astrology, astronomy, theology and common-sense experience. Unfortunately the Algmagest never provided a wholly satisfactory method of predicting planetary motion and as improvements to observational techniques were made, these inaccuracies provided increasing problems for Ptolemaic astronomy. During the first decade of the sixteenth century Nicolaus Copernicus, a distinguished mathe-matician and astronomer, attempted to revise Ptolemy’s Almagest, but he came to the conclusion that the Sun had to be located at the centre of the cosmos, and that the Earth, Moon and the planets all circle the Sun. The implications of this revision were enormous: the Earth no longer occupied the central position in the universe and was no longer held to be immobile. Furthermore, as merely one more planet in motion around the Sun, the Earth no longer occupied a unique and privileged position in the cosmos.
Today we speak of the Copernican revolution, but it must be emphasized that this is not how it appeared to Copernicus himself. Copernicus had been educated in the scholastic tradition and sought to show how his theory was supported by ancient authorities. Thus his De Revolutionibus was not so much a revolutionary text as a revolution-making text. For in the hands of his successors Ptolemaic astronomy and the Aristotelian cosmology were overturned. Moreover, Copernicus did not resolve all the anomalies of Ptolemaic astronomy, but he did convince Galileo and others that a Sun-centred astronomy was the direction to follow.
The post-Copernican cosmology took away most of the Aristotelian theories of interplanetary matter and motion. A new generation of astronomers and cosmologists went on to reject the two-sphere model, introduce the notion of infinite space, and even dreamt of worlds beyond our solar system and the possibility of extraterrestrial life. After Copernicus published his Sun-centred account of the planetary system, others were led into speculations regarding extraterrestrial life. With the aid of his telescope Galileo not only demolished the idea of an Earth-centred universe, but gave credibility to questions concerning the very uniqueness of Earth as an abode of life.
Attempts to establish contact with extraterrestrial intelligence have a long history. People have always believed in extraterrestrial beings; they called them Gods and named the stars and planets after them. In fact, the majority of pluralist theories have been associated with religious and mystical beliefs. In scientific terms, most of the early pluralist theories did not have ‘good reasons’ to support them. The process of bestowing scientific credibility on pluralistic theories of life in the universe nevertheless matured slowly with Copernicanism. However, the pre-Copernican belief that the Earth was the centre of creation survived in a religious and psychological sense long after the sixteenth century, and terrestrial interests continued to dominate speculation about other forms of life. Terrestrial analogies were employed in early telescopic observations of the Moon and Mars,
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which led to the naming of oceans and seas, thus influencing the expectation of other similarities. Most efforts to establish contact have revealed assumptions that ETI, should it exist, would be essentially similar to human intelligence, but perhaps a little more advanced. This chapter provides a brief survey of beliefs in ETI and of attempts to establish contact with our galactic neighbours.
The search for intelligent life in the universe
If extraterrestrial life is detected by one of the space probes or radio searches, then ours may be the last generation to think of itself as alone in the universe. If this is the case, then our successors will have a yardstick to ridicule us with, just as we now ridicule those who insisted that the Earth was flat. Speculation concerning extraterrestrial life is as old as philosophy itself. Aristotle maintained that the Moon was inhabited and, despite the collapse of the Aristotelian world-view in the sixteenth and seventeenth centuries, many supporters of the Copernican revolution were to revise Aristotle’s pluralism. When Galileo expressed puzzlement over the lunar cavities which he had detected with his telescope, Kepler offered the explanation that they were formed by intelligent inhabitants who had made their homes in caves. The power of terrestrial analogies influenced early telescopic observations by Galileo’s contemporaries. Kepler and others saw evidence of water, clouds and rain in the dark patches on the Moon. Thus Kepler, in what might be seen as the first work of science fiction, wrote of lunar inhabitants:
[who] have no fixed abode, no established domicile. In the course of one of their days, they roam in crowds over their whole sphere, each according to his own nature: some use their legs, which far surpass those of our camels; some resort to wings; and some follow the receding water in boats; or if a delay of several more days is necessary, then they crawl into caves.
(1967: 27)
The Copernican revolution, which eroded belief in the uniqueness of Earth, fostered a range of pluralist speculations which were partly responsible for the Church’s hostility to Galileo. The pluralist beliefs of Giordano Bruno played an important part – perhaps not as decisive as nineteenth-century historians held – in his burning by the Inquisition on 16 February 1600. Among the problems which worried the Church was the suggestion that the human race might not have descended from Adam, and whether Christ would have to be crucified many times in many worlds.
In his comprehensive survey of the debate on pluralism, Michael J. Crowe (1988) introduces the young Kant as one of the forerunners of SETI. In 1755 Kant published his Universal Natural History and Theory of the Heavens in which he assessed the intelligence of beings throughout the universe. According to Kant, the cosmos was characterized by chaos at the centre and increasing order towards the remoter regions, such that ‘the most perfect classes of rational beings
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