Extraterrestrial Civilizations - Isaac Asimov [131]
Would we, however, know we had come across a signal if we detected it? What ought we to look for?
We might take the optimistic attitude that though we can’t predict what the signals would be, we would recognize them if they were there. The detection of what seemed to be a network of Martian canals was a complete surprise, but was quickly taken as an indication of a high civilization.
We know now, though, that if life signals are obtained from anywhere it will have to be from the planetary systems of other stars (or possibly from automatic probes or free-worlds in interstellar space). The likelihood is that any signals we do get will come from many light-years away, and the question is whether it is reasonable to suppose that signals energetic enough to make themselves felt across such distances could be sent out.
It might be that we should not judge all civilizations by our own. What seems a high energy level to ourselves might not seem high at all to more advanced civilizations. In 1964, the Soviet astronomer N. S. Kardashev suggested that civilizations might exist at three levels. Level I is Earthlike and can dispose of energy intensities of the kind available through the burning of fossil fuels. Level II could tap the entire energy of its star, thus disposing of energy intensities 100 trillion times that of Level I. Level III could tap the entire energy of the galaxy of which it is a part, thus disposing of energy intensities 100 billion times that of Level II.
A signal from a Level-II civilization could easily have enough energy content to be detectable from any part of the galaxy of which it is part. A signal from a Level-Ill civilization could easily have enough energy content to be detectable anywhere in the Universe.
We might dismiss this at once by saying that we detect no signals anywhere but, in the first place, we are not really listening. In the second place, even if the signals forced themselves upon our consciousness, would we recognize them for what they are?
In 1963, for instance, the Dutch-American astronomer Maarten Schmidt (1929–) discovered quasars, extraordinarily bright and distant objects that show irregular variations in brightness. In 1968, the British astronomer Anthony Hewish (1924–) announced the discovery of pulsars, which send out regular pulses of radiation at very short but very slowly lengthening intervals. Beginning in 1971, certain intense x-ray streams that varied irregularly in intensity were ascribed to black holes.
Could it be that these objects represent the signal beacons of Level-II or Level-III civilizations? To be sure, the variations in intensity seem to be quite irregular in the case of quasars and black holes, and quite regular in the case of pulsars, and in either case don’t seem to have the kind of information that would be of intelligent origin—but may that be merely the result of our own inadequate understanding?
Perhaps! From the conservative position of this book, however, it is an extremely unlikely perhaps. We can only say that thus far there is no large-scale phenomenon in the Universe, involving the kind of energy output characteristic in intensity of stars or galaxies, where there is any evidence whatever of intelligent information content. Until such evidence arrives, we must delay a decision.
Of course, a signal might not be a deliberate beacon but the entirely involuntary accompaniment of a civilization’s activities. We are illuminating our cities and highways only for the convenience and safety of human beings, but it turns out to be a signal to any extraterrestrial civilizations that are close enough and attentive enough to note it.
If the Martian canals really existed, they would do so only to supply the Martian civilization with badly needed water for irrigation—but their existence would have signaled us.
In the same