John Rennie
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 18m answered LIGO discovery: what in the paradigm hierarchy is that that is not wibbling? 24m 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. 25m revised How is it that distortions in space can be measured as distances? Extend answer 35m answered Is there any issue/concern for a slight wavelength shift of the laser light in the LIGO experiments? 1h comment Light from the big bang 1h comment Light from the big bang The Big Bang didn't happen at a point 3h revised Electromagnetic Wave Propagation edited tags 3h comment Electromagnetic Wave Propagation Hi and welcome to the Physics SE! Please note that this is not a homework help site. Please see this Meta post on asking homework questions and this Meta post for "check my work" problems. 3h comment How to add my URL to StackExchange? Hi Mitesh, click the flag link and ask a moderator to move your question to the Meta. 4h answered Schwarzschild manifold 5h 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? 5h 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. 6h 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? 6h 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? 6h answered Exercise 18b in Schutz's First course in GR 6h awarded Guru 18h 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? 18h answered General Relativity, Curvature, and extra dimensions 19h revised According to Ohm's Law, shouldn't there be a zero electric potential within a capacitor since the current is 0? Tweak 19h revised How can I calculate how high an arrow goes when all I know is its initial speed? I'm not taking my clothes off in the name of physics