Einstein's Universe: Cosmological structure formation in numerical relativity

TL;DR

This paper presents large-scale cosmological simulations using numerical relativity to study structure formation and backreaction effects without relying on background cosmology, providing insights into cosmic web emergence and curvature variations.

Contribution

It introduces direct Einstein equation simulations of cosmic structure formation, a novel approach that bypasses traditional background assumptions.

Findings

Backreaction energy density is around 10^-8 of matter energy density.

Local spatial curvature varies by 2-3% on scales above the homogeneity scale.

Simulations show emergence of cosmic web without background cosmology.

Abstract

We perform large-scale cosmological simulations that solve Einstein's equations directly via numerical relativity. Starting with initial conditions sampled from the cosmic microwave background, we track the emergence of a cosmic web without the need for a background cosmology. We measure the backreaction of large-scale structure on the evolution of averaged quantities in a matter-dominated universe. Although our results are preliminary, we find the global backreaction energy density is of order $10^{-8}$ compared to the energy density of matter in our simulations, and is thus unlikely to explain accelerating expansion under our assumptions. Sampling scales above the homogeneity scale of the Universe ($100-180\,h^{-1}$Mpc), in our chosen gauge, we find $2-3\%$ variations in local spatial curvature.