A look at the Hubble speed from first principles
  We introduce a novel way of measuring $H_0$ from a combination of independent
geometrical datasets, namely Supernovae, Baryon Acoustic Oscillations and
Cosmic Chronometers, without the need of calibration nor of the choice of a
cosmological model. Our method builds on the \emph{distance duality relation}
which sets the ratio of luminosity and angular diameter distances to a fixed
scaling with redshift, for any metric theory of gravity with standard photon
propagation. In our analysis of the data we employ Gaussian Process algorithms
to obtain constraints that are independent from the underlying cosmological
model. We find $H_0=69.5\pm1.7$ Km/s/Mpc, showing that it is possible to
constrain $H_0$ with an accuracy of $2\%$ with minimal assumptions. While
competitive with current astrophysical and cosmological constraints, our result
is not precise enough to solve the Hubble tension in a definitive way. However,
we uncover some interesting features that hint at a twofold solution of the
tension.
