  We present an example where a justified modification of the law of
propagation of light in a Robertson-Walker model of the universe leads to an
identification of H_0 and q_0 different from that corresponding to the usual
law of propagation along null geodesics. We conclude from this example that
observed values which we would associate with the values of H_0 and q_0 with
the usual interpretation correspond in fact to the values of 2H_0 and $1/2
(q_0-1)$. It is therefore possible that observed values that we usually
interpret as corresponding to a moderately aged universe with accelerating
expansion may in fact correspond a much older universe with a decelerating
expansion.
