This Entry is based upon this entry by U149602.

Now, at the beginning of the 21st century, we know that the Earth and the other planets travel around the Sun in an elliptical pathes, at the same time rotating on their own axes. In addition, we know that the Earth is not the centre of the Universe. From the time of Aristotle and Ptolemy to 15th century Europe, people believed that the sky was made of concentric, crystal spheres, rotating around a central Earth and carrying the stars and planets. In the forth century BC, the philosophers of the time developed the idea that the stars were fixed on a celestial sphere which rotated about the spherical Earth every 24 hours, and the planets, the Sun and the Moon, moved in the ether between the Earth and the stars. They believed that perfect motion should be in circles.

Copernican Theory

A major shift in worldviews certainly did take place in the 16th and 17th centuries, but it was not simply a shift from faith to reason. It was a shift away from the authority of Aristotle to the authority of scientific observation. It was not a dominant worldview to say that the Earth was no longer at the centre of the universe, but rather a view which challenged establishment. In 1543, Nicolaus Copernicus published a painstaking mathematical analysis of Ptolemy's astronomical observations. Copernicus, who thought of himself as an Aristotelian, merely wanted to free astronomy from Ptolemy's complexities. Copernicus accepted Aristotle's views on the circular motions of the heavens and on the movement of the earthly bodies. But in a desire to simplify, Copernicus wondered whether many problems in astronomy might not disappear if one assumed that the Sun, not the Earth was the centre of the universe. Copernicus also wondered whether the sequence of day and night could not be caused by the daily rotation of the Earth on its axis, rather than by the orbiting of the sun around the Earth. As well as trying to simplify astronomy Copernicus was also trying to find a way to calculate the calendar more accurately. The Pope had asked for a more precise calendar so they would know when to celebrate their Saints days. Copernicus's work was to be based on observation, experimentation, mathematical analysis, and a new kind of conceptual thinking. As long as men lacked instruments of observation and measurement, they were forced to rely, like Aristotle, on their senses and their reason. While he was in Italy, Copernicus wrote a short account of what has since become known as the Copernican theory, namely that the Sun and not the Earth is at rest in the centre of the Universe. Copernicus constructed a model where the Earth rotated and, together with the other planets, moved in a circular orbit about the Sun. But the observational evidence of the time favoured the Ptolemaic system! Copernicus tried to keep as much as he could of the Aristotelian universe, but his Neo-Platonic feelings about mathematics caused him to introduce the motion of the Earth. In his research Copernicus built on the information that Aristotle and Ptolemy had left the world and had stood for over 1500 years. I must emphasise that Copernicus left behind him nothing that any reasonable person could consider as a proof that the earth revolved round the Sun, yet Copernicus was the right man at the right time.

Kepler's Laws

It is noted that the defenders of the Copernican theory included Johannes Kepler (1571-1630) and Galileo Galilei (1564-1642). Strong theoretical underpinning for the Copernican theory was provided by Isaac Newton's theory of universal gravitation (1687). Kepler had taken centuries of diverse and largely inexplicable observations of the heavens and condensed them into a few concise, overarching principles which give convincing evidence that the universe was arranged in accordance with elegant mathematical harmonies. Conjectural data and abstract mathematical reasoning at last meshed perfectly. And of particular importance to Kepler, the most advanced scientific conclusion affirmed both Copernican theory and the mathematical mysticism of the ancient Pythagorean and Platonic philosophers. Kepler showed that the planets moved round the Sun in an elliptical orbit. He also showed that a line joining the planet to the sun sweeps out equal areas in equal times as the planets describes its orbit. These were Kepler's first two laws. However scientists certainly did not accept Kepler's first two laws with enthusiasm. But Kepler also made an immense contribution to the method of science; he was the first to insist in the exact verification of theoretical results by the best observation available.

