So I'm reading Dreamsongs, an anthology of short stories written by George R. R. Martin. This selection of stories consists of his earliest work, some of it written when he must have been in high school and college. It is a very interesting series of short stories showing his development as a writer; from initial experimentations to Hugo and Nebula award winning short stories.
One story I particularly enjoyed was called "The Stone City", and was one of a number of science fiction shorts that were set in the same "universe". A future universe where humans have spread from Earth to inhabit a number of worlds in a relatively small portion of the galaxy. One of the themes in this story is trying to search beyond the human realm further out towards the galactic edge and inwards towards the core, and the previously unknown alien races that are found there. However there is a little more than finding alien races, it is also about how information about nearby cultures and races is known with certainty, and that information about those further away is less clear, and the further you go the more that it is difficult to disentangle myth and legend from reality. This gave the story an ambiance that I liked.
It made me think about the different types of science fiction universe that different writers have explored.
1) Humans have developed Solar system but there are no aliens (Grant Naylor's Red Dwarf)
2) Humans exist in a different galaxy with lots of aliens so no contact with Earth or Earth culture (George Lucas' Star Wars)
3) Humans have developed a scientifically sophisticated galaxy wide civilization where aliens abound where Earth was possibly the origin (Iain M. Banks Culture novels, Vernor Vinge's Fire series)
4) Humans have a multi-star system reach but connection with Earth is only through religious myth - not many aliens around (Frank Herbert's Dune)
5) Humans have left a post-apocalyptic Earth to populate a different Solar System - not many aliens around (Joss Whedon's FireFly)
6) Humans have a multi-star system reach based around Earth side by side with lots of other multi-star system aliens (Gene Rodenberry's Star Trek)
I couldn't find another similar analysis in a quick search although Wikipedia does have a list of fictional Galactic Empires. I guess these different flavours of the space travel science fiction sub-genre are largely derived from imagining humankinds possible spread through the galaxy. The universe that George R.R. Martin creates reminds me a little of Terry Pratchett's early science fiction novels. I guess the dimensions along which all these flavours vary is the number and distribution of sentient life forms that humans encounter; the characteristics of the interstellar transport mechanisms available, the spread of humanity and the fate of Earth. I guess I have half a mind that by understanding the way in which these things vary that I might be able to come up with a novel flavour ...
Themes that I haven't read or heard about yet are science fiction stories that involve no humans whatsoever, or stories that are beyond the scope of a single galaxy.