The Cosmic Timeline

From the initial state of the universe to the creation of structures and matter, through to the final de Sitter space

Planck Epoch

0 to 10⁻⁴³ seconds

The universe exists at the smallest possible scales where all fundamental forces are unified. The concepts of space and time as we know them break down.

Key Event: Quantum gravity dominates all physics

Temperature: ~10³² K

Grand Unification Epoch

10⁻⁴³ to 10⁻³⁶ seconds

Gravity separates from the other fundamental forces. The strong nuclear force remains unified with the electroweak force.

Key Event: Gravity decouples from the other forces

Temperature: ~10²⁹ K

Inflationary Epoch

10⁻³⁶ to 10⁻³² seconds

The universe undergoes exponential expansion, increasing in size by a factor of at least 10²⁶. This period solves several cosmological problems and creates the seeds for future structure formation.

Key Event: Exponential expansion flattens the universe and creates quantum fluctuations that will become galaxies

Temperature: Drops dramatically during inflation

Particle Genesis Epochs

10⁻³² seconds to 3 minutes

A series of phase transitions where fundamental particles and forces acquire their distinct identities.

Electroweak Epoch (10⁻³² to 10⁻¹² seconds): Strong force separates from electroweak force

Quark Epoch (10⁻¹² to 10⁻⁶ seconds): Universe is a quark-gluon plasma; too hot for hadrons to form

Hadron Epoch (10⁻⁶ to 1 second): Quarks combine to form protons, neutrons, and other hadrons

Lepton Epoch (1 second to 3 minutes): Leptons dominate the energy density of the universe

Temperature: Ranges from 10¹⁵ K to 10⁹ K

Nucleosynthesis and Structure Formation

3 minutes to 1 billion years

The universe cools enough for atomic nuclei and eventually atoms to form, followed by the emergence of cosmic structures.

Big Bang Nucleosynthesis (3 to 20 minutes): Protons and neutrons fuse to form light elements: 75% hydrogen, 25% helium, and trace amounts of lithium and deuterium

Photon Epoch (20 minutes to 380,000 years): Radiation dominates the universe; matter and radiation remain coupled

Recombination (380,000 years): Electrons combine with nuclei to form neutral atoms; universe becomes transparent (CMB radiation is released)

Dark Ages (380,000 to 150 million years): Universe is filled with neutral hydrogen gas; no light sources exist

Reionization (150 million to 1 billion years): First stars and galaxies form, emitting radiation that reionizes the hydrogen gas

Temperature: Drops from 10⁹ K to just a few degrees above absolute zero

Stellar Era and Cosmic Future

1 billion years to ultimate fate

The universe evolves through stellar formation and galactic development toward its eventual end state.

Stellar Era (1 billion to 10¹⁴ years): Stars form, evolve, and die; galaxies assemble; heavy elements are created in stellar interiors and supernovae

Degenerate Era (10¹⁴ to 10⁴⁰ years): Star formation ceases; remaining objects are brown dwarfs, white dwarfs, neutron stars, and black holes

Black Hole Era (10⁴⁰ to 10¹⁰⁰ years): Black holes dominate the universe, slowly evaporating via Hawking radiation

Dark Era (after 10¹⁰⁰ years): All black holes have evaporated; universe contains only isolated subatomic particles and radiation

Final State - De Sitter Space: The universe approaches a maximally symmetric, empty state dominated by the cosmological constant, undergoing exponential expansion forever

Cosmic Summary

The universe has progressed from an incredibly hot, dense state where forces were unified, through a series of phase transitions that gave rise to particles, nuclei, atoms, and eventually the complex structures we see today. The initial quantum fluctuations during inflation seeded all future structure. As the universe continues to expand, it appears to be heading toward a final state as empty de Sitter space, where the cosmological constant drives exponential expansion, eventually isolating all remaining particles beyond each other's cosmic horizons.