Galileo's Observations

Galileo, in a personal letter written to Kepler in 1596, stated that he was a believer in the theories of Copernicus. Galileo showed a marked tendency to use all his discoveries as evidence for Copernicanism and to do so with great verbal as well as mathematical skill. Except for this, and his great devotion to science Galileo differed from Kepler in almost every way. In 1613 Galileo wrote a letter in which he attempted to demonstrate that the Copernican theory was consistent with both Catholic doctrine and proper biblical interpretations. His astronomical discoveries had roused the interest and support of the Church In particular some Cardinals and then later Pope Urban VIII. His passionate defence of the Copernican system of the universe, coming at a time when the Catholic Church was in the throes of the Counter Reformation, amounted to nothing less than heresy. In 1632 Galileo published his first scientific masterpiece. In it he compared the Ptolmiac/Aristotilian theory to the Copernican view in order to show the Copernican theory was logically superior. He attempted in his book to make his support for the Copernican view diplomatic, and he seems to have believed that the Church authorities would be sympathetic, but he misjudged their resistance to novel ideas. With the telescope Galileo observed the moon and announced that it was not composed of Aristotelian quintessence but of material much like that of earth. Galileo also used the telescope to observe the planet of Jupiter; he also discovered the four moons of Jupiter. To Galileo, it seemed that if moons could orbit Jupiter, the planets could surely orbit the Sun just as Copernicus had claimed. Galileo has also been described as 'the precursor of the age of reason', and perhaps the most dramatic figure in the history of science and foremost amongst its martyrs.

Newton's Laws of Motion

At Cambridge University in 1661 Newton studied the core curricula based on the works of Aristotle from 384 to 322 BC and on Medieval and Renaissance commentators on and expositors of Aristotelian doctrines. The mechanics of the Copernican astronomy and of Galileo attracted him The young Newton applied himself to learning Aristotelian logic, ethics, rhetoric, metaphysics and natural philosophy. This work was the basis to the new kind of science, which replaced the ancient structure that stood for two thousand years. Kepler provided much of the raw material for Newton's later and more inclusive generalisations. Newton is best known for his work in mechanics. Here he drew in the work of Kepler, Galileo, Descartes, and others to construct a new scientific system. Only 54 years earlier the Pope had publicly condemned Galileo for asserting that the earth moved, and now Newton was providing mankind with an accurate working model of the entire planetary system. Newton by his own account found a proof that Kepler's law was a consequence of centrifugal forces, and he also showed that if the orbital curve is an ellipse under the action of central forces, then the radial dependence of the force is inverse square with the distance from the centre. Isaac Newton's work enabled him to revise and correct that of Kepler and Galileo, for instance he reformulated Kepler's three law of planetary motion into what became known forever after as, Newton's laws of motion. Newton concluded that the Universe must be an infinite and eternal sea of stars, each much like our own Sun.

Aristotle and the Protestant Church

In the beginning, the opposition for Copernicus did not come from the Catholic Church. Copernicus was a Canon in good standing at a Catholic cathedral and an esteemed consultant to the Church of Rome. After his death Catholic universities did not avoid using the De Revolutionibus in astronomy classes. Moreover, the new Gregorian calendar instituted by the Church was based on calculations according to Copernican's system. It was antagonism from the Protestant reformers that was aroused first and most forcefully. Luther called Copernicus an 'upstart astrologer' who foolishly wished to reverse the entire science of astronomy while flagrantly contradicting the Holy Bible. The Church defended Aristotle's theory, accusing Galileo of heresy in questioning his ideas. Galileo finished his life condemned to house arrest, and not able to communicate with others. Newton as an extremely religious man who believed that just as human artisans designed and ordered the intricate mechanical clocks, printing press, wind and water mills, so the deity had created a world-machine and set it in motion in ways that human beings could learn to understand. Nature reviled the work of the Great Mathematician, and Newton sought to know his God through it. Newton himself desired above all to restore religion to the pristine purity, power, and centrality it had once enjoyed in human life.

The Birth of the Science of Logic

Although Aristotle's picture of the universe was not the correct picture as we know it now, he was the first man to systematise formal logic; Aristotle also developed metaphysics as a way of thinking, which tries to answer such questions as 'What is the world we Know', and 'How do we know it'. Aristotle represented for most of us an icon of difficult or abstruse philosophical thinking. When he approached a problem, he would examine

1. What people had previously written or said on the subject,
2. The general consensus of opinion on the subject,
3. And the systematic study of everything else that is part of or related to the subject.

This is called inductive reasoning: observing as many examples as possible and then working out the underlying principles. Aristotle was much more of a scientist in his philosophy, observing the rules of language, or logic, but also the nature of ethics, of politics and of the Natural World, plants and animals. Aristotle's scientific analysis made it possible for the astronomical theories of Ptolemy to provide scientific theories, which would last right through the Middle Ages until the 17th century. He taught us to reason about the world we see and know. He invented the science of logic and the rules of thinking. Aristotle's gift of questioning and re-examination of every thing is what has lasted down the ages. His ideas were the strong foundations that science has been built on for the last two thousand years.