Aristotle in the 16th century

  In 1572 Tycho observed a star which suddenly appeared in the heavens (we now recognize this as an exploding star: a supernova). He noted that this ``new star'' did not change in position with respect to the other stars and should therefore be in the outer sphere of Aristotle's universe. But this was supposed to be an eternal, unchanging sphere! He published these observations in The Nova Stella in 1574. The same type of problems arose due to his observations of a comet which appeared in 1577, for he could determine that this object was farther than Venus again contradicting the Aristotelian idea that the universe beyond the Moon was perfect, eternal and unchanging. This is a case where better observations when pitted against the best theory of the time produced discrepancies which, in time, proved to be fatal to the current model and would eventually give rise to a better, more precise theory of the universe (see Sect. 1.2.1).

By this time also most of the Medieval approach to physics had been shed, though not completely. For example, the motion of a projectile was thought to be composed of an initial violent part (when thrown) and a subsequent natural part (which returns it to the ground). Still it was during this time that the importance of velocity and force in determining the motion of objects was realized.

The birth of new theories is not easy, however. In this case it was not until the late 17th century that a complete new view of the universe was polished and could be used as a tool for investigating Nature. By this time the Aristotelian doctrine was, finally, set aside. The first step in this long road was taken by Copernicus, the next by Johaness Kepler in his investigations of the motion of the planets and then by Galielo through his investigations on the nature of motion and his description of the solar system.