I don’t think we can ever achieve meaningful time-travel.

The concept of time-travel is an attractive one. It is very tempting to dream of meeting dead relatives just one last time, to be present at important historical events or to be able to visit a distant future where flying cars may be as commonplace as those narcissism-perpetuating selfies are today.

Traveling forward in time is, in theory, possible thanks to the implications of Einstein’s Theory of Relativity. You could travel to a distant future within your lifetime, if you somehow manage to travel very, very close to the speed of light.

The problems start when you want to go back in time. You could say that all you’d have to do was go faster than light, but that’s a real biggie, as Einstein’s theory says that nothing can go faster than light. And even if you could outrace light, I think it’s pretty likely that you could only see the past, but not interact with it. Pretty much in the same way we see the past of distant stars and galaxies, but cannot interact with them.
And assuming you could interact with the past we get back to the old question “What if you killed your grandfather?”. Changing the past would change the present, cause it to be inconsistent. Therefore I think it is extremely unlikely we’ll ever find a way to interact with the past.

Another way to possibly travel into the past is given by possibility that our own universe could be only one of (infinitely?) many, and that within these universes alternate versions of you and me run around and go about their lives. While I think there are other universes out there I cannot wrap my head around the view that there should be an alternate version of me running though a world with only one Korea or the dinosaurs have not gone extinct, or even an exact copy of our universe, with no differences whatsoever.

But let’s play that ball for a moment, because an infinite number of universes should also allow for an infinite amount of possibilities, which could certainly imply there’s a version of me that actually likes Hip Hop.
Since I think we can all agree that Hitler was quite an asshole (if you happen to disagree please be invited to jump from a nearby building) and the above implications also mean there should be a universe with a version of Earth currently going through the year 1920 let’s assume we’d want to travel back in time and kill Hitler.

So we found some way to get some other universe, maybe by traversing a black hole, which I currently happen to think of as the opposite end of a big bang starting a new universe, by traveling some sort of wormhole, or through some sort of  technological contraption that can do the trick, probably most likely by opening a wormhole to another universe.
For this thought experiment let us completely leave aside any problems that may arise through the quite likely necessity that from whereever we enter that universe we still need to find and travel to Earth, because I think we’ve got enough other problems to deal with already.

I think the biggest problem we face is this: How do you know this is the right universe? The universe where Earth is going through the year 1920. If we assume there is an infinite number of universes it’s also quite possible that none of the universes that are connected to ours would be the one we’re looking for. There could be an infinite number of “wrong” universes in between.

But let’s go on to assume that we somehow figure out how to travel to a specific universe. The one we actually want to go to. Or maybe we’re lucky and the universe we’re looking for happens to be connected to our own.
So we go there, kill Hitler, and then? Are we planning to stay there in 1920 and enjoy our success, but way back in the past, without Facebook, Twitter or our friends to share our success with? Or do you prefer to head back home to 2014 (or whatever year you happen to be reading this in)?

Because if you want to go back, what makes you assume that killing Hitler in that universe makes any difference to our own universe? For all we currently know nothing happening outside our own universe has an effect on it. We’d come back, all happy that we’ve succeeded, only to find a world that hasn’t changed a bit. The history-books are unchanged. We didn’t make any difference at all. At least not to our own universe.
In that other universe, the one we went to to kill Hitler, history would certainly go on a course very different from what happened here, but unless we stayed in that universe, and therefore in 1920, we wouldn’t be able to see what changes we’ve caused.

This brings me back to my initial statement: I don’t think we can ever achieve meaningful time-travel.

But let’s spend a moment to think about doing it the other way around. Maybe we have a relative suffering from a rare disease and hope to be able to get a cure from the future. We climb into our spaceship, accelerate to 99.999% of the speed of light (I know, I know, but this is a theoretical example, keep that in mind), fly around for a bit and return to Earth in the year 3514.

Assuming that, against all odds, mankind managed to survive until then, we might actually be able to get the cure we need, but in order to go back we’d need to go to another universe, one that at that time goes through the time at which you’ve left. Again we’d run into the problems outlined above. How do we know which universe to go to? Is it actually possible to reach the right universe?
And finally: There supposedly is another version of us in that universe. We can’t just take the place of our alternate version and go on living our life just like when we left. Of course you could argue that presumably the other “us” also went onto that same adventure, and therefore would come back in a different universe, thus opening the possibility for us to fill in that void and actually go on with our life. But what if in that universe we didn’t leave in the first place? Maybe we come back a few month before we leave, visit our relative, present them with the cure and by doing so eliminate the necessity of our alternate version to make that trip? Are we then gonna kill our other self in order to resume our life?

Going this way, to the future first and then back to the our own time, may make more sense than the other way around, but the “universe selection problem” still makes this extremely unlikely.

If we leave aside Relativity and also travel forward through time by going to another universe we could be able to have the possibility to return to the universe and time we came from. But still we’d have the same problems as in the previous examples, universe selection.

Mostly for that reason, that traveling back in time is quite likely not possible without traveling to another universe, if at all, I have to repeat once more: I don’t think we can ever achieve meaningful time-travel.

Relativity seems to offer us a very real way to be able to travel forward in time, if we ever manage to get close to the speed of light. Until then maybe we should try to shape the time and universe we actually inhabit in a positive way.

Thank you!
Dennis Wronka