The universe began with the Big Bang. Describe the evidence that supports the Big Bang theory and explain what this evidence tells us about the early universe.

Eduqas A-Level Physics — 4.3 Orbits and the wider universe · Describe and Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

1. The cosmic microwave background (CMB) radiation is detected coming from all directions in space.
2. The CMB is the remnant heat/energy from the Big Bang, i.e. the leftover from the very hot early universe.
3. Light from distant galaxies is red‑shifted – their wavelengths are increased or stretched.
4. Red‑shift shows that galaxies are moving away from us, indicating that the universe is expanding.
5. If the universe is expanding now, it must have started from a single point – all matter was once concentrated in one place (the Big Bang).

Examiner tips

  • Use the exact terms ‘cosmic microwave background’ and ‘red‑shifted’ as they are key words.
  • Show the logical sequence: CMB → evidence of early hot universe; red‑shift → expansion → origin from a single point.
  • Keep each point concise and directly linked to the evidence.

Mark scheme (5 marks)

  1. Cosmic Microwave Background (CMB) radiation is detected coming from all directions in space
  2. CMB radiation is the remnant heat/energy from the Big Bang (or: left over from the very hot early universe)
  3. Light from distant galaxies is redshifted (wavelength of light is increased/stretched)
  4. Redshift shows that galaxies are moving away from us / the universe is expanding
  5. If the universe is expanding now, it must have started from a single point / all matter was once concentrated in one place (Big Bang)

Key terms in this question

Big Bang

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