Astronomy › Section V · The Big Bang › Topic V.2
A model of the universe
To describe the whole universe, astronomers need only a few ingredients: the expansion, the assumption that the universe is the same everywhere, and its average density. Comparing that density with a critical value tells us how the universe has behaved and how it may end.
In this topic
- The ingredients of a model
- The scale factor and redshift
- Worked example: reading a redshift as a size
- Density decides
- Worked example: the critical density
- Four model universes
- Weighing the universe
- Distances depend on the model
- The far future
- Common mistakes to avoid
- Key takeaways
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