The Manhattan Project proved that Einstein was correct in predicting that matter was a solid form of energy. With the power unleashed by fission, mankind developed first the atomic bomb, then the hydrogen bomb, and finally the fission reactor. While the first two only destroyed, the third provided condensed energy at a price. However, fission waste proved difficult to process or to store. By the end of the 20th century, the world still had no solution for the long-term disposal of fission waste.