2
votes
1answer
138 views

Cyclic integral?

Can anyone explain me what is cyclic integral and give me some instructions how to show that there exist cyclic integral for Lagrangian $$L~=~\frac{1}{2}ma^2{\dot {\theta}}^2+\frac{1}{2}ma^2{\dot ...
11
votes
1answer
625 views

Thermodynamically possible to hide a Dyson sphere?

You build a Dyson sphere around a star to capture all its energy. The outer surface of the Dyson sphere still radiates heat at much higher temperature than the cold space background, so you're easy to ...
0
votes
0answers
644 views

Collision of 2 particles - calculating the mass and a speed after the collision

Lets say we have a particle of mass $m_1$ which has a kinetic energy $W_{k1}$. This particle collides with another same particle. How can i calculate mass $m_2$ and the speed $v_2$ of the particle ...
5
votes
0answers
164 views

Physics of Anathem

Disclaimer: I am not asking whether or not the events that occur in Anathem are possible. I understand that this book is a work of speculative science fiction and this site has no interest in it as ...
4
votes
1answer
366 views

The metric Tensor inside a massive shell [duplicate]

Given a fixed shell with the mass of $M$ and a radius $R$ , what would be the metric tensor for $r<R$? I do know that using Birkhoff Theorem the metric for $r>R$ should be schwarzschild. I'm ...
10
votes
1answer
419 views

Invariance of Functional Integration Measure

Let us consider the functional integral: \begin{equation} \int \mathcal{D} A e^{iS[A]} \end{equation} where $S[A]$ is the action for $U(1)$ gauge field and \begin{equation} \mathcal{D}A\equiv ...
6
votes
2answers
1k views

Why does a glass window reflect white objects white from an atomic scatterers’ viewpoint?

Related: Is a white object always white? If you are standing in front of a glass window during the day, you can see your dim white t-shirt’s reflection in the window. The reflection is dim because ...
1
vote
0answers
102 views

Why does angular velocity lies in the axis passing through the center of the circumference?

I understand that it can't be placed anywhere on the radius because it doesn't vary with it ( and so of course it doens't make sense to place it anywhere else on the plane), but why do we place it ...
11
votes
2answers
9k views

Is there a way to fill Tank 2 from Tank 1 through Gravity alone?

I am a newbie in water system design but I am currently faced with the exact situation below on my land, and I need to know whether gravity alone is sufficient in order to fill Tank 2 from Tank 1, as ...
2
votes
1answer
633 views

Constrained-search formulation of DFT: by Levy or by Levy-Lieb

I'm a bit puzzled about how to give the right references for the constrained-search formulation of DFT. Till now, I only heard it being called "Levy constrained-search" but came about some papers and ...
0
votes
1answer
72 views

Why is it suffice to show Tensorial identity on a tensor composed of two vectors?

I've encounter many proves of Tensorail identity that begin with assuming our tensor can be written in form of: $T^{\alpha\beta}=u^{\alpha}v^{\beta}$ . As helpful is it might be, I'm not sure if its ...
2
votes
4answers
408 views

SUSY and the Large hadron collider

Did the LHC rule out SUSY as a solution to the hierarchy problem ? What's the common belief among theorists regarding the possibility of discovering SUSY in the 2015 run of the LHC ? Did the absence ...
8
votes
2answers
7k views

Heisenberg Uncertainty Principle: Which formula is correct?

Some websites and textbooks refer to $\Delta x \Delta p \geq \frac{\hbar}{2}$ as the correct formula for the uncertainty principle whereas other sources use the formula $\Delta x \Delta p \geq \hbar$ ...
2
votes
4answers
231 views

Suggestions of a non-linear example for a small research project on numerical solution of ODEs?

I'm a first year undergrad and I'm doing a small research extension on numerically solving ODEs. I have done the main ODE course at my university, as well as physics. The second part of the project ...
0
votes
2answers
267 views

Frequency calculator

I have a bunch of readings of a wave consisting of volts and time. I need to calculate the frequency of the biggest wave, but i'm not sure exactly how. From what I've researched I'm thinking I need to ...
2
votes
0answers
93 views

Phase diagram of SO(5) rotor model

It was originally a problem from Professor Eugene Demler's problem set. Consider an SO(5) rotor model: \begin{align}\mathcal{H}=\frac{1}{\chi} ...
2
votes
1answer
488 views

What does this feynman diagram represent?

