Erik Høg
Abstract
The lecture presents the structure of the universe and the evolution of science during 5000 years, especially concerning the distances in the universe and the great changes which took place in the cultures of Babylon and ancient Greece up to modern Europe. For Dante Alighieri (1265-1321) the spiritual cosmos contained the Heavens, Earth, and Hell, and it was compatible with the physical cosmos known from Aristotle (384-322 B.C.). Dante's many references in his Divine Comedy to physical and astronomical subjects show that he wanted to treat these issues absolutely correctly. Tycho Brahe proved three hundred years later by his observations of the nova in 1572 and of comets that the heavenly spheres do not really exist. Since then it has become more and more difficult to reconcile the ancient ideas of a unified cosmos with the growing knowledge about the physical universe. Ptolemy, who lived more than a thousand years before Dante, derived a radius of 20,000 earth radii for the sphere of fixed stars. This radius of the visible cosmos at that time happens to be nearly equal to the true distance of the Sun, or 14 micro-light-years. Today the radius of the visible universe is a million billion (10 to the power 15) times larger than both Ptolemy and Tycho Brahe believed.