by Carl Sagan
How many black holes are there in the sky? No one knows at present, but an estimate of one black hole for every hundred stars seems modest by at least some theoretical estimates. I can imagine, although it is the sheerest speculation, a federation of societies in the Galaxy that have established a black hole rapid-transit system. A vehicle is rapidly routed through an interlaced network of black holes to the black hole nearest its destination.
At a typical place in the Galaxy, one hundred stars are encompassed within a volume of radius of about twenty light-years. If we imagine relativistic space vehicles for the short journeys – the local trains or shuttles – it would take only a few years' ship time to get from the black hole to the farthest star of the hundred. One year on board the relativistic shuttle would be occupied accelerating at about 1 g, the acceleration we are familiar with because of the gravity of Earth. After one year at 1 g, we would approach the speed of light. Another year would be spent doing a similar deceleration at 1 g at the end-point of the journey. A galaxy with such a transportation system, a million separately arisen civilizations and large numbers of worlds with colonies, exploratory parties, and work teams – a galaxy where the individuality of the constituent cultures is preserved but a common galactic heritage established and maintained; a galaxy in which the long travel times make trivial contact difficult, and the black hole network makes important contact possible – that would be a galaxy of surpassing interest.
I can imagine, in such a galaxy, great civilizations growing up near the black holes, with the planets far from black holes designated as farm worlds, ecological preserves, vacations and resorts, specialty manufacturers, outposts for poets and musicians, and retreats for those who do not cherish big-city life. The discovery of such a galactic culture might happen at any moment – for example, by radio signals sent to the Earth from civilizations on planets of other stars. Or such a discovery might not occur for many centuries, until a lone small vehicle from Earth approaches a nearby black hole and there discovers the usual array of buoys to warn off improperly outfitted spacecraft, and encounters the local immigration officers, among whose duties it is to explain the transportation conventions to newly arrived yokels from emerging civilizations.
The deaths of massive stars may provide the means for transcending the present boundaries of space and time, making all of the universe accessible to life, and – in the last deep sense – unifying the cosmos.