The Big Bang Theory describes the origin of the Universe. State two pieces of observational evidence that support the Big Bang Theory and, for each piece of evidence, explain how it supports the theory.

Cambridge International IGCSE Physics (0625) — 6.2 Stars and the Universe · State and 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. Redshift of light from distant galaxies – the light has a longer wavelength than expected, showing galaxies are moving away.
2. Cosmic microwave background radiation – a faint glow detected everywhere in space, predicted by the Big Bang and indicating the Universe was once hot and dense.

Examiner tips

  • Use the word ‘redshift’ and explain it causes longer wavelengths. Mention that redshift shows galaxies recede, proving expansion. State CMBR and link it to a hot, dense early Universe. Keep each point short, clear and to the point.

Common mistakes

  • Confusing redshift with blueshift. Saying galaxies are moving towards us. Omitting the link between CMBR and a hot, dense origin.

Mark scheme (4 marks)

  1. Redshift is observed in light from distant galaxies (accept: light from distant galaxies has a longer observed wavelength than expected)
  2. Redshift shows that galaxies are receding / moving away, indicating the Universe is expanding, consistent with originating from a single point (Big Bang)
  3. Cosmic microwave background radiation (CMBR) is detected at all points in space
  4. CMBR was predicted by the Big Bang Theory and its existence confirms that the Universe was once extremely hot and dense / originated from a very hot dense region

Key terms in this question

Big Bang Theory

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