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Casmir effect creating positive energies in vacumn

The Casmir force is explained by wave exclusion: Two parallel plates create a reduction in the possible modes of vacuum oscillations between them, reducing the energy of the vacuum. Since we define ...
261 views

Angular Momentum Conservation in Gravitational Interaction

thanks for any help. I'm trying to show that in a 2body problem, angular momentum is conserved given that $\dfrac{dp}{dt}=\dfrac{-GMm(rv)}{r³}$, where p is momentum, t time, G gravitational constant, ...
629 views

Angular Momentum Conservation in Gravitational Interaction [duplicate]

thanks for any help. I'm trying to show that in a 2body problem, angular momentum is conserved given that $\dfrac{dp}{dt}=\dfrac{-GMm(rv)}{r³}$, where p is momentum, t time, G gravitational constant, ...
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Question regarding waves squeezed

in one MOOC I am taking, the professor had a slide stating "when squeezed into a narrow space wave is amplified". I am not sure I understand what he meant by that, and I am trying to think into terms ...
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Analyse astronomical data

Recently I was told of a job offer to analyse astronomical data. The job offer states that they want somebody with knowledge of astronomical data analysis software and it will be a plus somebody who ...
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What does it mean that Bruno can hit $6\,\rm{kN}$?

Is it the momentum? But momentum is $\rm{Ns}$, not $\rm{N}$. http://www.skepticforum.com/viewtopic.php?f=32&t=14624 I'm not sure that 3,430 N is necessarily beyond human capability. Boxer ...
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Why does global supersymmetry commute with gauge transformations?

In particular, I would like to understand the following quotation from a paper by Witten: Nucl.Phys. B188 (1981) 513 (p. 515 at the top) His statement: This is so because in global supersymmetry ...
258 views

Intuition behind the formula for macroscopic entropy

Wikipedia says that the 'macroscopic' definition of entropy is: $$\Delta S = \displaystyle \int \dfrac{dQ_{\rm rev}}{T}$$ Where $T$ is the uniform absolute temperature of a closed system and ...
391 views

Information content of the electrostatic Maxwell equations vs Coulomb's Law vs Poisson's Equation

In electrostatics, we have Maxwell's equations: $\nabla \cdot E = \rho$ $\nabla \times E = 0$ These four equations (the second line standing for three equations) can also be written in terms of the ...
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Detecting if resistances are parallel or series in complex circuits

I know how to detect when resistors are arranged in parallel or series arrangement and I can also find their equivalent resistance in simple circuits or when resistances are connected in form of ...
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Spring with changing equilibrium

Suppose that we have two cars on a track, each with a different mass. Now suppose that the cars are connected with a spring. We smack one car. I would like to write down the equations of motion for ...
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How do the effects of semiconductor doping affect the Hall effect?

For instance, consider number 4 and 5 in the following sample: Using the right hand rule, B points downwards, conventional current points to the right (because of the 5V battery), and therefore, ...
384 views

