Timelines III

Maybe we need to be clearer about "timelines" and about hypothetical relationships between them? An sf story can be about timelines, about time travel or about both. Timelines are one solution to the time travel causality violation paradox, "changing the past." The only other paradox, circular causality, fits entirely within a single timeline. In my opinion, time travel within a single timeline is the only real time travel. Someone who travels from 2025 to 1939 and who then, by his own actions, puts himself into a timeline where he has assassinated Hitler, thus preventing World War II as we knew it, assuming of course that this is even possible, is no longer in our past which is surely what we want to visit if we time travel. If we travel through space, then we want to visit the Mars that exists in our Solar System. We do not want to wind up on either Edgar Rice Burroughs' or Ray Bradbury's version of Mars. Those would be interesting but they are not where Elon Musk is trying to go.

We inhabit a single timeline with three spatial dimensions and one temporal dimension, a four-dimensional continuum. We can conceptualize although not visualize four or more spatial dimensions. Can one timeline have two or more temporal dimensions? Maybe not. I think that a second temporal dimension would be not within a single spatiotemporal continuum but between two or more such continua. In a temporal relationship, timeline 2 would be not parallel to timeline 1 but subsequent to it. Within each timeline, each event would be either antecedent to or subsequent to other events but both timelines would be at right angles to the second temporal dimension connecting them. The Temporal language of Poul Anderson's Time Patrol needs more tenses than ours. At the end of "Delenda Est," it is true that Rome won the Second Punic War, in the history of the timeline protected by the Time Patrol, but it is also true that Rome lost that war in a now deleted timeline. Two past tenses are needed. If we try to discuss this in English with only one past tense, then conceptual confusion reigns.

Our timeline is one of many possible timelines even if it is not also one of many actual timelines. Regular readers will know that all of this is relevant to works by Poul Anderson although I have not being referring to particular titles - but here are some examples:

circular causality in a single timeline is in The Corridors Of Time, The Dancer From Atlantis and There Will Be Time;

multiple parallel timelines are in the Old Phoenix sequence;

deleted timelines, however explained, are in the Time Patrol series.

Our timeline has a particular set of physical laws and a particular course of Terrestrial history. Sf writers imagine:

alternative histories;

divergent histories;

different physical laws, e.g.: gods exist and/or magic works.

Poul and Karen Anderson's The King Of Ys Tetralogy is not alternative history because, in their account, the gods did manifest on Earth but have withdrawn.

In quantum theory, timelines possibly split and diverge every time a choice is made or a dice is thrown etc? In the Old Phoenix, Valeria Matuchek says that the multiple universes are distinct from the beginning but that the differences between them only become noticeable at some later point.

As a solution to the causality violation paradox, I prefer successive timelines to splitting timelines. The latter means entire universes being created. In change as we experience it, the entire three-dimensional spatial universe exists in a different state at every successive moment of a single temporal dimension. On exactly this model, an entire four-dimensional continuum can exist in a different state at every successive moment of a second temporal dimension.

Tempus fugit.

Tempora mutantur nos et mutamur in illis.

"Time, you old gypsy man..."

"No enemy but time."

"Bid time return."