Overview
This lecture explains the origin and development stages of the universe, focusing on the Big Bang theory and the sequence of cosmic epochs that shaped everything we observe today.
The Big Bang Theory
- The Big Bang theory posits the universe began as a hot, infinitely dense point about 13.7 billion years ago.
- This singularity exploded, marking the start of all matter, energy, space, and time.
Radiation Era
- The radiation era followed the Big Bang and was dominated by radiation rather than matter.
- The Planck epoch occurred first, containing only energy and the unified superforce.
- Gravity separated from the superforce at the end of the Planck epoch.
- The grand unification epoch saw the strong nuclear force split from the remaining forces.
- During the inflationary epoch, the universe expanded rapidly, growing from atomic to grapefruit size.
- The electroweak epoch ended with electromagnetic and weak forces splitting off.
- In the quark epoch, all fundamental particles existed, but it was too hot for them to form atoms.
- The hadron epoch allowed quarks to form protons and neutrons.
- During the lepton and nuclear epochs, protons and neutrons fused to create nuclei, forming helium, the first element.
Matter Era
- The matter era began once the universe could form elements and matter became predominant.
- In the atomic epoch, electrons attached to nuclei (recombination), forming hydrogen, the second element.
- Atomic clouds formed, and gravity caused these to cluster into clumps during the galactic epoch, seeding galaxies.
- Star formation marked the stellar epoch, the current stage of the universe.
- Stars fused hydrogen and helium into heavier elements, leading to the creation of planets, moons, and life.
Key Terms & Definitions
- Big Bang Theory — The scientific explanation that the universe began from an extremely dense and hot state.
- Singularity — An initial, infinitely dense point preceding the Big Bang.
- Epoch — A distinct period in the universe’s evolution.
- Superforce — The unified force before gravity separated from other fundamental forces.
- Recombination — The epoch when electrons combined with nuclei to form atoms.
Action Items / Next Steps
- Review the sequence of cosmic epochs and their defining events.
- Prepare to discuss how each epoch contributed to the universe's current structure.