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Why is the universe expanding at an ever-increasing rate? This is one of the most exciting yet unresolved questions in modern physics. Because it cannot be fully answered using our current physical worldview, researchers assume the existence of a mysterious "dark energy." However, its origin remains unclear to this day.

An international research team from the Center for Applied Space Technology and Microgravity (ZARM) at the University of Bremen and the Transylvanian University of Brașov in Romania has come to the conclusion that the expansion of the universe can be explained—at least in part—without dark energy.

In physics, the evolution of the universe has so far been described by the general theory of relativity and the so-called Friedmann equations. However, in order to explain the observed expansion of the universe on this basis, an additional "dark energy term" must be manually added to the equations.

This unsatisfactory solution prompted the researchers to take a different approach. Their findings, in the Journal of Cosmology and Astroparticle Â鶹ÒùÔºics, are based on an extension of general relativity (GR) by the later developed model of Finsler gravity. Unlike the original explanatory approach of GRT, the Finsler model allows for a more accurate modeling of the gravitational force of gases, as it is based on a more general spacetime geometry than GRT.

When the research team calculated the Finsler extension of the Friedmann equations, they made an exciting discovery: The Finsler-Friedmann equations already predict an accelerated expansion of the universe in a vacuum—without the need to introduce additional assumptions or "dark energy" terms.

"This is an exciting indication that we may be able to explain the accelerated expansion of the universe without dark energy, based on a generalized spacetime geometry," says Christian Pfeifer, ZARM physicist and member of the research team. "The new geometry opens up completely new possibilities for better understanding the laws of nature in the cosmos."