Answer:
The given blank can be filled with the steady state theory.
Explanation:
The theory based on the perfect cosmological principle is the steady-state theory. On the basis of this theory, the universe is isotropic, homogenous, and immutable. This hypothesis did not reject the expansion of the universe, however, it believed in the spontaneous generation of matter to counteract the observed expansion, that is, maintaining the average density same.
This theory was suggested by Bondi, Hoyle, and Gold in 1948. The steady-state theory lost its objectives when the discovery of the cosmic background radiation was done.
