Hubble expansion simulation
Every distant galaxy is moving away from us, and the further away it is, the faster it recedes. Hubble’s law, v = H₀d, is the signature of a universe that is expanding everywhere at once rather than exploding from a centre.
Interactive, free and runs in your browser. Part of the Frontier Physics simulations.
What you will see
A field of galaxies spreads apart as space expands. Galaxies twice as far away recede twice as fast, and the pattern looks identical from any galaxy you pick: there is no special centre. Change H₀ to speed the expansion up or slow it down.
Try this
- Compare the speed of a galaxy with one twice as far away.
- Imagine yourself on a different galaxy: the recession pattern looks the same.
- Raise H₀ and estimate how the age of the universe, about 1/H₀, would change.
Common misconception
The Big Bang was not an explosion at a point in space. Space itself is expanding everywhere, so every observer sees the others receding and no location is the centre.
Exam-style question
Taking H₀ = 70 km/s/Mpc, how fast is a galaxy 100 Mpc away receding, and roughly what age does 1/H₀ suggest for the universe?
v = H₀d = 70 × 100 = 7000 km/s. 1/H₀ = (3.09 × 10¹⁹ km/Mpc) / (70 km/s/Mpc) ≈ 4.4 × 10¹⁷ s ≈ 14 billion years.
Key equations
v = H₀ dt ≈ 1 / H₀
Curriculum
IB Physics E.5, enrichment: astrophysics and cosmology.