The Copernican Revolution - Copernicus, Kepler and Galileo

Nicolaus Copernicus
  • Copernicus was influenced by Renaissance Platonism and ancient Greek texts
  • The mathematical complexity of the Aristotelian-Ptolemaic system troubled Copernicus, who believed that truth was the product of elegance and simplicity.
  • He set out on a life-long task to work out mathematical explanations of how a heliocentric universe operated.
  • Because he did not want to engage in controversy with the followers of Aristotle, Copernicus did not publish his findings until 1543, in a work entitled On the Revolutions of the Heavenly Spheres.
  • The helio-centric view of the universe was a very influential book in history, even more than the Origin of Species by Charles Darwin because it literally made the humans to rethink and challenge their place in the universe. (e.g. If we were not the centre, doesn’t that mean we are not special & is the Bible credible/is it telling us the truth?)
  • Copernicus’ treatise on the universe retained some element of Aristotelian-Ptolemaic system.
  • Copernicus never doubted Aristotle’s basic notion of perfect circular motion of the planets or the existence of crystalline spheres within which the stars revolved, and he retained many of Ptolemy’s epicycles. Thus, some of his mathematical proofs were wrong and rejected.
  • But Copernicus proposed a heliocentric model of the universe that was mathematically simpler than Ptolemy’s earth-centred universe.
  • Thus, he eliminated some of Ptolemy’s epicycles and cleared up various problems that had troubled astronomers who had based their work on an earth-centred universe.
  • By removing the earth from its central position and by giving it motion - that is, by making the earth just another planet - Copernicus undermined the system of medieval cosmology and made the birth of modern astronomy possible. Because they were committed to the Aristotelian-Ptolemaic system and to biblical statements that supported it, most thinkers rejected Copernicus’ conclusions.
  • Significance: Started the Scientific Revolution with the publication of On the Revolutions of Heavenly Spheres

Johannes Kepler (1571 - 1630)
  • Kepler searched persistently for harmonious laws and planetary motion by making careful observations of the planetary objects.
  • He did so because he believed profoundly in the Platonic ideal: a spiritual force infuses the physical order; beneath appearances are harmony and unity; and the human mind can begin to comprehend that unity only through gnosis - a direct and mystical realisation of unity - and through mathematics.
  • Kepler believed that both approaches (Copernicus and Ptolemaic) were compatible, and he managed to combine them.
  • He believed in and practiced in astrology, and throughout his lifetime he tried to contact an ancient but lost and secret wisdom.
  • Kepler discovered three basic laws of planetary motions.
  • First, the orbits of the planets are elliptical, not circular as Aristotle and Ptolemy had assumed & the sun is one focus of the ellipse.
  • Kepler’s second law demonstrated that the velocity of a planet is not uniform, as had been believed, but increases as its distance from the sun decreases.
  • Kepler’s third law - that the squares of the times taken by any two planets in their revolutions around the sun are in the same ratio as the cubes of their average distances from the sun - brought the planets together into a unified mathematical system.
  • Significance
  • Kepler gave the mathematical proof to Copernicus’ theory
  • eliminated forever the use of epicycles
  • demonstrated that mathematical relationships can describe the planetary system

Galileo Galilei (1564 - 1642)
  • Believed that beyond the visible world lay universal truths, subject to mathematical verification (influence of Renaissance Platonism)
  • Also believed that only after experimenting can one discern the harmonious laws of the universe and give them mathematical expression - he was an adamant supporter of empiricism and his unwavering spirit of empiricism inspired many generations of scientists. Hence, it is arguable who (Copernicus or Galileo) was mainly responsible for the start of the Scientific Revolution.
  • established a fundamental principle of modern science - the order of uniformity of nature
  • invented the telescope
  • discovered that the Moon is not smooth, uniform and precisely spherical; it is uneven, rough and full of crevices [from his The Starry Messenger]. 
  • discovered the Sun has sunspots
  • The discovery about the Moon and the Sun challenged the conventional view that heavenly bodies (e.g. stars, planets) stay the same throughout. The heavenly bodies do go through changes just like the earthly bodies. Hence, there are no higher and lower worlds; nature is the same throughout.
  • also discovered the moons orbiting around Jupiter (aka Galilean moons: Io, Europa, Ganymede and Callisto) → supported the Copernican heliocentric theory: If Jupiter had moons, then all heavenly bodies did not orbit the earth.
  • Galileo was oppressed by the Catholic Church who viewed his discovery as a threat to their position rather than accepting his discovery as true science.
  • NOTE: The Starry Messenger mostly described the astronomical discoveries Galileo made using his telescope. It was the Dialogue Concerning the Two Chief World Systems [Geocentrism and Heliocentrism] that got Galileo in trouble with the Church. In it, he supported the Copernican view of the universe. The Dialogue was placed on the Index of Forbidden Books and banned by the Catholic Church for corrupting the minds of the people and challenging the biblical records of the movement of the Sun around the Earth.

By the middle of the seventeenth century, largely due to the work of Copernicus, Kepler and
Galileo, Aristotle and Ptolemy had been dethroned. People began to accept the heliocentric theory of the universe and abandoned the geocentric view of the universe. People took the philosophy of science in which nature, especially physical laws and motion, can be explained mathematically. However, what was missing was an overriding law that could explain the motion observed in the heavens and on earth. This law was supplied by Issac Newton (culmination of the Scientific Revolution).

<Further Reading> (Lecture 10: The Scientific Revolution, 1543 - 1600) (Lecture 11: The Scientific Revolution, 1600 - 1642) (Lecture 12: The Scientific Revolution, 1642 - 1730) (Trial of Galileo) (Dialogue Concerning the Two Chief World Systems)

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