time-di... | g9276 | [
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<p>Is there a word or phrase for when someone is testing for a certain result thereby skewing his findings? </p> | g9277 | [
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<p>What substance will have the largest specific heat capacity integrated from T=0 to, say, room temperature? In other words, given a finite amount of mass, what object or collection of objects has the largest number of degrees of freedom that can be excited as it absorbs energy starting from T=0? Would it be a compl... | g9278 | [
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<p>I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean?</p>
<p><strong>Edit:</strong> Is an XX spin chain in a magnetic field gapped? Why or why not?</p> | g9279 | [
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<p>Does Wick rotation work for quantum gravity? The Euclidean Einstein-Hilbert action isn't bounded from below.</p> | g9280 | [
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<p>Does a relativistic version of quantum thermodynamics exist? I.e. in a non-inertial frame of reference, can I, an external observer, calculate quantities like magnetisation within the non-inertial frame? </p>
<p>I'd be interested to know if there's a difference between how to treat thermodynamics in a uniformly acc... | g9281 | [
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<p>The Higgs mechanism allows massless fields to acquire mass through their coupling to a scalar field. But if the masses cannot be predicted because the couplings have to be fixed, what really is the utility of the Higgs mechanism? Instead of saying "Here are <em>a priori</em> couplings; the Higgs mechanism generates ... | g9282 | [
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<p>Classical electromagnetism says an accelerated charge would radiate. Is this understood in QED? </p>
<p>Is there QED derivation of Larmor's formula?</p> | g9283 | [
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<p>I have applied for a summer project in <a href="http://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_quantum_computer" rel="nofollow">NMR quantum computing</a> as I want to learn this field, but my professor wants me to tell him the project title. I have no idea about the field and what projects are good. Please ... | g9284 | [
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<p>I had this problem for a candidacy exam, but wasn't able to get the complete answer. Their spring constants and masses are not the same, find the equilibrium position and frequencies of the system. Apparently once you find their equilibrium position, i.e. when gravity and the spring forces cancel out, you can transf... | g9285 | [
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<p>I'd guess it has to do with the structure of helium-3 allowing for greater Coulomb repulsion between the protons, but I'm unsure.</p> | g9286 | [
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<p>When you stick ice in a drink, AFAICT (the last physics I took was in high school) two things cool the drink:<ul><li>The ice, being cooler than the drink, gets heat transferred to it from the drink (Newton's law of cooling). (This continues after it melts, too.)<li>The ice melts, and the cool liquid mixes with the d... | g9287 | [
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<p>Consider a closed system (say a box) of $n$ particles. There is a well-known idiom/meme/law in classical mechanics that says that the position and momentum of those $n$ particles is all that is needed to determine the future and past configuration of the system. (A minor question, does this idiom have a name?)</p>
... | g9288 | [
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<p>Analogy: an infinite number of lines can pass through a point.
Is there a limit on the number of lasers that can pass through a point?
