The idea that the orbits of celestial bodies were circular was one of the most persistent ideas in the history of science. It is common to hear that ancient astronomers thought that the planetary motion must be uniform and circular because of the divine nature of celestial bodies. In this seminar I will argue for an alternative possibility: that the Epicycle and Deferent System, which was the particular way in which ancient astronomers fulfilled the Platonic demand, could have been suggested not by the external influence of some conception of the divine, but by the solution to a specific mechanical problem, namely how to represent with gears the regular periods of the celestial bodies known by the Babylonians. I will show that the latest research on the Antikythera Mechanism, an ancient astronomical geared device, allows us to suggest that epicycles and deferents entered Greek astronomy, not because of natural philosophical considerations, but because of the application of geometrical images of gears to an astronomical problem. Thus, I will present the history of the discovery of the Antikythera Mechanism, as well as its main functions and structure. Then I will show that some particular details suggest that the Epicycle and Deferent System as an astronomical solution could have been inspired in solving some mechanical problems like those posed by the device. Finally, I will conclude that it is plausible to think that it was by consideration of gears and not of gods that astronomers came up with the circular orbits for the epicycle and deferent model.
Dr Christián C. Carman is Associate Professor and Researcher at the National University of Quilmes (Argentina) and Researcher at the National Council of Scientific and Technological Research (Argentina).