Copernicus and Tycho examined celestial physics purely to determine the Earth's mobility or immobility. The Copernican change of perspective made it unnecessary to revise the heavenly physics. Further, Galileo agreed with the old- fashioned viewpoint that the planets and the Earth moved circularly and uniformly around the Sun.
Modification of the old physical viewpoint followed an unusual course: the search for the mystical essence of the Universe. In the Secret of the Cosmos, Johann Kepler (1571-1630) imagined that God had used five regular polyhedra to establish the mutual distances of the six Copernican heavenly spheres. Kepler spent many years analysing Tycho's observational data in search of a more satisfying sense of the Universal architecture. The three planetary laws that Kepler discovered destroyed the circularity and uniformity of celestial motions, but implied a physical problem: how could the elliptical and non-uniform motion of a planet be produced? Kepler suggested that sunlight or magnetic force could be responsible for such motion.
The unification of terrestrial and celestial physics, partially attempted by Galileo, enabled Isaac Newton (1642-1727) to recognize that it was a universal principle that matter exerts a force of attraction on other matter, explaining perfectly why planets followed Kepler's laws. These laws were a natural consequence of the law of gravity and the three laws of motion that, in 1687, Newton included in his Mathematical Principles of Natural Philosophy. The new physics was the conceptual instrument which became indispensable for solving many astronomical problems. Sometimes, these problems led to unsuspected results: for example, the discovery of the planets Neptune (1846) and Pluto (1930). The path was opened for a new perception of the structure and future evolution of the Universe.