What is the Big Bang?

The Big Bang theory describes the origin of the universe as an expansion from an extremely hot and dense singularity about 13.8 billion years ago. Rather than an explosion in space, it was an expansion of space itself, causing the cooling and formation of matter, stars, and galaxies.

Observational Evidence

Several key observations support the theory:

• Cosmic Microwave Background (CMB) radiation – the afterglow of the early universe.
• Hubble’s law – galaxies recede from us at speeds proportional to their distance.
• Abundance of light elements – helium, deuterium, and lithium match predictions from nucleosynthesis.

Timeline of the Early Universe

From the first fractions of a second to the formation of the first atoms:

1. Planck epoch (10⁻⁴³ s): quantum gravity dominates.
2. Inflation (10⁻³⁶ to 10⁻³² s): exponential expansion.
3. Quark epoch (10⁻¹² s): quarks combine into protons and neutrons.
4. Recombination (≈380 kyr): electrons combine with nuclei, releasing the CMB.

Common Misconceptions

Many people think the Big Bang was an explosion in pre‑existing space or that it happened at a specific point in the universe. In reality, it happened everywhere simultaneously – every point in space was part of the initial hot, dense state.

Future Prospects

Upcoming missions like the James Webb Space Telescope and next‑generation CMB experiments aim to probe the earliest moments with unprecedented precision, potentially revealing physics beyond the Standard Model.