Timetraveller killing himself in the past

[rbj]

... it would allow the case that I find actually more perverse than the grandfather paradox: that Beethoven's 9th symphony has no author. Someone from the future goes to the past and hands the score to Beethoven, who publishes it, allowing future person to receive it.

how do you know that's not how it happened? something inspired Beethoven.

 

[torquil]

I go back to Shakespeare's time and discover he has some idea about the play Macbeth, but has writer's block and can't get it going. You give him a copy of Macbeth, he loves it and produces it (no plagiarism, since he wrote it). So who really wrote Macbeth?

That's quite easy to answer: Shakespeare. Just follow the "oriented" worldline of your Macbeth-book in the backwards direction, and it will eventually go towards a spacetime event whereby Shakespear writes it. This worldline will of course go back and forward in the time time dimension, since we are allowing time-travel in this example.

Cause and effect will always follow some allowed worldline. If time travel is allowed, then this "following the worldline backwards" method must be a valid form of causality. Macbeth will only appear "out of the blue" for those who are unable to examine the entire 4d worldline.

 

[PAllen]

That's quite easy to answer: Shakespeare. Just follow the "oriented" worldline of your Macbeth-book in the backwards direction, and it will eventually go towards a spacetime event whereby Shakespear writes it. This worldline will of course go back and forward in the time time dimension, since we are allowing time-travel in this example.

Cause and effect will always follow some allowed worldline. If time travel is allowed, then this "following the worldline backwards" method must be a valid form of causality. Macbeth will only appear "out of the blue" for those who are unable to examine the entire 4d worldline.

Your argument is not correct. The scenario I posited has only one (forward only) world line for Shakespeare. Your proposal does not follow from either the math of GR, nor from the Novikov assumption (in fact this situation being allowed is discussed in the literature on Novikov conjecture).

 

[torquil]

Your argument is not correct. The scenario I posited has only one (forward only) world line for Shakespeare. Your proposal does not follow from either the math of GR, nor from the Novikov assumption (in fact this situation being allowed is discussed in the literature on Novikov conjecture).

My proposal assumes that I'm allowed to draw a time-travelling worldline that turns backward in time (makes a U-turn in the time dimension), and perhaps that some sort of alternate future is generated each time the time-travelleler interacts with anything else, so as to render any paradoxes impossible. This may not be compatible with the assumptions that is made when discussing the Novikov self-consistency principle/CTCs/time-paradoxes.

I'll have a quick look at it then to educate myself a bit :-)

EDIT: That Gödel solution is far out!

 

[PAllen]

My proposal assumes that I'm allowed to draw a time-travelling worldline that turns backward in time (makes a U-turn in the time dimension), and perhaps that some sort of alternate future is generated each time the time-travelleler interacts with anything else, so as to render any paradoxes impossible. This may not be compatible with the assumptions that is made when discussing the Novikov problem.

I'll have a quick look at it then to educate myself a bit :-)

Your proposal about past interaction creating an alternate future has been made many times, and is a solution to causality problems. Unfortunately, it is not required by GR (purely classically, or with quantum corrections per ZapperZ's reference. Note that (as far as I can see), it cannot even be added as an additional conjecture, like Novikov. It requires that any forward pointing world line encountering a backward going world line, must split into two world lines. I am skeptical that such a solution is even mathematically possible in GR.

 

[torquil]

Your proposal about past interaction creating an alternate future has been made many times, and is a solution to causality problems. Unfortunately, it is not required by GR (purely classically, or with quantum corrections per ZapperZ's reference. Note that (as far as I can see), it cannot even be added as an additional conjecture, like Novikov. It requires that any forward pointing world line encountering a backward going world line, must split into two world lines. I am skeptical that such a solution is even mathematically possible in GR.

Agreed on all points.

 

[nitsuj]

Um. Did you mean case in point?

Ah ha, that one wasn't too bad for me. To maybe offer a laugh, up until I was about my early 20's I thought the term misdemeanor (small crime) was Mister Meaner lol. sorry for the side track all.