Answer:
The correct answer or fill in would be- but Change and evolve over time.
Explanation:
The perfect cosmological principle is a extended version of the cosmological principle. The perfect cosmological principle says that the universe is look same from all directions but can be change and evolve with time.
Steady state theory supports this theory as it also says that universe is expanding but also maintain its density even though it continuously creates stars and galaxies but still look same.
Thus, the correct answer is - but Change and evolve over time.
