Cosmological theories of special and general relativity - I

In the standard cosmological theory one uses the Einstein concepts of space and time as were originally introduced for the special theory of relativity and the general relativity theory. According to this approach all physical quantities are described in terms of the continuum spatial coordinates and time. Using general relativity theory a great progress has been made in understanding the evolution of the Universe. Cosmologists usually measure spatial distances and redshitfs of faraway galaxies as expressed by the Hubble expansion. In recent years this fact was undertaken to develop new theories in terms of distances and velocities (redshift). While in Einstein's relativity the propagation of light plays the major role, in the new theory it is the expansion of the Universe that takes that role and appears at the outset. The cosmic time becomes crucial in these recent theories, which in the standard theory is considered to be absolute but here it is relative. In this lecture this new approach to cosmology is presented.