Alternative Histories And Galaxies

Human history occurs on the surface of the Earth which is located in the Solar System, the Milky Way, the local group of galaxies and the universe even if these larger structures are never mentioned. Any reference to stars seen at night is in fact a reference to the galaxy. An alternative history occurs on an alternative Earth which implies an alternative Solar System etc. Every North America uninvaded by Europeans and every wilderness still haunted by sabre tooths entails an alternative Mars and Andromeda galaxy. Thus, alternative history sf and cosmic sf can be connected.

However, this aspect of alternative histories is rarely addressed because the emphasis is on altered historical events on Earth. SM Stirling has a terraformed Venus and Mars. His Draka move into their Solar System and their antagonists go further. But cosmic sf is mainly developed in the future of what fictitiously remains our unaltered timeline.

Poul Anderson
Spaceships able to make instantaneous jumps between galaxies; one such ship visiting a planetary system in intergalactic space.
A relativistic spaceship accelerating between groups of galaxies and beyond this universe.
Inorganic intelligences spreading through and beyond the galaxy at sublight speeds.

James Blish
Cities flying between stars; a planet flying to the metagalactic centre in time for a cosmic collision.
Star-dwelling energy beings communicating with civilizations in eleven galaxies and collapsing three galaxies.
A civilization spreading between galaxies, receiving messages from its future.