  It is often argued that inflation erases all the information about what took
place before it started. Quantum gravity, relevant in the Planck era, seems
therefore mostly impossible to probe with cosmological observations. In
general, only very ad hoc scenarios or hyper fine-tuned initial conditions can
lead to observationally testable theories. Here we consider a well-defined and
well motivated candidate quantum cosmology model that predicts inflation. Using
the most recent observational constraints on the cosmic microwave background B
modes, we show that the model is excluded for all its parameter space, without
any tuning. Some important consequences are drawn for the deformed algebra
approach to loop quantum cosmology. We emphasize that neither loop quantum
cosmology in general nor loop quantum gravity are disfavored by this study but
their falsifiability is established.
