If you like this kind of thing, try reading Star Maker by Olaf Stapledon. Similar themes, full novel, even older. It makes for interesting reading in that it more obviously represents a "path not taken" by science fiction (and by science?!) but still has that early-sci-fi spirit of fundamental curiosity.

Seconded, but note some paths were taken (at least partially), as in some way is a meta-book were each paragraph comprises an idea that deserves a full book on its own. Some Stapledon readers were clearly inspired by it, e.g. Dyson spheres were first postulated there, and Borges got the "The Garden of Forking Paths" idea also from it.. and also Virtual Reality (not bad for 1937!) . Asimov was also an Stapledon admirer and he said that Stapledon expanded s.f. to a cosmic scale, so I think that Stapledon influence is also very present in The Last Question.