Talk:Grandfather paradox

Orson Scott Card dealt with this in his book Pastwatch: The Redemption of Christopher Columbus. I'm not sure if his explanation is worth repeating in the article since the book isn't widely-known, but I will explain it somewhat here.

The moment you travel to a previous point in time, all time past that point ceases to exist. You (and anyone traveling with you) continue to exist physically, but you are not "tied" to the future in any way.

After looking at what I've typed I realize it's close to the parallel universe theorem, but Card's method was logical and well-written. Goatasaur

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Nice summary and notes on fiction authors 'dealing' with it. Would be nice to note the origin of the term. Carl Sagan said it was science fiction, others seem to claim Einstein made it up. Tempshill 05:57, 1 Dec 2003 (UTC)

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The grandfather paradox is rather overused though. For those people rather bored with killing their grandfather, there is an alternative which we'll dub "The Oedipus paradox". The essential physics is the same, but the story is different. In the Oedipus paradox the time traveller returns in time and 'loves his mother' (to quote Tom Lehrer). The time traveller then has the potential of never himself being conceived (as his mother is already pregnant at the time of his conception). To avoid the getout of the time traveller being his own father, which would be possible genetically, though statistically unlikely, this would have to take place several months prior to his own conception.

One could argue though, that Novikov could prevent this paradox from occurring - as many time travellers would not be able to follow the lead of Oedipus.

We aren't supposed to dub it anything at all. If this scenario happened in some science fiction story or other, a reference to that story could be made, but this just looks like a contributor's own ideas. As an encyclopaedia we are only supposed to report ideas that have already been made known elsewhere. -- Oliver P. 08:02, 1 Dec 2003 (UTC)

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This particular resolution works well because some consider Parallel universes to be a neccesity in order to travel in time. Consider a line. How do you move backwards in the line? Someone - either yourself or others in line must move to the side before you can move backwards.

Therefore for time travel to exist there must be a "side" space-time for you to enter and travel in. This "side" space-time must have physical laws that allow life to exist in it. Therefore if time travel is possible there must be a place where an alternate universe could develop. If there is space for one alternate universe why not an infinite number of them? If an infinite number of universes exist than there would be an infinite number of parallel universes.

Who believes this? Certainly not scientists. If science fiction authors then which ones?

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I'm curious about a proposed solution presented by Douglas Adams which was phrased (IIRC) "It all works out in the wash". In that you can travel back and kill your grandfather, which might prevent you from going back and killing your grandfather, but the other changes would make the "second take" of the intervening period of time slightly different. After enough "takes" of that particular period of time (which might be a very large number), one would work out that was consistent and stable and time would continue on from there. My questions are 1) did that make sense, and 2) is there a name for this idea? Matt 19:03, 23 Dec 2004 (UTC)

If I understand it correctly, it sounds like a variation on the Novikov self-consistency principle, i.e. the universe prevents paradoxes by making sure that no paradoxical action can succeed, only in Adams's scenario the universe is self-correcting; reactive rather than preventive. In practice, however, the two may be indistinguishable.

Consider - you go back in time and kill your grandfather. According to the NSCP, you either won't be able to do that, or if you succeed, it will turn out that he really wasn't your grandfather. In a self-correcting universe, if you go back in time and kill your own grandfather, history will alter itself so that you will discover he is no longer, and never was, your grandfather. Either way, the result is the same. -khaosworks 19:15, 23 Dec 2004 (UTC)

Terence Mckenna's solution

I don't know if this is significant enough to warrent inclusion, but Terence Mckenna offered an interesting solution to the grandfather paradox. He postulated that the realization of time travel would be either the catalyst for or the result of a sort of temporal singularity that he called Timewave Zero (see the article on Novelty Theory) and that the grandfather paradox would be negated by the fact that all events in time would then exist simultaneously. Or something like that, I don't have the source material on hand. If someone can supply citations for this it may be worth including either here or perhaps in the article on Novelty Theory.

Pogo Paradox?

OK, I consider myself a Star Trek fan and I have never heard of this. Can someone explain this? --Feitclub 03:08, Apr 20, 2005 (UTC)

My only theory is that it was mentioned in the Voyager episode where Braxton is teaching Seven about the rules of time travel. Ether that or it was something that Gene Roddenberry just mentioned once. Can anyone confirm how this Pogo thing relates to Star Trek? Arctic.gnome 17:45, 23 Apr 2005 (UTC)

It was mentioned in the Voyager episode as per Arctic.gnome —UTSRelativity 18:13, 23 Apr 2005 (UTC)

Restricted action resolution

About the "Restricted action resolution" - I'm not sure I understand the "free will" part, so I would like to make sure I got it currectly: does it simply mean that, if time travel is possible and this solution is correct - then every action in the past is consistent with every time travel in the future (and everything which lead to it), and therefore everything is deterministic and the future is already "set"?

Yes, that's pretty much it. It's the whole of history that's also set, since even if you go back in time and tell the inhabitants of the past what the future holds, there is no way for them to avert it. --khaosworks 13:07, Jun 8, 2005 (UTC)