Galileo's Battle for the Heavens
The Nova documentary, Galileo's Battle for the Heavens, presents Galileo as a heroic figure who challenged the status quo. This Galileo was a man whose guide was fact and experiment and not inherited wisdom; the father of modern science. In Against Method, Paul Feyerabend, also presents Galileo as a heroic figure who challenged the status quo. But for Feyerabend, Galileo's guide was often intuition not fact. Feyerabend believed that great science does not work the way it is painted in textbooks, and one support for this was that Galileo's commitment to Copernicism did not agree with facts known at the time. We now know that Copernicism was even contradicted by Galileo's personal observations (which he kept to himself). How do we reconcile these conflicting views of the same man.
The picture painted of a historical figure or event depends on which facts are considered and which are ignored. The NOVA documentary discussed Galileo's arguments for a sun-centered model of planetary motion. These arguments certainly had merit and were a challenge to the conventional view. What the program and website did not discuss was the scientific arguments against the sun-centered model. These arguments were equally compelling. There are necessary consequences of a moving earth. One of these would be the observation of stellar parallax (see Stellar Parallax). If the earth was moving relative to the sun it demands that viewers on earth be able to see some change in the relative positions of nearer and distant stars over the course of a year. No-one in Galileo's time was able to detect any change in the positions of the different stars. Stellar parallax was eventually detected, but not until 1838.
There was another, more pragmatic, criticism; the Copernican model of planetary motion did not seem to work better than the geocentric Ptolemaic model. It is often forgotten that it was Kepler who made the Copernican model work, and Galileo knew of his work and rejected it. We now know using computer analysis and modern statistical techniques that the original Copernican model was approximately as accurate as the Ptolemaic but performed worse for some planets. Galileo and Copernicus used perfect circles to model planetary motion. This would prevent their models from ever becoming much better than the geocentric model. .
The issues surrounding the Copernican controversy are not simple. There were powerful scientifically valid arguments against the Earth-centered models. But there were also powerful scientifically valid arguments against the sun-centered models. But for biographies such as Galileo's Battle for the Heavens the issues were simple and clear. Serious treatments of the controversy are not nearly as conclusive. In Against Method, Paul Feyerabend spends several chapters discussing Galileo and both the arguments and counter-arguments for Copernicism from a philosophical and scientific point of view. The noted philospher's conclusions are are at odds with the digested version of the controversy presented in the typical biography:
...while the pre-Copernican astronomy was in trouble (was confronted by a series of refuting instances and implausibilities), the Copernican theory was in even greater trouble (was confronted by even more drastic refuting instances and implausibilities).
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