The First Three Minutes

Where helium came from

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Nuclei formed a few minutes after the Big Bang, with about 1 neutron per 7 protons.
• Nearly all neutrons ended up in helium-4: about 25% of the mass.
• The observed helium fraction strongly supports the Big Bang model.

Steps

1. A cosmic furnace
2. Predict the helium
3. Tuning the neutrons
4. Why stop at helium?
5. A cosmic scale
6. Decaying neutrons