November 2, 2010

Leibniz Against Fine-Tuning

It appears that I'm going to be getting a bit behind on my Sobel series due to other commitments. Here is some Leibniz to make up for it.

One of the problems with those forms of teleological (design) arguments that posit necessary 'gaps' in naturalistic explanation is that they are revisionary with respect to scientific practice: that is, it is a principle of scientific methodology to keep looking for naturalistic explanations no matter what. Now, most philosophers think that taking a revisionary attitude toward scientific practice is bad since the track record of science, on its current methodology, is stellar and the track record of philosophy is, well, not. As a result, the thought goes, it would be silly to revise scientific practice on philosophical grounds.

As a result, many theistic philosophers prefer 'fine-tuning' arguments. According to these arguments the initial conditions and/or fundamental constants of the universe had to be just right in order for life to come about, and so God must have set it up that way. What philosophers sometimes don't realize is that this argument is also revisionary with respect to scientific practice: scientists, and especially physicists, don't see explanations involving fine-tuning as genuinely explanatory, and they look for more fundamental principles which will get rid of the fine-tuning.

Now here's where Leibniz comes in. As is well known, Newton was Leibniz's evil twin. In addition to the controversy over the discovery of calculus, Leibniz was highly critical of Newton's signature achievement, the Law of Universal Gravitation. However, contrary to popular belief, Leibniz never questioned the accuracy of the Law. Rather, according to Leibniz Newtonian gravitation is not genuinely explanatory. That is, in Leibniz's view, the (so-called) Law is a true generalization, but not just every true generalization explains its instances. (Leibniz does sometimes, e.g. in "Anti-Barbarus Physicus", express doubts about whether the Law is truly universal, but in general he accepts its accuracy.) In my view, although Einstein is closer to Newton than the Leibniz on the nature of space and time (see Tim Maudlin's excellent article, "Buckets of Water and Waves of Space: Why Spacetime is Probably a Substance"), I think that Einsteinian gravity counts, on Leibniz's theory, as a genuine explanation precisely because it makes space-time a genuine substance (space-time both acts and is acted upon) with a nature that can explain these interactions. It's not surprising that this is so: Einstein was famously troubled by the fact that Newton's theory countenanced "spooky action at a distance" - the very same thing Leibniz was troubled by. So in a limited sense, I think, Leibniz is vindicated by history, at least on this particular point.

All this by way of background. In a letter to the physicist Christian Huygens written in 1690 (three years after the publication of Newton's Principia), Leibniz criticizes Newton's scientific methodology. What is of interest to us is that action-at-a-distance is not Leibniz's only target. Rather, he brings this additional charge:

For although Newton is satisfactory when one considers only a single planet or satellite, nevertheless, he cannot account for why all the planets of the same system move over approximately the same path, and why they move in the same direction, using only impetuosity together with gravity. That is what we observe, not only for the sun's planets, but also for those of Jupiter and those of Saturn. This is good evidence for there being a common reason that determines them to behave in this way; and what other more probable reason can be brought to bear than that some kind of vortex or common matter carries them around? For to have recourse to the decision of the author of nature is not sufficiently philosophical when there is a way of assigning proximate causes; and it is even less reasonable to attribute this agreement among the planets of the same system to good luck, given that the agreement is found in all three systems, that is, in all the systems known to us. (Ariew and Garber, p. 310)

It had already been observed by 1690 that all of the planets are almost exactly co-planar, and move around the sun in the same direction. Furthermore, the moons of Jupiter and the moons and rings of Saturn had been observed to be co-planar and move in the same direction. Newton's Law of Universal Gravitation can explain the motion of the system, given exactly the right initial conditions. So, Newton thought, God must have just set things up that way. (Newton often appealed to God to solve problems in physics; Leibniz takes him to task for this in the correspondence with Clarke.) But this is not a satisfying explanation. In fact, according to Leibniz, it is insulting to the divine wisdom: God doesn't have to go mucking about in the created world to get things to turn out the way he wants. After all, he made up the laws himself, so we should expect the laws to guarantee the execution of his plans. As a result, we should look for the law or natural process which guarantees that the planets move in the same direction and are roughly co-planar. Such an explanation is provided by the vortex theory, advocated by Leibniz and Huygens, according to which the planets are caught in a sort of whirlpool of 'subtle matter' (ether) which carries them around the sun. In a sense, the nebular hypothesis brings back the vortex: the planets and the sun formed in a spinning disk of matter and are in the orbits they are in as a result of the motion of that disk. Of course, there is no 'subtle matter' involved; the vortex is gone now. However, the planets began their lives in a sort of vortex of (perfectly ordinary) matter, and that explains why they are co-planar and move the same direction.

It can be seen that, in this debate, Leibniz is taking Newton to task for accepting fine-tuning. The fine-tuning can be done either by God or by chance; either way it is unacceptable. We must find an explanation of the perfect initial conditions.

If correct scientific methodology tries to get rid of fine-tuning, what is to become of teleological arguments? There are, I think, two paths we can take. The first is Leibniz's own: according to Leibniz, the structure of the fundamental laws - not the constants - obeys certain design principles and serves certain ends, and this is evidence that the laws were instituted by a wise mind. Leibniz's example of the former is the principle of the most determinate in optics: the path taken by light is always either a maximum or a minimum, and this follows from more complicated laws which are not explicitly teleological. A better example, found since Leibniz's time, is the fact that the laws of classical mechanics are provably equivalent to the Principle of Least Action - a design principle if ever there was one. (The Principle was controversial among physicists for a long time for precisely this reason.) Examples of the latter would be Leibnizian miracles: cases in which the laws of nature seem to conspire to produce morally or religiously significant outcomes.

A second approach is that adopted by Del Ratzsch in his excellent article "Natural Theology, Methodological Naturalism, and 'Turtles All the Way Down'" Faith and Philosophy 21 (2004). In this article, Ratzsch argues that every success in eliminating the appearance of design (e.g. eliminating fine-tuning) has led us to a deeper level at which the appearance of design shows up again. It may well be, he suggests, that this goes on forever. This, he argues, would be excellent evidence for the existence of an intelligent creator.

Unlike 'gaps' arguments and fine-tuning arguments, neither of these approaches are revisionary with respect to scientific practice, and that's good. I think both of these approaches are worthy of attention and further development.

Posted by Kenny at November 2, 2010 9:54 AM
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