  Complex many-particle quantum entanglement is a central theme in two distinct
major topics in physics: the strange metal state found in numerous correlated
electron compounds, and the quantum theory of black holes in Einstein gravity.
The Sachdev-Ye-Kitaev model provides a solvable theory of entangled
many-particle quantum states without quasiparticle excitations. This article
reviews how this toy model has led to realistic universal models of strange
metals, and to new insights on the quantum states of black holes.
