Astronomy › Section V · The Big Bang › Topic V.3
The beginning of the universe
Run the expansion backwards and the universe grows hotter and denser. Using known physics, astronomers can follow it back to a fraction of a second after the start, and the first few minutes left a lasting signature: the amounts of hydrogen, helium and deuterium we see today.
In this topic
- From a primeval atom to a hot Big Bang
- Hotter and denser in the past
- Energy into matter
- Worked example: why photons no longer make matter
- The limits of the story
- The first second: neutrinos break free
- A few minutes of fusion
- Worked example: predicting the helium
- Helium and deuterium as evidence
- Common mistakes to avoid
- Key takeaways
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