Big Bang Nucleosynthesis


Now imagine winding the clock forward again...

As this "cosmic soup" expands and cools the nuclei of atoms are formed.

Putting in one unknown number we can predict exactly the mix of isotopes which comes out.

If we can then measure the mix in our actual Universe then we can work back to the unknown number.
This number can be expressed in terms of the density of ordinary matter in the Universe today
A key parameter we would like to find out!