In 1930, physicist Wolfgang Pauli proposed the existence of a new, unseen particle—later named the neutrino—to solve a troubling mystery in beta decay, a type of radioactive decay where a neutron transforms into a proton and emits an electron.
At the time, experiments showed that the energy and momentum of the emitted electrons varied unpredictably, which violated the principle of conservation of energy and momentum, fundamental laws of physics. To resolve this, Pauli suggested that another particle was also emitted during beta decay—one that was:
- Neutral (carrying no electric charge),
- Extremely light or possibly massless,
- Very weakly interacting with matter, making it difficult to detect.
This hypothetical particle would carry away the “missing” energy and momentum, restoring the balance in the decay process. Italian physicist Enrico Fermi later incorporated the idea into his theory of beta decay, and coined the term “neutrino” (meaning “little neutral one” in Italian).
Neutrinos were finally detected experimentally in 1956 by Clyde Cowan and Frederick Reines, confirming Pauli’s bold hypothesis.
Key facts about neutrinos:
- There are three types (or flavors): electron, muon, and tau neutrinos,
- They interact only via the weak nuclear force and gravity, making them extremely hard to detect,
- Neutrinos are produced in nuclear reactions, such as in the Sun, nuclear reactors, and supernovae,
- Their study has led to discoveries like neutrino oscillations, showing that neutrinos have tiny but nonzero mass.
Pauli’s proposal of the neutrino was a pivotal moment in modern physics, preserving fundamental conservation laws and opening a new window into the subatomic world.