Galileo Galilei

Galileo Galilei (15 February 1564 – 8 Galileo GalileiJanuary 1642) was an Italian physicist,mathematician, astronomer, andphilosopher who is closely associated withthe scientific revolution. His achievementsinclude the first systematic studies ofuniformly accelerated motion,improvements to the telescope, a variety ofastronomical observations, and support forCopernicanism. Galileo's experiment-based work is a significant break from theabstract approach of Aristotle. Galileo isoften referred to as the "father of modernastronomy," as the "father of modernphysics", and as the "father of science".The motion of uniformly acceleratedobjects, treated in nearly all high schooland introductory college physics courses,was studied by Galileo as the subject of kinematics.

Galileo was born in Pisa (then part of the Grand Duchy of Tuscany), the first of six children of Vincenzo Galilei, a famous lutenist and music theorist. Although as a young man he seriouslyconsidered the priesthood, at his father's urging he enrolled for a medical degree at the University ofPisa. He did not complete this degree, but instead studied mathematics, in 1589 being appointed tothe chair of mathematics in Pisa. In 1591 his father died, and he was entrusted with the care of hisyounger brother Michelagnolo. In 1592 he moved to the University of Padua, teaching geometry,mechanics, and astronomy until 1610. During this period Galileo made significant discoveries inboth pure science (e.g., kinematics of motion, and astronomy) and applied science (e.g., strength ofmaterials, improvement of the telescope). His multiple interests included the study of astrology,which in premodern disciplinary practice was seen as correlated to the studies of mathematics and astronomy.

Although a devout Roman Catholic, Galileo fathered three children out of wedlock with MarinaGamba. They had two daughters (Virginia in 1600 and Livia in 1601) and one son (Vincenzio, in1606). Because of their illegitimate birth, both girls were sent to the convent of San Matteo inArcetri at early ages and remained there for the rest of their lives. Virginia (b. 1600) took the nameMaria Celeste upon entering the convent. Galileo's eldest child was the most beloved and inheritedher father's sharp mind. She died on April 2, 1634, and is buried with Galileo at the Basilica di SantaCroce di Firenze. Livia (b. 1601) took the name Suor Arcangela and was ill for most of her life.Vincenzio (b. 1606) was later legitimized and married Sestilia Bocchineri.

In 1610, Galileo published an account of his telescopic observations of the moons of Jupiter, usingthis observation to argue in favor of the sun-centered, Copernican theory of the universe against thedominant earth-centered Ptolemaic and Aristotelian theories. The next year Galileo visited Rome inorder to demonstrate his telescope to the influential philosophers and mathematicians of the JesuitCollegio Romano, and to let them see with their own eyes the reality of the four moons of Jupiter.While in Rome he was also made a member of the Accademia dei Lincei. In 1612, opposition aroseto the Sun-centered solar system which Galileo supported. In 1614, from the pulpit of Santa MariaNovella, Father Tommaso Caccini (1574–1648) denounced Galileo's opinions on the motion of theEarth, judging them dangerous and close to heresy. Galileo went to Rome to defend himself againstthese accusations, but, in 1616, Cardinal Roberto Bellarmino personally handed Galileo an admonition enjoining him neither to advocate nor teach Copernican astronomy. In 1622, Galileowrote his first book, The Assayer (Saggiatore), which was approved and published in 1623. In 1624,he developed the first known example of the microscope. In 1630, he returned to Rome to apply for alicense to print the Dialogue Concerning the Two Chief World Systems, published in Florence in1632. In October of that year, however, he was ordered to appear before the Holy Office in Rome.

Galileo Galilei pioneered the use of quantitative experiments whose results could be analyzed withmathematical precision. (More typical of science at the time were the qualitative studies of WilliamGilbert, on magnetism and electricity.) Galileo's father, Vincenzo Galilei, a lutenist and musictheorist, had performed experiments establishing perhaps the oldest known non-linear relation inphysics: for a stretched string, the pitch varies as the square of the tension. These observations laywithin the framework of the Pythagorean tradition of music, well-known to instrument makers,which included the fact that subdividing a string by a whole number produces a harmonious scale.Thus, a limited amount of mathematics had long related music and physical science, and youngGalileo could see his own father's observations expand on that tradition. Galileo is perhaps the firstto clearly state that the laws of nature are mathematical, writing that "the language of God ismathematics." His mathematical analyses are a further development of a tradition employed by late scholastic natural philosophers, which Galileo learned when he studied philosophy.Although he tried to remain loyal to the Catholic Church, Galileo's adherence to experimentalresults, and their most honest interpretation, led to his rejection of blind allegiance to authority, bothphilosophical and religious, in matters of science. In broader terms, this helped separate science fromboth philosophy and religion, a major development in human thought.By the standards of his own time, Galileo was often willing to change his views in accordance withobservation. Philosopher of science Paul Feyerabend also noted the supposedly improper aspects ofGalileo's methodology, but he argued that Galileo's methods could be justified retroactively by theirresults. The bulk of Feyerabend's major work, Against Method (1975), was devoted to an analysis ofGalileo, using his astronomical research as a case study to support Feyerabend's own anarchistictheory of scientific method. As he put it: 'Aristotelians [...] demanded strong empirical support whilethe Galileans were content with far-reaching, unsupported and partially refuted theories. I do not[4]criticize them for that; on the contrary, I favour Niels Bohr's "this is not crazy enough."'In order to perform his experiments, Galileo had to set up standards of length and time, so thatmeasurements made on different days and in different laboratories could be compared in areproducible fashion. For measurements of particularly short intervals of time, Galileo sang songswith whose timing he was familiar.Galileo also attempted to measure the speed of light, wisely concluding that his measurementtechnique was too imprecise to accurately determine its value. He climbed one hill and had anassistant to climb another hill; both had lanterns with shutters, initially closed. He then opened theshutter of his lantern. His assistant was instructed to open his own shutter upon seeing Galileo'slantern. Galileo then measured the time interval for his assistant's shutter to open. Knowing the timeinterval and the separation between the hills, he determined the apparent speed of light. On repeatingthe experiment with more distant hills, Galileo obtained the same time lapse, concluding that thetime for the light to travel was much less than his and his assistant's reaction time, and therefore thatthe actual speed of light was beyond the sensitivity of his measurement technique.Galileo showed a remarkably modern appreciation for the proper relationship between mathematics,theoretical physics, and experimental physics.