The Expanding Universe

Hubble and the Big Bang

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Hubble's law: $v = H_0 d$. Space itself is expanding, with no centre.
• Running the expansion backwards leads to the Big Bang, about 13.8 billion years ago.
• The cosmic microwave background (2.7 K) is the Big Bang’s afterglow.

Steps

1. Galaxies flying apart
2. Hubble’s law
3. Everyone is the centre
4. Receding galaxy
5. Running it backwards
6. Fit Hubble’s law
7. Age from expansion