Extraterrestrial Civilizations - Isaac Asimov [41]
In the days when philosophers assumed all worlds were inhabited and when general statements to that effect were made, it is not clear whether any particular philosopher truly understood the nature of stars.
Perhaps the first clear statement of the modern view was that of Nicholas of Cusa (1401–1464), a cardinal of the Church, who had particularly striking ideas for his time. He thought that space was infinite and that there was no center to the Universe. He thought all things moved, including the Earth. He also thought the stars were distant Suns, that they were attended by planets as the Sun was, and that those planets were inhabited.
Interesting, but we of the contemporary world are less sanguine concerning habitability, and cannot accept in carefree fashion the notion of life everywhere. We know there are dead worlds, and we know that there are others, which while possibly not dead, are not likely to bear more than simple bacteria life forms of life. Why may there not be stars around which only dead worlds orbit? Or around which no worlds circle at all?
If it should turn out that habitability is associated with only a small percentage of the stars (as life seems to be associated with only a small percentage of the worlds of the Solar system), then it becomes important to determine whether there are stars other than those we happen to be able to see and if so, how many. After all, the greater the number of stars, the greater the chance of numerous life forms existing in space even if the chances for any one star are very low.
The natural assumption, of course, is that only those stars exist that can be seen. To be sure, some stars are so dim that excellent eyes can just barely make them out. Might it not seem natural to suppose that there are some that are fainter still and cannot be made out by even the best eyes?
Apparently, this seemed to occur to very few. Perhaps there was the unspoken feeling that God wouldn’t create something too dim to be seen, since what purpose could such an object serve? To suppose that everything in the sky was there only because it affected human beings (the basis of astrological beliefs) seemed to argue against invisible bodies.
The English mathematician Thomas Digges (1543–1595) did espouse views like those of Nicholas of Cusa and in 1575 maintained not only infinite space, but an infinite number of stars spread evenly throughout it. Italian philosopher Giordano Bruno (1548–1600) also argued the same views, and did so in so undiplomatic and contentious a manner that he was finally burned at the stake in Rome for his heresies.
The argument over the matter ended in 1609, however, thanks to Galileo and his telescope. When Galileo turned his telescope on the sky, he immediately discovered that he saw more stars with his instrument than without it. Wherever he looked, he saw stars that could not be seen otherwise.
Without a telescope one saw six stars in the tiny little star group called the Pleiades. There were legends of a seventh that had dimmed and grown invisible. Galileo not only saw this seventh star easily once he clapped his telescope to his eyes, he saw thirty more stars in addition.
Even more important was what happened when he looked through his telescope at the Milky Way.
The Milky Way is a faint, luminous fog that seems to form a belt around the sky. In some ancient myths, it was pictured as a bridge connecting heaven and Earth. To the Greeks it was sometimes seen as a spray of milk from the divine breast of the goddess Hera. A more materialistic way of looking at the Milky Way, prior to the invention of the telescope, was to suppose it was a belt of unformed star matter.
When Galileo looked at the Milky Way, however, he saw it was made up of myriads of very faint stars. For the first time, a true notion of how numerous the stars actually were broke in on the consciousness of human beings. If God had granted Abraham telescopic vision, the assurance