0
votes
0answers
3 views

Integral Over Hypersurface Simplification

How does one see it as obvious that $$\int_S \frac{\partial A_i}{\partial x^j} dS^{ji} = \int_S\frac{1}{2}(\frac{\partial A_j}{\partial x^i} - \frac{\partial A_i}{\partial x^j})dS^{ij}$$ where $d ...
-2
votes
1answer
13 views

Amperes Law problems for Homework

Having trouble with homework for an Electromag class. Not sure what the "circulation" is talking about. I know that with the right hand rule, a magnetic field will go in and come back out of loops. ...
0
votes
0answers
5 views

Definition of momentum-entangled particles

When we can say that two particle are momentum entangled ? I just read an article where it's said that two momentum entangled particles share the same momentum value in opposite directions no matter ...
0
votes
0answers
17 views

String theory and space-time supersymmetry

I actually want to know whether space-time supersymmetry is important for string theory consistency? I see that NS and GS supersymmetric strings have worldsheet supersymmetry, but the first one does ...
0
votes
0answers
11 views

Questions on the degenerate ground states and Lieb-Schultz-Mattis theorem?

For example, let's consider a $N$ spin-1/2 system on a lattice described by the Hamiltonian $H$. My questions are ordered as follows: (1) If $H$ has either global $SU(2)$ spin-rotation symmetry or ...
1
vote
1answer
19 views

How we can manipulate the momentum of a particle?

Is there any way to affect a particle's momentum value?
0
votes
1answer
17 views

Isobaric expansion work, W = p(V2-V1)

Isobaric process, so $W = p\Delta V$ according to my book. We have 10 kg of saturated steam at $x = 0.9$, P = 200 kPa. We add work at a rate of $700 W$ and we're interested in the time it takes. We ...
0
votes
0answers
18 views

Hyperbolic Cosine and Sine in Terms of 3-D Velocity

Intuitively, why are $\cosh(\theta) = \frac{1}{\sqrt{1-(v/c)^2}}$ and $\sinh(\theta) = \frac{v/c}{\sqrt{1-(v/c)^2}}$ true in special relativity? Is there some picture I can draw in Minkowski space ...
0
votes
1answer
15 views

How does a wave packet acts rigidly?

Particles can be represented as wave packet. So how does particles gets scattered? Waves superimpose on one another, they don't bounce on one another.
1
vote
4answers
283 views

Can we squeeze atoms?

Lets consider few water molecules (or monoatomic noble gas or $H^+$ ions or electron gas) to be present inside a vessel, now if we enclose the vessel with certain hard material which could act as ...
0
votes
0answers
35 views

Loop Quantum Gravity and Gauge theory

Are there any connection between Loop Quantum Gravity and Gauge theory? If so, how does the gauge theory is described? When exactly does the spin network of the foam is created in the era around the ...
1
vote
1answer
27 views

How does cosmic horizon work?

This is about the horizon which divides us from stuff that is too far to see because it's moving away from us faster than the speed of light. If point $A$ and $B$ are so far away that $B$ is a bit ...
0
votes
1answer
28 views

could the principle of sufficient reason adequately describe causation?

This is an excerpt from the Wikipedia article http://en.wikipedia.org/wiki/Theory_of_everything_%28philosophy%29. Nicholas Rescher Properties and impasse of self-substantiation In “The Price of an ...
5
votes
0answers
57 views

Building a wormhole

We regularly get questions about wormholes on this site. See for example Negative Energy and Wormholes and How would you connect a destination to a wormhole from your starting point to travel through ...
0
votes
1answer
21 views

How does conservation work in wormholes?

My questions might seem naive as I haven't plunged into the mathematical descriptions, but wormholes are interesting even if I don't actually know them :) First of all, is wormhole making two ...
0
votes
1answer
38 views

Need help solving a task - laws of conservation (leptons, baryons, charge)

We got a task from our teacher, a multiple choice task; and here it is: Which of the following reactions is correct, considering the conservation laws? Note: We have only learned to use the ...
0
votes
0answers
13 views

Markovianity vs Ohmic spectral density in Brownian Motion

It is a relationship between the assumption of taking for the spectral density a ohmic behavior ($J(\omega)\sim\omega$) and the fact that the Markovianity of the dynamics arise naturally? Someone has ...
0
votes
2answers
20 views

