Wednesday, July 16, 2008

Levels of Explanation

Does the acknowledgment that we live in a physical universe imply that everything can or should be explained by physicists? No.

[T]he natural scientist knows just as surely that our best account of that universe is, in many cases, not forthcoming from physics. We turn instead to chemistry or biology. The need for such “special” sciences that take higher-level structures as given does not compromise the bedrock ontological supposition that there is a single universe, made up of physical particles. One can have one’s materialism while admitting the autonomy of higher-level disciplines. There is much confusion on this point, and it seems to be bolstered by a fear that to be less than completely reductive in one’s explanatory posture somehow commits one to “spiritualism.”

The explanatory independence of biology, its irreducibility to physics, is consistent with biological entities being composed of and dependent upon physical entities. The biologist believes that the dog is made up of nothing but protons, neutrons, and electrons, but he does not try to give an account of the dog at that level. Is this merely due to the limitations of our current state of knowledge? Would it be possible in principle to construct a comprehensive understanding of the dog starting from particle physics? The consensus view appears to be that it is not possible even in principle, due to considerations of complexity and non-linearity, or thermodynamic irreversibility (take your pick). Even within physics, lower-level accounts sometimes presuppose structure that is identifiable only at a higher level, or depend upon boundary-conditions that cannot be generated from within the lower-level account. Even something as simple as a volume of gas displays “emergent properties” (here, an irreversible tendency toward equilibrium) that cannot be derived from the collisions between individual gas molecules (which are symmetric with respect to time).
The short version: there are perfectly valid, defensible, worthwhile explanations that lie somewhere between the motions of subatomic particles and the fuzzy woo of supernaturalism.

I'm not sure about the entirety of the long version as applied, but I think the part quoted above is very good.


maekitso said...

Another short summary that came to mind is this. The "scientific method" may not always yield the best or most useful results.

Dale said...

maekitso, thanks for the comment. While what you say may be a true statement -- that the scientific method may not be the most promising approach to every conceivable question -- I don't think that's what Matthew Crawford (the author quoted) was getting at.

Anonymous said...

Since ultimate reducibility is not even theoretically possible, the so-called "God of the gaps" could never be eaten up by science -- even theoretically, i.e. even assuming we had access to unlimited data. What are your thoughts on the foregoing statement. (Be nice to me. I'm not a scientist or a philosopher and I didn't go to Reed College).

Dale said...

Anonymous-who-didn't-go-to-Reed, I would simply say that the kind of reducibility you seek has no cash value in the world we actually inhabit. (And yes, "cash value" is an allusion to pragmatism, as I think science is pragmatic. It has to be.)

Think of anything that we think we understand scientifically -- say, the principles of heredity. We know that your genes will be, if inspected closely, a mix of your mother's and father's. We know the same of every fruit fly.

We know what causes malaria.

We know that water will boil at such-such temperature at sea level.

Extend the examples as far as you like.

We don't understand this down to the level of particle physics. That is, we don't have accounts of all of the above, either written by or carried in the heads of, people who have mastered the finer points of particle physics -- we don't have it expressed sheerly in terms of protons, quarks, etc.

What would we really have if we had that? Perhaps we'd have more elaborate, and much harder to understand, versions of what we already have. Or we might have something genuinely useful and fruitful, I suppose -- a different route, maybe a safer or faster or cheaper route to some cash value or other. Or maybe not.

This is why scientists continue probing -- in the highlighted article, people are looking at brain physiology to try to derive answers and patterns, whereas our best current answers and patterns come at the level of psychology / human behaviorial science.

We have explanations that yield testable hypotheses. We can predict that if dog 1 and dog 2 breed, any puppies they have will have the genes of their parents. We know that if we heat water to 100 celsius at sea level, it will boil. Etc.

We can draw extremely reliable inferences and make predictions that stack up against subsequent observations. And with that, we can solve real problems and stumble into unforeseen areas of research that will, or may, in their turn, yield yet more. Or maybe hit a wall.

We can note that not every single conceivable answer will be traceable to its particle-physics roots and do one of two things, it seems to me: declare it all futile and wave our hands about The Flying Spaghetti Monster in all his mysteries (by the way, nothing but a huge begged question), or proceed in the pragmatic fashion of science that seeks useable, repeatable, testable, workable, earth-bound-consequential answers.

Pragmatic here serves the purpose of saying that this ultimate particle-level explanation just doesn't matter in a great many cases. Even particle physicists would grant this. They would say: really, our labs aren't the best place to get to answers about elk migrations. This does not negate the explanations we do have.

We don't have the answers to that level on all questions and there's no apparent reason to actually care that we don't -- with the singular exception, I would note, of a feat of rhetoric born of a desire to kick dirt on science and try to drag it down to the level of faith. There's a line of faith-based apologetics that can't stop raising this objection. I'm not buying it.

Another way of putting all of this: there is no single best level of explanation that fits all scientific (or other?) questions.