Module 11 The Big Bang Theory - The Big Bang Theory Notes

Module 11: The Big Bang Theory

Early Research into the Origin of the Universe

  • Georges Lemaître (1894-1966)

    • Proposed the idea of all matter condensing into a "primeval atom".
    • Developed an early fission model, though it was later found incorrect.
    • Contributed to the formulation of Hubble's Law, outlining the expansion of the universe.

  • George Gamow (1904-1968)

    • Suggested a fusion model, emphasizing the combination of atoms.
    • Argued that the universe could not maintain high temperatures for extended periods.
    • Stated that most elements were formed through fusion in stars.
The Big Bang Begins and Inflation

  • Beginning of the Universe

    • Occurred approximately 13.8 billion years ago with hot particles mixed with light/energy.
    • Tiny particles combined to form atoms, leading to the creation of the first elements, stars, and galaxies.

  • Cosmic Inflation

    • During this early stage, the universe expanded faster than the speed of light for a brief moment.
    • Inflation explains the flatness observed in the universe today.
    • It possibly amplified density differences at the quantum level.
    • The end of inflation transferred energy into matter and light, culminating in the Big Bang.
The Big Bang – First Steps
  • First Second Post-Big Bang
    • Universe comprised a hot primordial soup of light and particles.
    • Nucleosynthesis occurred shortly after, where protons and neutrons collided.
    • Earliest elements formed:
    • Hydrogen
    • Helium
    • Small amounts of Lithium and Beryllium.
    • By five minutes post-Big Bang, helium formation nearly complete, but atomic nuclei couldn’t capture electrons due to extreme heat, causing opacity in the universe.
The Big Bang – Recombination
  • Epoch of Recombination
    • Occurred 380,000 years after the Big Bang as the universe cooled.
    • Atomic nuclei were able to capture electrons, allowing light to travel freely for the first time.
    • The formation of atoms emitted light, which we can still detect as the cosmic microwave background radiation, the oldest observable light in the universe.
The Big Bang – Dark Ages
  • Dark Ages
    • A period where the universe became opaque again for about 200 million years.
    • Only hydrogen, helium, and trace heavier elements existed during this time.
The Big Bang – Star Formation
  • First Stars
    • Gas distribution throughout the universe was non-uniform leading to clumpy formations.
    • Denser regions attracted more matter, increasing density and temperature, triggering nuclear fusion.
    • These first stars were significantly massive (30 to 300 times that of the Sun) and millions of times brighter.
    • Over time, these stars formed the first galaxies over several hundred million years.
The Big Bang – Reionization
  • Reionization
    • Starlight was initially scattered by gas surrounding the first stars, limiting its reach.
    • Ultraviolet light from stars eventually ionized hydrogen atoms, breaking them into electrons and protons, making the universe transparent.
    • By approximately 1 billion years post-Big Bang, the universe had transformed to a state where light travel was ubiquitous.
Evidence for the Big Bang

  • Patterns of Galaxies

    • Observations show galaxies are moving away, indicated by the redshift of their spectra.
    • Spiral galaxies form from collisions with other galaxies due to their expansion.

  • Cosmic Microwave Background Radiation

    • The remnant radiation from the Big Bang is still detectable.

  • Composition of Matter

    • The universe's composition matches Big Bang predictions: approximately 75% hydrogen and 25% helium.
The Universe - Current and Future
  • Initial assumptions of the universe's expansion slowing down were proven incorrect.
  • In 1998, discoveries of distant supernovae revealed they were fainter than expected, indicating a faster expansion rate.
  • The concept of dark energy was introduced to explain the acceleration of the universe's expansion.
  • Current cosmological theories suggest the universe is likely to continue expanding indefinitely.