question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Consider a surface that carries surface charge density. In electrostatics, boundary conditions are studied by showing that there is a discontinuity in the normal component of the electric field across the charged surface and that there is no discontinuity in the horizontal component.</p>
<p>My question is aren't th... | g15561 | [
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<p>I will try my best to ask the question that best fits something I have been pondering on for a few days.</p>
<blockquote>
<p><strong>Are virtual particles really constantly popping in and out of
existence? Or are they merely a mathematical bookkeeping device for
<a href="http://en.wikipedia.org/wiki/Quantum_f... | g15562 | [
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<p>So I have a problem with the LED with the spectrum shown below
<img src="http://i.stack.imgur.com/72jRs.jpg" alt="enter image description here"></p>
<p>I am asked to find the radiometric intensity in Watts/steradian given that the LED produces $5.6\times 10^{-3}$ mcd. We are also told to ignore the yellow spectrum... | g15563 | [
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<p>Can you please help me in modelling a circuit using the differential equation? In the following equation, $u(t)$ is the input voltage and $y(t)$ is the output voltage.</p>
<p>$$y(t)=2u(t)+3\frac{du(t)}{dt}+4\int_0^tu(t)dt.$$</p>
<p>How do I draw a circuit such that the input voltage $u(t)$ and the output voltage $... | g15564 | [
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<p>I saw a <a href="http://www.youtube.com/watch?v=FmL4datwJ3E" rel="nofollow">video</a> by Michio Kaku, showcasing levitation of a small object with a superconductor cooled by liquid nitrogen. It's the same technology used by some trains.</p>
<p>Hypothetically, how possible is it to achieve free human flight by some ... | g15565 | [
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<ol>
<li><p>I want to find experimental data from real launches, with some description of a rocket like full mass, fuel mass, thrust and so on. Just trying to model it. </p></li>
<li><p>Where to read about precise methods of calculating air resistance for rockets.</p></li>
</ol> | g15566 | [
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<p>Given that some systems may radiate energy in the form of gravity waves, and that gravitational waves weaken proportionally to the distance travelled, what would happen to the waves that never hit anything and just propagated infinitely?</p>
<p>Do they just become infinitesimally small? If so, would this imply that... | g15567 | [
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<p>Im mathematics there is a concept of infinity meaning that whenever you pick a number and say that it is the smallest/Largest there is a way to further reduce/increase that number by subtracting/adding any other number. </p>
<p>But in physics/chemistry i see that the absolute temperature does not have a negative re... | g278 | [
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<p>With the advancements in science and technology, how early can scientists of the world detect that a certain asteroid will hit planet earth and cause damage? Are there any impact avoidance strategies or a disaster recovery plan agreed upon by world nations?</p>
<p>Edit: This wikipedia <a href="http://en.wikipedia.o... | g15568 | [
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<p>Observables are self-adjoint elements of a $C^*$algebra. As such, this structure seems sufficient to describe physics. </p>
<p>A theorem by Gelfand and Naimark says that a <a href="http://en.wikipedia.org/wiki/C%2a-algebra" rel="nofollow">$C^*$algebra</a> can always be faithfully represented as bounded operators on... | g15569 | [
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<p><img src="http://i.stack.imgur.com/y0K7Q.png" alt="enter image description here"></p>
<p>So yeah , the answer seems true but i'm very skeptical about it since D3 is in the middle </p> | g479 | [
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<p>Feynman mentions in his lectures:</p>
<blockquote>
<p>...the concept of a molecule of a substance is only approximate and
exists only for a certain class of substances. It is clear in the case
of water that the three atoms are actually stuck together. It is not
so clear in the case of sodium chloride in the... | g15570 | [
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<p>Quite a few times now I have washed my hands, and while my hands are still wet I will touch something metal and get a static shock. I thought static electricity doesn't really build up when there's a lot of moisture, so that's why you don't get static shocks in the summer when there's more humidity. Even though it... | g15571 | [
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<p>I'm not sure if this is an acceptable place to ask this question, as it may have more to do with the biological workings of human eyes than with the physical properties of light, but I'd rather hear a physical explanation than a biological one (if one exists). </p>
<p>Essentially, we often describe the visible spec... | g170 | [
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<p>Energy storage seems to be a fairly major bottle neck in technological development at the moment, especially for important things like clean-energy powered transport, but also for consumer goods. Are there physical limitations of batteries for these and similar uses? Lithum-ion batteries seem to be the go-to for the... | g15572 | [
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<p>The system is $|1\rangle$ at time $t = 0$, while $|2\rangle$ at time $t$.
