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location New York City
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visits member for 3 years, 2 months
seen 9 hours ago

I do not participate on this site any longer, except to respond to comments regarding my own text, if that text is unavailable in another form. I do not accept the political moderation atmosphere here, it is not compatible with open science. I participate at physicsoverflow.org.


Aug
14
answered Where do the choice of basis in QFT come from?
Aug
14
answered What potential energy functions are mostly used in Schrodinger equation?
Aug
14
revised Did Einstein prove $E=mc^2$ correctly?
shorten, remove wikipedia-isms
Aug
14
answered Did Einstein prove $E=mc^2$ correctly?
Aug
14
comment Is this geometrical 'derivation' of Brownian motion legitimate?
I just wanted to add that in mathematics, a process which doesn't go anywhere on average is called a martingale, and this is called the martingale derivation of the sqrt(N) law. I think Levy of Levy flight fame did things like this.
Aug
14
answered Entropy of an empty universe
Aug
14
comment Why is there an absolute entropy?
This is correct, but I think it should be expanded to say that the entropy becomes a number because quantum states in finite volume/energy are discrete, so there is a number of them. In infinite volume, they become extensive but without the fine-graining classical ambiguity.
Aug
14
comment The entropic cost of tying knots in polymers
The unknot is only entropically favorable for short polymers, where you can calculate the entropy brute force, by simulating. For the long polymer limit, where you need a scaling analysis, the unknot would be unlikely. I was going to think about an answer in the long skinny polymer limit.
Aug
14
revised What does it mean that the neutral pion is a mixture of quarks?
explain why this works pretty well
Aug
14
answered What does it mean that the neutral pion is a mixture of quarks?
Aug
14
answered Why do we have so many dualities in string theory?
Aug
14
comment In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?
@Marty--- the question is not physics, it is mathematics--- can you find Schrodinger operators with identical spectrum. This is a trivial example. More trivial examples are any potential and its translates and reflections, and a less trivial example is any potential and its supersymmetric conjugate, when the ground state doesn't break supersymmetry.
Aug
14
revised In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?
oops
Aug
14
revised In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?
added 174 characters in body
Aug
14
comment In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?
@Everybody: you can add a constant to a potential. It's still a potential. What is this discussion?
Aug
13
awarded  Critic
Aug
13
comment Time in special relativity and quantum mechanics
And Dirac's approach (and Feynman's) makes time an "operator" (or equivalently an integration variable in the path integral). This answer is no more satisfying than saying "In classical mechanics, position is a function, and time is a parameter". That's true, but only if you choose to parametrize by time and not proper time. The same is true in quantum mechanics.
Aug
13
answered In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?
Aug
13
answered In dimensional analysis, why the dimensionless constant is usually of order 1?
Aug
13
comment What the heck is the sigma (f0) 600?
@Timatam: you're not the only person to have this idea. This particle was delisted for a long time, meaning people concluded that it was just a made up particle, just a bump in the cross section due to pion interactions. But the experimentalists shouted that it was really there, and people who do extrapolations of experimental data to extract particles now say that have a pole. I also used to think it was made up, this is why I am confused.