An Etymological Dictionary of Astronomy and Astrophysics

A cosmological model developped by Roger Penrose and colleagues according which the Universe undergoes repeated cycles of expansion. Each cycle, referred to an aeon, starts from its own “→ big bang” and finally comes to a stage of accelerated expansion which continues indefinitely. There is no stage of contraction (to a “→ big crunch”) in this model. Instead, each aeon of the universe, in a sense “forgets” how big it is, both at its big bang and in its very remote future where it becomes physically identical with the big bang of the next aeon, despite there being an infinite scale change involved, on passing from one aeon to the next. This model considers a conformal structure rather than a metric structure. Conformal structure may be viewed as family of metrics that are equivalent to one another via a scale change, which may vary from place to place. Thus, in conformal space-time geometry, there is not a particular metric g_ab, but an equivalence class of metrics where the metrics ğ_ab and g_ab are considered to be equivalent if there is a smooth positive scalar field Ω for which ğ_ab = Ω g_ab (R. Penrose, 2012, The Basic Ideas of Conformal Cyclic Cosmology).

See also: → conformal; → cyclic; → cosmology.