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Jul
2
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Mar
11
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Dec
21
comment on causality and The Big Bang Theory
arxiv.org/abs/1112.4508
Dec
4
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Oct
27
awarded  Nice Question
Oct
2
revised Why is the partition function called ''partition function''?
edited body
Sep
28
comment Is the firewall paradox really a paradox?
@Scott Aaronson: I don't understand why "a qubit that an infalling observer sees falling toward the singularity, also gets emitted from the horizon from an external observer's standpoint". Could you explain, or give a reference containing the explanation why both have to see the qubit? Is this because we want to save the information contained in the qubit from being lost, or there is another reason?
Sep
28
comment Is the firewall paradox really a paradox?
Very interesting answer! Concerning the amplitude for a black hole never to form, this bothers me too, since I don't understand how Hawking chose the measure to obtain this. The measure either has to make the black hole histories negligible, or make them to cancel one another, and I don't understand how.
Sep
28
comment In relativity, can/should every measurement be reduced to measuring a scalar?
Excellent update, it makes perfect sense!
Sep
28
revised In relativity, can/should every measurement be reduced to measuring a scalar?
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Sep
27
revised Is the firewall paradox really a paradox?
added 5268 characters in body
Sep
26
answered Is the firewall paradox really a paradox?
Sep
26
comment In relativity, can/should every measurement be reduced to measuring a scalar?
@Ben Crowell: They differ by the factor $-\chi^2$, but where in the paper is this relevant? Brown denotes $T^0_0$ by $-\rho$ (instead of $-\frac{\rho}{\chi^2}$) (4). Then, he uses that $-\rho$ instead of $T^0_0$ in some equations, which to my mind are correct. He could just have used everywhere $T^0_0$, but he preferred to note it by $-\rho$, which may not be customary. Maybe I am missing something, but I don't see where he made the claim that this is the true mass-energy density and not that from MTW, or a place where he used a wrong equation by identifying $T^0_{0}$ with $T_{00}$.
Sep
26
comment Is a QFT in a classical curved spacetime background a self-consistent theory?
Michael Brown is right. Search for QFT in curved spacetime (en.wikipedia.org/wiki/Quantum_field_theory_in_curved_spacetime), and algebraic QFT (en.wikipedia.org/wiki/Local_quantum_field_theory)
Sep
26
comment In relativity, can/should every measurement be reduced to measuring a scalar?
@Ben Crowell: The correct formula is that from MTW, in which $T_{\mu\nu}$ appears. Hence, $T_{\mu\nu}=diag(\rho,p_r,p_\theta,p_\phi)$, and if we raise an index, $T^\mu_\nu=diag(\rho',p_r',p_\theta',p_\phi')$. I think that Brown denotes directly the stress-energy tensor with mixed indices like this, $T^\mu_\nu=diag(-\rho,p_r,p_\theta,p_\phi)$. It is just a matter of notation.
Sep
26
revised In relativity, can/should every measurement be reduced to measuring a scalar?
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Sep
26
revised In relativity, can/should every measurement be reduced to measuring a scalar?
deleted 255 characters in body
Sep
26
revised In relativity, can/should every measurement be reduced to measuring a scalar?
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Sep
25
comment In relativity, can/should every measurement be reduced to measuring a scalar?
@Trimok: In the original answer, I used $i,j$ for indices of any frame. In the part about $T_{\mu\nu}$ I used $\mu$ and $\nu$ just to keep the notations from the question, but represent the same thing. $e_i{}^j$ simply represent the components of the vector $e_i$ in another frame. I considered both frames as general as can be. But in the tetrad formalism, in general one of the frames is orthonormal, and the other is a coordinate frame $(\partial_\mu)$. In general, people denote the coordinate indices differently than those from orthonormal vector frames. I did not use this in my answer.