Sixteen hundred was a year of jubilee. By February the broad streets of Rome were teeming with pilgrims from all over Europe; cardinals and parish priests, merchants and beggars, great noblemen and poor students mingled in the crowded squares and avenues of the Eternal City. Those few among the multitude who could read may have noticed a report in the primitive little Roman newspaper, the Avvisi, relating to "a Dominican monk of Nola, an obstinate heretic, who on Wednesday, at the palace of Cardinal Madruccio was shown to be the author of diverse horrid opinions in which he remained obstinate and still does despite theologians visiting him daily." Five days after this notice appeared, the Dominican monk, Giordano Bruno, was put to death by the Inquisition. In their mercy, the inquisitors were careful to avoid the shedding of blood. Bruno was burned at the stake.
The jubilee pilgrims scarcely noticed the burning of the Dominican monk. Why should they? During the course of the year the Inquisition rid Christendom of twenty-five heretics. The death of this particular dissenter was forgotten amidst the sacred processions, the chanting of litanies, and the dispensing of blessings.
Giordano Bruno had lived at the wrong time. His death occurred in the last twilight of the Italian Renaissance. A century earlier, a more tolerant church had spared and even admired great imaginative thinkers like this Dominican monk. A century later, his thought would have been more intelligible to European intellectuals. But in 1600 Christianity was drained of its earlier humanism, the great artistic masterpieces of the southern Renaissance were no longer being created, the Protestant Reformation was nearly a century old, and the Inquisition was in full force.
In this age of intolerance, the various sects and churches of Europe were persecuting one another relentlessly, and only the very rash or the very courageous dared to dissent from the prevailing religious opinions of their locality. Members of every church tended to make the same error — that since Christ was the central figure in history, then our own earth, the scene of Christ's death and resurrection, ought to be the central point in the universe. As a result, churchmen often persecuted scholars who did not, at least publicly, hold to the teachings of the great pagan philosopher Aristotle.
The Dominican monk whose "horrid opinions" caused him to be burned occupies an extremely important place in the history of astronomy. He was no astronomer himself, nor even a scientist in the formal sense. He was an itinerant philosopher, born in southern Italy, who spent most of his life wandering over the face of Europe. He studied and taught for several years in England, but spent the last seven years of his life in Rome — in an ecclesiastical prison. Born five years after the death of Copernicus, Bruno died ten years before the publication of Sidereus Nuncius in which Galileo reported his first telescopic discoveries, yet in a sense this wandering Dominican had greater vision than either Copernicus or Galileo.
To comprehend the achievements of Giordano Bruno, the state of astronomical knowledge in the sixteenth century must be understood. Up to the time of Copernicus, western Europe had accepted the Ptolemaic universe. The earth was the central ball around which seven transparent spheres glided, carrying the moon, the sun, and the five naked-eye planets. An eighth sphere carried the fixed stars. It would be fruitless to dwell on the picturesque medieval elaborations on this system in which other spheres were added, presumably as the dwelling places of various ranks of angels and archangels. Essentially, the Ptolemaic universe was a closed system with the earth at the center and the stars as fixed points of light on a huge sphere. The earth was motionless; day and night were caused by the revolution of the heavens. All orbits were circles, since according to Aristotle the circle is the perfect figure. Aristotle had also taught that the earth was corruptible, while the regions beyond the sphere of the moon were perfect and therefore unchanging.
The Copernican revolution, as everybody knows, placed the sun in the center of the universe instead of the earth. Day and night were explained by the rotation of the earth rather than the heavens. If one accepted the Copernican universe, the old belief of earthly corruptibility and heavenly incorruptibility would vanish, and the modern notion of a universe essentially similar throughout would appear in its place.
In spite of these remarkable insights, Copernicus was less emancipated from the medieval universe than most people imagine. His planetary orbits were still circles and so they remained until the time of Kepler. But most important of all, Copernicus retained the outer sphere of fixed stars and simply rearranged the order of the planets and the sun inside this great sphere. Copernicus retained the closed system — the bandbox universe of his predecessors — and as a result his sun-centered or heliocentric system has little more in common with the universe of the twentieth century astronomer than the geocentric structure of Ptolemy. It was not Copernicus or Galileo but Giordano Bruno who grasped the great truth that the so-called fixed stars were actually huge suns like our own. Bruno conceived of a universe extending outward infinitely, containing suns without end, each, perhaps, racing through space with its own family of planets; Bruno's cosmos was a bold concept indeed, when compared with the stiffing, enclosed systems of Ptolemy and Copernicus.
By the late sixteenth century, several rather clever arguments had been devised to disprove the heliocentric system. If the earth were moving, it was argued, then an object dropped from a high tower would not fall straight down, a cannon ball fired along a north-south line would deviate from its course. The earth, presumably, would have moved out from under these objects as it raced around the sun. If, as Bruno had declared, the stars were at various distances from us, there was the objection that the alleged motion of the earth around the sun would cause the nearer fixed stars to appear displaced with respect to the more distant ones. No such displacement, of course, was observed. Today, astronomers are able to measure just such displacement in the positions of the nearer stars, but the observation of this stellar parallax, as it is now called, was hopelessly beyond the capabilities of the crude astronomical instruments of the sixteenth century. Bruno resolved the problem correctly. He asserted that the stars were so far away that their apparent displacement due to the earth's revolution about the sun could not be detected.
