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1d
comment What general relativity predicts in such a situation?
@NayanTelrandhe: the point mass moves and will have a time varying quadrupole, so it will produce gravitational waves, but this will be a very, very small effect.
Feb
9
comment Why is it difficult for 2 black holes to merge?
It's hard to answer this directly, but the end answer will be "gravitational radiation is how the black holes fall in, and gravitational radiation is weak, because it couples with $G$ and the leading term is the quadrupole term"
Feb
4
comment Induced metric on a null hypersurface
It's been a long time since I've looked at this stuff, and I"m thinking of it to give you a better answer, but you should look at Sean Hayward's articles on this stuff.
Feb
4
comment Induced metric on a null hypersurface
however, I'm now trying to think through ane example where the statement is false. Note that when particles enter the black hole, the black hole horizon becomes a spacelike, not a null, surface, so this null geometry is no longer valid.
Feb
4
comment Induced metric on a null hypersurface
It's not true in general. Generally, the condition that the horizon is isolated, rather than dynamic, is equivalent to the null tangent vector being a killing field of the induced metric, which gives you the condition you're looking for.
Jan
5
comment What is gravitational energy in general relativity?
@ThomasElliot: it's true about gravitational waves, but definig where the wave is and what they are carrying energy from is a bit subtle.
Dec
28
comment About the complex nature of the wave function?
@ruskin23: I should have said <i>unphysical</i> time and space dependencies in the wave function. When you solve the Schrödinger equation, and you get an answer that depends on the spatial variables, it's giving you real information about where the particle is. It's different when you multiply by a phase -- that's not giving you information about where the particle is, it's giving you information about how that particle might interfere with other particles.
Dec
10
comment If there were infinite many stars
Or, alternately, the stars are receding so quickly that their light has been redshifted to below the visible spectrum.
Dec
3
comment Is there any evidence of black holes existing?
The only truly missing piece is gravitational waves, and we have indirect evidence of that, and hopefully LIGO or LISA (hey, LISA Pathfinder went into the sky yesterday!) will directly detect those.
Nov
25
comment Why is cold fusion considered bogus?
@Joshua: fine. But Tokamaks aren't economically viable, but <i>they can and have been built</i>.
Nov
10
comment How does the second law of thermodynamics forbid the possibility of perpetual machine of the second kind?
I understand, I was just asking for clarity.
Nov
10
comment How does the second law of thermodynamics forbid the possibility of perpetual machine of the second kind?
Which statement of the second law are you using? One of the statements is "no process can cause heat to go from cold to hot spontaneously", and this is pretty obviously violated by a machine like what you describe.
Oct
22
comment Are mass and angular momentum related at a quantum level?
Are you talking about the spin angular momentum, or the orbital angular momentum in an atom?
Oct
20
comment Can you take the integral of $ d^2x\over dt^2$?
@UysofSpades: why is integrating twice weird? You had to differentiate twice to get the thing you're integrating.
Oct
12
comment Is Parity really violated? (Even though neutrinos are massive)
Particles in a world consisting of nothing but left-handed particles move differently than particles in an otherwise identical world consisting of nothing but right-handed particles. Right? That's all that's meant by partity violation.
Sep
8
comment Is a plasma a distinct phase of matter?
Also, the quark-gluon plasma really wasn't a plasma in the sense that the OP is talking about, but yet another state of matter where quarks and gluons are de-localized.
Sep
2
comment Can atoms with top / bottom quarks exist?
@BrandonEnright: I don't see why you wouldn't get bound states of selectrons. You just wouldn't get the Pauli-exclusion driven phenomena like shell filling in multi-selectron bound states. But I don't see where there's any boson/fermion assumption in the derivation of the solution for Schrödinger's equation for the hydrogen atom.
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
23
comment Why curvature produced by electric field in spacetime is so small?
@TomAndersen: yes, you are correct.