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Start Giordano Bruno: the Philosopher of Astronomy
23 July 2015

Giordano Bruno: the Philosopher of Astronomy

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Being consistent has always been difficult. Caught up in the vortex of today’s accelerated world, it appears almost impossible. However, there are major historical examples of consistency that have allowed new scientific paradigms to become consolidated.

In the Valhalla of the heroes of science a special place is reserved for Giordano Bruno (9 February 1548 – 17 February 1600). He is a man we could call “martyr”, as he paid with his life for the daring with which he interpreted reality, opposing a coercive and, ultimately, violent orthodoxy. Among his most famous sayings are the following on the possibility of worlds outside the Solar System, in the work “De L’Infinito Universo E Mondi” of 1584:

And this space is what we call the infinite, because there is no reason, capacity, possibility, sense or nature that must limit it. There are infinite worlds similar to this one and no different from it in its type, because there is no reason or defect of natural capacity (I am referring both to passive and active power) by which, just as they exist in this space that surrounds us, they should not equally exist in the other space that by its nature is no different or diverse from this.“[1], Giordano Bruno (Fifth Dialogue).

There are therefore innumerable suns; there are infinite earths that equally revolve around these suns, in the same way as we see these seven (planets) revolve around this sun that is close to us.”[2]. Giordano Bruno (Third Dialog).

Since the discovery of the first planets outside the Solar System that orbit around stars like our Sun (Mayor and Queloz, 1995) there has been a veritable explosion of discoveries that have completely changed the existing paradigm of anthropocentric reminiscences. Here we have provided an overall view and have gone into more details in some cases. Exoplanetary ecology has diversified and many diverse niche environments have been found: from giant gaseous planets to others of a similar size to our Moon, in orbits that are very close to the stars or orbiting around binary stars. The search for more and for discovering their characteristics, including the properties of their atmospheres and how they are evolving, continues at the present time. In all of these discoveries the voice of Giordano Bruno still resonates.

Who was Giordano Bruno?

Giordano Bruno lived in the second half of the 16th century, from 1548 to 1600. He was therefore born five years after the publication ofDe revolutionibus, a work in which Nicolaus Copernicus set out his heliocentric theory, and in which for the first time for almost 2,000 years the Earth was displaced from its central position. We know about one experience that marked Bruno at an early age: an excursion to Vesuvius, the imposing volcano that dominates the Bay of Naples. On seeing the horizon change as he climbed, he realized that our senses can trick us, perhaps encouraging him later to adopt neo-platonic positions as a philosophical framework for interpreting reality. In any event, his treaties and the problems he tackled have led him to be called the philosopher of astronomy.

Belonging to the religious Dominican order, his intellectual models were Raimundus Lullus (Ramon Llull) and Thomas Aquinas, who lived in the same monastery where Bruno passed his novice years. Bruno probably never felt at ease in the convent, with its routine and discipline, and it is even possible that he was close or converted to Protestantism at some point in his life.

Unlike Copernicus, who delayed the publication of his theory by nearly 40 years, perhaps fearing the reaction of intellectuals or the Inquisition, Giordano Bruno’s imagination took him where the Pole never dreamed to aspire. Never at ease, he became a pilgrim who would travel around numerous European countries spreading his ideas.

He abandoned Naples, where he was born, for Rome, although he did not remain there for long. In the Protestant countries he realized that he could be an uncomfortable figure, recognizing that intolerance was a sign of the times (Geneva, dominated by Calvin, which he passed through, was a clear example). This intolerance was present even in the lands where religious reform had to a certain extent made speculation easier and where education had been extended to greater segments of the population apart from the elites. After passing through France Bruno took Copernican heliocentrism to England, and took part in a celebrated verbal clash at the University of Oxford in 1584, where he did not achieve any converts to his theological or intellectual positions.

Giordano Bruno returned to Italy after failing in his search for a permanent position in the Germanic states and the protection of one of its princes. What was planned as a temporary stay to print his works, ended with nine years in prison, a trial and the stake.

Always a heterodox, he would end up entering into conflict with the Signoria of Venice, to which he was denounced by the zealous follower Giovanni Mocenigo. Despite his interpretations of the Christian writings, the accusation barely included theology. Among the numerous charges were his theory of the unlimited universe and the infinity of worlds.

Bruno, as Galileo Galilei was to do, recanted in the face of the pressure of the trial. However, he then once more defended his initial positions, even when faced with possibility of torture. As in the case of Galileo in 1616, behind the trial and acting as an examiner of his beliefs was Roberto Belarmino. This Jesuit cardinal would be responsible for the condemnation of the theory of the Earth’s movement around the Sun and the prohibition on Galileo from publicizing it, except as a mathematical hypothesis.

He was transferred to Rome, condemned and turned over to the civil authorities (in other words, his custody was ceded for the process of his execution). He was burned at the stake on February 17 in the last year of the 16th century.

The final confirmation: Galileo and James Bradley

Although he was not strictly speaking a scientist, his vision was truly inspiring and his fame won pan-European recognition. Despite the public execution of Giordano Bruno, Galileo, who was never a hero and doubted at the start of his career whether to expose himself publicly (this is what he wrote to Kepler in one of the few letters he sent him), ended up by promoting the heliocentric theory after making extraordinary discoveries using a telescope for astronomical purposes for the first time starting in 1609. Fortunately for him, although he would be condemned for his intellectual positions and for the theological reinterpretation based on science in a trial riddled with fraud, he avoided the maximum punishment and was confined under house arrest in 1633. In any event, Pandora’s box had already been opened: the scientific revolution had begun.

The movement of the Earth would be demonstrated by James Bradley in 1729 through a phenomenon known as the aberration of light due to the combination of the Earth’s velocity with the finite velocity of light.

In any event, Giordano Bruno was not the first to speculate on this possibility. Since the time of Anaximander of Miletus, an erudite pre-Socratic who lived approximately between the years 610 and 547 B.C.E., there have been many intellectuals who have known how to escape accepted conventions, the explicit anthropomorphism in the interpretation of the cosmos and our position in it.

Whatever the case, Giordano Bruno has remained in the collective memory as an intellectual who was capable of defending his beliefs even while paying the maximum price for them. Without us having to go so far, he is still an example of consistency. And as in many fields, he is a palpable proof that modern discoveries are the direct successors to the humanistic science characteristic of the 15th and 16th centuries, whose attitude toward reality should serve as a model.

David Barrado Navascués

European Space Astronomy Center (ESAC, Madrid)


  1.  In the original Italian: “Cotal spacio lo diciamo infinito, perché non è raggione, convenienza, possibilità, senso o natura che debba finirlo:in esso sono infiniti mondi simili a questo, e non differenti in geno da questo; perché non è raggione né difetto di facultà naturale, dico tanto potenza passiva quanto attiva, per la quale, come in questo spacio circa noi ne sono, medesimamente non ne sieno in tutto l’altro spacio che di natura non è differente ed altro da questo”.
  2. In the original Italian: “Sono dunque soli innumerabili, sono terre infinite, che similmente circuiscono queisoli; come veggiamo questi sette circuire questo sole a noi vicino.
  3. Giordano Bruno, “Dialoghi italiani I, Dialoghi metafisici Nuovamente ristampati con le note di Giovanni Gentile”, Terza edizione a cura di Giovanni Aquilecchia, Sansoni – Firenze, Seconda ristampa 1985. Electronic edition of October 31, 2006.
  5. October 31, 2006. A version in Spanish was published in 1972 by Aguilar: Giordano Bruno, “Sobre el infinito universo y los mundos”, translation from the Italian, introduction and notes by Ángel J. Cappelletti.


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