- origin of the observable universe ~13.8 billion years ago
- initial state of extreme density and temperature, expanding and cooling ever since
- first seconds: quarks, leptons, photons; first minutes: hydrogen, helium nucleosynthesis
- cosmic microwave background radiation: snapshot of the universe at 380,000 years
- expansion governed by gravity, dark matter, dark energy
- stars formed from hydrogen clouds, nucleosynthesis forged heavier elements up to iron
- galaxies, clusters, cosmic web: large-scale structure emerged from quantum fluctuations
- the arrow of time and entropy originate here
- link to cosmology: the study of the universe’s origin, structure, and fate
- all geological time, all biology, all civilization trace back to this singular event