question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Im working through Zee and I'm having a little trouble with some integrals. I'm trying to reproduce the analogue of the inverse square law for a 2+1 D universe and I figured I could start with the statement for the energy
$$E=-\int \frac{d^2 k}{(2 \pi)^2}\frac{e^{i \vec{k}\cdot (\vec{x}-\vec{y})}}{k^2 + m^2}=-\int_{... | 5,832 |
<p>Look at this <a href="http://en.wikipedia.org/wiki/Subatomic_particle" rel="nofollow">here.</a> With respect to the sciences, the atom is obviously not the smallest piece of mass. Apparently, if people have already broken down the atom in to particles smaller than so, why haven't particles been understood yet?</p>
... | 5,833 |
<p>In my understanding the <a href="http://www.fyzikalni-experimenty.cz/en/mechanics/atmospheric-pressure-upside-down-glasses-of-water/" rel="nofollow">well-known</a> experiment of the glass full of water in equilibrium with a piece of paper, the atmospheric pressure acts on a small layer inside the glass (on the top) ... | 5,834 |
<p>So, i'm going over the Thorne's derivation of the quadrupolar radiation term, and they write the core term as:</p>
<p>$$ \frac{3 r_i r_j - 2 r^2 \delta_{ij}}{4 r^5} $$</p>
<p>But if i try to obtain this term by <em>Covariant</em> deriving the dipole term;</p>
<p>$$ \nabla_{ij}{ \frac{1}{r}} = - \nabla_{j}{ \frac{... | 5,835 |
<p>Building a bronze stature we make a mold and pour in the liquid bronze when the bronze hardens we remove the mold.
The mold is made of 3 Kg of steel and the statue has a mas of 1 Kg. The specific heat of bronze is 360 and the specific heat of steel is 165
If we cool the statue and the mold from 500 degrees C by dro... | 5,836 |
<p>If the Higgs field permeates all space, why some claim, that total universe energy equals (or is very close to) zero?</p> | 5,837 |
<p>I have read that holes in <a href="http://en.wikipedia.org/wiki/Semiconductor" rel="nofollow">semiconductor</a> are nothing but vacancies created by electrons. But how can this vacancy i.e. hole has a mass?</p> | 5,838 |
<p>The following question was posed at the end of Maury Goodman's June 2012 <a href="http://www.hep.anl.gov/ndk/longbnews/">long-baseline neutrino newsletter</a>.</p>
<blockquote>
<p>During the Venus transit of the sun, were more solar neutrinos
absorbed in Venus, or focused toward us by gravity?</p>
</blockquote>... | 5,839 |
<p>We might be killed if a bullet penetrates our brain. How about an elementary particle moving with high energy penetrates our brain? </p>
<p>Assume that we can have exactly a single elementary particle for this imaginative experiment.</p> | 5,840 |
<p>Here is a link to an article from phys.org describing what the scientists (M. Sonnleitner at the University of Innsbruck and Innsbruck Medical University in Austria, M. Ritsch-Marte at Innsbruck Medical University, and H. Ritsch at the University of Innsbruck) in the article call the blackbody force. <a href="http:/... | 5,841 |
<p>I'm trying to make an application for Hooke's law using a spring, but the law doesn't give any correct result with my spring, because when I hang a $100\,\mathrm{g}$ object on the spring it's elongates about $0.3\,\mathrm{cm}$ and when I hang a $200\,\mathrm{g}$ object the spring elongates about $1\,\mathrm{cm}$ whi... | 5,842 |
<p>I mean, when you have a full bathtub and then let it empty, under what conditions does a whirlpool form?</p>
<p>Could we devise an experiment and measure this effect? When it comes to fluids, I don't know why I can't think of anything to test a hypothesis.</p> | 135 |
<p>About a year ago I attended a talk at the University of Ottawa. The author described a method for achieving super time resolution images of a neuron firing. From what I can recall, the group found a small protein that acted as a photovoltaic cell (produced a voltage pulse in response to a photon) and engineered it t... | 5,843 |
<p>In Nekrasov et al's series papers <a href="http://arxiv.org/abs/hep-th/9803265" rel="nofollow">MNS</a>, they calculate such kinds of integral
$$ \frac{E_1 E_2}{N(2\pi i)^N(E_1+E_2) }\oint d\phi_1 \wedge d\phi_2\wedge \ldots\wedge d\phi_N \prod_{i<N} (-\phi_i) \prod_{i}(\phi_i+E_1+E_2) $$
$$\times \frac{\prod_{i\n... | 5,844 |
<p>I am having a bit of a tough time understanding the following:</p>
<pre><code>|____O____| <- 0A
|____O____| <- 12A
|____O____| <- 24A
| | <- 36A
|_[|||||]_| <- 36A
Legend:
O - A small lamp with 1Ω resistance.
