Time And Age

When generations succeed each other over centuries or millennia, we say that an sf series has become a future history but something else can happen in sf. Sometimes individuals find ways to prolong their lifespans indefinitely, e.g.:

John Amalfi and his colleagues in James Blish's Cities in Flight;

Hanno and his companions in Poul Anderson's The Boat Of A Million Years;

Louis Wu in Larry Niven's Known Space series;

Leto II Atreides in Frank Herbert's Children of Dune and God-Emperor of Dune.

After living for centuries, Leto II converses with the clone of a man killed in an earlier volume. When the focus is not on succeeding generations but on long-lived individuals, we lose the sense of the passage of historical time, especially when Amalfi and Hanno embark on long interstellar voyages so that we no longer see events either back on Earth or on any other planet apart from a fleeting visit. I was surprised, near the end of Blish's Earthman, Come Home, to realize that centuries had elapsed during that novel and the same thing happens for Hanno and his crew in The Boat Of A Million Years. It is a challenge to the author both to communicate the passage of so much time and also to show how this affects the psychology of his characters.