The base is orthonormal $\left\{|1\rangle, |2\rangle\right\}$. Epsilon and delta are positive constants, which have some energy unit. The system is:
$$
\hat{H} = \epsilon\left(-1|1\rangle\langle1|+|2\rangle\langle2|\right)+\delta\left(|1\rang... | g15573 | [
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<p>While on an expedition to a lake, it was noticed that the wind speeds gusted violently in seemingly periodic wakes and the proposed explanation was Von Karman vortex shedding off of nearby mountains that the lake was in the lee of. </p>
<p>Therefore I am attempting to calculate the amount of influence that a Karman... | g15574 | [
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<p>If a particle moves under the influence of a resistive force proportianal to velocity and a potential $U$, </p>
<p>$$F(x,\dot x)=-b\dot x-\frac {\partial U}{\partial x}$$
Where b>0 and $U(x)=(x^2-a^2)^2$</p>
<p>My thoughts were to make $F=0$, which would result in:
$$\dot x= \frac 1b(4x^3-4a^2x)$$
This means ... | g15575 | [
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<p>Our universe has 4 dimensions, 3 spacial and 1 temporal. We can add another spacial dimension and use math to explore it. I cannot think of any reason why we cannot add add another temporal dimension in the same way. So, what would a universe with 2 temporal dimensions be like? </p>
<p>These are some thought I ... | g480 | [
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<p>As far as I understand, the magnetic power of an ordinary permanent ferromagnet comes from and is maintained by the motion of molten iron in the Earth's core. So a fridge magnet would eventually come loose if no longer in contact with this source of replenishment due to the energy expenditure involved in constantly ... | g15576 | [
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<p>(I have rewritten the question some, with new understanding)</p>
<p>4d BF theory is classically presented as the TFT arising from the Lagrangian</p>
<p>$B\wedge F$,</p>
<p>where $B$ is an abelian 2-connection (locally a real 2-form) and $F$ is the curvature of a connection $A$. People often throw about this theor... | g15577 | [
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<p>The action for an electromagnetic field with source charges is given by</p>
<p>$$S= \int \left\{ \frac{1}{4\mu_0}F^{\mu\nu}F_{\mu\nu} - J^\mu A_\mu \right\}dx$$</p>
<p>By setting $dS=0$ and taking the <a href="http://en.wikipedia.org/wiki/Lorenz_gauge_condition" rel="nofollow">Lorenz gauge</a>, the resulting field... | g15578 | [
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<p>How does the surface area of a piece of glass (or any general material; sapphire isn't technically glass) correlate with strength? Strength as in resistance to pressure concentrated at a small point?</p>
<p>Intuitively, something tells me that the larger a piece of glass is, the less resistant it will be to pressur... | g15579 | [
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<p>A) The mass of the rock
B) The weight of the rock
C) Both the mass and the weight are important.