Casimir effect as an entropic force

When I first learned about the depletion interaction, my initial reaction was that it looks very similar to the Casimir effect. On making this remark to the professor, he replied somewhat mystically: ...
Inspired by this recent question, I would like to understand from a more general and mathematical perspective why closed orbits are only found for the Kepler ($V(r) \sim 1/r$) or harmonic ($V(r) \sim ... 0answers 954 views Proof of Furry's theorem i was wondering if anyone could give an explicit calculation or show a link that shows the proof to Furry's theorem. showing how the vacuum expectation value of any odd number of electromagnetic ... 1answer 372 views Scalar two loop diagram in$\varphi^4$theory Could someone explain how, or at least show me a link that explicitly shows the calculation of a two-loop corrections to scalar’s two-point function in$\varphi^4$theory in the massless limit. 1answer 196 views Which green spectral line(s) are emitted in a Thomson tube? Related: What is meant by boiling off electrons in a heater coil? In the Thomson tube we used in our class to produce an electron beam, the lab manual stated that the tube was filled with a low ... 1answer 106 views Water level rise due to body in water I recently came across a comment that when we push a rubber ball into water filled in a bucket, the water level rises because of the force applied by our hand (i.e. the more force we apply, the more ... 1answer 106 views A change of sign in the electron-hole second quantization form It is common to see people do a change of sign in the so called electron-hole representation, namely, $$b^{\dagger}_{-k}=a_{v,k}$$ similar argument also seen in 1992 mattuck's book "guide to ... 1answer 106 views How to relate wingtips vortices with the energy loss it engenders? On planes, wingtips vortices engender a loss in terms of lift, and an incresed of the drag, so an energy loss. Is there any possibilty to find a mathematical model relating both ? Thanks for the help. ... 1answer 333 views Minus Sign in Feynman Diagram I've been reading these notes and I can't figure out the why on P.120, it is said that The fermionic statistics mean that the ﬁrst diagram has an extra minus sign relative to the ψψ scattering ... 1answer 386 views Quantum tunneling effect in a potential of the kind$V(x)=A\frac{x^2}{1+x^4}$Given a potential: $$V(x)=A\frac{x^2}{1+x^4}$$ with$A\gt 1$and a quantum particle inside the well around the point$x=0$. I'm stuck on the calculation of the transmission and reflection coefficients ... 1answer 1k views What are the implications of the Holographic principle? What are the implications for the Holographic principle? I understand the basics of the principle, the relationship with black holes and string theory but what this is going to tell us? Does it help ... 1answer 401 views Lorentz Force Law and cycloid motion The question I have is from Intro to Electrodynamics by Griffiths (Page 206, Example 5.2) http://imgur.com/a/sfBlt When using the initial conditions$y(0) = z(0) = 0$, I get:$y(0) = 0$implies ... 1answer 375 views Is this a series or parallel connection? I am confused how the capacitors in this circuit are connected.$C_4$,$C_6$and$C_5$,$C_3$appear to be parallel, but both$C_4$and$C_6$seem to be in series with$C_1$as do$C_5$and$C_3$. Am ... 1answer 80 views Testing the speed of gravitational waves in superfluids Ok. Light can be slowed down in superfluids. I would like to know whether if a Cavendish like experiment could be possible within inside superfluids i.e, to rotate two balls such that to observe their ... 1answer 969 views What are the length and time scales in turbulence? I haven't been able to understand what are does someone mean by length and time scales, while talking about turbulence. Can someone explain it to me or give me a link where i can find a good ... 1answer 504 views Hubbard-Stratonovich transformation and mean-field approximation For an interacting quantum system, Hubbard-Stratonovich transformation and mean-field field approximation are methods often used to decouple interaction terms in the Hamiltonian. In the first method, ... 1answer 132 views How does a “hammer thrower” that we see in the Olympics, impart so much momentum How does a "hammer thrower" that we see in the Olympics, build so much momentum into the club? It's sort of like the golf swing, the more momentum, primarily in the club head, the further the ball ... 1answer 102 views Van der Waal's gas satisfies$U = \int_{0}^T C_VdT - a/V + K$(constant) I need to show that a Van der Waal's gas satisifes $$U = \int_{0}^T C_VdT - \frac{a}{V} + K$$ where$K$is constant. The equation of state of a VDW gas is $$\bigg(p + \frac{a}{V^2}\bigg)(V - b) ... 3answers 567 views Friction forces and sliding slabs I have 2 questions, one generalizing the other. Question 1: Suppose we have 2 slabs resting horizontally on a table. Assume there is friction between the 2 slabs as well as between the bottom slab ... 1answer 91 views About the three point function at one loop order Could someone explain how exactly do you calculate the trace of the three point function of one loop in QED. in the following link the expression from 1. a (2) ... 1answer 141 views How big an egg can be? [closed] Please hold on to flag as off-topic. Few days ago I received a question - how big an egg can possibly big? Can it be as big as 1 meter, as a human? (Imagining that there could be really huge animals ... 0answers 230 views At what angle do billiard balls scatter if they collide off center? The angle defined by joining a line from the centers of the balls must be important. But do they follow this angle when viewed in the rest frame of one of the balls or in the CM frame? The spheres ... 2answers 81 views Red Shift and Light Speed I read several questions/answers about red shift on this web site, but there is something I still don't understand. Why is red-shift considered to be the effect of expanding space-time, why it could ... 2answers 564 views Notation for anti-symmetric part of a tensor I know that A_{[a} B_{b]} = \frac{1}{2!}(A_{a}B_{b} - A_{b}B_{a}) But how can write E_{[a} F_{bc]} like the above? Can you provide a reference where this notational matter is discussed? 3answers 1k views Why is the absolute zero -273.15ºC? I can't find an answer of why the lowest temperature is -273.15ºC. Is it deduced theoretically or is it experimental? An explanation is that when any gas volume tends to zero, the temperature will be ... 1answer 2k views Why is the mechanical advantage of a wedge = length of slope/ width? Mechanical advantage is defined as Force Output/Force Input For a symmetrical wedge with the length of the slopes being equal and the width being the distance between the end points, the articles ... 4answers 588 views Why do lasers require mirror at the ends? 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 ... 1answer 91 views How to derive following thermodynamic relation? I'd would like to derive the following$$\bigg(\frac{\partial U}{\partial V}\bigg)_T = T \bigg(\frac{\partial p}{\partial T}\bigg)_V - p$$What I know is that the internal energy U is a function ... 1answer 162 views Entropy inequality Assume that you have two bipartite systems \rho_1^{AB},\rho_2^{AB} then I would like to prove the following:$$S(\frac{1}{2}( ... 3answers 408 views How does a pressure suit work? I recently learnt that a suit called pressure suit is worn by fighter plane pilots to prevent red-outs and black-outs. And it seems to be work by - "..applying pressure to selective portions of ... 1answer 224 views How does a roof top ventilator work? I have spotted this on the rooftops of industries, workshops, etc. I guess this is used for providing ventilation. This is not electrically powered. But then how does this work?? 0answers 38 views Buzzing/Vibration in body under power lines [duplicate] I am hoping someone can please give me an answer. I was at a dog park with my dog and son (hes 12), which is directly under high/loud voltage power lines. I went to brush some dirt of my sons neck ... 3answers 241 views Coordinate transformations of the metric tensor Let's have metric (it describes the space-time of uniformly accelerating observer in Minkowski space-time) $$ds^2 = v^2du^2 - dv^2. \qquad (.0)$$ I need to find expressions for$u = f(x, t), v = ...
Références: Ref $1$ : Henriette Elvang, Yu-tin Huang : Scattering Amplitudes Ref $2$ : Jaroslav Trnka : The Amplituhedron [For simplicity, the notations of the $2$ refs have been merged] The area ...