With the holiday season in full swing, I’m sure that you – like most of us – find your thoughts turning to… time travel. While not practical at this time, explorations of the furthest limits of general relativity and quantum physics bring us to the nearly inescapable conclusion that travel through time is almost certainly possible if we could just manage to get one of those pesky wormholes under control.
“Aha!” I hear you say. “That’s all well and good for you and your fancy pants quantum theory, but you still haven’t explained away the grandfather paradox, have you? So time travel is still rubbish.”
A common objection, and one you should be proud of. But actually, we have worked that one out and today I shall relieve the anxiety of the world and explain it once and for all. The answer is to be found in the parallel universe construction of the multiverse. The theory of parallel universes was first developed by Hugh Everett back in the fifties. There are a potentially infinite number of universes lined up side by side, sometimes bumping into each other, similar in many general ways but unique in the fine details. The concept of “side by side” may trip us up, because they are not separated by some measurable amount of space… they are separated by time.
You see, time and space are wrapped up together too tightly to separate, but they are still useful concepts for this discussion. Whether space is composed of ten or eleven dimensions (depending upon which string theoretician you ask) instead of the normal three, time is sort of locked in place in each universe. And in each one, the “starting point” of time is slightly staggered from the one preceding and the one following. Were we to use a wormhole to travel through time, we would arrive not only in a different time, but in a different, parallel universe of space as well. In fact, through the very act of traveling through the wormhole you would likely spawn an entirely new set of parallel universes, which we can more usefully think of as “timelines.” And this is why the grandfather paradox doesn’t really come into play.
To put it more simply, think of it this way: in order to test the grandfather paradox let’s say you hop through your trusty wormhole and travel back to 1938. You locate your grandfather and shove him down a set of stairs. Now you travel back through the wormhole to 2008 to see if you have disappeared. You have not. Why?
Because in our timeline, you never appeared in 1938 to do anything. Nothing has changed in this universe. If, however, you chose to hang around in the parallel universe where you eliminated your grandpa for eighty years or so, you could see what the world might be like without you. In a similar case, let’s imagine that you decided to travel twenty years into the future and give your future self a rare coin which would then be worth a vastly increased amount of money to ensure your comfortable retirement. If you returned “home” and waited twenty years, a younger you would completely fail to show up to bestow the treasure on you. That’s because the gift was presented in an alternate timeline which is locked into a future reference. In our universe you weren’t there.
There you have it. Time travel is not only possible, but the grandfather paradox is no longer in play. Merry Christmas and enjoy your time traveling.