Researchers have proposed an alternative to dark energy for the universe's accelerating expansion. Using an extended form of Einstein's general relativity called Finsler gravity, they show that cosmic speedup can emerge naturally from spacetime geometry. This approach, detailed in a recent study, challenges the standard cosmological model.
The universe's expansion has been accelerating for billions of years, a phenomenon that cosmologists typically attribute to dark energy, an invisible force whose nature remains elusive. Standard models rely on Einstein's general theory of relativity and the Friedmann equations, but these require an ad hoc addition of dark energy to match observations from telescopes.
A team from the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen in Germany, collaborating with researchers at the Transylvanian University of Brașov in Romania, offers a fresh perspective. Their study, published in the Journal of Cosmology and Astroparticle Physics in October 2025, employs Finsler gravity, an extension of general relativity that provides a more general description of spacetime geometry.
Finsler gravity differs from the standard theory by better accounting for the gravitational effects on gases, which proves key for modeling the universe at large scales. When applied to the Friedmann equations, the resulting Finsler-Friedmann equations predict an accelerating expansion even in empty space, without needing to insert a dark energy term manually.
"This is an exciting indication that we may be able to explain the accelerated expansion of the universe, at least in parts, without dark energy, on the basis of a generalized spacetime geometry," said Christian Pfeifer, a physicist at ZARM and a member of the research team. The authors, including Nicoleta Voicu, Annamária Friedl-Szász, and Elena Popovici-Popescu, titled their paper "From kinetic gases to an exponentially expanding universe — the Finsler-Friedmann equation."
This work builds on recent developments in Finsler gravity and suggests that rethinking spacetime's structure could resolve longstanding puzzles in cosmology, potentially simplifying our understanding of the cosmos's fate.