$H_0$ tension as a hint for a transition in gravitational theory
  We propose a cosmological model, \"u$\Lambda$CDM, based on {\it
\"uber-gravity}, which is a canonical ensemble average of many theories of
gravity. In this model, we have a sharp transition from (a purely) $\Lambda$CDM
era to a phase in which the Ricci scalar is a constant. This transition occurs
when the Ricci scalar reaches a critical scale or alternatively at a transition
redshift, $z_\oplus$. We use the observations of baryonic acoustic oscillations
(BAO) and Supernovae Ia (SNe), as well as the cosmic microwave background (CMB)
data to constrain \"u$\Lambda$CDM. This yields $H_0=70.6_{-1.3}^{+1.1}$
km/s/Mpc, $\Omega_m=0.2861 \pm{0.0092} $ and
$z_\oplus=0.537_{-0.375}^{+0.277}$, providing a marginally better fit with a
Akaike information criterion of 0.8. %After adding in the data from BAO in the
Lyman-$\alpha$ forest in quasar spectra, we get $\Delta\chi^2=-2.14$, where the
best fit occurs at $H_0=71.2_{-1.5}^{+1.8}$ km/s/Mpc, $\Omega_m=0.280\pm 0.013$
and $z_{\oplus}= 0.41^{+0.31}_{-0.29}$. Therefore, \"u$\Lambda$CDM can ease the
$H_0$-tension, albeit marginally, with one additional free parameter. We also
provide a preliminary study of the linear perturbation theory in
\"u$\Lambda$CDM which points to interesting potential {\it smoking guns} in the
observations of large scales structure at $z < z_{\oplus}$.
