Jerry Schirmer

Austin, TX

Age: 34

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.

8h
comment Why do people traveling FTL using Mass Effect Relays not experience time dilation?
@DougM: I have a phd in general relativity, fwiw. You are correct that a FTL drive wouldn't automatically be going backward in time. But if you had several of them, you would be able to work out time paradoxes relatively easily.
15h
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?
15h
answered Frame dragging -- is there a "non-tiny" example?
15h
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...
15h
comment Why do people traveling FTL using Mass Effect Relays not experience time dilation?
QM has absolutely zero to do with the question. And is consistent with special relativity.
15h
comment Why do people traveling FTL using Mass Effect Relays not experience time dilation?
@DougM: If you can travel in spacelike curves, you very well can go back to where you started, or before where you started. It's just a fact. It's not about powerful lenses or looking backward. It's just the fact that there is no Lorentz-invariant time ordering of spacelike seperate events. If you start letting observers travel along spacelike curves, causality no longer makes sense for those observers. It's not an "apparent" effect. It's a fundamental part of special relativity.
19h
comment Relatvity of Promise
@Iota: it put a limit on programming computers to do nonsense. But GIGO is totally true before you invoke relativity.
1d
comment Why it is meaningful that 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.
1d
comment Why it is meaningful that Light and Observers have different laws of physics
What's wrong with just saying that a ray of light is not a valid observer?
1d
comment Why do people traveling FTL using Mass Effect Relays not experience time dilation?
Quantum mechanics doesn't allow for superluminal causal influences. Special relativity is built into QFT, and is 100% consistent with it.
1d
comment Why do people traveling FTL using Mass Effect Relays not experience time dilation?
@DougM: but a third person, travelling in the opposite direction will see you age from an old man to a baby. Also, if you send a signal to a person travelling at 2c in the opposite direction, you can have them shoot your grandmother before you're born. The effect is really simple if you draw a spacetime diagram.
1d
answered Why do people traveling FTL using Mass Effect Relays not experience time dilation?
1d
comment Abuse over celebrity for Harry Potter: Did Dumbledore choose correctly?
Peter Pettigrew was considered dead.
1d
comment Why are Vulcan lips Human-reddish instead of green?
The didn't flinch at changing the appearance of the Klingons with the launch of TNG/the '80s movies, though.
1d
revised Does "dark matter" explain how I can have -1 apples?
added 36 characters in body
Jul
18
comment Finding the metric tensor from the Einstein field equation?
@ACuriousMind: if you were frustrated with the non-mathiness of Schutz, then you should pick up Wald's book. That was definitely the jumping off point for me.
Jul
18
comment Finding the metric tensor from the Einstein field equation?
Kerr's approach began with study of algebraically special spacetimes. Most of these turn out to be things like the Taub spacetime that don't really apply physically, but Kerr was insightful enough to see that he had found a generalization of the Schwarzschild spacetime. So, he did leverage symmetry, but it was a symmetry in the algebriac structure of the Weyl tensor, not of normal physical degrees of freedom.
Jul
18
comment how to measure the age of light?
@Jim: but we do it not by direct measurement, but by measuring the distance first and dividing by c. That was my point.
Jul
18
comment how to measure the age of light?
@Jim: sure, if you know the hubble law. But we generally use cosmological distance and redshift data to fit to the hubble constant, not the other way around (though it can be used to find ranges to newly discovered galaxies). Irrespectively, it's still a distance measurement, at least in my head. That is certainly the case with luminosity distance -- you measure the distance, and then infer the age. Not vice versa. In any case, the fundamental thing is the distance from which the light was emitted, not the travel time.
Jul
18
comment How long does it take to travel 36 light years with tolerable acceleration and deceleration?
In principle, you could have a design that picks up mass along the way, say by scooping up the ISM and using it as fusion fuel. This could reduce the fuel cost some.
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