“How do we compare, then, with the Xeelee? There are some who argue that there have been ten crucial steps in the evolution of humanity…”

The ten began with the development of a DNA-based genetic code, and continued with steps Pirius understood only a little: the exploitation of oxygen to provide free energy, the use of glucose in energy metabolism, the development of photosynthesis, and the incorporation of mitochondria — like miniature power plants — into complex cells. “The first great triumph of symbiosis,” Nilis said enigmatically. His remaining steps were the formation of a nervous system, the evolution of an eye, the development of an internal skeleton to allow the colonization of dry land, the evolution of the backboned animals.

“And finally,” said Luru Parz dryly, “the magnificent emergence of Homo sap ourselves.”

Nilis said, “You might get picky about some of the steps — and alien creatures, of course, would have their own set of developmental steps — but the idea is clear enough. And certainly, for better or worse, humanity has not progressed beyond my step ten.”

“But perhaps in the Xeelee,” said Luru Parz, “we get a glimpse of what step eleven might be.”

“Yes,” mused Nilis. “We see extensions of the possibilities of life. A deep merging with technology. And a symbiosis, not just with other denizens of the same biosphere, but with aliens, different biospheres altogether — even with creatures from different ages of the universe, creatures governed by different physical laws. It’s actually a remarkable vision,” he said, almost dreamily. “It’s as if the Xeelee are more deeply embedded in the universe than we are.”

“Oh, but this is all—” Gramm seemed outraged. “Is that the message you want me to take back to the Grand Conclave, Commissary? That the Xeelee do not only possess better firepower, processing capability, tactics — they are also, in some sense, biologically superior?”

Nilis sighed, the hollows around his eyes deepening. “Minister, to destroy something, you have to understand it. We now know that the Xeelee are far older than we are, that we are dealing with relics of the antiquity of the universe. This battle of ours concerns the past as much as the present, or future.”

That hung in the air for a long moment. Then the meeting continued, even more stormily than before.

Chapter 15

On the Moon, Torec spent long days and sleepless nights researching, chairing meetings, forcing face-to-face confrontation with recalcitrant techs, and scouring over every centimeter of her prototype setup.

Following Nilis’s advice, she tried to impose discipline on the project. She forced her warring bands of technicians to agree on the designs for the interfaces between their components, and to work to those designs. And she imposed a series of freeze points beyond which change outside certain boundaries wasn’t allowed. The techs grumbled, but they got on with the job. She even suspected they were glad to have her show a bit of toughness, as if this was how they had expected her to behave since the beginning.

But it took three weeks before she was satisfied; three weeks that used up all her remaining time before Gramm’s deadline. The next test run would be the last, come what may. It had to work.

This time she was the first on the viewing mound, not the last. Again Nilis’s anguished Virtual was here, and Gramm sent a copy of his advisor, the supercilious woman Pila.

But this time Luru Parz showed up, too.

Once more the monitor bots floated into their ready positions, and the technicians cleared away from the ungainly prototype. As numerals on a hundred glowing clocks counted down, Luru Parz came to stand beside Torec.

There was an extraordinary stillness about Luru Parz, Torec thought; she was as still as the ancient Moon itself. And she was dark. The light was bright, for this was noon of the long lunar day. But Luru seemed to soak up the light; though her Virtual cast no shadow, she looked oddly like a shadow herself. Torec was given to understand that this Virtual was not an avatar, a semisentient copy of an original with whom its memories would be merged after it had fulfilled its function. This Virtual was a mirror of life, which must mean, given the lack of any perceptible time delay, that Luru Parz herself was somewhere within the Earth-Moon system — or else she was linked to the Moon by some FTL channel, which would be hugely expensive.

Luru Parz said to Torec, “So you have codified Pirius’s time-hopping technique.”

“Yes, ma’am.”

“Describe your algorithm.”

Torec took a breath. Despite the way she had hammered away at her techs to get them to talk to her comprehensibly, the theory of the CTC software was still her weakest point. “We give the system a problem to solve, in the case of our prototype to find a particular protein geometry. And we give it a brute-force way to solve the problem. In the case of protein folding, we instruct the processor simply to start searching through all possible protein geometries. And we have a time register, a special cache that stores a flag if a signal has been received from the future.

“The basic CTC program has three steps. When the processor starts, the first step is to check the time register. If a signal has been received — if the solution to the problem is already in memory — then stop. If not, we go to step two, which says to carry out the calculation by brute force, however long it takes. When the answer is finally derived, we go to step three: go back in time, deliver the solution and mark the time register.”

Luru nodded. “So the timeline is redrafted. In the first draft timeline, the problem is solved by brute force. In the final version of the timeline, the answer is sent back through time to the moment when the question is posed. So it isn’t necessary to run the computation at all.”

“That’s correct.”

Luru sighed. “The joy of time-travel paradoxes. You can get the answer to a problem without needing to work it out! But there must be a good deal more to your design. Your closed-timelike- curves must be pretty short.”

“Actually just milliseconds.”

“Surely you can solve no problem which would take longer to solve than that length of time.”

Torec smiled, her confidence growing. “No. By breaking a problem down into pieces you can solve anything.” She described how the problem was broken up into a hierarchy of nested subcomponents. At the base level were calculations so trivial they could be handled within the processor’s short CTC periods. The answers were passed back in time to become the input for the next run-through, and so on. That way an answer was assembled piece by piece and looped back repeatedly to the zero instant, until the overall problem was resolved. “The technical challenge is actually decomposing the problem in the first place, and controlling the information flow back up the line,” she said.

Luru laughed, an odd, hollow sound. “You’re computing with multiple time loops, and you think that’s the only challenge? Ensign, you’re a true pragmatist… I think it’s nearly time.”

Over the glittering, much-patched array of the prototype processor, the bots hovered, utterly motionless against the greater lunar stillness. Behind the prototype, the blank Virtual screen hovered, waiting to display the solution.

The last seconds wore away.

And at zero, the screen filled with a molecular diagram. Just like that, with no time elapsed. It was almost anticlimactic, Torec thought.

There was utter silence on the common loops; nobody moved, none of the techs or the observers from the Navy or the Ministry, not even a bot. But on the screen the diagram whirled, as it was ferociously analyzed for verification. After ten seconds, the screen turned green, and numerical results scrolled over its surface.