D) Either the mass or the weight, as they are related by a single multiplicative constant, <em>g</em>.</p>
<p>Similarly, if the large rock merely sits on your toe, which concept is most important in determining how much... | g15580 | [
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<p><em>I am practising for the elementary-physics -course Tfy-0.1064, this puzzle is a simplified version of the problem 3A <a href="http://tenttiarkisto.fi/exams/9916.1.pdf" rel="nofollow">here</a> (sorry not in English). My basic idea here is to understand a scenario with one loop and then understand the solenoid cas... | g15581 | [
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<p>Has anyone developed a vector-scalar theory of gravity using an acceleration field equation that is based on a ratio in which the numerator is the familiar Newtonian vector sum of all masses times the inverse square of their respective distances, and the denominator is the scalar (not vector) sum of the very same fo... | g15582 | [
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<p>I am writing a program that incorporates calculating the principal moment of inertia for a protein residue based on its component atom XYZ coordinates. I am exceedingly confused about which formulas to use in calculating principal moment of inertia for my situation.</p>
<p>Thus far my program does the following:</p... | g15583 | [
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<p>We know that while pouring water in a glass, there is close to no foam, but if pouring beer, there is much foam (unless pouring "slowly"). So, can the most prominent factors that contribute to foam formation be listed and explained?</p>
<p>I've found <a href="http://www.aem.umn.edu/people/faculty/joseph/archive/do... | g15584 | [
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<p>From renormalization group equation
$$
t \frac{d \bar{g}(t , g)}{dt} = \beta (\bar{g}(t , g)), \quad \bar{g}(1 , g) = g
$$
(here $t$ is momentum scale factor, $g$ is initial coupling constant and $\bar{g}$ is an effective coupling constant) and
$$
\tag 1 \beta (g) = ag^{2}
$$
we can get
$$
\bar{g}(t , g) = \frac{g}... | g15585 | [
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<p>I am reading <a href="http://arxiv.org/abs/hep-th/0206063v1" rel="nofollow">the review on instantons</a>. When I tried to derive formula (2.27) on page 17,
I always get the different coefficient of $gF_{mn}$ term. My calculation is just directly expanding the first term $-\frac{1}{2} \int d^4x {\rm{tr_N}} F^2_{mn}$ ... | g15586 | [
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<p>There is a common statement running around that we as a species has enough nuclear weapons to blow up the earth several times over. What I want to know is: by how many orders of magnitude is that a wrong statement? (Just getting a lower bound would be fine.)</p> | g15587 | [
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0.002321762964129448,
0.011940978467464447,
0.028093695640563965,
0.02738838642835617,
-0.03206724673509598,
0.007737117353826761,
-0.06515924632549286,
0.02148028090596199,
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0.02322344295680523,
-0.025964124128222466,
0.02935... |
<p><a href="http://en.wikipedia.org/wiki/Gauss%27s_law" rel="nofollow">Gauss' Law of electrostatics</a> is an amazing law. It is extremely useful (as far as problems framed for it are concerned :D. I do not have a real world-problem solving experience of using Gauss' Law).</p>
<p>However, I don't really understand why... | g758 | [
0.021800735965371132,
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<p>I have spectral radiance data in SRUs (spectral radiance units), as a function of wavelength:
$$a = \mu W cm^{-2} sr^{-1} nm^{-1} $$</p>
<p>However, I am working with software which requires my data in the form:
$$b=mWcm^{-2}sr^{-1}\mu m^{-1}$$</p>
<p>Are these two units are equivalent?</p> | g15588 | [
-0.014653677120804787,
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0.08274009078741074,
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<p>Here is the problem I am working on</p>
<blockquote>
<p>For what temperatures are the atoms in an ideal gas at pressure P quantum mechanical ? Hint: use the ideal gas law P V = N kT to deduce the interatomic spacing (the answer is $T < (1/k)(h^2/3m)^{3/5} P^{2/5})$. Obviously we want m to be as small as possib... | g15589 | [
0.010486789979040623,
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0.... |
