Saturday, May 17, 2008

Ptolemaic Cosmology: The Life of a Garden

Ptolemy, an Alexandrian Greek, of the 2nd Century AD, articulated a cosmological theory that explained the apparent movement of the Sun and the planets. Beginning from an unshakable assumption that the universe was geocentric, which we know is not true, and an equally strong belief that the planets' movement was defined by perfect circles, again not true, Ptolemy was faced with a problem. Because the solar system is heliocentric and the orbits are elliptical, it happens from time to time that the planets appear to move backward in their paths. Ptolemy was faced with explaining this retrograde motion. He devised, or adopted, a system of cycles and epicycles wherein the plants move in small circular orbits on top of a large circular orbit. Through the years, in an attempt to match the observed motions of planets more accurately to this concept, very complex configurations were devised. The complexities of time in the garden reflect and rival the intricacies of Ptolemaic cosmology. [This picture shows a construct of the 14th Century Muslim astronomer Ibn al-Shatir; epicycles are piled upon epicycles. (the image is in the common domain)]

The Diurnal cycles of days in our gardens ride epicyclically upon the circle of the seasons that is the year; the circles of the years in turn years roll along the linear path that is the passage of time. Actually it could be more complicated. While Judaeo-Christian metaphysics suggest that time is a straight-line, that is not true of all Religions and Philosophies. Maybe there are cycles upon cycles upon cycles. The whole thing is frightening and makes the idea of designing a garden seem like an insurmountable task. I am not sure whether it is arrogance or ignorance that allows me to continue; I expect it's a good bit of both.

The good thing is that Nature is forgiving and the worst choices we make in the garden tend to have aspects with some redeeming value. If we focus our attention on what is working and looks good and try to fix the really bad problems, we can usually stumble onto a workable scheme. Anyway, thats my system.

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