The Perfect Cosmological Principle states that the Universe

Universe

The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

 is homogenous

Homogeneity (physics)

In general, homogeneity is defined as the quality or state of being homogeneous . For instance, a uniform electric field would be compatible with homogeneity...

 and isotropic

Isotropy

Isotropy is uniformity in all orientations; it is derived from the Greek iso and tropos . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix an, hence anisotropy. Anisotropy is also used to describe situations where properties vary...

 in space and time. In this view the universe looks the same everywhere (on the large scale), the same as it always has and always will. It is the principle underpinning steady-state theory and emerging from Chaotic inflation theory

Chaotic inflation theory

The Chaotic Inflation theory is a variety of the inflationary universe model, which is itself an outgrowth of the Big Bang theory. Chaotic Inflation, proposed by physicist Andrei Linde, models our universe as one of many that grew as part of a multiverse owing to a vacuum that had not decayed to...

.
The Perfect Cosmological Principle is an extension of the Cosmological Principle

Cosmological Principle

In modern physical cosmology, the cosmological principle is the working assumption that observers on Earth do not occupy an unusual or privileged location within the universe as a whole, judged as observers of the physical phenomena produced by uniform and universal laws of physics...

, which accepts that the universe changes its gross feature with time, but not across space.