Knowing The Past

I recommend Audrey Niffenegger's The Time Traveler's Wife as a novel that ingeniously addresses the same kind of time travel paradoxes as Poul Anderson's There Will Be Time (New York, 1973).

In Anderson's novel, if a time traveler tries to change a known event, then something happens to prevent the attempted change so that the time traveler soon learns to stop trying. If he persists, then he might be stopped by a fatal accident. Thus, often, when an events occurs that a time traveler does not like, the only reason why he does not change it is because he does not try to change it. In these cases, there need not be any preventing event waiting in the wings to occur if necessary.

In the time travel fight described a few posts ago, if Havig had seen himself kill Mendoza, then he would have killed Mendoza but, because he does not see himself do this, he does not do it.

This does strain credulity and plausibility. Havig's group could conduct some controlled experiments in attempted causality violation, e.g., a time traveler tries to appear at a time and place at which it is known that he did not appear in order to find out what, if anything, will prevent him. If nothing prevents him, then they are instantly in a different scenario, more like that of the Time Patrol. They can never be completely sure that this will not occur.

If a lot of time travelers try to change a lot of known events, then the laws of probability will have to change to prevent them. For example, will a hundred time travelers each suffer a fatal heart attack just before setting off on a mission to change the past?