The Hubble parameter is defined by: H(t) = a'(t) / a(t) where a is the scale factor which is a function of cosmological time t. This definition is equivalent to the Hubble relation: v(t) = H(t) r(t) where v(t) and r(t) are the proper velocity and distance of an object at cosmological time t. I assume that this relationship is exact provided that we acknowledge that the Hubble parameter H(t) is constant only in space and *not* in time. It can be interpreted as simply asserting that space is expanding uniformly at a rate H(t). Now let us assert that a universal speed limit exists, namely the velocity of light c. We know this is true observationally as the redshift diverges as v -> c. This assumption allows us to define the Hubble radius R(t) by c = H(t) R(t). Then the Hubble radius, R_0, at the present time t_0 is given by: c = H_0 R_0 where H_0 is the present Hubble parameter value. As we have: R(t) = R_0 a(t) R(t) = (c / H_0) * a(t) Therefore a'(t) / a(t) = c / R(t) a'(t)/ a(t) = H_0 / a(t) So that finally a(t) = H_0 * t or equivalently R(t) = c * t Thus we seem to have derived a scale factor with a linear time dependence using only two facts: 1. Space is expanding uniformly. 2. A cosmological speed limit, namely c, exists. Is this correct? I expect I'm also assuming that space is flat. This very simple scale factor time dependence, the so-called coasting cosmology, is actually close to what is observed.