Does Reductionism Explain Anything?

Continuing my earlier conversation with Wavefuntion.

Wavefunction says:

Since pretty much every fact about the present universe (and certainly most of biology) has somehow been influenced in a major way by chance, a failure of reductionism to predict these facts would render the doctrine almost impotent.

Reductionism isn’t in the business of predicting facts (it’s an account of the relationship between physical facts and higher-level facts). Of course, if physics is indeterministic, then there will be some facts that cannot – even in principle – be predicted (with certainty, anyway). But this certainly doesn’t render physics “impotent” (although perhaps we could say it’s less “powerful” than in a deterministic universe, in a sense).

And keep in mind that if some event cannot — in principle — be predicted by physics, then it cannot be predicted by any other (higher-level) science either. So physics is always more powerful (as far as predictions go, more on this below) than any other science.

As far as reductionism goes, I’d say that its virtue lies in being true. As a metaphysical thesis it rarely has much “power.” It’s true that there is nothing non-physical in the world, but that doesn’t tell you how to cure cancer or reduce CO2 emissions. (But I suppose it might tell you that attempts to use astral projection to align the Earth’s chakras isn’t going to produce any results.)

Wavefunction:

The only kind of “reductionism” we will be left with then is the hollow and obvious declaration that everything is made up of quarks or strings and that these “somehow” must account for everything that we see in our universe.

Well, yes and no.

No, because physicalism not only claims that things are made up of quarks (let’s say), but it also says that the laws governing quarks don’t change when the quarks come together to form a complex high-level system. This rules out a strong form of emergentism that claims that the behavior of complex systems cannot be accurately predicted merely from the knowledge of the physical laws and states. (This sort of emergentism was popular a century ago and was defended, e.g., by C.D. Broad). Physicalism is quite specific: It doesn’t say that quarks, electrons, and the various forces “somehow” account for everything it the world; it offers an account of the laws that these things follow and makes the claim that the evolution of the physical state under these laws exhaustively captures everything that happens in our world. So physics offers a complete account of the universe in that all actual complexity and structure is captured by the physical state of any system.

Yes, in that we are often much more interested in the structures than we are in the quarks that instantiate that structure. We often don’t particularly care that some process is physical; what we really care about is how the process works and knowing that it’s physical will tell you little about how it works.

(Again, it will say something, however, in that it will rule out any processes that violate known laws of physics or that are inconsistent with the known physical state of the universe. Thus, for example, if someone suggests that the cause of an illness is the alignment of the planets, we can point out that no physical force from those planets is strong enough to affect the diseased cells. Note that this claim is not just about the laws of physics, but also about the physical state – obviously if the planet were closer, it could have a very strong, even lethal, impact on our health.)

Wavefunction:

But stating the prehistory is far from being able to state the reason for its existence.

Here I think it might be helpful to differentiate between a few of different notions that get lumped together under the label “reductionism”:

• (1) Ontological reductionism is what I call “physicalism”: it claims that everything in the world is physical. This is the main thesis I’m inclined to defend.
• (2) Causal reduction claims that all higher level causes and dispositions are manifestations of lower-level physical dynamics. Many philosophers reject this causal reductionism while still trying to accept ontological reductionism. In my view, this doesn’t work, because (1) requires that physical laws are not violated, and this tells us what can and cannot happen. Thus higher-level causes cannot be independent; instead they are the result of an insensitivity to some of the micro-physical details.
• (3) Theoretical reductionism claims that one can derive higher-level theories from lower level theories. I’m not a defender of this form of reductionism, in part because the higher-level special sciences often don’t take the form of dynamical theories the way this view supposes. Further, the fact that specific historical details are often quite important means that there’s often not a very good sense of “derivation” to be had here.
• (4) Explanatory reductionism claims that anything that can be explained by any other science can be explained equally well – or better – by physics. If there are any legitimate forms of explanation that aren’t captured by physical explanation, then this form of reduction fails. I’m not inclined to insist on this form of reduction either.

I take it that you and Deutsch mainly interested in rejecting (4), explanatory reduction, and here I’m willing to agree with you – up to a point, at least. However, I will insist on (1) and (2), and I’ll argue that these claims are non-trivial.

The reason it makes sense to claim that higher-level explanations are “autonomous” of physics is that explanation is tied to understanding (I’m inclined to think that an explanation is just a piece of information that enables understanding). And it seems reasonable to suppose that understanding often depends on how information is packaged. A close up of all the pixels of some picture might provide you with all the information that is in the picture, but you might not understand that it’s a picture of a cat unless you can step back and register the large-scale relations between the pixels that allow you to recognize the image of a cat. And, of course, the pixels could be changed in various ways while still retaining the high-level cat-like structure.

