associated with unstable de Sitter in the future*

Modern precision measurements of the Hubble expansion H(z) introduce two integral constraints on background models derived from early and late-time cosmology, based on Planck observations of the BAO and, respectively, H₀, here normalized to ΛCDM. For H(z) coupled to non-local dark energy Λ = (1 – q)H² of zero wave-number modes of cosmological spacetime with deceleration parameter q(z). We infer a coupling constant g < 1 for H₀ in tension with ΛCDM associated with a de Sitter instability in the future consistent with the swampland conjectures. Results from the Local Distance Ladder give g ≃ 1 - ξα with ξ = 0.49 ± 0.10. This points to H₀ = (73.37± 0.54) km s^-1 Mpc^-1 for ξ = 1/2, anticipating (73.30±1.04) km s^-1 Mpc^-1 of Riess at al. arXiv:2112.04510v1 (2021). This may serve as a first observational hint of quantum cosmology, breaking T-duality in the Friedmann scale factor a(t) to the same order. (van Putten, 2021, PLB 823 136737.)