The CMS experiment at CERN’s Large Hadron Collider (LHC) has completed a search for microscopic black holes produced in high-energy proton-proton collisions. No evidence for their production was found and their production has been excluded up to a black hole mass of 3.5-4.5 TeV (1012 electron volts) in a variety of theoretical models. Microscopic black holes are predicted to exist in some theoretical models that attempt to unify General Relativity and Quantum Mechanics by postulating the existence of extra “curled-up” dimensions, in addition to the three familiar spatial dimensions. At the high energies of the Large Hadron Collider, such theories...