Italian philosopher, astronomer, scientist and mathematician, Galileo Galilei (1564 – 1642) is probably best remembered for his work in support of Copernicus’ heliocentric theory of the solar system. For the sake of his life, Galileo recanted his views in 1633, admitting that the earth did not spin on its own axis. It is unlikely that the recantation was sincere and he nevertheless remained under house arrest.
In 1608 the Dutchmen Lippershey invented the telescope. Within two years Galileo used it to dramatic effect, showing by his astronomical observations that the Ptolemaic or geocentric theory which held that the Earth was at the centre of the universe, was seriously flawed. Galileo also observed that the Milky Way was in fact made up of many millions of individual stars. He observed the phrases of Venus and discovered the moons of Jupiter, which had theological experts up in arms. Indeed, Galileo’s findings attracted such sharp criticism, both from secular and ecclesiastical quarters that he felt compelled to offer, both in his defence and in reply to his critics, the Letter to the Grand Duchess Christina in 1615. In the Letter, Galileo argues that scientific and theological matters should not be confused. Science could not cast doubt on religious doctrine, only strengthen it. Nonetheless he was condemned by the Inquisition, first in private communication in 1616 and later in 1633, when he publicly recanted.
Although his work was instrumental in bringing the Copernican system into prominence, Galileo was far more than just an astronomer. Much of his important work lay in dynamics and the principles of movement. He was the first to discover the law of falling bodies, or constant acceleration, published after his recantation and whilst still under house arrest in 1638, in his Discourse on Two New Sciences.
Moreover, what would later be Newton’s celebrated first Law of Motion was directly taken from Galileo’s principle of inertia, namely that a body moves in a straight line with uniform velocity unless acted upon.
This principle was important in helping to support the Copernican theory. Critics of Copernicus had claimed that if the heliocentric theory were true, then a falling body should not fall in a straight line, but in fact land somewhat to the west of the point from which it was dropped, on account of the eastwise rotation of the Earth. It had been proven by experiment that this was not the case, a result which led many to dismiss Copernicus as wrong even if they did not share the religious reasons for dismissing him. It took Galileo’s work in dynamics to show why the prediction was not fulfilled. Simply put, the falling stone retains the rotational velocity of the Earth.
Philosophically, Galileo held that “the book of nature is written in the language of mathematics.” He was heavily influenced by Greek philosophy and a great admirer of Archimedes. He also maintained, like John Locke, that there was a metaphysical distinction between the primary and secondary qualities of bodies. The former are essential and inherent in objects, whereas the latter exist only insofar as they cause certain effects in the minds of observers. Undoubtedly, Galileo was a great thinker who risked much in the pursuit of truth, helping to set free the quest for knowledge from the chains of religious dogmatism.
[Summarized from Philosophy 100 Essential Thinkers by Philip Stokes, 2012]
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