# The universe is thought to have begun with the Big Bang approximately 13.8 billion years ago. Cosmic Microwave Background (CMB) radiation is detected coming from all directions in space. Explain what CMB radiation is and why it supports the Big Bang theory.

> AQA A-Level Physics (7408) — 3.9.3 Cosmology · Explain · 5 marks

## Mark scheme (5 marks)

1. CMB radiation is (low-frequency / microwave) electromagnetic radiation that fills the whole universe / detected from all directions
2. CMB radiation is the (thermal / heat) energy left over from the Big Bang / released shortly after the Big Bang
3. At the time of the Big Bang / early universe, temperatures were extremely high / the universe was very hot and dense
4. As the universe expanded it cooled, causing the radiation to (redshift to / stretch to) longer wavelengths / lower frequencies / microwave wavelengths
5. The fact that CMB radiation is uniform / detected from all directions supports the idea that the Big Bang happened everywhere / the universe expanded from a single point / it is consistent with the Big Bang model

## Key terms

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

## Related

- [Revision notes for AQA A-Level Physics (7408)](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/the-universe-is-thought-to-have-f854f052) · Published by Druglandscape Ltd.