<p>I'm reading a text about equations of state of dense nuclear matter. It is often stated that the phase with maximum pressure is preferred. Why is that?</p> | g15590 | [
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<p>Layman here. EE and BS physics. I am "content" in viewing photons/electromagnetic radiation as an "emergent" property of spacetime? due to the electrons ("particles..?") and all their activity jumping around in atoms. [or is this likely too simple?] ... in the "same" manner that sound and water waves are an "emerge... | g15591 | [
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0.033331613... |
<p>It is often said that the classical charge $Q$ becomes the quantum generator $X$ after quantization. Indeed this is certainly the case for simple examples of energy and momentum. But why should this be the case mathematically?</p>
<p>For clarity let's assume we are doing canonical quantization, so that Poisson brac... | g15592 | [
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<p>How is $a_{R}=v_T^{2}/r$ derived for changing tangential speed? ($a_R$-centripetal component $r$-distance from axis $v_T$- tangential speed)</p> | g15593 | [
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<p>I want to create a program that will accurately simulate a condensor. I want to use the data in <a href="http://en.wikipedia.org/wiki/Psychrometrics#Psychrometric_charts" rel="nofollow">psychrometric charts</a>. But I cannot and hence want to use equations that show similar data. Any idea where to start?</p> | g15594 | [
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<p>I'm interested in understanding the dynamics of the <a href="http://www.google.com/search?as_q=discrete+Landau+Lifshitz+equations" rel="nofollow">discrete Landau-Lifshitz system</a>. It's solutions to equations like
$$\frac{\partial X_n}{\partial t} = X_n\times (X_{n-1}+X_{n+1})$$
where the $X_n$ are unit vectors in... | g15595 | [
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<p>We know that:</p>
<p><a href="http://en.wikipedia.org/wiki/Goldstone_boson"><strong>Nambu-Goldstone bosons</strong></a> come from Goldstone theorem: a spontaneous (continuous)-symmetry breaking of the system leads to massless scalar modes.</p>
<p><a href="http://en.wikipedia.org/wiki/Anomaly_%28physics%29"><strong... | g15596 | [
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<p>For example, in the sentence "there is no incoming radiation at past null infinity".</p> | g15597 | [
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<p>I remember to have read somewhere an interesting special relativity "paradox" considering two perpendicular rods $A$ and $B$ of equal proper length $L$ fixed at point $O$.</p>
<p><img src="http://i.stack.imgur.com/ULxzd.png" alt="rest frame"></p>
<p>In the "rest" frame equal (in magnitude) forces are applied on th... | g15598 | [
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<p>My gut feeling tells me things should have energy because of their charge, like they have energy because of their mass.</p>
<p>Is this possible? Has it been shown? If not then what is missing to make such an equivalence possible?</p> | g15599 | [
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<p>I've been working on a question and there seem to be two possible solutions. My own solution does not match the one given in the book. However, after resolving forces and taking moments with both pairs of solutions, they both seem to be consistent, i.e. they both seem to be valid. Here is the question:</p>
<blockqu... | g15600 | [
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0.012393058277666569,
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-0... |
<p>Bosonic closed <a href="http://ncatlab.org/nlab/show/string+field+theory">string field theory</a> is <a href="http://ncatlab.org/nlab/show/string%20field%20theory#ReferencesHomotopyAlgebra">famously governed</a> by a <a href="http://ncatlab.org/nlab/show/L-infinity+algebra">Lie n-algebra</a> for $n = \infty$ whose $... | g15601 | [
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0.001800002995878458,
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0.019095340743660927,
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... |
<p>I recently co-authored a paper (not online yet unfortunately) with some chemists that essentially provided answers to the question, "What do chemists need from computer scientists?" This included the solution of theoretical problems, like combinatorial enumeration and the sampling of certain classes of graphs; and ... | g15602 | [
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... |
<p>I have this problem.
