Prologue and epilogue: The de sitter universe

Abstract

In this final chapter we would like to take one small step beyond the special theory of relativity in order to briefly address two issues that have been conscientiously swept under the rug to this point. These are related, although perhaps not obviously so. The first is the issue of gravitation which we quite explicitly eliminated from consideration very early on. We have proposed Minkowski spacetime as a model of the event world only when the effects of gravity are “negligible”, that is, for a universe that is effectively “empty”, but it is doubtful that anything in our development has made it clear why such a restriction was necessary. Here we will attempt to provide an explanation as well as a gentle prologue to how one adapts to the presence of gravitational fields. Then, as an epilogue to our story, we will confront certain recent astronomical observations suggesting that, even in an empty universe, the event world may possess properties not reflected in the structure of Minkowski spacetime, at least on the cosmological scale. Remarkably, there is a viable alternative, nearly 100 years old, that has precisely these properties and we will devote a little time to becoming acquainted with it.