Star Maker, Olaf Stapledon
This is related to Stapledon's other book The First and Last Men but with even grander scope. Through the viewpoint of a disembodied man it follows the social and evolutionary development of a multitude of alien species. It crosses from the very beginning of the universe, it's slow and gradual decline, and beyond. Driving this exploration is a continual search for the Star Maker and his reason behind it all. This is a difficult book to get into with no real plot to drive it forward. It is worth the effort in the end. While it doesn't completely satisfy it's build up that would been amazing considering it's scale.
