This document discusses nuclear energy, including its history beginning with Einstein's discovery of the mass-energy equivalence equation, the process of nuclear fission, how nuclear reactors work to generate electricity, and debates around the advantages and disadvantages of nuclear energy. It notes that nuclear energy currently provides around 12-18% of the world's electricity but produces radioactive waste, and discusses open questions around its long term future as a source of energy given limited uranium reserves and risks of accidents or weapons proliferation.