The Big Bang should have left an empty universe — nobody knows why matter survived

The problem

Every particle has an antiparticle, and they are created and destroyed in pairs — so the early universe should have ended as pure light, with no atoms left. Instead, some unknown mechanism left roughly one extra matter particle per billion pairs, and that residue is everything we see. Physics does know one loophole: matter and antimatter can behave slightly differently ('CP violation'), discovered in kaons in 1964 — but the amount predicted by the Standard Model is many orders of magnitude too small to account for the observed asymmetry. In 2025 the LHCb experiment at CERN opened a new front, observing CP violation for the first time in baryons — the particle family that includes protons and neutrons — and it is still far too small to explain the cosmos.

Why it matters

This is the question of why anything exists rather than nothing. The mechanism that spared matter must involve physics beyond the Standard Model, and finding it would expose that new physics.

Progress so far

• 1928Paul Dirac's equation predicts antimatter; Carl Anderson discovers the positron in 1932
• 1964CP violation discovered in kaon decays (Cronin and Fitch, 1980 Nobel Prize)
• 1967Andrei Sakharov formulates the three conditions for generating a matter excess
• 1973Kobayashi and Maskawa build CP violation into the Standard Model, predicting six quarks (2008 Nobel Prize)
• 2025LHCb observes CP violation in baryon decays for the first time, published in Nature — still far too small to explain the cosmos

References

1. CERN — Dirac's prediction, Anderson's positron, and the one-in-a-billion survival puzzle
2. Nature (LHCb Collaboration, 2025) — first observation of CP symmetry breaking in baryon decays