Cosmology seminar: Phil Bull: Measures of acceleration in cosmology

A wide range of cosmological observations imply that the expansion of the Universe
is accelerating -- if they are interpreted within a homogeneous and isotropic "FLRW"
model. On considering inhomogeneous models, however, we find that "acceleration"
becomes a rather ambiguous concept. In this talk, I describe how the question of
whether spacetime is accelerating depends on what measure of acceleration is being
used, and explain how this affects attempts to solve the dark energy problem.