[This dialog is a draft for a section of my story. I'm posting it here but I'm not sure where it will go in the story, so it's pretty much out of sequence. Dess and Joli are talking about hyperspace travel. Joli is a social-sciences person and not much into the "what's under the hood of my spaceship" questions. Dess is the physics geek.]
"Okay, I know I'm not too bright about this kinda stuff," Joli is saying. "Explain this hyperspace thing one more time?"
"Well, there are other universes parallel to this one - maybe infinite numbers of them - and some are almost identical to the one we're in right now. When you make a hyperjump, you leave one universe and enter another. Jumping allows you to pick the point in spacetime where you enter."
"But if I'm going into another universe like this one ... why don't I run into another one of me?"
"It's like musical chairs. At the same time that you're making your hyperjump, the 'other you' is making a jump into still another universe."
"Hmm. I think I see. But in musical chairs, you're always short one chair."
"That's true! And when you hyperjump, there's always a small chance that the 'other you' is making a different decision. So theoretically, there's always the possibility that you might meet her. Hypertravel is never completely predictable."
"Dess, we've both hyperjumped lots of times ... it seems weird to think that you're not the same person I saw before my last jump."
"Well, think of it this way: I'm not the same person you saw yesternight, either. Or an hour ago. I've changed - and so have you. The universe is always changing, and we change with it."
"Can you change the past and future with hypertravel?" Joli asks.
"You don't need hypertravel to change the future. You do that at every moment, with every choice you make in life. But I think I know what you're asking. Suppose you traveled to the future - say tomorrow - and then you threw a pair of dice. You might see an eight on your dice, but if I stayed where I was, and waited until you arrived, I might see you roll a three or an eleven. Why? Because you - the 'you' that I saw leave - are now in a different timeline.
"Now," Dess goes on, "suppose you traveled to the past. Let's say you went back in time, and ... " She's about to say, " - and killed your mother" because that's the example people usually use; but she stops herself, because she doesn't want to bring up painful memories for Joli. So instead she says, " - and, uh, did something to change the future, maybe you visited your mother when she was young and convinced her not to have babies. That wouldn't make you stop existing, because nothing you could do in the new timeline would affect anything in your own past."
There's a long pause. Dess has a moment of dread, because she's afraid Joli is goiing to ask her whether her mother is alive in another universe. And Dess doesn't know how she's going to answer that one. But that's not what Joli asks.
"Are there people from our future out there? And why haven't we seen them?"
The question catches Dess off-guard.
"Hmmmmm. Well, remember, they wouldn't be our future, exactly ... "
Dess is stalling, and Joli knows it. "But they'd be from a future like ours, right?"
"Yeah," Dess says quietly.
"So where are they? Has anybody seen a Gilkesh spacecraft from, say, 500 years in the future?"
The answer, as far as Dess or anybody else knows, is no.
"Well," Dess says awkwardly, stalling again, "there are limits on how far you can travel in hyperspace. Even our best ships can't travel five hundred years into the future."
"But in the future they'd have better technology, right? So why haven't they ever come to us?"
"Maybe they're just not that interested. We're their past. Maybe they're not all that interested in where they came from."
"But isn't everybody?"
This time, the silence is total. In a way that neither one can articulate, Joli's question has revealed a fundamental difference in their natures.
With no answer from Dess, Joli breaks the silence.
"Well, maybe they can't. Maybe they're stuck inside some kind of space-time bubble or something."
Dess thinks about this. "Yeah," she says at last. "Or maybe we are."