Red-shift and the Big Bang
Learn Red-shift and the Big Bang for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: light from distant galaxies is red-shifted, providing evidence that the universe is expanding and supporting the Big Bang theory.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
There is an observed increase in the wavelength of light from most distant galaxies. This shift towards the red end of the spectrum is called red-shift. This is a Triple-only topic.
The more distant the galaxy, the greater the observed red-shift, and the faster it is moving away from us. This is evidence that the whole universe is expanding, and it supports the Big Bang theory.
The Big Bang theory states that the universe began from a very small region that was extremely hot and dense. Since 1998, observations of supernovae suggest that distant galaxies are receding ever faster, and dark mass and dark energy have been proposed to explain this, though there is still much that is not understood.
Revision notes
Red-shift
The light from most distant galaxies shows an increase in wavelength, shifting it towards the red end of the spectrum.
The more distant the galaxy, the greater the observed red-shift and the faster it is receding from us.
Evidence for expansion
Red-shift provides evidence that the whole universe is expanding.
It supports the Big Bang theory, which states that the universe began from a very small region that was extremely hot and dense. It is currently the only theory that explains all the available evidence.
Dark mass and dark energy
Since 1998, observations of supernovae suggest that distant galaxies are receding ever faster.
Dark mass and dark energy have been proposed to explain this and to explain how galaxies rotate. There is still much that is not understood about the universe.
Key points
- Red-shift is an increase in observed wavelength.
- It shifts light towards the red end of the spectrum.
- More distant galaxies show greater red-shift.
- They are also receding faster.
- Red-shift is evidence the universe is expanding.
- The Big Bang theory explains the available evidence.
Worked examples
Example 1
Explain what is meant by red-shift. [2 marks]
Model answer
Red-shift is an observed increase in the wavelength of light from distant galaxies (1 mark), shifting it towards the red end of the electromagnetic spectrum (1 mark).
Example 2
Explain how red-shift provides evidence that the universe is expanding. [3 marks]
Model answer
The light from distant galaxies is red-shifted, showing they are moving away from us (1 mark). The more distant the galaxy, the greater the red-shift and the faster it is receding (1 mark). This pattern is what would be observed if the whole universe were expanding (1 mark).
Example 3
State what the Big Bang theory says about the origin of the universe. [2 marks]
Model answer
The universe began from a very small region (1 mark) that was extremely hot and dense (1 mark).
Common mistakes
Saying red-shift means galaxies are red.
It means their light has increased in wavelength, shifting towards the red end.
Saying all galaxies show red-shift.
Most distant galaxies do; a few nearby ones are approaching and show blue-shift.
Saying the Big Bang was an explosion in space.
It describes the expansion of space itself from a very small, hot, dense region.
Saying dark energy is fully understood.
It is a proposal to explain observations, and much remains unknown.
Exam tips
- Define red-shift as an increase in observed wavelength.
- Link greater distance to greater red-shift and faster recession.
- State that the Big Bang explains the available evidence.
- Remember this is a Triple-only topic.
Key terms
- Red-shift
- An observed increase in the wavelength of light from a receding source.
- Big Bang theory
- The theory that the universe began hot, dense and very small.
- Expanding universe
- The conclusion drawn from red-shift observations.
- Dark energy
- A proposal to explain the accelerating recession of galaxies.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.