* 1609: Kepler published his first two laws of planetary motion, based on his analysis of Tycho Brahe's observations. These laws described the elliptical orbits of planets and the speed at which they move around the Sun.
* 1619: Kepler published his third law of planetary motion, which relates the orbital period of a planet to the size of its orbit.
* 1619: In the same work that outlined his third law, Kepler also theorized about the *physical causes* of planetary motion, suggesting a force emanating from the Sun that pushed planets around. This was a step towards the concept of gravity, although his explanation wasn't quite correct.
Therefore, while Kepler's work on planetary motion can be pinpointed to specific dates, it's difficult to define a specific date for a "universe theory." His work provided the foundation for Newton's later development of the law of universal gravitation, which gave a more complete explanation of the workings of the solar system and the universe.
