The Big Bang theory is the currently accepted model for the origin of the universe. Describe the two pieces of evidence that support the Big Bang theory, explaining in each case how the evidence supports the theory.

Pearson Edexcel International GCSE Physics (4PH1) — 8.3 Cosmology · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

1. Red‑shift of light from distant galaxies – the observed wavelength is longer than the emitted wavelength, indicating the galaxies are moving away from us.
2. Red‑shift shows the universe is expanding from a single point, which is consistent with a Big Bang origin.
3. Cosmic microwave background radiation (CMBR) is detected in all directions across the sky.
4. CMBR is the stretched (longer wavelength) remnant of the high‑energy short‑wavelength radiation released by the Big Bang as the universe expanded.

Examiner tips

  • Use the word ‘red‑shift’ and explain it as increased wavelength. Mention that red‑shift shows expansion. State that CMBR is seen everywhere. Explain CMBR as stretched radiation from the Big Bang.

Common mistakes

  • Confusing red‑shift with blue‑shift. Saying CMBR is a new source of light rather than a remnant. Omitting that CMBR is detected in all directions.

Mark scheme (4 marks)

  1. Red-shift: light from distant galaxies has an increased (observed) wavelength / galaxies are moving away from us
  2. Red-shift shows the universe is expanding (from a single point), consistent with a Big Bang origin
  3. Cosmic microwave background radiation (CMBR) is detected in all directions across the sky
  4. CMBR is the stretched (longer wavelength) remnant of the high-energy short-wavelength radiation released by the Big Bang as the universe expanded

Key terms in this question

Big Bang theory

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