New mathematical research suggests that dark energy might not be needed to explain why the universe is expanding faster. This challenges the standard model of how the universe works.
Mathematicians are now questioning if dark energy is truly responsible for this accelerating expansion.
Challenging the Standard Model
A new study in Proceedings of the Royal Society A presents mathematical evidence. It suggests that the Einstein-Euler equations show instabilities. These equations combine general relativity and fluid dynamics. They are used to model galaxies, black holes, and the universe's expansion.
We're a new kind of news feed.
Regular news is designed to drain you. We're a non-profit built to restore you. Every story we publish is scored for impact, progress, and hope.
Start Your News DetoxThe findings challenge the Lambda-cold dark matter model. This is the main framework for Big Bang cosmology.
Blake Temple, a distinguished professor emeritus of mathematics at UC Davis, compared the standard model to a pencil balanced on its tip. He said that while the forces are balanced, it's unstable. A small disturbance can make it fall.
Friedmann Spacetime Instability
Temple's team found that Friedmann spacetimes are unstable. These are mathematical models used to describe how the cosmos expands. They are unstable at both small and large scales near the Big Bang. This makes them the most unstable solutions.
Temple explained that unstable solutions are not considered physical. They are never observed in nature.
He believes this instability points to a simpler explanation. This explanation stays within Einstein's original theory of gravity.
Temple noted that the instability of all Friedmann spacetimes suggests a more natural reason for the universe's acceleration than dark energy.
The Return of the Cosmological Constant
Dark energy was first suggested almost 30 years ago. It aimed to explain why the universe's expansion seems to be speeding up.
The idea comes from Einstein's 1915 equations of general relativity. Einstein added an antigravity term, the cosmological constant, to create a static universe. Later, Edwin Hubble found that the universe was expanding. Einstein then called the cosmological constant his "biggest blunder." Without it, his equations would have predicted expansion.
However, in the 1990s, the cosmological constant was brought back. It was linked to dark energy as a possible reason for the accelerating expansion. Modern models of the universe are based on a "Friedmann universe." In this model, matter expands while staying evenly spread out in space at any given time.
Finding Another Explanation
Temple and his team thought there were mathematical issues with this idea. This led them to look for other causes of cosmic acceleration.
Temple said their first idea was that a shockwave might be causing the expansion. The unusual acceleration would be the expanding wave behind that shockwave. They then realized there are self-similar solutions during the Big Bang's radiation era. These might model that expanding wave.
Self-similar equations describe systems that keep the same overall pattern or structure at different scales.
Instability Revealed by Self-Similar Equations
In the new study, researchers used a self-similar version of Einstein's equations. This version was developed in earlier work. It represented the standard cosmological model as a rest point of the equations. This allowed them to analyze the model's stability. They also looked at the stability of all Friedmann spacetimes during the Big Bang's matter-dominated era.
Temple stated that they proved Friedmann spacetimes are unstable to radial perturbation at large scales. This is similar to Einstein's static model. He believes this rules out the Lambda-cold dark matter model as a stable solution of Einstein's equations. This is true whether dark energy is included or not.
He added that the Big Bang should generally look like a Friedmann spacetime near the center. But far from the center, one should generally see accelerations away from Friedmann.
Cosmic Acceleration Without Dark Energy
The researchers concluded that the universe's accelerating expansion comes naturally from the Einstein-Euler equations. It does not need a cosmological constant or dark energy.
Their findings also question the Copernican principle. This principle states that Earth does not have a special place in the universe.
Temple noted that both the Lambda-cold dark matter model and a spherically symmetric spacetime require a special place for us to be physically plausible. If this principle rules out one, it must rule out the other.
Deep Dive & References
The instability of critical and underdense Friedmann spacetimes at the Big Bang as an alternative to dark energy - Proceedings of the Royal Society A: Mathematical Physical and Engineering Science, 2026
