Arguably, Galileo Galilei’s most interesting and important view is his support of heliocentrism, which is a cosmological model in which the Sun is assumed to lie at or near a central point while the Earth and other cosmic bodies revolve around it. His observations of our solar system and the Milky Way have revolutionized our understanding of our place in the Universe. Lying behind the idea of his support of heliocentrism is Galileo’s philosophy of scientific method which can be analyzed into three steps, intuition or resolution, demonstration, and experiment.
Before introducing Galileo’s view of heliocentrism, first we need to understand the background of philosophy and theology in Galileo’s day.
In seventeenth century, Philosophy, Science, and Theology were not completely separated as they are today and they were all controlled by the Catholic Church. Philosophers were expected to build upon the theory of Greek philosopher Aristotle and not contradict the ideas of Aristotle or the bible. Aristotle believed that Earth was spherical and the center of the universe: the Sun, Moon, planets, and all the fixed stars revolved around it while Earth is eternally unmoved. Aristotle’s view of the universe was widely accepted from its inception until the emergence of the scientific revolution that took place during the 16th and 17th centuries. Galileo is definitely one of the central figure of the Scientific Revolution. He dealt a powerful blow to traditional cosmology and began replacing the Greek view that had dominated science for almost 2000 years. At his time, Galileo’s support for heliocentrism was considered as heresy and he was sentenced to life imprisonment by the Roman Catholic Church in 1633.
In Galileo’s Dialogue Concerning the Two Chief World Systems, he wrote, “I should think that anyone who considered it more reasonable for the whole universe to move in order to let the Earth remain fixed would be more irrational than one who should climb to the top of your cupola just to get a view of the city and its environs, and then demand that the whole countryside should revolve around him so that he would not have to take the trouble to turn his head.” Although Galileo was not the first person who proposed the idea of heliocentrism, (it was first presented by Renaissance astronomer Nicolaus Copernicus ) is discovery provided great evidence and strong support for heliocentrism. In his book Dialogue Concerning the Two Chief World Systems, Galileo used 4 days’ of philosophical discussion among two philosophers and a layman which contains many astronomical topics and other comtemporart science. One of the philosopher Salviati argues for Galileo’s view while the other philosopher Simplicio supports Aristotelian Universe and is against Copernican heliocentrism. Galileo refuted the theory that the composition and properties of celestial bodies were completely different from those of the Earth. He denied the ancient view that immutability is a sign of nobility and perfection. Furthermore, he made an insight that later became important, that movement is not a change, it does not lead to growth or destruction.
Galileo’s scientific methods contributed to the scientific revolution as most beliefs at the time were based on philosophy or religion and is significant to future development of science and philosophy. He carefully experimented and observed, using experimental evidence to prove that his theory. He relied on accurate measurements from instruments which is revolutionary in his days. He was the first to construct a telescope and with which he discovered Jupiter’s four largest satellites, spots on the Sun, phases of Venus, and hills and valleys on the Moon, which is contradictory to Aristotle’s theory that celestial objects are perfectly spherical. The findings proved Galileo’s hypothesis that Earth is not the center of the universe.
Glossary:
Aristotelian Universe: the Earth-Centered Universe in which the Earth is eternally unmoved and everything else revolves around it in concentric spheres.
Heliocentric: Sun-centered.
Copernicus’ solar system: the astronomical model developed by Nicolaus Copernicus which positions the Sun at the center of the universe, motionless, and the Earth and other planets orbiting around it in circular pathes.
Sources:
Galilei, Galileo, Dialogue concerning the Two Chief World System-Ptolemaic and Copernican, translated by Stillman Darke. https://rauterberg.employee.id.tue.nl/lecturenotes/DDM110%20CAS/Galilei-1632%20Dialogue%20Concerning%20the%20Two%20Chief%20World%20Systems.pdf
Machamer, Peter and David Marshall Miller, “Galileo Galilei”, The Stanford Encyclopedia of Philosophy (Summer 2021 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/sum2021/entries/galileo/
Spencer, J. Brookes , Osler, Margaret J. and Brush, Stephen G.. “Scientific Revolution”. Encyclopedia Britannica, 26 Nov. 2019, https://www.britannica.com/science/Scientific-Revolution.