[|||||] - A 12V battery.
</code></pre>
<p>There is 12V flowing across eac... | 5,845 |
<p>I'm looking for a way to construct a representation for a simple Lie group such that one particular subgroup is manifest. I learned the branching rules from Cahn, Georgi and Slansky, but I'm still not sure how to derive the explicit representation from the weight system deformed by extended Dynkin diagram?</p>
<p>T... | 5,846 |
<p>Is there any way to affect a particle's momentum value?</p> | 5,847 |
<p>For example, let's consider a $N$ spin-1/2 system on a lattice described by the Hamiltonian $H$. My questions are:</p>
<p>(1) If $H$ has <em>either</em> global $SU(2)$ spin-rotation symmetry <em>or</em> time-reversal symmetry, then $\forall $ <strong>finite</strong> $N=$odd, there must be <strong>exact degenerate</... | 5,848 |
<p>In <a href="http://www.isfdb.org/cgi-bin/title.cgi?47559" rel="nofollow">the 1944 SF story “Off the Beam” by George O. Smith</a>, an electron gun is constructed along the length of a spaceship. In order to avoid being constrained by a net charge imbalance, it is built to also fire the same number of protons in the o... | 5,849 |
<p>I was trying to reproduce example 3.3 of <a href="http://arxiv.org/pdf/quant-ph/0001106v1.pdf" rel="nofollow">Quantum Computation by Adiabatic Evolution</a> by Edward Farhi et. al. This is an adiabatic algorithm to solve an instance of three qubits 2-SAT problem.</p>
<p>I think I have created the initial Hamiltonia... | 5,850 |
<p>A radio antenna creates EM waves through switching the polarization in the antenna at a certain frequency. I assume the the energy of the photons produced in this process amount to E=hf for each photon. So good so far, but classically, i read that the EM field is an oscillation of the electric field between positi... | 5,851 |
<p>So sound is a wave and is basically just vibrations, an atom vibrates causing another next to it vibrate and so on until it finally reaches our ears to become sound.</p>
<p>If that's normally how waves behaves, what about light? I understand it's also a particle but <strong>something must have caused its starting p... | 206 |
<p>When considering the Doppler shift, the 'canonical equation' is
$$f=\frac{c+vr}{c+vs}f_0$$</p>
<p>However, this equation seems to run into trouble in the following situation: A light source inside water is moving at a speed $v$ towards a receiver outside the water. Can we modify the above equation to deal with a t... | 807 |
<p>Powerful <a href="http://en.wikipedia.org/wiki/LASER" rel="nofollow">lasers</a> are highly intense, diverge negligibly and are also coherent. These radiations are emitted through partially reflecting mirrors after simultaneous reflections within the lasing medium. Don't these EM radiations affect the lasing medium o... | 5,852 |
<p>How can I show explicitly that the bell state $$|\psi^{-}>=\frac{1}{\sqrt{2}}(|0>|1>-|1>|0>)$$ is invariant under local unitary transformations $U_{1}\otimes U_{2}$ ?</p> | 5,853 |
<p>Is it true that whenever an action takes place it is dependent on both its past and future? I mean if we already know that whatever we are doing is dependent on future as much as it is dependent on the past. If that is the case how can you not tell what I will be typing next?</p> | 5,854 |
<p>I remember hearing about this in one of the programs in discovery science. The physicist claimed that the maximum possible information in the universe is (10)^(10^123) whereas the maximum possible information that can be known by man is (10)^(10^90). Can anyone explain to me how can we arrive at such a specific numb... | 5,855 |
