Bruno was, notoriously, burned to death in the Campo dei Fiori in Rome, after eight years of imprisonment and condemnation by the Roman Inquisition. One of the judges who condemned him was the learned Jesuit, Robert Cardinal Bellarmine, who would later play a prominent role in the Galileo affair (and who is now Saint Robert Bellarmine).
So why should a sixteenth-century heretic be associated with the search for extra-terrestrial life, a search that involves thousands of computers scanning the electromagnetic spectrum for that longed-for (or perhaps dreaded) signal, that suggests we are not alone in the universe?
Bruno, along with Galileo, was one of the first defenders of Copernican cosmology. Indeed he seems to have been the first to note that the anonymous preface to Copernicus’s De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) was not written by Copernius himself. We now know that preface to be written by the Lutheran theologian Andreas Osiander. It offers an instrumentalist interpretation of Copernicus’s cosmology, arguing that his picture of the universe should not be understood as a description of the way it actually is, but as a mere instrument for calculating heavenly movements. Along with Johannes Kepler (1571–1630) and Galileo (1564–1642), Bruno denied that this was Copernicus’s intention and held to a realist interpretation of his cosmological scheme.
But in many respects Bruno went beyond Copernicus. He followed the Roman poet Lucretius (ca. 99–55 BC), as well as some late medieval thinkers, in affirming the existence of a universe that is infinite in extent. While Bruno coupled this with a defence of Copernican cosmology, he realized that such an idea rendered moot debates about the centre of the universe. As Lucretius had already written in his De rerum natura (I,1070), “there can be no centre to that which is boundless” (medium nil esse potest infinita). In his De la causa, principio et uno (Fifth Dialogue), Bruno expresses a similar idea with a paraphrase of the words of Nicholas of Cusa (1401–64). One can affirm with equal truth, he writes, that “the centre of the universe is everywhere, and the circumference nowhere” (il centro de l’universo è per tutto, e che la circonferenza non è in parte alcuna) or that “the circumference is everywhere, but the centre is nowhere” (la circonferenza è per tutto, ma il centro non si trova).
Of more interest to the SETI League is the fact that Bruno believed this infinite universe to be populated by an infinite number of worlds, in the sense of planetary systems orbiting other suns. He claimed that these worlds were inhabited by creatures like, or even superior to, ourselves.
Such ideas sound very modern. But should we regard Bruno as a pioneer of modern science? This idea was vigorously contested by Frances Yates, who in her 1964 book Giordano Bruno and the Hermetic Tradtion, argued that Bruno is better thought of as a Renaissance magus. More recently, Hilary Gatti, in her book Giordano Bruno and Renaissance Science, has tried to reforge a link between Bruno and the new natural philosophy of the sixteenth and seventeenth centuries. But even Gatti is loathe to describe Bruno as a practitioner of the new science. He is merely “a friend and supporter of the new science,” who, while supportive of aspects of that new knowledge, is also “deeply suspicious of some of its outcomes and consequences.”
What’s important to note is that Bruno does not reason in the same manner as, say, Galileo, who in a letter to Fortunio Liceti in 1639 admitted that he could not decide if the universe is infinite or bounded. Bruno has no such hesitations. As Gale Christianson writes (Science Fiction Studies March 1976), Bruno “soared into the metaphysical realm unencumbered by the ballast of scientific thinking.”
In particular, Bruno’s belief in an infinite universe populated by a plurality of worlds is not based on any empirical data. In fact, he believes there could be no empirical evidence for such a claim. As he writes near the beginning of De l’infinito universo, “no corporeal sense can perceive the infinite. None of our senses could be expected to furnish this conclusion; for the infinite cannot be the object of sense-perception” (non è senso che vegga l’infinito, non è senso da cui si richieda questa conchiusione; perché l’infinito non può essere oggetto del senso).
Rather than being based on empirical evidence, Bruno’s conviction is based on a theological principle. It is based on the idea that an infinite creator could not do anything other than create an infinite world. To suggest that God would create a finite universe is to accuse the Creator of being miserly or envious (invidioso), since he would be refusing to share his own goodness (De l’infinito universo First Dialogue). It follows, as Bruno writes, that “we insult the infinite cause when we say that it may be the cause of a finite effect” (infinita causa injuriose finiti dicetur effectus causa) (De immenso et innumerabilibus I, 9).
It is deeply ironical that Bruno, who was put to death by the Church, argued for a revolutionary scientific conclusion on theological grounds
So is Bruno a pioneer of modern science? In some of his conclusions, yes, perhaps he is. But in the manner in which he is reasoning he certainly is not. In fairness to the SETI League, they also recognize this fact. While naming an award after Bruno, they have also posted a critical essay by Richard Pogge, suggesting that Bruno’s thought has little to offer the modern searcher for extra-terrestrial intelligence.
There is, of couse, a lesson to be learned here. Before we describe a thinker as a precursor of some modern ideas, we need to examine, not merely the conclusions at which he arrived, but the ways in which he arrived at them. This may involve styles of reasoning that are far removed from those we would consider scientific.