Radiation Pressure Inside a Collapsing Shell

Birkhoff’s theorem says that the spacetime inside a spherically symmetric collapsing shell is Minkowskian. Given this fact, signals exchanged between the shell and a central observer as well as between observers on the shell itself are examined, and it is shown that these signals will become infinitely blueshifted as the shell approaches its Schwarzschild radius. It is also shown that the space inside the shell will contract to zero volume in the frame of a shell observer as the shell approaches its Schwarzschild radius.