19,137 reputation
141100
bio website lightandmatter.com
location Fullerton, California
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visits member for 3 years
seen 8 hours ago

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


Jul
26
comment Time Energy symmetry in General Relativity (not asking about energy conservation)
@ticster: A solution to an equation can lack a symmetry possessed by the equation. Note that not all solutions to the Friedmann equations have a preferred time direction. Solutions that recollapse to a Big Crunch are symmetric.
Jul
26
answered Time Energy symmetry in General Relativity (not asking about energy conservation)
Jul
26
comment Mathematical proof of the Second Law of Thermodynamics
duplicate of physics.stackexchange.com/q/81465
Jul
26
comment Can statistical mechanics explain the second law completely?
How is this different from other questions such as this one? physics.stackexchange.com/q/81465
Jul
26
comment Do the standard cosmology models spontaneously break Lorentz symmetry?
@Void: I don't think it's possible for "all matter-energy" in the early universe "to be in a well causally-connected [...] state." We know that the early universe wasn't all causally connected, and that's why the horizon problem is a problem.
Jul
26
revised Do the standard cosmology models spontaneously break Lorentz symmetry?
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Jul
26
answered Do the standard cosmology models spontaneously break Lorentz symmetry?
Jul
26
comment Do the standard cosmology models spontaneously break Lorentz symmetry?
There exists a reference frame S, such that for any point P in S I don't quite follow what you mean here. A frame of reference is basically a timelike, normalized vector, not a set of points.
Jul
26
revised $F=ma$ calculation taking relativity into account?
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Jul
26
revised $F=ma$ calculation taking relativity into account?
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Jul
26
answered $F=ma$ calculation taking relativity into account?
Jul
26
comment $F=ma$ calculation taking relativity into account?
What I'm saying is that the answer doesn't present a complete argument. You haven't connected the dots.
Jul
26
comment $F=ma$ calculation taking relativity into account?
Why is the size of the force relevant? If it were possible to accelerate past c with some force F, then it would also be possible with any smaller force F'; it would just take longer.
Jul
26
comment $F=ma$ calculation taking relativity into account?
In the sentence "Since momentum ... it becomes clear that...," I don't see the logical connection.
Jul
25
revised How would wormhole-based FTL violate causality?
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Jul
25
comment How would wormhole-based FTL violate causality?
Note that the scenario in the paper by Echeverria referred to in my answer (see their fig. 1) explicitly contradicts your implicit solution that I refer to in the preceding comment as #3.
Jul
25
comment How would wormhole-based FTL violate causality?
I think this answer could be improved. It treats wormholes using SR, and this could use some justification, since wormholes are phenomena of curved spacetime. The assumptions seem to be: (1) the spacetime is asymptotically flat, so we can approximate spacetime far from the wormholes as Minkowski space; (2) each mouth of the wormhole must be at rest relative to the other; and (3) traversing the wormhole is equivalent to instantaneous teleportation in the mutual rest frame of the two mouths. All three of these are false in general, but can probably be assumed for the sake of making an example.
Jul
25
answered How would wormhole-based FTL violate causality?
Jul
25
revised How does the nature of nuclear force change between attractive or repulsive based on distance?
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Jul
25
awarded  Revival