Outmoded Science

(This cover shows the Altaian rings.)

Combox discussion here indicates that the planet Altai as described in Poul Anderson's "A Message in Secret" might not have a breathable atmosphere although Anderson would have tried to make his narrative scientifically accurate at the time of writing.

Future histories become outmoded not only because real events diverge from the fiction but also because science advances. When willingly suspending disbelief, we have to imagine not only that history goes differently but also that the laws of physics differ. Anderson's Tau Zero and Starfarers have different cosmogonies and cosmologies although we can imagine them coexisting in the multiverse.

A fictional account of an interstellar journey cannot be based only on current knowledge because such a journey would extend knowledge. The travellers would acquire not only factual information, e.g., as to whether a particular extra-solar planet was inhabited, but also new data affecting theories about the size and age of the universe. Thus, sf has to combine scientific knowledge with creative imagination.