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In a novel I am writing one of the antagonists travels to Earth because at the end of the novel, he travels back in time and brings himself to Earth. I'm sorry that it's a little confusing. Essentially he is transported directly to Earth from his own planet by a wormhole opened by himself who has traveled into the past after being brought by himself (the same event). Essentially, he is brought into that dimension and needs to reconcile the timeline, I think, but would this work? Or am I missing a law of time-travel?

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    $\begingroup$ There are no laws of time-travel, because as far as physics is concerned, travelling back in time (or sending information back in time) is impossible. So as long as you have that reality-check tag on the question, no, it wouldn't work, because it can't. $\endgroup$ – jdunlop Mar 18 at 23:14
  • $\begingroup$ I'm saying, if time travel was possible, that is. $\endgroup$ – Peter Nielsen Mar 18 at 23:17
  • $\begingroup$ Do you mean conventions in fiction which follow some kind of 'common sense' logic? There are those, maybe for magic too. If your protagonist does do as you say, then he's creating a causal loop or bootstrap paradox. Maybe you invented the idea and send it back in time at some point in the future so it can have been popular for so long. $\endgroup$ – A Rogue Ant. Mar 18 at 23:52
  • $\begingroup$ It's unclear what the question is. His past self has the means to generate said wormhole, so by the rules of your own universe it's possible to do it. Why he does it is a matter of character motivation, not worldbuilding. If he must do it (for time travel reasons) that is a rule you are imposing on your universe. $\endgroup$ – rek Mar 19 at 3:16
  • $\begingroup$ This is a very classic bootstrap scenario in time travel stories. It's also called a causal loop. You can find it in Teminator, for example, where John Connor sends Kyle Reese back in time to save his mother but it turns out that Kyle Reese becomes the father of John Connor. $\endgroup$ – VLAZ Mar 19 at 7:44
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There are no laws of Time Travel

The issues is paradoxes and how you handle them. You cannot have paradoxes.

1: Time is fixed. You cannot change time. If someone goes back, it was they always were going to go back. They will always do exactly what they were going to do. In the movie 12 Monkeys, the time travelers are going back to get information to cure the virus in the future. They already know they cannot stop the virus from starting.

2: Time sprouts off a new branch. When you go back in time, it makes a new timeline. You can go back and kill your grandfather because you're already been born in another timeline.

3: You don't actually travel in time. You actually hop infinite dimensions to an identical dimension but less chronologically advanced. Again, you don't need to preserve the timeline because you were born elsewhere.

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  • $\begingroup$ Bear in mind, if you choose option 1, no one has free will. $\endgroup$ – jdunlop Mar 18 at 23:38
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    $\begingroup$ But if they don't know what they'll do, they still have the illusion of free will. $\endgroup$ – Thorne Mar 18 at 23:39
  • $\begingroup$ True, but it's pretty trivial to conclude that you have no free will if it's revealed that travel into the past that doesn't change your present is possible. Of course, since you have no free will, the Author can just have you never realize that. $\endgroup$ – jdunlop Mar 18 at 23:40
  • $\begingroup$ Comes down to the whole argument about God having omniscience. If god knows what we will do, we can't possible have freewill and if we don't have freewill, why are we sentenced to hell for our sins when it's all part of god's plan? $\endgroup$ – Thorne Mar 18 at 23:44
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    $\begingroup$ You can't screw up omniscience. Either you know everything or you don't know everything. An oops means you don't know everything. $\endgroup$ – Thorne Mar 19 at 0:11
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This is not necessarily a problem.

What you've described is a tautology: if X, then X. What you need to avoid is a paradox: if X, then not X.

The problem with tautologies is getting X to happen at all. That becomes part of your premise, in this case, unless there's a "first timeline" where the portal was opened in a different way.

If you do take this path, be aware that it's an unstable equilibirum: a small change can push it from "everything works" into progressively larger problems. Consider if the future part of the time-portal is delayed by a minute, which elts your character get into the habit of being late, so they're now two minutes late to open the portal ... and eventually are running late to something are are hit by a truck.

This is why most stable time loops use the "one and only way" fixed-future model. The author is already sculpting one exact past and future, and doesn't complicate it further.

(The problem with paradoxes is that they stop themselves directly.)

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