Cosmology Theories and Arguments

The Big Bang Theory

  • Universe began ~13.7 billion years ago with the Big Bang.
  • All matter and energy were concentrated in a single, hot, chaotic mass.
  • The Big Bang caused rapid expansion; matter, energy, and space emerged from this event.
  • Early universe: hot and dense, cooled as it expanded.
  • Protons, neutrons, and electrons formed within seconds.
  • Hydrogen formed after a few minutes; nuclear fusion created helium.
  • Gravity caused matter to clump, forming stars, galaxies, and other structures.

Evidence for the Big Bang

  • Background Radiation: Discovered in 1964, a uniform background radiation of ~3 K, is left over from the Big Bang.
  • Distant galaxies: Light from distant galaxies shows the universe as it was shortly after the Big Bang.

First-Cause Cosmological Arguments

  • Proposed by St. Thomas Aquinas.
    A. Things cause other things to happen.
    B. Everything that happens/moves has a cause.
    C. Chain of causes can't go back forever.
    D. There must be a first cause (God).
    E. Therefore, God exists.

The Kalām Cosmological Argument

A. If something starts to exist, something caused it.
B. The universe can't have existed forever.
C. Universe started to exist.
D. Something caused the universe to exist.
E. The best explanation is God.
F. Therefore, God exists.

Multiverse

  • The multiverse theory suggests other universes may exist beyond our observable universe.
  • Inflationary cosmology suggests that after the Big Bang the universe grew rapidly, and this could continue creating bubble universes.

Oscillating Universe Theory

  • Combines Big Bang and Big Crunch: the universe exists between these events.
  • Postulates the universe expands then contracts, potentially bouncing back due to quantum gravity.
  • Current CMBR measurements suggest continuous expansion potentially leading to a Big Freeze or Heat Death.
  • Dark energy: If dark energy's behavior differs from current understanding, the Oscillating Universe Theory could be viable.

Steady-State Theory

  • Proposed as alternative to Big Bang, suggests the universe has always existed and remains uniform.
  • Key Ideas:
    1. Universe is eternal with no beginning or end.
    2. Universe stays the same overall.
    3. Matter is continuously created.
    4. Universe is uniform in all directions and times.
    5. Universe expands smoothly at a constant rate.

Evidence Against Steady-State Theory

  1. Cosmic microwave background radiation (CMBR): Indicates a hot, dense origin.
  2. Accelerating expansion: Distant galaxies recede faster, implying a finite age and influence of dark energy.