AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER
Red-shift and the Big Bang
Space physics · Lesson 4 of 4
Teacher copy - includes the notes for whoever is teaching from it.
Warm-up
Answer each one, then check.
1. What is light?
An electromagnetic wave
2. What is wavelength?
Distance between corresponding points on adjacent waves
3. What colour has the longest wavelength in visible light?
Red
4. What is a galaxy?
A huge group of stars
5. What is an ambulance siren's pitch change called?
The Doppler effect
Learning Objectives
1. Explain the observed red-shift of light from distant galaxies.
2. Explain why red-shift is evidence that the universe is expanding.
3. Describe the Big Bang theory.
4. Explain why the red-shift is greater for more distant galaxies.
5. Describe dark matter and dark energy.
Red-Shift
The light from most distant galaxies is shifted towards the red end of the spectrum: its wavelength is increased. This is red-shift. It shows the galaxies are moving away from us, and that the universe is expanding.
The more distant the galaxy, the greater the red-shift, so the faster it is moving away.
Red-shift
|
Longer wavelength means redder. |
Spectral lines from a distant galaxy shifted towards the red end compared with a stationary source.
The Big Bang Theory
Follow the steps.
|
1 Start All the matter and energy in the universe was in a very small, hot, dense point. |
2 Explosion It expanded violently about 13.8 billion years ago. |
3 Expansion Space itself has been expanding ever since. |
4 Evidence Red-shift of galaxies and cosmic microwave background radiation (CMBR). |
Evidence for the Big Bang
Learn the two main pieces.
|
Evidence |
What it shows |
|---|---|
|
Red-shift |
Galaxies are moving away and the universe is expanding; further galaxies move faster |
|
CMBR |
Leftover microwave radiation from the early universe, in all directions |
Red-shift and Distance
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Galaxy A has a greater red-shift than galaxy B. What can you conclude? |
1. Red-shift
Greater for A
2. Speed
A is moving away faster than B
3. Distance
A is further away than B
Answer: A is moving away faster and is further away than B.
Dark Matter and Dark Energy
What we don't know.
▸ Dark matter. Matter we cannot see that explains how galaxies rotate; it interacts gravitationally.
▸ Dark energy. A form of energy thought to cause the universe's expansion to accelerate.
▸ Open questions. Their nature is not yet understood.
▸ Theories change. Scientists keep testing theories with new evidence.
Key Terms
|
Red-shift The increase in the observed wavelength of light from distant galaxies because they are moving away. |
Big Bang theory The theory that the universe began from a very small, hot, dense region and has been expanding ever since. |
|
CMBR Cosmic microwave background radiation; leftover microwaves from the early universe. |
Dark matter Matter that does not emit light but has gravitational effects. |
|
Dark energy An unknown energy thought to be driving the accelerating expansion of the universe. |
Expanding universe The idea that space is getting larger over time. |
Your Task: Red-shift Talk
10 minutes
|
Explain to a partner why red-shift shows that the universe is expanding. Then explain why a galaxy twice as far away seems to move away twice as fast. 1. All galaxies are moving away. |
A good answer shows: The wavelengths are lengthened because the galaxies move away; this happens in all directions, so the universe is expanding. Further galaxies show a greater shift, so they move faster.
Note: Ask about the Doppler effect with an ambulance.
Can I...?
☐ Define red-shift.
☐ Explain the expansion.
☐ Describe the Big Bang.
☐ Name the evidence.
☐ Explain distance and red-shift.
☐ Define CMBR.
☐ Define dark matter.
☐ Define dark energy.
Summary
✓ Light from distant galaxies is shifted to longer wavelengths.
✓ The universe is expanding.
✓ Big Bang: small, hot, dense start about 13.8 billion years ago.
✓ Evidence: red-shift and CMBR.
|
EXAM FOCUS State what red-shift shows about the universe. (1 mark) It is expanding. |
Exam Practice: Red-shift and the Big Bang
Answer all questions. Use the mark allocation as a guide to how much to write. · 16 minutes
▸ Question 1 · 2 marks · State. Describe what is meant by red-shift.
▸ Question 2 · 3 marks · Explain. Explain why red-shift is evidence that the universe is expanding.
▸ Question 3 · 3 marks · Describe. Describe the Big Bang theory of the origin of the universe.
▸ Question 4 · 3 marks · Explain. Two galaxies are observed. Galaxy P has a greater red-shift than galaxy Q. Explain what this shows about P and Q.
▸ Question 5 · 4 marks · Explain. Explain why the discovery of cosmic microwave background radiation (CMBR) supports the Big Bang theory, and state what is still not…
Question 1 · 2 marks · State
|
“Describe what is meant by red-shift.” |
HOW TO ANSWER IT Command word: State. Worth 2 marks, so plan before writing.
Question 1 · mark scheme
2 marks available. Award a mark for each point made.
▸ Wavelength increases. 1 mark
▸ Shift towards the red end. 1 mark
▸ Model answer. The wavelength of light from a distant galaxy is longer than expected, shifted towards the red end of the spectrum.
Question 2 · 3 marks · Explain
|
“Explain why red-shift is evidence that the universe is expanding.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 2 · mark scheme
3 marks available. Award a mark for each point made.
▸ Red-shift means the galaxies are moving away. 1 mark
▸ All directions. 1 mark
▸ Further galaxies move faster. 1 mark
▸ Model answer. Light from distant galaxies is red-shifted, which means the galaxies are moving away from us. Galaxies in all directions are moving away, and the further they are the faster they move, so the universe is expanding.
Question 3 · 3 marks · Describe
|
“Describe the Big Bang theory of the origin of the universe.” |
HOW TO ANSWER IT Command word: Describe. Worth 3 marks, so plan before writing.
Question 3 · mark scheme
3 marks available. Award a mark for each point made.
▸ Small, hot, dense region. 1 mark
▸ Explosive expansion. 1 mark
▸ Still expanding. 1 mark
▸ Model answer. All the matter and energy in the universe was originally in a very small, hot, dense region. It expanded explosively about 13.8 billion years ago and has been expanding since.
Question 4 · 3 marks · Explain
|
“Two galaxies are observed. Galaxy P has a greater red-shift than galaxy Q. Explain what this shows about P and Q.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 4 · mark scheme
3 marks available. Award a mark for each point made.
▸ P moving away faster. 1 mark
▸ Greater red-shift means faster recession. 1 mark
▸ P is further away. 1 mark
▸ Model answer. P is moving away from us faster than Q. Since galaxies further away show a greater red-shift, P is also further away.
Question 5 · 4 marks · Explain
|
“Explain why the discovery of cosmic microwave background radiation (CMBR) supports the Big Bang theory, and state what is still not understood about the universe.” |
HOW TO ANSWER IT Command word: Explain. Worth 4 marks, so plan before writing.
Question 5 · mark scheme
4 marks available. Award a mark for each point made.
▸ CMBR is leftover radiation from the early universe. 1 mark
▸ Observed in all directions. 1 mark
▸ Dark matter not understood. 1 mark
▸ Dark energy not understood. 1 mark
▸ Model answer. CMBR is radiation left over from the early hot universe, stretched to microwaves as space expanded, seen from all directions, as the Big Bang predicts. The nature of dark matter and dark energy is still not understood.