Schild’s Ladder

Tchicaya gazed into the simulation. Our side of the border is completely sterile. All these millennia looking for life, scratching around on rare balls of dirt for even rarer examples of biochemistry, only to find that the entire substrate of the visible universe was a kind of impoverished badlands. Life had still arisen here, thirty orders of magnitude up the length scale, as heroic and miraculous as some hardy plant on a frozen mountain peak, but all the while, infinitely richer possibilities had been buzzing through the superposition that the dead vacuum concealed.

He said, "Keeping this quiet is insane. People have evacuated whole planets for fewer microbes than there are in one atom-sized speck of the far side."

"Not always enthusiastically," Rasmah replied dryly.

For a moment, Tchicaya was certain that she knew what he’d done. Mariama had revealed their secret, whispered it in a few well-chosen ears, to punish him for his hypocrisy.

That was absurd, though. It was common knowledge that compliance with the ideal of protective isolation had often been begrudging, and everyone suspected that there’d been cases where the evidence had been ignored, or destroyed.

"This could win us the Wishful Xenophiles," he persisted. "One glimpse of this, and they’d desert en masse." Not all Preservationists shared the view that cultural upheavel was the worst consequence of Mimosa; a sizable minority were more afraid that it might obliterate some undiscovered richness of near-side alien life. Four known planets dotted with microbes — whatever potential they offered for evolutionary wonders in a few hundred million years' time — might not be worth fighting for, and most people had abandoned hope that the galaxy contained other sentient beings, but unexplored regions could still be home to alien ecologies to rival Earth’s. Now, that uncertain possibility had to be weighed against life-forms by the quadrillion, right in front of their noses.

"These aren’t sophisticated creatures," Hayashi pointed out. "We can quibble about the definition of life in different substrates, but even if that’s conceded, these things really aren’t much more complex than the kind of RNA fragments you find in simulations of early terrestrial chemistry."

"That’s true," replied Suljan, "but who says we’ve seen all the life there is to see?" He turned to Umrao. "Do you think these could just be the bottom of the food chain?"

Umrao spread his hands helplessly. "This is very flattering, but I think some of you are beginning to ascribe oracular powers to me. I can recognize life when I see it. I can extrapolate a little, with simulations. But I have no way of knowing if we’re looking at the equivalent of Earth in the days of RNA, or if this is plankton on the verge of disappearing into a whale."

Yann said, "Now we’re talking xennobiology!" Tchicaya shot him a disgusted look, though on reflection the hideous pun seemed inescapable. A complex organism based on similar processes to the primitive ones they’d seen probably would be about a xennometer in size.

Suljan wasn’t satisfied with Umrao’s modest disclaimer. "You can still help us take an educated guess. Start at the bottom, with what we’ve seen. I don’t think we should try to imagine evolutionary processes; we don’t know that these things are primeval, we just know that they seem to be ubiquitous. So we should ask, what else can fit in the same picture? The vendeks don’t really prey on each other, do they?"

"No," Umrao agreed. "Where they coexist in a stable fashion, it’s more like exosymbiosis. In totality, they create an environment in the graph where they can all persist, taking up a fixed share of the nodes. A given vendek in a given place in the graph will either persist or not, depending on the surrounding environment. At least in the sample we’ve seen, most do better when surrounded by certain other species — they don’t flourish in a crowd of their own kind, but they can’t make do with just any sort of neighbor. In microbiology, you get similar effects when one species can use the waste of another as food, but there’s nothing like that going on here — there is no food, no waste, no energy."

"Mmm." Suljan pondered this. "No vacuum, no timetranslation symmetry, no concept of energy. So even if there’s another level of organisms, there’s no particular reason why they should eat the vendeks."

"They might have subsumed them, though," Hayashi suggested. "Imagine the equivalent of multicellularity. A larger organism might have different vendeks playing specialized roles. Different tissues of a xennobe might consist of — or be derived from — some of the species we’ve seen."