Do H_0 and q_0 really have the values we believe they have?

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.