- The law of conservation of energy guarantees that in all isolated systems, the amount of energy before and after an interaction must be the same.
- In 1933, a nuclear (radioactive) process was discovered which appeared to violate this law. This process is called beta decay.
- During beta decay, a neutron inside the nucleus of an atom can change into a proton and an electron, but the energy of the initial neutron is greater than the energy of the proton plus the electron.
- This was extremely puzzling!
- Wolfgang Pauli, an Austrian physicist, hypothesized that another particle was created (but not seen) along with the electron and the proton. This particle would account for the missing energy. The theorized particle was named 'neutrino' by the Italian physicist Enrico Fermi.