question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>One can take a spacetime and maximally extend it, so that geodesics end only on singularities, where they have to end -- not on coordinate singularities, which are not physically significant. But when we do this, we seem to get <em>spacetimes</em> that are not physically significant. For example, the maximally exten... | g17570 | [
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<p>From <a href="http://arxiv.org/abs/hep-ph/0001149" rel="nofollow">hep-ph/0001149v1</a>:</p>
<p>(1) an Odderon contribution is absolutely necessary to reproduce quantitatively
well the data; while its presence is not explicitly needed at $t = 0$, its
inclusion is necessary to have a good fit of the other $|t|$ data,... | g17571 | [
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<p>See this video about 30 sec in. <a href="http://www.youtube.com/watch?v=dL6Pt1O_gSE">http://www.youtube.com/watch?v=dL6Pt1O_gSE</a></p>
<p>Is this a real effect? Why does it seem to turn periodically?
Can it be explained by classical mechanics alone?
Is there a simple equation that models this behaviour?</p> | g17572 | [
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<p>I wonder what's the way to regenerate O2 in air without using consumable chemicals (where one can use electricity through electrolisis or using UV lamps)?</p>
<p>We can dissolve water into O2 & H2, but it won't remove CO2 from air.</p>
<p>Any ideas?</p> | g17573 | [
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<p>I've run into this concept of 'screening' several times before, but I admit I've never sat down and really thought about why the process works. My understanding of the effect is that mobile electric charge carriers (say in a fluid) are able to arrange themselves in such a way that reduces or effectively cancels out ... | g17574 | [
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<p>Although I don't have any problems with <a href="http://www.google.com/search?as_q=vectors+physics" rel="nofollow">vectors</a> when using them in Mathematics but I am having a hard time using them in physics. It is really frustrating me.<br>
Can you please recommend me some good resources for learning how to use vec... | g17575 | [
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<p>I understand the form of operators in use for quantum mechanics such as the momentum operator:
$$\hat{\text{P}}=-ih\frac{d}{dx}$$ My question is in what ways can I use it and what am I getting back? For example: if I simply apply th momentum operator to the wave function $$-ih\frac{d}{dx}\Psi$$ Will I get an Equati... | g17576 | [
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<p>For time-like geodesic, the affine parameter is the proper time $\tau$ or its linear transform, and the geodesic equation is </p>
<p>$$\frac{d^{2}x^{\mu}}{d\tau^{2}}+\Gamma_{\rho\sigma}^{\mu}\frac{dx^{\rho}}{d\tau}\frac{dx^{\sigma}}{d\tau}=0. $$</p>
<p>But proper time $\Delta\tau=0$ for null paths, so what the phy... | g17577 | [
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<p>I'm talking about a Weighing Balance shown in the figure:</p>
<p><img src="http://i.stack.imgur.com/Rkhle.jpg" alt="enter image description here"></p>
<p>Press & Hold on onside of the horizontal beam and then release it. It makes some oscillations and comes back to equilibrium like shown in the figure.</p>
<p... | g535 | [
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<p>The (relativistic) mass of an object measured by an observer in the $xyz$-frame is given by
$$m = \frac{m_{rest}}{\sqrt{1 - \left(\frac{v}{c}\right)^2}}.$$
Mathematically $v$ could be greater than the speed of light, but the mass $m$ would become imaginary. Physically we would have to get to the speed of light first... | g17578 | [