I want to find the wave function in the momentum space for the particle in a 1D box.</p>
<p>We know that the wave function in the position space is:</p>
<p>$$Y_n(x) = A\sin{(n\pi x/L)}$$</p>
<p>Well, if I write the Schrödinger equation in the moment space I have:</p>
<p>$$\frac{p^2}{2m}Y_n(p... | g15603 | [
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0.0... |
<p>What is the current thinking on the little hierarchy problem in light of a potential Higgs mass above 120 GeV? A few years ago, at least, I remember various phenomenologists saying that this at least makes life rather difficult for the MSSM.</p> | g15604 | [
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<p>I wanted to know if the discussion on Wilson loops and Polyakov loops (and their relationship to confinement and asymptotic freedom) is present in the three volumes of Weinberg's QFT books but in some other name or heading. </p>
<p>At least I couldn't naively find these topics in that book.</p>
<p>I was hoping to ... | g15605 | [
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<p>In the formula $$\int \frac {d^{4-2\epsilon} l} {(2\pi)^{4-2\epsilon}} \frac 1 {(l^2-\Delta)^2} = \frac i {(4\pi)^{2-\epsilon}} \Gamma(\epsilon) \left(\frac 1 \Delta\right)^\epsilon,$$ how should I deal with the case when $\Delta<0$?</p> | g15606 | [
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<p>Follow-up to my other question <a href="http://physics.stackexchange.com/questions/36182/how-does-sols-magnetic-field-continue-to-exist-at-such-high-temperatures">How does Sol's magnetic field continue to exist at such high temperatures?</a></p>
<p>Assuming Sol's magnetic field is generated by convective curren... | g15607 | [
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<p>When reading about the <a href="http://motls.blogspot.com/2011/01/twistor-minirevolution-goes-on.html">twistor uprising</a> or trying to follow a corresponding Nima talk, it always annoys me that I have no clue about how twistor space, the twistor formalism, or twistor theory works. First of all, are these three ter... | g15608 | [
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... |
<p><img src="http://i.stack.imgur.com/UqW8O.png" alt="enter image description here"></p>
<p>I want to design a thermal model of the Sun heating up the Earth. The circuit below is my own design (I don't know if there is a better way to model it. If there is, please tell me.). I want to simulate this system, by assignin... | g15609 | [
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... |
<p>What is a good and easy to read introductory text for an adult with limited basic scientific knowledge to astronomy for someone without a telescope and lives in a big city and why do you think that text is good for a beginner? </p> | g15610 | [
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... |
<p>Pardon that this is strictly speaking not a question about physics but about a quote about physics, but I'm not sure where else to turn to.</p>
<p>A while back I read a quote by Feynman in which he says something to the effect that the more different ways one can solve a physics problem the more deeply one understa... | g15611 | [
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<p>Since we know that there are some oracle problems which can be solved on a quantum computer, but not on an NP machine with the same oracle, the idea of nondeterministic (i.e. infinitely parallel) machine is not sufficient to describe what is going on in quantum mechanics.</p>
<p>The question then arises--- what is?... | g15612 | [
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0.02382884919643402,
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0.047370102256536484,
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0.02... |
<p>I have two stars, both of which have <a href="http://en.wikipedia.org/wiki/Balmer_series" rel="nofollow">Balmer lines</a> at the same wavelength positions. The depths of the Balmer lines on each star are different, and the stars are different as well. </p>
<p>Why does this pattern exist?</p> | g15613 | [
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0.006304081529378891,
0... |
<p><em><a href="http://www.sunposition.info/sunposition/spc/locations.php#1" rel="nofollow">SunPosition Calculator</a></em> calculates the Sun's postion based on the location and time. What is the equation used for such a calculation?</p> | g15614 | [
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0.004887581802904606,
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0.03705016151070595,
0.057283733040094376,
0.004... |
<p>My question is, the number of following equations
$$\nabla\cdot E=\frac{\rho}{\varepsilon}$$
$$\nabla\times E=-\frac{\partial B}{\partial t}$$
is 4 while the number of unknown variables $E=(E_1,E_2,E_3)$ is 3. Intuitively, the equation is overdetermined and the solution may not exist unless four equations are correl... | g289 | [
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0.012368373572826385,
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<p>I was reading through Penrose's <em>Road to Reality</em> when I saw his interesting description of the Dirac electron (Chapter 25, Section 2). He points out that in the two-spinor formalism, Dirac's one equation for a massive particle can be rewritten as two equations for two interacting massless particles, where th... | g15615 | [
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0.012098707258701324,
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-0.00226... |
<p>I have just watched this <a href="http://www.youtube.com/watch?v=PENT_hnyO-o" rel="nofollow">video</a> made by discovery channel, and you can hear the narrator at 0:51 saying that : "even though it is moving at 720 THOUSANDS kilometers per hour..."</p>
<p>I stopped once I heard this, because I never thought an aste... | g15616 | [
0.06293124705553055,
0.03463846072554588,
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0.002221701666712761,
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0.0693034753203392,
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<p>I'm interested in building a Fairing for a recumbent bicycle.</p>
<p>A fairing is just a rigid curved surface (usually plastic or fiberglass) that surrounds the bike in order to reduce wind drag. Apparently it can increase your speed dramatically (as much as 300% with zero wind relative to the ground).</p>
<p>Ques... | g15617 | [
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<p>I am an engineering student (CSE) in India..But recently I have developed a strong love to physics..I want to learn physics and understand it in deep..I know physics is the search of deep fundamental laws of nature.That means I need to start from first principles and extrapolate from it?How should i learn physics?</... | g40 | [
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<p>what are the conditions to check point type singularity in a bianchi type model ?
