Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
7.9P Describe evidence supporting the Big Bang theory, limited to…
Full specification wording
Topic 7 – Astronomy: 7.9P Describe evidence supporting the Big Bang theory, limited to red-shift and the cosmic microwave background (CMB) radiation
The Big Bang theory states that the Universe began from a very small, hot, dense region and has been expanding ever since.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 8 of 18
Study notes
From the checked teaching notes for this specification point.
The idea
The Big Bang theory states that the Universe began from a very small, hot, dense region and has been expanding ever since. Two pieces of evidence support it. First, red-shift: light from distant galaxies is shifted towards longer wavelengths (the red end of the spectrum), and the further away a galaxy is, the greater its red-shift. This shows galaxies are moving away from us and that the Universe is expanding. Second, the cosmic microwave background (CMB) radiation: a faint microwave radiation detected in every direction, interpreted as leftover energy from the hot early Universe. Together these support an expanding Universe that was once hot and dense. The specification limits the evidence to these two, so answers should not rely on other evidence such as the abundance of light elements.
What earns the marks
- Identifies red-shift as light from distant galaxies shifted towards longer wavelengths.
- Explains that greater red-shift for more distant galaxies shows the Universe is expanding.
- Identifies the cosmic microwave background as faint microwave radiation detected in all directions.
- Explains that the CMB is interpreted as leftover energy from the hot, dense early Universe.
Common mistakes and how to put them right
States that red-shift means galaxies are moving towards us.
Put it right by saying red-shift shows galaxies moving away, so the Universe expands.
Treats the CMB as light from stars or galaxies.
Put it right by describing it as faint microwave radiation filling all of space, left over from the early Universe.
Claims red-shift proves the Universe is contracting.
Put it right by linking red-shift to expansion.
Adds evidence beyond red-shift and the CMB.
Put it right: Keep to the two pieces the specification names.
Exam tips
- Read the question carefully to check whether it asks about red-shift, the CMB or both.
- Link each piece of evidence to what it shows: expansion for red-shift, a hot early Universe for the CMB.
- Eliminate options that describe galaxies moving towards us or that name evidence outside the specification.
Try the lesson
The start of the Topic 7 – Astronomy: 7.9P Describe evidence supporting the Big Bang theory, limited to red-shift and the cosmic microwave background (CMB) radiation lesson, made from checked teaching notes for this specification point.
Have a go first
What is meant by the red-shift of light from a distant galaxy?
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