Matter and antimatter annihilate when they meet. If the early universe made equal amounts of each, they should have mostly erased one another, leaving radiation—and no stars, planets, or people. Yet a little matter remained.
Experiments show that some particles and antiparticles behave slightly differently, a phenomenon called CP violation. CERN’s LHCb experiment measures these asymmetries with increasing precision. Such effects are real, but the known sources in the Standard Model are too small to account for the universe’s matter surplus.
Physicists therefore search for additional processes that could have tipped the balance in the first moments of cosmic history. The precise mechanism is unknown, and recreating the full early-universe conditions in a laboratory is impossible. Measurements of rare particle decays may reveal missing clues without directly replaying the beginning.