Scientists use observations of distant stars and galaxies to investigate the large-scale structure of the universe. One important observation is that more distant galaxies are moving away from us faster than closer ones. Explain what this tells us about the origin and history of the universe.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The observation that more distant galaxies move away faster shows the universe is expanding – all galaxies are moving apart from each other.
If the universe is expanding now, it must have been much smaller in the past; all matter would have been compressed into a very dense, hot state.
This is evidence that the universe began with a Big Bang – a sudden, rapid expansion from a single point.
Because the farther a galaxy is, the longer it has been moving, the greater its speed – this pattern is consistent with a single starting event and continuous expansion since then.
If the universe is expanding now, it must have been much smaller in the past; all matter would have been compressed into a very dense, hot state.
This is evidence that the universe began with a Big Bang – a sudden, rapid expansion from a single point.
Because the farther a galaxy is, the longer it has been moving, the greater its speed – this pattern is consistent with a single starting event and continuous expansion since then.
Examiner tips
- Use the phrase "expanding universe" and "Big Bang". Show the causal link: faster recession → expansion → past compression. Include the distance–speed relationship to justify the origin.
- common_mistakes
- :
- Saying the universe is contracting or static. Missing the link between distance, speed and time. Using vague terms like "big explosion" without specifying the Big Bang.
Mark scheme (4 marks)
- The universe is expanding / galaxies are moving apart / everything is moving away from everything else
- If the universe is currently expanding, in the past all matter must have been closer together / compressed into one point
- This is evidence that the universe began with a Big Bang / a massive explosion / a sudden rapid expansion from a single point
- The greater speed of more distant galaxies shows the universe has been expanding since the beginning / the further away a galaxy is, the longer it has been moving, so it is further away — consistent with a single starting event
Related
- All WJEC GCSE Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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