Galileo Galilei was a great scientist, and therefore not afraid of causing controversy, even if he had to pay a great price. His public advocacy of the Copernican over the Aristotelian system of the universe flew directly in the face of biblical authority and ecclesiastical tradition. Condemned and placed under house arrest by the Inquisition, Galileo nonetheless devoted his last years to the completion of his Dialogues Concerning Two New Sciences, which deals with motion and the resistance of solids. The Two New Sciences, which Galileo called his most important work, may be regarded as the summary statement of a life devoted to scientific experimentation and free inquiry untrammeled by tradition and authority.