bianchi type model are of Type I,II,III,IX,IV or u can say we use different Bianchi type models having some specific metric or line element as i know .</p> | g15618 | [
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<p>I read here <a href="http://www.sciencedaily.com/releases/2013/07/130709115344.htm" rel="nofollow">http://www.sciencedaily.com/releases/2013/07/130709115344.htm</a> that Prof. Lewandowski's work suggests that different particles may experience different spacetimes. His work is in the context of Loop Quantum Gravity.... | g15619 | [
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<p>I have another question in Polchinski's string theory book volume 1, namely how to derive Eq. (1.2.32)?</p>
<p>$$(-\gamma')^{1/2} R'=(-\gamma)^{1/2} (R-2 \nabla^2 \omega) \tag{1.2.32}$$</p>
<p>I have awared his Eq. (1.2.21) for the transformation of world-line metric
$$\gamma_{ab}'(\tau,\sigma)=\exp(2 \omega(\tau... | g15620 | [
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<p>Let $u^\mu$ be the velocity of a particle , and $\xi^\mu$ be a killing vector. would taking a contravariant derivative of to scalar product $\xi_\mu u^\mu$ , and showing that it equals to 0 shows that this scalar is preserved ?</p> | g15621 | [
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<p>I want to calculate stress matrix in a cube with two faces parallel to x axis and perpendicular to z axis (sorry I don't know how can I put a picture in this post).</p>
<p>There are two force uniform distributions (that we'll indicate with p) over this two surfaces: the superior is in the x direction, the inferior ... | g15622 | [
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<p>I'm looking for the most readable <strong><em>quantitative</em></strong> explanation, with the least amount of difficult mathematics. Rather than an answer with just a number, I'd like to see the derivation from the CKM matrix.</p> | g15623 | [
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<p>So it is summer, which means I have to deal with insects. Today one has made it into my room and while I tried to work this insect was constantly in my face, which caused me waving my hands in the air. Now I have actually hit it 3 times but it kept coming back. Then I was wondering, why don't insects actually really... | g15624 | [
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<p>Freight train is more efficient than truck due to lower <a href="http://en.wikipedia.org/wiki/Rolling_resistance" rel="nofollow">rolling resistance</a>. And I wonder which one has lower rolling resistance<>, small diameter or larger one or it doesn't not depend on diameter at all? Both are steel wheel on steel ra... | g15625 | [
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<p>It seems to me that Hamiltonian formalism does not suit well for problems involving instantaneous change of momentum, like particle collisions with hard wall or hard sphere gas model. At least I could not apply it straightforwardly to the simplest possible problem of 1D particle hitting a wall:</p>
<pre><code> ... | g15626 | [
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... |
<p>Hubble's constant $a(t)$ appears to be changing over time. The fine stucture constant $\alpha$, like many others in QFT, is a running constant that varies, proportional to energy being used to measure it. Therefore, it could be agued that all running constants have 'evolved' over time as the Universe has expanded an... | g15627 | [
