A little exchange over at The Curious Wavefunction that I thought I’d reproduce here.
I didn’t take the time to discuss different varieties of reduction. I’m mostly thinking of metaphysical supervenience in my response, which I think is fair since Wavefunction specifies that s/he is interested in ontology not epistemology.
There are, of course, denials of reduction coming from nonreductive physicalists that are supposed to be compatible with supervenience, but it doesn’t seem to me that Wavefunction has any of these in mind (but perhaps I’m wrong).
A common claim is that higher level causal powers cannot be reduced to lower-level physical causal powers, but this claim is (mostly) wrong. That’s for another day, however. For now, here’s my comment over there.
Wavefunction argued that a Laplacian demon (or a “superfreak” to use a term from the Bernstein review that introduces the post) who knows all the laws of physics would be unable to predict the existence of giraffes because biological details depend on historical accidents. Wavefunction takes this to show that biology is not reducible to physics.
If physics is deterministic (so let’s suppose that a nonlocal hidden variable interpretation of quantum mechanics is correct), and if our superfreak (or Laplacian demon, as the more traditional account has it) knows the complete physical state in addition to all the laws (and has an unlimited computational capacity), then the superfreak will be able to predict the existence of giraffes and every other biological detail.
Leaving out relevant physical details (i.e., the initial conditions) does not not show that biology is non-physical. Of course, it is true that physical dynamics alone will never tell us what sort of creatures evolve and which don’t, but why would we ever think it might? Mere physical laws can’t even tell us that there will be protons and neutrons.
And a follow up:
Curious Wavefunction says:
If we can truly reduce biology to physics, it must mean that we should be able to . . . construct the present biological world starting from the basic laws of physics.
Again, this form of “reduction” is just a non-starter. If you insist that we only have reduction when the laws (and only the laws) specify some feature of the world, then nothing can be reduced (except the laws themselves).
The physical laws are compatible with the complete absence of matter, so the laws are never going to tell you whether there’s matter or a total vacuum.
The criterion for reduction that you’re using is unhelpful, because on this account nothing can be reduced to physics.
A much more useful account of reduction is one which asks whether we can predict some feature if we are given both the laws and the complete physical state (and unlimited computational power, since we’re interested in ontology not epistemology).
In this case, it seems clear that the Laplacian demon (superfreak) would predict the existence of giraffes (though the demon might not call them “giraffes”).
Even if the structure of the mammalian heart could be predicted in principle, it would be impossible to predict beforehand that the most important function of the heart among myriad others is to pump blood.
I know famous people like Fodor and Searle make this claim (I didn’t realize Kauffman did; I’ll have to look at his book at some point), but it’s just wrong:
(a) Even if we insist that one needs to know the evolutionary history of a trait to know its “real function,” the Laplacian demon would have all of that information available. It knows the complete history of the total physical state of the universe.
(b) If our demon (“superfreak”) is smart enough to care about which functions are “the most important” then it should have little difficulty recognizing that the function of the heart is to pump blood (even without peaking at the past). It would be able to recognize certain self-regulating processes that maintain themselves against the flows of entropy, and it would be able to recognize that the heart’s circulating blood is an important component of this self-sustaining process (whereas, for example, the sound the heart makes is not).
Now, if we stipulate that our demon is not allowed to care about any structure or order above the level of particles, then you’re right that the demon will be ignorant of biological facts. But with this stipulation, the demon would also be ignorant of the shape of planets, the temperatures of stars, the rigidity of ice, and so on and so on. But this just shows that we shouldn’t make such a stipulation if we’re trying to figure out the ontology of the world.