Concept of the Big Bang

• • The Big Bang Theory is the most widely accepted scientific explanation for the origin of the universe.
  • It states that the universe began about 13.8 billion years ago from an extremely hot, dense, and tiny point called a singularity.
  • This point expanded rapidly in an event known as the “Big Bang”.
  • It was not an “explosion in space” but rather an expansion of space itself.

Early Stages of the Universe

• • First second: Formation of fundamental particles (quarks, electrons, neutrinos).
  • First 3 minutes: Quarks combined to form protons and neutrons. Nuclei of hydrogen, helium, and lithium were formed (known as nucleosynthesis).
  • 380,000 years later: Universe cooled enough for electrons to combine with nuclei → atoms formed. This event is called recombination. Light could now travel freely (producing the Cosmic Microwave Background Radiation).
  • Millions of years later: Gravity pulled matter together to form stars and galaxies.

Evidence for the Big Bang

• • Redshift of galaxies (Hubble’s discovery): Galaxies are moving away from us, meaning the universe is expanding.
  • Cosmic Microwave Background Radiation (CMBR): Leftover “afterglow” from the Big Bang, discovered in 1965, uniform across the universe.
  • Abundance of light elements: Observed hydrogen and helium proportions in the universe match Big Bang predictions.

Alternative Theories (less accepted)

• • Steady State Theory: Suggested the universe has no beginning or end, and matter is continuously created. Rejected because it cannot explain CMBR.
  • Oscillating/Cyclic Universe Theory: Suggests the universe goes through repeated cycles of expansion and contraction.

Current Understanding

• • The Big Bang Theory, supported by strong observational evidence, remains the best model for the origin and evolution of the universe.
  • Ongoing research explores mysteries like dark matter and dark energy, which influence the universe’s expansion.