The Bondi universe: Can negative mass drive the cosmological expansion?

TL;DR

This paper proposes that the universe's transition to accelerated expansion can be explained by the nonlinear dynamics of mixed positive and negative mass configurations, without dark energy.

Contribution

It introduces a cosmological model with equal positive and negative Bondi masses showing a natural link between coupling transition and acceleration onset.

Findings

Mixed mass configurations are unstable and drive the system toward strong coupling.

Long-time N-body simulations show three expansion phases, including a late acceleration phase.

The acceleration phase coincides with the coupling parameter crossing unity.

Abstract

We identify a new cosmological coincidence that parallels the well-known matter/dark-energy coincidence: the present-epoch transition of the universe from a weakly coupled (collisionless) to a strongly coupled (collisional) gravitational regime. Within a cosmological model containing equal amounts of positive and negative Bondi masses -- consistent with the weak equivalence principle and momentum conservation -- we show that this coupling transition naturally coincides with the shift from a coasting to an accelerating expansion. A linear response analysis of the corresponding Vlasov-Poisson system reveals that mixed positive-negative mass configurations are always unstable, with growth rates that increase at shorter wavelengths, thereby driving the system toward strong coupling. Using long-time, exact one-dimensional N-body simulations, we demonstrate that the universe undergoes three successive expansion phases: an initial ballistic regime, an intermediate random-walk acceleration driven by sporadic Bondi encounters, and finally a uniformly accelerating phase triggered by the formation of stable positive/negative mass pairs. The onset of this last phase occurs precisely when the coupling parameter crosses unity, linking the two cosmological coincidences through a single dynamical mechanism. These results suggest that cosmic acceleration may arise from the nonlinear dynamics of a gravitationally neutral mixed-mass universe, without invoking dark energy or a cosmological constant.