 This contrast can be clarified in terms of the “physics horizon” (Ellis 2007), which delimits the physical regime accessible to terrestrial experiments and observations, roughly in terms of energy scales associated with different interactions. The horizon can be characterized more precisely for a chosen theory, by specifying the regions of parameter space that can be directly tested by experiments and  observations.[23]  Aspects of cosmological theories that extend past the physics horizon cannot be independently tested through non-cosmological experiments or observations; the only empirical route to evaluating these ideas is through their implications for cosmology. (This is not to deny that there may be strong theoretical grounds to favor particular proposals, as extensions of the core theories.)