Big Bang

The Big Bang is the prevailing scientific theory explaining the origin and evolution of the universe. It describes how the universe expanded from an extremely hot, dense state approximately 13.8 billion years ago to its current form.

The Theory

According to the Big Bang theory, the universe began as a singularity - a point of infinite density and temperature. This singularity expanded rapidly in an event called cosmic inflation, cooling as it expanded and allowing matter and energy to form.

Evidence Supporting the Big Bang

Multiple lines of evidence support the Big Bang theory:

• Cosmic Microwave Background (CMB): The afterglow of the Big Bang, discovered in 1965
• Abundance of Light Elements: The ratios of hydrogen, helium, and lithium match Big Bang predictions
• Large-Scale Structure: The distribution of galaxies and galaxy clusters
• Time Dilation of Distant Objects: More distant galaxies appear younger, consistent with expansion

Key Stages

1. First 10^-36 seconds: Quantum gravity era (not well understood)
2. 10^-36 to 10^-32 seconds: Cosmic inflation - extremely rapid expansion
3. 3 minutes: Formation of light elements (Big Bang nucleosynthesis)
4. 380,000 years: Recombination - atoms form, universe becomes transparent
5. 13.8 billion years: Present day

Ongoing Expansion

The universe continues to expand today, with distant galaxies moving away from us faster than nearby ones. This expansion is currently accelerating due to dark energy.

The Big Bang theory successfully explains observations from the smallest scales (particle physics) to the largest scales (cosmology), making it one of the most well-supported theories in science.