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bio website motls.blogspot.com
location Czech Republic
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visits member for 3 years, 9 months
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Hi, I am a string theorist and a publicist.


Jan
2
answered What frequency photons are involved in mediating physical force?
Jan
2
answered General parameters of the stress energy tensor in local inertial frame
Jan
2
comment Lagrangian for Euler Equations in general relativity
Dear Ondřej, with the ideal gas equation, you added one new variable and one new condition, so you didn't change anything. You may view it as a definition of $T$ and it doesn't change that there are undetermined things. If you made $T$ increase with local friction etc., then you face the same irreversibility problems as those with viscosity, and there won't be any "ordinary" action. Your preference for the variation-defined tensor is legitimate although it is a subjective choice. The Noether currents may still be the primary things in various contexts and the symmetry of the tensor secondary.
Jan
1
answered Lagrangian for Euler Equations in general relativity
Jan
1
comment Simple Harmonic Motion. Why am I wrong? Why is my equation wrong more importantly?
Dear Jak, imagine that one more keyword is "sign". This seems like a homework or exam of yours so maybe people shouldn't fully solve it for you.
Dec
31
comment Which physically acceptable quantum interpretations do not require the existence of any observer at all?
This video has a recipe for anyone who doesn't find QM (and QED) sufficiently psychologically easy and philosophically pleasing: youtube.com/watch?v=iMDTcMD6pOw
Dec
31
comment Which physically acceptable quantum interpretations do not require the existence of any observer at all?
Well, MWI is an ill-defined framework and no one agrees what it is exactly supposed to mean. But if you have a version of MWI which makes physics as observer-independent as classical physics, then you should call it a classical theory, and it can't be a valid description of the world around us which is not classical. It is not equivalent to any classical theory. Every picture that tries to "reinterpret" quantum mechanics as an objective, observer-independent description of some objective reality is classical and wrong whether or not it is "philosophically pleasing" to anyone.
Dec
31
comment Which physically acceptable quantum interpretations do not require the existence of any observer at all?
Dear Kenneth, classical mechanics may be thought of as a description of a "real world" that exists independently of observers, but quantum mechanics cannot. That's why it's quantum mechanics. If it were describing an objective world, it would be classical physics. So every correct "interpretation" of quantum mechanics agrees with the fact that it is a tool to give probabilistic answers to well-defined questions chosen by observers, according to some logical scheme. It is not a description of a objective world that exists independently of observers.
Dec
31
answered What would be pressure of 1 kg of photon gas at room temperature put in a volume of 1 liter?
Dec
30
awarded  Good Answer
Dec
29
comment Need some basic help with notation and the Christoffel symbols
Dear @Ben, eqn 2, as you wrote it, is nonsensical because the right hand side is tautologically zero - second derivatives of $x$ with respect to another component of the same $x$. Maybe you omitted some primes for a different coordinate system? When you wrote that you "rewrite equation 1 more explicitly", you suddenly lose all derivatives with respect to $\tau$ and produce lots of partial derivatives with respect to $x$. In my opinion, this means that you don't understand that the dot means differentiation with respect to $\tau$.
Dec
29
answered Newton's Second Law the real one. Is my theory correct?
Dec
28
comment Identifying fragments when there is a superposition of fragments in quantum Darwinism
I find it very hard to isolate the question you're asking or the hypothetical paradox or incompleteness that you seem to claim to have found. The environment is a "witness" to the state of the system, and what are the particular observables that it may see of course does depend on the dynamics, much like the outcome of Darwin's selection in biology does depend on the animals' eating of each other. The outcome isn't determined in advance. Well, one may guess the outcome in advance, but in that case, he obviously has to know as much as possible about the processes that will take place.
Dec
28
revised Need some basic help with notation and the Christoffel symbols
added 316 characters in body
Dec
28
answered Need some basic help with notation and the Christoffel symbols
Dec
28
answered Do all planets rotate around the sun with the same acceleration?
Dec
27
revised How do we know the geodesic is a minimum?
added 137 characters in body
Dec
27
comment Spin angular momentum of a system of particles : Is there any energy associated with it?
Dear Rajesh, I don't think there's a contradiction. This answer quantifies exactly what I meant, turns it into equations. The comment that "it" only works for rigid bodies is true in the sense that only rigid bodies have their own "constant" value of the moment of inertia. For non-rigid systems of particles, you may define the value of $I$ for which the energy splits in this way but it's useless because $I$ may change arbitrarily, too.
Dec
27
answered how many times have the first photons lapped the universe?
Dec
27
revised How do we know the geodesic is a minimum?
added 488 characters in body