Overview
This lecture explores the origins and evolution of the universe from the Big Bang through the first million years, covering major cosmological theories, key physics concepts, formation of matter, and the unresolved mysteries of dark matter and energy.
The Origin of the Universe
- The universe began 13.8 billion years ago with the Big Bang, potentially from "nothing."
- Theories include inflation, eternal inflation (multiverse), Big Bounce cycles, and string theory's dimensional collisions.
- Space and time are intrinsic to our universe; before the Big Bang, these may not have existed.
The Early Universe: Plank Era and Grand Unification
- The Plank Era lasted ~10⁻⁴⁴ seconds after the Big Bang, governed solely by gravity at quantum scales.
- Quantum gravity theories (graviton, loop quantum gravity, string theory) attempt to unify general relativity and quantum mechanics.
- General relativity and quantum mechanics are incompatible in this era; a unified theory is still sought.
- Following the Plank Era, three forces (strong, electromagnetic, weak) were unified; gravity separated first.
Inflation and Its Consequences
- Inflation is a period of exponential universal expansion, resolving the horizon, flatness, and monopole problems.
- Quantum fluctuations during inflation became the seeds for galaxies and large-scale structure.
- After inflation, the universe cooled and forces separated further, setting conditions for matter formation.
Formation of Matter and Forces
- The four fundamental forces: gravity, electromagnetism, strong nuclear, weak nuclear.
- The Standard Model of particle physics: six quarks, six leptons, force-mediating bosons, and the Higgs boson.
- Higgs field gives particles mass; experimentally confirmed in 2012.
Baryogenesis and Matter-Antimatter Imbalance
- Early universe saw nearly equal creation of matter and antimatter, which annihilated each other.
- Subtle asymmetries (possibly from weak force or unknown neutrino types) favored matter, allowing the universe to exist.
Nucleosynthesis and First Elements
- In the first few minutes, Big Bang nucleosynthesis created hydrogen, helium, and trace lithium.
- Ratios depend on initial proton/neutron balance, crucially shaped by particle masses.
Formation of Atoms and Light
- At around 380,000 years, electrons combined with nuclei to form neutral atoms.
- Universe became transparent; photons from this era form the cosmic microwave background (CMB).
Large Scale Structure and Dark Components
- Dark matter (non-luminous, interacts via gravity) shapes galaxy and cluster formation; visible matter is only ~5% of the universe.
- Dark energy, discovered via supernova studies, drives accelerated expansion and comprises ~68% of the universe.
Key Terms & Definitions
- Big Bang — the explosive event that marks the beginning of the universe.
- Inflation — rapid exponential expansion in the early universe.
- Plank Era — the earliest time interval where quantum gravity dominates.
- Standard Model — framework describing fundamental particles and interactions (excluding gravity).
- Higgs boson/field — particle and field that give mass to other particles.
- Dark Matter — unseen matter detected via gravitational effects.
- Dark Energy — unknown energy causing universal expansion to accelerate.
- Cosmic Microwave Background (CMB) — relic radiation from the recombination era.
- Baryogenesis — process creating the matter-antimatter asymmetry.
Action Items / Next Steps
- Review particle physics basics, focusing on the Standard Model and Higgs mechanism.
- Read about cosmic inflation and evidence supporting it.
- Explore the cosmic microwave background and its significance.
- Research current searches for dark matter and dark energy candidates.