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<p>As far as I interpret it, the law of ever increasing entropy states that "a system will always move towards the most disordered state, never in the other direction".</p>
<p>Now, I understand why it would be virtually impossible for a system to decrease it's entropy, just as it is virtually impossible for me to sol... | g17579 | [
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<p>Consider a tight-binding square lattice in 2D. This lattice has two different nearest neighbor tunneling rates along the x and y directions; call them $J_{x}$ and $J_{y}$. All longer range tunneling rates are zero. How can I compute the response of the expected momentum of a very low momentum particle to a force app... | g17580 | [
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<p>I'm calculating some properties of the photon gas. That gas is defined by
$$U=aVT^4$$
$$P=\dfrac{1}{3}aT^4$$</p>
<p>I calculated photon gas entropy:</p>
<p>$$S = \dfrac{4}{3}aT^3V $$</p>
<p>I could calculate $c_V$. Also, I know that $c_P$ and $\kappa_T$ are not defined because it's impossible to change temperatu... | g17581 | [
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<p>Normally T-duality is introduced perturbatively by computing world-sheet spectrum of fundamental strings, and one of the conclusions is that it switches between momentum mode and winding mode of fundamental strings. My question is that does this switching extend beyond fundamental strings, namely, is it true that T-... | g17582 | [
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<p>Why is the inductive reactance written as jωL?</p>
<p>I know that multiplying by j rotates the inductive reactance on the j axis, but why do we do that?</p>
<p>Why is it not on the same axis as the resistance?</p> | g17583 | [
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<p>Consider the fourth rank tensor $$S_{\mu \nu \rho \sigma} = a(\epsilon_{\mu \sigma}\epsilon_{\nu \rho} + \epsilon_{\mu \rho}\epsilon_{\nu \sigma})f(x^2),$$ </p>
<p>in 2D where $a$ is a constant and $f(x^2)$ is a Lorentz invariant function (not important for this question). I want to show this reduces to a linear c... | g17584 | [
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<p>I've heard conflicting answers, and would like to see the record set straight:</p>
<p>An jet/propeller airplane is traveling on a giant treadmill at takeoff speed. Will the plane takeoff, or will it remain on the runway, and why?</p> | g542 | [
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<p>Can you please assist with a really simple question?</p>
<p>I have a hydraulic scissor jack table with the following: 2 hydraulic cylinders, each with a cylinder stroke of 240mm, a cylinder bore of 50mm and a hydraulic pressure of 15Mpa.</p>
<p>I need to calculate the lifting capacity of this table (ignoring the ... | g17585 | [
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<p>From Quantum Field Theory by Franz Mandl and Graham Shaw page 4. </p>
<p>When we are expanding the vector potential as a Fourier series;</p>
<p>$\renewcommand{\vec}[1]{\mathbf{#1}}\vec{A}(\vec{x},t) = \sum\limits_{k}\sum\limits_{r}(\frac{\hbar c^2}{2V\omega_k})^{1/2}\vec{\varepsilon_r}(\vec{k})[a_r(\vec{k},t)e^{i\... | g17586 | [
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<p>I have just watched a <a href="https://www.youtube.com/watch?v=2LqzF5WauAw" rel="nofollow">trailer</a> for the upcoming movie <em>Interstellar</em> and started to wonder about some physics involved. In the end of the trailer, they are obviously plunging into a Black hole hoping to travel into a different universe. L... | g17587 | [
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<p>I was trying to work with some data for a lab report I'm writing about capacitively coupled RLC circuits.
