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Galileo di Vincenzo Bonaiuti de’ Galilei (/ˌɡælɪˈleɪoʊ ˌɡælɪˈleɪiˌ/, Italian: [ɡaliˈlɛːo ɡaliˈlɛi]; Pisa, February 15, 1564 – Arcetri, January 8, 1642) was an Italian physicist, astronomer, philosopher, mathematician, writer and academic, considered the father of modern science. A key figure in the Scientific Revolution for his explicit introduction of the scientific method (also called the “Galilean method” or “experimental method”), his name is associated with major contributions to physics and astronomy. Also of primary importance was his role in the astronomical revolution, with his support for the heliocentric system and the Copernican theory.
The first son of Vincenzo Galilei, musicologist, and Giulia Ammannati, of an illustrious but decayed family, in Florence (where his father had moved to devote himself to trade) he had his first cultural education, mainly humanistic-literary. In 1581, on the advice of his father, he enrolled at the Faculty of Medicine of the University of Pisa, where he had the opportunity to study Aristotelian physics, following the courses of F. Bonamico; in fact, Galilei never showed any particular interest in the study of medicine, which he abandoned definitively in 1585. Previously he had begun the study of mathematics under the guidance of O. Ricci, who initiated him to the reading of the great works of the Greeks, in particular of Archimedes, from whom he derived a practical and instrumental conception of mathematics, typical of all his later thought.
Leaving the university without having obtained any degree, he returned to Florence where he wrote his first works in which he alternated the literary interest with the scientific one. Of 1588 are the two lessons “On the shape, place and size of Dante’s Inferno”, while, in close connection with his studies Archimedean, since 1586 had continued the research of mechanics and had created the hydrostatic balance for determining the specific weight of bodies, in 1586-87 had discovered some theorems on the center of gravity that were published only in 1638.
In 1589, thanks to the help of Guidobaldo Dal Monte, he obtained the chair of mathematics at the University of Pisa with a three-year contract with little remuneration because it was a secondary teaching. While in the classroom he kept to the traditional subjects, privately Galilei continued his researches on the isochronism of the pendulum (whose first intuition he had in 1583, according to tradition, while he was in the Cathedral of Pisa), the experiences on the fall of bodies and, above all, the studies on the problem of motion, also in the light of the theory of impetus that had reached a wide diffusion in Italy thanks to Giambattista Benedetti and Niccolò Tartaglia; The representative document of his positions, still scholastic, is the De motu, which remained unpublished. He did not, however, neglect literary studies, as can be seen from the writings “Considerazioni sul Tasso” and “Postille sull’Ariosto”.
Scientific and philosophical thought
The central nucleus of Galilean research is represented by dynamics, which, as Lagrange said, Galilei “baptized”. Even if Galilei did not explicitly formulate the three laws as they are found in Newton, we owe to him the overcoming of ancient conceptions and the clarification of the basic concepts of dynamics. We must also remember: his studies on magnetism; his investigations on hydrostatics; his researches on the oscillations of the pendulum, which led him to observations on acoustic phenomena, in particular on resonance and musical intervals; his researches on resistance and on the force of machines (among which Galilei included animal bodies), similar but of a different scale, which are at the basis of the study of biological mechanics.
The breadth and depth of the turning point that Galilei’s work contributed so significantly to Western culture was possible because of the methodology he elaborated and the general philosophical attitude that is the most controversial part of his thought. Considered Platonic because of the role of mathematics in his physics, the Aristotelian elements of his thought have also been emphasized, while others have emphasized mainly the methodological aspects to the detriment of a dogmatic philosophical vision.
The fact that Galilei sought points of contact and support for his work in the various philosophical systems known at the time, rather than trying to adapt his work to one or another of these systems, perhaps highlights the priority that Galilei gave to scientific problems over philosophical ones, and thus the priority of the methodological aspect over that of systematic coherence. In this fact lies perhaps the neuralgic point of Galilean investigation. From this point of view, the destruction of Aristotelian physics, the liberation of science from the principle of authority, its liberation from philosophical problems, reproached by Descartes, are configured more as consequences, as points of arrival, than as the driving forces of his thought.