Obviously, with lasers the “point” would be a sphere with the diameter of the beams. </p> | g9289 | [
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<p>I know that for close by stars (<50 LY) we can use the parallax effect. And for distant galaxies we use red-shift (& hubble's constant). So how do we measure how far is a star lets say 50,000 LY from the earth?</p>
<p>I know I am missing something, I just don't know what. </p>
<p>How can we assume there is ... | g9290 | [
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<p>Let us consider a rod having a young's modulus $Y$. Let it be of length $l$, and suppose it is suspended from a point P. Let us pull the rod with a force $F$ at a point Q which is at a distance $2/3l$ from the point P. Next let us apply the same force at the other end point of the rod. Is the length of the rod in b... | g9291 | [
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<p>Let us consider an ideal gas. Let it be present initially in a state $(p_1,v_1,t_1)$. Now let it be driven to another state $(p_2,v_2,t_2)$. Why is it so that during this process the maximum work can be obtained if the ideal gas is transformed from one state to another by a reversible process ?</p> | g9292 | [
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<p>I'm having trouble understanding the motivation for the definition of the expectation of a self adjoint operator $A$:</p>
<p>$$\langle A \rangle _\psi=\int_{\mathbb{R}}\psi^*A\hspace{0.2cm} \psi \hspace{0.2cm} dx$$</p>
<p>where $\psi(x,t)$ is a normalised state.</p>
<p>I can understand the expectation of the posi... | g9293 | [
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<p>Suppose an ideal gas in a piston cylinder has some initial pressure $p_1$, volume $V_1$, and temperature $T_1$. A pin, which holds the piston in place, is suddenly removed, and the gas quickly expands. Once equilibrium is reached, the final pressure of the gas is $p_2$.</p>
<p>I am looking at a textbook solution ... | g9294 | [
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<p>Does back emf occur in transformers and if so does it reduce the efficiency of the transformer and can it be reduced?</p> | g9295 | [
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<p>A large thick copper wire(or bar if you like,) passes a magnetic field. What formula is best to calculate the $EMF$ here?</p>
<p>$$\epsilon = \frac{\Delta \Phi \
}{\Delta t} $$</p>
<p>or,</p>
<p>$$\epsilon = -vBL $$</p>
<p>Example:</p>
<p><img src="http://i.stack.imgur.com/n8r6i.png" alt="enter image d... | g9296 | [
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<blockquote>
<p>Two thermally iso- lated cylinders, A and B, of equal volume, both equipped with pistons, are connected by a valve. Initially A has its piston fully withdrawn and contains a monatomic gas at temperature $T_0$, while B has its piston fully inserted and the valve is closed. Calculate the final gas tempe... | g9297 | [
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<p>I have a homogeneous thin rod $AB$. $A$ can slide along $z$-axis, $B$ along $xy$ plane. There is no friction. We have any initial conditions. Now the question is to write down the equation of motion of the rod.</p>
<p>It is assumed that I don't know Lagrangian mechanics. I believe I should write some conservation t... | g9298 | [
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<p>I am building a truck from trash as materials. I have one small motor and a a few small gears, but no other engineered materials are allowed. The truck must carry a load for a distance of 3m. The winning truck is the truck with the greatest ratio of load carried:time.</p>
<p>What do you think would be the best appr... | g9299 | [
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<p>Electroweak symmetry breaking is manifested by the nonzero masses of the weak W and Z bosons, and requires the existence of a Higgs boson or some other yet unseen mechanism. To solve the problem of flavor.</p>
<ul>
<li><p>why there are six quarks and six leptons forming three families?</p></li>
<li><p>why these par... | g9300 | [
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0... |
<p>We start with the metric tensor
\begin{equation}
g_{\mu\nu}(x) = \eta_{\mu\nu} + h_{\mu\nu}(x)
\end{equation}
in the linearised theory, or
\begin{equation}
g_{\mu\nu}(x) = \bar{g}_{\mu\nu}(x) + h_{\mu\nu}(x)
\end{equation}
in the more general case with a curved background. However, in both cases, we apparently nee... | g9301 | [
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<p>I have been under the impression that chirality is at least in part a way to sneak in a Lorentz invariant version of helicity for particles that mass. <a href="http://www.quantumdiaries.org/2011/06/19/helicity-chirality-mass-and-the-higgs/">Flip Tanedo</a> seems to espouse this view in <a href="http://www.lepp.corne... | g9302 | [
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<p>I'm developing a 2D game including collisions between many disks. I would like to know how I can get the angle corresponding to the new direction of each disk.
