Inhomogeneous structure formation may alleviate need for accelerating universe

TL;DR

This paper suggests that considering the universe's inhomogeneous matter distribution could explain observed cosmic acceleration without invoking dark energy, by showing how inhomogeneities affect global curvature and dynamics.

Contribution

It introduces a semi-quantitative analysis demonstrating how inhomogeneities and structure formation can mimic cosmic acceleration effects without dark energy.

Findings

Inhomogeneities induce negative curvature regions that grow over time.

Global curvature remains close to zero despite local curvature variations.

Inhomogeneity effects can account for apparent acceleration in the universe.

Abstract

When taking the real, inhomogeneous and anisotropic matter distribution in the semi-local universe into account, there may be no need to postulate an accelerating expansion of the universe despite recent type Ia supernova data. Local curvatures must be integrated (over all space) to obtain the global curvature of the universe, which seems to be very close to zero from cosmic microwave background data. As gravitational structure formation creates bound regions of positive curvature, the regions in between become negatively curved in order to comply with a vanishing global curvature. The actual dynamics of the universe is altered due to the self-induced inhomogeneities, again more prominently so as structure formation progresses. Furthermore, this negative curvature will increase as a function of time as structure formation proceeds, which mimics the effect of "dark energy" with negative pressure. Hence, the "acceleration" may be merely a mirage. We make a qualitative and semi-quantitative analysis, using newtonian gravity corrected for special relativistic effects, which works surprisingly well, to corroborate and illustrate/visualize these statements. This article may be seen as a plea to start taking seriously the observed inhomogeneous distribution and the nonlinearities of nonperturbative general relativity, and their impact on the dynamics and behavior of the cosmos.