The golden age of physics was the 19th century. According to Emilio Segrè, in Italy it came to an end in the 18th century, after the time of Alessandro Volta. He reported in his autobiography that Enrico Fermi felt that it was coming to an end in 1933. A golden age of physics began with the simultaneous discovery of the principle of the conservation of energy in the mid-19th century. A golden age of physics was the years 1925 to 1927. The golden age of nonlinear physics was the period from 1950 to 1970, encompassing the Fermi–Pasta–Ulam–Tsingou problem and others. This followed the golden age of nuclear physics, which had spanned the two decades from the mid-1930s to the mid-1950s. A golden age of physics started at the end of the 1920s.