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<p>I have the spectrum obtained by an NMR analysis of Ethylene glycol :</p>
<p><img src="http://i.stack.imgur.com/CLm4Y.png" alt="Structural formula of ethylene glycol">
<img src="http://i.stack.imgur.com/mZCdB.png" alt="Ethylene glycol NMR spectrum "></p>
<p>I would like to explain the number of peaks in this spectr... | g15628 | [
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0.006345455069094896,
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0... |
<p>I'm writing a program to calculate NLO cross sections for semi-inclusive high-$p_T$ pion production in proton-proton-collisions for my bachelor thesis.</p>
<p>I've got a paper describing the production cross section as function of the differential cross sections of the partons $\frac{d\sigma}{dv}$ and $\frac{d\sigm... | g15629 | [
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... |
<p>When you drop water to dress actually the color changes, that is the color of dress becomes dark, but when you add water to color, for example water color or poster color it becomes light. Why is it so?</p> | g481 | [
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<p>Show that the maximum possible uncertainty for any observable is $\frac{1}{2}|x_2 - x_1|$ where $x_1$ and $x_2$ are the extreme eigenvalues of <strong>X</strong> (Maximize $\Sigma_i p_ix_i^2 - (\Sigma_i p_ix_i)^2$) with respect to $p_i$ subject to $\Sigma_i p_i = 1$ and each $p_i \geq0$</p>
<p>Using Lagrange multip... | g15630 | [
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<p>How can I derive the expression for the magnetic field due to a long straight current carrying wire using the <a href="http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law" rel="nofollow">Biot-Savart law</a>?</p>
<p>The final expression should be:</p>
<p>$$B=\frac{\mu_0I}{4πr(\sin(a)+\sin(b))}$$</p>
<p>Facing dif... | g15631 | [
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<p>I just saw <a href="http://www.youtube.com/watch?v=OmWO4Vtk-s8" rel="nofollow">this YouTube video</a> (only 3 mins long) of Neil deGrasse Tyson explaining what happens when two black holes collide. He says that when the black holes are rotating around each other, there exists a path that you could follow that would ... | g15632 | [
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<p>Because an object's temperature is inversely proportional to the wavelength of blackbody radiation which it emits, physicists have theorized the existence of <a href="http://en.wikipedia.org/wiki/Planck_temperature" rel="nofollow">Planck temperature</a> at around $1.4×10^{32}$ K. </p>
<p>Does this imply that temper... | g667 | [
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<p>I computed eigenvalues and eigenvectors of a density matrix for state $a|0\rangle+b|1\rangle$.
For eigenvalue $0$ for example, I obtain an eigenvector $(-b^*/a^*, 1)$ before normalization. Now I would like to normalize it. After finding the common denominator for normalization factor, I have $(a^*)^2 + (b^*)^2$ in i... | g15633 | [
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<p>I wanted to ask what is the difference between a pulse and a wave.
According to the definitions of them , they are almost the same.
