I put forward a simple unidimensional mechanical analogue of the three-dimensional universe models of modern relativistic cosmology. The main goal of the proposal is the appropriate appreciation of the intrinsic relationship between Hubbles law and the homogeneity of expanding relativistic models.
Redshift observations of galaxies outside the Local Group are fairly common in extragalactic astrophysics. If redshifts are interpreted as arising from radial velocities, these must be corrected by the contamination of the solar motion. We discuss th
e details of such correction in the way it was performed by the American astronomer Edwin Hubble in his 1929 seminal paper. The investigations of spiral nebulae undertaken by the Swedish astronomer Knut Lundmark, in 1924, are also considered in this context.
I briefly present the foundations of relativistic cosmology, which are, General Relativity Theory and the Cosmological Principle. I discuss some relativistic models, namely, Einstein static universe and Friedmann universes. The classical bibliographi
c references for the relevant tensorial demonstrations are indicated whenever necessary, although the calculations themselves are not shown.
Einsteins static model is the first relativistic cosmological model. The model is static, finite and of spherical spatial symmetry. I use the solution of Einsteins field equations in a homogeneous and isotropic universe -- Friedmanns equation -- to c
alculate the radius of curvature of the model (also known as Einsteins universe). Furthermore, I show, using a Newtonian analogy, the models mostly known feature, namely, its instability under small perturbations on the state of equilibrium.
Graphical representations of classical Friedmanns models are often misleading when one considers the age of the universe. Most textbooks disregard conceptual differences in the representations, as far as ages are concerned. We discuss the details of
the scale-factor versus time function for Friedmanns solutions in the time range that includes the ages of model universes.
