Over at his Scientia Salon, philosopher Massimo Pigliucci wrote a piece on the disunity of science, discussing favorably some arguments against a unified scientific view (favoring instead a fragmented worldview, where each domain is covered by its own theory). The discussion really revolves around reduction – are high-level domains, such as (say) economics, reducible to lower-level domains, such as (say) psychology? Ultimately, the question is whether fundamental physics is the “general science” that underlies everything and presents a single unified nature, with all other sciences (including other branches of physics) being just “special sciences” interested in sub-domains of this general science. All domains and disciplines therefore reduce to physics. This is the Unity of Science view that Pigliucci seems opposed to.
I’m on the side of reduction. What are the arguments against it? Well, first off lets clarify that no one is disputing “that all things in the universe are made of the same substance [e.g. quarks]” and that “moreover, complex things are made of simpler things. For instance, populations of organisms are nothing but collections of individuals, while atoms are groups of particles, etc.” Everyone agrees that this type of reduction, ontological reduction, is true. The arguments instead are aimed at theoretical reduction, which is roughly the ability to reduce high-level concepts and laws to lower-level ones. Putting arguments from authority to the side, Pigliucci raises a few arguments against theoretical reduction:
(1) The Inductive Argument Against Reduction: “the history of science has produced many more divergences at the theoretical level — via the proliferation of new theories within individual “special” sciences — than it has produced successful cases of reduction. If anything, the induction goes [against reduction]”
However, this argument is based on the false premise that if reduction is true then reductive foundations for a science would be easier to find than new high-level sciences. This premise simply does not follow from reduction, however. Instead, reduction entails that
(A) As science progresses more and more examples of successful use of reduction will be developed. This prediction is borne out by things like the calculation of the proton’s mass from fundamental particle physics, the identification of temperature with molecule’s kinetic energy, the identification of (some) chemical bonds with quantum electron-sharing, and so on.
(B) As science progresses, no contradiction will be found between the predictions of the lower-level theories and the higher-level ones. For example, it won’t be found that the proton should weight X according to fundamental physics yet weighs Y in nuclear physics; it won’t be found that a reaction should proceed at a certain rate according to physics yet that it proceeds in a different way according to chemistry. Clearly, the success of this prediction is manifest.
Thus the inductive argument against reduction is very wrong-headed, misunderstanding what reduction predicts and ignoring the real induction in its favor.
(2) How would reduction even look like?
Pigliucci further maintains that we reductivists are bluffing; we don’t really even know what reduction could possibly look like. “if one were to call up the epistemic bluff the physicists would have no idea of where to even begin to provide a reduction of sociology, economics, psychology, biology, etc. to fundamental physics.”
This is again false – we know in general terms how this reduction takes place (chemistry is the physics of how atoms bond into molecules and move; biology is the chemistry of how numerous bio-molecules react; psychology is the biology of how organisms feel and think; and so on). The only caveat here is that consciousness is somewhat problematic; the mind-body issue aside, however, the picture of how reduction proceeds is clear enough (even if vague and not at all actually achieved, of course) to make this objection moot.
(3) Cartwright’s disjointed theories
Supposing that all theories are only approximately-true phenomenological descriptions (something most scientists would agree to), Pigliucci somehow concludes that therefore “science is fundamentally disunified, and its very goal should shift from seeking a theory of everything to putting together the best patchwork of local, phenomenological theories and laws, each one of which, of course, would be characterized by its proper domain of application.”
But the fact that some theories apply only in some cases does not imply that they are not part of a bigger theory that applies in all these cases. There is no case being made against reduction here – reduction is perfectly comfortable with having multiple phenomenological theories, as long as they all reduce to the fundamental physics. It is even comfortable with there being an infinite series of “more fundamental physics”, as long as each theory reduces in turn to an even-more fundamental theory.
What is Reduction?
I was prompted to write this post because one may not make long/many comments over at Scientia Salon. The thing I wanted to say there was what reduction is. Reduction, as is meant by those actually believing it, is something like “Physics + Weak Emergence”.
Reduction = Physics + Weak Emergence
By “Physics” I mean that what ultimately exists is described by fundamental physics – things like “atoms and void”, “quarks and leptons”, and so on.
By “Weak Emergence” I mean that high-level concepts are arbitrarily defined, and then used to analyze the lower-level descriptions. When this is done, it is revealed that the high-level phenomena that the high-level concepts describe actually exist. This is rather abstract, so consider a simple example: temperature in a gas canister. The gas molecules can be fully described at the low, microscopic level by things like the molecules’ position and velocity. “Temperature” is then defined to be their average kinetic energy. Doing the math, one can show from the microscopic state that the gas indeed has a certain temperature.
In this way the temperature is “reduced” to the lower-level concepts like the molecules’ speed and mass. But the concept of “temperature” was defined by us, it isn’t to be found in the microscopic physics or state!
For this reason, Democritus said “Sweet exists by convention, bitter by convention, colour by convention; atoms and Void [alone] exist in reality”. The idea isn’t that temperature doesn’t exist in reality, however, but rather that we choose to consider nature in terms of temperature by arbitrary choice, by “convention”.