3,533 reputation
1614
bio website
location
age
visits member for 2 years, 4 months
seen 3 mins ago

Jan
31
revised How do we know that heat is a differential form?
clarified non-quasi-static and irreversible case
Jan
31
comment How do we know that heat is a differential form?
@LubošMotl: no, I don't disagree; perhaps a better way to phrase what I was ultimately thinking about is this: given initial and final states in thermodynamic equilibrium, can we decide if a reversible or irreversible process has happened from (total) work and heat alone; it's true that this goes beyond the original question, so the best thing to do is probably just mention that the differential formalism just does not apply...
Jan
31
comment How do we know that heat is a differential form?
@LubošMotl: but initial and final states are well defined, and we can connect those via quasi-static processes, and I started wondering if these could reproduce the $Q,W$ of the irreversible process, and if so, whether that's even a meaningful question; then I started thinking about the fact that even in the irreversible case, we still have a $Q(t), W(t)$ and thus a $\Delta U(t)$ as well as at least some of our other state variables; in fact, in an irreversible quasi-static process, all of them would be well-defined; then I went to lunch, and here we are ;)
Jan
31
comment How do we know that heat is a differential form?
I'm wondering if the claim that no path could give the correct answer is actully true in general - it seemed obvious at first, but I think we all know how that can go ;)
Jan
31
comment How do we know that heat is a differential form?
@LubošMotl: I think the more interesting part of the question is the PS about non-quasi-static (and thus irreversible) processes; I just asserted that integration our forms over reversible curves would never give the correct answer, but now I'm wondering if that is actually the case...
Jan
31
revised How do we know that heat is a differential form?
answer 2nd part
Jan
31
revised How do we know that heat is a differential form?
fix sign convention
Jan
31
revised How do we know that heat is a differential form?
added 132 characters in body
Jan
31
answered How do we know that heat is a differential form?
Jan
30
answered What is this form of notation called?
Jan
29
comment Why does a floating balloon in an accelerated train moves forward but the pendulum moves backward?
see physics.stackexchange.com/questions/86774/…
Jan
28
comment Lorentz transformation implemented by a non-unitary operator.
or arXiv:0712.0997
Jan
28
comment Lorentz transformation implemented by a non-unitary operator.
@LoveLearning: you can also make use of the fundamental theorem of projective geometry, but if you want to start from scratch, that just shifts the burden around
Jan
28
revised In there such a thing as the Black Hole Information Paradox?
added analogy
Jan
28
comment In there such a thing as the Black Hole Information Paradox?
@MBN: I may have missed something obvious, but I don't think that's it: after all, we only end up with a mixed state because we trace out irrevocably lost degrees of freedom - but they are only irrevocably lost if there are no hairs
Jan
27
asked In there such a thing as the Black Hole Information Paradox?
Jan
27
comment Why is the charge on protons == to charge on electrons?
@dmckee: note that it's only half a duplicate as it contains two separate questions
Jan
27
comment Why is the charge on protons == to charge on electrons?
@jinawee: cough form factor cough
Jan
27
revised Can a small change in the Earth temperature give rise to large-scale climate changes?
spelling
Jan
27
comment Can a small change in the Earth temperature give rise to large-scale climate changes?
@annav: you're aware of the timescales involved? as rendered ($800\times600$), a hundred years corresponds to less than 0.2 pixels...