post by imagining that the international interactions of Terrestrial history might be followed by something like the interstellar interactions of Poul Anderson's Technic History, I really think that the future history of Anderson's Genesis is much more plausible: post-human intelligences spreading at sub-light speeds through a mostly lifeless galaxy - or maybe through a galaxy where, although organic life is common, everything else - multi-cellularity, consciousness, intelligence, civilization and technology - is rare. All that life requires is energized complex molecules changing randomly until one of them becomes self-replicating. Everything else requires a great deal more.
However, here is a paradox. If a writer of fiction imagines space travellers crossing an immense distance, like to the galactic centre or to another galaxy, but confines his account of those remote regions to what is known about them at the time of writing, then he is definitely wrong. Merely by travelling that far, explorers will learn considerably more than is known at present. As yet, not a single living molecule has been detected off Earth - but extrasolar planets are being detected all the time whereas none were known to exist when I read about the universe in the 1960s. More will be learned but none of it will be anything like what has been imagined.