Encountering Life in the Universe: Ethical Foundations and Social Implications of Astrobiology

4. Beyond Horatio’s Philosophy: Biological Evolution and the “Plurality of Worlds” Concept - Martinez J. Hewlett

80 chapter four Beyond Horatio’s Philosophy Biological Evolution and the “Plurality of Worlds” Concept Martinez J. Hewlett Department of Molecular and Cellular Biology, University of Arizona and Dominican School of Philosophy and Theology, Graduate Theological Union There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy. Shakespeare, Hamlet, act 1, scene 5 The discourse in the Western world on the possibilities of life on other worlds is as ancient as the philosophical tradition itself. Even to the present day the latest missions to Mars, aimed at the discovery of water and molecular evidence for the possibilities of life, excite the popular imagination at the same time that they challenge our notion of self and our place within the cosmos. Hamlet’s words to Horatio, after his first encounter with the ghost of his dead father, the king, ring true for us in preparation for our initial, and perhaps inevitable, encounter with the other. The Ancient and Medieval Arguments But just what is our philosophical preparation for this? Within the Western tradition the idea of worlds other than our own goes back at least to Greek intellectual reflection. In that setting, it was the atomists, led by Beyond Horatio’s Philosophy · 81 Democritus and Leucippus, who held that other worlds were not just possible but, in fact, inevitable. If, they maintained, the Universe is infinite, and if everything within it is made up of the same material particles as our own world, then it must be that other such worlds exist (Ruse 2001). Although what the atomists meant by “matter” was very different from our current scientific interpretation of that word, their position with respect to the existence of other worlds is in many ways echoed by our modern enthusiasts who search for signs of life. I would argue that this philosophical stance of inevitability is implicit in the Search for Extraterrestrial Intelligence (SETI) Project. Countering the atomists on this topic was the Athenian school founded by Socrates and continued by his two disciples Plato and Aristotle. While differing in their approach to understanding the observable world, they were united in their rejection of the possibility of other worlds. There were two objections. First, both Plato and Aristotle argued that the Creator of all that can be observed is unique and therefore there can be only one such creation. Other worlds, in this case, would represent other creations, which would not be possible. A second objection involved an understanding of physics and the structure of the cosmos as Aristotle conceived them to be (Aristotle 1952). In his treatise De Caelo (On the Heavens) Aristotle makes the case for a Universe with the Earth at the center and the heavenly bodies circling in ever-increasing spheres. The elements that make up the Earth were fire, air, water, and earth, whereas the heavens consisted of the ether or quintessence , the “fifth element.” Given this geocentric view, Aristotle concluded that bodies like our own and the things around us had a “natural place.” Rocks, for instance, fell to the ground when dropped. How could it be that rocks existed elsewhere in the cosmos, when their natural tendency would be to fall to the Earth? Therefore, other worlds that would necessarily consist of the same four elements could not exist beyond the Earth (Aristotle 1952). The Platonic tradition and subsequently the Aristotelian approach became the basis for the intellectual life of Christian scholars in the West. St. Augustine used Platonic idealism to formulate his support for Christian dogma. St. Thomas Aquinas incorporated the newly reencountered philosophical methodology of Aristotle to understand the nature of creation and humans in a Christian philosophical and theological context. Throughout this period of Western history the cosmological model did not change. For both Aquinas and Aristotle, the geocentric concept worked. It must be emphasized that this model did not incorporate our modern 82 · Encountering Life in the Universe understanding of the nature of the Moon, the planets, and the stars. In fact, for both of these philosophers the Earth itself consisted of the corruptible four elements—fire, air, earth, and water. Everything else, the stars and planets, existed in the realm of the incorruptible fifth element, the quintessence. When Aquinas questioned the possibility of extraterrestrial life, he did so within the framework of this Aristotelian worldview. Given that there is only one Universe, if other worlds did, in fact, exist, they...