Cosmology and the Origins of the Universe

Jul 3, 2024

Cosmology and the Origins of the Universe

Lecturer: Professor Dave

Introduction

  • Cosmology: Subfield of astrophysics studying the origin and development of the universe.
  • Began to answer the universe's origins scientifically in the 20th century.
  • The universe began around 13.8 billion years ago from a single point, an event known as The Big Bang.

Common Misconceptions about the Big Bang

  • Many picture it as a loud explosion with complex objects flying out.
  • Reality: It's the emergence of simple elements from a single point, not formed planets and stars.

Current Models of the Universe's Birth

  • Understanding starts around 10^-36 seconds after the Big Bang.
  • Prior to that is largely speculative.
  • The initial state: A single point of immense energy.

Heisenberg Uncertainty Principle

  • Key to understanding the initial quantum fluctuation that allowed particles to emerge.
  • Energy and time are complementary variables.
  • Virtual particles pop in and out of existence constantly.

Formation of the Universe

  1. Planck Epoch (10^-43 seconds):
    • Universe size: minuscule
    • Temperature: Over 10^32 Kelvin
    • Four fundamental forces unified.
  2. Grand Unification Epoch (10^-43 to 10^-36 seconds):
    • Temperature cooled to 10^29 Kelvin
    • Gravity decoupled from other forces (electrostrong force).
    • Symmetry breaking led to different particles.
  3. Electroweak Epoch (10^-36 to 10^-32 seconds):
    • Strong nuclear force decouples from the electrostrong force.
    • Temperature: 10^28 Kelvin
  4. Inflationary Epoch (concurrent):
    • Universe expanded by ~26 orders of magnitude.
    • Produced hot plasma of quarks, anti-quarks, and gluons.
  5. Quark Epoch (10^-12 seconds):
    • Symmetry breaks, decoupling electromagnetic and weak nuclear forces.
    • Four distinct forces.
    • Particles gain mass (Higgs field).
  6. Hadron Epoch (10^-6 seconds to 1 second):
    • Quark-gluon plasma forms hadrons (protons and neutrons).
  7. Lepton Epoch (1 to 10 seconds):
    • Hadrons annihilate, leaving leptons and anti-leptons.
    • Matter asymmetry leaves a fraction of original matter.
  8. Photon Epoch (~600 light years later):
    • Protons and neutrons form hydrogen and helium (big bang nucleosynthesis).
    • Universe expands and cools.
  9. Recombination and Photon Decoupling (~377,000 years):
    • Electrons combine with nuclei to form neutral atoms.
    • Universe becomes transparent, radiation moves freely.
  10. Dark Ages (up to 150 million years):
    • Universe cools significantly.
    • No stars yet, just hydrogen and helium plumes.
    • Gravity pulls matter together, leading to future star formation.

Next Steps

  • Further discussions will dive into how stars formed and the subsequent transformations in the universe's structure.