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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.


2d
comment Why is gravity such a unique force?
Why are bimetric theories ruled out?
2d
comment Can you ever exert more downwards force than your weight?
@theonlygusti: no. Whenever you jump, you exert a downward force on the ground that is greater than your weight.
2d
comment When will the pringles can fall?
Do you understand torque?
Apr
25
comment How to debunk 'The Electric Universe'?
Also, why is there a ton of plasma toward the edges of glalaxies, but none near galactic cores? Why does it seem important for globular clusters, but not for solar system dynamics?
Apr
25
comment How to debunk 'The Electric Universe'?
@Giffyguy, um, that's not what $\Lambda$CDM does. And the existing cosmological models come at the relative abundance of dark matter using various methodologies, all of which predict the same result.
Apr
25
comment How to debunk 'The Electric Universe'?
@Giffyguy: great. Point me to a calculation where the electric universe calculates the relative helium abundance correctly in the absence of dark matter.
Apr
23
comment Does metal sublimate?
Mercury is a liquid at room temperature, so it's boiling, not sublimating.
Apr
22
comment Noether's theorem in general relativity
If you're considering an arbitrary geodesic in a fixed spacetime background, then the charges you get out of Nother's theorem will depend on the fixed metric and its symmetries.
Apr
21
comment Black hole with two singularities?
@HarryJohnston: the short answer is because the time of an internal observer and an external observer is different. The long answer would look at HOW the horizon evaporates and would involve drawing a Kruskal diagram of this spacetime, and singularity formation would depend on this answer.
Apr
21
comment Naked Time ( Is there such a thing ?)
And you can come up with observer-dependent notions of time, but these will ultimately reduce down to one of the classical notions that one of those philosophers I cited used.
Apr
21
comment Naked Time ( Is there such a thing ?)
No. it's part of the underlying spacetime geometry. It cannot be meaningfully separated from space in relativistic theories.
Apr
21
comment Naked Time ( Is there such a thing ?)
This question has been treated pretty massively by the ancient Greeks and pretty much any natural philosopher since. I think it would be helpful for you to at least read on the Aristotelian notion of time, which does not explicitly rely on measurement. Hume also had useful things to say about this. I'm sure Kant did too, but it's been so long since i"ve read his impenetrable nonsense, that I don't remember.
Apr
20
answered Does Energy have a similar effect on time as Mass would when considering the gravitational field both exert?
Apr
20
comment Black hole with two singularities?
@HarryJohnston: OOOOHH. Yes. That's true. I'm kind of suggesting a bit of a cheat -- break up the spacetime into a foliation of spacelike surfaces, and then call each of these surfaces "an instant". It's an unphysical construction, but it works mathematically.
Apr
20
comment Black hole with two singularities?
@HarryJohnston: there's a topology change in the spacetime-- you go from two black holes to one. Any spacelike foliation will have this state. Similarly, the horizon is a coordinate-independent thing. How long the period lasts and the like may be coordinate-dependent, but a middle period where the horizons have merged, but the singularities have not IS something that can be defined in a foliation-independent way.
Apr
20
comment Black hole with two singularities?
They can, of course, be made precise, given an appropriate foliation of the spacetime.
Apr
18
awarded  Nice Answer
Apr
17
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.
Apr
17
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.
Apr
17
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