Bradley Monton, an atheist professor of philosophy at the University of Colorado at Boulder (his blog), is much maligned by Intelligent Design critics, though I'm not sure why. He has written a paper, "Design Inferences in an Infinite Universe," criticizing design inferences from the origin of life and irreducible complexity. I would think that would place him squarely in the ID critics' camp. But I'm not interested in psychologizing the critics. I'm interested in his paper.
He bases his argument on empirical evidence that the universe is infinite:
The mainstream view of contemporary cosmologists is that the evidence suggests that space is infinite. Specifically, the evidence suggests that on a large scale space is not curved. For example, the Wilkinson Microwave Anisotropy Probe (WMAP) was recently used to measure the Cosmic Microwave Background radiation. The temperature fluctuations in the radiation suggest that space is flat, and hence infinite. (p.3)
He develops this evidence into a premise:
Let's suppose that the universe is in fact spatially infinite, and that matter elsewhere in the universe is similar to matter here, and that there was randomness in the initial conditions for different regions of the universe. (p.4)
After considering the improbability of life arising spontaneously in a finite universe, he asks,
…how probable is it that life would spontaneously arise from non-life on a particular planet? (p.5)
And his answer is,
As long as the probability is not zero, then if the universe is spatially infinite we should expect life to arise somewhere in the infinite universe….In fact, we can draw a much stronger conclusion. We should expect life to arise an infinite number of places in the universe…. (p.5-6)
My conclusion is that one shouldn't use the development of life from non-life, or the existence of irreducibly complex biological systems, to argue for design. (p.6)
Monton provides a replacement model for inferring design, or inferring that God is the designer. Essentially, he thinks that the occurrence of miracles — such as a man walking on water — would allow for valid inferences to God. Why?
As a final topic, it's worth making explicit why we can infer design in the seeming miracle case, but not in the origin of life case or the irreducible complexity case. After all, one might think that the cases are analogous — in each case, there's the possibility that God did it, and the (highly improbable) possibility that it happened due to chancy naturalistic processes. So since we could infer design if a seeming miracle were to occur, why not already infer design based on the existence of irreducibly complex life?
Here is one key difference. In explaining why one can infer design on the basis of the seeming miracle, I pointed out that the seeming miracle would be more likely to occur under the supposition that God exists than it would under the supposition that there is no designer. This is what leads to the probability shift in favor of the designer hypothesis. In the existence of life case, though, it would be reasonable to think that there would be no more life in the universe under the supposition that God exists than under the supposition that there is no God. After all, even under the supposition that there is no God, we would expect there to be life in an infinite number of places in the universe. I see nothing in Christian theology, for example, which suggests that the density of life in the spatially infinite universe would be greater than it would be if there were no God. (p.16)
My very brief critique of Monton's argument is this: He has this argument exactly backwards. Let us take, as an example, the existence of toaster ovens. In an infinite universe, we should expect to find toaster ovens in an infinite number of places. However, toaster ovens are more likely to be found under the supposition that toaster oven designers exist than under the supposition that toaster oven designers do not exist. Likewise, given the extreme improbability of life spontaneously arising (which Monton grants), life is more likely to be found under the supposition that designers of life exist, than under the supposition that designers of life do not exist. Having found life, it is therefore more likely that designers of life exist than that they do not.