The Big Bang Theory

⚙️ The Big Bang Theory

The Big Bang theory describes the origin of the universe from an extremely hot, dense state approximately 13.8 billion years ago. It is the leading scientific explanation for the origin of the universe, supported by multiple independent lines of evidence.

The Logic of the Big Bang

If the universe is currently expanding (as shown by red shift), then at earlier times it must have been smaller. Running the expansion backwards:

• 1 billion years ago — universe was smaller
• 5 billion years ago — much smaller
• 10 billion years ago — very much smaller
• 13.8 billion years ago — all matter, energy, space, and time compressed into an incredibly hot, dense state, then rapidly expanded

The Big Bang was not an explosion in space — it was the creation of space (and time, and matter, and energy). There was no "before" the Big Bang in the usual sense because time itself began at that moment.

What Happened After the Big Bang

In the first fraction of a second, the universe was unimaginably hot and dense — too hot for even subatomic particles to exist. As it expanded and cooled over the following minutes, hours, and millions of years:

• First seconds: quarks combined to form protons and neutrons
• First few minutes: protons and neutrons fused to form hydrogen and helium nuclei
• About 380,000 years: universe cooled enough for electrons to combine with nuclei, forming neutral atoms — releasing the light that became the CMBR
• Hundreds of millions of years: gravity caused hydrogen and helium to clump into the first stars and galaxies