The setup is pretty simple and looks like that:
<img src="http://i.stack.imgur.com/gURa1.jpg" alt="Schematic"></p>
<p>Where $C^{'}$ is the coupling capacitance.</p>
<p>I took some data using an oscilloscope, I... | g17588 | [
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<p><a href="http://www.monolithic3d.com/2/post/2011/09/is-there-a-fundamental-limit-to-miniaturizing-cmos-transistors1.html" rel="nofollow">This site </a> has a formula for the transmission probability over a barrier (in transistors):</p>
<p>$$ T \propto \exp [-2(2m^*/\hbar ^2)^{1/2}(q\phi)^{1/2} d ]. $$</p>
<p>Where... | g17589 | [
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<p><strong>Context</strong>: Solid state physics, lattice dynamics.</p>
<p><strong>Question</strong>: At point $X$ the LO and LA branches have the same energy. Is this something that can be expected before doing the experiment or is it just it ?</p>
<p><img src="http://i.stack.imgur.com/BL8S1.png" alt="enter image de... | g17590 | [
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<p>From what I understand, it's extremely difficult/ impossible to compress atoms closer together.</p>
<p>I'm wondering how this applies in the case of graphite and diamond, where the carbon atoms adopt a different structure under different temperatures and pressure.</p> | g17591 | [
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<p>Okay, so the <a href="http://www.youtube.com/watch?v=-tnxzJ0SSOw">trailer</a> for the new Spider Man movie is out and appearently our friendly physicist from the neightborhood came up with something. However I can't find out what this is. </p>
<p><img src="http://desmond.imageshack.us/Himg3/scaled.php?server=3&... | g597 | [
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<p>I am asking this question here because I think the answer has something to do with the way light is bent as it's captured through the eye.</p>
<p>I saw a show a while ago about tiny screens on contact lenses to pull up data on objects you see in the real world, I also just saw this article about Google testing the ... | g17592 | [
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<p>Why x-ray are stopped by atmosphere while they are more energetic than UV or IR?</p>
<p>They certainly interact with atmosphere but I can't understand which phenomenon stop them.</p> | g17593 | [
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<p>Paraphrased from <a href="http://en.wikipedia.org/w/index.php?title=Light&oldid=551635571#Electromagnetic_spectrum_and_visible_light" rel="nofollow">Wikipedia</a>:</p>
<blockquote>
<p>Infrared sensing in snakes depends on a kind of natural thermography, by which tiny <strong>packets</strong> of cellular water... | g17594 | [
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<p>I am studying heat transfer And understanding <a href="http://www.phs.d211.org/science/smithcw/Chemistry%20332/Quarter%201%20Unit%202/9%20Types%20of%20Heat%20Transfer.pdf" rel="nofollow">the vacuum flask example</a> that involves <strong>conduction, convection, and radiation</strong></p>
<p>Do you know other exampl... | g17595 | [
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<p>As a non physicist I can understand how Newtonian mechanics falls short in cases of high velocity etc. and is properly generalized by the special theory of relativity.</p>
<p>What is not clear to me is how universal gravitation falls short: under what conditions does it fail to make accurate predictions? What are ... | g17596 | [
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<p>The interior of a curved cylinder is an Einstein manifold (the Ricci Curvature Tensor is proportional to the Metric $R_{\mu\nu}=kg_{\mu\nu}$) since it has a constant curvature.</p>
<p>Using the metric
$$
{g_{\mu \nu }} = \left[ {\matrix{
{ - 1} & 0 & 0 & 0 \cr
0 & {{{{C^2}} \over {{C^2} - 2{... | g17597 | [
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0.04646722227334976,
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0.04690709710121155,
-0.02... |
<p>For a charged particle moving in free space, we can say from the homogeneity of space-time, that it moves along a geodesic.</p>
<p>Is there an analogous principle for the evolution of the electromagnetic field in space-time?</p> | g543 | [
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<p>So my teacher told me that when you have two identical balls in a perfectly elastic collision, the first ball A will collide with B and afterwards A will stop and B continue. Why is this? Doesn't Newton's 3rd law imply both balls would get an equal force into opposite direction during the collision? And if A was hea... | g17598 | [