<p>Inspired by <a href="http://what-if.xkcd.com/7/" rel="nofollow">this xkcd</a>, which calculated the energy requirements for accelerating individual humans to escape velocity (regardless of consideration for what that would do to your organs), I am interested to know if a trebuchet (or catapult) could be built that c... | 5,856 |
<p>The experiment goes like this: </p>
<p><img src="http://i.imgur.com/p4EtV.png" alt=""></p>
<p>Allow a moving cart to move from the top of an incline plane ($x_0$) downwards. The time taken will be recorded by the picket fence (those things you see wired up). Distance ($D$) is reduced by 10cm each time. And a set o... | 5,857 |
<p>For example: let's consider a static sphere on an horizontal rough surface. I apply an impulse $J$ parallel to the ground and in the middle of the sphere.
If, like my book says, the friction is not an impulsive force, then I can use $J=\Delta p=mv_{CM}-0$, so $v_{cm}(0)=J/m$. But this is counterintuitive, because if... | 5,858 |
<p>I have been trying to learn about the randomness in Quantum Physics. But of the many sources I referred to, some say about "Randomness in Quantum physics" and some others say about "Quantum indeterminacy". So my question is do these two mean the same or are they completely different? Is randomness because of that in... | 5,859 |
<p>I'm currently trying to familiarize myself with the physics of ion and particle traps, especially with linear Paul traps. Many scientific experiments I've come across use segmented electrodes (like in <a href="http://www.nature.com/ncomms/2013/130807/ncomms3290/fig_tab/ncomms3290_F1.html" rel="nofollow" title="this ... | 5,860 |
<p>In standard 3+1 dimensional spacetime, the metric tensor is of order 4 and had ten independent coefficients, hence there are 6 terms off the diagonal in the corresponding $4\times 4$ real symmetric matrix. On the other hand, superstring theory postulates that there are 6 additional spatial dimensions that have to be... | 5,861 |
<p>According to $F = ma$, force is a result of acceleration and mass, right? </p>
<p>However, I don't understand why velocity is not used instead of acceleration. A train moving at 100 miles/hour will still impart a great force on you even though it has no acceleration. Further, dropping a book at 10ft will impart a g... | 5,862 |
<p>This questions stems from Axiomatic Quantum Field Theory and is mathematical in nature. However, I feel that an answer from physicists is more in line with what I will be asking. </p>
<p>Let $\phi$ be a real quantum field, namely $\phi$ is an operator-valued distribution. One of the requirements of $\phi$ is that i... | 5,863 |
<p>It's my understanding that whenever an object gains or loses electric charge this actually corresponds to losing/gaining electrons (protons do not move). So how can a positive charge always move from higher to lower potential?</p> | 5,864 |
<p>I am having some trouble understanding how to use the tetrad formalism. I will start with what I have so far, my question will be after that.</p>
<p>I begin with the metric</p>
<p>$$ \text{d}s^2 = e^{2a} \text{ d}t^2 - e^{2b} \text{ d}r^2 - r^2 \text{ d} \theta^2 - r^2 \sin^2 \theta \text{ d} \phi^2 $$</p>
<p>Whe... | 5,865 |
<p>How was the polarization experimentally measured in the <a href="https://en.wikipedia.org/wiki/BICEP_and_Keck_Array#BICEP2" rel="nofollow">BICEP2</a> experiments and why did they look specifically at <a href="https://en.wikipedia.org/wiki/B-modes" rel="nofollow">B-modes</a>? Why is it implying the existence of gravi... | 5,866 |
