BRUNO, GIORDANO

(b. Nola, Italy, 1548; d. Rome, Italy, 17 February 1600), philosophy, physics, cosmology. For the original article on Bruno see DSB, vol. 2.

Bruno was slow to gain recognition for his scientific contributions for two reasons. First, he was condemned to the stake for his heretical theological views, and this led to efforts to expunge all traces of his works from public memory (damnatio memoriae). Hence, his works tended to be forgotten. Second, his conception of Nature was not mechanistic. He even took an interest in natural magic as a way to understand Nature. These aspects of his thinking have led historians of science, who tend to view the development of science as the development of mechanistic philosophy, to consider Bruno as more philosopher and magus than scientist. Yet between 1584 and 1588–1591, Bruno was the first to propose a scientific theory of the relativity of motion, spatial lengths, and time intervals.

An Infinite Universe. Bruno assented to the Copernican world system, but he went beyond it. He eliminated all the celestial spheres, to which celestial bodies were considered bound. He gave a physical basis to the new astronomical system: His alternative to Aristotelian physics was the medieval theory of impetus. To this theory he added a

dynamic atomism. Atoms, or monads, are not purely material and inert, but have power and form, as Democritus asserted. The vacuum is not empty but full of ether.

Since the thirteenth century the Church had condemned many points of Aristotelian physics, and a Christian natural philosophy of a sort had tentatively been constructed. Christian theology progressively deconstructed Aristotelian physics and cosmology by arguing from the standpoint of God’s absolute power (de potentia Dei absoluta). According to Bruno, the power of God’s love is actually infinite, and so the creation must be actually infinite, that is, made of living worlds and atoms, full of powers, without limit. Atomism and Christian theology thus led Bruno to conceive of the universe as infinite.

After the Reform had destroyed the univocal Catholic interpretation of the Bible, Bruno argued that the Bible gives people only ethical indications and no scientific truth about the universe. Bruno also had scientific reasons for holding that the universe is infinite. These include his atomistic physics and cosmology, and Tycho Brahe’s new astronomical observations of comets. Bruno himself argued that the stars only seem fixed because of their distance from people on Earth, and hence that the fixity of the stars cannot be used to show that the universe is finite. He also argued that mathematical abstractions can never correspond to physical measures and to physical reality. He thus countered mathematical arguments for a finite universe.

Relativity of Motion. According to Bruno, the motions of celestial bodies are not really circular, but rather are completely free in infinite ethereal space. Each body has a dynamic consistency, determined by that body’s own impetus, and is in motion in infinite space, as there are no bodies at rest. Moreover, there is no mathematical or physical center to the universe. Because no body is at rest, it is impossible to give an absolute measure of motion. Consequently, all motions are relative.

In The Ash Wednesday Supper (La cena de le ceneri, 1584, dialogue 3), Bruno sought to prove the Copernican system by arguing for the relativity of motion on a ship, an example already used in a simpler form by Jean Buridan, Nicole d’Oresme, Nicholas of Cusa, and Galileo Galilei. The relativity of motion considered by Bruno was based on the idea that everything belonging to a system participates in the motion of the system in such a way that any motion (uniform or nonuniform, rectilinear or curvilinear) without rotation does not modify any phenomenon. One cannot feel the Earth revolving around the Sun, because this motion does not affect phenomena. Rotations make a difference, but they are intrinsically relative motions among the different parts of the body. Bruno also argued that gravity is relative, giving a sort of principle of dynamic general relativity.

Galileo, in his Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican (Dialogo sopra i due massimi sistemi del mondo, 1632), repeated some of Bruno’s arguments, but he never quoted him because Bruno was condemned by the Inquisition. Hence, people must attribute the principle of the relativity of motion to Bruno, not Galileo.

Relativity of Time and Space . The relativity of time follows from an infinite universe, as Bruno discussed in The Abruptly Ended Discourse in the College of France(Camoeracensis Acrotismus1588, XXXVIII) and The Immense Universe, the Numberless and Figureless Worlds(De innumerabilibus, immenso et infigurabili1591, VII.7). According to Aristotelian and medieval definitions, time is physically and cosmically given by the motion of the eighth sphere of fixed stars, because this motion is perfectly uniform, continuous, and simple, as required by a definition of time. If the universe is infinite, there are no spheres at all, and hence there is no privileged, perfectly uniform, continuous motion for the definition of time. The universe contains infinite motions, any one of which could be used for the definition of time. Since motion is used to measure time intervals, different motions define different, nonhomogeneous proper times. Motion affects time. Thus, the relativity of motion implies the relativity of time.

The relativity of space is already implicit in the notion that space is infinite and lacks a center, but for Bruno, spatial lengths and distances are also relative. He argued for this position in Camoeracensis Acrotismus(1588, XXVII, XXXII, XXXIV, XXXV, XXXVII), De innumerabilibus, immenso et infigurabili(1591, IV.6), and The Threefold Minimum and the Measure(De triplici minimo et mensura1591, II.5). Bruno started from a radical epistemological critique of measurability: motion affects, and places limits on, exact measurements. Measurements of space under different conditions of motion imply different spatial lengths. Hence, lengths are relative.

Galileo followed only Bruno’s idea that motion is relative, and only when motion is limited to uniform motion and relativity is considered as kinematic relativity, and not as dynamic relativity. Bruno’s general dynamic relativity was followed only by Gottfried Wilhelm Leibniz. In different perspectives, Bruno’s dynamic relativity was reconsidered, through Leibniz’s influence, by Henri Poincaré in his special relativistic dynamics and, through the influence of Poincaré, Benedict de Spinoza, and Ernst Mach, by Albert Einstein in his theory of general relativity.

SUPPLEMENTARY BIBLIOGRAPHY

Italy’s Instituto Nazionale di Studi sul Rinascimento has devoted a Web site to Giordano Bruno, available from http://giordanobruno.signum.sns.it/ that includes a bibliography of Bruno’s work. A complete archive of Bruno’s texts in Latin and in the vernacular, including indexes, is also available from this site, at http://giordanobruno.signum.sns.it/bibliotecaideale/.

Giannetto, Enrico R. A. “La relatività del moto e del tempo in Giordano Bruno.” Physis 38 (2001): 305–336.

——. “Giordano Bruno and the Origins of Relativity.” In Albert Einstein, Chief Engineer of the Universe: One Hundred Authors for Einstein, edited by J. Renn. New York: Wiley, 2005.

Enrico R. A. Giannetto