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<p>Under Newtonian model of gravity, a perfect sphere creates the same gravitation field as a point mass in its center.</p>
<p>General Relativity describes gravitation differently. How much this difference affect the above equivalence? If it does not hold, what kind of difference (qualitatively) there is?</p> | g17599 | [
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<p>Say I have a detached bicycle wheel and I roll it down an infinite, flat, asphalt inclined plane, in air (ie there will be a terminal velocity). When, if ever, will the wheel fall over?</p>
<p>I've been wanting to try this and see, but I don't know of a suitable hill near my house. My second question is if someone ... | g17600 | [
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<p>Consider a linear, isotropic material. We can then write:
$$\textbf{D}(\textbf{r},\omega) = \epsilon(\textbf{r},\omega)\textbf{E}(\textbf{r},\omega)$$
In phasor notation. The complex emissivity $\epsilon'$is defined as: $$\epsilon' = \epsilon - \frac{j\sigma(\textbf{r})}{\omega}$$
We can also write:
$$\textbf{B}(\t... | g17601 | [
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-0.0... |
<p>I am doing ray tracing and I do the refraction of the ray using the following relation (I got it from PDF called "Reflections and Refractions in Ray Tracing"):</p>
<p><img src="http://i.stack.imgur.com/LqEOB.png" alt="enter image description here"></p>
<p><img src="http://i.stack.imgur.com/MA8ii.jpg" alt="enter ima... | g17602 | [
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... |
<p>I would like to ask for an example (a lagrangian) both in classical and quantum level for which the action is maximaized (rather than minimized). What is special in these cases?</p> | g544 | [
0.01132609136402607,
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<p>I will Illustrate the question using an example problem:</p>
<blockquote>
<p>We have a mass $m$ connected to a mass $m$ by a rod of length $l$, and also to a mass $4m$ by another rod of length $l$. The rods are massless, the masses are pointlike. The outer masses are positioned on a flat, slippery plane in such a... | g17603 | [
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<p>One consequence of the Ward identity (cf. Di Francesco et al) is that it means variation of correlators under infinitesimal transformation is zero. This can be seen by integrating the ward identity, and using the Gauss divergence theorem to integrate over the surface at infinity, and setting the surface term to zero... | g17604 | [
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<p>The Stress-Energy Tensor for electromagnetism is given by:
$$ T_{\mu \nu} = F_{\mu}\,^{\alpha}F_{\nu\alpha}-\frac{1}{4}g_{\mu\nu}F_{\alpha\beta}F^{\alpha\beta} $$</p>
<p>How can I find $F_{\mu\nu}$ in terms of $T_{\mu\nu}$?</p>
<p>Rewriting the above equation using:
$$ T_{\mu\nu}=- F_{\mu \alpha} g^{\alpha\beta} ... | g17605 | [
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<p>Please look at the following mechanism for contra-rotating propellers: <a href="http://youtu.be/W8jn3NuHtlU?t=43s" rel="nofollow">YouTube video</a></p>
<p>When a CCW torque acts on the upper gear and a same torque acts on the lower gear (both seen from above), the torques act against each other.</p>
<p>But: does t... | g17606 | [
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<p>In transistor as an amplifier, we have NPN transistor (base in the middle and emitter and collector at the sides). The collector has electrons in majority because it is N-type. similarly, holes are in majority in base, but as it is lightly doped, it has very little amount of hole. Now, when a small signal of alterna... | g17607 | [
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<p>When two resistors, each of resistance 4.0 ohms, are connected in parallel with a battery, the current leaving the battery is 3.0 A. When the same two resistors are connected in series with the battery, the total current in the circuit is 1.4 A. Calculate the internal resistance of the battery. The solution started ... | g17608 | [
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0.06663801521062851,
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0.07044117152690887,
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0.002601... |
<p>I'm having a question concerning the Lindhard function.
The reference I'm using is the standard text "Quantum Theory of Solids" by Charles Kittel.
