Future Histories And Time Travel

Future histories and time travel are two different sf ideas although Poul Anderson does link them in There Will Be Time.

Anderson's main contribution to future histories is his Technic History. In particular, The Technic Civilization Saga introduces three major characters separately in Volume I, brings them together in Volume II and presents the climax of their careers at the beginning of Volume III which then advances the History to its next main phase.

I think that Anderson's main contribution to time travel is that he wrote both the Time Patrol series and There Will Be Time. Without either ignoring or forgetting The Corridors Of Time etc, I do focus on the Time Patrollers and on the mutant time travellers. There are problems with time travellers being able to change the past and with them not being able to change it so Anderson, of course, addresses both sets of problems.

When many people start to think about time travel, they imagine different times as if they were different places coexisting at the same time. I travel from 2025 to 1925. Half an hour after I have departed from 2025, a second time traveller follows me to 1925. So he arrives in 1925 half an hour after I did? No, if he followed me to exactly the same time to which I had travelled, then he arrives in 1925 simultaneously with me. But he could also have arrived in 1925 five minutes before I did and have already been there/then waiting for me.

If there is a single timeline, then anything that I did in 1925 had already been done long before I departed from 2025. Any consequences of my actions in 1925 are not waiting to come into effect after I have departed from 2025. They have already happened. On the other hand, if the consequences of my actions in 1925 occur in a divergent timeline, then they do not affect the timeline from which I depart to 1925. The Time Patrol is unnecessary.