<p>I am using constant density wave propagators to model seismic waves in the subsurface. What I want with these acoustic waves is to estimate the energy of them at a certain grid point at a given time. One approach is using Poynting vectors based on the pressure distribution of the wave </p>
<p>$$
\vec{S} = \dot{p} ... | 5,867 |
<p>This is probably a question with a very simple answer, but I want to make sure before I write too much.</p>
<p>I'm doing an investigation on Electromagnetic fields, in particular eddy currents and how they decelerate magnets, by sliding a magnet down an incline, recording the time taken and changing the thickness o... | 5,868 |
<p><strong>Can we get the information of things that are gone in black hole?</strong></p> | 207 |
<p>In the 2-slit experiment, is it possible to "account" for all of the energy in the incoming beam - i.e. does all of the incoming energy show up in the bright spots or is some of it "destroyed" when destructive interference takes place?</p>
<p>If it is destroyed, what form is it converted into?</p>
<p>If it's NOT d... | 5,869 |
<p>The following is a question from a practice Physics GRE exam (found online at ETS's website).</p>
<blockquote>
<p>The circuit shown in the figure consists of eight resistors, each with resistance <em>R</em>, and a battery with terminal voltage <em>V</em> and negligible internal resistance. What is the current fl... | 5,870 |
<p>I've been watching a video about dark mater and a lot of the mass is missing in our universe. Astronomers got to this by measuring the speed that stars orbit the center of the galaxy and when they did this it didn't match the amount of gravity/mass in the galaxy. </p>
<p>However I thought that the mass of the black... | 5,871 |
<p>Is there a tutorial explanation as to how decoherence transforms a wavefunction (with a superposition of possible observable values) into a set of well-defined specific "classical" observable values <em>without</em> the concept of the wavefunction undergoing "collapse"?</p>
<p>I mean an explanation which is less te... | 5,872 |
<p>Very quick question, does a magnet contain energy? The general consensus seems to be, it does not. And this is generally confirmed by the fact that it would break the first law of thermodynamics. Whatever the hell that is (joke:)</p>
<p>The reason I ask is because a) I'm no genius and b) because I'm perplexed. So m... | 5,873 |
<p>Say I have a bipartite state</p>
<p>$\rho = \sum_ip_i|\psi_{i}\rangle \langle \psi_{i}|_{AB}$</p>
<p>Where $\{|\psi_{i}\rangle_{AB}\}$ forms an orthonormal basis.</p>
<p>I now perform some local quantum operation on subsystem B, bringing my system to a new state:</p>
<p>$\rho' = \sum_iq_i|\phi_{i}\rangle \langle... | 5,874 |
<p>Recently, there was a rapid communication published in Phys.Rev.D (<a href="http://prd.aps.org/abstract/PRD/v83/i2/e021502">PRD 83, 021502</a>), titled <em>"Gravity is not an entropic force"</em>, that claimed that <a href="http://prd.aps.org/abstract/PRD/v67/i10/e102002">an experiment performed in 2002 with ultra c... | 708 |
<p>So I am trying to reproduce results in <a href="http://arxiv.org/abs/1007.1031" rel="nofollow">this</a> article, precisely the 3rd chapter 'Virasoro algebra for AdS$_3$'. I have the metric in this form:</p>
<p>$$ds^2=-\left(1+\frac{r^2}{l^2}\right)dt^2+\left(1+\frac{r^2}{l^2}\right)^{-1}dr^2+r^2d\phi^2$$</p>
<p>An... | 5,875 |
