There are three known flavors of neutrinos: the electron neutrino ν_e, the muon neutrino ν_μ and the tau neutrino ν_τ, named after their partner leptons in the Standard Model. Experiments probing energy scales thousands of times larger have not revealed the existence of any additional neutrinos therefore it is widely believed that there are only three. Also the anecdotal correspondance between the six quarks in the Standard Model and the six leptons, including three neutrinos, provides a hint that serves as further proof to some that there can be only three neutrinos. Nevertheless, proof that there are only three neutrinos remains an elusive goal of particle physics.

In a phenomenon known as neutrino oscillation neutrinos are observed to take a well defined mass only after a corresponding measurement. In fact, before measurement the flavor of the neutrino is considered to exist as a superposition of the multiple, generation 1 through generation 3 states. Whereas conventional wisdom implies that there are separate neutrino and antineutrino states, observation implies otherwise. Although, it cannot presently be ruled out that neutrinos have zero mass, the phenomenon of neutrino oscillation provides a compelling solution to the solar neutrino problem and seems to be experimentally validated. A neutrino with zero mass would not exhibit observable oscillation and therefore would not provide an explaination to the solar neutrino problem.