I'm concerned with Chapter 6, subchapter "Method of the self-consistent field".</p>
<p>The goal is to solve the quantum mechanical eigenvalue problem of the Hamiltonia... | g17609 | [
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0.026915596798062325,
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<p>I know that a mass term for an intermediate boson is not compatible with the gauge symmetry. But in principle a mass term for the electron field does not violate a gauge symmetry. However to build an electroweak theory consistent with the observation of the non-conservation of the parity of the neutrino, the electro... | g17610 | [
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0.0... |
<p>We have a complex electric field. Is there any definition for absolute and imaginary part of a complex electric field? What do they stand for?</p> | g295 | [
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<p>Why is commutation relations the first step in quantization?</p> | g17611 | [
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<p>By definition a conformal transformation of the coordinates is an invertible mapping $x\rightarrow x'$ which leaves the metric invariant upto a scale factor:
\begin{equation}
g_{\mu\nu}'(x') = \Lambda(x) g_{\mu\nu}(x)
\end{equation}</p>
<p>I am facing problems in deriving the scale factor for special conformal tra... | g17612 | [
0.038161732256412506,
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<p>So I was wondering about the event horizon on a black hole. And wondering if the point of no return for radio waves vs gamma rays would be different. I guess the logic being, since gamma rays have more energy than radio waves, their point of no return might be different.</p>
<p>But I'm not sure if gravity has the s... | g17613 | [
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<p>I assume if light can't escape a black hole, then light is in a black hole. Does the light 'shine' inside a black hole</p> | g17614 | [
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... |
<p>It is well-known that light of two different frequencies illuminating a detector will produce an output with a component at the difference frequency. While such considerations are eminently useful (various heterodyne measurement techniques) it has not been practical until lasers came along. Regardless of practicalit... | g17615 | [
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<p>Can we take a single lone hydrogen atom (proton and electron?) and set it in one place and observe it staying there?</p>
<p>How about just a proton?</p>
<p>A neutron?</p>
<p>How about just an electron?</p> | g17616 | [
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<p>If an electron travels as a wave, can it therefore not be aimed with any precision?</p>
<p>If you fire an electron gun, can't you aim it at a particular slit?</p>
<p>If the electron travels as a wave, will an electron gun hit anything at a 180 degree angle from the barrel? 360 degrees?</p> | g17617 | [
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<p>How does crystal growth affect its scintillation properties? What are possible ways in which growth of CaWO crystals grown via <a href="http://en.wikipedia.org/wiki/Czochralski_process" rel="nofollow">Chochralski method</a> could be modified to avoid non-linearity in its scintillation output with respect to incident... | g17618 | [
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<p>We have a spring attached to a wall and at the other part an object on a frictionless surface.
I tried to calculate the spring oscilation period. I used the conservation of energy and kinematics equations for the average acceleration. $$\frac{1}{2}kA^2 = \frac{1}{2}mv^2 \Rightarrow v^2=k\frac{A^2}{m}$$
$$v^2=2aA+v_0... | g545 | [
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0.02... |
<p>I have been teaching myself quantum field theory, and need a little help connecting different pieces together. Specifically, I'm rather unsure how to tie in renormalization, functional methods, and the calculation of scattering amplitudes.</p>
<p>Now, I understand how the <a href="http://en.wikipedia.org/wiki/LSZ_r... | g17619 | [
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<p>Under this question <a href="http://physics.stackexchange.com/questions/36475/quantum-field-theoretic-models-of-decoherence">quantum field theoretic models of decoherence</a> @DanielSank gave a wonderful answer. Can I implement his answer to every material body? What about I'm thinking is that on the surface of ever... | g17620 | [
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-0.... |
<p>I need to find an analytic solution via asymptotic expansion for the following system of equations:
\begin{align}
& i(u_t+u_x) + v = 0 \\
& i(v_t-v_x) + u = 0
\end{align}</p>
<p>\begin{equation}
u(x,0) = Ae^{-x^2} \hspace{0.1 in} v(x,0) = -Ae^{-x^2}
\end{equation}</p>
<p>I uncoupled them
\begin{align}
&am... | g17621 | [
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0.009304019622504711,
