George Saliba


On his book Islamic Science and the Making of the European Renaissance

Cover Interview of October 22, 2009

A close-up

I use the example of Copernicus, who literally picked up from Arabic texts almost all of the mathematical theorems he needed for the construction of his astronomy; these theorems were not found in the classical Greek texts.

When you mention Copernicus everybody gets a little jumpy, because we attribute to him the discovery of the earth moving around the sun.  That Copernicus did not get from any Islamic astronomer that I know of.  No Islamic astronomer I know of would believe in heliocentrism, or would allow a cosmology that is heliocentric.  None of them, including Copernicus, had the ability to explain the physical structure of the universe—that explanation depended on an essential law that was yet to be discovered by Newton, a hundred years after Copernicus.

Yet, to explain how a planet moves around the sun, Copernicus needed the mathematical mechanisms that accommodate the movements of the planets.  He needed a predictive model, to tell where the planet would be seen from the earth, at such and such a time.  If you ask the question of where the planet will be seen from the earth, then you are already solving the problem for an earth-centered universe.  And all of those answers were already found in the Islamic domain.

The question remains.  Why did Copernicus do that?  There are many people who answer that in so many different ways.  But none of them is really cosmologically convincing.  Because you would have to account for the force that holds the planets attached to the sun.  Even Kepler, who comes after Copernicus, who should really be called the father of modern astronomy, even he was thinking that planets are attracting each other like magnets.  Kepler used magnetism as a metaphor of that attraction because he still did not yet have Newton’s universal law of gravitation.

On the other hand, if you only think of it mathematically, it is irrelevant whether the center of the universe is at the sun or at the earth.  This is how all the mathematics that was developed in the Islamic domain could be simply turned around and made heliocentric by Copernicus.