April 19, 2005

Looking closely at scientific history

Since I started looking more closely into the history of science, there are two things that I have learned that I have recast into principles.

The first is that the more closely we examine important historical events in science, the less resemblance they bear to the popular condensed capsule versions that are learned in school or college or portrayed in the popular media. The earlier posting about Columbus and the flat Earth is a case in point.

The second principle is that while science textbooks are usually good for teaching the current principles of science, they tend to be bad for teaching anything about the history of science or the nature of science. In those cases, what they usually describe is better described as folklore rather than history.

Take for example one of the most famous of all scientific revolutions, the one associated with Copernicus. The popular version of this story goes as follows:

The ancient Greeks, while pretty good at mapping the stars and motion of planets, tended to create models of the universe that were strongly influenced by religious, philosophical, and aesthetic considerations, rather than on observation and experiment. Hence they came up with the idea that the Earth was the stationary center of the universe (which pleased those religious people who wanted to give pride of place to the home of God's greatest creation – human beings) and that the stars and planets were embedded on the surface of a sphere that rotated around the Earth in circles, which pleased those philosophers with highly refined sensibilities who felt that since the circle and sphere were the most perfect geometric shapes, they had to play a central role in the cosmos.

The story continues that the prestige of these ancient Greek philosophers such as Aristotle (384-322 BCE) was so great, and commitment to religious doctrine so strong, that many people gave blind adherence to these ideas and stubbornly tried to retain them in the face of contrary evidence. For example, the planet Mars usually moves in the eastward direction in the sky but sometimes shows retrograde motion (i.e., zig-zags, briefly heading westward before going eastward again). To explain this and other peculiar behavior epicycles were incorporated were incorporated into the Earth-centered circular orbits.

To visualize how an epicycle works, imagine a child on a merry-go-round who, while being carried around in a big circle (called the deferent) by the merry-go-round, is herself running around one of the horses in a smaller circle (the epicycle). When viewed from the stationary center of the merry-go-round, her resulting motion is quite complicated, and sometimes she will appear to be moving in the direction opposite to the merry-go-round itself. This model was used to explain retrograde motion of Mars when viewed from the Earth.

But while this helped, it did not explain all the features of planetary motion and this required adding even more complicated epicyclic motion, culminating in the comprehensive mathematical system developed by Ptolemy (100-178 CE), and written up in his Almagest, which became the standard model.

When Nicolaus Copernicus came along with his model of a Sun-centered system, his ideas were fiercely opposed by the Roman Catholic Church because they displaced the Earth from the center of the system and this was seen as a demotion for human beings and counter to the teachings of Aristotle. This resulted in the inquisitors of the Spanish Inquisition persecuting, torturing, and killing for heresy those people who advocated Copernican ideas, although popular history is hazy on what exactly was done to which scientist. Galileo Galilei is thought to have been most affected by the Inquisition. It was Isaac Newton's monumental work on motion and gravity that finally sealed the acceptance of Copernican ideas.

The above version of the Copernican story, that blind adherence to the doctrines of great philosophers like Aristotle, supported by religious dogmas, hampered the development of science, is what is popularly believed and passed on in science textbooks, which usually provide a breezy and quick synopsis of the above scientific history, with minor variations.

For example, take the introductory physics textbook Physics by Fishbane, Gasiorowicz, and Thornton. It is a very good textbook as far as the physics goes (I used it when I taught the introductory physics courses) but says things like "Blind reverence for authority impedes scientific progress, and for a long period the work of ancient Greeks was regarded with crippling irreverence." (p. 1) and "[Ptolemy's] theory was limited by a culturally imposed belief that perfect, circular motion describes celestial motion." (p. 321) Even Copernicus is gently chided for his rigid adherence to some aspects of orthodoxy. "Unfortunately, Copernicus continued to insist on describing all motions with circles and, because the true motions of the planets about the Sun are not circles, epicycles continued to be needed in the Copernican description to accommodate the observations of planetary motion." (p. 320)

The Greek philosophers are often spoken of (at least in physics circles) as being great philosophers but rotten scientists. One gets the strong feeling, in reading such accounts, that because of the dogma imposed on people by the ancient Greeks and the Church, scientific progress was held back for a thousand years or so.

So that, I assert, is what people generally believe about this aspect of scientific history. Is this a straw man? Perhaps, but it is close to what I believed until I started looking more closely at scientific history. In later postings we will see how much of this popular story stands up to closer scrutiny.


Trackback URL for this entry is: The myth concerning circular orbits
Excerpt: In this posting we will examine the myth that the Copernican revolution was hampered by its insistence that the orbits...
Weblog: Mano Singham's Web Journal
Tracked: April 25, 2005 08:52 AM


Hi, Mano,

I never have the time to give your entries the attention they deserve, so I'm making a Mano folder to save them (and since I'm really electronically challenged, this will be a task). But I figure at some point I'll have a folder good for a science class. Except you won't be there.

By the way, do you have any idea where the current (new) pope stands on science? I can't imagine anything good, but I really don't know. I know he's been hell on the liberation church, which for my money is the only thing Catholicism has to be proud of these days. It's okay for me to say that, I'm an ex. Cathie

Posted by catherine on April 19, 2005 02:06 PM

I have no idea where he stands on science. It will be interesting to see the reaction to his election.

Posted by Mano Singham on April 19, 2005 02:55 PM