isotropy

Isotropy means uniformity in all directions. This assumed to be statistically true regarding space (the universe), which is one of the assumptions of the cosmological principle, and in turn, an assumption of the Big Bang theory: though there are individual galaxies, stars, and clouds in each direction, in a general way, you find similar demographics of these. The absence of isotropy is anisotropy. Both terms are used regarding the cosmic microwave background (CMB) to describe the fact that it comes at us from all directions: it is basically isotropic but its very small anisotropy is of much research interest.

Isotopic radiation is radiation from a body that is emitted from it equally in all directions, such as electromagnetic radiation (EMR) from a star. When an especially bright source is discovered, such as with a redshift showing great distance, yet bright enough to observe at our distance, an immediate question is whether this is isotropic radiation or is anisotropic, e.g., beamed in our direction. If it is indeed isotropic, then its luminosity (its power; in this case, its isotropic radiant energy output) must be extreme and its high-luminosity mechanism is of research interest.