Historical Causality Violations

Both the original Time Patrol collection, Guardians Of Time, and the later Time Patrol novel, The Shield Of Time, culminate with the crisis of a changed history that must be rectified by the Patrol. These changes are not both "causality violations" because that paradox involves an event preventing its cause whereas, in the second case, earlier events have changed randomly.

In The Shield..., Anderson takes the opportunity to present a far more detailed discussion of this issue but also acknowledges the limits of the discussion. To summarize a dialogue in The Shield... (New York, 1991), p. 304 -

A Chinese cosmonaut: You spoke of persons who entered the alternate future... Apparently, only a relative few entered it... Why not many?

Everard: Those were just the ones who happened to cross the crucial moment, bound uptime, in that larger section of time during which there were related events, like the Patrol's salvage work. We've got a longer section now, with a lot more traffic in it, so our problem is correspondingly bigger. I hope you understand what I'm saying. I don't.

Komozino: It requires a metalanguage and metalogic accessible to few intellects...We haven't time to quibble about theory. The span in which we can use this base without seriously perturbing things is limited. So is the number of personnel, therefore the total lifespan at our disposal.

When Everard flounders, Komozino rescues him first by invoking "metalogic," then by calling to action. If the Patrollers had needed more time "to quibble about theory," then they could have traveled into the further past to do it before returning to address the crisis.

In the Time Patrol scenario, whenever a time traveler leaves his present to visit the past, then returns to the present, it may be to an altered present but why does he sometimes find the present altered and sometimes not? Everyone traveling futureward from far enough back in the past travels through the moment at which the change occurs.

Maybe there is an element of randomness. We are told that randomness is a factor in the mutable timeline. Because Wanda Tamberly departed from 18,244 BC to return to the twentieth century just before Everard was informed of the temporal change, he assumed that she would enter the alpha timeline but I think it is possible that, like many other futureward time travelers, she would enter the Patrol-guarded timeline and therefore, if she stayed in it, would be "deleted" with it.

Another possible explanation is complicated causal relationships involving time travelers. Thus, to invent the simplest possible example:

after a journey to the past, Everard returns to his familiar twentieth century;

then, the timecycle that he had used is stolen by a time criminal;

 

that time criminal uses the stolen timecycle to change history in the Middle Ages;

therefore, when Everard on his next pastward trip using a different timecycle travels further into the past and returns to the present, it is to an altered present.