In the websites I looked at , the difference between them was described by examples which not reflect the difference itself.</p> | g15634 | [
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<p>Is Dark Matter evenly spread out? If no, could we ever find a correlation between the amount of dark matter and matter in a specific place?</p> | g15635 | [
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<p>I am going to apply for a programme of mathematical and theoretical physics for graduate studies and I'm currently studying maths. What is a good area to do a thesis (that is to say, considerable extra work and research) in? Here "good" means useful for my following studies and possibly making a good impression in t... | g15636 | [
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<p>I just read yet another graphene discovery and saw <a href="http://phys.org/news/2014-05-physicists-unlimited-graphene.html" rel="nofollow">this STM image</a>:</p>
<p><img src="http://i.stack.imgur.com/G7hsL.jpg" alt="enter image description here"></p>
<p>Nice photo, it begs two questions:</p>
<ol>
<li><p>What is... | g15637 | [
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<p>One of the results obtained by LHC is the following diagram for p-Pb collisions:
<img src="http://i.stack.imgur.com/YFtle.jpg" alt="enter image description here"></p>
<p>I would like to understand what is actually depicted in the figure, what should we expect based on theoretical approach? what can explain the ridg... | g15638 | [
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<p>This question concerns Eq. (2.10) of the paper <a href="http://arxiv.org/pdf/hep-th/0305116v2.pdf" rel="nofollow">http://arxiv.org/pdf/hep-th/0305116v2.pdf</a> by Bena, Polchinski and Roiban.</p>
<p>In section 2.1 they are showing that the infinite number of conserved quantities for the principal chiral model</p>
... | g15639 | [
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<p>For the reversible isothermal expansion of an ideal gas:
$${∆H}={∆U}=0 \tag1$$
This is obvious for the case of internal energy because
$${∆U} = \frac {3}{2} n R {∆T} = 0 \tag2$$
and
$${∆U} = -C_P n {∆T} = 0 \tag3$$
For the case of enthalpy it is easy to see that
$${∆H} = -C_v n {∆T} = 0 \tag4$$
I've also seen
$${∆H... | g15640 | [
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<p>My lecturer told me that the mu is the <a href="http://en.wikipedia.org/wiki/Chemical_potential" rel="nofollow">Chemical potential</a> is zero or negative, in the following example, mathematically it acts as a Normalisation constant. But is there any Physical insight about why Boson gas can be zero or negative?</p>
... | g15641 | [
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<p>we often come across the phrase superselection sector. I have couple of questions from that. </p>
<p>First of all, I learned from some references about it (as a overview) and how is it related to superselection rules etc. There is of course this mathematical definition (from C* algebra, unfortunately I haven't gone... | g15642 | [
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<p>In an electron gas with no mechanism of production or destruction of electrons is it possible to prepare an state which is superposition of states with different number of electrons? $|\psi\rangle=|N=1\rangle+|N=2\rangle+\cdots$ </p> | g15643 | [
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... |
<p>I'm trying to compute the exact QED amplitude with one external photon. Suppose that the photon has 4-momentum $q$ and polarization $\varepsilon^\mu$. </p>
<p>Peskin and Schroeder (p318) claim that ignoring the contribution from the external photon line we get the amplitude</p>
<p>$$\langle\Omega |S|q\rangle = -ie... | g15644 | [
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<p>I was pondering about this question for a while now. And with my limited knowledge of physics I can answer myself - if parallel universe theory is true and if indeed there is gravitation leakage from 1 universe to the other, there would be infinite number of universes and thus unimaginable amount leakage would occur... | g15645 | [
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<p>My notes say that this is the equation for the "advection of a quantity <strong>A</strong> at speed <strong>v</strong>":</p>
<p>$$ \frac{\partial \mathbf{A}}{\partial t} = \nabla\times(\mathbf{v}\times\mathbf{A}) .$$</p>
<p>Is this true? How can I see (mathematically) that this equation corresponds to advection?</... | g15646 | [
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<p>Is it possible to theoretically measure the resistance of passing of electrical current through liquid electrolyte (distilled water + NaOH) ?</p> | g15647 | [
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<p>The question came about when I was using a gradiometer to detect ferrous metal. From the datasheet they recommend a certain depth range for a larger ferrous metal buried in the ground. </p>
<p>My question is, if I have an "infinite ferrous metal volume", would I be able to detect the metal no matter how deep it is ... | g15648 | [
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<p>Assume that we have massless spin-1/2 particles. The Dirac-spinor is the solution of the Dirac equation:</p>
<p>$$ p^\mu \gamma_\mu u_\pm(p) = 0, \quad p^2 = 0$$</p>
<p>The subscripts $\pm$ denote two different solutions, belonging to two different helicities. Is it possible to find a representation for the $\gamm... | g15649 | [
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<p>Why do you see half of the moon when you can see both the sun and the moon from earth at the same time on some days? </p> | g15650 | [
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<p>I've found Landau 's book for a first course in physics (not theoretical physics, its title is general physics),the book is freely and legally avaible on archive.org ,but it's from 1967,is that okey,or this material in it outdated? What's the most recommended first course in physics? </p>
<p>Which such books/re... | g98 | [
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