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bio website motls.blogspot.com
location Czech Republic
age 40
visits member for 3 years, 9 months
seen 6 mins ago

Hi, I am a string theorist and a publicist.


Jan
4
comment Does the measured mass of earth include that of the atmosphere?
Well, the mass of Earth can be and has been measured by Kepler's method as well – from the orbit of the Moon – and this method makes it completely clear that the atmosphere, like anything else linked to Earth, is included just like the bulk of the Earth.
Jan
4
revised Why is E6 favored over E8 for GUT building?
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Jan
4
revised Why is E6 favored over E8 for GUT building?
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Jan
4
answered Why is E6 favored over E8 for GUT building?
Jan
3
comment How is causal patch complementarity compatible with behavior during inflation?
Great question. I have some guesses but I would love to hear someone's answer that has a confident logical argument beneath it.
Jan
3
answered Does the potential energy of fluid rising on a string change?
Jan
3
revised What is the symmetry that corresponds to conservation of position?
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Jan
3
revised What is the symmetry that corresponds to conservation of position?
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Jan
3
comment What is the symmetry that corresponds to conservation of position?
Constants such as $c$ or $\hbar$ or $\pi$, for that matter, are not considered conserved quantities because they're not really "quantities". By a quantity, we a priori mean a nonconstant function of the observables describing the system, such as $x_i$ and $p_i$, i.e. things that become operators (not $c$-numbers) in quantum mechanics. So the constants you mentioned are not conserved quantities. To say the least, they aren't independent conserved quantities.
Jan
3
comment What is the symmetry that corresponds to conservation of position?
Dear @Revo, "I was wondering if I can generalize your answer by saying that not every conserved quantity can correspond to a useful symmetry." - My point was exactly the opposite, it was Noether's theorem. Whenever there is a [useful] conserved quantity, there is a [useful] symmetry, and vice versa. This rule is known as Noether's theorem. In this particular case, neither the symmetry nor the conservation law was valid for a sensible physical system.
Jan
3
answered Is there really no meaning in potential energy and potential?
Jan
3
comment What are the advantages of the ILC over the LHC?
"There have to be more reasons why the ILC is more advantageous than the LHC." - Well, you're essentially wrong, Michael. There don't have to be any other reasons. jdm's answer is detailed and exhaustive but it confirms the basic thesis you summarized by the word "cleaner".
Jan
2
revised What is the symmetry that corresponds to conservation of position?
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Jan
2
comment Regularization of the Casimir effect
Tao is great but this is simply not a valid answer to the original question. Tao's text is pretty much purely mathematical and makes no physics (QFT, renormalization) analysis of the situation whatsoever - namely the coupling constants, counterterms or regulators, symmetries constraining the laws of physics if any, and the dependence or independence of physical observables on these things. So -1.
Jan
2
comment Regularization of the Casimir effect
Good physics answer, +1, as opposed to just cheap production of URLs to worshiped Fields medal winners who, despite their greatness, provide pretty much zero contribution to the answer to the original question, namely what is adjustable about the parameters describing these physical situations (plates vs other geometries).
Jan
2
answered Why is cosmological acceleration expressed in terms of an energy density?
Jan
2
comment Conjugate Variables and Fourier Transforms in Classical Physics
He apparently means Fourier transform over the time coordinate.
Jan
2
answered What is the symmetry that corresponds to conservation of position?
Jan
2
comment General parameters of the stress energy tensor in local inertial frame
Thanks for your understanding, Ondřeji.
Jan
2
answered What frequency photons are involved in mediating physical force?