“Even if there’s no disaster,” someone said, “what if the planet is uninhabitable within a few decades?”

They started talking ocean acidification, atmospheric nitrogen, food web collapse.

“What if we’re only eighty percent sure it’s the apocalypse?” someone else asked.

Laurence tried to hear the ghost of Patricia that he had been keeping in his head since they’d been separated. What would Patricia be saying if she were here? He couldn’t imagine. She didn’t even believe ethics were derived from universal principles, like the greatest good for the greatest number. She seemed farther away than ever, as though he’d already gone to a different planet than her. But then it hit him: They were talking about maybe condemning Patricia to death, along with billions of others, on the assumption that they were all doomed anyway. He couldn’t even picture himself starting to unspool that for Patricia.

Laurence opened his mouth to say that of course they should pull the plug, this was insane. But at that moment he caught sight of Isobel, who had stopped rocking in her chair and now looked just immobilized. Isobel’s eyes were furrowed and she was inhaling through her nose with her lips pulled inward, and you could almost believe she was about to bust out laughing. Her dishwater bob was getting shaggy and her white wrists were like saplings. Isobel looked so breakable. Laurence felt a stabbing cardiothoracic pain, like a more grinding version of a panic attack, at the thought of hurting Isobel.

Then he flipped the question around in his head: He tried to imagine how he’d feel if humanity really did run out of hope in a year or ten and they didn’t have this radical option to offer. How would he explain that to some hypothetical person, in this apocalyptic panic? We might have had a solution, but we were too scared to pursue it.

“We can’t give up now,” Laurence heard himself say. “What I mean is, we can carry on with the research, for now, in the hopes that we’ll find a way to make it totally safe. And we can all agree we won’t even test the machine unless things look really, really bad. But if it comes down to a choice between the whole human race dying out in some nuclear holocaust or total environmental collapse, and a few hundred thousand people making it to a new planet, that’s no choice at all, right?”

Milton was nodding with his arms folded. Isobel snapped back to life with a gasp, as though he’d done CPR on her just in time.