21,272 reputation
13468
bio website
location Austin, TX
age 35
visits member for 4 years, 6 months
seen May 19 at 6:41

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.


May
15
comment Planet Sized Generator
That said, if there is a way to ablate out a borehole or something, this could be a way to convert chemical energy into electrical energy. Obviously, that's not super practical, either.
May
15
comment If proton spin emergence from quarks and gluons is mysterious, why is silver atom spin not?
Isn't this more about the fact that you don't have a clean definition of quarks in a bound state? Like, the proton is made up of a complicated set of parton distribution functions due to flavor mixing and the rest. To a very good approximation, the silver atom is made up of electrons and a nucleus. The analogous statement about protons and quarks isn't true--the binding energy is much larger than the masses of the constituent quarks.
May
13
answered Light trajectory
May
13
comment Faster than light
Another thing he may have been talking about is virtual photons, which are internal recordkeeping entities in certain calculations in quantum mechanics, and are not independent entitites with objective existence that you can use to send signals.
May
13
comment Is spacetime flat inside a spherical shell?
I"m reading the paper you linked now, but I have to say that it contradicts relatively simple arguments derived from just using Einstein's equations directly, as in Weinberg's book. And your answer seems to confuse some core concepts of how you paste together solutions.
May
13
comment Is spacetime flat inside a spherical shell?
I don't even get what you're talking about. Birchoff's theorem is exactly true in general relativity. Who cares if you call the parameter the "Schwarzschild radius" or whatever. it's a constant in the solution, and it is zero inside a spherical cavity. And you don't assume anything about the volume of a sphere when deriving these results.
May
12
comment Is spacetime flat inside a spherical shell?
$R$ is just a parameter in the theory. It comes out when you assume spherical symmetry. YOu don't have to assume anything special about the coordinate system at all. See Weinberg's Cosmology book for explicit detail about this.
May
11
comment Milky Way galaxy central black hole and time contraction of life story
For what it's worth, the time dilation from the matter between SgrA* and Earth is going to be a lot larger than that due to SgrA* itself.
May
11
answered Milky Way galaxy central black hole and time contraction of life story
May
8
comment How can a black hole have a charge?
It's really not best to think of static fields in terms of force-carriers. The photon field is a disturbance in the electromagnetic field, and the field of a black hole or any isolated static charge is a nice static charge best described in terms of the field.
May
7
answered speed of light and conservation of linear momentum
May
5
answered Why is the photon-sphere around a Kerr Black Hole spherical and not ellipsoid?
May
4
comment Why is Einstein solution to the twin paradox different from the one on the internet?
@Abc2000ro: they're equivalent because the acceleration connects two different inertial frames. The paradox would also be resolved if the first twin sent information about their age to someone travelling in a rocketship moving in the opposite direction. You don't really have any acceleration in that case, but you still have a frame shift. Acceleration is just a special case of switching sets of inertial frames.
May
4
comment How to debunk 'The Electric Universe'?
@Giffyguy: and I'm sorry if I came on too strong. I do just strongly believe that new theories really do have to explain the successful predictions of old theories.
May
4
comment How to debunk 'The Electric Universe'?
Seriously, how do you even resolve Olbers' paradox in this model?
May
4
comment How to debunk 'The Electric Universe'?
Seriously, how can this model pass both solar system tests and explain galactic dynamics, AND predict the correct helium abundance? Show me that link, rather than some preachy youtube article about skepticism. I'm applying skepticism to the positive statemetns your'e making. I'm already willing to consider alternatives to dominant models. I'm just not willing to consider crap.
May
4
comment How to debunk 'The Electric Universe'?
@Giffyguy: I've given talks on MOND. I've proposed papers to Bekenstein and Milgrom on explaining the bullet cluster in a TeVeS model. I'm totally willing to consider alternate models. This particular model is loaded with problems. Dark matter and dark energy are problems with the $\Lambda$CDM model, but there are theoretical reasons why things like dark matter and dark energy might exist, and there are deeper, bigger problems with alternative models (Or, like TeVeS, they have even MORE adjustable parameters and degrees of freedom). And that link does not address any of my concerns.
May
2
comment Can the coefficient of friction be derived from fundamentals?
Note taht the simple $F_{fr} = \mu F_{N}$ relationship you learn in intro physics isn't quite right. For instance, in that link that pentane provides, the derived $\mu$ is a function of the normal force.
May
1
comment Any tips on evaluating Riemann tensor?
@EdisonCesar: I would actually recommend implementing your own engine in mathematica -- it will teach you how the vector multiplication engine works, and will also teach you how to do the calculation by hand.
Apr
30
comment Is current in superconductors infinite? If they have 0 resistance then I (V/R) should be infinite?
It's probably better to think of superconductors as materials where current can freely flow without an applied voltage.