Description
Matt and I have been asking similar questions for 4 decades, for a time as collaborators and for longer as colleagues in Aotearoa / New Zealand. I will tell the story of our superposition of states, with a focus on the cosmos. In the last 2 decades, I have developed the timescape cosmology to explain apparent cosmic acceleration in the statistical regime of general relativity. As inhomogeneities in density and expansion grow, they back-react on average cosmic expansion, which differs from conventional FLRW models. Average homogeneity and isotropy is not assumed but is explained as a consequence of extending Einstein's strong equivalence principle from local frames to quasilocal regions. Observationally, dynamical spatial curvature arises as time-varying gradients of the kinetic energy of expansion, depending directly on the volume fraction of cosmic voids. The timescape expansion history is close to ΛCDM, but with differences at a precision which we are now finally probing. Whereas ΛCDM is increasingly challenged, independent observational tests now favour timescape. I will survey the current status relative to foundational questions I believe we still have to answer before arriving at a full theory of quantum gravity: What is the geometrical description of the origin of scale? How is infinity physically characterized when fitting one geometry in another? How is quasilocal energy to be accounted for in energy conditions?