Cosmology and astrophysics
The Big Bang model and Hubble’s law
Explore the cosmic-expansion model: vary galaxy distance d and the viewing angle to measure recession speed/redshift. Verify the Hubble–Lemaître law and the meaning of center-less expansion.
Equipment
- 3D expanding-universe model with galaxies
- Distance d (Mpc) and Viewing-angle sliders
- Recession-speed/redshift readout and Pause button
Procedure
Measure recession speed vs distance
Sweep «Distance d (Mpc)» from 1 to 10 and read the matching recession speed. Plot v versus d: points lie on a line through the origin — the slope is the Hubble constant . Record from your fitted slope.
Change viewpoint: center-less expansion
Use «Viewing angle» to place the «observer» on a different galaxy in the model. Notice that from every galaxy, all others recede — spatial expansion has no center, like dots on an inflating balloon's surface.
Redshift as the expansion signature
Read the redshift z at several distances and relate to the recession speed (for v ≪ c). Explain: the photon is stretched along with expanding space — this is cosmological redshift, not quite the Doppler shift of motion through static space.
Predict the past and the far limit
From your measured slope, estimate the «expansion age» (with H₀ ≈ 70 km/s/Mpc → ~14 billion years). Predict: if v = H₀d holds at all d, far enough galaxies recede faster than c — still valid since space itself expands; discuss the observable horizon.