re: #90 commadore183

How about what Michael Crichton used for time-travel in that novel “Timeline”? Been awhile since I’ve read the book, but it involved shrinking people down to sub-atomic levels and having them travel through “quantum foam” or something like that.

That or black holes? That’s something that I’ve been interested in for a while.

Well time travel just is not going to happen if you mean going back in time.

Though an interesting point… If causality is real, and you could go back in time it would mean that you have no free will.

Why?

Well you can’t change history because you didn’t - this is the only way out of the grandfather paradox - i.e. you go back in time and clip your grand father - meaning you couldn’t go back in time in the first place to kill him, so lived and you were born anyway!

You might say well I wouldn’t want to shoot grandpa! OK so say someone else might. Suppose you went back in time to kill Hitler! We can all agree that capping that bastard is worthy. However, say you could, then you never had the reason to go back in time to kill him in the first place. Future you never even heard of him, and he lives!

So you have to conclude that if you go back in time, whatever you do is constrained to not upset causality, and given butterfly effects, that makes your trip completely determined. No free will.

But what about the present then would we have free will here?

Nope. Your grand daughter could come back from your future to visit you. She couldn’t change history because she didn’t, which means everything that happened in her relative “past” still has to happen in exactly the same way. That would make all free will impossible in all time frames.

Now there are some interesting things about wormholes and orbits of black holes which could be seen as a time machine.

Two big problems, the orbits of a black hole that would act that way are withing the event horizon, so you aren’t coming out, and there is no way to make a worm hole without creating negative mass.