<p>I am working on a high school project that is related to projectile motion. I am exploring how exactly the position of the center of mass affects the trajectory of a long but thin, javelin-like projectile. I have created a special launching machine that gives each projectile an identical impulse, filmed all flights ... | 5,876 |
<p>When we have two bodies and a central force acting towards the center of each other, we could treat the whole problem as a one body problem by introducing the relative coordinate. My question is, when you were to calculate the relative coordinate, you are working out the acceleration of a fictitious particle, which ... | 5,877 |
<p>Assume that you have two bipartite systems $\rho_1^{AB},\rho_2^{AB}$ then I would like to prove the following:</p>
<p>$$S(\frac{1}{2}( \rho_1^{AB}+I^A\otimes\rho_2^B))+S(\frac{1}{2}(\rho_2^{AB}+I^A\otimes\rho_1^B)) \geq S(\frac{1}{2}(\rho_1^{AB}+I^A\otimes\rho_1^B))+S(\frac{1}{2}(\rho_2^{AB}+I^A\otimes\rho_2^B))$$<... | 5,878 |
<p>Laser uses mirrors to reflect photons in order to stimulate atoms to emit photons, but why this is so?. I mean, why does a photon stimulate atoms to produce more photons? If a photon made an atom to produce a photon, is not the first photon absorbed by the atom and therefore there is not total gain in the process?</... | 5,879 |
<p>This paper was posted to arxiv a couple of weeks ago: <a href="http://arxiv.org/abs/1309.1067" rel="nofollow">http://arxiv.org/abs/1309.1067</a></p>
<p>From the abstract:</p>
<blockquote>
<p>The effects of Wheeler's quantum foam on black hole growth are explored from an astrophysical perspective. Quantum fluctua... | 5,880 |
<p>I need to do phase reconstruction from time series data. In doing so, I encountered <a href="http://en.wikipedia.org/wiki/Takens%27_theorem?" rel="nofollow">Takens' embedding theorem</a> and Cao's minimum embedding dimension $d$ by nearest neighbor method. In paper "Optimal Embeddings of Chaotic Attractors from Topo... | 5,881 |
<p>I read that the <a href="http://en.wikipedia.org/wiki/Canonical_commutation_relation" rel="nofollow">canonical commutation relation</a> between momentum and position can be seen as the Lie Algebra of the <a href="http://en.wikipedia.org/wiki/Heisenberg_group" rel="nofollow">Heisenberg group</a>. While I get why the ... | 5,882 |
<p>When a system has a dopant, how much does the Fermi level shift?</p>
<p>For example, say a finite concentration of substitutional dopants replace some bulk atoms, and each has one extra electron. Ignore any changes in geometry. Say we do some DFT calculations that show the charge transfer to be 0.1 between the impu... | 5,883 |
<p>In classical mechanics you construct an action (involving a Lagrangian in arbitrary generalized coordinates, a Hamiltonian in canonical coordinates [to make your EOM more "<a href="http://books.google.ie/books?id=YkFLGQeGRw4C&pg=PA68&dq=gelfand%20%20calculus%20of%20variations%20%22we%20obtain%20a%20much%20mo... | 5,884 |
<p>I know that under $SU(2) \times SU(2)$, the left-handed electron transforms under $ ( \frac{1}{2},0 ) $ representation and the vector gauge field $A_\mu$ under $ ( \frac{1}{2},\frac{1}{2}) $.</p>
<p>Since the electron transforms under $U(1)$, there must be a represenation under which it transforms. What is this r... | 5,885 |
<p>As is usually done when first presenting string theory, the Nambu-Goto Action,
$$
S_{\text{NG}}:=-T\int d\tau d\sigma \sqrt{-g}
$$
($g:=\det (g_{\alpha \beta})$ is the induced metric on the world-sheet and $T$ is a positive real number interpreted as the string tension), is introduced as the natural generalization o... | 5,886 |
