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location Austin, TX
age 34
visits member for 3 years, 8 months
seen 12 hours ago

I am a Ph.D. general relativist working as a software engineer. I like to still go and do physics as a hobby, and to keep up my skill and knowledge.


17h
comment How can space be euclidean when light bends?
Space can be made aribitrarily close to Minkowski(spatial part Euclidean) by choosing a small enough four-cube of spacetime. So, sufficiently small volumes are, in a sense, exactly Euclidean.
18h
comment Maximum curvature in a black hole
Could you expand this question a little bit? It reads to me like "If a is true, then is it possible that a is valid?"
20h
comment On the coordinate independence of general relativity
In particular, there are several solutions to Einstein's equation in vacuum that are NOT just Minkowski space, because they contain gravitational radiation, for example (other, more exotic contents are possible)
20h
comment Is there a substance that doesn't reflect OR absorb light from the visible light spectrum?
Well, incoming energy can always be transmitted.
20h
comment Lagrangian for FRW metric
are you sure, that's not supposed to be $\left(\frac{d{\vec x}}{dt}\right)^{2}$?
22h
comment On the coordinate independence of general relativity
Flat space is <b>Riemann</b> flat, not Ricci flat. All Riemann flat spacetimes differ from the Minkowski metric by a coordinate change. It's actually true that Einstein's equation will have multiple solutions, IN GENERAL for a given stress-energy tensor. You also need to specify initial conditions and boundary conditions for the metric.
Jul
26
comment $F=ma$ calculation taking relativity into account?
@BenCrowell: and with elementary questions like this, I'd rather provide hints and places to look and things to think about than I would provide a comprehensive answer.
Jul
26
comment $F=ma$ calculation taking relativity into account?
@BenCrowell: force increases the momentum, but the asymptote in the formula for momentum allows the momentum to increase without bound, even while $v < c$
Jul
26
revised $F=ma$ calculation taking relativity into account?
edited tags
Jul
26
answered $F=ma$ calculation taking relativity into account?
Jul
24
comment number of gravitons launched by a proton
Though I do hesitate to say that the off-shell particles are "there" at all. The feynman diagram above is, after all, ultimately an artifact of perturbation theory, which depends on our approximation scheme, not on physics.
Jul
24
comment Electrostatics coloumb's Law
@SeñorO: the question is poorly phrased, but not incorrect. Are the spheres conducting? How far apart are the surfaces of the two spheres? I will not answer this question, however.
Jul
24
awarded  Revival
Jul
22
answered Why Light and Observers have different laws of physics
Jul
21
comment The problem in Sredniki's textbook: How do I calculate loop corrections for $\phi\phi\to\phi\phi$ with this Lagrangian?
How can the theory be truly nonrenormalizable if it is related to an exactly solveable one by a change of variables?
Jul
21
answered Frame dragging — is there a “non-tiny” example?
Jul
21
comment Frame dragging — is there a “non-tiny” example?
Just for a point of clarity: there is no shell theorem for an axisymmetric spacetime like there is for a spherically symmetric spacetime. We therefore don't expect the spacetime outside of a spinning mass to be exactly the Kerr metric, as the actual geometry would depend on the multipole moment distribution of the matter distribution. Now this wouldn't matter much in most practical cases, since we would be expanding to first order in the angular momentum in any case...
Jul
21
comment Relatvity of Promise
@Iota: it put a limit on programming computers to do nonsense. But GIGO is totally true before you invoke relativity.
Jul
21
comment Why Light and Observers have different laws of physics
It doesn't rule out anything about the physics of light. It just tells us that we cant' look at physics <b>from the light's perspecive</b>. It is still 100% consistent to talk about the influences of light rays, and the interaction of the electromagnetic field with matter. There is just no observer that will be able to look at an electromagnetic wave and say that it is static. This makes sense, because it would otherwise break Maxwell's equations.
Jul
21
comment Why Light and Observers have different laws of physics
What's wrong with just saying that a ray of light is not a valid observer?