The re-examination of light propagation in space described by the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric reveals surprisingly that this metric does not predict the cosmological redshift as so far incorrectly supposed. It is shown that the change in the frequency of light is always connected with time dilation, similarly as for the gravitational redshift. Therefore, the conformal time must be considered as the cosmic time at the high redshift universe and the original FLRW metric must be substituted by its conformal version. The correctness of the proposed conformal metric is convincingly confirmed by Type Ia supernovae (SNe Ia) observations. The standard FLRW metric produces essential discrepancy with the SNe Ia observations called the ‘supernova dimming’, and consequently dark energy has to be introduced to comply theoretical predictions with data. By contrast, the conformal FLRW metric fits data well with no need to introduce any new free parameter. Hence, the discovery of the supernova dimming actually revealed the failure of the FLRW metric and introducing dark energy was just an unsuccessful attempt to cope with the problem within this false metric. Obviously, adopting the conformal FLRW metric for describing the evolution of the Universe has fundamental cosmological consequences.