We do not live in the R_h = c t universe
  We analyse the possibility that our Universe could be described by the model
recently proposed by Melia & Shevchuk (2012), where the Hubble scale R_h=c/H is
at all times equal to the distance ct that light has travelled since the Big
Bang. In such a model, the scale factor is proportional to cosmic time and
there is neither acceleration nor deceleration of the expansion. We first point
out problems with the very foundations of the model and its consequences for
the evolution of the Universe. Next, we compare predictions of the model with
observational data. As probes of the expansion we use distance data of
supernovae type Ia, as well as Hubble rate data obtained from cosmic
chronometers and radial baryon acoustic oscillations. We analyse the redshift
evolution of the Hubble parameter and its redshift derivatives, together with
the so-called O_m diagnostic and the deceleration parameter. To reliably
estimate smooth functions and their derivatives from discrete data, we use the
recently developed Gaussian Processes in Python package (GaPP). Our general
conclusion is that the discussed model is strongly disfavoured by observations,
especially at low redshifts (z<0.5). In particular, it predicts specific
constant values for the deceleration parameter and for redshift derivatives of
the Hubble parameter, which is ruled out by the data.
