 The basic challenge in cosmology regards how to test and evaluate cosmological models, given our limited access to the unique universe. As discussed above, current cosmological models rely in part on extrapolations of well-tested local physics along with novel proposals, such as the inflaton field. The challenge is particularly pressing in evaluating novel claims that only have cosmological implications, due to the physics horizon  (§2.4).  Distinctions that are routinely employed in other areas of physics, such as that between laws and initial conditions, or chance and necessity, are not directly applicable, due to the uniqueness of the universe.