Maybe he creates a new timeline/universe, and so on.
My question is more fundamental. Why is 12/7/2018 considered “right now” for me? As opposed to some event that happened a week, month or year ago? Where did last week/month/year “go” that I can travel back to it?
Right; it makes no obvious sense how a time-traveller “first” starts out in 1985 and “later” appears in 1955 (remembering what hasn’t happened yet!)
I vaguely remember a series of science fiction stories (Poul Anderson? Time Patrol?) with the premise that the universe strongly resists any changes brought about by time travel. I think it starts with a man being recruited by the patrol at the moment he is shot by his wife. “You’re about to die, why not join the Time Patrol.” He decides to join up with the secret intent of going back and preventing his own death. He repeatedly fails. (I think in the final effort, just as he’s rejoicing at defeating his wife, sipping champagne on the roof, a meteorite kills him.)
Another version has the molecules in the past being fixed (so that rain drops are as fixed in place and solid as concrete), so when the time traveler goes back he is immediately killed because there is no “space” for him to enter, it’s “solid”.
These have the opposite premise of this thread. Here we seem to be assuming safe entry such that a minor change would have a large impact. These stories assume that great efforts would be required.
As I see it, the creation of a new timeline has at least four possible mechanisms.
1/ You go back in time from your own ‘present day’, change the past and thereby also change the future (and your own ‘present day’); this destroys your old timeline and you cannot ever go back to an unaltered ‘present day’. That is gone, and everyone in it never existed. Congratulations! You are a mass murderer!
2/ You go back in time and create a new timeline, and also your old timeline continues to exist. I call this the single branching timeline scenario. Creating a branching timeline (in this mechanism) can only be caused by time travelling meddlers, so it is a rare event. Using the right technology you might be able to skip between the two branches, but these are the only two possibilities in the universe (even if they are very different).
3/ You go back in time and create a new timeline; because this is part of a multiple- or many-worlds scenario, every decision you ever make (or anyone makes) creates a new timeline, so the fact that you have created a new timeline is a trivial event. Your alternate timeline is only one among countless zillions of alternates out there. Using the right technology you might be able to skip between the alternates, but the single alternate timeline you created is not qualitatively different to any of the others, even if it is entirely different to your original ‘present day’.
4/ You go back and change time, but somehow, with no plausible explanation, the changes you have made ‘revert to the norm’ and the future ends up looking identical to your original ‘present day’. I can’t see any possible way that this could happen, but it does have the advantage that it is ‘self-consistent’ without resorting to multiple timelines, and so it may be the real deal.
I should also mention the fifth option, which is (I believe) favoured by many physicists and philosophers and which solves many problems associated with time travel paradoxes; Novikov Consistency, which simply states that you can’t change the past, even if you have access to a time machine. If you go back in time you are going back to a time which has always had you in it, so sneezing or displacing air molecules won’t have any effect, because you have always been there to displace them.
That Novikov thing is trippy, and I’m glad you introduced me to the concept; but ultimately I think it’s too cute by half.
Stephen King’s novel 11/22/1963 is the story of a man who discovers a wormhole to the past and tries to prevent the Kennedy assassin. He find out the past does not want to changed, and when he finally succeeds, the future is changed for the worst (isn’t it almost always). He has to go back to the past and set things right.
There was also an episode of the new Twilight Zone and a man goes back in time and kills the baby Adolph Hitler. The baby’s father is so worried the death will make his already wacky wife go totally bonkers, so he goes out and buys a gypsy’s baby to replace the dead one. And guess who the gypsy’s baby will grow up to be?
Time travel and changing the past is an interesting hobby, but I hope we never find out what happens for real.
Speaking of baby Hitler: You (and only you) are given a once in a lifetime chance to time-travel back to the Hitler home while Adolph’s mother, Klara is breastfeeding her baby. If you accept the trip, you’d pop into the kitchen adjacent to the sitting room containing mother and baby. No one else is in the house. You can’t bring anything with you—you’re naked (but, the Hitler kitchen is well-supplied with cutlery, etc.). You’re allotted 5 minutes in the house before you are zapped back to present day. No one will know your identity (past or present), whether you kill baby Adolph or not.
What do you do?
That’s a tough question. I’d have no problem killing adult Adolph in order to (hopefully) prevent ~6+million innocent people from being tortured and exterminated.
But, a cute little baby? A baby thus far innocent of whatever twisted nature/nurture/psychological aberration that ultimately turns older Hitler into a monster? And killing him in front of his, so far as I know, innocent mother? I just don’t know what I’d do. That would be an ethical dilemma, for sure.
Now, if I walked into the sitting room and baby Adolph was sporting his Charlie Chaplin mustache and mother Hitler was giving him the Nazi salute—my decision would be easier.
What about you?
Sounds like the episode of Red Dwarf where the crew accidently prevents the Kennedy assassination and convince JFK to act as the “grassy knoll” gunman and kill his other self.
Tibby: I don’t think I could kill a baby, not even baby Adolf.