Story is about a man who possesses a very high IQ and is accepted to a space station (planet?) where others like him also live. He is able to travel back in time and watch the battle of Hastings. He questions why he is there
Sounds quite a bit like Macroscope by Piers Anthony.
As Sean Duggan points out there may not be anything about the Battle of Hastings in Macroscope (been a while since I read it) but the remaining elements are a close match so it's at least worth checking out. It's a fun book by Piers Anthony in his prime