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Feb
13
answered Is the cosmological time grosso modo isochrone?
Feb
13
comment If magnetic force (hence torque) does no work, how does a dipole placed in a magnetic field have a potential energy associated with it?
Magnetic dipole or electric dipole?
Feb
13
revised LIGO discovery: if the space “time” metric is changed, how is it measured?
Oops
Feb
13
revised Is there any issue/concern for a slight wavelength shift of the laser light in the LIGO experiments?
Oops
Feb
13
revised How is it that distortions in space can be measured as distances?
Oops
Feb
13
answered LIGO discovery: if the space “time” metric is changed, how is it measured?
Feb
13
comment How is it that distortions in space can be measured as distances?
@JoeBlow: I've extended my answer to address your and related comments. Light is stretched by changes in the metric, but in the LIGO experiment the timescale for this is much slower than new unstretched light is shone into the arms.
Feb
13
revised How is it that distortions in space can be measured as distances?
Extend answer
Feb
13
answered Is there any issue/concern for a slight wavelength shift of the laser light in the LIGO experiments?
Feb
13
comment Light from the big bang
And the universe doesn't have a centre
Feb
13
comment Light from the big bang
The Big Bang didn't happen at a point
Feb
13
answered Schwarzschild manifold
Feb
13
comment Is the cosmological time grosso modo isochrone?
igael, are you asking whether any regions of the universe differ significantly from the comoving frame? That is, are there regions of the universe with significant peculiar velocities?
Feb
13
comment Exercise 18b in Schutz's First course in GR
@MathematicalPhysicist: Oh I see, you're arguing that any null vector normal to $A$ must be zero. I would say instead that to be normal to $A$ any (non-zero) vector $B$ must have the form $(0, b_1, b_2, b_3)$ and therefore must be spacelike not null. But either approach is fine.
Feb
13
comment Exercise 18b in Schutz's First course in GR
@MathematicalPhysicist: typo? Did you mean $\vec{B}^2 \gt 0$ i.e. $\vec{B}$ is spacelike not null?
Feb
13
comment Is the cosmological time grosso modo isochrone?
I don't understand what you mean by grosso modo isochrone and googling doesn't help. Can you clarify what you are asking?
Feb
13
answered Exercise 18b in Schutz's First course in GR
Feb
13
awarded  Guru
Feb
12
comment Spring constant and a spring's decompressed length
Related and possibly a duplicate: Does the stretching of a spring depend on its rest length?
Feb
12
answered General Relativity, Curvature, and extra dimensions