Cities in Flight

In that utmost of dead silences, the upsetting whisper of continuous creation proved to have two voices. Each pinging birth-pang was not a single note, but a duo. As each atom of hydrogen leapt into being from nowhere into the universe of experience, a sinister twin, a hydrogen atom of anti-matter, came there in that instant to die, from … somewhere else.

And there it was. Even what had seemed to be fundamental, ineluctable proof of one-way time and continuous creation could also be regarded as inarguable evidence for a cyclical cosmology. In a way, to the Hevians, it was satisfying; this was physics as they knew it to be, an idiot standing at a crossroads shouting “God went that-away!” and managing to point down all four roads at once. Nevertheless, it left them a legacy of dread. This single many-barbed burr of a datum, which could have been obtained under no other circumstances, was also sufficient in itself to endorse the existence of an entire second universe of anti-matter, congruent point for point with the universe of experience of normal matter, but opposite to it in sign. What appeared to have been the birth of a hydrogen atom of anti-matter, simultaneous with the birth of the normal hydrogen atom, was actually its death; there was now no doubt that time ran backwards in the anti-matter universe, and so did the entropy gradient, one being demonstrably a function of the other.

The concept, of course, was old—so old, in fact, that Amalfi had difficulty in remembering just when in his lifetime it had become so familiar to him that he had forgotten about it entirely. Its revival here by the Hevians struck him at first as an exasperating anachronism, calculated only to get in the way of the real work of practical men. He was in particular rather scornful of the notion of a universe in which negative entropy could be an operating principle; under such circumstances, his rustily squeaking memory pointed out, cause and effect would not preserve even the rough statistical associations which they were allowed in the universe of experience; energy would accumulate, events would undo themselves, water would run uphill, old men would clump into existence out of the air and soil and unlearn their profitless ways back toward their mothers’ wombs.

“Which is what they do in any event,” Gifford Bonner had said gently. “But actually, I doubt that it’s that paradoxical, Amalfi. Both of these universes can be regarded as unwinding, as running down, as losing energy with each transaction. The fact that from our point of view the anti-matter universe seems to be gaining energy is simply a bias built into the way we’re forced to look at things. Actually these two universes probably are simply unwinding in opposite directions, like two millstones. Though the two arrows of time seem to be pointing in opposite directions, they probably both point downhill, like fingerboards at the crest of a single road. If the dynamics of it bother you, bear in mind that both are four dimensional continua and from that point of view both are wholly static.”

“Which brings us to the crucial question of contiguity,” Jake said cheerfully. “The point is, these two four-dimensional continua are intimately related, as the twin events the Hevians observed make very plain; which I suppose must mean that we must allow for a total of at least sixteen dimensions to contain the whole system. Which is no particular surprise in itself; you need at least that many to accommodate the atomic nucleus of average complexity comfortably. What is surprising is that the two continua are approaching each other; I agree with Miramon that the observations his people made can’t be interpreted any other way; up to now, the fact that gravitation in the two universes is also opposite in sign seems to have kept them apart, but that repulsion or pressure or whatever you want to call it is obviously growing steadily weaker. Somewhere in the future, the near future, it will decline to zero, there will be a Pythagorean point-for-point collision between the two universes as a whole—”

“—and it’s hard to imagine how any physical framework, even one that allows sixteen dimensions of elbowroom, will be able to contain the energy that’s going to be released,” Dr. Schloss said. “The monobloc isn’t even in the running; if it ever existed, it was just a wet firecracker by comparison.”

“Translation: blooey,” Carrel said.