The question: What can science fiction tell us about God?

A character in my novel, Learning the World, parodies a certain kind of philosophical argument: "From the principle of plenitude, we conclude that God would have created aliens. From the Fermi Paradox, we conclude that if there are aliens, they would be here. But there are no aliens. Therefore God does not exist. Discuss."

This is a joke, of course, but the principle of plenitude – that God would have created all he could have created – was once a hot topic, of science as much as of religion. On 30 June the popular SF website io9.com ran a fascinating article, titled: Cosmic pluralism: How Christianity briefly conquered the solar system. In the 18th and 19th centuries, many astronomers were persuaded, by this very theological argument, that just about every cosmic body was inhabited by rational beings. Theologians, likewise, were persuaded by astronomers that the scale of the universe was, well, astronomical, and that Christians had better take this into account – particularly as deists such as Thomas Paine were using the plurality of worlds as an argument against Christianity: "The two beliefs can not be held together in the same mind; and he who thinks that he believes both, has thought but little of either."

Paine's thrust was parried by theologians including, surprisingly perhaps, some who might now be considered fundamentalist evangelicals: the great Scottish churchman Thomas Chalmers (1780-1847) warily admitted the possibility of intelligent beings elsewhere, while the more exuberant but no less orthodox Rev Thomas Dick (1774-1857) estimated that Saturn's rings sustained 8,141,963,826,080 souls. We may charitably attribute the precision to a rounding error.

These debates make a poignant contrast with their like today. Theology's relationship to science has become damage limitation rather than enthusiastic embrace. One factor in this change has been not geology or Darwin – which the 19th century churches assimilated within months of the Origin's publication – but the ever-widening influence of science fiction.

This isn't because SF writers are atheist – most aren't – or because SF is explicitly atheistic in its texts or subtexts. It's because SF dramatises life in the universe that science has discovered: a universe vast, ancient and indifferent. That discovered universe, and its so-called laws of nature, precisely fit the slot in the human mind once occupied by another infinite, omnipresent, and all-powerful reality: God. And as Spinoza well understood, one infinite reality leaves no room for another. Science fiction is almost the only way that recognition of this vast non-human reality impinges on literature and the arts. In mainstream fiction, unless the plot requires Australia, the Earth might as well be flat. If science is the theology of nature – with the wilder reaches of physics standing in for its scholastic philosophy – SF is its mythology, its folklore, its peasant superstition. Television, film, anime and computer games supply the statues and holy pictures, which (this time) really do move.

SF does more than popularise the natural sciences: it does the same for the similarly subversive discoveries of anthropology and psychology, teaching cultural relativism as much as physical relativity. For a readership mainly – though no longer exclusively – among the colonisers rather than the colonised, it compels at least some recognition of what it would be like for the boot to be on the other foot, or to encounter a completely different set of moral and religious beliefs among people you could hardly dismiss as "primitive" (eg because they have starships, and you have not). Imaginary alien theologies may not trouble sophisticated theologians, but I still remember how, as a nominally devout teenager, they troubled me.

Perhaps one way forward, as congruent with religion as with science, would be to take the plurality of worlds and the apparent absence of intelligent life thereon as an absent or hidden God's way of telling us something. The various bodies of the solar system and indeed the universe may be uninhabited, but that's only because God, or Nature, has left it up to us to fill them. In another century, the rings of Saturn may be singing with trillions of electronic intelligences. The Christian cosmic pluralists' principle of plenitude would then turn out to have been right, but only because we were the intelligences that chose to make it so. Discuss.