For every disk I have this information : <strong>direction</strong> (integer), <strong>speed</strong> (float), and <strong>position</strong> ($x$;$y$, which... | g136 | [
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<p>Many introductory quantum mechanics textbooks include simple exercises on computing the de Broglie wavelength of macroscopic objects, often contrasting the results with that of a proton, etc.</p>
<p>For instance, this example, taken from a textbook:</p>
<blockquote>
<p>Calculate the de Broglie wavelength for</p>... | g379 | [
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0.0... |
<p>Consider the concept of these videos <a href="http://www.youtube.com/watch?v=Zip9ft1PgV0&sns=em" rel="nofollow">http://www.youtube.com/watch?v=Zip9ft1PgV0&sns=em</a> and <a href="http://www.youtube.com/watch?v=cUhgKFV5Ri4&sns=em" rel="nofollow">http://www.youtube.com/watch?v=cUhgKFV5Ri4&sns=em</a> bu... | g9303 | [
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0.0191... |
<p>How do I calaculate the amount of heat energy radiated from the sun in one minute?? Well, i tried some stefan method, but the answer seems far off from the correct one....well, i would thus strongly want to have some help in this regard..</p> | g9304 | [
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<p>From what I have read, the problem with modern semiconductors/electronics seems to be quantum tunnelling and heat. The root of these problems is the size of the devices. The electrons are leaking out, and currents are causing active materials to melt.</p>
<p>How far have we become in this regard? Can we make our de... | g9305 | [
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<p>Say we have a single, solid circular loop of wire rotating at a constant angular velocity in a uniform magnetic field. There is an induced EMF creating a current in the wire. <em>At the absolute minimum</em>, we should be able to say that the potential V is 2pi periodic (it should have a single value at a single p... | g9306 | [
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<p>The current is maximum through those segments of a circuit that offer the least resistance. But how do electrons know beforehand that which path will resist their drift the least?</p> | g510 | [
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<p>I've read that free neutrons decay into a proton, electron and neutrino with an average lifespan of about 15 minutes. Is there anything physically different about a neutron that has existed for 14 minutes and one that has only existed for one minute? Does a random outside event trigger the decay or is something inte... | g9307 | [
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<p>Okay. I have two ways of working out the height of the atmosphere from pressure, and they give different answers. Could someone please explain which one is wrong and why? (assuming the density is constant throughout the atmosphere)</p>
<p>1) $P=h \rho g$, $\frac{P}{\rho g} = h = \frac{1.01\times 10^5}{1.2\times9.81... | g9308 | [
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<p>If both electrons are in ground state, characterized by $(1s)^2$, this means that n =1, l = 0. The two electrons occupy the same energy and space (why doesn't pauli exclusion principle prevent this?), so the spatial part is symmetric. </p>
<p>So in order for the state to obey fermi-dirac statistics, the overall wav... | g9309 | [
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<p>It happened to me quite often (most recently with my wireless keyboard) that a battery stopped to work and then, if I unplug it and then plug it back in it works again, not just for a couple of minutes but even for a day or two, then you can repeat the process but this time it will last less and so on until it fina... | g9310 | [
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<p>I recently learned about breeder reactors, which are able to create more fissile material than they consume. They seem to be superior to the types of nuclear reactors currently in use. What are the reasons why breeder reactors are not more prevalent.</p> | g9311 | [
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<p>I had this Homework Problem with a capacitor (parallel plate) that has a group of 3 dielectrics between it like so : </p>
<p><img src="http://i.stack.imgur.com/WbQx2.jpg" alt="Descriptive Image"></p>
<p>Now We were asked to find the equivalent capacitance and the distance of separation between the plates was $d$ a... | g9312 | [
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<p>From the perspective of a far-away observer, matter falling into a black hole never crosses the boundary. Why doesn't a basic symmetry argument prove that Hawking radiation is therefore also frozen on the boundary, and therefore not observable? Wouldn't the hawking radiation have to have started its journey before t... | g9313 | [
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<p>To my knowledge if you calculate the coordinate time (time experienced by an observer at spatial infinity) it takes an infinite amount of time for an object to fall past the horizon of a Schwarzschild black hole. Doesn't this imply that it takes an infinite amount of coordinate time for a Schwarzschild Black Hole to... | g9314 | [