This feynman diagram represents the elastic proton scattering of electrons. The $e^-$ has an initial momentum $k$ and a final $k^\prime$. The circle represents that the target(the proton that is) ...
1
vote
1answer
227 views

Relation/meaning between momentum and contours of constant equal phase of a wave function

Sometimes, mainly due to my limited knowledge of experimental modern physics, whenever I fancy and think about quantum physics, things appear really amusing and counter intuitive, and when if I don't ...
3
votes
3answers
4k views

how to add two plane waves if they are propagating in different direction?

In the undergraduate course about the wave, there stated for two harmonic waves propagating in opposite direction, then the resulting wave will be a standing wave. In math, it is like $$y_1 = ...
0
votes
2answers
442 views

What's an “Action” and what does the Lagrangian equation mean exactly?

How and why would a particle take the shortest path? $L=KE-PE$? What's the $KE-PE$ mean in English? I understand the 'mechanics' but not the idea itself. Please explain simply, I do know Calculus ...
0
votes
1answer
384 views

Does strong interaction care about mass? (+ Isospin question)

So in the journey of trying to understand more about the strong interaction I have encountered some passages linking mass with strong interaction. Like from Greiner and Müller Quantum Mechanics - ...
1
vote
2answers
248 views

Operator on Function of Momentum (QM)

I have exactly 0 clue on how to start this problem, but I would be forever grateful for a hint in the right direction. Given the operators $\hat x=x$ and $\hat p=-i\hbar \frac{d}{dx}$, prove the ...
1
vote
1answer
660 views

Lack of symmetry of the canonical stress-energy tensor

Why in the general case of classical field theory canonical stress-energy tensor doesn't have symmetry of the permutation of the indices? For explanation, let's have a "derivation" of an expression ...
2
votes
1answer
64 views

How does an optic-mechanical laser read and send binary bytes to a CPU?

Thid greatly concerns physics, since a more refined version of my title will be rehearsed below: How is the physical structure of the mechanical eye use a laser to read binary bits held on an optical ...
0
votes
1answer
78 views

Life time of a wave

Let us consider, we have guessed a potential for a wave like non linear, which is propagating through space. We guess a Lagrangian for the wave $$L= \int r^{d-1} dr \left[\frac{1}{2}\dot \phi^2 ...
6
votes
1answer
178 views

Decomposition of Representation Multiplication

How can the multiplication of spinor representations (of $SO(8)$) $8_+ \otimes 8_-$ be decomposed into $8_v \oplus 56_v$? Where can I read more about the decomposition rule of different ...
8
votes
2answers
622 views

rotational oblateness

I am trying to compute the amount of oblateness that is caused by planetary rotation. I picture the force of gravity added to the centrifugal force caused by the rotation of the planet as follows: ...
0
votes
1answer
53 views

What is the limit of vanishing density?

I've been asked to examine the limit of vanishing density for the virial equation of state derivation of $\left(\frac{\partial U}{\partial V}\right)_T$ and quite frankly, I have no idea what this is ...
17
votes
4answers
964 views

Why is it often assumed that particles are found in energy eigenstates?

Energy eigenstates provide a convenient basis for solving quantum mechanics problems, but they are by no means the only allowable states. Yet it seems to me that particles/systems are assumed to be in ...
0
votes
2answers
283 views

Conditions for heat exchange and evaporation

I wonder if there is any law for heat exchange. I have learnt that heat exchange between systems occurs when the temperature of the systems differ , but in case of evaporation, the process creates a ...
4
votes
2answers
603 views

Unitary spacetime translation operator

Srednicki writes: We can make this a little fancier by defining the unitary spacetime translation operator $$ T(a) \equiv \exp(-iP^\mu a_\mu/ \hbar) $$ Then we have $$ T(a)^{-1} \phi(x) T(a) = ...
6
votes
1answer
526 views

Energy-momentum tensor of Bosonic Ghost Action in String Theory

When quantizing bosonic string theory by means of the path integral, one inverts the Faddeev-Popov determinant by going to Grassmann variables, yielding: $$ S_{\mathrm{ghosts}} = ...
7
votes
0answers
739 views

Mechanical similarity in Landau

I've read this very short paragraph from Landau & Lifshitz's Mechanics (Chap.2, Par.10) (that you can find here) about Mechanical similarity. I was looking for some more detailed explanations of ...
0
votes
0answers
43 views

Viscous force in a conductor

I was told that in a conductor there is a dissipative force and if Ohm's Law is valid for a component, the component has to be dissipative. I'm trying to prove it, but I have some problems. I know ...
17
votes
2answers
1k views

Is the Ground State in QM Always Unique? Why?

