A Century of Gravity: 1901--2000 (plus some 2001)

TL;DR

This paper reviews the evolution of gravity over the past century and presents new findings on higher spin fields in cosmological backgrounds, highlighting the impact of the cosmological constant on unitarity regions.

Contribution

It introduces novel results on the properties of higher spin fields in cosmological backgrounds, especially regarding gauge invariances and unitarity phases influenced by the cosmological constant.

Findings

Higher spin fields exhibit gauge invariances in certain massive models.

The unitarity region shrinks to flat space as spin increases.

Presence of the cosmological constant creates discrete massive models with specific properties.

Abstract

This lecture consists of two parts. The first is a (totally unsystematic) survey of some of the high points in the evolution of gravity and its successors, primarily in the course of the past century. The second summarizes some new work on surprising properties of higher $(> 1)$ spin fields in cosmological backgrounds: the presence of $\L$ gives rise to discrete sets of massive models endowed with gauge invariances, that divide the ($m^2, \L$) plane into unitary and non-unitary phases. The unitary region common to fermions and bosons shrinks to flat space ($ \L \to 0 $) as their spins increase.