Tuesday, 5 May 2015
Sometimes a work of science fiction ends by explaining why the world remains unchanged despite a fictional invention or discovery.
time travel has not been confirmed because the Time Traveler never returned;
there is no interplanetary travel because Cavor remained on the Moon and the Cavorite sphere was lost;
the Mongols did not conquer North America because the Time Patrol prevented them;
Boat presents an excellent example -
"There is simply a radius, on the order of a light-century or two, beyond which it is unprofitable to search farther. Having foreseen this, you have never built self-multiplying von Neumann machines." (p. 596)
So, yes, there are extrasolar intelligences but, no, no robotic explorers from their civilizations have ever entered the Solar System. Starfarers, to which I will return shortly, describes von Neumanns mutating and thus never completing their missions.