Copernicus grasped the fact that the earth was a planet, but by placing the sun in the center of a closed system, he made the sun unique. Bruno tore down the outer boundaries of the old system and envisioned something remarkably similar to the modern universe. For him, space was boundless, and was filled with countless solar systems: "There are innumerable suns and an infinite number of planets which circle around their suns as our seven planets circle around our Sun." We do not see planets revolving about other stars "because of their great distance or small mass . . ."
Bruno's universe had no center. "In the Universe," he wrote, "no center and no circumference exist, but the center is everywhere . . ." Elaborating upon this point he remarked:
As to us on Earth, the Earth seems to be the center of the Universe, so to inhabitants of the Moon, the Moon will appear as such ... Each world has its center, each its up and down; these differences are to be assigned relatively . . .
To the modern mind, immersed as it is in relativism, such statements as these seem rather obvious. But with Bruno, relativism begins. The Dominican monk was on fire with a great vision of worlds without end in a universe which extended outward forever. With this vision Bruno had wandered the highways of Europe, lecturing and arguing in the courts and universities of many countries.
Just as the universe is composed of an infinity of stars, argued Bruno, so the stars themselves and, indeed, all matter must be composed of innumerable atoms. This atomic theory was not worked out with any precision by Bruno, nor was it entirely original. The ancient philosopher Democritus had suggested a similar theory. But in Bruno's time the theory was unheard of and his endorsement of it marked a distinct departure from the traditions of the sixteenth century.
Giordano Bruno's conception of the Universe
It is chiefly the visionary aspect of Bruno's thought which separates it from modern astronomical knowledge. The astronomical universe of today is built upon incredible amounts of painstaking research, endless observation, and rigorous mathematical analysis. Bruno built his cosmos without the aid of telescopic observation; he even lacked precise naked-eye observations such as those which his contemporary, Tycho Brahe, was then in the process of making. Bruno knew little mathematics and used none in his cosmology. Rather, he depended upon logical and metaphysical arguments. If the universe is finite, what lies beyond the outermost edge of it? Suppose a man stood on the boundary of the universe and shot an arrow outward. Would the universe expand with the arrow or would the arrow leave the universe?
These arguments fortified Bruno's daring and perceptive insights into reality. He was able to cast aside old and useless theories and to grasp actuality in a flash. He saw that much more was implicit in the heliocentric system than Copernicus had realized. If the earth moves, why not the sun, itself? If the earth is not in the center of space, why should the sun be? Indeed, space has no center. The sun, if far enough away, would resemble a star, and the so-called fixed stars, themselves great blazing suns, are hurtling through infinite space too distant for their motion to be detected.
Bruno did not attempt to improve upon Copernicus' description of the solar system itself. He grasped the system's essential simplicity and its superiority to the old geocentric scheme. Indeed, Bruno did a great deal toward spreading Copernican ideas throughout Europe. If he did away with the outer sphere of stars, Bruno retained the idea of circular planet orbits just as Copernicus had done. But, in the absence of exact observational data with which to check the circular orbit hypothesis, there was little else Bruno could have done. When Kepler advanced his theory of elliptical orbits, he was able to base his conclusions upon the painstaking planetary observations of his predecessor, Tycho Brahe. Yet it is doubtful that, even with data as precise as that collected by Tycho, Bruno could have produced general laws of planetary motion such as those of Kepler; Bruno, with his mind seeking to grasp infinity, had neither the mathematical knowledge nor the patience to do such work.
It has been justly observed that Aristarchus of Samos and others developed the heliocentric theory nearly 2,000 years before Copernicus. Bruno also had his precursors. The great Roman scientist, Lucretius, propounded the concept of an infinite universe, but he had no notion that the stars were suns. Generally speaking, the medieval scholars believed that only God could be infinite, although the fifteenth century philosopher, Nicholas of Cusa, tried to reconcile an infinite God with an infinite universe. While God, alone, is "positively" infinite, explained Nicholas, the universe is "relatively" or "privately" infinite. Having thus clarified the matter, Nicholas returned to his metaphysics. In 1576, the English astronomer, Thomas Digges, a contemporary of Bruno, wrote of "that fixed orbe garnished with lightes innumerable and reaching up in Sphericall altitude without ende" (his italics). But even in the infinite universe of Thomas Digges, the "lightes innumerable" were not suns.
Although Bruno was no scientist, he was among the first to urge the greater use of experimental method. He had the insight and imagination to become a champion of the Copernican system at a time when most European scholars scorned it, and he possessed the creative genius to go far beyond Copernicus. It was Bruno, not Copernicus, who introduced to the world the immense universe of modern astronomy with its countless billions of suns shining across space from incredible distances, a universe in which both earth and sun shrink to insignificant size and importance.
For those and other "diverse horrid opinions" Giordano Bruno was burned at the stake in the jubilee year of 1600, nine years before the telescope first was turned toward outer space. So it was that a great prophet of modern cosmology was destroyed by the dying fury of the Middle Ages.
(From Sunrise magazine, March 1975. Reproduced with permission from the Griffith Observer, February 1975)