Observational background of TREDER's gravitation theory in cosmology and the role of viscosity

Abstract Starting from solutions of T REDER'S field equations for a homogeneous and isotropic universe filled with incoherent matter ( p = 0) relations between observation quantities are derived and discussed. The F RIEDMANN time is of the order of H UBBLE age, the deceleration parameter may principally possess any positive or negative value, hence it is also possible to explain any m,z ‐relation completely in the frame of this theory. A decision between E INSTEIN'S theory and T REDER'S by cosmological observations is impossible. – Considering a realistic medium which consists of particles and radiation, energy dissipation originating from bulk viscosity (due to the interaction of particles and quanta) prevents cosmological singularities. Thereby entropy, now present in form of relict radiation, is produced. This process generates large amounts of restmass‐free energy in the phase of maximum contraction and therefore could as well explain the large luminosity of compact single objects (quasars?). Models with energy dissipation are not invariant with respect to time reflection t → – t in contrast to E INSTEIN'S theory. If demanding the universe to be free from singularities the direction of cosmic time is uniquely determined. This demand then restricts the possible relations between observation data to the case q 0 = + 1 being in accord with the latest determination by S ANDAGE .