I read this story in the 70s or 80s (it might however be older). I think it was a short story, and not a novel.
These are two scenes I remember:
In the beginning of the story a guy (lets call him Albert, not the real name) sits in a room, when suddenly a disk appears and somebody (Balbert) drops through it (it turns out it is Albert himself). Soon after this a third guy (Calbert, again an older version of Albert) appears, they all struggle a bit and then Albert falls through the disk (and into the past to appear as Balbert).
Somewhere in the story he reaches some kind of far future where he meets an old man (which later turns out to be Albert again) who explains him how to operate the machines.