 One challenge to establishing theories of the initial state is entirely epistemic. As emphasized in  §2.4,  we lack independent experimental probes of physics at the relevant scales, so the extensions of core theories described above are only tested indirectly through their implications for cosmology. This limitation reflects contingent facts about the universe, namely the contrast between the energy scales of the early universe and those accessible to us, and does not follow from the uniqueness of the universe per se. Yet this limitation does not imply that it would be impossible to establish laws. There are cases in the history of physics, such as celestial mechanics, where confidence in a theory’s laws is based primarily on successful application under continually improving standards of precision.