# Explain why red-shift from distant galaxies and cosmic microwave background radiation (CMBR) together provide strong evidence for the Big Bang Theory.

> Edexcel A-Level Physics (9PH0) — 7.1 Electric fields · Explain · 5 marks

> Astronomers observe that light from distant galaxies has a longer wavelength than expected. They also detect low-level microwave radiation coming from all directions in space.

## Mark scheme (5 marks)

1. Red-shift shows that distant galaxies are moving away from Earth / the universe is expanding
2. If the universe is currently expanding, it must have originated from a single small, hot and dense point (the Big Bang)
3. CMBR is electromagnetic radiation detected in all directions throughout the universe
4. CMBR is the stretched / red-shifted remnant of the high-energy radiation released by the hot young universe shortly after the Big Bang
5. The Steady State Theory cannot explain CMBR, so the Big Bang Theory is the more accepted model as it accounts for both red-shift and CMBR

## Key terms

- [red-shift](https://www.gradenine.co.uk/glossary/red-shift)
- [cosmic microwave background radiation (CMBR)](https://www.gradenine.co.uk/glossary/cosmic-microwave-background-radiation-cmbr)
- [Big Bang Theory](https://www.gradenine.co.uk/glossary/big-bang-theory)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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/explain-why-red-shift-from-distant-galaxies-44fb229c) · Published by Druglandscape Ltd.