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visits member for 4 years, 9 months
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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.


Aug
27
comment Do matter that falls in a black hole go to the future and the end of the universe?
If a black hole completely evaporates, there is no event horizon. If it is net-evaporating, there isn't even an isolated or dynamical horizon, only an apparent horizon.
Aug
24
comment Pertaining to Newton's laws, how do so many objects acheive perfect equilibrium?
It's the nature of tension to adjust itself to be equal to the weight. It's inherently a response force.
Aug
24
comment Why are gravitational forces always attractive?
the deep quantum field theoretic reason for this is that the underlying theory of gravity is propogated by a spin-2 particle.
Aug
23
comment Why curvature produced by electric field in spacetime is so small?
@TomAndersen: yes, you are correct.
Aug
23
comment Why curvature produced by electric field in spacetime is so small?
@AcidJazz: no, this is the force on an uncharged particle. For a charged particle, we'd have to also consider the electric field at the point, which I did not include.
Aug
21
comment How do we know that the CMBR is the oldest light?
@AlexAdic: because any older light would have had to have passed through the pre-recombination plasma, and would have been scattered. Any older light would be the equivalent of shining a laser through one side of the sun, and expecting to see a beam on the other side.
Aug
19
comment If there is a boson that carries mass, why not space, or time?
@Zach466920: I can't teach you quantum field theory and work through several chapters on spontaneous symmetry breaking in a comment thread. tox, it's more complicated than that, but most people wouldn't call the Higgs, generically, a force-carrying particle.
Aug
19
comment If there is a boson that carries mass, why not space, or time?
@tox123: you'd still have an electroweak force without the higgs, though. It just would be a long-range force with four bosons, though.
Aug
19
comment If there is a boson that carries mass, why not space, or time?
@Zach466920: well, it's not a mass. It's an apparent mass caused by an interaction. And if the particles had intrinsic mass, you'd break most of particle physics. It's a non-obvious answer to a puzzle that baffled particle physicists for twenty years. Particles not having an intrisic mass is a simpler axiom than them all having them. If you want a weird thing, it's why all of the eparticles have different Yukawa couplings, and why there seems to be this flavor hierarchy. (for instance, why isn't the top quark lighter than the charm quark?)
Aug
19
comment If there is a boson that carries mass, why not space, or time?
@tox123: three particles DO carry the weak force, the two $W$ particles and the $Z$
Aug
19
comment If there is a boson that carries mass, why not space, or time?
@Zach466920: read what I wrote. There's a sense in which the question makes sense, and a proposed particle for it. And the Higgs doesn't give all mass in the universe. 99% of all particle mass comes from the binding energy of quarks, which has nothing to do with the Higgs mechanism, and, again, these phenomena are wholly unrelated. And I'm not biased by experience. I just have studied these things in detail, and distilling detailed models down to single paragraphs like the OP can often cause important distinctions to be lost.
Aug
19
comment If there is a boson that carries mass, why not space, or time?
What would it mean to carry volume or distance or time? These properties in general relativity are described by (but are not completely equivalent to) the metric tensor, and changes in the metric ARE carried by the hypothetical massless boson called the graviton. None of this has to do with the Higgs mechanism, though. The Higgs does not carry mass, but rather, interactions of particles with the Higgs give those particles an apparent mass.
Aug
18
comment Would warp bubbles emit gravitational Cerenkov radiation in general relativity?
Asymptotic flatness doesn't force zero gravitational radiation. The metric for a binary black hole system is asymptotically flat, too, after all.
Aug
18
comment Would warp bubbles emit gravitational Cerenkov radiation in general relativity?
@HDE226868: any stress-energy souce with a time-varying quadrupole moment will emit gravitational radiation. Certainly, the setting up and tearing down of the warp bubble would involve a time varying gravitational field involving (exotic) matter, so, genericically, I'd expect gravitational radiation.
Aug
14
comment Anti-matter repelled by gravity - is it a serious hypothesis?
@gox: see edit. I fixed this.
Aug
12
comment What happens to light that falls into a black hole?
Another unstable orbit is, of course, $r = 2M$, ${\dot r} = {\dot \theta} = {\dot \phi} = 0$, of all of the outbound light emitted by things just as they crossed the horizon. This orbit is also unstable, since the horizon will expand once matter enters the horizon.
Aug
11
comment Is there a reason why a relativistic quantum theory of a single fermion exists, but of a single scalar not?
You have the same sorts of problems in single-particle dirac theory: en.wikipedia.org/wiki/Dirac_sea
Aug
10
comment General relativity without energy?
@Conifold: the clear way of writing this would be $\partial_{a}g_{bc} =0$
Aug
7
comment Why not “A” big bang
en.wikipedia.org/wiki/Multiverse
Aug
6
comment What happens to quantum fluctuations near the schwarzschild radius?
The other thing to realize is that virtual particles aren't observable things in any sense. They are really, fundamentally, just computational tools that make it easier to figure out perturbation theory. In particular, virtual particles aren't constrained to travel locally at speeds less than $c$, this is something that is only a restriction on causal modes. So, the virtual particle inside the horizon isn't trapped there. It's only when it is looked at by an observer far away, with a different notion of "real and virtual particle" that the formerly virtual particle appears "real"