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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
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?
added 8 characters in body
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?
added 95 characters in body
Apr
28
revised Is the Portal feasible in real life?
added 141 characters in body
Apr
28
revised Is the Portal feasible in real life?
added 141 characters in body
Apr
28
revised Is the Portal feasible in real life?
added 295 characters in body
Apr
28
answered Is the Portal feasible in real life?
Apr
24
comment How fictitious are fictitious forces?
let us continue this discussion in chat
Apr
24
comment Why do objects follow geodesics in spacetime?
Newtons first is a bad example for a comparison. The law introduces "inertial frames", i.e. defines its meaning. If the law would say "An inertial frame is one in which bananas speak" the law would still "correspond to reality" (there just would be no inertial frames). An "because nature is lazy" argument is imho bad, because the fact that we can model the world using general relativity is what makes the equation possible. So in a world where we could not come up with that theory, we could neighter say "is not lazy" nor "it's lazy". And "intuitive "explainations" are merely more information.
Apr
24
comment How fictitious are fictitious forces?
It's not necessary to make this pseudo force construction here - the last line explains why the third line is no problem. In the beginning claim "she experiences a force mg downwards" you'd have to explain what "experiences" means because if you consider her to be a point particle, then as you said, she doesn't effectively feel any acceleration. The principle says exactly that, namely that if you're in free call, you locally don't know that there is a gravitational field around. Notice there is no global inertial frame in that example. Also, don't post questions as an answer (this is no forum)
Apr
24
comment How fictitious are fictitious forces?
@Pygmalion: "more disagreement" is not really appropriate, since what I pointed out is a fallacy, which can be avoided. Funny enough, the first sentence of the wikipedia quote makes the same mistake. The problem described in what follows is a totally different kind of problem. To quote Einstein: "The weakness of the principle of inertia lies in this, that it involves an argument in a circle: a mass moves without acceleration if it is sufficiently far from other bodies; we know that it is sufficiently far from other bodies only by the fact that it moves without acceleration."