In the previous post, I considered the intrinsic probability of theism, arguing that it was not too low. In this post, I consider some important lines of evidence for theism provided by science, mostly by physics. When I was younger, the progress of science seemed like a threat to theism. It’s not that I had a problem reconciling science with my beliefs, as might be the case with, say, someone who thinks it’s very important to interpret Genesis literally. The problem was instead that it seemed like science threatened to render God an “unnecessary hypothesis.” As science explained more and more, it seemed that God was needed to explain less and less. One could say that God had created a mostly self-sufficient cosmos, but there didn’t seem to be much reason to say it, and parsimony considerations like those discussed in my last post seemed to tell against it.
I don’t think this way any more. I am still impressed by science’s ability to explain what goes in the world–it still seems to me that the world God created is mostly self-sufficient. But I now think that certain features of the world which science has helped discover, along with the fact that science has been as successful as it has, are much more likely if theism is true, and are therefore powerful evidence for theism.
One of the most striking pieces of relevant evidence is the so-called “fine-tuning” of the universe for life. Recent science has provided strong evidence that even tiny variations in the form of the laws of nature, the values of the constants which appear in those laws, or in the initial conditions of the universe would have resulted in a universe incapable of sustaining life. So, to take an example of each type:
- Without the Pauli Exclusion Principle, complicated chemistry would not be possible;
- If the strength of gravity had been one part in 1060 stronger, the universe would have collapsed back in on itself after the Big Bang, whereas if it was one part in 1060 weaker, stars would not form;
- If the entropy of the initial conditions was not extraordinarily low, stars would not have been able to form. Roger Penrose calculates that the states allowing life to arise represent 1 in 1010^123 of the possible states. If 1010^123 were written out in the ordinary way, it would be a 1 followed by 10123 zeros–by contrast, the entire universe has only around 1080 particles. (However, Penrose’s calculation isn’t uncontroversial, so don’t treat it as too exact.)
There are many, many other examples; some can be found on pages 211-222 here. It could turn out that some of these examples will be explained away by future science, but it seems very unlikely that they will all be explained away like this, given that there are many examples of many different types.
In light of these facts, if our universe is the only one which exists, then it seems extraordinarily unlikely that it would just happen to be able to support beings like us. On the other hand, it seems like there’s at least some chance that a good God would create a universe which could support beings like us–we have at least a few positive qualities, after all. Accordingly, the existence of fine-tuning initially seems to be many, many times more likely on theism than it would otherwise be, and so seems to be powerful evidence for theism.
The most serious response to this line of reasoning involves claiming that we live in a multiverse. If there exists a tremendous number of universes, each with different laws and constants, then perhaps it is not surprising that one or another might be able to support life. And it is hardly surprising that we would find ourselves in one of the life-permitting universes. (After all, we’re alive.) For all I know, we may well live in a multiverse.
However, it’s not clear that this really succeeds in explaining away the fine-tuning problem. We might distinguish, as Robin Collins does, between physical and metaphysical multiverse theories. Physical multiverse theories, which tend to have been developed by physicists, posit some physical thing–such as a quantum vacuum–which generates the various universes involved in the multiverse. Some such theory may well be true, but the most plausible of these multiverse generators themselves tend to require a form of fine-tuning (both to produce life at all and to avoid the conclusion that we should have been so-called “Boltzmann brains”), and so only push the problem back a step rather than eliminating the need for theistic fine-tuning (see, e.g., pages 262-271 here). (Of course, Dawkins’ “Ultimate Boeing 747” argument is meant to show that theism pushes the problem back in an even worse way, but I explained before why I don’t think that’s right.)
Meanwhile, metaphysical theories, which tend to have been developed by philosophers, suggest that the multiverse itself makes up the fundamental structure of physical reality, without the universes being generated by any physical mechanism. However, these theories face other severe problems. The most prominent form of a view like this is David Lewis’ “modal realism,” which asserts that every possible universe concretely exists. But there are many devastating objections to modal realism. (For instance, in a paper in progress, Nevin Climenhaga and I argue that the success of inductive reasoning provides powerful evidence against modal realism. For further arguments, see Part III of this book.)
