jld
Reputation
2,250
Next privilege 2,500 Rep.
Create tag synonyms
 Nov 18 comment Most general second-rank symmetric tensor in Einstein theory You could also include higher-order terms, i.e. terms like $g_{\mu \nu} R^2$, $g_{\mu \nu} R^{\alpha \beta} R_{\alpha \beta}$, etc. But once you include those you aren't talking about GR anymore. Nov 18 comment What Would Negative Mass Do To Spacetime? Newton's inverse-square law is equivalent to general relativity in the limit where everything is moving slowly and the gravitational field is weak. So, the first (and easiest) thing to check would be to see what happens if you plug a negative mass into Newton's gravity law. The answer, of course, is repulsive gravity. I.e. a negative mass would be repelled by ordinary matter. Nov 17 comment Derivation of correction to canonical stress energy tensor due to addition of total divergence to Lagrangian Nov 17 comment How is strong time dilation consistent with weak tidal forces? No problem. Don't worry about the points, they don't particularly matter to me. Nov 17 comment How is strong time dilation consistent with weak tidal forces? Actually (axial) tidal forces fall off as $1/r^3$ to leading order. But that just highlights your point further. Nov 17 comment How is strong time dilation consistent with weak tidal forces? A body in orbit doesn't feel the force of gravity, save tidal forces. That's why astronauts in the ISS are weightless! :) Nov 17 revised Time Dilation Experiment added 190 characters in body Nov 17 answered Time Dilation Experiment Nov 17 comment Time Dilation Experiment It would help if you described what you meant by "nullify" the effects of time dilation. Relative to a stationary observer at infinity, both gravitational and velocity-related effects work to slow clocks, so there is never any sense in which they cancel each other. Or did you mean relative to a stationary observer on Earth? The latter is do-able. I'll post how below. Nov 17 answered 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? Oct 23 comment Having trouble understanding some stuff about delta functions Haha, you beat me. Oct 23 answered Having trouble understanding some stuff about delta functions Oct 13 answered Transformation to a uniformly rotating frame Oct 13 comment What is $V^\mu$ if $\nabla_{\mu} V^{\mu}$=scalar? I'm not sure what you mean. $V^\mu$ is a vector with components $V^0$, $V^1$, $V^2$, $V^3$. Oct 11 comment Special Relativity: Finding the Euler Lagrange of a massive particle I don't understand this. You can certainly choose $\lambda = \tau$ if you want to. Oct 11 comment Special Relativity: Finding the Euler Lagrange of a massive particle Why keep the square root? Remember that if $L$ satisfies the E-L equation then $L'=f(L)$ will also satisfy them as long as your parameter $\lambda$ is affine. I suggest using $L'=L^2$ to get rid of the square root - it will make things much easier. Oct 11 comment Geodesic equation from Euler - Lagrange You can always change indices which are summed over because they are just dummy indices! And as long as your free indices match up, your equations should make sense. Oct 11 answered What is the cause of gravitional force of attraction? Oct 10 comment Why particle number operator $\hat{N}$ is $\hat{a}^\dagger\hat{a}$ rather than $\hat{a}\hat{a}^\dagger$? I think he means that $a^\dagger a$ kills the vacuum while $a \, a^\dagger$ doesn't. Sep 23 answered Special relativity; rocket moving towards a mirror