# Cosmic microwave background radiation (CMBR) is detected all around us. Explain how the existence and properties of the CMBR provide evidence for the Big Bang theory.

> Pearson Edexcel International GCSE Physics (4PH1) — 8.3 Cosmology · Explain · 4 marks

> Astronomers can point a telescope in any direction in the sky and detect low-energy microwave radiation. This radiation is present throughout the universe and is nearly uniform in all directions.

## Mark scheme (4 marks)

1. Shortly after the Big Bang, a large amount of high-energy / short-wavelength radiation was released
2. As the universe expanded, this radiation was stretched to longer wavelengths / became microwaves
3. CMBR is detected in all directions / everywhere in the sky
4. This is consistent with the Big Bang, where the universe expanded from a single point, so the radiation fills all of space

## 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)

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- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/cosmic-microwave-background-radiation-cmbr-is-6399984e) · Published by Druglandscape Ltd.