Cosmic microwave background (CMB) radiation is detected uniformly across the entire sky. Explain what CMB radiation is and why its existence supports the Big Bang theory.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Astronomers can detect a faint microwave radiation coming from all directions in space. This radiation was first detected accidentally in 1965 and has since been studied in great detail.
Model answer (4 marks)
CMB radiation is electromagnetic radiation in the microwave region that fills the whole universe.
It is the remnant energy left over from the Big Bang.
The Big Bang theory says the universe began extremely hot and dense; as it expanded the early radiation has cooled and stretched.
Because CMB is detected uniformly in every direction, it shows the universe expanded from a single point, supporting the Big Bang.
It is the remnant energy left over from the Big Bang.
The Big Bang theory says the universe began extremely hot and dense; as it expanded the early radiation has cooled and stretched.
Because CMB is detected uniformly in every direction, it shows the universe expanded from a single point, supporting the Big Bang.
Examiner tips
- Use the exact terms ‘microwave radiation’, ‘remnant energy’, ‘hot and dense’, ‘expanded from a single point’.
- Show the link between cooling/stretching and expansion.
- Explain why uniformity supports the theory.
Common mistakes
- Calling CMB visible light or infrared instead of microwave.
- Saying it is ‘created now’ rather than a remnant.
- Missing the point that uniformity indicates a single origin.
Mark scheme (4 marks)
- CMB radiation is electromagnetic/microwave radiation that fills the entire universe
- CMB radiation is the remnant/leftover energy/radiation from the Big Bang itself
- The Big Bang theory states the universe began extremely hot and dense, and this early radiation has been cooling/stretching as the universe expanded
- The fact that CMB radiation is detected uniformly in all directions supports the idea that the Big Bang occurred everywhere at once / the universe expanded from a single point
Key terms in this question
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