 In his theory of conformal cyclic cosmology, Penrose claims that as the big bang is approached, massive objects play a negligible role, so that the physics is governed by degrees of freedom that are invariant under rescaling of lengths and times. Such degrees of freedom are called “conformal invariants.” Thus, Penrose claims, we make a mistake to model the early universe by a Lorentzian manifold with a metric (as is done in classical general relativity). Rather, spacetime should be described by a conformal manifold, which is essentially a conformal equivalence class of general relativistic spacetimes. The “cyclic” part of Penrose’s cosmology comes from noticing that the future of one ever-expanding universe can be smoothly bridged to the past of another big-bang universe by means of such a conformal manifold. In this case, the big bang is not a true beginning, but only a sort of phase change from one “epoch” to another (Penrose 2010).