"Universe or multiverse, that is the question?"

Of late, it is fashionable among leading physicists and cosmologists to suppose that alongside the physical world we see lies a stupendous array of alternative realities, some resembling our universe, others very different. The multiverse theory comes in several varieties, but in the most ambitious the "other universes" have different physical laws. Only in a tiny fraction of universes will the laws come out just right, by pure accident, for conscious beings such as ourselves to emerge and marvel at how bio-friendly their world appears.

The multiverse has replaced God as an explanation for the appearance of design in the structure of the physical world. Like God, the agency concerned lies beyond direct observation, inferred by inductive reasoning from the properties of the one universe we do see.

The meta-question is, does the existence of these other universes amount to more than an intellectual exercise? Can we ever discover that the hypothesized alternative universes are really there? If not, is the multiverse not simply theology dressed up in techno jargon? And finally, could there be a Third Way, in which the ingenious features of the universe are explained neither by an Infinite Designer Mind, nor by an Infinite Invisible Multiverse, but by an entirely new principle of explanation.

Paul Davies, a physicist, writer and broadcaster, now based in South Australia, is author of How to Build a Time Machine.