Gauge Gravity and the Unification of Natural Forces

Liu, Chuang (2001) Gauge Gravity and the Unification of Natural Forces.

Abstract

Physics seems to tell us that there are four fundamental force-fields in nature: the gravitational, the electromagnetic, the weak, and the strong force-field (or interactions). But it also seems to tell us that gravity cannot possibly be a force-field, in the same sense as the other three are. And yet the search for a grand unification of all four force-fields is today one of the hottest pursuits in it. Is this the result of a simple confusion? This paper aims at clarifying this situation by doing the following: (i) examine the conception of unification of force-fields; (ii) review the gauge-field program in view of the above examination; (iii) review the various attempts at a gauge theory of gravity; and (iv) articulate the nature of 'gauging' and using it to explain the difference between gravity and the other force-fields.