  In 1917 Einstein introduced into his field equations a cosmological term
having the cosmological constant as a coefficient, in order that the theory
should yield a static universe. Einstein desired to eliminate absolute space
from physics according to "Mach's ideas". De Sitter objected to the
"world-matter" in Einstein's world, and proposed a vacuum solution of
Einstein's field equations with the cosmological constant and with no
"world-matter". In 1920 the world-matter of Einstein's world was equivalent to
"Mach's Ether", a carrier of the effects of inertia. De Sitter's 1917 solution
predicted a spectral shift effect. In 1923 Eddington and Weyl adopted De
Sitter's model and studied this effect. Einstein objected to this "cosmological
problem". In 1922-1927, Friedmann and Lamaitre published dynamical universe
models. Friedmann's model with cosmological constant equal to zero was the
simplest general relativity universe. Einstein was willing to accept the
mathematics, but not the physics of a dynamical universe. In 1929 Hubble
announced the discovery that the actual universe is apparently expanding. In
1931 Einstein accepted Friedmann's model with a cosmological constant equal to
zero, which he previously abhorred; he claimed that one did not need the
cosmological term anymore. It was very typical to Einstein that he used to do a
theoretical work and he cared about experiments and observations. This paper is
a new interpretation to Einstein's cosmological considerations over the period
1917-1931.
