# Explain why scientists believe the universe began with a Big Bang. In your answer, refer to the motion of galaxies and the nature of the cosmic microwave background radiation.

> WJEC GCSE Physics (Wales) — 2.6 Particle physics and using physics to investigate the universe · Explain · 4 marks

> Astronomers observe that distant galaxies are moving away from us. They also detect microwave radiation arriving at Earth from all directions in space.

## Mark scheme (4 marks)

1. Galaxies are moving away from us / the universe is expanding
2. More distant galaxies move away faster (greater red-shift), supporting the idea that everything originated from a single point
3. Cosmic microwave background (CMB) radiation exists / is detected from all directions in space
4. The CMB is the remnant / afterglow of the intense heat from the Big Bang, consistent with a very hot, dense origin

## Key terms

- [Big Bang](https://www.gradenine.co.uk/glossary/big-bang)
- [cosmic microwave background radiation](https://www.gradenine.co.uk/glossary/cosmic-microwave-background-radiation)

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-scientists-believe-the-universe-e5e69d13) · Published by Druglandscape Ltd.