Conclusion


The CMB photons are the most ancient ones we can study.
They carry the imprint of cosmological information from an era when the physics of the universe was very simple.
The CMB also acts as a "back-light" shining through the era of structure formation.
We can use the Sunyaev-Zel'dovich effect to study the rate at which massive galaxy clusters form.
This also provides excellent constraints on cosmological models.