4,032 reputation
11430
bio website
location Belgium
age
visits member for 3 years, 8 months
seen 48 mins ago

"I would never die for my beliefs because I might be wrong."

-- Bertrand Russell


Dec
11
comment Irreversible expansion and time reversal symmetry
It is not essential to the argument because I can start in a special state like the one constructed in 1, and then the time to reach the corner will be very small. So the real point is in explaining why such trajectories are rare.
Dec
11
comment Irreversible expansion and time reversal symmetry
Time is not important, only the relative sizes of the phase space volumes is important. I concentrated on the configurational part because that's the most easily explained and suffices to drive the point home. Second, I'm well aware that ergodicity of the system implies that the system will visit the corner again sooner or later (I implied it at the very end of the second part.) I could have added an extra computation of how long exactly it would take for a typical configuration to get in the vicinity of the corner state. But that is not the crux of the argument.
Dec
11
comment Orbital mechanics of Dragon's Egg
I've read the book's plot on the wikipage, and I just realize that a Star Trek Voyager episode, "Blink of an Eye", basically stole the plot from Dragon's Egg.
Dec
11
answered Irreversible expansion and time reversal symmetry
Dec
11
revised Electron transitions in an infinite square well
edited title
Dec
11
revised Orbital mechanics of Dragon's Egg
added 3 characters in body
Dec
11
awarded  Organizer
Dec
11
revised What does an atom radiate: a wave packet or a single photon?
added 9 characters in body; edited title; added 2 characters in body; edited tags; edited title
Dec
11
comment White Holes and Time-Reversed Oppenheimer-Snyder collapse
Yes, and the entropy of an egg is the same regardless of wether it comes before the chicken or after the chicken. But which evolution is more likely, the one where a chicken lays an egg out of which comes a new chicken or the one where a chicken gets into an egg and hops inside another chicken?
Dec
11
awarded  Enthusiast
Dec
11
awarded  Enlightened
Dec
11
awarded  Nice Answer
Dec
10
comment Nonlinear optics as gauge theory
Ansatz is fine, one could substitute the word postulate for it, or guess as wikipedia suggests. In his 2D Ising paper, Onsager used "eigenwert" for eigenvalue. Actually, an even better translation would be "proper value". There are a lot of German words that entered science, mainly during the period from the end of the 19th to early 20th century. "Gedankenexperiment" is another one.
Dec
10
comment Nonlinear optics as gauge theory
Look, you are tackling this way too abstractly. Maybe you should start with a specific material with nonlinear optical properties and see how you can describe it. Try to make a gauge-invariant nonlinear field equation for it. If you can't, there's not much point to break your head over it. If you can, you've got a basis to try to generalize. But you'll achieve very little if you can't even model the simplest nonlinear material in this way.
Dec
9
comment Why doesn't air freeze?
I agree that the complete explanation is more complicated. It's true that the exact melting point will depend on the structure that the solid will adopt. But I was more interested in giving a general feeling of why one might expect that small molecules will be more motile over than large ones. Although it is not true in the absolute of course.
Dec
9
answered Why doesn't air freeze?
Dec
8
comment How many Onsager's solutions are there?
I think when I studied the 2D Ising model in the mathphys course I had, we used the Peierl's method. But it's such a long time ago, I barely can remember if we really did the full proof or if it was just mentioned. I'm not sure I still have the text of that course. That's a pity. I'm quite busy lately, and I didn't find the time to read Onsager's paper. Besides I'm a bit upset by Onsager's sloppiness.
Dec
8
comment How many Onsager's solutions are there?
The connection between quaternions and spinors should show that Onsager's original approach probably just nicely maps onto Kaufman's approach. Quaternions form a Clifford algebra, and Spin(n) are also Clifford algebras I think, or at least related. Seems like you can take the +100 points. ;)
Dec
8
awarded  Nice Answer
Dec
6
comment What sort of experiment would directly test time reversal invariance?
If space-time is discrete in ultimate analysis, a violation of Lorentz invariance is not unthinkable. But would this also mean a violation of CPT? Probably depends on the kind of theory.