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<p>Is there an easy (aka intuitive) way to understand that the conserved quantity from time translation symmetry is just what we call energy?</p>
<p>In other words, we use two definitions of energy. One is with Noethers theorem, and I've been told this is the fundamental one. The other is what is you learn in school a... | g9315 | [
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<p>Can a Feynman diagram end with more matter than it began with? The answer should be no because it would break the law of conservation of mass, right?</p>
<p>Example:
I learned that two up-quarks could interact to create a Higgs boson (via what I learned as "vector fusion"). If this new Higgs were to decay into an u... | g9316 | [
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-0.004710642620921135,
0.... |
<p>The equation of motion of a general anharmonic oscillator includes a position-dependent force that can be expanded in a Taylor series as</p>
<p>$$m\ddot{x}+2\mu\dot{x}+k_0+k_1x+k_2x^2+k_3x^3\ldots=F.$$</p>
<p>I am considering a case with force $F$ higher than the critical amplitude, which means I'm in the <a href=... | g9317 | [
0.03287733346223831,
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... |
<p>In this video, a pool of liquid nitrogen in a metal bowl can cool it enough so that oxygen from the air condenses at the bottom:</p>
<p><a href="http://www.youtube.com/watch?v=Ojl10zMCYkY&list=PLmyvBUHJ4pVC3FrSXsT_5S7dFMKPLG_pS&index=1" rel="nofollow">http://www.youtube.com/watch?v=Ojl10zMCYkY&list=PLmy... | g9318 | [
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<p>Imagine we have two thermodynamic systems, one a mass of ice and the other an equal mass of liquid water, with both at 273.16K. Each system is isolated, except that they can interact with each other across a boundary that permits the exchange of heat but not matter or work.</p>
<p>What will the two systems look lik... | g9319 | [
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... |
<p>There is a somewhat widely accepted argument that the second law of thermodynamics exists because the universe began in a low-entropy state. I'm writing a paper that mentions this (and must be finished today), but I've realised that I don't know who originated this idea. So does anyone know the original reference fo... | g9320 | [
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<p>So on a homework assignment, we are give the width of a well, $a$, and the mass of the particle $m$ and we want to find the average velocity of the particle at the n=1 state. So here is my attempt at the solution:</p>
<p>Using, $\psi (x) = \sqrt{\frac{2}{a}} sin(\frac{\pi x}{a})$, I was able to integrate
$$\langle... | g9321 | [
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0.008010939694941044,
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0... |
<p>I'm reading Quantum Field Theory and Critical Phenomena, 4th ed., by Zinn-Justin and on page 154 I came across the statement that the functional integral of a functional derivative is zero, i.e.
$$\int [d\phi ]\frac{\delta F[\phi]}{\delta\phi^{\alpha}(x)} = 0$$ for any functional
$F[\phi ]$. </p>
<p>I would be mos... | g9322 | [
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0.00... |
<p>Herbert Dingle and H. Bondi debated the twin paradox on BBC radio before 1971. Does anyone have a link to the audio of this debate? thanks</p> | g9323 | [
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<p>If I have a grounded conducting material, then I know that $\phi=0$ inside this material, no matter what the electric configuration in the surrounding will be. </p>
<p>Now I have a conducting material that is not grounded, then there will be (as long as I am dealing with static problems) no electric field inside th... | g9324 | [
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<p>I have been doing some research on all kinds of sound-related topics lately and have been a bit confused by the different uses of the term "frequency". Of course, the most general meaning of frequency is just how many times something happens during a certain period of time (a second, usually). However, I've also com... | g9325 | [
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<p>As far as i know Zeppelins were abandoned because they were not safe, back in time. Is it still the case in 2011 though? In my opinion it is more economical to operate a Zeppelin than a plane and they are more stable as there is less acceleration so the interior has tables and chairs etc.</p> | g9326 | [
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<p>Black hole complementarity states that two observers, one falling into a black hole, and one observing outside, experience two different histories but since they can not communicate there is no inherent contradiction..imagine an observer far from a black hole watching some matter fall into a black hole. The observe... | g9327 | [
