Lest Darkness Fall by L. Sprague de Camp
Bring The Jubilee by Ward Moore
"Delenda Est" by Poul Anderson
Let me present a line of argument. The main difficulty is to clarify the argument enough to avoid ambiguity.
(i) A time traveller is someone who disappears from his "present" and who either has already appeared at an earlier time, eg., Twain's Connecticut Yankee in the Arthurian period, or will reappear at a later time, e.g., Wells' Time Traveller in 802,701 AD.
(ii) A fictional character with memories of having disappeared from his "present" appears in what he thinks is the past during a Roman Empire indistinguishable from the empire of that name that existed in our historical past.
(iii) In this character's remembered history, the Roman Empire fell as it did in ours.
(iv) However, he now prevents the Fall of the Empire.
(v) Therefore, he has not appeared in the past of his remembered history.
(vi) Therefore, he is not a time traveller.
We can discuss where and when he has appeared but, in any case, he has not appeared in the past of his remembered history because, in that history, the Roman Empire fell. If his memories are entirely fallacious, then his remembered history has not first existed, then ceased to exist, but has never existed. Poul Anderson's Time Patrol series inconsistently alternates between these two different ways of describing a situation.
If the character's remembered history has never existed, then his appearance in the Roman Empire period is creation ex nihilo. Such creation is counterintuitive but logically possible and is not time travel.
19 comments:
That's a matter of whether "infinite discontinuities in the world-lines" are possible or not.
Kaor, Paul!
Ugh! No wonder trying to make sense of time traveling gives me, metaphorically, headaches!
The reasoning in your six points makes me conclude that what happened in TO TURN THE TIDE was a splitting off of the Roman Empire of that book into an alternate world or timeline, diverging from our timeline.
Merry Christmas! Sean
Mr Stirling,
I do need an explanation of what "infinite discontinuities in the world-lines" means!
Paul.
Paul: basically that you can exist without an accessible past.
From the viewpoint of -your- world-line, you have a past which 'no longer' exists but which you remember. That is, it exists in electrochemical state in your head, but nowhere else.
From anyone else's viewpoint, it never existed.
Both viewpoints are simultaneously valid.
If a) time travel is possible, and b) time is mutable, this is the necessary consequence.
Which means that cause-and-effect chains aren't universal, merely a special case. You can exist without a cause except in your own memory.
I might add that in TO TURN THE TIDE, the jury is out on whether they're modifying their own history or starting a new 'branch', because the viewpoint characters have no way of testing either hypothesis.
One or the other has to be true, but there is no way for them to falsify either.
And a non-falsifiable/untestable hypothesis is a semantic null set -- it simply has no meaning at all.
So when you come right down to it, it doesn't matter and they shrug and go on. They want to change the future they remember either way, and from their viewpoint it simply doesn't matter which is 'true'.
Sean: and btw, there's a very subtle hint in TO TURN THE TIDE that that 2032 CE is not quite our timeline... 8-).
I do that whenever I write in a near-future setting. It deals with the problem of rapid "dating", since predicting the future is impossible.
A longer response from me when time permits.
Kaor, Paul and Mr. Stirling!
Paul: Besides what Stirling wrote above, Anderson's "preface" to THREE HEARTS AND THREE LIONS might help to clarify the matter of alternate/parallel/divergent timelines splitting off from one another.
Mr. Stirlig: Dang! Your hint was so subtle I completely missed it despite twice reading Chapter I of TO TURN THE TIDE. At least the hint was in that chapter.
Merry Christmas! Sean
I meant to say: "At least I THOUGHT the hint was in that chapter." Dang!
Sean
I accept that it is logically possible that there can be a timeline that can be described as "discontinuous" in the sense that one or more persons in that timeline have memories that do not correspond to any events within that timeline. I would not describe this as "infinite discontinuities" but I think we are agreed on the possibility of such a timeline.
We can say either that the remembered events simply do not exist and never have existed or that they "no longer" exist. If we say the latter, then we refer to a temporal sequence not within a particular timeline but between timelines.
I do not think that there is a significant difference between starting a new timeline and modifying an already existing timeline. To modify anything is to change it. Change involves a relationship between a state changed from and a state changed to. That is a relationship of before and after which is a temporal relationship. We can say either that timeline B succeeds timeline A along the second temporal dimension or that state B of the timeline succeeds state A along the second temporal dimension. This is a terminological difference.
Kaor, Paul!
I'm by no means competent at discussing such matters, but I'm not sure all physicists would agree with you. Some do seem to accept the possibility of divergent/alternate/parallel universes existing. And that something happens to cause Timeline B to change and split off from Timeline A, where that change did not happen and events continued to happen as recorded for A. And that was, IMO, Anderson's view as well.
Merry Christmas! Sean
Sean: I'll be merciful -- it's not in that chapter. Another hint: if you were in that timeline, you'd probably discover the difference within a day or two... but it's not obvious in any aspect of everyday life.
Paul: remember that each individual has his/her own "world-line".
Each person IS described as a world-line when considered as extended in four dimensions in space-time.
Maybe Timeline B does not succeed Timeline A in a second temporal dimension but coexists with it along a fourth spatial dimension or maybe both timelines occupy the same three-dimensional space but vibrate at different rates. We can only clarify and list possibilities.
If Timeline B exists either in a fourth spatial dimension or at a different vibratory rate, then the time traveller has left Timeline A and has created an entire universe de novo ex nihilo whereas, if Timeline B exists at a later moment of a second temporal dimension, then the time traveller has merely changed a state of affairs in the second temporal dimension as we habitually change states of affairs in the first temporal dimension. The latter explanation is more parsimonious.
Kaor, Paul!
Too bad there is no known way of proving or disproving any of these possibilities.
Ad astra! Sean
For SFnal purposes, we can use any of them as assumptions; in the real world, we simply don't have the means to test any of them.
Kaor, Mr. Stirling!
I agree! And I have made some effort at PRETENDING to understand such things by reading books like Fran Tipler's THE PHYSICS OF CHRISTIANITY and Sean Carroll's SOMETHING DEEPLY HIDDEN.
Readers of Anderson should recall how he used some of Tipler's in his novel THE AVATAR.
Happy New Year! Sean
Grrrrrrr!!! I meant "...some of Tipler's IDEAS in..."
Sean
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