The ELI Event B007R5LTNS

If you were from here—I mean, this time, right now—you’d know all this anyway. You haven’t given me anything terribly convincing.” He glanced at the magazine again; the woman on the cover was still smiling, still cooking. “Well... except for that.”
    Aurora nodded. “Granted. What else would you like to know, then?”
    “Well, I’d like to know why you think you can change history, for one thing. I thought that didn’t really work. I mean, what about the inconsistencies of saving or taking lives while in the past?”
    “A fair question,” Denes admitted. “You’re referring, I believe, to what is known as the grandfather paradox?”
    Arty nodded slowly.
    “Until about fifty years ago in our time—two and a half centuries into your future—temporal displacement was the realm of science fiction. Most of what we believed about time travel was really just speculation based on writers’ imaginations.
    “With the discovery of the Final Unification Theory and the development of upstream travel as a practical reality, we began to perform small, carefully controlled experiments to test our hypotheses. We made short jumps, effected precise changes on specific, temporally localized events, and then examined the results back at the point of origin.
    “Not surprisingly, much of what we thought we knew turned out to be quite false. The grandfather paradox, multiple realities, parallel universes—all wrong.”
    “So I could go back in time and kill my grandfather.”
    “Oh, absolutely.”
    “But wouldn’t that create two different timelines, one where I was born and one where I wasn’t?”
    “No, no, we’ve found it doesn’t really work that way. There is only one timeline, one reality.”
    Arty shook his head, frowning. “I don’t get it. Then if I change something, what happens to that one reality?”
    Aurora continued the explanation. “That was our question as well, and its answer was our epiphany. It turns out the universe is far more consistent, Arty, more resilient than we give it credit for. Changing a past event certainly damages the timeline, literally rips it apart, without doubt. Causing an event to happen differently than it once did effectively nullifies its entire sequence of consequences, erases a whole stream of causality, undoes the reality that originally stemmed from the event.
    “But as the consequences of that change emerge into reality and the effects propagate downstream, the timeline repairs itself, knits itself into a new pattern all the way down the line which may or may not resemble the previous one. And for any person at any given point in the timeline, a single, new present is born,” she said thoughtfully, “with its own events and consequences, its own self-consistent causality—”
    “And its own history,” Arty finished. “So the me that went back and killed my grandfather would still exist in the past, but having prevented my original birth, that me would then be the only one that existed anywhere in the timeline.”
    Aurora nodded approvingly. “Quite so. Very good, Arty.”
    “Our colleague Lucinda is the theoretical temporalist among us,” Denes offered. “She posits that any event caused or changed by a traveler, however unlikely, nevertheless had a finite probability of occurring naturally anyway. Thus she believes that what we perceive as paradoxes, while not strictly impossible, are highly unlikely, statistically speaking.”
    Arty’s mind was racing. Bizarre as all this was, it almost made sense. But something was nagging at him. “Then what about the whole meeting-yourself thing? Isn’t that a problem? Doesn’t that cause total annihilation of the universe or something?”
    Denes smiled and shook his head. “Another science fiction fantasy, thankfully, and one with the same explanation. There are no inconsistencies in traveling within one’s own lifetime, and no consequences—no temporal ones, at least—of two such people meeting. Remember, they are in fact two different individuals, just from different points in reality.”
    Arty smiled as the puzzle pieces began to fall into place. “So the bottom line is, anyone traveling, um, upstream is truly an independent entity, and their actions may change history and alter the downstream timeline forever.”
    “Or not,” Denes added. “We have also discovered that some definitively altered events in the past seem to have no effect whatsoever on the timeline. Sometimes, the future