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location New York City
age 40
visits member for 3 years
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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.


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.
Aug
13
awarded  Revival
Aug
13
comment The entropic cost of tying knots in polymers
Why do you think it's a cost, and not a benefit? There is a way of calculating this--- figure out the statistics of prime decomposition of a random closed path. But its going to be peaked at something like a given number of prime knots per length. Will you accept an answer which is negative?
Aug
13
awarded  Commentator
Aug
13
awarded  Citizen Patrol
Aug
13
comment What is the difference between complex field and two scalar fields?
@Jerry; You are confusing Dirac masses with Weyl masses. A Weyl mass is the same as a Majorana mass in 4d.
Aug
13
revised Does the Unruh effect violate Mach's principle?
specious is the right word
Aug
12
awarded  Student