Galilei freed physical research from Aristotelianism, but his anti-Aristotelian position, which goes back to the Pisan period, was determined by the denial of logical deduction as a fundamental criterion of scientific research. An example is the distinction between primary and secondary qualities of substances, according to which the former are “sizes, figures, crowds, and late or fast movements”, to which Galilei attributes a reality that he denies to the latter, namely “colors, tastes, smells, sounds”. This distinction, which Galilei certainly owes to Greek atomism, was of considerable importance for the subsequent development of philosophical thought, but it does not indicate a skeptical attitude on his part; rather, it is due to the measurable character of the primaries and thus to their use in physical research.
Galilei does not give an abstract exposition of his scientific method, but through his works one can follow the process of its formation. His method is not something improvised or uprooted from the tradition, but a synthesis of those reworkings and those elements that characterize a part of the thought of the XV-XVI centuries. First of all, it should be noted that the influence of the craft and engineering tradition of the Middle Ages and the Renaissance influenced Galilei’s method only to the extent that it allowed him to prepare instruments suitable for preparing and carrying out experiments. Against the traditional theses, mostly supported by verbal arguments and based on common experience, Galilei opposed the results obtained by experiments in which a particular phenomenon is isolated and studied in its physical-mathematical configuration. On the other hand, the belief that equal causes correspond to equal effects led him to eliminate the existence of “celestial physics” and “terrestrial physics” of different nature, to affirm the existence of a universal physics.
The approach of the Galilean method is thus represented by the verification of a hypothesis through an experiment in which only those elements are considered that are measurable: it was thus possible to apply to the procedure the instrument that for Galilei gave more guarantee of correctness and precision, that is mathematics. The fact that he applied the laws of mechanics to all fields had as a consequence a mechanistic vision of the world.
The figure of Galilei, his work and his trial have become a symbol for subsequent philosophical and scientific thought, a symbol that has often been extended beyond its actual historical meaning, so as to be used from time to time as a banner in the struggle against the principle of authority in issues related to the relationship between science and faith, between science and society, and between the fragmentation of scientific knowledge and philosophy. There is no doubt, however, that Galileo’s liberation of science from philosophy and theology marked a profound change in both the way of thinking and the way of looking at the problem of knowledge, just as it marked the beginning of the development of modern science and its increasing specialization as the study of reality deepened.
Literary style and linguistic innovation
His familiarity with letters and poets, his love for Ludovico Ariosto and Ruzante (Angelo Beolco) can be seen in the prose of his works, even in the sparse scientific exposition. In addition to the passion that the subject arouses in the author, to the polemical force that permeates certain pages, to the urgent rhythm or the sharp tone that he sometimes adopts, there is an attempt to make the language used more and more subservient to the subject treated. He has bent the linguistic instrument to the needs of the scientific argument and, at the same time, carried out a revision of the related terminology, which he considered necessary in order to achieve greater clarity.
Beyond the unquestionable literary value of Galileo’s prose, it is worth noting the reasons that led Galileo to use both Latin and Italian in his scientific works: while the former was used only for communication with the official scientific world, the latter was considered a valid instrument for the diffusion of new scientific conquests and a new conception of the world. In Galilei’s eyes, the Italian language also had the merit of being freer from the conditioning of the old way of doing science. This attention to the linguistic problem is an essential component of Galilei’s cultural struggle, which is aimed not only at the acquisition of new knowledge, but also at the diffusion of this knowledge to ever greater numbers of people.