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0.04560365155339241,
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0.03196105733513832,
0... |
<p>I need to estimate averaged signal of a generator with known phase noise and the amplitude noise can be neglected.</p>
<p>The averaged signal of the generator is expressed as:
$$ \langle A\exp{i(\Omega t + \varphi)}\rangle + \mathrm{c.c.}
= Ae^{i\Omega t} \langle \exp{i\varphi} \rangle + \mathrm{c.c.}, $$
with... | g17622 | [
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<p>I am trying to understand theory behind the Gyroscope. I found <a href="http://www.real-world-physics-problems.com/gyroscope-physics.html" rel="nofollow">this article</a> that explains things in much detail.</p>
<p>But I am unable to understand how that perpendicular acceleration components (a1, a2) are coming on b... | g17623 | [
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0.008439... |
<p>Ok so I finished by A-levels last year (english exams 18 year olds take) and we defined in my physics course we defined <a href="http://en.wikipedia.org/wiki/Field_line" rel="nofollow">field lines</a> (for an electric field) as: The path a free positive test charge would follow if acted upon no other force but the f... | g17624 | [
0.03390293940901756,
0.030527904629707336,
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<p>How do I show that the compactification of Minkowski is given by the quadric
$$uv-\eta_{ij}x^{i}x^{j}=0$$
with an overall scale equivalence in the coordinates.I get that for $v \neq 0$, the surface can be parametrized with the Minkowski coordinates. Now for $v=0$, I can have arbitrary values of $u$, which means basi... | g17625 | [
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0.03182710334658623,
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0.005113290157169104,
0.015568631701171398,... |
<p>I am studying <em>Structure Optimization</em>, and the teacher took a few weeks to detail dual methods, but I don't get why it is useful.</p>
<p>From an optimization problem with <code>n</code> design variables and <code>m</code> active constraints, the dual methods introduce an equivalent <code>dual problem</code>... | g17626 | [
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<p>A dominant method to obtain 3D images in the cinemas seems to be circular polarization. Separate pictures are projected with (alternating) circular polarization filters and passive glasses of the viewers block the wrong images for each eye (left-handed is OK for the left eye and right-handed is OK for the right eye,... | g17627 | [
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<p>Some of my questions haven't been well received, because I seem like I'm challenging well respected theories without having done the proper university training and study. </p>
<p>I have been studying this online as a hobby for over five years though. I have a problem with the idea of Hawking radiation. </p>
<p>If ... | g17628 | [
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<p>I've been very interested in mathematics for a while now and, after being inspired by reading Feynman's biography, would also like to learn about physics. My mathematics background is fairly extensive. I've taken courses through calc BC, the basics of multivariable calculus and a fair amount of linear algebra, wit... | g98 | [
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0.008... |
<p>I have a current waveform from my circuit which goes up and down the x-axis.</p>
<p>x-axis represents time and my y axis represents current. How should I calculate total area under the curve? Should I take the absolute for negative part of current or just waveform integral will work?</p> | g17629 | [
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<p>Warning: Students, stay away from antiquities. The aim to learn is to survive.</p>
<p>Hi. Today the nomenclatures <a href="http://www.google.com/search?as_q=&as_epq=Feynman+gauge" rel="nofollow"><em>Feynman gauge</em></a> and <a href="http://www.google.com/search?as_q=&as_epq=Landau+gauge" rel="nofollow"><e... | g17630 | [
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<p><img src="https://docs.google.com/drawings/pub?id=1cm2nq5OKck4zKphMYgMIJuCREZDO9JlNriRA0_4pUTc&w=400" alt="enter image description here"></p>
<p>This diagram is of a block (b) moving down a ramp unaided.</p>
<p>Taking gravity (g) as $9.8ms^{-2}$, and the mass of the block (b) as $0.2kg$, how can I find the for... | g17631 | [
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<p>I am reading the chapters on characteristic classes and the index theorems in Nakahara. It is proven in the text that any chiral or gravitational anomaly $\mathcal{A}$ is given by</p>
<p>$$\mathcal{A}=\int I^1_{2r}$$</p>
<p>with $I^1_{2r}$ given by the descent equation,</p>
<p>$$I_{2r+2}=d I_{2r+1}$$</p>
<p>$$\d... | g17632 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/9708/is-fire-matter-or-energy">Is fire matter or energy?</a> </p>
</blockquote>