I've seen a few references that say that in quantum mechanics of finite degrees of freedom, there is always a unique (i.e. nondegenerate) ground state, or in other words, that there is only one state ...
1
vote
0answers
110 views

Can universe be a closed manifold?

I had a question at MSE which gave a rise to another question. Maxwell equations can be written in form $$d\star F = J$$ Then by Stokes theorem we have $$ \int_U J = \int_U d \star F = ...
1
vote
1answer
381 views

Is pressure invariant under Lorentz transformations?

In an article from the reference there are following words (page 2): "...pressure P is a Lorentz invariant... the result follows from standart properties of the relativistic stress-energy tensor...". ...
17
votes
2answers
1k views

Is Newton's universal gravitational constant the inverse of permittivity of mass in vacuum?

Is it possible to consider Newton's universal gravitational constant, $G$, as inverse of vacuum permittivity of mass? $$\epsilon_m=\frac {1}{4\pi G}$$ if so, then vacuum permeability of mass will ...
3
votes
1answer
468 views

Stokes' theorem in complex coordinates (CFT)

I am studying CFT, where I encounter Stokes' theorem in complex coordinates: $$ \int_R (\partial_zv^z + \partial_{\bar{z}}v^{\bar{z}})dzd\bar{z} = i \int_{\partial R}(v^{z}d\bar{z} - v^{\bar{z}}dz). ...
1
vote
1answer
132 views

Formulation of the uncertainty principle for a system?

There is a biological system that I can indeed describe by a simple quantum Hamiltonian $H$ having eigenstates $|q\rangle$ labelled by the numbers $q$, and having energies proportional to $f(q)$ - ...
1
vote
1answer
120 views

Slicing a surface concentration from a volumetric number concentration

Assume I have a given volumetric concentration $c$ of $N=10000$ particles in a qubic box of volume V: $$c = \frac{N}{V}$$ The units of $c$ are $$[c] = \frac{[\#]}{[m^3]}$$ Now if I introduce an ...
3
votes
2answers
658 views

conceptual doubt in method to find moment of inertia about an axis

I asked this question before about whether I can take a component of angular velocity along another axis and say that the body spins about that axis with that component. Now I have another doubt: ...
0
votes
2answers
255 views

Temperature in a calorimeter [closed]

A closed calorimeter of negligible water equivalent contains 1kg ice at 0 degree Celsius. 1kg of steam at 100 degrees Celsius is pumped into it. Find the resultant temperature of the mixture. I ...
8
votes
2answers
343 views

radiation thermodynamics paradox

This question is concerned with a thermodynamic paradox for radiating bodies and radiation in a cavity of a specific shape. Consider two nested shells that are axisymmetric ellipsoids with the same ...
3
votes
1answer
239 views

physical difference between A and B

We all know that when we say A it sounds different than when we say B. I was wondering what exactly can be the difference between saying A and B in terms of physics. I first thought that it may due ...
4
votes
1answer
948 views

Negative Energy and Wormholes

Apparently to create wormholes you need negative energy/matter. Say you had negative matter/energy, how would it be applied towards making a wormhole?
1
vote
1answer
1k views

Gravitational Field from Irregular Object

How does one calculate the gravitational field of an irregularly shaped object? I was thinking specifically of the gravitational field due to a human, and tried to see if modeling a human as an ...
2
votes
1answer
226 views

about laser wavelength and wave form

I watched a short introduction video online. There are few concepts which are a bit confusing. 1) The video said the laser is single mode (monochromatic), the wavelength is 780nm, so what is that ...
3
votes
2answers
720 views

Why do some air-conditioned stores blast you with jets of air as you enter?

I went to a grocery store on a hot day that was very well air-conditioned, and I noticed as I went through the open entrance that there seemed to be a very powerful downward air current right at the ...
1
vote
1answer
62 views

is it possible to load a transversal wave with a longitudinal wave

like in communication engineering for sending information what we do, we take a high frequency carrier and modulate it with the message signal so can we do the same thing like take a high ...

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