Topic 10: Space — Edexcel A-Level Physics
Test yourself on Topic 10: Space with PEARSON EDEXCEL A-Level practice questions.
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Topic 10: Space explained
The Hubble constant H₀ sets the present expansion rate, and the Hubble time 1/H₀ gives a rough age estimate for a uniformly expanding universe.
Read the full explanation
Different measurement routes give values that disagree by more than their stated uncertainties: distances calibrated with Cepheids and Type Ia supernovae tend to give a larger H₀ (roughly 70–74 km s⁻¹ Mpc⁻¹), while cosmic microwave background fits within the standard cosmological model give a smaller value (near 67 km s⁻¹ Mpc⁻¹). Because age scales as 1/H₀, a larger H₀ implies a younger universe, so the disagreement becomes a controversy about age as well as expansion rate. Dark matter, inferred from galaxy rotation curves and cluster dynamics, adds unseen mass that changes how expansion and structure formation proceed, and its amount and nature affect predictions of the ultimate fate.
Your focus
- Explain how the value of the Hubble constant links to an estimate of the age of the universe.
- Describe why differing measurements of the Hubble constant create a controversy.
- Outline how the possible existence of dark matter influences predictions of the universe's ultimate fate.
Topic 10: Space exam tips
Marking Points
- States that the Hubble constant H₀ is the present rate of expansion, with units such as km s⁻¹ Mpc⁻¹.
- Explains that the Hubble time 1/H₀ gives an approximate age, so a larger H₀ corresponds to a younger universe.
- Recognises that different measurement methods (local distance-ladder versus cosmic microwave background) yield H₀ values that disagree beyond their uncertainties, creating the controversy.
- Describes dark matter as unseen mass inferred from dynamical evidence such as galaxy rotation curves, affecting expansion and structure formation.
- Links the amount and behaviour of dark matter and dark energy to predictions about the ultimate fate of the universe.
- Distinguishes the age question (set by H₀ and the expansion history) from the fate question (set by how dark energy and matter density evolve).
Examiner Tips
- 💡Always attach units to H₀ and show the 1/H₀ relationship when discussing age.
- 💡Name the two broad measurement routes (local distance ladder and cosmic microwave background) rather than saying vaguely that 'scientists disagree'.
- 💡Separate the age argument from the fate argument in your answer so each clause of the statement is addressed.
Common Mistakes
- Treating H₀ as a fixed constant with no uncertainty: the correction is that measured values from different routes disagree, and that disagreement is the controversy.
- Assuming a larger H₀ means an older universe: the correction is that age scales as 1/H₀, so a larger H₀ gives a younger estimate.
- Confusing dark matter with dark energy: the correction is that dark matter is unseen gravitating mass, whereas dark energy drives accelerated expansion.
- Quoting a single H₀ value as definitive: the correction is that the range of published values and their tension is the point being assessed.