Insulators close to the metal insulator transition exhibit interesting collective electronic phenomena which still present major challenges for our theoretical understanding. A prominent experimental feature is the purely electronic nature of activated hopping transport which is strikingly inconsistent with the standard theory of phonon-assisted hopping conduction, and has remained a puzzle for several decades. The puzzle became even bigger recently when theories of "many body localization" predicted a metal insulator transition at finite temperature and ruled out purely electronic transport.

In this talk I will resolve this puzzle by analyzing Anderson insulators with a single-particle localization length that is much larger than the mean distance between electrons. Under these circumstances Coulomb interactions drive the electrons into a strongly correlated quantum glass phase with non-trivial collective behavior. I will show that the complicated glassy landscape leads to a nearly gapless spectrum of collective electronic excitations which act as a bath with which individual electrons can exchange energy. This results in a purely electronic hopping transport mechanism with an almost universal pre-exponential factor in good agreement with many recent experiments.