Extraterrestrial Civilizations - Isaac Asimov [117]
Could black holes someday make interstellar travel or even intergalactic travel possible? By making proper use of black holes, and assuming them to exist in great numbers, one might enter a black hole at point A, emerge at point B (a long distance away) almost at once, and travel through ordinary space to point C, where one enters another black hole and emerges almost at once at point D, and so on. In this way, any point in the Universe might be reached from any other point in a reasonably short time.
Naturally, one would have to work out a very thorough map of the Universe, with black-hole entrances and exits carefully plotted.
We might speculate that once interstellar travel starts in this fashion, those worlds which happen to be near a black-hole entrance would prosper and grow, and space stations would be established still nearer the entrance.
Those space stations can serve as power stations as well, since the energy radiated by matter falling into a black hole can clearly be enormous. We might even visualize space projects that consist of the moving of dead and useless matter into a black hole to increase the energy output (like fueling a furnace).
In fact, this offers still another explanation for the Universe being full of extraterrestrial civilizations that nevertheless do not visit the Earth. It could be that Earth happens to be in a distant backwater as far as the black-hole networks are concerned. The extraterrestrial civilizations might know all about us, but find us not worth the time and expense of visiting.
Yet the exciting picture of a black-hole-riddled Universe converted into a kind of super-subway-system for interstellar flight has its drawbacks.
In the first place, we don’t really know how many black holes there are in the Universe. Outside the centers of the Galaxy and of globular clusters, there might be only half a dozen black holes per galaxy for all we know, and these would be of no use except to a few planetary systems near an opening, none of which might contain a habitable planet.
Second, the suggestion that matter entering a black hole will emerge elsewhere is by no means certain. Many astronomers believe there is nothing to this theory.
Third, even if matter entering a black hole does emerge elsewhere, nothing material can enter a black hole without being thoroughly smashed, right down to a powder of subatomic particles or less, by the incredible tidal effects of the unimaginably intense gravitational field of the black hole. It may be that some advanced technology will learn how to fend off all gravitational effects and keep the spaceship from serving as fuel to the black-hole furnace or from being torn apart by the tides—but at the present moment that seems impossible even in theory.
Looked at in the light of the Universe as it appears to us today, there seems no reasonable hope that the speed-of-light limit will be defeated in any practical way.
We must see what can be done at speeds below that of light.
TIME DILATATION
One peculiar phenomenon predicted by Einstein’s equations (and verified by studies of speeding subatomic particles) is that the rate at which time seems to progress slows with speed. This is called time dilatation.
On a rapidly moving spaceship everything would go more slowly; atomic motions, clocks, the metabolism of human tissue. Because everything on a ship slows down with exact synchronism, people on board such a ship would not be subjectively aware of the change. To them it would simply seem that everything in the outside world had speeded up. (This is analogous to the manner in which one isn’t aware of motion in a train moving smoothly forward at a station; instead the station and the countryside seem to be moving backward.)
The slowing of time becomes more marked as one moves faster relative