<p>Conventional horizontal axis wind turbines use lift force generated in the blades to turn a turbine. </p>
<p>But what is the mechanics of vertical axis wind turbine? What would be the free body diagram of the blades of a VAWT? </p>
<p>Is Vertical axis wind turbine more efficient that a horizontal axis wind turbine... | 5,887 |
<p>I would like to know how important the <a href="http://en.wikipedia.org/wiki/Cosmic_censorship_hypothesis" rel="nofollow">cosmic censorship conjecture</a> is? Should a quantum theory of gravity must obey this? It was never rigorously proved in classical GR too. What would be the consequences if it turns out that CCC... | 5,888 |
<p>I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source. </p>
<p>I wish to convert this to $\frac{\text{photon}}{ cm^{2} s}.$ </p>
<p>Can anyone tell me how to do this? </p> | 635 |
<p>In Jackson's book about classical electrodynamics, this formula comes up:
$$q_{lm} = \int \mathrm d^3 x' \, Y^*_{lm}\left(\theta', \phi'\right) r'^l \rho\left(\vec x'\right)$$</p>
<p>What does that $^*$ mean?</p> | 5,889 |
<p>Suppose I set up a <a href="http://en.wikipedia.org/wiki/Foucault_pendulum" rel="nofollow">Foucault pendulum</a> and observe that it precesses at a rate of 216.528 degrees per day. While I am observing this, a total solar eclipse occurs. Where am I, and what is the date?</p>
<p>My professor NEVER went over anything... | 5,890 |
<p>A particle bound in an infinite potential wall at $x=0$ will apply a force on the wall. For a plane wave and imagining it as a fluid bouncing off the reflection wall at $x=0$, find the force in terms of $\phi'(0)$, the derivative of wave function at $x=0$. </p>
<p>We know, for a reflecting fluid, $\textrm{force }= ... | 5,891 |
<p>In a quantum mechanics, there is the following formula to derive the zero energy $E_0$ of a perturbed Hamiltonian $$H = H_0 + V$$ knowing the zero energy $W_0$ of the free Hamiltonian $H_0$:
$$E_0 = W_0 + i\frac{d}{dt}\text{ln}R(t)|_{t\rightarrow\infty(1-i\eta)}$$
The exponential killing the excited states faster th... | 5,892 |
<p>I'm having trouble understanding something in one of my text books:</p>
<blockquote>
<p>Let’s have a look at the implications of each circuit configuration.
Figure 3.13 shows the Conventional representation of a parallel
circuit. If you assume that the resistance of the wires can be
neglected, then the volt... | 5,893 |
<p>The Poisson bracket is defined as:</p>
<p>$$\{f,g\}_{PB} ~:=~ \sum_{i=1}^{N} \left[
\frac{\partial f}{\partial q_{i}} \frac{\partial g}{\partial p_{i}} -
\frac{\partial f}{\partial p_{i}} \frac{\partial g}{\partial q_{i}}
\right]. $$</p>
<p>The anticommutator is defined as:</p>
<p>$$ \{a,b\} ~:=~ ab + ba. $$</p>... | 5,894 |
<p>I'm working through a problem involving energy conservation. Unfortunately, I cannot calculate the work done by a spring.</p>
<pre><code>Before:
+------------+
| |
| spring | d1
| |
+------------+
After:
+------------+
| |
| spring |
| | d2
| |
| ... | 5,895 |
<p>I am a math guy, so sorry for the naivety. When I peruse the wikipedia I see many "variants" of quantum field theory...conformal quantum field theory, topological quantum field theory, axiomatic/constructive quantum field theory, algebraic quantum field theory, etc. Whether or not these are actually variants of some... | 5,896 |
<p>Consider a free theory with one real scalar field:
$$
\mathcal{L}:=-\frac{1}{2}\partial _\mu \phi \partial ^\mu \phi -\frac{1}{2}m^2\phi ^2.
