The Expanding Universe
Use wavelength shifts and astronomical measurements to reason about expansion, age, unseen matter and cosmic history.
How to study Higher Physics
Move between physical models, relationships, units, graphs and justified conclusions, while using current official materials for exact paper and assignment conditions.
Core concepts
Concept 1
Doppler effect and cosmological redshift
Exam cue: A longer observed wavelength is redshift.
Concept 2
Hubble–Lemaître relationship
Exam cue: Treat Hubble–Lemaître graphs as evidence connecting recession speed and distance.
Concept 3
galaxy mass, dark matter and dark energy
Exam cue: Distinguish direct observation from an inference supported by a model.
Concept 4
stellar temperature and radiation distribution
Concept 5
Big Bang evidence: cosmic microwave background, hydrogen and helium abundance, Olbers’ paradox and predominantly redshifted galaxies
Risk pitfalls and guardrails
Confusing a wavelength shift with a change in the emitted atomic spectrum.
Guardrail: Check assumptions, prefixes, units, significant figures and whether the statement is supported by evidence.
Treating Hubble’s constant as a speed.
Guardrail: Check assumptions, prefixes, units, significant figures and whether the statement is supported by evidence.
Presenting dark matter and dark energy as the same phenomenon.
Guardrail: Check assumptions, prefixes, units, significant figures and whether the statement is supported by evidence.
Memory anchors
Redshift
Observed wavelength exceeds emitted wavelength for a receding source.
Redshift value
z = (λobserved − λrest)/λrest.
Slow-galaxy approximation
For low recession speeds, z ≈ v/c.
Hubble–Lemaître law
Recession speed is proportional to distance: v = H₀d.
Hotter stellar object
Its spectrum peaks at a shorter wavelength and it emits more radiation per unit area per unit time.
Big Bang evidence
Cosmic microwave background, hydrogen and helium abundance, Olbers’ paradox and predominantly redshifted galaxies support the model.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A sound source moves toward a stationary observer. How does the observed frequency compare with the emitted frequency?
A source emitting 500 Hz moves toward an observer at 20 m s⁻¹. Sound speed is 340 m s⁻¹. Using fₒ=fₛv/(v−vₛ), find the observed frequency.
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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