But (as I hope is obvious), none of this implies that the cat-structure of the picture is something above and beyond the structured collection of colored pixels. That is, (1) and (2) are still going to hold.

Further, I think we can make a case for the claim that anytime there is an accurate higher-level explanation of some fact, there will always be a physical explanation in the neighborhood that is at least closely related to that explanation. Of course, if we’re interested in the structures, then the physical details are typically going to be irrelevant, but the fact that they are physical structures (i.e., structures of physical stuff, governed by physical laws) means that physics isn’t going to be silent about what goes on.

In the end, I think that much is going to hang on what gets to be counted under the umbrella of “physics.” Toy example: we have a few dozen physical particles that are arranged in a perfect circle. The location of each particle is given by physics – it is fixed by the physical state. Now, is the circular shape part of the physical account/explanation or not?

Obviously one could learn the coordinates of all the particles and not realize they formed a circle. One then might count the property/relation of circularity as an emergent property that could explain features left unexplained by the mere locations of the particles. (E.g., if the particles are charged, the fact that there is no net charge inside the circle.)

Equally obviously, however, the circular shape is not something extra above the locations of the particles. One can deduce the shape from the locations (ignoring questions of idealization, etc.), the shape supervenes on the locations, etc. Further, even if we didn’t notice that the particles formed a circle, we still reach all the right conclusions about the effects of the particles at the specified locations. (So, for example, an explicit calculation of the forces due to their charges would yield zero for points inside the circle.) So, as I said, there will be some explanation in the neighborhood.

Wavefunction offers a passage from Deutsch in which he considers “one particular copper atom at the tip of the nose of the statue of Sir Winston Churchill” and offers an explanation in terms of the history of Britain, the practice of honoring people with statues and so on:

There is no reason why there should exist, even in principle, any lower-level explanation of the presence of that copper atom [other?] than the one I have just given. . . . Even if you had the superhuman capacity to follow such lengthy predictions [of micro-physics] of the copper atom’s being there, you would still not be able to say, ‘Ah yes, now I understand why it is there.’ You would merely know that its arrival there in that way was inevitable (or likely, or whatever), given all the atoms’ initial configurations and the laws of physics.

As I said above, I agree with general complaint to a degree. Even though the emergent structural features are fixed by the underlying microphysics, one could only think about the microscopic processes and miss very important high-level structural features. Understanding requires not only knowing the details, but also knowing how the details fit together.

However, I think Deutsch’s passage goes a bit to far (as is often the case with anti-reductionist arguments). First, a minor point: Deutsch claims to be offering an explanation for why that “particular copper atom” is there. But his explanations in terms of the practice of building statues etc. are only going to explain why some copper atom or another would be found at that location. If he wants to get to the level of specificity of tracing a particular atom, then he can’t avoid specifying the state of the world (or at least part of that state) all the way down to the atomic level. The sculptor obviously doesn’t care about which copper atoms show up and which don’t. (It’s interesting that on the standard interpretation of quantum theory, there might not always be an answer to the question “which particle is which?”, but that’s a story for another day.)

The more substantial error lies in his claim that there is”no reason why there should exist, even in principle, any lower-level explanation of the presence of that copper atom” other than the one that specifically refers to high-level features like politics etc. But, of course, there is an explanation in terms of the physical evolution of the physical state of the universe, which does indeed exist unless we are stunningly mistaken about the nature of physics. Now, that might not be the explanation you’re looking for, because it doesn’t highlight the structures and regularities that allow you to “understand” the situation, but it surely is a “lower-level explanation of the presence of that copper atom.”

Now to Wavefunction’s final point:

[T]here are several cases in which higher-level phenomena are more accurate in capturing the essence of a fact. . . . In this case it’s pretty clear to me that higher-level phenomena are far more accurate in answering the “why” of a particular situation than lower-level phenomena. So while I do agree that higher-level phenomena are not always more accurate than lower-level ones in explaining a particular fact, I think there are several cases in which they succeed in giving us a more accurate description.

I agree that higher-level accounts will often offer more explanatory power – in part due to the very fact that they prune away irrelevant physical detail. So I agree that higher-level theories will answer “why” questions that are left unanswered by physics (though it’s important that the information is there in the physics to construct the higher-level theory).

I’m not very happy calling the higher-level account a “more accurate description,” but I suspect the issue here is primarily terminological. I’m inclined to separate out predictive accuracy from explanatory power. Indeed, these two scientific goals can sometimes (often?) pull in different directions. So I’d be inclined to insist that physics gives us the most accurate account in that it offers maximal specificity about whether a particular event will or will not occur in the actual world. Of course, this is an account that can only be given in principle – very rarely can it be given in practice. But it’s the question of principle that’s important for metaphysics.