Aristotelian physics: why objects fall to the center
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In class, young Rafal recites the canonical proof of geocentrism: “As Aristotle said, heavy objects go down. Objects fall to the ground because the Earth is the lowest sphere at the center of the Universe.” The argument is unanimous. No one then imagines it could be wrong.
The subject in depth
Aristotle’s physics rests on the idea of natural place [Wikipedia] . Each of the four earthly elements has a place that belongs to it: earth at the bottom, then water, air, and fire at the top. An object away from its natural place seeks to return to it, which explains why a stone falls and a flame rises.
From this followed a seemingly airtight proof of geocentrism: if heavy bodies fall downward, and “down” is the center of the world, then the Earth, made of the heavy element par excellence, must lie at that center, motionless. The motion of falling thus served as a cosmological argument.
This physics is wrong, but not absurd: it faithfully describes everyday experience. Its error is to confuse local down (the direction of gravity) with an absolute center of the Universe. It took Galileo, then Newton with universal gravitation, to understand that objects fall toward the mass of the Earth, not toward a privileged point of the Cosmos. The same cause then explains both the fall of apples and the orbit of the Moon.
Going further
Sources
- Physics (Aristotle) (Wikipedia)
- Arthur Koestler, The Sleepwalkers (1959)
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