For the last 25 years, most scientists have believed that about 70% of the universe is formed by something called ‘’dark energy.’’ This invisible energy was used to explain why the universe is expanding and in a very fast way. However, a new study suggests that maybe that mysterious energy is not necessary and the researchers propose that the issue may lie in how we understand gravity itself.
The research was conducted by an international team from the Center of Applied Space Technology and Microgravity at the University of Bremen and the Transilvania University of Brașov, and published in the Journal of Cosmology and Astroparticle Physics. So, let’s find out more about the universe.
Dark energy
In 1998, astronomers saw that certain distant exploding stars, known as supernovae, were weaker than expected. This showed that they were further than they should. The surprising conclusion was that the universe is expanding at an accelerating rate. Instead of slowing down due to gravity, as many expected, the expansion was speeding up.
According to Einstein’s theory of general relativity, gravity should gradually slow the expansion of the universe because matter pulls everything inward. To make the equations match the observations, scientists added a new term to the equations that represented a constant energy filling all of space: dark energy.
Over time, dark energy became a central part of modern cosmology. Today, scientists estimate that it makes up roughly 70% of the universe. However, there has always been a problem: dark energy did not naturally emerge from known physical laws. It was introduced to make the mathematical model fit the data.
A new way to understand universe expansion
The new study proposes analyzing gravity from a different perspective. Einstein’s theory describes space and time using a type of mathematics called Riemannian geometry. This framework depends on position in space but does not consider the direction or speed of moving objects in a more detailed way.
Researchers used a more general version called Finsler geometry, which does consider position, direction, and movement speed. This change might seem like nothing, but on a larger scale it can alter how gravity influences the expansion of the universe. In the traditional model, only one part of how matter behaves influences gravity through what is known as the energy-momentum tensor. However, in the Finsler framework, more aspects of particle motion and distribution can influence the gravitational field.
To describe how the universe evolves with the passage of time, scientists developed what they call the Finsler Friedmann equation to determine how the size of the universe changes and how space-time is structured.
Universe accelerating with no dark matter
The most surprising part about this study is what happens when analyzing an empty universe, with no matter, and without adding a cosmological constant (which represents dark energy in standard cosmology), the equations naturally allow for exponential expansion.
In this solution, the structure of spacetime is only slightly different from the standard Friedmann–Lemaître–Robertson–Walker model used in conventional cosmology. For slowly moving objects, the predictions of both models are very similar.
Christian Pfeifer, a physicist at ZARM and co-author of the study, described the result as an exciting indication that accelerated expansion might be explained without treating dark energy as a separate ingredient. He suggests that this geometric perspective could open new ways of understanding the laws of nature at cosmic scales.
What changes and what doesn’t
This advance is mainly theoretical. It doesn’t mean that telescopes have proven dark energy doesn’t exist, what proves is that a wider version of space-time geometry can replicate the same effect that’s normally related to dark energy.
To make this new theory a solid alternative, it must match current observations, including the cosmic microwave background and the growth of large-scale cosmic structures.
In our daily life nothing changes, the night sky looks the same. However, on a scientific level, the idea is important because it suggests that if accelerated expansion comes from the structure of spacetime itself, then the universe may be simpler than previously thought.