Wheels within Wheels

In the previous post, I left off the history of astronomy with Claudius Ptolemy, the last and greatest of the astronomers of ancient times. It was Ptolemy who brought the science of astronomy to its apex in classical times. In his treatise, the Almagest, as the Arabs came to call it, Ptolemy worked out the geocentric model with the complex system of epicycles that the ancients believed described the universe, along with a catalog of stars and constellations and tables of information on the motions of the planets and eclipses of the Sun and Moon. So well did Ptolemy do his work that the Almagest was the accepted text on astronomy for over twelve hundred years.

The science of astronomy did not stand still after the time of Ptolemy. The Western Europeans were a little distracted by the fall of the Roman Empire in the West and contributed little to the progress of learning for some centuries. Fortunately the ancient learning was preserved in the Greek East and when the Arabs conquered much of the Middle East in the century after the death of Mohammed, they were able to learn much from the peoples they ruled and soon began to make contributions of their own in science and philosophy. The Arabs translated many Greek texts into Arabic which Western scholars discovered and translated into Latin. The contributions made by the Arabs can be seen by the fact that Ptolemy’s standard text is known by its Arabic title and that many stars still retain names derived from  Arabic

Throughout the Early Middle Ages, the Muslims translated Greek texts into Arabic and so helped to preserve them until Western scholars could translate them into Latin once things had settled down in the West. The importance of the Arabic contribution can be seen by the fact that Ptolemy’s book is known by its Arabic title, not to mention that many stars are known by names derived from Arabic; Betelgeuse, Algol, Aldebaran, Deneb, Vega, and many others.

Over time, the Arabs, and later the Europeans, developed better instruments for observing the positions of the stars and planets in the sky and to predict the motions of the planets. As their techniques improved, astronomers were able to revise and update the information on planetary motions collected by Ptolemy, and they also found that more epicycles were needed to explain and predict planetary motions. The Ptolemaic model began to seem increasingly over complicated. The last major revision of the tables of planetary motions was commissioned by King Alfonso X of Castile in the thirteenth century. Alfonso, called “the Wise” was known as a patron of many branches of learning and was himself conversant in the science of astronomy. He is supposed to have remarked that if God had consulted him during the creation, he might have suggested a simpler system than the complicated bicycles of Ptolemy. The king almost certainly did not say this, but the sentiment was shared by many who began to believe the universe shouldn’t be so complicated.

Among these was a Polish priest who lived some two hundred years after Alfonso. This priest was named Mikolaj Kopernik, better known by the Latinized version of his name, Nicolaus Copernicus. Copernicus was a true renaissance man who was learned in such diverse fields as mathematics, canon law, medicine, economics, classical languages, diplomacy, politics, and astronomy. It is in that last subject that he is remembered today. Copernicus came to realize that understanding the motions of the planets would be much easier if he simply assumed that the planets revolved around the Sun rather than the Earth.



The retrograde motions of the planets could simply be explained by their overtaking the Earth as they orbit the Sun. Copernicus seems to have developed his heliocentric theory by 1514 and spent much of the rest of his life working on his book “De revolutionibus orbium coelestium” or “On the Revolutions of the Heavenly Spheres”. Although Copernicus showed the manuscript to his friends and interested scholars, he was reluctant to actually publish his masterpiece for fear of the public ridicule such a radical theory might bring him. It was only after his friends assured him that the book would be favorably received and he was dying that Copernicus agreed to publish De revolutionibus in 1543.

De revolutionibus was favorably received by the few people who actually read it. The fact was that Copernicus’s book was so abstruse and technical that only astronomers and mathematicians could really appreciate and understand it.

It was in Latin and the script was hard to read too.

It was in Latin and the script was hard to read too.

Copernicus’s heliocentric model was not generally accepted for some time. The fact that the assumption that the Sun was at the center of the Solar System made calculating the motions of the planets less complicated did not necessarily made that assumption true and there was good reason not to believe the Earth moved. In fact, the Copernican model did not make the calculations that much less complicated. Like Aristotle and Ptolemy, Copernicus believed that the planets moved in perfect circles and his theory still required some epicycles to agree with observations. It was not until 1610 when Johannes Kepler proposed his first law of planetary motion, that the planets orbit the Sun not in circles that the need for epicycles was finally done away with. The heliocentric model then clearly provided a simpler means of understanding the motions of the planets and so was quickly adopted by most astronomers even though there was not yet clear proof that it was actually true.

Which brings us back to Galileo and the Church. In 1632, the year Galileo was tried by the Inquisition, the heliocentric model was rapidly gaining acceptance, yet from a strictly scientific viewpoint, the Church was quite correct in regarding the model with skepticism, even if it was not correct from any viewpoint to put Galileo on trial, although as I said Galileo himself was mostly to blame for his troubles. And, here I have to ask again, why was the heliocentric theory adopted a century before it could be proven beyond a reasonable doubt?

Scientists like to portray themselves cool, logical, unbiased observers interested only in the facts, that is the results of their observations and experiments. Any hypothesis, no matter how attractive, must be put aside if the observations do not agree with it. In fact, scientists are subject to the same sorts of biases as everyone else and a candid view of the history of science will show many instances when scientists have clung to a hypothesis even when the facts seem to show otherwise. This is not always a bad thing. I would even go further and state that this is often a good thing. Sometimes intuition serves as a better guide to discovering the truth than logic and sometimes finding the truth requires ignoring the facts that seem to point in a certain direction while pursuing an underlying truth.

One of the biases that has proven to be most useful in understanding the nature of the universe we live in is the idea that the universe is, as bottom, a simple place that we can understand. If things get to be overly complicated, it is usually taken as a sign we are moving in the wrong direction and should seek a simpler explanation. This is no scientific reason for believing this is the case, yet this bias has proven to be useful over and over again. Ptolemy’s epicycles became more and more complicated, so astronomers switched to the simpler heliocentric system, and were proven right. Physicists and chemists in the nineteenth century were dismayed to discover more and more chemical elements with no clear pattern, until they discovered that all these elements could be explained by the three particles, electrons, neutrons, and protons found in the atoms of every element. Physicist were then confused by the many sub atomic particles they kept discovered, until they learned that these particles were composed of a handful of still smaller particles called quarks. This is really the essence of science, to find simple patterns to explain complex phenomena and this process requires intuition and imagination as much as it requires logical thinking and careful observation. So, Galileo was right, even when he was wrong.


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