The Big Bang Theory

This lesson covers the Big Bang theory and its supporting evidence — as required by the Edexcel GCSE Physics specification (1PH0), Topic 7: Astronomy. This is a Paper 2 topic. You need to understand what the Big Bang theory states, know the two key pieces of evidence (red-shift and cosmic microwave background radiation), and understand why the CMBR is the strongest evidence.

---

What Is the Big Bang Theory?

The Big Bang theory states that:

• The universe began from an extremely hot, dense point (sometimes called a singularity) approximately 13.8 billion years ago.
• Since then, the universe has been expanding and cooling.
• All matter, energy, space and even time itself were created in the Big Bang.
• The expansion continues today — and is accelerating.

Key Points

• The Big Bang was NOT an explosion in space — it was the rapid expansion of space itself.
• There was no "outside" the Big Bang — the Big Bang created all of space.
• Before the Big Bang, there was no "before" in the conventional sense — time itself began with the Big Bang.