These thoughts illustrate my general sense of the state of multiverse-based replies to fine-tuning. Some multiverse theories face powerful independent objections, and so are unlikely to be true. Meanwhile, others may well be true, but the most plausible of these themselves require a form of fine-tuning. A multiverse theory like the latter might be true, but if so, it, too, might provide evidence for theism. Further, note that naturalistic multiverse hypotheses don’t seem to provide a ready explanation for the other two pieces of data to which I’ll appeal, for reasons we’ll see.
Another striking fact is the beauty of the universe. There is, of course, beauty in various macro-level objects–in stars, galaxies, etc. But there is also tremendous beauty woven into the laws of nature themselves, which orchestrate the myriad workings of matter according to extremely elegant mathematical principles. Indeed, at times, mathematicians have developed abstruse systems of mathematics for purely aesthetic or intellectual reasons, only to later realize that these systems described the behavior of actually existing physical systems (so, for instance, Riemannian geometry was developed in the nineteenth century for aesthetic reasons, but was discovered, after the development of the theory of relativity, to describe the curvature of space-time).
This is confirmed by Steven Weinberg, an atheist and Nobel-prize winning physicist, when he writes that “mathematical structures that confessedly are developed by mathematicians because they seek a sort of beauty are often found later to be extraordinarily valuable by the physicist,” and even that “we are beginning to suspect that” the appearance of beauty in our fundamental physical theories “is not merely an accident, that there is a beauty in these laws that mirrors something that is built into the structure of the universe at a very deep level.” (As an atheist, Weinberg thinks the “uncanny” implications of this can ultimately be explained away, but nonetheless does “have to admit that sometimes nature seems more beautiful than strictly necessary.”) 
I suggested earlier that the best objection to the claim that the universe is fine-tuned for the existence of life was to suggest that there were very, very many universes; perhaps very few of these are life-permitting, but, obviously, it’s not surprising that we find ourselves in one of the life-permitting ones. The same move doesn’t seem to work here; there is no clear reason why we couldn’t have found ourselves in a universe that wasn’t beautiful. But we can see why a good and powerful God might value beauty in God’s creations, and bring it about that those creations were beautiful; the probability of such beauty on theism is higher than it would otherwise be.
Another striking feature is the discoverability of the universe–the fact that it is structured in such a way that we are able to understand its fundamental workings. It seems that in principle, the universe might have been very chaotic–too disorderly and unintelligible for us to be comprehensible. Even apart from this possibility, going in, one would not particularly expect beings like us, with minds evolved to help us survive the kinds of practical challenges faced by our ancestors, to be able to discover such astonishing things as the composition of far-off stars or the conditions present during the universe’s earliest moments.
The discoverability of the universe is made even more striking by work from Robin Collins, who suggests that it, too, requires a particular kind of fine-tuning. So, for instance, Collins calculates that the baryon to photon ratio could have had any one of a wide range values without compromising the ability of the universe to support life, but that, within this range, it is finely-tuned to maximize the intensity of the cosmic microwave background radiation–the feature of the universe which allowed us to discover the Big Bang. Collins’ work is cutting-edge, and the evidence of fine-tuning for discoverability is not yet as well-established as that for fine-tuning for life. But it is nonetheless intriguing.
Again, there doesn’t seem to be any particular reason why we couldn’t exist in a universe which wasn’t discoverable; indeed–especially if Collins is right–it seems much more likely that we would find ourselves in such a universe than in one like ours. On the other hand, we can see why a good God would have reason to favor the intellectual goods involved in learning and comprehending the fundamental workings of the world, along with the ability to appreciate the beauty God had instilled in the deepest workings of creation, so that we have more reason to expect these features if the universe is created by God. Discoverability, too, therefore provides powerful evidence for theism.
In the next post, I will discuss evidence from moral knowledge and miracles.
 If you’re wondering why Weinberg rejects theism, only one of his reasons (as he acknowledges) has particularly to do with physics: he thinks that “though we shall find beauty in the final laws of nature, we will find no special status for life or intelligence.” Apart from the question of exactly what this means or the theological significance of it, I take it that the other considerations I raise in this post call it into question. His other reasons are fairly standard statements of fairly standard objections, some of which are serious (evil, religious disagreement) and some of which aren’t (“the lessons of religious experience seem to me indelibly marked with the stamp of wishful thinking.”).