# The Cosmic Microwave Background (CMB) radiation is observed uniformly across the entire sky. Explain what the CMB radiation tells us about the origin and early conditions of the universe.

> WJEC GCSE Physics (Wales) — 2.1 Light, lenses and the universe · Explain · 4 marks

> Scientists detected a faint microwave radiation arriving from all directions in space with almost exactly the same intensity, now known as the Cosmic Microwave Background radiation.

## Mark scheme (4 marks)

1. The CMB radiation is evidence for the Big Bang / universe began with a Big Bang
2. The early universe was very hot (and dense)
3. The CMB radiation is the remnant / leftover energy / radiation from the very early universe (after the Big Bang)
4. The universe has expanded and cooled since the Big Bang, which is why the radiation is now detected as microwaves (low energy / long wavelength)

## Key terms

- [Cosmic Microwave Background (CMB)](https://www.gradenine.co.uk/glossary/cosmic-microwave-background-cmb)
- [universe](https://www.gradenine.co.uk/glossary/universe)

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/the-cosmic-microwave-background-cmb-radiation-dbc35551) · Published by Druglandscape Ltd.