I am trying to find a book that I read a long time ago but I can't remember the author or title.
Time travel was like an elevator and the main characters (man and his girlfriend) travel to the distant future and distant past. I remember the extreme future mankind has gone but I remember the planet was sentient.
Part of the story revolved around a blockage in a section of time, this turned out to be blocked by an alien presence from one of our gas giants. These aliens were also trying to stop humans from developing space travel. Not much to go on but I also remember that the temperature in space was a theme used to stop the development of space travel.