Loop quantum gravity

Summary

Loop quantum gravity is an approach to quantum gravity that quantizes general relativity directly, without a background metric. It rewrites the theory in terms of an $SU(2)$ connection, the Ashtekar variables, and uses as basic observables the holonomies of this connection along curves. Its quantum states of space are spin networks, and areas and volumes have discrete spectra. It was developed from the late 1980s by Abhay Ashtekar, Carlo Rovelli, Lee Smolin, Thomas Thiemann and others.