It's a blog! Mainly of book reviews.
Dirac makes the observation that each term in the metric tensor can be viewed as a potential and in the Newtonian approximation the bits that are non-zero are equivalent to the grad operator. The section on gravitational redshift is incomprehensible due to a notation I've never seen before and can't find the meaning of. This makes me worry about the material later on that I've never seen before.