<p>What is the basic form of fire? physics defines every entity by a basic form either solid or liquid or as a gas,</p>
<p... | g546 | [
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0.0004541500238701701,
... |
<p>Which diode (semiconductor material) has the lowest voltage in the direction of conductivity?</p> | g17633 | [
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<p>If you have a bowl of ice that's melting, so the ambient temperature is just above 0 °C, what happens to the temperature of the water when you add salt?</p>
<p>I know that the freezing point of salt water is less than 0 °C (it goes down to around -21 °C for a fully saturated solution), but that's not what this ques... | g17634 | [
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<p>In meteorology, the atmosphere is considered to be divided into <a href="http://en.wikipedia.org/wiki/Air_mass">air masses</a>, regions of relatively uniform temperature and humidity with <a href="http://en.wikipedia.org/wiki/Weather_front">fronts</a> on their borders. But why doesn't the air from different air mass... | g17635 | [
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<p>What is the quantum canonical momentum operator corresponding to arbitrary canonical position. For example, in Cartesian coordinates ($x^i$), the canonical momentum operator with respect to each $x^i$ is $-i\hbar \frac{\partial}{\partial x^i}$. For arbitrary canonical coordinates $q^i$, would the corresponding canon... | g17636 | [
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0.021575968712568283,
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0... |
<p>Can steam (water vapour) exist in a vacuum, and if so does it look and behave the same as in air? Let's assume the actual case is a kettle boiling in a vacuum.</p>
<p>Note that I'm talking about a gas-less vacuum, not truly empty space devoid of all particles except the water.</p> | g17637 | [
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<p>I am trying to simulate a game in Box2D(Physics engine). The game that I am trying to simulate is very simple and can be found here: <a href="http://www.makaimedia.com/#/speartoss" rel="nofollow">http://www.makaimedia.com/#/speartoss</a></p>
<p>What I want to know is that, is the spear in that game following real p... | g17638 | [
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<p>In the high-pressure area it is mostly likely that there is sun. In low pressure area it is mostly likely that rain will occur.</p>
<p>Because of the law that <code>p * V = (c) * T</code> where <code>p</code> is pressure, <code>V</code> is volume, <code>T</code> is temperature and <code>(c)</code> is a constant val... | g17639 | [
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<p>I am a student of class 12th and as far as i know when anything reaches about 99.99% of the speed of light it starts traveling in time or time for it slows down so that it don't breaks the speed barrier. So according to this light photons are immortal. Please clear my doubt. </p> | g361 | [
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<p>According to many physicist what ever goes near to a black hole is pulled by it sucked up in a parallel universe. As far as i know black holes are also made up of material particles as any other thing is made up of so why isn't it sucked up in the parallel universe. And if it is true that it sucks up everything and ... | g17640 | [
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<p>I just started learning about optics, and in the book I'm reading they explain how the electrical field caused by a single charged particle could be described by a series of field lines, and compare them to ropes, to provide an intuition of the concept.</p>
<p>Then they say that and that if we wiggle the particle u... | g17641 | [
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0.002394778188318014,
0.018... |
<p>I thought the Hamiltonian was always equal to the total energy of a system but have read that this isn't always true. Is there an example of this and does the Hamiltonian have a physical interpretation in such a case?</p> | g17642 | [
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<p>I have no formal training at all in relativity. But I was just wondering if our perception of time is altered by different events. Here are some examples I had in mind:</p>
<ul>
<li><p>If I touch a stove for 10 seconds versus enjoying chocolate for 10 seconds would I experience a time distortion? An observer who ... | g17643 | [
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<p>Why do all of the planets in our solar system move is (more or less) the same plane? It would seem that the planets should all have very different orbital planes, each at a different angel to each other. The fact that all of their orbits are so closely parallel suggests that a force is pulling and/or maintaining t... | g231 | [
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<p>Why is the net velocity of electrons (drift velocity) considered to be zero, before setting up any electric field?
