# Explain why the Big Bang Theory is the currently accepted model for the origin of the universe, whereas the Steady State Theory has been rejected.

> Edexcel A-Level Physics (9PH0) — 7.2 Capacitors · Explain · 5 marks

> Scientists have proposed different theories to explain how the universe began. Two of these are the Big Bang Theory and the Steady State Theory.

## Mark scheme (5 marks)

1. The Steady State Theory cannot account for / does not explain cosmic microwave background radiation (CMBR)
2. CMBR is electromagnetic radiation found everywhere in the universe / detected in all directions in the sky
3. CMBR is explained by the Big Bang Theory as the stretched / red-shifted high-energy radiation left over from the hot, early universe
4. Red-shift shows that galaxies are moving away from us / the universe is expanding
5. Because the universe is expanding, it must have started from a single small, hot, dense point / this supports the Big Bang Theory

## 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)

## 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-da85886a) · Published by Druglandscape Ltd.