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May
21
comment Do Lorentz Boosts in the same direction form a group?
Right, +1. And as you (and I) recently discussed in a different answer, physics.stackexchange.com/questions/23625/… , the relationship of $a,b$ which are additive and form the group $({\mathbb R},+)$ to the velocities $v$ defining the boosts is $v/c=\tanh(a)$ or $\tanh(b)$, respectively.
May
21
revised What exactly does $S$ represent in the CHSH inequality $-2\leq S\leq 2$?
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May
21
answered What exactly does $S$ represent in the CHSH inequality $-2\leq S\leq 2$?
May
21
revised Quantum Entanglement - Measuring Twice
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May
21
revised Auxiliary field and loop expansion
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May
21
comment Theoretical proof forbidding Loschmidt reversal?
While you're right about the "unreality" of the paradox for everyday large enough systems (and only for those, entropy is macroscopic), you're not right about the recurrences in principle (the first paragraph). First, it is not known whether the Universe is spatially closed and even if it is not, the Poincare recurrences do occur because the entropy of our Universe is at most $10^{120}$, as determined by the de Sitter cosmic horizon, and by the black hole complementarity applied to the cosmic horizons, it applies everywhere. After $\exp(10^{120})$ units of time, there have to be recurrences.
May
21
comment How to get Planck length
Try e.g. page 3 of Joseph Polchinski's "String Theory" or the first chapter of any other basic textbook about the subject.
May
21
comment What are Jones matrices and how to derive them?
Hi! Could you please try to study en.wikipedia.org/wiki/Jones_matrix and if something is unclear over there, be more specific about what it is?
May
21
answered Quantum Entanglement - Measuring Twice
May
21
revised Auxiliary field and loop expansion
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May
21
answered Auxiliary field and loop expansion
May
21
revised daylight length variation from year to year
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May
21
comment How to get Planck length
No, this is not the case. In modern era, every physical theory – such as classical GR on one side or non-gravitational QFT on the other side – is a body of knowledge that offers us some approximate laws describing some physical systems; but it's also an approximate theory that knows its limits. Classical general relativity allows us to compute the limits where it starts to break down even in the absence of any detailed theory of quantum gravity and the scale is of order the Planck scale. It's popular to trash talk physics but popularity doesn't mean that there's anything right about your words
May
21
revised The Faddeev-Popov Lagrangian
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May
21
comment EM wave function & photon wavefunction
Two answers above, "morally wrong" should have been "morally right".
May
21
comment How to get Planck length
So for generic elementary objects that are much (or at least visibly) heavier than the Planck mass, one may use classical GR without QM to describe what's going on at a great accuracy. On the contrary, for objects much (or at least substantially) lighter than the Planck mass, one may use QFT without gravity as an excellent approximation. So a full consistent theory of QG – i.e. string theory – is really needed for the relatively narrow transition regime just in the vicinity of the Planck scale. Approximations that neglect either gravity or QM are good on both sides.
May
21
comment How to get Planck length
Concerning your question "How in the absence of a consistent theory of QG one may claim...", there are two points to say. First, it is not true that we don't have a consistent theory of QG. We have known we have one for almost 40 years at this point, it's known as string theory. Second, it was the very point of my answer that one doesn't really need QG to address these points. It's the very point of the Planck scale that for black holes (much) larger than that, one may ignore quantum effects and classical GR becomes a good description.
May
21
comment How to get Planck length
One may prove that distances shorter than the Planck scale fail to obey the laws of geometry in many independent ways, from semiclassical GR to individual full-fledged consistent descriptions of string/M-theory, from AdS/CFT to Matrix theory.
May
21
comment How to get Planck length
Dear Arnold, according to which established, experimentally verified theory can one assert what I did? The theory you're looking for is known as general relativity. One may prove that with a sufficient concentration of energy in a small volume such as one I described, one inevitably forms black holes. This has been known since the singularity theorems due to Penrose and Hawking from the 1970s. Also, for radii larger than the Planck length, one may show that the corrections to GR are small so that the conclusion is unchanged.
May
21
revised daylight length variation from year to year
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