In The Existence of God, Richard Swinburne begins his cumulative case for theism by presenting a Bayesian formulation of the cosmological argument, which he summarizes like so:
There is quite a chance that, if there is a God, he will make something of the finitude and complexity of a universe. It is very unlikely that a universe would exist uncaused, but rather more likely that God would exist uncaused. Hence the argument from the existence of the universe to the existence of God is a good C-inductive argument. (2004, 152)
Swinburne’s argument rests crucially on the claim that the probability of there being a physical universe is substantially higher given theism than given atheism. In other words, Swinburne argues that P(U|T) >> P(U|~T), where T = theism and U = the existence of the physical universe. We can call this PROBABILITY CLAIM.
How might one go about justifying PROBABILITY CLAIM? Well, we can begin by noting (as Swinburne himself does) that the universe is extremely complex: it consists of a great multitude of physical objects, falling into a variety of natural kinds, all with highly specific and seemingly arbitrary properties. Without even considering the specific properties in question (e.g. by asking whether they give rise to life-permitting laws), we are already in a position to say that such a universe is intrinsically very improbable: if there is no God, one would not at all expect there to be a complex physical universe.
On the other hand, if there is a God, then it is not all improbable that there should be such a universe. For starters, Swinburne argues that God would be quite likely to create humanly free agents, and that since “these creatures would need to have bodies… there would need to be a physical world” (2004, 151). Therefore, P(U|T) will not be less than the probability that God would make humanly free agents (which, as previously mentioned, Swinburne argues to be quite high). And of course, “God might create a physical universe, even if he does not create humanly free agents” (ibid., 151). There are any number of reasons why he might do this; for instance, creating a complex physical universe would enable God to realize all manner of great aesthetic goods (think of stars, galaxies, mountains, and so on).
One can also present a Thomistic argument for why God would create a complex physical universe. Aquinas writes:
[God] brought things into being in order that His goodness might be communicated to creatures, and be represented by them; and because His goodness could not be adequately represented by one creature alone, He produced many and diverse creatures, that what was wanting to one in the representation of the divine goodness might be supplied by another. For goodness, which in God is simple and uniform, in creatures is manifold and divided and hence the whole universe together participates the divine goodness more perfectly, and represents it better than any single creature whatever. (ST, 1.47.1)1
The basic idea here is that “God’s motivation in creating a being is something like creating an image of himself” (Pruss 2016, 230).2 Since no single creature (or kind of creature) could possibly come close to expressing God’s great goodness, God could be expected to create a large variety of creatures, so that (as Aquinas puts it) “what was wanting to one in the representation of the divine goodness might be supplied by another” (ST, 1.47.1). As Tim O’Connor puts the point, “since God’s perfection is multifaceted, perhaps infinitely faceted, a created reality that contains widely diverse kinds of good creatures would seem to better manifest his glory than one that is more uniform” (2021, 237). This gives us good reason to expect that God would make a complex physical universe, since by doing so, he could bring about a great variety of creatures.34
The upshot of all of this is that the probability of there being a complex physical universe is quite low if God does not exist, yet rather high if he does. So PROBABILITY CLAIM is true, and the existence of a complex physical universe provides us with relatively strong evidence for the existence of God.
This also helps to explain why God would bother to make a physical universe, rather than contenting himself with immaterial beings: even if he does make purely spiritual creatures (such as angels), the cause of variety is better served by his also making physical creatures. Oderberg (2021) is potentially relevant here.
Even if we reject the claim that God creates so as to image his own goodness (perhaps because we think that some genuine goods are not mere imitations of some aspect of God), there is still plausibly something valuable about God’s creating a diverse array of good things (see e.g. Mawson 2023), and this will give him reason to create a physical universe, so as to realize the unique goods which physicality makes possible. So the aforementioned line of thought will likely go through even if one is not sympathetic to the exemplificationist account of goodness which lies in the background. For further discussion of such accounts, see e.g. Kemp (2022) and Ward and Jeffrey (forthcoming).
Good post. I'm actually a huge fan of Swinburne's inductive cosmological argument as well as Timothy O'Connors abductive argument, and I think based on the considerations you mention here, they could easily be combined to form a pretty powerful argument.