$$
We write this positive coefficient in front of $\phi ^2$ as $\frac{1}{2}m^2$, and then start calling $m$ the mass (of who knows what at this point) and even interpret it as ... | 5,897 |
<p>I envision a longitudinal wave as a series of vertical lines like that drawn on the board in an introductory physics class. This image contains no angles. Sound is a longitudinal wave.</p>
<p>Some audiovisual references claim that sound is composed of sine waves.</p>
<p>I am trying to reconcile how longitudinal ... | 5,898 |
<p>I apologize if this kind of idle theorizing is frowned upon here, but I was wondering if it is possible that the Second Law of Thermodynamics is a consequence of quantum uncertainty. </p>
<p>I've heard entropy of a system defined as the number of micro-states that it can have to correspond to the macro-states it h... | 5,899 |
<p>It occurred to me in passing that the Lorentz contraction of a black hole from the perspective of an ultra-relativistic (Lorentz factor larger than about 10^16) particle could reduce the thickness of a black hole to less than the DeBroglie wavelength of the particle.</p>
<p>It would seem to me that under those cond... | 5,900 |
<p>Page 580, Chapter 12 in Jackson's 3rd edition text carries the statement:</p>
<blockquote>
<p>From the first postulate of special relativity the action integral must be a Lorentz scalar because the equations of motion are determined by the extemum condition, $\delta A = 0$</p>
</blockquote>
<p>Certainly the extr... | 5,901 |
<p>Let's say we want to freeze a banana. Would it freeze faster if we insert it into an empty freezer, or into one that already contains many frozen bananas?</p> | 5,902 |
<p>In the Hamiltonian formulation, we make a Legendre transformation of the Lagrangian and it should be written in terms of the coordinates $q$ and momentum $p$. Can we always write $dq/dt$ in terms of $p$? Is there any case in which we obtain for example a transcendental equation and cannot do it? </p> | 5,903 |
<p>I have been reading and watching videos about this subject for a while now. I just can not seem to grasp the idea. Let's say we have two clocks. I leave one at home and keep one in my pocket. Then, I started running at speed that is close to speed of light to my school then come back to my house. If I compare th... | 5,904 |
<p>A bob of mass m = 0.250kg is suspended from a fixed point with a massless string of length L = 25.0cm . You will investigate the motion in which the string traces a conical surface with half-angle θ = 21.0 deg
<img src="http://i.stack.imgur.com/nTGlD.jpg" alt="enter image description here"></p>
<p>So what is the re... | 5,905 |
<p>I have an elevator accelerating upwards at an acceleration of $a$. A mercury barometer measures the atmoshperic pressure at this point. Will the reading be less than, more than or equal to $76 \ cm$ of $Hg$?</p>
<p>I remembered from my class that the pressure in a liquid in an nonintertial frame accelerating upward... | 5,906 |
<p>Now there are two papers</p>
<p><strong>The quantum state cannot be interpreted statistically</strong></p>
<p><a href="http://arxiv.org/abs/1111.3328" rel="nofollow">http://arxiv.org/abs/1111.3328</a></p>
<p>(It was discussed <a href="http://physics.stackexchange.com/questions/17170/consequences-of-the-new-theore... | 5,907 |
<p>I keep hearing this rule that an object must have a bigger size than the wavelength of light in order for us to see it, and though I don't have any professional relationship with physics, I want to learn the explanation for this. Also I may have expressed my question wrong, but I hope you get the idea of what I'm tr... | 5,908 |
<p>There is a electric dipole which is fixed. So angular momentum isn't conserved. And there is charge $Q$ which has initial velocity $u$.</p>
<p>My question is: What is the tangential velocity of the charge $Q$ as a function of $r$ and $\theta$ and beyond that, what is the $r$ and $\theta$ as a function of time?</p>
... | 5,909 |
<p>What is the exact reason that normal matter can not exist within an event horizon?</p>
<p>I can understand how a super-dense object like a neutron star could accrete mass until its physical radius is less than its Schwarzschild radius and an event horizon forms around it. </p>
<p>But why can't the neutron star rem... | 208 |
