“I want to ask something…” She wished she’d dragged Dr. Khan over, because she wasn’t sure Cam could do layperson’s explanations. “About time travel. Into the past.”

“This is, of course, impossible,” Cam explained smoothly.

“Well, that’s what Auruthmer said, but Murther seemed to think there was some way. And Murther’s their top scientist. And I was thinking…we’re about to cut ourselves off from everything, from all those other worlds. I understand it’s necessary, if that’s the only way to save everything. But what if we could go back, somehow? If we could change things before they got so bad, maybe there would be another way…?” She let her voice peter out under a withering stare that was almost certainly in her head. Stupid girl asking stupid questions again, being interested in time-wasting things, you’ll never make anything of your life. She suddenly felt just like she had at school, or back at home. Like she did with anyone except Mal.

“Nothing can travel backwards in time,” Cam pronounced. “However, the formation of parallel timelines does in itself involve the collapsing of a waveform of potential here and now. This mandates the existence of a deviation point, prior to the moment that the waveform collapses. Nothing can travel backwards, but the new timeline’s divergence is anchored in the past, sometimes considerably further back in the past. Murther knows this, because she oversaw the project by which her people generated your Earth’s parallel. By this means, they discovered that their own genetic line had become functionally extinct in their newly created timeline fifty thousand years before their experiment was initiated in their own.”

“So could we make a branch where the collapsing-timelines problem was fixed fifty thousand years earlier?” Lee demanded. “I mean, maybe if someone had thought about it then, we wouldn’t have to…?”

Cam hung there for a long moment. “I do not know what would happen, should that be attempted. I suspect it may be impossible to bring into being a timeline with a past that interacts with all the other timelines—or else it would have been accomplished already. And we would have observed the effects. However, the question is a worthy one, and if we had more time…My calculations suggest that at this late stage in the morbidity of the originating life form, we are out of time. The only new branches that could be generated would be rooted in the very recent past. This would afford us dwindling possibilities, meaning that the opportunity to reset events is now profoundly limited.”

Lee blinked, digested that, blinked again. “Would we know?” she asked.

A pair of toothed arms clicked down over Cam’s compound eyes, then up again, copying her. “I do not understand your question, Lee.”

“Would we know if this was happening to us? If new timelines were being created, resets put into motion?”