I got so sick of the smug attitudes that Rosenberg, Coyne, Harris and others derive from their acceptance of determinism — obviously without having looked much into the issue — that I delved into the topic a bit more in depth myself. As a result, I’ve become agnostic about determinism, and I highly recommend the same position to anyone seriously interested in these topics (as opposed to anyone using his bad understanding of physics and philosophy to score rhetorical points).
A good starting point from which to get a grip on the nuances and complexities of discussions concerning determinism is a very nicely written article by Carl Hoefer in the Stanford Encyclopedia of Philosophy, as well as several of the primary sources cited there, particularly John Earman's Primer on Determinism.
So, here are some of the somewhat surprising things you’ll learn from Hoefer’s article that you may want to raise the next time “determinism!” is hurled at you in the midst of a philosophical discussion:
* The philosophical roots of the notion of determinism are to be found in Leibniz’s (now largely discredited) principle of sufficient reason, though modern discussions of it can be recast avoiding Leibniz.
* Predictability is an issue entirely separate from determinism, since we can have deterministic (chaotic) systems that are for all effective purposes unpredictable, and (possibly, more on this in a moment) stochastic (quantum) systems that are nonetheless predictable to a very high degree of accuracy.
* As John Earman said (in the above mentioned book), when people talk about causal determinism they often “seek to explain a vague concept — determinism — in terms of a truly obscure one — causation.” And good luck with both. (See Bertrand Russell’s well known critique of the notion of causation, published in 1912: Russell, B., “On the Notion of Cause,” Proceedings of the Aristotelian Society, 13: 1–26.)
* Believers in determinism frequently cite the notion of laws of nature as if it were uncontroversial, but this is far from being the case. Talk of nature’s laws is metaphorical, and many philosophers simply take “laws of nature” to be our best assessment of regularities in the history of the universe, regularities that for all we know could be contingent, or have a limited domain of application. There are also philosophers who think that laws of nature are, as Hoefer puts it, ontologically derivative, with actual physical events playing the role of brute facts that make laws (as opposed to the other way around). Moreover, some philosophers (Nancy Cartwright and Bas van Fraassen, for instance) hold to the position that laws of nature simply do not exist. I am agnostic on this point, but again the issue is far from settled, and if you believe in laws of nature you do need to come up with an account of their ontology (and if you are not a theist, obviously you can’t avail yourself of a law giver).
* Because of chaos, it may very well be impossible on empirical grounds to establish whether the universe is deterministic or not, which would clearly take the debate out of science altogether, pace Rosenberg. Hoefer cites a 1993 paper by Suppes which concludes: “There are processes which can equally well be analyzed as deterministic systems of classical mechanics or as indeterministic semi-Markov processes, no matter how many observations are made ... Deterministic metaphysicians can comfortably hold to their view knowing they cannot be empirically refuted, but so can indeterministic ones as well.” Oops.
* Contra popular misconceptions, current theories of physics do not settle the question of determinism at all. As it turns out, even classical mechanics is compatible with indeterminism, in a variety of technical ways explained by Hoefer and the references he cites. Special relativity is most friendly to determinism, but we know it’s incomplete. General relativity is — on the contrary — very friendly to indeterminism (did you know that? I didn’t. It has to do with the existence of so-called naked singularities). As for quantum mechanics, the well known standard Copenhagen interpretation of it leans toward indeterminism, while the empirically equivalent Bohm interpretation is deterministic. We don’t know which is correct, and in fact we know that both quantum mechanics and general relativity are incorrect (or at the least incomplete).
* Not even future theories of physics are likely to settle the issue. Again, Hoefer: “first, we may have difficulty establishing whether the Final Theory is deterministic or not — depending on whether the theory comes loaded with unsolved interpretational or mathematical puzzles. Second, we may have reason to worry that the Final Theory, if indeterministic, has an empirically equivalent yet deterministic rival.”
* And one final point: particularly when it comes to discussions of free will, we keep hearing that the latter is impossible because in a deterministic universe the past determines the future. But as Hoefer points out (and he has expanded on this in a 2002 paper: Hoefer, C., “Freedom From the Inside Out,” in Time, Reality and Experience, C. Callender (ed.), Cambridge: Cambridge University Press, pp. 201–222), the “laws” of physics treat time as symmetrical, which means that the present and the future “fix” the past just in the same way in which the past “fixes” the present and the future. No particular area of the time axis has priority over the others. Chew on that for a while.
The next time someone confidently says that this or that “surely” follows from the “fact” that science has now established the notion of determinism, go over the above list (or better, Hoefer’s original article) and use it to punch a nice hole in their inflated metaphysical balloon. And please, let me know what happens.