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A duck walks into a bar. Animal control is promptly called and the duck is released into a near by park.


May
7
comment Can a force in an explicitly time dependent classical system be conservative?
@episanty: Yes, could be. I'm not even sure if $\frac{d}{dt}\frac{\partial L}{\partial{q'}}$ is a better definition, I don't know. The Lagrangian doesn't display force as obvious as the Newtonian one, or energy as clear as the Hamiltonian approach. And what does not realistic mean here? The task is to pic out the cases in which it works I guess.
May
7
revised Can a force in an explicitly time dependent classical system be conservative?
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May
7
comment Can a force in an explicitly time dependent classical system be conservative?
@KarsusRen: I mean both, but I should have written curl, yes. And it's not "easy", but still to easy, that's the point.
May
7
revised Can a force in an explicitly time dependent classical system be conservative?
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May
6
revised Can a force in an explicitly time dependent classical system be conservative?
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May
6
revised Can a force in an explicitly time dependent classical system be conservative?
added 16 characters in body
May
6
asked Can a force in an explicitly time dependent classical system be conservative?
May
3
comment We tend to think the action of a constant force…?
@Igor: I'm not sure if I understand you. If you are in a enviroment without any noticable forces around you (say you're floating through empts space, and there is no gravity, which would make things more compliated to compute) and you push one object (say your sunglasses) then you act on that object by a force for only one moment. This is where you accelerate the object and it will then have some velocity relative to you. Because of this velocity, i.e. because of this small push for one moment, it will float away from you forever into deep space.
May
3
answered We tend to think the action of a constant force…?
May
3
comment Questions concerning some parts of the section on one-particle states in Weinberg's first volume on QFT
I always wondered if posting copies of book pages here is legal.
May
3
comment General Relativity - Einstein field equation and quantum field theory
@user27515: Our QFTs work on a flat spacetime, and flat spacetime is a solution of the Einstein equations. Then again, to put those puzzle pieces together in a detailed model, you would only be allowed such fields, which produce an energy, which corresponds to the generated gravitational field (flat metric). There lies the problem. If by "with quantum field theory" you mean the standard model, then there aren't too many possibilities you can go, I believe.
May
3
revised How to distinguish 4D and 3D vectors in handwriting?
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May
3
answered How to distinguish 4D and 3D vectors in handwriting?
May
1
comment How could $\textbf{S}^2$ not be a multiple of the identity?
su(n) is always fun. Btw. I would write "the Operator S^2" in the title, because I was expecting a sphere or at least two circles.
Apr
29
comment Why do we use Planck's constant?
@RonMaimon: Also, I'm from Wien. ;)
Apr
29
comment Why do we use Planck's constant?
@RonMaimon: I'd put names on people on the top of the not-to-spell-wrong list.
Apr
28
comment Why do we use Planck's constant?
@RonMaimon: Do you mean Wien? Wein is wine and Wien is Vindobona a.k.a. Vienna.
Apr
28
revised Is the Portal feasible in real life?
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Apr
28
revised Is the Portal feasible in real life?
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Apr
28
revised Is the Portal feasible in real life?
added 141 characters in body