In the last couple of lectures we shall consider basic cosmology. This will require extending our knowledge slightly to a small piece of the general theory of relativity, thus allowing us to look at more interesting versions of space-time than the flat, feature-less space-time of special relativity.
Space-time in general relativity is active, curved and allows for much more phenomena to occur and allows us to consider possible evolutions of the universe.
We state the four assumptions that determine the cosmology of our universe, namely that space (not including time) is homogeneous, isotropic, flat and expands over time.
From those assumptions we develop an appropriate coordinate system and associated metric, and in this context derive Hubble's constant.