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<p>My question might be based on a false premise, so here's why I asked. If you look up the meaning of the moment magnitude scale for measuring earthquake size, the articles usually say that each increase in magnitude by 1 point represents a tenfold increase in the amplitude of the wave, but a 31.6 increase in energy... | g9328 | [
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<p>I was watching an outtake of Prof. Brian Cox talking to a tv producer about "gravity waves". Their discussion got a bit side-tracked, because the non-scientist didn't seem to understand what a wave "would look like", and also because there seemed to be some difficulties with the phrase "moving through", with Prof C... | g9329 | [
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<p>What is the exact dependence of the refractive index of air and the temperature? Is there a theoretical derivation of it?</p> | g9330 | [
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<p>When reporting barometric pressure, weather stations normalize the
result to sea level using a well-known formula (approximately, add 1
inch to the measured pressure for every 1000 feet above sea level, but
I believe the formula they use is more precise). </p>
<p>Does a similar concept exist for temperature? As ... | g9331 | [
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<p>If the universe is made up of ~95% dark matter, and it interacts only gravitationally then why didn't Newton and Kepler discover it before ? Why does it show itself only in the radial velocity profile of stars in galaxies and not in that of planets around the Sun ?</p> | g9332 | [
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<p>The mass of the car is 1500 kg. The shape of the body is such that its aerodynamic drag coefficient is $C_D=0.330$ and the frontal area is $2.50 m^2$. Assuming that the drag force is proportional to $v^2$ and neglecting other sources of friction, calculate the power required to maintain a speed of $100 km/h$ as the ... | g9333 | [
0.038309987634420395,
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<p>I'm solving the heat equation with time dependent boundary conditions numerically in a 2D system using the <a href="http://en.wikipedia.org/wiki/Alternating_direction_implicit_method" rel="nofollow">ADI scheme</a>. For the purpose of this question, let's assume a constant heat conductivity and assume a 1D system, so... | g9334 | [
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<p>Suppose a particle p of three momentum $\vec p$ decays into two particles of 3-momentum $\vec p_1$ and $\vec p_2$. I know the question might sound stupid but right now my brain is full stop:
Is the following "ok" $$\langle \vec p_1, \vec p_2 \vert \vec p\rangle = (2\pi)^3 \delta^3(\vec p-\vec p_1-\vec p_2)?$$ If on... | g9335 | [
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<p>Is something special for a quantum system with infinite degeneracy like free particle levels?
$E=\frac{\hbar^2 \vec{k}.\vec{k}}{2m}$</p>
<p>Edit: I mean what is physical (or mathematical) significance of infinite degeneracy? </p> | g9336 | [
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<p>From Sakurai eq. 6.4.21a we have that
$$\langle {\bf k} \vert E,l,m \rangle=\frac{\hbar}{\sqrt{M k}}\delta\left(E-\frac{\hbar^2 k^2 }{2M}\right) Y_l^m({\bf\hat k}),$$ where $M$ is the mass of the particle in question. Now I wonder what the generalization of this formula is. What if we have a two particle system whe... | g9337 | [
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0.... |
<p><strong>Quantum entanglement</strong> is one of the most fascinating and mysterious phenomena in nature. It needs no interactions, or any sort of exchange for it to take place. It is possible, not against any rules of physics as far as we know, that all matter that was created in the early universe was in an entangl... | g9338 | [
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... |
<p>I’ve a got a question; and I am hopeful that you can provide any information or direct me to a better resource. I'm not a physicist; so please correct me if I'm wrong.</p>
<p>Scanning Probe Microscopy (SPM) can be used to probe and map the surface of electrical potential distribution. For example, let’s say that a ... | g9339 | [
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0.06547190994024277,
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<p>According to the paper <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.47.6573&rep=rep1&type=pdf" rel="nofollow">Quantum Mechanics Beyond Hilbert Space</a> by J.P. Antoine, several mathematical structures have been devised to make mathematical sense of Dirac's formulation of quantum mechani... | g9340 | [
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<p>I am looking for a book explaining physics from, say, Galileo and Newton till now;
the book should be written using some math, similarly to my physics books when
I was at the university (Halliday Resnik). I am searching a book that take care of explaining the true "evolution" of reasoning, discoveries, experiment to... | g9341 | [
