  In this paper I discuss what we truly know about dark energy. I shall argue
that up to date our single indication for the existence of dark energy comes
from distance measurements and their relation to redshift. Supernovae, CMB
anisotropies and observations of baryon acoustic oscillations, they all simply
tell us that the observed distance to a given redshift is larger than the one
expected from a Friedmann Lemaitre universe with matter only and the locally
measured Hubble parameter.
