Actually "entropy" doesn't have much meaning in a reversible system as a whole. It only starts taking on meaning when you look at _part_ of the system, such that you have only partial information. I actually have an enormous nit to pick with the way thermodynamics is taught. Physicists focus on "energy" and "entropy", whereas "information" is really much more important. And, _no_, "information" is much more than "negative entropy", because physicists never really get around to being precise about entropy in the first place. E.g., "temperature" is defined as being some sort of integrating function in some textbooks! For example, when physicists talk about a "closed" thermodynamic system, they talk about it being insulated from "heat" (whatever that is!) and insulated from the transfer of "energy" (at least _that_ seems to be reasonably well defined!). However, one can conceive of such systems as being insulated in the normal physical sense, but _not_ insulated from the transfer of information in/out. Due to this imprecision, most of the papers I've read about Maxwell's Daemon are nonsensical. Maxwell's Daemon works perfectly well so long as the energy cost of gathering the information is less than the energy gained. As a situation becomes more complex, the energy variations (hence the amount to be gained) becomes smaller, while the cost to gain the information becomes larger, and it eventually becomes not worth the effort. All "life" is a version of Maxwell's Daemon in action. Modern quantum physics makes it essentially impossible to have a "closed" subset of a quantum universe. What quantum physics is really telling us is that information about the evolution of the system seems to pervade all of the universe. An interesting question is whether even black holes can hide the information within -- I conjecture not even temporarily. (See Ahranov-Boehm (sp?) effect.) So it may be that "thermodynamics" needs even more of a reworking for quantum physics than it has gotten so far. At 06:32 PM 7/5/03 EDT, asimovd@aol.com wrote:
"Entropy increases" is not a law of physics, but rather a consequence of initial conditions. In our universe it can be traced back to our local stars' having "advanced" rather than "retarded" radiation, or more accurately to their radiation being emanated toward us in the same direction that we perceive ourselves to grow older. (So if there are stars with "retarded" radiation, i.e., being emanated in the time direction we call negative, their local life forms would see those stars just as we see ours, timewise.)
--Dan