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12755
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location Austin, TX
age 34
visits member for 3 years, 10 months
seen 6 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.


13h
comment Proof of equality of the integral and differential form of Maxwell's equation
@Tobias: only if you don't believe in delta functions.
17h
comment What is entropy really?
Your second equation is more of a definition of the temperature in the microcanonical ensemble.
18h
comment How did Pauli and Fermi deduce the existence of the neutrino?
Charge conservation works with or without the neutrino, since it's uncharged.
18h
answered How did Pauli and Fermi deduce the existence of the neutrino?
1d
comment How fast until you feel wind in space?
You'd have to stop using that Newtonian pressure formula once you started approaching the speed of light -- the momentum transfer with the ISM particles would start becoming relativistic, so you'd have to calculate the 3-force.
1d
comment Advanced kinematics problem regarding $F = ma$
This is not a kinematics problem, it's a dynamics problem. And considering that "advanced" usually means "graduate level or above" here, I would argue that this is not "advanced", either.
2d
awarded  Enlightened
2d
awarded  Nice Answer
2d
comment How does velocity relate to energy difference in Compton scattering?
OH, you're saying that it WOULD, if I had just formatted differently.
2d
comment How does velocity relate to energy difference in Compton scattering?
@KyleKanos I fixed it already. I was hoping the thing would autoformat.
2d
answered How does velocity relate to energy difference in Compton scattering?
2d
comment Can a lone black hole in a closed Universe evaporate?
@Void: you can only do that gluing in Minkowski space due to the fact that it has so many nice Killing vectors. Add a black hole, and it's nontrivial to identify one side of the universe with another without leaving some sort of singularity in the seam.
2d
comment Can a lone black hole in a closed Universe evaporate?
If the universe is closed, then it is not empty.
2d
comment Can a lone black hole in a closed Universe evaporate?
Hawking radiation leaves the horizon above escape velocity.
2d
comment Why do we only talk about three options when it comes to the Shape of Spacetime?
@MarioCarneiro: the light bending is observed in galactic clusters. The gravitational rotation curve stuff happens near the outside of the galaxy, where motions are slow and overall forces are weak, and Newtonian mechanics is sufficient to model the rotation. Of course, if MOND is true, then GR needs to be modified as well, but to describe the galactic rotation curves, you only need Newtonian mechanics.
2d
comment Why do we only talk about three options when it comes to the Shape of Spacetime?
@MarioCarneiro: like I said, we can use that data to assume that Newtonian theory is wrong (on DM scales, you're below relativity's applicability), and construct models about HOW it is wrong. The result you get is more complicated than just assuming dark matter.
2d
comment Why do we only talk about three options when it comes to the Shape of Spacetime?
And also, things like hydrogen absorption lines are the same in other galaxies, so we know that non-gravitational laws of physics are likely the same.
2d
comment Why do we only talk about three options when it comes to the Shape of Spacetime?
@MarioCarneiro: dark matter is a local assumption to fix galactic data. It is almost certainly present in the local galaxy, far below cosmological scales, and MOND models to "account" for it are more complicated than the dark matter assumption is.
2d
comment Why do we only talk about three options when it comes to the Shape of Spacetime?
@CuriousOne: when you construct the model, it's an assumption. I agree that it's an observational fact (note my last sentence), at least to the extent that the void models have finally been completely ruled out.
2d
answered Why do we only talk about three options when it comes to the Shape of Spacetime?