For nearly 30 years, scientists have believed that a mysterious force called dark energy is causing the universe to expand faster and faster.
But a new mathematical study suggests that dark energy may not be needed at all.
Researchers from the University of California, Davis have published a paper in Proceedings of the Royal Society A arguing that the standard model used to explain the universe’s expansion may have a serious flaw.
Their calculations suggest that the mathematical framework behind the model is unstable, raising questions about whether it can accurately describe the real universe.
The study focuses on the Einstein-Euler equations, which combine Albert Einstein’s theory of general relativity with equations used to describe the motion of fluids.
Scientists use these equations to study many cosmic objects and events, including galaxies, black holes, and the expansion of the universe itself.
The researchers examined a widely used model known as the Lambda-Cold Dark Matter (Lambda-CDM) model, which is currently the standard explanation for how the universe evolved after the Big Bang. This model includes dark energy as a key ingredient.
According to study author Blake Temple, the problem is that the mathematical solutions behind this model appear to be unstable. He compares the situation to a pencil balanced perfectly on its tip. While it is technically possible for the pencil to stand upright, even the slightest disturbance will cause it to fall.
Temple argues that the mathematical models used to describe cosmic expansion behave in a similar way. They may satisfy the equations, but they are so unstable that they would be unlikely to exist in nature.
The team studied mathematical descriptions called Friedmann spacetimes, which assume that matter is spread evenly throughout the universe. These models form the foundation of the standard cosmological theory.
Their analysis found that Friedmann spacetimes become unstable at both very small and very large scales. If this conclusion is correct, it would suggest that the standard model of cosmology is not a realistic solution to Einstein’s equations, whether dark energy is included or not.
Instead, the researchers propose that the universe’s accelerating expansion could emerge naturally from Einstein’s original equations without requiring dark energy or a cosmological constant.
The findings also raise questions about the Copernican principle, the long-standing idea that Earth does not occupy a special location in the universe. The researchers argue that both the standard cosmological model and their alternative explanation require observers to be in a particular region of space to match observations.
While many cosmologists will likely debate these conclusions, the study highlights that fundamental questions about the universe remain unresolved. If the new mathematics proves correct, scientists may need to rethink some of the most widely accepted ideas about how the universe expands and evolves.
