Cosmic Neutrino Background

The Cosmic Neutrino Background (CνB) is a faint glow of neutrinos—tiny, nearly massless particles—that filled the universe shortly after the Big Bang. These neutrinos decayed and traveled through space for billions of years, so they form a background "rain" of particles that permeates the cosmos. Unlike the more famous cosmic microwave background (light), the CνB is extremely difficult to detect directly because neutrinos rarely interact with matter. Its existence is a key prediction of Big Bang cosmology, offering insight into conditions in the universe’s earliest moments and helping us understand fundamental physics.