Gort, Klaatu berada nikto.

(The Day the Earth Stood Still, Warner Brothers, 1951)



This chapter examines proposals for communication with extraterrestrial intelligence (ETI). Some of the ancient cosmologies, such as the Aristotelian model of the universe, are described by way of an introduction to the post-Copernican vision of a universe populated with many worlds similar to our own. Nevertheless, it will be argued that pre-Copernican beliefs regarding the centrality of the Earth in the cosmos and analogies with terrestrial conditions have survived in modern astronomy. Early in the twentieth century, beliefs in the existence of Martians drew heavily on scientific and political analogies with life on Earth. Modern radio searches, which offer the first empirical solution to the search for ETI, are nevertheless dependent upon analogies with technological developments during the past century on Earth. This chapter ends with some brief speculations regarding the effects of contact with ETI and the possibility of a galactic network of communicating beings.


Ancient cosmology and the Copernican revolution

The desire to make sense of the cosmos and understand our place in it is as old as human history. From earliest times people have speculated on the nature of the universe and have gazed upon and wondered at the night sky. Out of this wonderment emerged the earliest cosmologies and beliefs about the origins of earthly life and the possibility of extraterrestrial life. The ancient cosmologies, however, had one feature in common; they were fashioned on terrestrial concerns. Thus the heavens were perceived of as an enclosure for the Earth, and were peopled with beings who were not fundamentally distinct from those found on Earth. Indeed, the Gods and other extraterrestrial beings were frequently portrayed in various forms of intercourse with the inhabitants of Earth. The













Egyptians, for example, depicted a heaven consisting of platters surrounded by water, ultimately supported by a God. This perception was a reasonable reflection of the Nile environment. And just as human nobles and kings rode in horse-drawn chariots so too did the various Gods make their way across the night sky in heavenly chariots.

One of the influential Greek cosmologists was Anaximander of Miletos, who depicted the stars as portions of air in the shape of  rotating wheels filled with fire. The Sun was a chariot wheel 28 times the size of the Earth, and was also made of fire. This indicated an advance over the Egyptians, as Anaximander described heavenly bodies as natural mechanisms, rather than Gods. From the fourth century BC the Greeks saw the Earth as a tiny sphere suspended stationary at the geometric centre of a larger rotating sphere which carried the stars. Beyond that – nothing, no space, no matter. In fact, this is the view that the modern world inherited from the ancient world. Thomas Kuhn (1957: 27) described it as ‘the two-sphere model of the universe’. This  framework of thought found expression in the idea of an interior sphere for human beings and Earth-life, and an external sphere for the stars and heavenly forms of (after) life. It was a model which was to survive, with variation, for about 2,000 years. It was supported by observations of the ‘domed’ heavens of the Egyptians and Greeks, and by aesthetic opinion related to the apparent uniform rate of motion of  the stars. Plato’s Timaeus is a classical portrayal of the two-sphere model which is based on an appeal to aesthetic and religious grounds.

Appeals to conceptual economy also lent support to the two-sphere model. The heavens are not displayed in a random pattern, but reveal an order which can be comprehended. The most favoured model of the universe was of a gigantic sphere, bearing the stars, rotating westwards on a fixed axis every 23 hours and 56 minutes, with the Sun moving steadily eastwards around the elliptic once every 365 and a quarter days. With this model one can organize observations of the heavens, apply them to the practical art of navigation, and employ them for astrological predictions. It might be noted that astrology, which depicts human destiny in terms of the positions of the stars, would naturally favour a two-sphere model of the universe.

The foremost exponent of the two-sphere model was Aristotle, who held that the cosmos was closed and finite, and consisted of a series of revolving spheres with an immobile Earth at the centre. The natural motion of heavenly bodies, he held, was circular and the celestial spheres circled the Earth while  the Sun, Moon and planets moved in complex circles within these spheres. About 150 AD Aristotle’s cosmology was developed by Claudius Ptolemy who constructed an astronomical table, the Almagest, which provided a means of predicting the positions of the planets. The Almagest was also employed for practical purposes such as navigation, the prediction of eclipses  and  dates of the equinoxes.

Despite numerous modifications, the Aristotelian model of the universe remained dominant until well into the sixteenth century and was supported by




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