Time Travel And Future Histories

I prefer time travel to future histories with certain reservations and qualifications. Time travel has to be done very well if it is to be done at all. Thus, Isaac Asimov's time travel novel, The End of Eternity, is so incoherent that it has to rate even lower than his future history.

HG Wells' The Time Machine is a greater and more lasting work than his The Shape of Things to Come despite being much shorter than it. Olaf Stapledon incorporated mental time travel into his future history, Last and First Men, so that, in his case, we do not have to compare two different works.

Poul Anderson presents a long future history series, the Technic History, and a shorter, but still long, time travel series, the Time Patrol. I find more to think about and discuss in the former but there is also another issue here. When a fictional character visits Mars, he remains on a single version of Mars. He does not slip sideways onto an alternative version of that planet. When a time traveller visits the past, I want him to remain in the single real past, not to slip sideways into a divergent or alternative past. The fundamental premise of the Time Patrol series is a mutable timeline. When Time Patrol agents are in a timeline where Hannibal sacked Rome, they are not in our past, arguably the past. 

From this point of view, Anderson's The Corridors of Time, There Will Be Time and The Dancer from Atlantis are genuine time travel narratives. In The Dancer..., the past seems to have been changed but has not been, which is the cleverest way to do it. However, a circular causality narrative is closed whereas a future history is open-ended.