# All Questions

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### Interpretation Born-Von Karman boundary conditions

The cyclic Born-Von Karman boundary condition says that if we consider a one dimensional lattice with length $L$, and if $\psi(x,t)$ is the wavefunction of an electron in this lattice, then we can say ...
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### Fermion field structure in non-abelian gauge theories

I am trying to understand the structure of the fermions in non-abelian gauge theories. Disclaimer: my question might be very trivial (I suspect the answer could simply be "a change of basis"), but I ...
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### Why do people with bigger hands/wrists have bigger torque advantages in arm wrestling?

I have arm wrestled people with less strength than me who win simply because they have thicker wrists, or larger hands. It has nary to do with having better technique either, because their wrist size ...
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### How is it possible to move something without completely lifting it?

For example, let's assume a chair here: It can be "slid" across the force if we use minimal upwards force, but not enough to actually "lift" the chair. Why should it move? Here's a better example: I ...
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### Was Joule's experiment able to show: thermal energy = $mgh$

Is my understanding of this experiment correct? There is the quantity $MC\delta \theta$ associated to the heat which I think is not an absolute value to be compared with $mgh$ since the \$\delta ...
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### What “time” is it for or on Voyager 1? If you could be “still” in the Universe who fast would time be? [duplicate]

I just sent this to JPL but am not putting all my eggs in one basket so thought I would try some other clever people. :-) I think about physics and space quite a lot but I'm not a maths genius so do ...
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### Anti-matter as matter going backwards in time? (requesting further clarification upon a previous post)

I understand this question has already been asked here, however, I don't have enough reputation points to place a comment (I suppose that's the reason) on a specific answer to request a reference. A ...
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### A few simple questions about Grassmann numbers: commutation relations and derivatives

I'm trying to learn about Grassmann numbers from the book "Condensed Matter Field Theory" by Altland and Simons, but I am currently encountering some difficulties. I have several smaller questions ...
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### Understanding the time dilation calculation in Brian Cox's Doctor Who lecture

Background My son has just watched Brian Cox's fascinating "The Science of Doctor Who" lecture on space-time and was particularly intrigued by the part (at 22m:22s) where he said: Let us say that ...
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### What is the use of this formula 1 Tesla = 1 Newton/Ampere/Meter?

What does Newtons/Ampere/Meter stand for? From this formula: 1 Tesla = 1 Newtons/Ampere/meter what can it be used for? To do what? Ampere/meter Is the same unit as a field's intensity H? Or what is ...
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### Why are high voltage lines “high voltage?”

If I have two spheres of the same size and one sphere has a small amount of charge compared to the other that has a lot more charge, then clearly the sphere with the larger charge has a larger voltage ...
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### Problem with (grad school) physics education? [closed]

(Just to anticipate, having looked at other closed threads about physics education, I don't think this question should be too opinion based or broad.) Since being in a lab now for a couple years, ...