The Big Bang Theory describes how the Universe expanded from an extremely hot, dense state
about 13.8 billion years ago.
It wasn’t an explosion in space — it was an expansion of space itself.
Evidence of the Big Bang
Cosmic Microwave Background (CMB) — afterglow of the early Universe.
Redshift of galaxies — galaxies moving away shows expansion.
Elemental abundances — hydrogen, helium, lithium formation ratios match predictions.
What Happened in the First Moments?
10⁻³⁶ seconds: Inflation rapidly expands space.
3 minutes: Light elements form.
380,000 years: Atoms form → Universe becomes transparent.