Educate yourself below the click!
As we all know, if you go back in time to change something then when you get back, everything will be different. But that makes no sense. Let me explain why. I promise I won’t use the words timey-wimey or spacey-wacey.
The possibility of time-travel basically hinges on the premise that everything everywhere is happening all at once and our perception of time is an illusion. Thus, history is still out there somewhere and we can somehow access it. Time is just another dimension we have no control over, much like those of 3D space: depth, width and height. (If you’re already confused, then you’re not going to enjoy this at all) If you think you control your location in the first three dimensions, consider this: in the time it takes you to read this sentence, the Earth has traveled over one thousand kilometers around the sun. In the same time, the sun itself has traveled around thirteen thousand kilometers around the galactic core. Since you started reading this article, we’ve all flown over one hundred thousand kilometers through space. AND BOY ARE MY ARMS TIRED!
This man taught me all I know about astrophysics
Anyway, the point is: unless you have a machine like Primer (where time travel is slow like radiation poisoning) or you’re one half of the Wyld Stallyns (where time is like the internet - a series of tubes) then you need a machine that can pop across all four spatial dimensions at once.
Literally everything is tubes - time, the internet... my digestive tract...
Except it’s even more complicated than that. It turns out there’s way more than just four dimensions - according to string theory, there could be ten or eleven ‘depending on how you look at it’. Science is still figuring out the exact details (like what this honestly even means) but keep that in mind as we discover just how the entirety of Creation is actually even more terrifyingly huge than you imagined.
Let’s imagine that any causal narrative is a line. Where things could have gone differently, the line diverges:
Answer wisely, you are deciding the destiny of the universe
According to the 'many worlds' hypothesis, both of these realities now exist. Two versions of reality have been created. This was the basic plot of Sliders, that TV series where they had a dimension-hopping portal. In each reality they traveled to, the world was different somehow, whether a minor thing like a squeaky garden gate or a major thing like humanity never evolved and Earth is ruled by malicious fire-beasts. As I understand it, even the flip-flop of a single neutrino still counts, so what you end up with is an infinite rate of divergence during every pico-second. But that kind of thinking gives me a headache, so let’s stick to Sliders as an analogy.
We're told the problem with time-travel is that the slightest thing you do has an impact on the narrative. If you go back and change something, it’s like you’ve taken a different junction in the timeline. Then you head back to your original present like the time machine fast-forwards reality, finding yourself in a different universe to the one you left – one where Biff Tannen owns a casino or your toaster is trying to kill you or whatever. But here’s a key thing: as far as the universe is concerned, it’s all just matter moving around through space-time. The galaxy won’t be destroyed if you meet yourself. You can touch your past self repeatedly and nothing will explode (well, depending on where you touch your past self. I think you get my meaning). You’re not going to slowly fade away if you accidentally prevent your mother and father from meeting. The universe doesn’t care. Physics will not come to repossess your atoms like an extra-dimensional bailiff.
Also, as far as people from your ‘present’ are concerned? You’ll just have vanished. If you change something in the past, they will NOT slowly start to realize their pasts are being altered in real-time. They won’t be aware that anything used to be different.
Wait… Didn’t I used to be a girl my whole life? Oh Doctor, you scamp!
All times and places and also all versions of reality must all exist at once. In order to perform traditional, meaningful time-travel you’ll need to find an infinitely tiny spot in space-time that contains a past version of Earth, never mind a version where humans actually evolved. If you can land yourself in Hill Valley in 1955 or Victorian London in 1899 or New Orleans in 2006 (Deja Vu starring Denzel Washington), I’m sure you can also calculate a set of home coordinates for a reality similar to the one you left, possibly even slotting yourself into a you-shaped hole in the air just after your past-self vanished.
Yes, there are versions of reality where you arrived in the past and changed something. But that doesn’t mean you destroyed the place you left behind. All the different changes you could have made result in their own realities. Even if you only popped into that time for half a second, your neutrino-spins resulted in infinite realities all on their own. This also includes a version where you used the time machine and never arrived in the past, but just vanished entirely. For the sake of argument, let’s call that ‘home’ – the you-shaped hole in the air just after you teleported away. Home still exists somewhere out there, like a tiny diamond on the ocean floor. Worrying about changing the past because it might affect your present is ridiculous. I cannot stress enough that everything, everywhere that might ever have happened (or might ever happen) must all exist at once. If you can navigate the infinite universe of space, time and possibilities then you happily always have a backup reality.
If you know how to get back to the exact time, place and version of reality you left then it doesn’t matter what you do. If you don’t know how to get home, it doesn’t matter what you do because you’ll be quantum leaping forever anyway. Either way you can absolutely shag the brains out of Cleopatra, Marylyn Monroe and/or a young Harrison Ford without killing your family. Time travel is basically just one big party with no real consequences!
Wait, no! I mean to say: please give me a time machine, I promise to be responsible.
NEXT TIME: I explain how all this relates to specific examples of fiction (basically just swearing at Star Trek Voyager and the most recent episodes of Doctor Who) and tell you how to build a proper time machine. No, seriously. Not even kidding. A proper time machine. For you.