Passing Polarized light through multiple polarizers in series

This is a question that has been troubling me from many days: Suppose we pass a linearly polarized light through a system of 3 successive polarizers. The 1st polarizer is offset 30$^{\circ}$ from the ...
0
votes
0answers
14 views

Hydrogen Transition Rate from n',l to n',l'

I am trying to solve Problem 9.22 in Griffiths' Intro to Quantum Mechanics (2nd Ed.) that asks to show the spontaneous emission rate for a transition from n,l to n',l' in hydrogen is given by ...
3
votes
2answers
116 views

Tokamaks and the reason they are not efficient

I'm curious about why tokamaks are inefficient as generators. In laymans terms, what is the main reason(s) tokamaks still cannot be used as generators? My limited understanding of tokamaks tells me ...
3
votes
4answers
473 views

Why are people weightless whilst in orbit around the Earth? ISS? Satellites? [duplicate]

Had physics for 2 years now on highschool, but there is a thing I am wondering about. You know the in the height above the earth surface around where the satellites are (Or the ISS), I've calculated ...
0
votes
1answer
21 views

Could compression of electromagnetic waves cause red shift

One argument against "tired" light as a possible cause of red shift is that supernovae judged to be closer to us, based on luminescence, appear to be moving away from us faster than distant supernovae ...
0
votes
0answers
19 views

Quantum physics particle in a box [on hold]

A problem I've been given states: Without calculation, write down and explain the energy expectation value $\langle H\rangle$ and the uncertainty $σ_H$ for the $ψ_n$ energy eigenstate of the ...
0
votes
1answer
41 views

Index Notation with Del Operators

I'm having trouble with some concepts of Index Notation. (Einstein notation) If I take the divergence of curl of a vector, $\nabla \cdot (\nabla \times \vec V)$ first I do the parenthesis: ...
-2
votes
2answers
44 views

Difference between two equations

So again I have two equations: $$K= \frac{1}{2} m v^2 + \frac{1}{2} I \omega^2$$ And $$K_w = \frac{1}{2} I \omega^2 $$ What's the difference between these two? Thanks.
0
votes
1answer
68 views

How many years would it take to travel 490 light-years? [on hold]

NASA has discovered so many new planets and galaxies, one may indeed be a habitat in the future for man kind. This new discovery they think by size and location of sun like star, just might have water ...
0
votes
1answer
22 views

simple question about collimating lens

Let me preface this by saying that I have a very limited knowledge of optics -- basically, I know enough to be dangerous. So I have a square Fresnel lens that measures about 10.5 inches on a side. The ...
0
votes
0answers
19 views

Examples of symmetric field collapse to produce asymmetry

It would really help me with an idea I have if I could see how something such as a symmetric field could collapse to something asymmetric. I know that if $x$ occures before $y$ is symmetric, then $y$ ...
0
votes
1answer
24 views

Electric and Water Flow Analogy

I’ve been studying electricity lately and it has been quite hard to understand the terminology, and picturing it in my mind. After struggling to understand what each property of electric currents ...
-1
votes
0answers
13 views

Momentum of a divided sphere [on hold]

I have a problem with a exercise, please, anyone knows where I wrong? I can not find the error in my solution... Basically I consider that the equation of the horizontal momentum is equal the initial ...
-1
votes
1answer
36 views

Two equations for $y$ in projectile motions

I have two equations on my equation sheet: $$y=v_o t \sin \theta - \frac{1}{2} g t^2.$$ And then another: $$y_{\max} = \frac{v_o^2 \sin 2 \theta }{2g}.$$ I understand that the first one is an ...
1
vote
1answer
17 views

How is “Band Intensity” related to absorption coefficient

I am interested in the linear absorption of 762nm light near a transition of molecular oxygen. I need to find some experimental numbers that will tell us how far the 762nm light will propagate before ...
3
votes
0answers
39 views

Hamilton-Jacobi equation with time dependent Hamiltonian

I was struggling with this exercise about Hamilton-Jacobi equation. I have to solve by menas of Hamilton's principal function the system with Hamiltonian: $$ H=\frac{p^2}{2m}-mAtx $$ with $A$ constant ...
0
votes
2answers
42 views

Why does gravitational lensing bend light rather than absorbing it?

