Mathematicians at the University of California, Davis published findings in Proceedings of the Royal Society A suggesting that cosmic acceleration could emerge naturally from Einstein's equations without requiring dark energy.
The researchers, led by Blake Temple, a distinguished professor emeritus of mathematics, analyzed the Einstein-Euler equations, which combine general relativity with fluid dynamics. Their calculations indicate that Friedmann spacetimes, the mathematical foundation of standard cosmological models, are unstable at both small and large scales.
Temple compared the instability to a pencil balanced on its tip. "All the forces are in balance when a pencil is standing on end, so it is a 'solution of the equations,'" he said. "But it's unstable. Any breath of air and it falls away."
The team found that radial perturbations, disturbances that change with distance from a central point, can cause the expanding universe to depart from standard Friedmann model predictions. According to Temple, this instability suggests the universe could behave like the standard model predicts near a central region but exhibit different expansion behavior farther away.
"The instability of all Friedmann spacetimes to accelerated expansion suggests a simpler, more natural explanation for the acceleration of the universe than dark energy," Temple said. He argued the answer could already be contained within Einstein's original theory of gravity rather than requiring a separate form of energy.
Temple stated the work appears to rule out the Lambda-cold dark matter model as a stable solution of Einstein's equations. The researchers also note their findings raise questions about the Copernican principle, which holds that Earth's location in the universe is not fundamentally special.
The study represents a theoretical challenge to standard cosmology. Confirming whether this alternative explanation describes the actual universe would require comparing its predictions against astronomical observations.