I mean in the derivation of the equation drift velocity:</p>
<p>$$ v =-\frac{Eet}{m} $$</p> | g17644 | [
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<p>Given any <a href="http://en.wikipedia.org/wiki/Pseudo-Riemannian_manifold#Lorentzian_manifold" rel="nofollow">Lorentzian manifold</a> containing three distinct <a href="http://en.wikipedia.org/wiki/World_line#World_lines_in_general_relativity" rel="nofollow">time-like world lines</a> $L$, $A$ and $B$ such that<br>
... | g17645 | [
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<p>Quoting from Wolfram Mathworld: " It is the shape used in the construction of soccer balls, and it was also the configuration of the lenses used for focusing the explosive shock waves of the detonators in the Fat Man atomic bomb (Rhodes 1996, p. 195)." but further insights are not provided. (http://mathworld.wolfram... | g17646 | [
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<p>I am confused on why would the propagation speed of any EM waves at ANY frequency is constant in the free space (vacuum) but they seem to disperse in any other materials as the propagation speed of EM waves in other materials depends on the frequency? Can someone give me a good proof of this phenomena with appropria... | g298 | [
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<p>Consider the Earth to be a flat infinite plane having linear mass density equal to the mass density of the actual earth. </p>
<ol>
<li><p>Can there be an analogous Gauss' law that can give the gravitational field for any point on a particular Gaussian surface. </p></li>
<li><p>If yes, what would be the substitute f... | g17647 | [
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<p>Is it possible to 3D print a mirror with todays available materials?</p>
<p>If so, would there be a reduction in image quality?</p> | g17648 | [
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<p>I am shortly due to begin a summer project lasting roughly 6 weeks with the aim of performing some relatively basic calculations in the theory of open quantum systems. However, at this stage in my undergraduate physics degree, I am yet to have studied <em>any</em> quantum mechanics at all. As such, the first part of... | g98 | [
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<p>I'm musician (drummer) and I'm trying to figure out what can I study (related to Physics) for better understanding of the drumsticks and wrist movements, the force applied and the better way to apply it and introduce some theory in my training.</p>
<p>I'm really awful at physics, so I really don't know what areas a... | g17649 | [
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0.... |
<p>I'm trying to understand how one can generate bounds on the effective number of voxels (volumetric pixels) in a hologram, or information density, provided various metrics for the two-dimensional holographic film being used. For example, I often come across film parameters for grain size, resolving power (usually re... | g17650 | [
0.0033867396414279938,
0.027021922171115875,
0.0067603434436023235,
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-0.... |
<p>I'm currently learing kinematics, specifically projectile motion and as an example in my textbook is a bullet fired at some angle. I understand the derivation of formulas to describe that motion and that the only acceleration acting on the bullet is $g$ directed downwards. But then it states that $g$ could be "broke... | g17651 | [
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-0.0194... |
<blockquote>
<p>Displacement of an object is related to time $x=at+bt^2-ct^3$ where a, b and c are constant motion.Then the velocity of an object when it's acceleration is zero is given by</p>
<ol>
<li>$a+\frac{b^2}{c}$</li>
<li>$a+\frac{b^2}{2c}$</li>
<li>$a+\frac{b^2}{3c}$</li>
<li>$a+\frac{b^2}{4c}$</... | g17652 | [
0.06236892193555832,
0.07733660191297531,
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-0.023240... |
<p>I am trying to find a definite answer whether the following version of the double-slit experiment has ever been performed.</p>
<p>Calculate/observe what interference pattern should appear by emitting
photons individually one-by-one through the double-slit barrier and onto a detector
screen behind it, with all equip... | g17653 | [
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0... |
<p>I don't understand, if everything in this world is relative to something else, then cannot we essentially say that nothing exists independently? We say that the universe is considered to be the ultimate 'background'. However, if we say the universe is expanding, shouldn't it be expanding relative to something? </p> | g17654 | [
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0.0... |
<p>When you pour water out of a bottle, normally you have a smooth stream. However, if you pour it too fast it glugs, which is to say, comes out in quantized bursts. What is the formula for calculating the glug point angle, and what is the formula for calculating the size of the glug quanta and glug quanta frequency?</... | g17655 | [
0.026880508288741112,
0.01836155727505684,
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0.02... |
<p>I have a photon counting system that uses a gated avalanche diode to detect single photons. The repetition frequency of the gates is $f_1$ and the temporal gate width is $\tau_1$ (so the duty cycle is $\tau_1 f_1$)</p>
<p>I want to get an estimate of the quantum efficiency $\eta_{\lambda}$, i.e., the probability of... | g17656 | [
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0.053778860718011856,
-0.04055488482117653,
0.05542876198887825,
0.003988989163190126,
0.039... |
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