I've read that gravitational lensing bends the light; I am a little confused about black holes and why lensing produces different results. Black holes absorb light whereas lensing should have also ...
0
votes
1answer
35 views

How would you connect a destination to a wormhole from your starting point to travel through it?

Lets say it was possible to create as massive traversable wormholes as we want. Say we started from earth and wanted to cross to alpha centauri. How would I create the wormhole so that it leads ...
2
votes
3answers
45 views

Is it possible to extract energy from mass rotating in space?

Consider a single isolated rotating mass (for example planet), is it possible to extract energy out of its rotation? If yes, how could that theoretically be achieved?
4
votes
0answers
51 views

Lebesgue integration [on hold]

I know this question is probably not adequate to this SE either, but let me explain my situation: I'm civil engineering's college, so, there isn't a SE for civil engineering, and my doubts about ...
1
vote
2answers
51 views

Photons emitted at the event horizon?

While looking through the questions, a came across a section about black holes. I immediately though; what would happen if an atom is orbiting a black hole and emitted a photon perpendicular to the ...
1
vote
2answers
138 views

Why do we orbit around the sun instead of one the other stars?

I am still very new to many physics theories, however while sat in class today, a thought came to mind that I have not been able to answer from simple googling. What is so specific about our sun ...
1
vote
2answers
35 views

Showing that Hamiltonian expectation value is time independent

I want to check that I am getting the concept right here, and my question is: if the expectation value of a Hamiltonian is the same whether you use the time dependent version or not. I thought I had ...
0
votes
0answers
29 views

Coupled Oscillation Simulation

I'm looking for an online coupled oscillation simulation. The best I have got so far is this --- https://phet.colorado.edu/sims/normal-modes/normal-modes_en.html But I'm looking for something which ...
2
votes
3answers
52 views

Does Contraction at High Speeds Happen in Any Dimension Besides Length?

I'm not sure if this is a duplicate. Whenever physics buffs talk about Einstein's relativity (I forget which kind) at high speeds, they always talk about "length contraction", or shortening of the ...
0
votes
0answers
18 views

What do folded concentric circles and rectangles form a hyperbolic paraboloid? [migrated]

Here is a "self-forming" origami that I made from folding concentric circles - it would also happen if I folded concentric rectangles. How can the fold shapes such a saddle-like geometry?
1
vote
1answer
48 views

Rotation and fictitious forces

A bug eats through an apple and forms a vertical, infinitesimally thin canal parallel to the vertical diameter at a distance $\frac{R}{2}$ from the center. The apple rotates at angular velocity around ...
1
vote
0answers
43 views

How to solve the Laplace equation in ellipsoidal coordinates?

It seems that popular textbooks on electrodynamics do not discuss how to solve the Laplace equation in ellipsoidal coordinates. I could not find any reference, but there must be references about this. ...
-1
votes
1answer
25 views

What would be the change in gravitational potential energy? [on hold]

QUESTION ------------ A rope of length L and mass M is connected to a chain of length L and mass 2M and hung vertically from a point. What is the change in potential energy if the system is INVERTED ...
-2
votes
0answers
13 views

How does the chain rule work for more than one variable? [migrated]

I know that that $$\dfrac{d\sqrt{x}}{dt} = \dfrac{d\sqrt{x}}{dx} \dfrac{dx}{dt}$$ In this equation there you only have 1 variable, namely $x$. But why is the following correct?: $$T = \frac{1}{2} ...
1
vote
2answers
29 views

Does the induced charge on a conductor stay at the surface?

My textbook says that when a conductor is placed in an electric field, the electrons in it realign so that the net electric field inside the conductor is zero. There isn't a proof for this. It merely ...
0
votes
1answer
46 views

Transverse part of a current

I am reading Many particle physics (3rd edition by Mahan). On page 51, there is a current of the form $$\vec{j}(\vec{r})=\vec{J}_0e^{i\vec{k}\cdot\vec{r}}$$, the transverse part of it is: ...
3
votes
1answer
53 views

W + jets at NLO

I would like to calculate $pp \rightarrow W (\rightarrow \ell \nu)$ + n-jets (n=2, maybe also 3) at NLO, with some cuts and plot some distributions. I used MadGraph extensively for LO processes and I ...

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