Explain why cosmic microwave background radiation (CMBR) provides evidence for the Big Bang Theory but cannot be explained by the Steady State Theory.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
CMBR is electromagnetic radiation that is found in every direction in the sky.
It originated as high‑energy, short‑wavelength radiation emitted by the very hot, young universe shortly after the Big Bang.
As the universe expanded, this radiation was stretched to longer wavelengths, becoming microwaves.
The Steady State Theory cannot account for CMBR because it proposes the universe has always existed in the same state and therefore predicts no such remnant radiation from an early hot, dense phase.
It originated as high‑energy, short‑wavelength radiation emitted by the very hot, young universe shortly after the Big Bang.
As the universe expanded, this radiation was stretched to longer wavelengths, becoming microwaves.
The Steady State Theory cannot account for CMBR because it proposes the universe has always existed in the same state and therefore predicts no such remnant radiation from an early hot, dense phase.
Examiner tips
- Use the word "originated" to show cause and effect. Mention "every direction" to show isotropy. Explain the wavelength stretching as a consequence of expansion. State the Steady State prediction explicitly to contrast with the Big Bang.
Common mistakes
- Saying the CMBR is only in one direction. Claiming the Steady State predicts a hot early universe. Omitting the expansion‑stretching explanation.
Mark scheme (4 marks)
- CMBR is electromagnetic radiation found all around the universe / in every direction in the sky
- CMBR originated as high-energy / short-wavelength radiation emitted by the very hot, young universe shortly after the Big Bang
- As the universe expanded, this radiation was stretched to longer wavelengths, becoming microwaves
- The Steady State Theory cannot account for CMBR because it proposes the universe has always existed in the same state and therefore predicts no such remnant radiation from an early hot, dense phase
Key terms in this question
cosmic microwave background radiation (CMBR) · Big Bang Theory · Steady State Theory
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- All Edexcel GCSE Physics (1PH0) revision notes →
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