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Old April 17 2014, 08:07 PM   #18
YellowSubmarine
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Re: time travel real?

I'd argue that all things being equal, time travel within the same timeline is many orders of magnitude (if not many infinitesimal orders*) less likely than time travel to an alternative timeline. Alternative timelines per se are just as likely as ours, so time travelling there does not increase complexity (save for the time travel itself).

Travelling to your own magnifies the complexity for the reasons you've stated. Not only you'd have the grandfather paradox hanging over our entire species and historical records, the whole idea of cause and effect that are the essence of evolution and human history could go out of the window. For that to not happen, time travel needs to be limited in exactly the ways that is necessary for the world as we know it to continue to exist. Perhaps the world itself would also require its own adjustments to be susceptible to non-destructive time travel. That's a whole bunch of unnecessary complexity that you get rid of by simply getting rid of time travel. Since no time travel is in any way necessary for what we observe to exist, Occam's razor would suggest that unnecessary complexity (and time loops) aren't there.

This doesn't mean that time loops are impossible. On one hand, time travel still could be both difficult and limited, allowing safe travel to your own (e.g.. if it is only practically impossible it would still be safe ). On the other, if time travel to alternative timelines is possible, and people were to keep taking advantage of that, at one point the timelines might start to repeat themselves for the lack of options, hence time loops might suddenly become a possibility in special-case alternative timelines that are identical to the original ones. Unfortunately, in the latter case, each time jump you find yourself in a less likely timeline (just like every wavefunction collapse puts you in a less likely universe by its inherent - now more complicated - configuration). Hence, the time loop timeline is incredibly, incredibly unlikely in itself, so we can't be at the receiving end of it. That's why there are no time travelling historians around us.

I recently had another idea that might give some credibility to the notion of time travel. Perhaps a universe with unlimited time travel, i.e. a universe without a time dimension, is simpler and hence the default option, but it is incredibly boring, full of nothing, without any causal links between states, incapable of supporting intelligent life, so one of the dimensions needs to be specialised as much as possible to support evolution by separating cause and effect. And here we are, but the specialisation is shaky, so some causes might sneak before the effects. (For example, one might interpret portions of quantum mechanics as time travel at the microscopic level, alas if that's all you have, you can't do much with it. See practical impossibility.)

* Maybe the probability of our universe is equal to zero, hence we're dealing with some form of infinitesimals. I have no knowledge on either the theory or the terminology in that field, so forgive me if that's a nonsensical thing to say.
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