A number of shows have appeared on TV lately about time travel. Let’s assume for a moment that I have an actual time machine like the ones in the movies. Time travel into the future based on physics is really just a distortion of the time traveler’s perception of time, and you can’t get back, which is not useful for “travel” as we know it (being able to get back to when/where you started).
The truly interesting things happen with time travel into the past, and how it might affect timelines. I have been considering two interesting thought experiments based on a generalization of the grandfather problem:
1. if you time travel into the past, could you stop yourself from time traveling in the first place?
The first assumption of “you could not stop yourself” assumes that the past into which you travel is on the same timeline as the present day that you came from. However, once you are in the past, the timeline has changed already, so maybe you could prevent the new you (the one where you exist alongside of it) from also going back and making a 3rd you… maybe you have to prevent yourself from going back or else there will be an infinite loop.
If you could prevent yourself from time traveling because you’re already in the past, that assumes that there is an enormous space-time warp at the point where you co-exist with yourself. Otherwise, how could the same atoms exist in two places at the same time? I assume that the amount of energy necessary to hold you next to yourself like that with a hole in space-time would be quite significant.
Another option is that upon time travel into the past, your older self completely replaces your younger self. This would have to include an atom-for-atom replacement, so to everyone else in the past, you’d appear to age instantly to much older. If this happens, I imagine you wouldn’t really be able to get back to the future unless you somehow had remained entangled with your future self — and then going back might kill your younger self when you separate back… weird stuff.
2. if someone invents time travel at some point in the future, can’t we just leave them a message to come back to “now”?
Here assumptions abound: they have to see and understand the message, their machine has to bring them back to a specific place and time, and they have to be willing to actually do it. I assume their biggest reason for not coming back is that they assume our reaction would be one of hostility. As Calvin and Hobbes once said, “the surest sign of alien intelligence is that none of it has tried to contact us.”
