Explain how red-shift and cosmic microwave background radiation (CMBR) each provide evidence for the Big Bang Theory.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Astronomers studying light from distant galaxies notice that the wavelength of the light received is longer than expected. Separately, sensitive detectors pick up low-level microwave radiation arriving from all directions in space.
Model answer (4 marks)
Red‑shift shows that the wavelength of light from distant galaxies is increased, shifting it towards the red end of the spectrum.
Red‑shift indicates that galaxies are moving away from Earth, meaning the universe is expanding; this expansion implies it must have started from a single point.
CMBR is low‑level microwave radiation detected in all directions throughout space.
CMBR is the remnant high‑energy radiation from the very hot early universe – the Big Bang – whose wavelength has since increased or stretched as the universe expanded.
Red‑shift indicates that galaxies are moving away from Earth, meaning the universe is expanding; this expansion implies it must have started from a single point.
CMBR is low‑level microwave radiation detected in all directions throughout space.
CMBR is the remnant high‑energy radiation from the very hot early universe – the Big Bang – whose wavelength has since increased or stretched as the universe expanded.
Examiner tips
- Use the word ‘red‑shift’ and explain the shift to longer wavelengths. Show that red‑shift means galaxies recede, proving expansion. Mention CMBR is isotropic and a remnant of the hot early universe. Link the stretching of CMBR wavelengths to expansion.
Common mistakes
- Confusing red‑shift with blueshift. Saying CMBR is only a background glow without linking it to the early hot universe. Forgetting to mention that CMBR is present in all directions.
Mark scheme (4 marks)
- Red-shift shows that the wavelength of light from distant galaxies is increased / shifted towards the red end of the spectrum
- Red-shift indicates galaxies are moving away from Earth / the universe is expanding, so it must have originated from a single point
- CMBR is low-level microwave radiation detected in all directions throughout space
- CMBR is the remnant high-energy radiation from the very hot early universe / Big Bang, whose wavelength has since increased / stretched as the universe expanded
Key terms in this question
red-shift · cosmic microwave background radiation (CMBR) · Big Bang Theory
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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