What entropy doesn't mean to me

[mmcirvin]

I'm not even sure why I got involved in all the arguing over Leon Wieseltier's review of Daniel Dennett's book last week, given that I haven't even read the book and have no plans to. But one good thing that came out of it was that somebody, probably Brian Leiter, pointed to this article on David Hume and religion, which by way of background brought up a notion Hume rejected, the theological principle of causal adequacy:

The second principle is that of causal adequacy or the order of causes: No cause can produce or give rise to perfections or excellences that it does not itself possess.

I read that and immediately thought, "Hey, it's the creationist misreading of the second law of thermodynamics!" I think that the reason they like to bring up the second law so often, and claim that it forbids evolution, is that it sounds sort of like this 17th/18th-century axiom of religious apologetics. You just take the colloquial reading of entropy as "disorder", go from there to interpreting it as the opposite of perfection or excellence, and Bob's your uncle.

This is also why the common scientific counterattack, that the second law only applies to closed systems (which the Earth definitely is not), is true but rhetorically unsatisfying. The Sun shines down on the Earth and waste heat radiates away, but it's not obvious that it's raining excellence or perfection, so if you still imagine the second law as a translation of the principle of causal adequacy, the response doesn't seem sufficient.

A better opening response would amount to "the principle of causal adequacy is not a physical law, and entropy is not what you think it is." It is, in fact, Boltzmann's constant times the natural logarithm of the number of microstates. In my old tutorial on the Boltzmann factor, I noted that there's some connection here with intuitive concepts of "disorder", but also cautioned that to equate entropy with disorder without making sure you're actually talking about the number of microstates is fraught with peril. To equate it with old theological notions of perfection is deeply incorrect.

In the process of writing something to this effect in a comment on Orac's blog, I Googled for the phrase "causal adequacy", and discovered to my great delight that Intelligent Design advocate William Dembski likes to toss it around as if it were a scientific principle (the author of that essay even assumes that Dembski made it up, little realizing that it's a centuries-old, contested philosophical concept). Case closed.

Comments

[mmcirvin.livejournal.com]

I think the Maxwell demon is pretty well understood by now, but the full role of gravity in stat. mech. is not, because you need to know more than anyone does about the fundamental physics of gravity in order to count microstates confidently (and also because gravity does such funky things with time and space). These days, people who have proposed a quantum gravity theory always feel very proud if they can pull Hawking's formula for the black hole entropy out of it, that being assumed to be an important consistency condition, but then there's also the question of how much that really tells you.

And then there's the question of whether you can explain the thermodynamic arrow of time by somehow deriving the cosmic boundary conditions. It's a fertile area of study and argument.