# Explain why cosmic microwave background radiation (CMBR) provides evidence for the Big Bang Theory but cannot be explained by the Steady State Theory.

> Edexcel GCSE Physics (1PH0) — 7.1 Astronomy (Phys only) · Explain · 4 marks

## Mark scheme (4 marks)

1. CMBR is electromagnetic radiation found all around the universe / in every direction in the sky
2. CMBR originated as high-energy / short-wavelength radiation emitted by the very hot, young universe shortly after the Big Bang
3. As the universe expanded, this radiation was stretched to longer wavelengths, becoming microwaves
4. The Steady State Theory cannot account for CMBR because it proposes the universe has always existed in the same state and therefore predicts no such remnant radiation from an early hot, dense phase

## Key terms

- [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)
- [Steady State Theory](https://www.gradenine.co.uk/glossary/steady-state-theory)

## Related

- [Revision notes for Edexcel GCSE Physics (1PH0)](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-cosmic-microwave-background-radiation-f22b5200) · Published by Druglandscape Ltd.