Extraterrestrial Civilizations - Isaac Asimov [128]
The Austrian astronomer Joseph Johann von Littrow (1781–1840) suggested instead that canals be dug, and that kerosene arranged in mathematical forms be floated on the water and set on fire at night. Again, mathematical symbols would be seen from other worlds.
The French inventor Charles Cros (1842–1888) suggested something more flexible—a vast mirror that could be used to reflect light toward Mars. It could then be so manipulated as to send the equivalent of Morse code and actual messages could, in this way, be sent (though they might not necessarily be interpreted, of course).
Interest in establishing communication with extraterrestrial civilizations mounted to the point where, in 1900, a prize of 100,000 francs was offered in Paris to the first person to carry through this task successfully. Communication with Mars was excluded, however. That was thought to be too easy a feat to be worth the money.
All such nineteenth-century suggestions are useless, of course, since there are no intelligent beings on the Moon, Venus, or Mars, and it is doubtful whether the unsophisticated techniques suggested could reach farther (if, indeed, that far).
Besides, in the twentieth century we have, ironically enough, sent out even more spectacular messages with no special effort on our part.
The invention of the electric light and the gradually increasing illumination of our cities and highways has steadily intensified the glitter of Earth’s surface at night, at least over the land areas that are industrialized and urbanized. Astronomers on Mars, puzzling over the light emerging in steadily increasing intensity from Earth’s dark side would be sure to come to the conclusion that a civilization existed on Earth—if there were astronomers on Mars.
The nineteenth-century suggestions made use of light, since that was the most easily manipulable radiation known to cross the vacuum of space at that time. Around the turn of the century, however, radio waves were discovered (like light waves, but a million times longer) and put to use. By 1900, the Yugoslavian-American inventor Nikola Tesla (1856–1943) was already suggesting that radio waves be used to send messages to other worlds.
No deliberate attempt of the kind was made, but it didn’t have to be. With the passing decades radio waves were generated by human beings with ever increasing intensity. Those that could penetrate the upper layers of Earth’s atmosphere did so, and as a result there is a sphere of radio-wave radiation swelling out from Earth in every direction.
Again, astronomers on Mars, if they were aware of this radiation and if they noted that it was growing steadily stronger, would be forced to come to the conclusion that there was a civilization on Earth.
By the second half of the twentieth century, however, it was quite clear that extraterrestrial civilizations did not exist in the Solar system and that if we were to send messages it would have to be to the stars.
This introduced formidable complications. In the Solar system, we at least know where we might aim our messages—at Mars, at Venus, and so on. There is, on the other hand, no way of knowing which star it would be best to aim at.
Furthermore, radiation aimed at the stars would have to be very energetic if it were to maintain sufficient intensity, in view of inevitable dispersion over the light-years, for it to be picked up at even the distance of the nearest stars.
We are, as I have already said, sending out radio-wave radiation to the stars quite involuntarily. The radio waves that have leaked through the upper layers of our atmosphere have expanded now into a vast ball dozens of light-years in diameter. The outer fringes have passed by many stars already, and although the intensity is excessively minute, it could conceivably be picked up.
However, signals so excessively weak might not seem to the distant astronomers to be incontrovertible proof of a civilization existing somewhere in the neighborhood of our Sun. Even if the astronomers