Lecture Notes: Origin of the Universe and the Big Bang Theory

Introduction

• The universe encompasses everything — particles, galaxies, space, time, and life.
• Multiple theories and myths exist regarding its origin.
• The Big Bang Theory is the most widely accepted explanation for the universe's beginning.

Big Bang Theory

• Universe began as a hot, infinitely dense point (similar to a supercharged black hole).
• Occurred approximately 13.7 billion years ago.
• The "Big Bang" was the explosion that created all matter, energy, space, and time.

Two Major Stages in Universe's Evolution

1. Radiation Era

• Dominated by radiation post-Big Bang.
• Consists of smaller stages known as epochs.

Key Epochs:

• Planck Epoch:

  • No matter existed, only energy and a superforce (precursor to the four forces of nature).
  • Gravity split away from the superforce.

• Grand Unification Epoch:

  • Involved three unified forces of nature.
  • Strong nuclear force separated during this epoch.

• Inflationary Epoch:

  • Rapid expansion of the universe.
  • Universe grew from atomic size to grapefruit size almost instantly.
  • Contained electrons, quarks, and particles.

• Electroweak Epoch:

  • Electromagnetic and weak forces split.

• Quark Epoch:

  • All universe's ingredients present, but too hot for subatomic particles to form.

• Hadron Epoch:

  • Universe cooled; quarks formed protons and neutrons.

• Lepton and Nuclear Epochs:

  • Protons and neutrons fused to create nuclei.
  • Formation of first chemical element, helium.

2. Matter Era

• Defined by presence and predominance of matter.
• Spans billions of years and includes today's universe.

Key Epochs:

• Atomic Epoch:

  • Universe cooled, allowing electrons to attach to nuclei (recombination).
  • Formation of the universe's second element, hydrogen.

• Galactic Epoch:

  • Formation of atomic clouds.
  • Clusters of atoms, seedling of galaxies.

• Stellar Epoch:

  • Formation of stars.
  • Stars convert helium and hydrogen into other elements — building blocks for planets, moons, and life.

Conclusion

• The universe's development through various stages made life as we know it possible.
• Many questions remain about the universe's origins; answers are likely to emerge over time.