Why Ptolemy?

I mean, he was wrong, right?

First of all because Bill liked the cool quotation.

Secondly, because it's kind of an obscure reference and we all like arcana.

But why choose someone whose theory is certainly wrong? Well, to begin with Ptolemy's explanation of the motions of the planets was accepted for over 1400 years. That's not a bad run; certainly no modern theory has lasted that long. And more to the point, it was the best theory available for all those years. Later developements notwithstanding, Ptolemy was doing good science with the data that was available to him.

The essence of science is that it can and does replace old and successful theories with new ones when the new ones are shown to be superior. When Tycho Brahe's much improved data and Kepler's laborious calculations showed that a heliocentric theory fit the data better, Ptolemy's days were numbered. But this is not a simple nor a painless process. Giordano Bruno was burned at the stake for espousing Copernicus's theory. Galileo spend the last years of his life under house arrest for similar reasons. But eventually Copernicus's view prevailed and Ptolemy's passed into history. But history is important. Ptolemy is important today not for the details of his theory but as an example of how science works.

Science is not a collection of facts nor a collection of true theories. It is a process, a process of continually replacing old ideas with new ones that better fit the facts. The transition from Ptolemy's ideas to Copernicus's is a dramatic and historically important example of that process.

Finally, I am sure that Ptolemy would have been one of the first to embrace the Copernican revolution had he had the chance to evaluate it. Though much evil was done in his name, Ptolemy himself was not a bigot nor overly fond of dogma. The actual details of his theory did not sit comfortably with the dogma of his day but he stuck with it because it worked.

( OK, its really somewhat more complicated than that. No one is perfect, not even heros. )

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Bill Arnett; last updated: 2000 Oct 10