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Jan
13
answered Where does a spinning figure skater's energy go when she slows down?
Jan
11
comment Nothing can travel faster than the speed of light. In what frame of reference?
@WillO: modulo acceleration/gravity (but instantaneous proper speed will of course remain $c$)
Jan
10
comment Why do we order the variables in certain physics questions the way we do?
I'd go with the terms constant, parameter, variable instead
Jan
6
comment How can the Lorentz transformation cause two objects' masses to both increase?
the concept of relativistic mass aside, there's not really anything particularly special going on in the relativistic case - in a non-relativistic world, the same 'astonishing' thing happens for any other velocity-dependent quantity, eg kinetic energy
Jan
5
revised Why does the moon not revolve around the sun directly?
fix typo
Jan
5
revised Why does the moon not revolve around the sun directly?
add intermediate step
Jan
5
answered Why does the moon not revolve around the sun directly?
Jan
5
comment Why does the moon not revolve around the sun directly?
see also math.nus.edu.sg/aslaksen/teaching/convex.html
Jan
5
revised Can a macroscopic body have wavelength as that of electron?
added 107 characters in body
Jan
5
answered Can a macroscopic body have wavelength as that of electron?
Dec
18
comment Better explanation of the common general relativity illustration (stretched sheet of fabric)
see xkcd.com/895 ; while these pictures are misleading, they are not totally wothless eg when explaining geodesic motion: compare p.twimg.com/Ak1EkH_CIAAJcuz.gif vs physicsoftheuniverse.com/images/relativity_curved_space.jpg
Dec
15
comment What is the reasoning behind the Hill Sphere?
see also math.nus.edu.sg/aslaksen/teaching/convex.html
Dec
15
comment Are all scattering states un-normalizable?
did you just forget the square in your normalization condition?
Dec
15
comment Parallel Transport of a 4-vector
I saw some papers and a book (co-)authored by J.G. Pereira on teleparallelism, but the ones I read were mainly concerned with introducing the formalism; it's conjectured that the teleparallel formalism might be more amenable to quantization, but I have yet to see any validation for that claim; from a quick search on arxiv, the main research interest appears to be cosmology and models beyond GR ($f(T)$ gravity)
Dec
15
comment Parallel Transport of a 4-vector
Is this so? That's it exactly, and in contrast to Einstein-Cartan theory, we don't get any new degrees of freedom (there's apparently a whole family of connections related by a sort of gauge symmetry with torsion-free Levi-Civita connection and curvature-free Weitzenböck connection as the limiting cases)
Dec
15
comment Parallel Transport of a 4-vector
What this means is that there is no set of vector fields on the manifold whose tangents we can use as reference vectors. Wouldn’t that be easy? That's called teleparallelism and it leads to a competing theory of gravity mostly equivalent to general relativity (as in same equations of motion, but a different geometry)
Dec
13
comment Derivative with respect to ${\not}{p}$
{\not}p yields ${\not}p$, which looks prettier than \not{p} rendered as $\not{p}$
Dec
12
comment Point masses and infinite densities
@I'm-A-Crackpot-QUACK-CRANK: because it's convenient; oftentimes, we're only interested in the center-of-mass coordinate, and internal structure is an unnecessary complication, unknown or out of scope of the theory (eg quantum); of course, sometimes such a simplification doesn't work (eg point particles are problematic in classical electrodynamics)
Dec
11
revised Is position fundamentally different from other observables?
deleted 7 characters in body
Dec
11
answered Is position fundamentally different from other observables?