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Jun
25
answered What does it mean to say that “remembering the future and not the past?”
Jun
16
comment Quantum superposition of macroscopic objects
the disintegration of the nucleus entangled both the macroscopic state of the cat and the nuclear decay, but everything you do afterwards happens under the same rules of delayed-choice experiments
Jun
16
comment What determines the spatial variation in phase in a superconductor?
oh this is a very interesting question..
Jun
16
comment Quantum superposition of macroscopic objects
well, suppose that you simplify the cat and just replace it with a sturdy 1x1x1 cm block of ferromagnetic material at 1 Kelvin in a vacuum chamber and you use some resonance to set all the spin up and down in superposition. Decoherence time would be reduced by several orders of magnitude right?
Jun
16
asked Quantum superposition of macroscopic objects
Jun
15
comment How would the laws of nature behave if we reversed time?
such a clock is a reversible system, but it still measures time
Jun
15
comment How would the laws of nature behave if we reversed time?
you could have a zero-energy consumption clock that has zero dependency on thermodynamics: just take some objects to serve as time markers, draw a little red point in the object to represent the direction. Each time marker represents a decimal digit for the number of seconds since some arbitrary point in time. Now go to space and put the markers in a inertial frame on a vacuum chamber. You can adjust the angular velocity and angular position of each marker to be accurate up to some precision. This clock will work for hundreds of billions of year with nearly no energy dissipation.
Jun
12
asked Magnetic dipole near black hole
Jun
11
comment Hawking Temperature of the BTZ Black Hole
also, probably there are other quantum forms of extremality related to 'quantum hair' that is not accounted on the classic theory. Check this question: physics.stackexchange.com/q/47668/10531
Jun
11
comment Hawking Temperature of the BTZ Black Hole
check out this answer: physics.stackexchange.com/a/46868/10531
Jun
11
comment Hawking Temperature of the BTZ Black Hole
actually, there is an intuitive reason: extremality means that a large part of the mass of the black hole can be extracted via the Penrose or the Blandford-Znajek process, so it is in some sense on a ordered state that can be reverted without increasing the entropy. The mass of the black hole when is uncharged, nonspinning represents the entropic energy content that can't be extracted, and seems to be purely thermal
Jun
11
comment Hawking Temperature of the BTZ Black Hole
no intuition, but it seems to be consistent with other calculations of temperatures for spinning and charged black holes
Jun
11
answered Is Venus in the habitale zone of a robot (transistor CMOS brain, metal body) ? Any definition by NASA?
Jun
10
comment Hawking Temperature of the BTZ Black Hole
did you verify if on the extremal limit that temperature goes to zero?
Jun
6
comment Invariance of Lagrangian in Noether's theorem
ok, I understand it a little better now, the on-shell variation is always a total derivative because the integrand is zero, and there are only boundary terms left. But for the sake of finding $f$ that goes into Noether currents, we are only concerned with the off-shell variations?
Jun
4
accepted Trivial conserved Noether's current with second derivatives
Jun
4
comment Trivial conserved Noether's current with second derivatives
I guess my doubt amounts to this: you have to compute the variation of the action in all cases to obtain $f$? will $f$ be simply equal to all the boundary terms on the final variation?
Jun
4
comment Trivial conserved Noether's current with second derivatives
would $f$ (which I understand to be pure boundary terms) be a different function for different symmetry transformations? Is not clear to me how to compute the $f$ that goes at the end of the $Q$ expression in the general case. Would it be different for translations, rotations or time shifts?
Jun
3
comment Trivial conserved Noether's current with second derivatives
"The error in OP's derivation seems to be that it is basically non-existing" I don't understand, what you mean by this? what exactly is non-existing?
Jun
2
asked Trivial conserved Noether's current with second derivatives