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

> Edexcel A-Level Physics (9PH0) — 7.1 Electric fields · Explain · 5 marks

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

## Mark scheme (5 marks)

1. The Big Bang Theory states that the universe expanded from an initially very small, hot and dense point
2. Red-shift provides evidence for the Big Bang Theory because galaxies are moving away from us, showing the universe is expanding
3. Cosmic microwave background radiation (CMBR) is found all around the universe and is evidence for the Big Bang Theory
4. The Steady State Theory cannot explain CMBR / does not account for cosmic microwave background radiation
5. Observations show the universe has evolved over time (e.g. different types of stars existed at different eras), which contradicts the Steady State Theory's claim that the universe remains the same at all times and places

## 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-cd0a8194) · Published by Druglandscape Ltd.