[Paper Review] Cosmological Acceleration from Gravitational Waves

Л. С. Марочник|arXiv (Cornell University)|Nov 21, 2015

Cosmology and Gravitation Theories5 references3 citations

TL;DR

This paper proposes that super-horizon gravitational waves in an empty universe can drive de Sitter-like accelerated expansion, offering a classical explanation for dark energy. The authors argue that these long-wavelength gravitational waves induce cosmological acceleration, which could account for the observed late-time acceleration of the universe, particularly as it becomes increasingly empty.

ABSTRACT

It is shown that the classical gravitational waves of super-horizon wavelengths are able to form the de Sitter accelerated expansion of the empty (with no matter fields) Universe. The contemporary Universe is about 70% empty and asymptotically is going to become completely empty, so the effect caused by emptiness should be already very noticeable. It could manifest itself as the dark energy.

Motivation & Objective

• To investigate whether classical gravitational waves with super-horizon wavelengths can induce cosmological acceleration in an empty universe.
• To explore the possibility that such gravitational wave effects could explain the observed dark energy-driven acceleration of the universe.
• To analyze the role of gravitational waves in the asymptotic, matter-free phase of cosmic evolution.
• To assess the detectability and significance of gravitational wave-induced acceleration in the current and future universe.

Proposed method

• The study employs classical general relativity to analyze the dynamics of long-wavelength gravitational waves in a vacuum spacetime.
• It focuses on super-horizon modes, which are not subject to causal constraints and can persist over cosmological scales.
• The analysis examines the energy-momentum tensor of gravitational waves and its backreaction on spacetime geometry.
• The paper derives conditions under which these waves can generate an effective cosmological constant-like term.
• It considers the asymptotic evolution of the universe toward a matter-free state, where such waves dominate.
• The model assumes a spatially flat, homogeneous, and isotropic universe with no matter or radiation fields.

Experimental results

Research questions

• RQ1 Can gravitational waves with wavelengths larger than the Hubble radius drive de Sitter-like expansion in an empty universe?
• RQ2 To what extent can the energy density of super-horizon gravitational waves account for the observed cosmological acceleration?
• RQ3 How does the backreaction of long-wavelength gravitational waves affect the large-scale geometry of spacetime?
• RQ4 Is the effect of these waves significant enough to explain dark energy in the current and future universe?

Key findings

• Super-horizon gravitational waves can generate an effective cosmological constant-like term through their energy-momentum tensor.
• The resulting spacetime evolution exhibits de Sitter-like expansion, consistent with the observed accelerated expansion of the universe.
• The effect becomes increasingly relevant as the universe evolves toward a matter-free state, which is expected to dominate in the far future.
• The paper suggests that the current 70% empty universe may already be experiencing measurable effects from these gravitational wave contributions.
• The model provides a classical, geometric explanation for dark energy without introducing new scalar fields or exotic matter.
• The original version of the paper was withdrawn by the author and incorporated into arXiv:1508.07312, which is the published version.