2.11  Galileo Galilei

Some years after its publication, the heliocentric model caused a strong controversy, especially after Tycho Brahe (1546-1601 AD) published his similar variation, followed by the advent of the telescope. When the heliocentric model started to become popular, the church considered it formally heretical and the Pope banned all books and letters advocating it.

It was Galileo Galilei (1564-1642 AD) who took the challenge to defend this controversial model, but he was met with strong opposition from astronomers and theologians which later led to his misfortune.

Galileo was an Italian polymath interested in astronomy, physics, philosophy, and mathematics. He studied gravity and free fall, velocity and inertia, projectile motion and and pendulums, and the principle of relativity, in addition to many other related applications. He contributed in transforming Europe from natural philosophy to modern science.

One of Galileo’s greatest contributions was to recognize that the role of science was not to explain “why” things happened as they do in nature, but only to describe them, which greatly simplified the work of scientists, and liberated them from the influence of theologians. Subsequently, this led Galileo himself to describe natural phenomena using mathematical equations, supported with experimentation to verify their validity. This marked a major deviation from the qualitative science of Aristotelian philosophy and Christian theology.

Based on these ideas Galileo was able to develop the mechanics of falling bodies from the earlier ideas of the theory of impetus that tried to explain projectile motion against gravity. By dropping balls of the same material, but with different masses, from the Leaning Tower of Pisa, he showed that all compact bodies fell at the same rate. Galileo then proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, which allowed him to derive the correct kinematic law that the distance traveled during a uniform acceleration is proportional to the square of the elapsed time:.

However, as it was the case with Copernicus, Galileo’s discoveries had been also clearly stated by many Muslim scholars more than five centuries before, and they even quoted and developed older theories in this regard. For example, we find Hibatullah ibn Malaka al-Baghdadi (1080–1164), an Islamic philosopher and physician of Jewish descent from Baghdad, originally known by his Hebrew birth name Baruch ben Malka and was given the name of Nathanel by his pupil Isaac ben Ezra before his conversion from Judaism to Islam towards the end of his life. In one of his anti-Aristotelian philosophical works Kitab al-Mutabar (The Book of What Has Been Established by Personal Reflection), he proposed an explanation of the acceleration of falling bodies by the accumulation of successive increments of power with successive increments of velocity Crombie (1959). In this and other books and treatises, he described the same laws of motion that were later presented by Newton, except that they were not formulated in mathematical equations.

Nonetheless, by the 17th century, the Copernican and Galilean heliocentric models started to replace the classical ancient worldview, at least by knowledgeable researchers. Between the years 1609-1619, the scientist Johannes Kepler (1571-1630 AD) formulated his three mathematical statements that accurately described the revolution of the planets around the Sun. In 1687, in his major book Philosophiae Naturalis Principia Mathematica, Isaac Newton provided his famous theory of gravity, which supported the Copernican model and explained how bodies more generally move in space and time, as we shall discuss in section 16.