The authors express the inclusive hadronic decay rate of the tau lepton as an integral over the spectral density of the two-point correlator of the weak hadronic current which they compute fully nonperturbatively in lattice QCD. In a lattice QCD computation with all systematic errors except for isospin breaking effects under control, they then obtain the CKM matrix element with subpercent errors showing that their nonperturbative method can become a viable alternative to superallowed nuclear beta decays for obtaining .