I've had God on my mind lately, as I've been finishing an invited essay for the upcoming Blackwell Companion to Science and Christianity. The title is "Does the Universe Need God?", and you can read the whole thing on my website by clicking. I commend the editors, Jim Stump and Alan Padgett, for soliciting a contribution that will go against the grain of most of the other essays. As you might guess, my answer to the title question is "No," while many of the other entries will be arguing "Yes" (or at least be sympathetic to that view). I think of my job as less about changing minds than informing -- I want thoughtful people who are committed Christians reading this volume to at least understand where I am coming from, even if they don't agree. Think of it as an elaboration of "Why (Almost All) Cosmologists Are Atheists," which was a bit breezier. Hopefully there is still a bit of time for tweaking the essay before the editors get back to me with their comments, so please let me know if you think I'm getting something importantly wrong. Again, the whole thing is here, but I'm including the final section (minus the footnotes) as a teaser below the fold. In the earlier sections I do more nitty-gritty cosmological stuff, talking about the Big Bang, the anthropic principle, and meta-explanatory maneuvers. In this section I finally evaluate the God hypothesis in scientific terms.God as a theory Religion serves many purposes other than explaining the natural world. Someone who grew up as an altar server, volunteers for their church charity, and has witnessed dozens of weddings and funerals of friends and family might not be overly interested in whether God is the best explanation for the value of the mass of the electron. The idea of God has functions other than those of a scientific hypothesis. However, accounting for the natural world is certainly a traditional role for God, and arguably a foundational one. How we think about other religious practices depends upon whether our understanding of the world around us gives us a reason to believe in God. And insofar as it attempts to provide an explanation for empirical phenomena, the God hypothesis should be judged by the standards of any other scientific theory. Consider a hypothetical world in which science had developed to something like its current state of progress, but nobody had yet thought of God. It seems unlikely that an imaginative thinker in this world, upon proposing God as a solution to various cosmological puzzles, would be met with enthusiasm. All else being equal, science prefers its theories to be precise, predictive, and minimal – requiring the smallest possible amount of theoretical overhead. The God hypothesis is none of these. Indeed, in our actual world, God is essentially never invoked in scientific discussions. You can scour the tables of contents in major physics journals, or titles of seminars and colloquia in physics departments and conferences, looking in vain for any mention of possible supernatural intervention into the workings of the world. At first glance, the God hypothesis seems simple and precise – an omnipotent, omniscient, and omnibenevolent being. (There are other definitions, but they are usually comparably terse.) The apparent simplicity is somewhat misleading, however. In comparison to a purely naturalistic model, we’re not simply adding a new element to an existing ontology (like a new field or particle), or even replacing one ontology with a more effective one at a similar level of complexity (like general relativity replacing Newtonian spacetime, or quantum mechanics replacing classical mechanics). We’re adding an entirely new metaphysical category, whose relation to the observable world is unclear. This doesn’t automatically disqualify God from consideration as a scientific theory, but it implies that, all else being equal, a purely naturalistic model will be preferred on the grounds of simplicity. There is an inevitable tension between any attempt to invoke God as a scientifically effective explanation of the workings of the universe, and the religious presumption that God is a kind of person, not just an abstract principle. God’s personhood is characterized by an essential unpredictability and the freedom to make choices. These are not qualities that one looks for in a good scientific theory. On the contrary, successful theories are characterized by clear foundations and unambiguous consequences. We could imagine boiling God’s role in setting up the world down to a few simple principles (e.g., “God constructs the universe in the simplest possible way consistent with the eventual appearance of human beings”). But is what remains recognizable as God? Similarly, the apparent precision of the God hypothesis evaporates when it comes to connecting to the messy workings of reality. To put it crudely, God is not described in equations, as are other theories of fundamental physics. Consequently, it is difficult or impossible to make predictions. Instead, one looks at what has already been discovered, and agrees that that’s the way God would have done it. Theistic evolutionists argue that God uses natural selection to develop life on Earth; but religious thinkers before Darwin were unable to predict that such a mechanism would be God’s preferred choice. Ambitious approaches to contemporary cosmological questions, such as quantum cosmology, the multiverse, and the anthropic principle, have not yet been developed into mature scientific theories. But the advocates of these schemes are working hard to derive testable predictions on the basis of their ideas: for the amplitude of cosmological perturbations, signals of colliding pocket universes in the cosmic microwave background, and the mass of the Higgs boson and other particles. For the God hypothesis, it is unclear where one would start. Why does God favor three generations of elementary particles, with a wide spectrum of masses? Would God use supersymmetry or strong dynamics to stabilize the hierarchy between the weak scale and the Planck scale, or simply set it that way by hand? What would God’s favorite dark matter particle be? This is a venerable problem, reaching far beyond natural theology. In numerous ways, the world around us is more like what we would expect from a dysteleological set of uncaring laws of nature than from a higher power with an interest in our welfare. As another thought experiment, imagine a hypothetical world in which there was no evil, people were invariably kind, fewer natural disasters occurred, and virtue was always rewarded. Would inhabitants of that world consider these features to be evidence against the existence of God? If not, why don’t we consider the contrary conditions to be such evidence? Over the past five hundred years, the progress of science has worked to strip away God’s roles in the world. He isn’t needed to keep things moving, or to develop the complexity of living creatures, or to account for the existence of the universe. Perhaps the greatest triumph of the scientific revolution has been in the realm of methodology. Control groups, double-blind experiments, an insistence on precise and testable predictions – a suite of techniques constructed to guard against the very human tendency to see things that aren’t there. There is no control group for the universe, but in our attempts to explain it we should aim for a similar level of rigor. If and when cosmologists develop a successful scientific understanding of the origin of the universe, we will be left with a picture in which there is no place for God to act – if he does (e.g., through subtle influences on quantum-mechanical transitions or the progress of evolution), it is only in ways that are unnecessary and imperceptible. We can’t be sure that a fully naturalist understanding of cosmology is forthcoming, but at the same time there is no reason to doubt it. Two thousand years ago, it was perfectly reasonable to invoke God as an explanation for natural phenomena; now, we can do much better. None of this amounts to a “proof” that God doesn’t exist, of course. Such a proof is not forthcoming; science isn’t in the business of proving things. Rather, science judges the merits of competing models in terms of their simplicity, clarity, comprehensiveness, and fit to the data. Unsuccessful theories are never disproven, as we can always concoct elaborate schemes to save the phenomena; they just fade away as better theories gain acceptance. Attempting to explain the natural world by appealing to God is, by scientific standards, not a very successful theory. The fact that we humans have been able to understand so much about how the natural world works, in our incredibly limited region of space over a remarkably short period of time, is a triumph of the human spirit, one in which we can all be justifiably proud.