 A dynamical approach, even if it is successful in describing a phase of the universe’s evolution, arguably does not offer a complete solution to the problem of initial conditions: it collapses into one of the other two approaches. For example, an inflationary stage can only begin in a region of spacetime if the inflaton field and the geometry are uniform over a sufficiently large region, such that the stress-energy tensor is dominated by the potential term (implying that the derivative terms are small) and the gravitational entropy is small. There are other model-dependent constraints on the initial state of the inflaton field. One way to respond is to adopt Penrose’s point of view, namely that this reflects the need to choose a special initial state, or to derive one from a previous expansion phase. The majority of those working in inflationary cosmology instead appeal to the third approach: rather than treating inflation as an addition to standard big-bang evolution in a single universe, we should treat the observed universe as part of a multiverse, discussed below. But even this must have a theory of initial conditions.