Thursday, 13 October 2011

And Yet It Moves! Part I

Galileo Galilei
Galileo Galilei was a great man, a brilliant thinker and a pioneer of astronomy, physics and science in general. He was described by Stephen Hawking as “… responsible for the birth of modern science,” and by Einstein as the “father of modern science.” He has also become an icon for the struggle of science against faith. The tale of his conflict with the Church; of how he was indicted by the Church for the heresy of claiming the earth moved and brought before the Inquisition to answer for his beliefs. The tale recounts the fearless disputation where Galileo pitted science against blind dogmatic faith but was forced to silence the truth after the aged astronomer was faced with the torture. The final scene in the saga tells of the scientist, who has been forced to gainsay his conscience and say that the earth remains the motionless centre about which the celestial objects move, hobbles out of the court, murmuring under his breath in a whisper that echoes throughout history “Eppur si muove” (translation from the Italian “And yet it moves”).

           It is a compelling tale and is undeniably based on historical reality. But whenever we come across a wonderful tale from history, with clearly defined heroes and villains, we must suspect that the reality is more complex.

Martin Luther
            In the early 1500’s the Renaissance was in full swing. The Catholic Church, far from prohibiting the new learning and arts was in fact the largest patron of them. However, political tensions and concerns about the increasing corruption within the church meant that when Martin Luther wrote the Ninety-Five Theses and started a revolution against the church, the church was unable to stop him. The German princes, concerned about the growing power of the Habsburg Emperor (who was supposedly their overlord) sheltered the fugitive from papal and imperial power and the Reformation began. Europe now became a virtual and, in many cases, a literal, battleground of ideologies and religious beliefs. This time of struggle (like most times of struggle in actual odd fact), combined with the new learning of the Renaissance, proved a backdrop for a major increase in learning.

            Science was in an interesting state at that time. For hundreds of years, all across Europe and the Middle-East, the works of Aristotle had been held to be almost entirely true and the sheer brilliance of the Greek thinker had fooled many scholars into thinking that between Aristotle and the other Greek philosophers, every thing worth discovering had been discovered. Thomas Aquinas, the greatest philosopher of the Middle Ages, had codified Aristotelian learning in such a way that it had become (and still is) the official philosophy of the Catholic Church, and one of the things Aristotle had said was that the earth was the centre of the Universe.

            Previous Greek thinkers had speculated that the Earth might revolve around the Sun but Aristotle had “disproved” them with a simple thought experiment. I’ll give a version of it here. Imagine you are driving at speed in an open top convertible and you throw an object directly up in the air. Does it land behind you or back in the car? (Aristotle used a chariot for his example but the principle is the same.) Common sense says that it lands behind you. Yet when we stand still upon the surface of the earth and throw an object straight up into the air it reaches its zenith and then falls directly downwards. Aristotle reasoned that if the earth was moving then the object should fall hundreds of feet (or maybe even miles away) because of the speed of the earths rotation, therefore, the earth cannot move. I should mention that this example is taken from my dodgy memories of undergraduate college, so if there are any experts on Aristotle out there who feel that this is inaccurate, I would welcome any clarifications or corrections.

There were a number of other astronomical arguments against heliocentrism as well. For the earth to be in constant motion, the stars should be observed to shift position according to the Earth's rotation. The Greek conception of the Universe found it difficult to imagine that the stars could be located at such immense distances from the earth as to make these shifts indiscernible to the naked eye. I should take a brief moment to clarify that Aristotle was very clear about the earth being a sphere. In fact the Greeks had clear knowledge of the spherical nature of the earth from around 240 BC when Erastosthenes provided an empirical proof. The whole notion of people fearing Columbus would fall off the edge of the world is total nonsense.

Claudius Ptolemy
            The problem with the Earth being at the centre of the Universe is that it makes astronomy very awkward but Claudius Ptolemy, a Greek mathematician, had provided a model that allowed the Moon, Sun, Planets and Stars to rotate around the Earth on basically circular orbits. Simple circular orbits would require the planets to move in perfect, regular orbits in the night sky but instead, they “regress” or appear to track back on themselves in their orbits. This was explained by using “epicycles” which were conceived as mini-spins that the planets would do at a certain period of their orbit that would explain their apparent backwards motion.

The Ptolemaic system (i.e. the system first invented by Ptolemy) was refined throughout the Middle Ages and Renaissance. As astronomy improved it became clear that more epicycles were needed and that in fact, the centre of the orbits was not the earth but some point in space near the earth. The system was based on notions that the celestial bodies moved in perfect circles and yet had to have odd spins at seemingly random points of their rotations. The Earth was at the centre and yet not at the centre. The system was extremely complicated and complex and yet it provided a very poor model for predictions about planetary motions. As the brilliant minds of the Renaissance thinkers pored over the data, a new theory that would better explain the appearances was sought and the stage was set for a scientific revolution.

Enter Copernicus. Copernicus was an astronomer from what is now Poland. He became convinced that there was a simpler way to explain the data. For a variety of reasons he believed that the Sun, not the Earth, was at the centre of the Universe. He began work on a book entitled “On the Revolution of the Celestial Spheres” where he argued his point. At that time writers and thinkers all over Europe communicated closely through letters, so even though Copernicus refused to publish his work, the secret could not be kept and soon all the world of the intelligentsia was abuzz to hear that (as the Protestant theologian Melanchthon put it) there was an “astronomer who moves the earth and stops the sun.”

There is quite a bit of background needed to provide a backdrop to Galileo’s work so click here for the second post about the subject.