# Explain why the Big Bang Theory is accepted as the model for the origin of the universe, whilst the Steady State Theory has been rejected. In your answer, refer to red-shift and cosmic microwave background radiation (CMBR).

> Edexcel A-Level Physics (9PH0) — 7.3 Magnetic fields and electromagnetic induction · Explain · 5 marks

> Scientists have proposed different theories to explain the origin and evolution of the universe. Two such theories are the Big Bang Theory and the Steady State Theory.

## Mark scheme (5 marks)

1. Red-shift shows that distant galaxies are moving away from Earth / the universe is expanding
2. Both theories can account for red-shift / Steady State Theory explains red-shift by the continuous expansion of the universe
3. CMBR is electromagnetic radiation found in small quantities all around the universe / detected in every direction
4. CMBR is explained by the Big Bang Theory — the very hot, dense early universe emitted high-energy radiation which has been stretched / red-shifted to microwave wavelengths as the universe expanded
5. The Steady State Theory cannot explain CMBR, so it is rejected / the Big Bang Theory accounts for all experimental evidence so it is the currently accepted model

## Key terms

- [Big Bang Theory](https://www.gradenine.co.uk/glossary/big-bang-theory)
- [Steady State Theory](https://www.gradenine.co.uk/glossary/steady-state-theory)
- [red-shift](https://www.gradenine.co.uk/glossary/red-shift)
- [CMBR](https://www.gradenine.co.uk/glossary/cmbr)

## 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-the-big-bang-theory-e6173906) · Published by Druglandscape Ltd.