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0.033146608620882034,
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0.05222539231181145,
0.03892... |
<p>Which will go further if a batter manages to hit it with a baseball bat: a baseball thrown to the batter at 90 miles per hour or one thrown at 60 miles per hour?</p> | g9342 | [
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0.008249080739915371,
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<p>I am in the middle of a discussion with a friend about the meaning of the term "clockwise".</p>
<p><a href="http://en.wikipedia.org/wiki/Clockwise">Wikipedia</a> indicates that a clockwise rotation goes as <strong>top-right-down-left</strong>.</p>
<p>However, my friend argues that "the clock is facing opposite to ... | g9343 | [
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0.08131523430347443,
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... |
<p>This might be a little naive question, but I am having difficulty grasping the concept of irreducible tensors. Particularly, why do we decompose tensors into symmetric and anti-symmetric parts? I have not found a justification for this in my readings and would be happy to gain some intuition here. </p> | g9344 | [
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<p>I once had an old microscope, that included a projection screen that could be mounted instead the eyepiece. It showed a quite decent palm-sized image. </p>
<p>Now I have a new microscope, and removed the eyepiece to mount a single lens reflex camera. However, the image projected on the ground glass, and also on the... | g9345 | [
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<p>I was going through Griffiths chapter on potentials and fields just to brush up on a few old things. He gets to <a href="http://en.wikipedia.org/wiki/Jefimenko%27s_equations" rel="nofollow">Jefimenko's equations</a> by this general path: </p>
<ol>
<li><p>Maxwell's equations</p></li>
<li><p>Introduce scalar and vect... | g9346 | [
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0.00027334204060025513,
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0.014401311054825783,
0.03256356343626976,
... |
<p>Of course, I mean that the edge of the disk is traveling at the speed of light. This is a question that popped into my head a few years ago when I was learning about some basic relativity in high school.</p>
<p>According to what I learned, if an object were to move at near-light-speed, it would be "compressed" alon... | g306 | [
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0.015053555369377136,
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0.04344206675887108,
-0.03098... |
<p>This is a question I've been mulling over for a while and I'm hoping someone here can point me in the right direction. Sorry if it's a bit of a novice question. For the record, I don't fully know GR, but don't let that stop you from using it in the answer.</p>
<p>Since the universe is expanding - that is, the space... | g9347 | [
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<p>Suppose we have 1 kg of wood and 1 kg of uranium and if we need to find out how much energy would each of the substance give, we'd have to use Einstein's mass-energy relation as follows:</p>
<p>In the case of wood, $E_{wood} = 1 × (3×10^8)^2 = 9 × 10^{16} J$</p>
<p>In case of Uranium, $E_{uranium} = 1 × (3×10^8)^2... | g9348 | [
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<p>I'm reading often that a possible reason to explain why the Nobel committee is coping out from making the physics Nobel related to the higgs could be among other things the fact that the spin of the new particle has not yet been definitively determined, it could still be 0 or 2.</p>
<p>This makes me wonder if the s... | g9349 | [
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<p>I found this part in the book of Bernard Schutz on GR. (Sec 12.2: General Relativistic Cosmological Models). </p>
<blockquote>
<p>Robertson-Walker metrics: We shall adopt the following assumptions about the universe: (i) spacetime can be sliced into hypersurfaces of constant time which are perfectly homogeneous a... | g9350 | [
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<p>if the potential is bounded below $ V(x)=V(-x) \ge a $ for some real number a</p>
<p>and we can be sure that as $ x\rightarrow \infty $ we know that $ V(x) \ge 0 $ then does it mean that the energies for our one dimensional system will be positive ??</p>
<p>my idea WKB quntization $ N(E)= 2\int_{0}^{a} \sqrt {E_{n... | g9351 | [
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<p>We know the Schrodinger equation for free Hamiltonian is : </p>
<p>$$
i\hbar\frac{\partial\psi}{\partial t} = H_f \psi
$$
the wave function could be written as
$$
\psi(x,t)=\hat{S}(t) \psi(x,0)
$$
$$
\hat{S}(t)=\exp\left(-\frac{i}{ \hbar }H_ft\right ) .....(1)
$$
I want to know that how exponential term arisen in... | g9352 | [
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0.0... |
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