Everyone Gets Time Travel Wrong

Extremely random time travel post. I just finished a SF time-travel series (Dark), which hinges on the usual tangled web of causality. No idea if quantum physics has theories about time travel, but I think everyone always gets it wrong (based on my deep understanding of theoretical physics).

If you managed to go back in time, your very presence would be the cause of a new timeline. It has to be. I even wonder if Everett came up with his many-worlds theory via this very thought experiment. 

The thing is, two realities can't coexist simultaneously. We always hear the thing about not disturbing the timeline, but a human appearing out of the blue is a big disturbance! No matter what happens next, the world starts on a new trajectory thanks you your presence. This seem true even according to non-quantum theories of causality. By beaming into another timeline, you have created a paradox. You can't both have a timeline you never beamed into and also have a timeline where you did. The second you enter your past, it becomes a different past. 

So, let's say you manage to get back to Austria and find little Adolf playing with his toys. If you killed him to save the world from the Nazis and returned to your own timeline--which was created in incredibly complex ways by nearly infinite interactions--you wouldn't find a world without Hitler. Indeed, since you had altered your own world by leaving, you wouldn't actually be able to return to "your" time. You might return to a splinter that looks a great deal like your time, but it wouldn't be yours. In yours, you no longer exist. You may have saved the lives of millions (big may), but unless you hung around that timeline, you’d never experience it yourself. 

This isn't so obvious when we think our our ordinary selves leaving, but you can imagine what happens if someone like the president left. The result would be very exaggerated if he "returned" a year later. You may think, well, he could return a split second later. But that in no way prevents the split, it just makes the continuity less drastic. And of course, you could return to a time where “you” exist, but that also immediately becomes a new time. 

Time travel is a one-way ticket, which doesn’t mean it’s not interesting. But all these narratives about bouncing back and forth as if time were a solid, unchanging world is nonsense. 

You’re welcome. 🙂