Superposition of FLRW universes

Abstract

We show that (1) the Einstein field equations with a perfect fluid source admit a nonlinear superposition of two distinct homogenous Friedman-Lemaitre-Robertson-Walker (FLRW) metrics as a solution, (2) the superposed solution is an inhomogeneous geometry in general, (3) it reduces to a homogeneous one in the two asymptotes which are the early and the late stages of the universe as described by two different FLRW metrics, (4) the solution possesses a scale factor inversion symmetry and (5) the solution implies two kinds of topology changes: one during the time evolution of the superposed universe and the other occurring in the asymptotic region of space.

Conformal scale factor inversion for domain walls and holography

“…The idea of a scale factor inversion map is very similar in nature to the "scale factor duality" (SFD) transformations used in cosmology. The paradigmatic example of scale factor duality is the one found by Veneziano [32], but other maps between cosmological solutions have also been called by the same apellation, e.g., [33,34,37,48]. The analogous of our map for cosmological spacetimes, in particular, has been called a scale factor duality in [33,34].…”

FLRW-cosmology in generic gravity theories

“…FLRW metric is mainly used to describe the universe as a homogeneous isotropic fluid distribution [1][2][3][4][5]. For inhomogeneous cosmological solutions, see for example [6][7][8]. On the other hand, current cosmological observations indicate that our universe is undergoing an accelerating expansion phase.…”