The Big Bang theory is the currently accepted model for the origin of the universe. Describe how the observed red shift of light from distant galaxies supports the idea that the universe began from a single point.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Astronomers studying light from galaxies across the universe have found that the wavelength of light received from almost all galaxies is longer than expected.
Model answer (4 marks)
Red shift means the wavelength of light from galaxies is increased or stretched compared with the same light source on Earth.
Red shift shows that galaxies are moving away from us, indicating that the universe is expanding.
More distant galaxies show a greater red shift, meaning they are moving away faster.
If galaxies are moving apart in all directions, tracing this back in time suggests that everything was once at a single point, supporting the Big Bang model.
Red shift shows that galaxies are moving away from us, indicating that the universe is expanding.
More distant galaxies show a greater red shift, meaning they are moving away faster.
If galaxies are moving apart in all directions, tracing this back in time suggests that everything was once at a single point, supporting the Big Bang model.
Examiner tips
- Use the term "red shift" and explain it as stretched wavelengths. Show the link between red shift and galaxy recession. Mention the distance–velocity relationship. Conclude that back‑tracing gives a single origin point.
Common mistakes
- Confusing red shift with blue shift. Saying galaxies are moving towards us. Omitting the distance–velocity relationship. Not linking the expansion back to a single point.
Mark scheme (4 marks)
- Red shift means the wavelength of light from galaxies is increased / stretched (compared to the same light source on Earth)
- Red shift shows that galaxies are moving away from us / the universe is expanding
- More distant galaxies show a greater red shift, meaning they are moving away faster
- If galaxies are moving apart in all directions, tracing this back in time suggests everything was once at a single point / the universe started from a single point (Big Bang)
Key terms in this question
red shift · Big Bang · universe
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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