The Padua period
The death of his father, economic hardship and the hostility of the academic environment led him to seek and obtain the chair of mathematics at the University of Padua (1592), where he remained for 18 years in a “lively and stimulating environment” where the Serenissima guaranteed a wide freedom of thought. During this period he was the companion of Marina Gamba, with whom he had three children: Virginia (1600), Livia (1601) and Vincenzo (1606). Galilei’s research during these years went in several directions. First, he dealt with practical matters of immediate civil and military use for the Republic of Venice. He published, among other works, the Treaty of Fortification (Trattato di fortificazione, 1593-94) and The Operations of the Geometric-Military Compass (Le operazioni del compasso geometrico-militare, 1606), which led to a bitter dispute with a certain Baldassarre Capra about the priority of the discovery of the instrument. He also worked on problems related to electrical and magnetic phenomena, with particular reference to magnets. Meanwhile, he regularly gave lectures of a decidedly Ptolemaic orientation, which were then published in the Treatise of the Sphere or Cosmography (1597).
At the center of his interests, however, were the dynamics and theoretical questions of astronomy. In the treatise of clear Archimedean setting Le mecaniche, published only in 1634 by M. Mersenne, he extended the principle of virtual speeds, already used by Guidobaldo Dal Monte, to the study of levers and pulleys, to the study of inclined planes and all other related machines. In 1604, in a letter to P. Sarpi, he gave the first, imprecise, formulation of the law of falling bodies.
As for astronomy, in 1597, in two letters addressed to Iacopo Mazzoni and Kepler, had the opportunity to declare his adherence to the Copernican thesis, he also claimed to be in possession of valid arguments in favor of it, but not made known. The first public statement was made in 1604, when Galileo interpreted the phenomenon of the appearance of a new star in three lectures as a confirmation of the Copernican theory, which was strongly criticized by scientific circles more loyal to the tradition.
A real turning point came in 1609, when his attention was drawn to news of the invention of the telescope by Dutch spectacle makers. Once the instrument was perfected and built, Galileo fully appreciated its possibilities and used it for astronomical observations (January 1610) that led him to discover the mountainous nature of the Moon, the four satellites of Jupiter, the Milky Way as a cluster of “tiny stars,” and the phases of Venus. In March of that year, he published the Sidereus nuncius with the news of his discoveries, which collapsed the Aristotelian theory of the perfection of the heavenly bodies and demonstrated the correctness of the heliocentric system.
The Florentine Period
The importance of these discoveries, while causing lively controversies, enormously increased the fame of Galilei and Cosimo II, to whom the satellites of Jupiter were dedicated with the name of “Medicean planets”, called him in Florence, appointing him “primary mathematician and philosopher” of the Grand Duchy of Tuscany. At first Galilei received the recognition of Kepler and partly of the Jesuit astronomers. The journey undertaken for this purpose in Rome in the early months of 1611, despite the triumphant welcome, allowed Galilei to realize some considerable resistance, in particular from Cardinal R. Bellarmino.
On his return to Florence, he published the Discourse on the Things that are on the Water or that move in it (1612), in which he demolished, from an Archimedean point of view, the Aristotelian theory of the elements and which met with strong opposition in philosophical circles. Meanwhile Galilei openly professed Copernicanism and the publication (1612) of three letters to Marco Welser, duumvir of Augsburg, on sunspots, in addition to a long dispute with the Jesuit C. Scheiner on the priority of the discovery, caused the reaction of theologians against the Copernican theory, considered heretical because in contradiction with what is said in the Bible on the movement of the Earth, which resulted in a real complaint presented to the Holy Office by the Dominican N. Lorini. Galilei replied to these attacks in a letter addressed to his pupil Benedetto Castelli (1613), circulated in many copies among friends and acquaintances, in which, starting from the assumption that “one proceeds equally from the divine word, from the Holy Scripture and from nature”, he states that the disagreement between faith and science is not an indication of a double truth, but it is the effect of a difference in language and that, as far as the scientific aspects are concerned, it is in the light of the progress of science that “the true senses of the sacred places must be found”.
Galilei still defended his scientific position and attempted a propaganda and diffusion action in three more letters, two of them addressed to Monsignor P. Dini, mathematician in Pisa, and one to the Grand Duchess of Tuscany, Christine of Lorraine (1615). But by now the Church was going to take a stand against the Copernican theories and against Galileo, which was not worth a second trip to Rome at the end of 1615 to support the defense of his thesis.
