You'll have heard of physicists talking about a theory of everything, a kind of summary equation behind which lies a self-explanatory universe. (Actually the most famous exponent of such a view, Stephen Hawking, doesn't hold to the possibility any more, but that's a different story.) So what about a theological theory of everything?

This is the question to which the ever lucid Keith Ward addressed himself at the Scientific and Medical Network conference today entitled 'God or Multiverse'. After all, he mused, many philosophers have today become a little bored by decades of talk on what words might mean. Maybe there is scope again for big theory.

Of course, religion is primarily based upon experience; theology seeks to make sense of it. But given that multiverses are in favour in many physics departments these days, perhaps theology has something to contribute. Augustine and Nicolas of Cusa are just two theologians to have pondered the possibility way back, thinking it quite likely that the generous creativity of God would overflow into the formation of other universes.

Theologians and scientists differ in many respects, vis-a-vis their disciplines. Theology, for example, puts mind at the base of all things; science at least proceeds as if matter was the brute fact of existence (though that does not mean that individual scientists cannot believe that mind is actually the ultimate nature of things: arguing they must be philosophical not just practical materialists to be good scientists is a mistake, as Voltaire pointed out to Enlightenment atheists like Diderot). Ward, himself, believes that there is a clear demarcation between science and religion in terms of their respective explanatory power. Science goes for reductive explanations; theology for purposive explanations. There is a place for both - in spite of the assertion, Ward added, of Richard Dawkins who in The God Delusion accuses Ward of not understanding what explanation must entail. Dawkins assumes that only reductive ones count. But if I ask myself why I am now blogging, a reductive explanation - neurons presumably firing, finger-muscles twitching - adds a little in terms of understanding. But only a purposive explanation can make full sense of such an activity. In general a purposive explanation rests on the human capacity to form an idea of the future in the present and then go about causing it - in this case, a blog entry for today.

Ward knows that some materialist philosophers and scientists deny the irreducibility of purposive explanations. But they are actually small in number and seem self-contradictory since in denying purposive explanations, in favour of reductionist materialist ones, they are having thoughts which whilst correlating to certain brain states also clearly have a primarily immaterial nature, or so it seems obvious to Ward.

What has this to do with the multiverse? For theists, consciousness is ontologically prior to everything else. So in a sense the possibility of the multiverse makes perfect sense already. It would be every possible state of things that could exist, formed in the mind of God - who must be able to conceive of everything possible since that is implicit in the concept of divinity.

Now, this thought might come up against another objection. For it is sometimes said that God cannot be an explanation of things in the world since God is a vastly more complex idea than the things in the world that God is supposed to explain. If this is taken as true then that would seem to rule out a theological theology of everything. But, Ward, continued, this is a false argument for at least two reasons. First, God is traditionally taken as in fact being simple, in the sense of being indivisible, realised, one. Second, not all explanations of things are simpler than the things they are explaining (the multiverse as an explanation for the apparent fine-tuning of our universe being an obvious case in point, but there are many others). Also, it is not at all clear what it means to say that a law of nature is simple anyway.

Ward pushed on: any theory of everything rests on the dream of discovering something fundamental that must necessarily be the case. The appeal of such necessity today stems from mathematics, maths being a system that can't be other than it is, and moreover doesn't come into being since it exists by necessity. In fact, maths looks rather like God - the former being necessary thinking, the latter necessary being.

However, if modern cosmology comes up with the multiverse as the fundamental, necessary proposition (at least in one version, it says that all possible worlds necessarily exist somewhere, we just happen to be in the one that we happen to be in), then Ward put it that the proposition of God as the fundamental necessity is actually a far simpler conjecture. In the theological case, all possible worlds would be said to exist in the mind of God, though quite possibly only a limited number of universes, and perhaps only one, actually exist. Occam would presumably have been much happier with that thought than heaped infinities of actually existing universes.

God's role in creation, then, is to allow only the universes that do exist, to exist. On what criteria might God base such decisions? In short, the reason would be that a universe exists because it is good that it exists. Or to put it another way, God prevents truly bad universes from coming into being - which for the sake of argument are universes where there is no possibility of goodness winning out whatsoever. Another way of talking about this admittedly speculative theology (though what is not speculative when it comes to modern cosmology?) would be to say that the world becomes actual with the possibility of moral consciousness in it: it is independent consciousness with the capacity of acting for the good, as human beings have, that leads to a possibility that otherwise only exists in the mind of God to come into actuality. If that sounds a bit like certain interpretations of quantum theory then I'm sure Ward meant it.

This would be a purposive explanation of the universe. Purposive explanations require knowledge of things, discrimination between things, an appreciation of goodness, and the power to chose good over evil. So to put it all another way, the big question in the cosmology debate is that of evaluation: how do you evaluate one theory over another? Even materialist theories are engaged in evaluative judgments - choosing one because it is aesthetically pleasing or simpler. Ward's theory - and to reiterate, it is only a theory not a proof since religious belief ultimately rests on experience not theology - just introduces the criterion of goodness into the debate, a rather obvious thing for human beings to do. Or rather, it is not Ward's idea but Aristotle's proposed afresh for the modern age.

In fact, this theory of everything is even older than Aristotle. It goes back to the origins of Judeo-Christian religion which is to say way before Judeo-Christian religion. For at the risk of sounding pious, it can be summed up not in an equation but in a Biblical-sounding phrase. Why is there a universe? Behold, it is good.