Albert Einstein is known for his groundbreaking theories on nuclear fission, which fundamentally changed the field of physics. His theory of relativity reshaped our understanding of space, time, and energy, laying the groundwork for modern physics. Einstein's work also opened the door to advancements in technology and energy, influencing the development of nuclear power. Although not directly involved in the Manhattan Project, his letter to President Roosevelt in 1939 spurred the U.S. government to explore nuclear research. Einstein’s contributions have had profound effects on science and society, bridging theoretical concepts with practical applications.