Kepler's contemporary, the Italian scientist and astronomer Galileo Galilei (1564-1642), in his most renowned experiment dropped two bodies of different weights from the Leaning Tower of Pisa, and clearly demonstrated that all bodies fall at the same speed regardless of their weight. This was indisputable proof that Aristotle's theory and the Church's dogma were fundamentally mistaken. Galileo also revolutionized astronomy when he was the first to apply the telescope to the study of the heavenly bodies. His observations led him to discover the moons of Jupiter and the phases of the planet Venus, and convinced him that Copernicus' heliocentric model was right. In 1633, Galileo was brought before the Inquisition for a grave suspicion of heresy. He was forced to formally renounce his beliefs, and was sentenced to life-long house arrest.

Claiming that the sun was at the centre of the universe, Copernicus directly challenged the Church's sacred worldview, which was based on the Aristotelian model. He was the first to challenge, but what he started was unstoppable, and many followed.

Johannes Kepler (1571-1630), a German astronomer, developed the Copernican model into his three major laws of planetary motion, which are still in use nowadays. These mathematical laws could accurately account for all planetary observations. However, by suggesting that the planets were moving in elliptical orbits around the sun, and not in the heavenly perfect circular motion, Kepler deviated even further from the Aristotelian model that was the base for the worldview of the Church. He was excommunicated from the Lutheran Church in 1612

As we have seen in our last posting in this blog Copernicus, who postulated a model in which the sun was at the centre of the universe. knew that the clear advantages of his model would not protect him from the hostile reaction of the orthodox authorities and the Inquisition, and it was not until 1543 – the year of his death – that he eventually published his complete work On the Revolutions of the Heavenly Spheres.

It is clear from the extent of the criticism of his work that Copernicus challenged not only the knowledge of the cosmos, as portrayed by the church, but he challenged knowledge itself: Should our impartial experience determine our understanding, or is it our knowledge that the world should conform to?

For example, Tolosani, a contemporary of Copernicus, wrote:

[Copernicus] seems to be unfamiliar with Holy Scripture since he contradicts some of its principles, not without the risk to himself and to the readers of his book of straying from the faith. ... in his imagination he changes the order of God's creatures in his system. ... he seeks to raise the Earth from its lower place to the sphere where everybody by common consent correctly locates the Sun's sphere, and to caste the sphere of the Sun down to the place of the Earth, contravening the rational order and Holy Writ, which declares that heaven is up, while the Earth is down.

It was most likely, therefore, that the Church would have condemned Copernicus’ work, had it not been for an introduction inserted by the publisher. The introduction stated that the book merely presented a simpler way to calculate the positions of heavenly bodies, and that “the hypotheses contained within made no pretense to truth that, in any case, astronomy was incapable of finding the causes of heavenly phenomena.” This unauthorized insertion, although appalling to many, ensured the book was not immediately condemned. In fact, it was publicly available for over 70 years before it was subject to censorship.

Although some were sentenced to death for their support of Copernicus’ heliocentric system (for example, Giordano Bruno was burnt alive in 1600) it was not until 1616 that the Church placed the work on the List of Prohibited Books (Index Librorum Prohibitorum) and decreed that “the propositions that the Sun is immobile and at the center of the universe and that the Earth moves around it, judging both to be ‘foolish and absurd in philosophy,’ and the first to be ‘formally heretical’ and the second ‘at least erroneous in faith’ in theology.” By then, however, Copernicus’ mathematics had already been widely in use, and although many still viewed it as a hypothetical calculation model, it was unavoidable that questions about the nature of the cosmos as derived from the model would arise.

The scientific revolution had begun.

So let's continue our exploration of the birth of modern science ...

Since early history, the scientists who studied the heavens were the only scholars to use mathematics, and the terms astronomer, astrologer and mathematician were virtually interchangeable. They calculated the dates of the holy days, developed methods to draw astrological charts, and forecast the position of the zodiac signs and the movement of the planets. However, despite their skillful observations, measurement and calculations, many questions remained unanswered. They could not account for the changes in the brightness of the planets, nor for their apparent retrograde movement. Their models did not explain why Venus and Mercury were never seen far from the sun, and they could not even agree on the order of the planets. However, it was not their role to ponder such theological matters. They were mathematicians, and calculation was what they did.

All this changed in 1514, when a Polish astronomer, Nicolaus Copernicus (1473-1543) circled amongst a few of his friends an unsigned hand-written book, Little Commentary. In his book, Copernicus introduced the heliocentric model, in which the sun, rather than the earth, was at the center of the universe, and all planets, including earth, were orbiting around it. With a single model, Copernicus could explain the apparent movement of the planets, the sun and the stars. His model could also account for the changes in the brightness of the planets, and offered a singular method of ordering them and calculating their relative distances from the sun with amazing accuracy (less than 10% difference from our current measurements.) Copernicus knew, however, that the clear advantages of his model would not protect him from the hostile reaction of the orthodox authorities and the Inquisition, and it was not until 1543 – the year of his death – that he eventually published his complete work On the Revolutions of the Heavenly Spheres.

Unlike most other studies, the study of alchemy did not challenge the Church’s view of the world and could, therefore, be practiced. For over 900 years, from about 500 to 1400, philosophers in Western Europe, surrounded by a cloak of secrecy, predominantly occupied themselves with the search for the mythical philosopher’s stone (the substance that could supposedly transform everyday material to gold and produce the elixir of immortality). During this Dark Age of European science, Arab philosophers cultivated an environment that encouraged the sharing of ideas, discussion and debate. The scientific framework they had developed – based on experiments to distinguish between competing scientific theories, citation, peer review and open inquiry – led to many invaluable breakthroughs in all areas of science: chemistry, physics, optics, astronomy and mathematics.

It was the fall of Constantinople (now Istanbul) that brought Arab science to the attention of the Western European philosophers. Constantinople, the capital of the Byzantine Empire, had been a major intellectual center. Its conquest by the Turks in 1453 led to an exodus of scientists and philosophers to Western Europe. Owing to the recent invention of printing by Gutenberg around 1450, the scientific knowledge these scholars brought with them (including Arab science) became widely available. The seeds for a new worldview were planted, and science of the stars – the oldest of all natural sciences – was the natural place for them to germinate.