The universe is thought to have begun with the Big Bang. Explain how observations of light from distant galaxies provide evidence that the universe is still expanding.

Eduqas GCSE Physics — 2.1 Light, lenses and the universe · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Light from distant galaxies is shifted towards the red end of the spectrum (red‑shift).
2. Red‑shift means the wavelength of light received is longer and its frequency lower than expected.
3. This indicates that the distant galaxies are moving away from us.
4. The greater the red‑shift, the faster/further away the galaxy is, showing the universe is expanding.

Examiner tips

  • Use the word ‘red‑shift’ and explain it as a longer wavelength. Show the link between red‑shift and recession velocity. Mention that larger red‑shift = greater distance/velocity. Keep the answer concise and use the exact terminology.

Mark scheme (4 marks)

  1. Light from distant galaxies is shifted towards the red end of the spectrum (red-shift)
  2. Red-shift means the wavelength of light received is longer / frequency is lower than expected
  3. This indicates that distant galaxies are moving away from us
  4. The greater the red-shift, the faster / further away the galaxy is, showing the universe is expanding

Key terms in this question

universe · expanding

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