This thread got me looking at Neutrinos for the very first time. They are the most recently discovered fundermental particles, the Tau Neutrino was first observed only 11 years ago in 2000. The neutrino was first postulated in 1930 by Wolfgang Pauli to preserve the conservation of energy, conservation of momentum, and conservation of angular momentum (spin) in beta decay. This was done by adding an undetected particle that Pauli termed a "neutron" to the proton and electron already known to be products of beta decay: n0 → p+ + e− + νe He theorized that an undetected particle was carrying away the observed difference between the energy, momentum, and angular momentum of the initial and final particles. The electron neutrino is said to be associated with the electron because in the above beta decay they are produced together. Since Neutrinos interact very weakly with ordinary matter it appears that matter is being continually converted all the time through beta decay into something which no longer interacts with matter.