Friday 29 February 2008

Second Law of Thermodynamics

Take an enclosed container partitioned in the middle, one half filled by some gas and the other vacant. Remove the partition and keep an eye on the second half which was initially vacant. Observe for a life time and tell me if you ever get to see that vacant again. That's the classic example you would be taught if you were a student of statistical mechanics.

Now take a soft ball and drop it from a height. Observe it bouncing back couple of times and finally settling down. That's a very natual sight, isn't it? Now tell me if you ever get to see a ball that was lying dead on the ground, suddenly coming to life and bouncing back by itself. One wouldn't even consider that possibility!

In the first case, statistical mechanics tells us that it's merely by chance that you don't get to see the second half vacant. Meaning, there is nothing stopping it to go that way, only thing is that the probability so infinitesimal that would problably never get to see it. After all, you can theoritically reverse the motion picture to get back to the original picture. Nothing against the laws of physics - you're just not fortunate enough to see that dramatic event.

But the second case seems to be interesting. Kinetic energy dissipating into heat/sound energy is quite natural but the reverse is not so. The second law of thermodynamics says that system tends to achieve thermal equilibrium, and there is some irreversibility somewhere. An arrow of time?

The question here is if the second law of thermodynamics is purely statistical in nature, or is it an absolute law. And does it say that the things can never become organised by themselves? If so, doesn't it contradict the theory of evolution of life - which says we grow into more and more organised species?

(still to conclude...)

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