In early 1616, the two propositions on the motion of the Earth and the stability of the Sun were condemned, the reading of Copernicus’ work was forbidden pending revision, and Galilei was warned in a non-formal way not to “profess, defend, teach, either orally or in writing” the condemned propositions. This bitter defeat was followed by years of silence, interrupted only by Galilei’s indirect participation in the controversy with the Jesuit Orazio Grassi on the nature of comets (three of which had appeared in 1618), after which he wrote Il Saggiatore, which he published in 1623, encouraged by the recent appointment of Maffeo Barberini to the papal throne, Urban VIII.
Beyond the misinterpretation of the comet phenomenon presented in this work, Il Saggiatore is of great interest both for the general issues it addresses (mathematics as the language of nature, criticism of the incorruptibility of the heavens, distinction between primary and secondary qualities) and for the extremely clear exposition of its methodological criteria. Favorably impressed by the favorable reception of the work by the pope, whom he had the opportunity to meet in Rome in 1624, Galilei decided to complete the great work he had been thinking about for a long time, destined, in his intentions, to take stock of the controversial issue of astronomical systems.
After some vicissitudes of censorship, the Dialogue on the Two Great Systems of the World was completed in 1630. This work compared the two great astronomical systems, the Ptolemaic and the Copernican. The lively criticism of the scholastic culture and the Aristotelian distinction between terrestrial and celestial physics, the still imprecise enunciation of the principle of inertia and the very important one of the principle of relativity, developed with the famous simile of the ship, according to which mechanical phenomena occur in the same way on land as on a ship moving in a uniform rectilinear motion with respect to it, as well as the argument of the ebb and flow of the sea, presented (falsely) as proof of the movement of the Earth, make the work a true Copernican manifesto. Aristotle’s mechanics was definitely compromised by the Dialogue, and a new mechanics was outlined that was able to give physical and real consistency to the Copernican “hypothesis”.
The process and the final years
Despite the imprimatur obtained by Father N. Riccardi, which allowed the publication of the work on February 21, 1632, the reactions were immediate and violent. On October 1 of that year, Galileo was summoned to Rome by the Inquisition. The scientist, now advanced in years and in poor health, arrived in Rome in February 1633. Once again, his defenses, his attempts, and his influential protectors and friends were useless; first for the investigation, then for the trial, Galilei was “vehemently suspected of heresy, that is, of having held and believed false doctrines, contrary to the Holy and Divine Scriptures, that the Sun is the center of the Earth and does not move from east to west, and that the Earth moves and is not the center of the world.
Forced to abjure, Galileo was condemned to life imprisonment, a sentence that was commuted first in absolute isolation at the house of Bishop Piccolomini, his former student and friend, and then at his villa in Arcetri. Here he spent the last years of his life, saddened by the death of his daughter Virginia, who had been a great comfort to him, by the loss of his eyesight and by his increasingly precarious health. He continued, however, his studies in physics and in 1638 in Holland were published in the Discourses and mathematical demonstrations around two new sciences, the second major work of Galilei, which gathered, expanded and revised the studies on mechanics that he had pursued for over forty years. The work is in the form of a dialogue and is divided into four days: the first two are devoted to the exposition of the first new science around the resistance of materials and the constitution of corpuscular matter, the other two days deal with the second new science, dynamics, and more specifically of local motions, the motion of projectiles, the isochronism of the oscillations of the pendulum. In the appendix there are some demonstrations related to the center of gravity of solids, taken from the youthful treatise De motu.
With the establishment of a new dynamics, essential to support the Copernican system, the Discorsi, although not dealing with astronomical issues, brought a fundamental contribution to the affirmation of the heliocentric theory. Galileo continued to work on mechanical problems related to the construction of pendulum clocks and published a famous treatise on moonlight (Sopra il candore della Luna, 1640). The closeness of friends and students, including V. Viviani and E. Torricelli, helped to make the last days of the great scientist, who died on January 8, 1642, less sad and lonely. In 1992, at the end of the work of a special commission established by Pope John Paul II, the Church solemnly rehabilitated Galileo, acknowledging the errors of the Holy Office.