What is a "thought experiment"? How did Newton's laws of motion lead to space travel? Why were Newton and fellow scientist Robert Hooke sworn enemies? Isaac Newton lived at a time called "The Enlightenment", when scholars began to question traditional ideas and to use reason to think of their own theories. He used mathematics, experiments and scientific method to test his ideas, and in doing so became the leading scientist of his day. His groundbreaking work changed the way we understood the world.