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bio website motls.blogspot.com
location Czech Republic
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visits member for 3 years, 11 months
seen 6 hours ago

Hi, I am a string theorist and a publicist.


Apr
27
comment What's the difference between an entangled state, a superposed state and a cat state?
Dear @Hiatus, after some subconscious thinking, I actually think that the "cat state" wasn't meant to be a Schrödinger cat state but rather the ket state. ;-) Isn't it a funny hypothesis?
Apr
27
awarded  Enlightened
Apr
27
revised Correlators at large N and large N factorization
added 9 characters in body
Apr
27
comment $\frac{1}{\sqrt{2}}$ (|Independent particle Model⟩+ |Strong Interaction Model⟩)?
The right framework is called Quantum Chromodynamics, QCD. You describe a nucleus with $A$ nucleons as a bound state of $3A$ valence quarks (plus infinitely many other quarks and gluons) interacting via the strong force and creating an environment that is similar to a liquid, you take a supercomputer, and get results that may be accurate but in principle don't teach you much about the nuclei beyond the two phenomenological models.
Apr
27
comment What are constraints on a “purity” operator in quantum mechanics?
There is obviously no nontrivial "purity operator" on the Hilbert space because all states $|\psi\rangle$ in the Hilbert space are pure. You could define a "purity operator" on the space of density matrices but it wouldn't be a linear operator because one may get (and usually gets) mixed states by making superpositions of pure states. These non-existences shouldn't be surprising because "purity" is not an observable. An observable is something that you may measure in 1 repetition of an experiment, to get 1 number. Purity can't be measured in this sense.
Apr
27
answered The 4D Physics of a Superstring Background
Apr
27
awarded  Nice Answer
Apr
26
comment Could a fish in a sealed ball, move the ball?
Exactly, @Peter Shor, that's the right analogy. Bjorn writes a similar thing below - the fish may distribute the angular momentum to take a part, and force the remainder of the ball to rotate in the opposite way - and in this case, it resembles your hamster. Also, the center-of-mass remains at the same spot, so even without a rotation, if the fish heavier than water moves in one side, the water and glass goes in the opposite. Except that a floating fish is optimized so that it is as heavy as water in average, otherwise it wouldn't float, Peter. ;-)
Apr
26
comment What is the force on the arms in a pushup?
+1 for the pretty illustration. ;-) Time for me to do my regular 160 pushups...
Apr
25
answered The chiral ring of N=2 WZW models
Apr
25
comment Does Quantum Mechanics assume space and time are continuous?
Dear David, I have written complete proofs that discrete dynamical spacetimes are inconsistent at hundreds of other places. This is not a place to write it for the 101th time because this is a question about continuity of space and time in quantum mechanics, and not a question about quantum gravity, and the answer to this question is unambiguous.
Apr
25
comment Does Quantum Mechanics assume space and time are continuous?
Dear madR, the Lorentz symmetry mixes space and time, $(t,x)\to (t',x')$, so if this symmetry is preserved, it follows that if $t$ is continuous, $x$ has to be continuous as well.
Apr
25
answered Does Quantum Mechanics assume space and time are continuous?
Apr
24
answered Causality and Determinism
Apr
24
answered How can I understand counterintuitive units like $\text{s}^2$?
Apr
24
awarded  gravity
Apr
23
answered Lattice Yang-Mills
Apr
23
awarded  Electorate
Apr
23
revised Neutralino Dark Matter Detection
added 324 characters in body
Apr
23
answered Neutralino Dark Matter Detection