Felix Writes: Fun With Time Travel

DigitalThoughts / Fun With Time Travel

A recent Tweet pointed me at this funny story, which the tweeter jokingly suggested is indicative of time travelers. Never mind that actual time travelers would be a lot more awkward. (Anyone cares to guess at a rational explanation for the weird couple?) In any event, that prompted me to think about time travel again, and all the problems associated with the concept.

Sure, at the movies it's pretty simple: the big bad cyborg goes back in time to change history. Fireworks ensue. Things become complicated when it turns out the trip itself was what enabled the future cyborg to be built at all. That's called a stable time loop, and it's crazy enough to give some people headaches. But it can be worse. Ever heard of the grandfather paradox? It goes like this: I went back in time to kill my grandfather... but now I was never born in the first place... so I couldn't go back in time to kill him... so I was born after all... so I went back in time... That's the exact opposite of a stable time loop, and it's unclear what would actually happen.

But that assumes changing history is possible in the first place, and if you stop to think about it, the grandfather paradox would apply to any such attempt. Let's take everyone's favorite example: killing Hitler before he gets nominated Chancellor. So, I went back in time and did it; now World War II never happened... which means I have no reason to go back in time... so nobody killed Hitler... so WW2 did happen after all... so I decide to go back in time...

Fun!

But even if history can be changed, there's another problem few people grasp: how would anyone ever know it? Think about it: someone goes back in time and kills Hitler. Now every single one of us will have grown up in a world where there hasn't been a second world war. For all intents and purposes, that's now THE history. How can you tell it was made by someone from the future, and not one of the dozens of Hitler contemporaries who actually tried to kill him back then?

Or perhaps you'd rather go with the many-worlds interpretation. So, you went back and made the big change. Now there are two parallel timelines: one in which the change never took place, and one where things were different from the start. In either timeline, for those who came after the events, history was always that way; there's no way to tell anything "changed".

For all we know, time travelers could be hopping back and forth all the time, tweaking events here and there. There's just no way to tell.

Luckily, this probably isn't happening. Relativity tells us it takes literally cosmic amounts of energy to bend time and space even a tiny bit; the scale required for time travel is just too big. But there's another possibility: if recent results from the Large Hadron Collider are correct, neutrinos may be traveling faster than light. If that's true, it means they're also moving backwards in time like the hypothetical tachyons... which means we could use them to message our past selves! The bad news is, of course, that neutrinos move only a tiny bit faster than light, and since they also move through space, that means you can only send messages into the past between distant stars. Not really useful until we have a galactic empire.

Don't despair, though! All this thinking about sending stuff into the past obscures a perfectly feasible way to travel in time. It's called "waiting", and while it can only take you forward, that can be remarkably useful. Don't believe me? Watch the mindblowing Dr. Who episode Blink... or ask any historian. They even invented something called time capsules for this very purpose.

I took such leaps in time myself, when visiting certain neighborhoods of Bucharest for the first time after twenty years (and the 1989 Revolution). It's a special experience that makes me think about roads not taken, and what we can do now to influence the future. Because for now that's the best we may hope for, and it matters, as we're going to live in that future.

Too bad we can't have the hindsight of a time traveler. Be wise instead.

2011-11-19