Cosmology and astrophysics
Expansion of the universe
Plot recession speed against distance, determine the slope H₀, and distinguish expansion of space from an explosion into pre-existing space.
Equipment
- Galaxy catalogue with distance and redshift-derived recession speed
- Adjustable Hubble constant and cosmic-time control
- Velocity–distance graph and cosmic microwave background display
Procedure
Collect galaxy measurements
Use a real catalogue with independently estimated distances and redshifts. Convert redshift to recession speed only in the regime where the approximation is justified, and note measurement uncertainties for both quantities.
Plot and fit the Hubble relation
Plot v on the vertical axis and d on the horizontal axis. Fit a straight line over the selected low-redshift range; its slope estimates H₀. Inspect residuals and avoid forcing the line through the origin unless the analysis justifies it.
Compare expansion eras and the background
Vary H₀ and cosmic time in the model, recording how the v–d slope and galaxy separations change. Move toward earlier epochs to reveal the cosmic microwave background as relic radiation from the hot early universe; it is not light from the Big Bang instant itself.