Some Time Travel Comparisons

(i) Poul Anderson's Time Patrol series and SM Stirling's Make The Darkness Light series are opposite answers to the question whether to change history. (Assuming that you can, of course.)

(ii) Anyone who is just starting to time travel cannot know whether their timeline is mutable or immutable. Anderson's Jack Havig tries to prevent his father's death before he learns not to try. All the evidence indicates that Audrey Niffenegger's Henry DeTamble also inhabits an immutable timeline. However, wanting to be sure that he will always return to the future in which he is married to Claire, DeTamble takes extra care not to do anything that might change the course of events. Stirling's American time travellers have to find out what kind of timeline they are in. Recruits to Anderson's Time Patrol are told as part of their training.

(iii) Both HG Wells' The Time Machine and Anderson's There Will Be Time, the latter featuring Havig, describe events rushing past a time traveller.

Thus, we compare Anderson with Stirling, Niffenegger and Wells. Anderson's comprehensive treatment of both time travel paradoxes, causality violation and circular causality, makes his works a pivotal point of comparison with other time travel authors.

Now consider a time travel conundrum in Tim Powers' The Anubis Gates. I could have discussed this on the Logic of Time Travel blog but far fewer people would have read it there. In fact, I have tried to redirect readers from that blog to this one: see About Time Travel. We will find that issues raised by Powers have already been addressed in (i) or (ii) above. 

Trapped inside a burning tent, Doctor Romany can escape only by jumping through time:

"...he tried to decide what time to jump to. Sometime in the future? No, not when it meant leaving tonight's debacle as established history. Better to jump into the past, fix things up so that the situation tonight's aborted effort was supposed to remedy never would have arisen in the first place."

-Tim Powers, The Anubis Gates (London, 1986), 9, p. 274.

Romany, thinking in terms of (i), does not yet known that he is living in an immutable timeline as in (ii). Nevertheless, it is sensible, from his point of view, to travel into the past when he can use his knowledge from the future to try to counteract the effects of the situation that he had wanted to remedy. You can do a lot in the past as the hero of Robert Heinlein's The Door Into Summer learns.

Also in The Anubis Gates, in 1810, Brendan Doyle finds a hand-written volume recording events on 4 February, 1684. On the endpaper, in his own handwriting although faded with age, he reads:

"IHAY, ENDANBRAY, ANCAY OUYAY IGITDAY?" (8, p. 258)

Needless to say, later in the novel, Doyle visits 1684 and writes this mocking note to his younger self.

If I knew at what point to start writing a circular causality narrative, I would do it.