In James Blish's Golden Age SF novel A Clash of Cymbals
, the concluding volume of the "Cities in Flight" tetralogy, scientists make a momentous discovery: we are not the only universe. A parallel universe, separated from ours across a fourth spatial dimension, is drawing ever closer. When the two universes collide, they will mutually annihilate and start a new cycle of the cosmic story.
I liked Blish's story as a teen, but found the basic premise hard to swallow. I am all the more astonished to discover that Paul Steinhardt and Neil Turok (hereafter, S&T), both highly respected cosmologists, have proposed a similar scenario and argued for it at length. There are a few differences, of course. In Blish's story, the other universe was made of antimatter, and the S&T one is normal matter; also, Blish has the collision occurring in 4004 A.D., while S&T more conservatively estimate that it will happen about a trillion years from now. All the same, the two versions are surprisingly similar. Even more surprisingly, no one seems to have told the two scientists about their fictional precursor. They quote Asimov's short story The Final Question
with evident approval, but there's not a mention of poor old Blish.
S&T seem disappointed that hardly anyone is prepared to take them seriously, despite all the work they've done. They make some good points. "Inflation", the current mainstream theory of the very early universe, is a bit of a mess: in particular, it relies on an expansive force which only had effect right at the beginning of time, and whose nature is still obscure. Originally it was supposed to be caused by the Higgs field, but it turned out that that didn't work; now it's claimed to be something similar
to the Higgs field, but distinct from it. The properties of the "inflaton" field seem rather ad hoc, and have to tuned carefully to fit the data. S&T point out that we already know about one universal expansive field, dark energy. Their theory uses dark energy to do all the expanding and smoothing that inflation is supposed to do. Each trillion year cycle of the universe ends up with space-time ironed flat by dark energy; it then collides with the parallel universe, releasing a huge amount of energy and kicking the cycle off again. Some parts of this idea seem to have been borrowed by Penrose in his recent book Cycles of Time
S&T have detailed mathematical models for everything, and there's no doubt that it's real science. It makes concrete predictions: if inflation happened, it ought to have given rise to strong gravitational waves, whose effects we should fairly soon be in a position to detect by the way they would polarize the Cosmic Background Radiation. S&T, in contrast, predict much weaker gravitational waves. We only need to be able to measure the polarization a little more accurately to be able to distinguish the two theories. Stephen Hawking (a colleague of Turok) has apparently made one of his famous bets to the effect that these measurements will disprove the cyclic theory. Right now, however, it seems that no one knows what's going on.
So the jury's still out, but I'm afraid my reaction is the same as it was when I read Blish's novel in the early 70s: it's just too bizarre to think that there's an invisible universe alongside ours, which periodically collides with us. I gather that my reaction is pretty much the usual one. All the same, the book is responsibly written and contains a lot of interesting detail about how the world of modern cosmology works. If you're into that kind of thing, I warmly recommend it.
I wrote to Steinhardt yesterday to ask if it really was the case that he had not come across the James Blish novel. He thanked me and said that I was the first person to point out the connection. I do feel sorry for Blish. Evidently his book is utterly forgotten, a mere 50 years after it was first published.