Overview
This lecture explains the origin and evolution of the universe, focusing on the Big Bang theory and the key eras and events that shaped everything we see today.
The Big Bang Theory
- The Big Bang theory is the leading explanation for the universe's origin.
- The universe began as a hot, infinitely dense singularity about 13.7 billion years ago.
- This singularity exploded, creating all matter, energy, space, and time.
Radiation Era
- The radiation era followed the Big Bang and was dominated by radiation rather than matter.
- It consisted of several epochs:
- Planck Epoch: Only energy and a unified superforce existed; gravity separated here.
- Grand Unification Epoch: Strong nuclear force split from the remaining forces.
- Inflationary Epoch: The universe rapidly expanded from atomic size to grapefruit size.
- Electroweak Epoch: Electromagnetic and weak forces split.
- Quark Epoch: All universe's ingredients present, but too hot for subatomic particles.
- Hadron Epoch: Universe cooled for quarks to form protons and neutrons.
- Lepton and Nuclear Epochs: Protons and neutrons fused into nuclei, forming helium, the first element.
Matter Era
- Defined by the presence and dominance of matter in the universe.
- Consists of three epochs:
- Atomic Epoch: Universe cooled so electrons attached to nuclei, forming hydrogen.
- Galactic Epoch: Hydrogen and helium formed clouds; gravity caused clusters, creating galaxies.
- Stellar Epoch: Stars formed within galaxies, producing heavier elements that became planets, moons, and life.
Key Terms & Definitions
- Big Bang Theory — The idea that the universe began from a hot, dense point and expanded.
- Singularity — An infinitely dense and small point from which the universe emerged.
- Epoch — A specific period or stage in the universe's development.
- Recombination — Process where electrons joined nuclei to form atoms.
- Superforce — Unified force encompassing all fundamental forces at the universe's beginning.
Action Items / Next Steps
- Review the sequence and significance of each cosmic epoch.
- Prepare to identify key cosmic events and their impact for future quizzes.