Here I show some of the calculations done during this practicum and how they can help us to feel the Physics.
Computing is one of the best way to have a good feeling
of how things work. In this appendix we will put some of the
computations done in the framework of understanding the
Raychaudhuri equation 
that we saw in chapter
page .
Here is not the place to put the derivation of the equation
page . It gives nothing
about the physics we want to know. Instead let us work out
the Raychaudhuri equation in some cases like the Roberston and
Walker metric
(Notice that the derivation of the Christoffel symbol
can be easily done thanks to GR-Tensor but
the aim of this computation was to understand the mechanism,
this computation has to be carried out by hand at least one
time).
The form of the metric used is the following:
With 
. It is the solution of the Einstein
equation for our universe.
First let us calculate the geodesics of the spacetime.
