Its certainly possible that the universe will end in a crunch or a rip, and all this speculation will be for naught. But thermodynaics is still a perfectly valid way of looking at these things, and hasn't been changed much by the addition of quantum mechanics except that we now talk about probability distributions within phase space instead of points. Its basically the same stuff, with the same consequences.
Entropy is much more than just dS = dQ/T. I mean, that equation is mostly valid the same way that Newton's laws are mostly valid, but you won't be able to get any sort of feel for it approaching the subject that way. Imagine a mathmatical space with six dimensions for every particle, three for position and three for momentum. The state of the universe is a single point moving in this space according to pre-defined rules. Now, we don't know which point or microstate corresponds to our universe, because we can only make crude measurements of statistical aggregates of particles like temperature and pressure and so forth. So by making these measurements we can narrow which universe we're in to a set of these microstates, a 6N-k dimensional region of the 6N dimensional space that we'll call a macrostate. The entropy of an observed macrostate is proportional to the log of the number of microstates that a macrostate contains, S = k log W. In a sense, Entropy is a measure of our ignorance of which universe we're in, which is ultimately why Maxwell's demon doesn't work.
Please note, the above does contain simplifying assumptions which don't change the main point. For the full story, go get a physics minor at a good university or start reading Wikipedia[1] and asking your physics major friends questions until you can re-derive the laws of thermodynamics yourself.
Entropy is much more than just dS = dQ/T. I mean, that equation is mostly valid the same way that Newton's laws are mostly valid, but you won't be able to get any sort of feel for it approaching the subject that way. Imagine a mathmatical space with six dimensions for every particle, three for position and three for momentum. The state of the universe is a single point moving in this space according to pre-defined rules. Now, we don't know which point or microstate corresponds to our universe, because we can only make crude measurements of statistical aggregates of particles like temperature and pressure and so forth. So by making these measurements we can narrow which universe we're in to a set of these microstates, a 6N-k dimensional region of the 6N dimensional space that we'll call a macrostate. The entropy of an observed macrostate is proportional to the log of the number of microstates that a macrostate contains, S = k log W. In a sense, Entropy is a measure of our ignorance of which universe we're in, which is ultimately why Maxwell's demon doesn't work.
Please note, the above does contain simplifying assumptions which don't change the main point. For the full story, go get a physics minor at a good university or start reading Wikipedia[1] and asking your physics major friends questions until you can re-derive the laws of thermodynamics yourself.
[1]http://en.wikipedia.org/wiki/Statistical_thermodynamics