Quotation of the day
Aristotle argued that an object needed constant attention from a source of motion in order to keep moving. … In the same fashion, Aristotle suggested, the planets revolved around the earth due to the constant force exerted on them by a “prime mover.” To the medieval monks of Paris [especially Jean Buridan, 1300–58, and Nicholas Oresme, 1323–82], this sounded like nonsense. Specifically, they questioned why God should have to continuously intervene to impart motion to one of the planets when a simple impetus of motion from the start of the cosmos should have been sufficient to last for the duration of the universe. What may seem today to sound like a theological quible actually cleared the cobwebs of Greek preconceptions out of the European mind, allowing a more abstract approach to the theory of motion, so that by the time of Leonardo da Vinci and Copernicus, the idea of inertial motion, imparted by and depending only an initial force, was virtually taken for granted by astronomers.
— John Farrell, The Day Without Yesterday: Lemaître, Einstein, and the Birth of Modern Cosmology (New York: Thunder’s Mouth Press, 2005), pp. 42–43
3 comments Christopher Heard | history, science and technology, theology
“imparted by an depending only”?
There is a word missing, perhaps “object.”
Thanks for the heads-up, John. Actually, I only left out one letter: “imparted by and depending only …”
“imparted by and depending only an initial force” should probably be “imparted by and depending only on initial force.”
I’m not sure the eminent author is quite right. How were the planets conceived in the 1300s? Because they don’t actually appear to circle anything – they double back on themselves, as seen from the point of view of an observer on Earth. The idea of a constantly applied force therefore makes more sense, until/unless you come to see the planets as circling the sun rather than the Earth, and the doubling-back as an illusion.
Also, the time of Copernicus was not the time of Da Vinci – it can look that way if you look at the dates (Leonardo 1452-1519, Copernicus 1473-1543), but in fact Copernicus knew that the Earth and planets went round the sun, and Leonardo did not.