The old questions recur in sf. Can circular causality (causing the past) and causality violation (changing the past) occur in a single timeline? One rationale of the latter states that any time traveler arriving in his "past" either initiates a divergent timeline or enters a parallel/"later" timeline. If that is the case, then he cannot cause his past.
Poul Anderson's Time Patrol series has both paradoxes occurring in a single sometimes mutable timeline. In SM Stirling's Change series, the time traveling island of Nantucket either initiates a divergent timeline or alters events in a subsequent timeline whereas a time traveling individual, Orlaith, ensures that some events in her personal past occur on schedule.
For a more general discussion, see The Logic of Time Travel: Part I.
3 comments:
Kaor, Paul!
I well remember how your commentaries on Anderson's Time Patrol stories raised issues I had never thought of. I esp. liked your arguments that "annulled" were not snuffed out, made to never having existed at all, rather they became inaccessible to time travelers from the Patrol's timeline. And you mentioned that Anderson basically accepted your reasoning and said he would have to keep that in mind for any Patrol stories he might have written after "Death and the Knight." I did not like the idea of entire universes of thinking beings simply not EXISTING.
Sean
Sean,
Poul Anderson definitely said that he accepted some of what I said about the Time Patrol and that he would keep my letters for reference in the event of writing any more about time travel, as did James Blish. On the deleted timelines issue, my memory is that PA was still defending the way that he presented the issue in the series rather than accepting my analysis.
Paul.
Kaor, Paul!
But I hope Poul Anderson would have come to accept your arguments that "deleted" timelines were not actually snuffed out, but became simply inaccessible to travelers from the Patrol's timeline.
Sean
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