The Big Bang
The origin and early evolution of our expanding universe.
Overview
The Big Bang theory describes the universe expanding from a hot, dense state ~13.8 billion years ago — not an explosion in space, but expansion of space itself.
Why It Matters
The Big Bang is the foundation of modern cosmology, explaining the CMB, elemental abundances, and large-scale structure.
Scientific Explanation
Run the expansion backward: early universe was hot and dense. At t ~380,000 yr, electrons combined with nuclei (recombination), releasing the CMB. Nucleosynthesis in first minutes made H, He, Li. Inflation (10⁻³⁶ s) explains horizon and flatness problems.
Historical Background
Hubble's expansion (1929). Gamow predicted CMB (1948). Penzias & Wilson detected CMB accidentally (1965, Nobel). COBE, WMAP, Planck refined parameters.
Visual Explanation
Raisin bread analogy: raisins (galaxies) move apart as dough (space) expands — no center, every point sees others receding.
Key Discoveries
- ✦ Hubble's law: universe expands
- ✦ CMB discovery confirms hot early universe
- ✦ Planck: age 13.8 Gyr, flat, 68% dark energy
- ✦ Primordial gravitational waves sought in B-mode polarization
Important Astronomers
Interactive Simulation
Visualize cosmic expansion with raisin bread analogy.
Expansion of the Universe — Visual Lab
Open in Visual Lab →Reflection Prompt
We are the universe observing itself. Does cosmology change your sense of meaning?
Write in Journal →