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12962
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location Austin, TX
age 34
visits member for 4 years
seen 13 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.


17h
awarded  Revival
20h
comment On which basis we think there is something more than just super dense matter in black holes?
Well, this is true unless you believe that all black holes evaporate. This makes the horizon two-way transversible, and if you believe that they completely evaporate, there is no event horizon at all, just an apparent horizon.
23h
comment Why scalar function of vector can only depend on norm of vector?
Can't you have a third step function that is equivalent to a choice of parity, since you can independently choose a parity and a time-orientation,a nd the Lorentz transforms will respect that?
2d
comment Triple integral $\iiint_{\mathbb{R}^3} d^{3}q ~\delta^{3}(\vec{q})\frac{(\vec{p}\cdot\vec{q})^2}{q^{2}} $ involving Dirac Delta function
Why complicate this with cylindrical coordinates? just use Cartesian coordinates, and let $\delta^{3}({\vec p}) = \delta(p_{x})\delta(p_{y})\delta(p_{z})$
Nov
23
comment How to compute speed without knowing mass or charge values?
Technically, you should consider the recoil of the gold nucleus, so you'd have $\frac{1}{2}mv^{2} + \frac{1}{2}MV^{2}$ on the RHS of your equation, and you'd have to conserve momentum in addition to energy.
Nov
20
comment Scalar field in a Schwarzschild metric
@Danu -- not confluent, DOUBLE confluent!
Nov
20
comment Scalar field in a Schwarzschild metric
Yeah, the schwarzschild metric is a special case of the kerr-newman metric. It's quite an achievement exactly solving the Klein-Gordon equation in a Kerr background.
Nov
20
comment Is there any limit on movement of space itself?
@daniel.sedlacek: what is being gotten at is that it's very difficult to remove the motion of objects from the "motion" of the underlying space in any objective way. There are certain limits where you can talk about the "warping and stretching and bending" of space relative to flat space, but these things are largely metaphors, and not proper, rigorous terms. And in the abstract, there is no upper limit on, say, the relative apparent velocity of two distant galaxies in a cosmology.
Nov
20
comment New subatomic particles
And the non-existence of the Higgs would mean that the standard model was fundamentally wrong in some way. If you dont' find some particular baryon, it probably means that we've been doing qcd calculations incorrectly. And if the Higgs was much heavier than it is, it would mean that we would likely would have had to abandon supersymmetry, and therefore, also string theory.
Nov
19
comment Was the Big Bang actually cold?
Note that the total energy of the universe isn't a particularly well-defined thing if you take General Relativity at face value -- the metric is time-dependent, so you don't have a time translation symmetry, so the magic is broken.
Nov
18
comment Can time be calculated without actually involving any matter?
At a certain level, it's not horribly meaningful to talk about energy as completely distinct from matter.
Nov
18
comment Movement of a cylinder filled with water
(because the water will behave differently in the adiabatic limit than it will when you get waves and the like started.
Nov
18
comment Movement of a cylinder filled with water
I have a feeling you're going to get radically different behavior in your bottle depending on how quickly you spin it.
Nov
18
comment What's the escape velocity of Naked Singularities?
In addition to what @BenCrowell, it is also the case that timelike singularties can exert repulsive forces, so that a geosdesic coming in to the singularity will bounce and emerge from a future horizon. Extended solutions for non-trivial black holes are weird.
Nov
17
comment How is strong time dilation consistent with weak tidal forces?
@jld: yeah, you're right. I was just pulling "force" in the $r$ direction (you know that, future people reading this might not)
Nov
17
answered How is strong time dilation consistent with weak tidal forces?
Nov
17
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@ACuriousMind: fair enough, I guess I don't distinguish too much betwen "particle" and "waveform moving through background field"
Nov
17
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@ACuriousMind: classical electromagnetism is definitely not action at a distance -- all influences happen according to retarded potentials. If I do something over here, the effect on the field over there only happens after it has had time to propogate over there.
Nov
17
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@PeterShor: depends on what formalism you're using. If you do lattice QCD, you can directly calculate the path integral. Irrespectively, if you're doing perturbative field theory, the question of how many virtual particles there are, and what "paths" they take is meaningless. No one diagram happens, just the sum of all of them.
Nov
17
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@PeterShor: nothing is forcing you to calculate amplitudes using perturbation theory. If you dont' use it, then you never need to invoke Feynman diagrams and virtual particles at all.