Unstable Space-Time II

Poul Anderson, Time Patrol (New York, 2006).

By investigating Veleda's new religious movement, the Time Patrol caused it. But why did they investigate? This could have been a simple causal circle. For example, if Jens Ulstrup, Patrol ethnographer in residence among the German barbarians, had reported a new movement that contradicted the records, then they would have had to investigate. However, Ulstrup was unaware of the new myths until Everard and Floris, already investigating, alerted him to them.

In the timeline guarded by the Patrol, Tacitus records that Veleda helped to arrange the armistice that ended the Northern revolt. Sociologists studying Rome in the early second century acquire an altered text, "Tacitus Two," according to which Veleda instead preached against peace and, with a big following, began to change German religion in a way that in turn can be expected to change European history. I think that such an altered text could only be acquired in the alternative timeline described by that same altered text. However, Everard and Floris, investigating, travel to the period of the Northern revolt from the twentieth century of the timeline guarded by the Patrol.

Arriving during the revolt, they necessarily arrive at a date earlier than the acquisition of Tacitus Two, which describes an alternative ending to the revolt. Yet they have come from a future in which Tacitus One gives the historically accurate account of the end of the revolt. This looks like a contradiction. Either timeline can exist but not both.

I suggested a solution in correspondence with Poul Anderson. As Floris tells Everard, sociologists studying Rome and wanting to consult Tacitus acquired a contemporary copy rather than "...send uptime for a data file." (p. 486) If they had simply extracted a copy of Tacitus Two from a contemporary library, then they would already have been in the altered timeline. Therefore, the twentieth century guarded by the Patrol and containing both Everard and Floris would not have existed in their future.

Instead, let us say this. The sociologists were in Rome at a time when the Tacitus One and Tacitus Two versions of events were both potential futures. Unable to enter an immediately contemporary library without being noticed by the locals, one of the sociologists instead traveled a short distance uptime to a moment when he would be able to enter a library unobserved. By doing this, he entered the potential Tacitus Two timeline. He returned with a copy to a moment when Tacitus One and Tacitus Two were still both potentials. From that moment, it was possible to communicate with the twentieth century of the Tacitus One timeline.

This idea is an addition to the physics of time travel already established in the series but it is the only way that I can account for the existence of a Tacitus Two text in a Tacitus One timeline.