massive-neutrino hypothesis

The massive-neutrino hypothesis suggests that neutrinos, which are subatomic particles with no electric charge and very little mass, might contribute significantly to the universe's mass. These particles, subject to the weak force, were theorized by Wolfgang Pauli in 1930 to explain energy loss in radioactive decay.1

Cosmology studies the universe's evolution, and the Big Bang model posits that the early universe was a hot fireball of radiation and neutrinos. Neutrinos, interacting weakly with matter, form the cosmic neutrino background, pervading the universe with an estimated 10⁸ low-energy neutrinos per cubic meter. While their mass is extremely small, the sheer number of neutrinos could account for a portion of the universe's nonluminous "dark matter". Experiments are ongoing to precisely measure neutrino masses and understand their role in cosmic evolution.2345