1) Explain in your own words how we know that the Perfect Cosmological Principle doesn't apply to the Universe?
2) Why does the Universe become transparent to radiation at the epoch of recombination?
3) What is the frequency of a photon whose energy is the same as the rest mass of a proton? What portion of the electromagnetic spectrum is this? You'll have to look up the mass of an electron.
4) The Cosmic Microwave Background has a temperature of 2.735 K. What is the wavelength of the radiation at which most of its radiation is emitted? Show your work.
5) The Hubble constant today has a value of 72 km s-1 Mpc-1. What is the value of the Hubble constant in s-1?