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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.


1d
awarded  Nice Answer
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comment Black hole with two singularities?
And there are other, vague restrictions you have to make for physicality -- the hole could have a nonzero Taub charge or something, but this answer is right enough for the puroposes of the question.
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comment Solving Lagrangian equations of motion for two point-bodies with gravitational interaction
It will make deriving the equations a lot easier if you do the substitution first.
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comment Solving Lagrangian equations of motion for two point-bodies with gravitational interaction
If you do this, then you'll see that your answers are yes, yes, and yes
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comment Solving Lagrangian equations of motion for two point-bodies with gravitational interaction
You'll save yourself a lot of time and energy by replacing ${\vec r_{1}}$ and ${\vec r_{2}}$ with ${\vec r} = {\vec r_{1}} - {\vec r_{2}}$ and ${\vec R} = \frac{1}{m_{1}+m_{2}}\left(m_{1}{\vec r_{1}} + m_{2}{\vec r_{2}}\right)$
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answered Black hole with two singularities?
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comment Was Nikola Tesla right about his ether theory?
I don't doubt that Tesla said something like that. He was probably refuting older theories that tried to assert that the field wasn't real. Also note that the dominant paradigm in chemistry at the time was Wilhelm Ostwald's energeticism, which asserted that there were no atoms and matter was infinitely divisible. In this mindset, electric "matter" was just another fluid. In 1890, this was plausible. By 1930, it was all definitively shown to be completely wrong.
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comment Was Nikola Tesla right about his ether theory?
sigh Nicola Tesla did the bulk of his work before Einstein did his. He worked in the old paradigm. For a while after Einstein's paper and the michelson-morely experiment, there was some debate about special relativity. There is no longer any room for debate on the matter. A large chunk of our modern machinery needs special relativity and/or quantum mechanics to work.
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comment How exactly does curved space-time describe the force of gravity?
This derivation is actually wrong, because $\frac{delta R}{\delta g^{ab}}$ is only equal to $R_{ab}$ up to boundary terms, which is enough to obtain the field equations, but will give you the wrong Hamiltonian, etc. And you have to take the variation inside of the integral.
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comment How exactly does curved space-time describe the force of gravity?
However, I would say that if you're going to go into the technical details of taking the variation of the Hilbert action, you shoudl be honest enough to work through all of the details, and the variation above is fudged to work out right, but doesn't follow the rules of either the standard variation, or the Palantini version -- the $\frac{\delta R}{\delta g^{ab}}$ bit is just sleighted away. Of course, it takes Landau-Lifschitz 15 pages to do it.
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comment How exactly does curved space-time describe the force of gravity?
I never got why Wheeler wasn't as famous as Feynman. He had that same magical way of reducing things down to really clear, simple statements that made complicated things seem obvious.
2d
answered Is there any physical meaning for the inverse metric?
Apr
15
comment What is the significance of angular frequency $\omega$ with regards to wave functions?
Maybe this image can help... echteinfach.tv/formeln/geometrie/animations/…
Apr
12
comment Physical intuition on $\mathbf{v}\otimes \mathbf{w}$
@PyRulez: what I gave is more physical than any of the other answers. and a (1,1) tensor is equivalent to a (0,2) tensor in a metric space, which is every space that the OP has ever seen.
Apr
12
answered Physical intuition on $\mathbf{v}\otimes \mathbf{w}$
Apr
12
comment Does Peskin & Schroeder Eq. (4.26), $U(t_1,t_2)U(t_2,t_3) = U(t_1,t_3)$ imply $[H_0,H_{int}] = 0$?
This fails already with simple massless $\phi^{4}$ theory. Clearly, $\phi^{4}$ cannot commute with $\Pi_{\phi}$, and it will therefore not commute with the Hamiltonian.
Apr
10
answered Are we really sure that the whole universe is expanding?
Apr
8
comment Do all “normal” black holes rotate?
but yes, I wouldn't conclude too much from kruskal topology.
Apr
8
comment Do all “normal” black holes rotate?
@irishphysics: well, I wouldn't say that Schwarzschild is useless. It's TREMENDOUSLY less complicated than Kerr, and the kerr corrections fall off a factor of $r$ faster than the schwarzschild terms, so for many cases, schwarzschild is perfectly good. Not to mention all o fhte birchoff-style reuslts you can get.
Apr
8
answered Do all “normal” black holes rotate?