• What is the Big Bang Theory? 
  The Big Bang Theory explains the origin and expansion of the universe. It is also called the expanding universe hypothesis. 
• Evidence by Edwin Hubble (1920): Hubble discovered that galaxies are moving away from each other, indicating that the universe is expanding. 
• Key Stages of the Big Bang 
  • Singularity: Initially, all matter was concentrated in an extremely small, hot, and dense point called a singularity. 
  • Explosion and Expansion: Around 13.7 billion years ago, this tiny point exploded violently, causing the universe to expand rapidly. 
  • Energy to Matter: During expansion, energy converted into matter. 
  • Atom Formation: Within the first 3 minutes, the first atoms began to form. 
  • Universe Transparency: After 300,000 years, the temperature dropped to 4,500 Kelvin, allowing atoms to form freely and the universe became transparent. 

• Ongoing Expansion: The universe continues to expand today, but the expansion rate has slowed down since the initial burst. 
• Alternative Theory – Steady State: Fred Hoyle proposed that the universe is unchanging over time. However, increasing evidence supports the expanding universe theory instead. 
• Why is this important? 
  The Big Bang Theory is the most accepted scientific explanation of how the universe began and evolved, shaping our understanding of cosmology and the physical world. 

 Key Stages in the Evolution of the Universe