MYP Physics · 16 · extended response
From galaxy spectra to an expanding-universe model
Space physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 8
- Topics
- 2
- Answer
- Complete
Spectral lines from most distant galaxies are observed at longer wavelengths than the same atomic lines measured in a laboratory. More distant galaxies generally show a larger shift. A media post claims this single observation ‘proves every detail of the Big Bang.’
- a
Distinguish Distinguish the observation from the inference made from it.
2 marks - b
Explain Explain how the distance–redshift pattern supports an expanding-universe model.
3 marks - c
Evaluate Evaluate the wording of the media claim and propose a more scientifically responsible conclusion.
3 marks
Ready to self-mark?Reveal the detailed answer guide
a
Distinguish Distinguish the observation from the inference made from it.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Identifies shifted spectral-line wavelengths and the distance trend as observations.
- 2
Identifies recession or expansion of space as an interpretation or inference from those observations.
b
Explain Explain how the distance–redshift pattern supports an expanding-universe model.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Links longer observed wavelength to redshift.
- 2
Links greater redshift, in this context, to greater recession rate.
- 3
Explains that the general increase with distance matches the prediction that large-scale separations grow over time.
c
Evaluate Evaluate the wording of the media claim and propose a more scientifically responsible conclusion.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Rejects ‘proves every detail’ because one evidence line does not uniquely establish all parts or parameters of a model.
- 2
Recognises the need for independent evidence, uncertainty, calibration, and consideration of alternative explanations or model limits.
- 3
Proposes wording such as ‘provides strong evidence for cosmic expansion and is consistent with a hot early-universe model when combined with other evidence.’
Private on this device