I want to draw Prosblogion readers' attention to a very interesting paper by CalTech physicist Sean Carroll, "Does the Universe Need God?" (hat tip: ex-apologist). The article is to be published in The Blackwell Companion to Science and Christianity. The article is a model of constructive dialog between philosophy and physics. Carroll shows engagement with the major philosophical arguments under discussion, and does not come off as condescending or dismissive. He also provides concise and helpful summaries of the relevant physics. Additionally, the article shows an admirable degree of epistemic humility, noting that there are many unsolved problems in physics and that our theory of the early universe is not polished and completed, while still arguing that we have enough information to shape our views on origins. The article is quite readable, and would certainly be helpful for students.
Let me make a few remarks on Carroll's actual arguments and positions. Near the beginning of the article, Carroll quickly summarizes the possible responses to 'first cause'-type cosmological arguments. It seems to me that he is on firm ground here: it is unclear whether there even is a first moment, and if there is then it is not clear that it even makes sense to ask what caused the state of the universe in that first moment, if we are looking for another cause in the series of causes. Besides (although Carroll does not make this point), classical philosophical theology does not conceive of God as one more cause in the series of causes. So the first cause argument isn't really going anywhere. I myself think that insofar as the first cause argument is tempting, this is because it gets confused with the argument from contingency: people aren't really asking what caused the first state of the universe, they are asking why was the state of the universe as it was, and it's quite clear that, if there really is a first moment, then the answer to that question could not possibly be another ordinary physical cause: either it has no answer, or it has an answer of a very different sort.
Carroll next offers detailed criticism of the 'fine-tuning' argument. The main point Carroll makes here is that the multiverse hypotheses which physicists take seriously are not just introducing enormous numbers of universes as ad hoc posits for the purpose of getting rid of fine-tuning. One sort of multiverse, for instance, falls neatly out of inflationary cosmology, which is a well-verified physical theory. (Brian Greene's latest book, The Hidden Reality, surveys the range of multiverse theories and the different degrees of evidence for them.) So to say that the multiverse is excessively complex and so should be rejected is to misunderstand the sort of simplicity we should be looking for. Now, Carroll runs over some distinctions between different multiverse theories here; my understanding on the basis of Greene's book is that the multiverse theories that do the most to eliminate fine-tuning are the least well-supported and widely accepted among those on offer, and that it is true of some of these theories that their main attraction for their adherents is to get rid of fine-tuning. I'm not, however, convinced that that's bad: apparent fine-tuning is one of the things physicists try to explain. If a particular multiverse hypothesis provides a simple explanation of a particular apparent fine-tuning, then good for it. And I agree with Carroll on what simplicity should mean here. Leibniz said that God would create the world which was simplest in principles and most varied in phenomena (see, e.g., DM 5). This is the kind of simplicity that matters here: simplicity of the fundamental principles. If they generate many and varied phenomena (e.g. an enormous variety of universes), this is no stroke against them. Again, point Carroll.
Near the end of the article, Carroll does come to discuss the argument from contingency. Unfortunately, he does not, in my view, take it as seriously as it deserves. He essentially says that, although we ought always to look for explanations with respect to things in the universe, there can be no such explanation of the universe as a whole or its most basic laws. In The Principle of Sufficient Reason: A Reassessment Alexander Pruss makes the case that the PSR cannot be restricted in any non-ad hoc way without undermining the assumptions of explainability made in ordinary scientific practice. Carroll ultimately simply pronounces that "There is no reason, within anything we currently understand about the ultimate structure of reality, to think of the existence and persistence and regularity of the universe as things that require external explanation." He doesn't give an adequate account of exactly what restrictions he is placing on explainability, or how they are justified. He seems to be supposing that what things we take to be in need of explanation depends on our physical theory. The trouble is, our practices with respect to explanation must be at least partly a priori in character: we have to start looking for explanations before we've got any explanations. Furthermore, Carroll's example, that in modern physics there is no need for Aristotle's Prime Mover because of the Law of Inertia, neglects the fact that an appeal to the Law of Inertia is itself an explanation of why objects continue in their state of motion. It is not that we've discovered that these things don't need explanation, but rather that we've discovered that the correct explanation is of a very different sort from what Aristotle had in mind.
The argument from contingency, however, takes God outside the realm of physics. God here provides a different kind of explanation to a different kind of problem. This, to my mind, is one of the key reasons why the argument from contingency and the ontological argument are far more credible than either the first cause argument or the fine-tuning argument. That theism is not a credible physical theory is transparently obvious. Whether it is a credible metaphysical theory is another question entirely. I also note that the standards of credibility for metaphyiscal theories are quite lax compared to those for physical theories. Might theism enjoy the same level of (objective) support as quantum field theory? Not a chance. Might it enjoy the same level of (objective) support as (say) our best theories of universals? On this latter point I would say, it can, and it does.