Tuesday, January 20, 2009

Kepler on God and the physical world

Historian of science, Owen Gingerich, has a nice essay in Nature (Jan 1st, 2009) on the early impact of telescope on understanding our place in the universe. One of the key departures from the past: observations of stars and planets tell you something real (physical) about the world - and are not simply for calculations:
Galileo's persuasiveness was helped along by Kepler, whose landmark volume of theoretical astronomy was also published in 1609. His aptly named Astronomia nova or 'New Astronomy' relied heavily on looking at the physical causes of planetary motion — a critical departure from the past, when astronomers used strictly geometrical modelling to explicate the heavens. Even Kepler's teacher and mentor, Michael Maestlin, urged him to forget about physics and stick to astronomy (that is, geometry). But Kepler believed in a physically real cosmos, and even ahead of Galileo advocated the Sun-centred system.

Heliocentrism as it had come down from Copernicus, however, was flawed. Copernicus used entirely different geometrical models for the latitudes of planets than for the longitudes, whereas for a physically real system, the same model should work for both coordinates. According to Copernicus, the planets moved in circles (the main ones eccentrically placed with respect to the Sun), and Earth did not move faster when closest to the Sun. It was Kepler's requirement for plausible physical explanations that drove him ultimately to postulate an ellipse as the basic form of planetary orbits, ironing out these difficulties.

And here is a fantastic quote from Kepler that is equally applicable to evolution-creation debates today. In the introduction to Astronomia nova, Kepler wrote:
"Perhaps there is someone whose faith is too weak to believe Copernicus without offending his piety. Let him stay at home and mind his own business. Let him assure himself that he is serving God no less than the astronomer to whom God has granted the privilege of seeing more clearly with the eyes of the mind".
All we have to do here is to replace Copernicus with Darwin (or evolution) and astronomer with biologist, and we are all set for the 21st century. Ok - so science has become more professionalized in the last 400 years - but the quote is still applicable for many.

If you have subscription to Nature, you can read the full article here.


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