Saturday, September 03, 2011

Time, heat, and origins

Ten things everyone should know about time. I really like the list overall, but #9 would better titled "aging can be reversed, in principle" (as opposed to what will happen in practice, which is very speculative).

I feel compelled to give a more substantive clarification of #8:

8. Complexity comes and goes. Other than creationists, most people have no trouble appreciating the difference between “orderly” (low entropy) and “complex.” Entropy increases, but complexity is ephemeral; it increases and decreases in complex ways, unsurprisingly enough. Part of the “job” of complex structures is to increase entropy, e.g. in the origin of life. But we’re far from having a complete understanding of this crucial phenomenon. (Talks by Mike Russell, Richard Lenski, Raissa D’Souza.)
Yes, there are complex very-low-entropy configurations (human bodies) and there are simple very-low-entropy configurations (perfect crystals). However, complexity and entropy are not completely orthogonal. The very-high-entropy configurations of the gas molecules in my apartment is better described as random than complex. What complexity it has, such as macroscopic airflow patterns ornamented with turbulence, is due to the configuration not having as a high an entropy as it could. If my apartment was a closed system, without electricity coming in to power the fans and the air conditioner, and without food coming in to keep the residents breathing and moving, then all these patterns would decay, leaving nothing but random microscopic motion. On a grander scale, the heat death of the universe really would be the death of us all.

Evolution is consistent with the second law of thermodynamics because living organisms are not closed systems; they use energy to pump out their entropy into their surroundings. The author, in #9, makes exactly this point using the example of refrigerators, which take in energy and use it to pump entropy from the food inside them into the air outside them. (If evolution wasn't consistent with the second law, then, given the quality of the evidence for evolution, the better inference might be that the second law is wrong, not that the theory of evolution is wrong.)

In the context of the origin of life, "complexity comes" is actually a very bold scientific hypothesis. The second law is consistent with the earth transitioning from lifeless to full of life, but so far all estimates of the probability of such a transition are highly speculative. Even if we knew the probability, I don't think it would settle the question of our ultimate origin. If life is probable, a theist would say that God made the universe conducive to life. If life is improbable, an athesist would say that say that we're in one of the lucky universes.


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