Vacuum polarisation and regular gravitational collapse

It is the goal of this thesis to revisit and revise the problem of black hole formation and evolution in semiclassical gravity -- a theory in which spacetime is treated classically, while matter admits a quantum description, coupling to gravity through an expectation value of a stress-energy tensor operator. We examine the vacuum expectation value of this operator in a variety of spacetimes in which trapped regions form or are close to forming, drawing conclusions regarding the semiclassical dynamics of spacetime in these scenarios.