Penrose's basic construction is to connect a countable sequence of open Friedmann–Lemaître–Robertson–Walker metric spacetimes, each representing a Big Bang followed by an infinite future expansion. Penrose noticed that the pastconformal boundary of one copy of FLRW spacetime can be "attached" to the future conformal boundary of another, after an appropriate conformal rescaling. In particular, each individual FLRW metric is multiplied by the square of a conformal factor that approaches zero at timelike infinity, effectively "squashing down" the future conformal boundary to a conformally regular hypersurface. The result is a new solution to Einstein's equations, which Penrose takes to represent the entire universe, and which is composed of a sequence of sectors that Penrose calls "aeons".
Physical implications
The significant feature of this construction for particle physics is that, since bosons obey the laws of conformally invariant quantum theory, they will behave in the same way in the rescaled aeons as in their former FLRW counterparts. For such particles, the boundary between aeons is not a boundary at all, but just a spacelike surface that can be passed across like any other. Fermions, on the other hand, remain confined to a given aeon, thus providing a convenient solution to the black hole information paradox; according to Penrose, fermions must be irreversibly converted into radiation during black hole evaporation, to preserve the smoothness of the boundary between aeons. The curvature properties of Penrose's cosmology are also convenient for other aspects of cosmology. First, the boundary between aeons satisfies the Weyl curvature hypothesis, thus providing a certain kind of low-entropy past as required by statistical mechanics and by observation. Second, Penrose has calculated that a certain amount of gravitational radiation should be preserved across the boundary between aeons. Penrose suggests this extra gravitational radiation may be enough to explain the observed cosmic acceleration without appeal to a dark energy matter field.
Empirical tests
In 2010, Penrose and Vahe Gurzadyan published a preprint of a paper claiming that observations of the cosmic microwave background made by the Wilkinson Microwave Anisotropy Probe and the BOOMERanG experiment contained an excess of concentric circles compared to simulations based on the standard Lambda-CDM model of cosmology, quoting a 6-sigma significance of the result. However, the statistical significance of the claimed detection has since been disputed. Three groups have independently attempted to reproduce these results, but found that the detection of the concentric anomalies was not statistically significant, in that no more concentric circles appeared in the data than in Lambda-CDM simulations. The reason for the disagreement was tracked down to an issue of how to construct the simulations that are used to determine the significance: The three independent attempts to repeat the analysis all used simulations based on the standard Lambda-CDM model, while Penrose and Gurzadyan used an undocumented non-standard approach. In 2013 Gurzadyan and Penrose published the further development of their work introducing a new method they termed the "sky-twist procedure" in which WMAP data is directly analysed; in 2015, they published the results of Planck data analysis confirming those of WMAP, including the inhomogeneous sky distribution of those structures. In a paper published on August 6, 2018 Daniel An, Krzysztof Antoni Meissner, Pawel Nurowski and Penrose presented a continued analysis of the CMB data as it seemed to them that “…anomalous points provide an important new input to cosmology, irrespective of the validity of CCC.” They also suggest that those anomalies could be what in CCC are Hawking points i.e. remnant signals from “…Hawking evaporation of supermassive black holes in the aeon prior to ours” and claim that a B-mode location found by the BICEP2 team is exactly at one of these Hawking point as predicted by CCC.
In 2015, Gurzadyan and Penrose also discussed the Fermi paradox, the apparent contradiction between the lack of evidence but high probability estimates for the existence of extraterrestrial civilizations. Within conformal cyclic cosmology, the cosmic microwave background provides the possibility of information transfer from one aeon to another, including of intelligent signals within information panspermia concept.
