Conformal Cyclic Cosmology from Varying Fundamental Constants

Abstract

We investigate a bimetric cosmological model in which the gravitational and matter sectors are described by distinct metrics related through a time-dependent function $\alpha(t)$. This relation leads to dynamical gravitational parameters, with $G(t)\propto\alpha^{-3}$ and $c_{\rm grav}(t)\propto\alpha^{-1}$, where $c_{\rm grav}$ denotes the propagation speed of gravitational interactions. We consider a class of solutions for which $\alpha\rightarrow\infty$ at a finite cosmic time, resulting in $G\rightarrow0$ and $c_{\rm grav}\rightarrow0$. For an analytically tractable solution, we show that the final singularity occurs at finite conformal time and possesses a conformal structure compatible with a possible transition between successive cosmological cycles. The Tipler and Kr\'olak criteria indicate that the singularity is strong. We further discuss the physical consequences of the weakening gravitational interaction, including the dissolution of gravitationally bound structures and the shrinking of black-hole horizons. These effects suggest a possible mechanism leading toward an effectively radiation-dominated final state, which may be relevant for Conformal Cyclic Cosmology. The results provide a motivation for extending the analysis to more general scalar--tensor theories of gravity.