Five cut me off impatiently. “A Keystone with a TOE is inexplicable without all of human history, and all prior human knowledge. And just as every biological ancestor or cousin requires their own quota of space and time to inhabit and observe – their own body, their own food and air, their own patch of ground to stand on – every intellectual predecessor or contemporary requires their own partial explanation of the universe. It all fits together, in a mosaic reaching back to the Big Bang. If it didn’t, we wouldn’t be here.

“But the Keystone’s burden is to occupy the point where all explanations converge into a kernel concise enough to be apprehended by a single mind . Not to recapitulate all of science and history – merely to encode it.”

This was futile. I couldn’t beat them at their own game; they’d had years in which to ponder all the obvious objections, and convince themselves that they’d answered them. And if mainstream ACs – sharing almost the same mindset – hadn’t been able to sway them, what hope did I have?

I tried another angle. “And you’re happy to believe that you’re nothing but a bit player in some jumped-up TOE theorist’s dream? Dragged into the plot to save ver from having to invent a way for intelligence to evolve in a species with only one member?”

Five regarded me with pity. “Now you’re talking in oxymorons. The universe is not a dream . The Keystone is not … the avatar of some slumbering god-computer in a higher reality, threatening to wake and forget us. The Keystone anchors the universe from within . There’s nowhere else to do it.

“A cosmos can have no more solid foundation than a single observer’s coherent explanation. What would you consider less ethereal than that? A TOE which is simply true – for no reason? And what would we be, then? A dream of inanimate pre-space? Figments of the vacuum’s imagination? No. Because everything is exactly what it seems to be, whatever underlies it. And whoever the Keystone is, I’m still alive, I’m still conscious” – he kicked the leg of my chair – “the world I inhabit is solid. The only thing that matters to me is keeping it that way .”

I turned to the others. Three was gazing at the floor; he seemed embarrassed by the whole unnecessary business of trying to justify anything to an ungrateful world. Nineteen and Twenty regarded me hopefully – as if expecting me to abandon my stubbornness at any moment and finally embrace their ideas.