 A more adequate criterion of when a cosmological model is consonant with creation ex nihilo would require a detailed analysis of singular spacetimes (for extensive discussion of the latter topic, see Earman 1995). The best current account of when a spacetime is truly singular (as opposed to merely being described with inadequate coordinates) is when it contains inextendible geodesics of finite length. Intuitively, a geodesic is the path that would be followed by a clock in freefall. If a clock were travelling on a past-inextendible geodesic, then at some finite time in the past, the clock did not exist; more strongly, spacetime itself did not exist. Thus, the big-bang theologian would do best to claim that creation ex nihilo is confirmed precisely by those cosmological spacetimes that have inextendible geodesics. (Indeed, this criterion does hold for FRW models.) The main problem with such a proposal is that it ties a robust, intuitive theological doctrine down to an extremely precise technical feature of Lorentzian manifolds (as described by differential geometry). The risk then is that by doing so, one would add extraneous content to the theological doctrine: a future model might fail the technical criterion while still being consistent with the theological doctrine. Furthermore, many Christian theists claim that core theological doctrines are perspicuous—in particularly, not understood exclusively by an elite class of priests or scholars. But the notion of a Lorentzian manifold having incomplete geodesics can hardly be said to be accessible to the average layperson.