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Before crossing the border, they’d planned to initiate contact with the builders of the signaling layer by a simple act of mimicry: scribing a layer of vendeks of their own which beat out the same sequence of primes. Back in the honeycomb, that would have been straightforward; here, it would have been like trying to communicate by waving a white silk banner in a blizzard.

They consulted with the toolkit, and eventually settled on a reasonable compromise. They unfurled a sturdier kind of banner, flexible enough to cope with the vendek flows. Its precise geometry remained prey to the weather, but instead of encoding anything in its position, its degree of transparency to the sprites flickered between two states, flashing out the primes like a shutter held up to the light.

The airflower drifted on, apparently indifferent to the signal. They could only guess as to how it might pursue a conversation with its own kind, but if this creature had constructed the signaling layer in the alien environment of the far side’s shallows — with the intention that it be noticed by beings from an even stranger realm — why would it remain oblivious to a version of the same message suddenly appearing in front of it?

It was possible that it was completely blind to the sprites. They seemed like the obvious basis for perception here, but the airflowers might have evolved before them. If that was the case, it could take months of painstaking work to discover the creature’s actual sensory modalities.

Tchicaya had asked the toolkit to run simulations of the known species of Planck worms interacting with the bottom of the honeycomb, and as he pondered his next move, the verdict arrived. By sheer force of numbers, the worms would almost certainly stumble upon the necessary mutations to find their way through. Once they managed that, they’d bring the near-side vacuum into play against the Bright, unraveling the intricate tapestry of vendeks into isolated deserts of homogeneous physics.

The toolkit had found no certain way to prevent this, but it was studying one possibility. It looked as if it might be feasible to transform the whole region into a kind of tar pit, deep enough to trap and drown every last species of Planck worm. The worms acted as conduits for correlations with the vacuum, but not every interaction with them induced decoherence. The honeycomb vendeks had made short work of some of the earlier would-be invaders, and a sufficiently diverse mixture of vendeks, tailor-made for the purpose, would have a chance of dealing with the entire current wave in the same fashion.

Along with every native inhabitant of the Bright.

"Would you sacrifice all of this," he asked Mariama, "to save whatever lies beneath it?"

She said, "Ask me that again when we know ten times more."

Tchicaya shook his head. "That’s always going to be the right answer. Until it’s too late for anything we do to make a difference." The toolkit’s simulation was riddled with uncertainties, but to the extent that the risk could be quantified at all, within a few ship days it would cease to be insignificant.

"Don’t be so pessimistic," she countered. "Don’t assume that we’re going to have to choose between utter recklessness and some paralyzing quest for perfect knowledge."

"Perfect knowledge? There could be a billion times as many sentient beings beneath us as the rest of the galaxy has ever contained, or we might already be looking at the pinnacle of far-side life — which might be a miracle of xennobiology but dumb as a cactus, or might be conscious in ways we’re too stupid and parochial to fathom. How do you cope with that kind of ignorance?" Dwelling on it was enough to make his faithfully simulated body sick to the stomach. Part of him screamed that the only thing to do in the face of such barely comprehensible stakes was to bow out, to withdraw from any possibility of intervention — as if showing the appropriate humility was more important than the outcome.

But Mariama refused to be cowed by the gravity of the situation. "We keep exploring," she insisted. "We keep narrowing the gap between what we know and what we need to know."

"What I need to know is when we have no choice but to stop gathering information and make a stand."

Tchicaya gazed into the strange machinery of the airflower. This creature was a thousand times more sophisticated than anything that had been found away from Earth before, but if the signaling layer was an artifact at all, he did not believe that he was looking at its maker.

He said, "We need to go deeper."

With the refinements to its hull, the Sarumpaet traveled faster. For half a day they were alone in the Bright again, but then they began to spot more of the airflowers. The sightings became more frequent as they descended; at first they were seeing one or two an hour, but it soon reached the point where half a dozen were always in view.