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Student, Oxford Brookes University

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I've always found my self in debates with people about how they could solve the paradoxes with time travel. I'm interested in your ideas and hypotheses about how time travel would work, the paradoxes I mean.

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• #### Christophe Cop500+

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Jul 12 2011: three thoughts...

1) Time travel only exists if the receiver part gets built first (no time travel possible before that)
2) There is never a first-time, nor change: the time bending is part of the total causal chain of the universe... so you could not go and kill your grandfather, as he would have been killed, and you would not exist... the first time of passing the loop is exactly the same as the second time.
3) multiple off-shoots of an infinite amount of parallel worlds

=> these are theoretical possibilities, though maybe they have been dismissed already (I don't know)
• #### Robbie Smith

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Jul 12 2011: Very well put...
• #### Ali Farzanehfar

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Jul 12 2011: Nice points with 1 and 3. But the thing I don't get about number 2 is that do you mean we can't change anything when we do go back? in that case how do we know we've gone back if we can't change anything?
• #### Christophe Cop500+

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Jul 12 2011: Everything that comes through the receiving end of a time-portal comes out the first time too, nothing more, nothing less... and no-one could come out of it to kill a fore-father, because he would have killed him the first time, not being able to have existed at all, so not being able to come through the time-gate either.

to visualize: take a sheet of paper and cut a strip that is still attached on one short side, then fold it back to make a loop: that is the time loop, where the whole sheet represents space-time. there simply is no flat sheet in the first place: the loop was there all along.
• #### Raj Bhakta

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Jul 15 2011: I wish I was a physicist(im just a college student) but I'm not so my answer wont the most educated answer that will be provided here.

Well, if we take Hugh Everetts's interpretation of Quantum Mechanics which says that with every Quantum Mechanical observation the universe splits into another universe (et al), and if that is found to be scientifically plausible then we could circumvent this paradox by going into an alternate universe and then doing whatever we want there. Theoretically, this would stand only if this were true. As for multiverses, Sean Carrol has a TED talks about how he's detected another Universe as do other Physicists interestingly. The funny thing isthat the concept of Multiverses is a metaphysical concept in science as philosophically, we can't really know anything outside of our Universe.

Of course, my answer wasn't really good but I just wanted to add to this conversation.
• #### Ali Farzanehfar

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Jul 12 2011: Personally I think that when we travel back in time, we've already messed with causality and because we have been able to do that then we should be able to do everything else, like stop my mom and dad from meeting and in the same time not tampering with my existence. I also think there won't be any more versions of me in that world because by traveling though time, backwards especially, we haven't tampered with anything but causality so there should be no reason for another version of me to exist. So to sum it up, I think traveling backwards in time itself will be a violation of causality and if that were possible then all the other paradoxes should not be regarded as paradoxes.