The Big Bang should have produced equal amounts of matter and antimatter, which would have annihilated each other completely, leaving no universe of matter at all. The known laws of particle physics do not explain the small asymmetry, thought to be about one extra matter particle per billion matter-antimatter pairs, that let the observable universe of stars, planets and everything else exist.
What would resolve this Discovery of a new source of charge-parity violation, beyond the small amount already observed in known particle interactions, sufficient to account for the measured cosmic matter-antimatter imbalance.
OpenParticle physics and physical cosmologyParticle Physics (Wikipedia)