<p>For a while I've been doing research on methods of obtaining conservation laws via the symmetries of differential equations (DEs). I'm presently doing research on identifying financial indicators/phenomena that can be associated with the conservation laws of the <a href="http://en.wikipedia.org/wiki/Black%E2%80%93Sc... | 5,910 |
<p>Recently, I was contemplating the beautiful formulation of electromagnetism (specifically Maxwell's equations) in terms of differential forms:
$$F=\mathrm{d} A\implies \mathrm{d}F=0 \hspace{1cm}\text{and}\hspace{1cm} \mathrm{d}\star\mathrm{d}F=\mu_0 J $$
I started thinking about the history of this way of looking a... | 5,911 |
<p>I learnt that in astrophysical spectroscopy, the emission spectrum of distant stars is used to determine what they're made of. So why is it that our own Sun is emitting the whole spectrum ? (or is that information incorrect)</p> | 5,912 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2175/is-it-possible-for-information-to-be-transmitted-faster-than-light">Is it possible for information to be transmitted faster than light?</a> </p>
</blockquote>
<p>imagine this theoretical situation:<... | 4 |
<p>I was reading the question <a href="http://physics.stackexchange.com/questions/80159/why-has-earths-core-not-become-solid">Why has Earth's core not become solid?</a>, and one of the answers says that </p>
<blockquote>
<p>The core is heated by radioactive decays of Uranium-238, Uranium-235, Thorium-232, and Po... | 5,913 |
<p>A particle has two energy states having energies $E_0$ and $E_1$ with degeneracies $g_0$ and $g_1$. The respective probabilities are $p_1$ and $p_2$. What is the entropy in terms of $p_1$, $p_2$, $g_1$ and $g_2$ ? </p> | 5,914 |
<p>When I put ice cubes in a glass of water, I find that sometimes they will stick together and form a sort of "bridge" between them as they melt. There is usually a visible line where one ends and the other begins, and they break apart if pushed (but for the most part they stick together if they aren't interfered wit... | 5,915 |
<p>I just wanted to see if I am doing this right. </p>
<p>$$\Omega(z) = U(z+\frac{a^2}{z})$$</p>
<p>So to find the stagnation point:</p>
<p>$$\Omega'(z) = U(1-\frac{a^2}{z^2})=0$$</p>
<p>Therefore stagnation points occur at:</p>
<p>$z = +/-\sqrt{\frac{a^2}{U}}$</p>
<p>These both occur on the x-axis and I see the ... | 5,916 |
<p>This is a follow-up question on the topic that I opened a few days ago,
<a href="http://physics.stackexchange.com/questions/79924/wilson-loops-as-raising-operators">Wilson Loops as raising operators</a>.</p>
<p>The paper </p>
<blockquote>
<p>Topological Degeneracy of Quantum Hall Fluids. X.G. Wen, A. Zee. <a hre... | 5,917 |
<p>Can somebody please provide me with a reference where the method of evaluating the heat kernel for spin-1 fields,i.e. vector laplacians on a 2-sphere is given?
Please suggest some references accessible for physicists.</p> | 5,918 |
<p>You can find the symbol of love, the heart, by looking at the motion of a charged particle that's emitted from a hot wire in a specific electromagnetic field. The electric field is directed radially from the wire and has strength $1V/m$ everywhere. The magnetic field $B=1T$ is parallel with the wire axis. If the cha... | 5,919 |
<p>Can anyone give me a quantum mechanical explanation of the theory of valence? (i.e. why atoms bond just enough to have a complete orbital)</p>
<p>EDIT: To clarify, I already have an idea of why atoms bond, and the molecular orbit makes sense to me. The problem is that the valence bond theory provides a simple and f... | 5,920 |
<p>In general relativity, light is subject to gravitational pull. Does light generate gravitational pull, and do two beams of light attract each other?</p> | 815 |
<p>I am trying to solve this simple excercise:</p>
<p><strong>Question</strong></p>
<p><em>You throw a small coin upwards with</em> $4 \frac{m}{s}$ <em>. How much time does it need to reach the height of</em> $0.5 m$ <em>? Why do we get two results?</em></p>
<p><strong>Answer</strong></p>
<p>(We get two results for... | 5,921 |
<p>So, the Fermi level in crystals is pretty easy to understand. Been using it and talking about it in terms of the highest occupied level forever. However, I'm now reading about disordered systems. A lot of researchers mention the existence of empty states randomly distributed above and <em>below</em> the Fermi level.... | 5,922 |
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