For many years, scientists have believed that the Universe is expanding faster because of a mysterious force called dark energy. This unknown energy makes up nearly 68% of the Universe, but scientists still do not know what it really is.
The most accepted explanation is that dark energy is a constant energy of space, known as the cosmological constant (Λ). This idea is part of the standard model of cosmology called ΛCDM, which successfully explains many observations about the Universe.
However, recent observations have started raising an important question: What if dark energy is not constant? What if it changes with time?
A new study by Gil-Ocaranza and his team explores a fascinating possibility — that neutrinos, tiny particles that are everywhere in the Universe, may help create a changing form of dark energy.
The researchers suggest that interactions between neutrinos and a very light particle called a scalar field could produce a dynamic dark energy effect. This means dark energy may not be a fixed force but something that evolves as the Universe changes.
The Mystery of Dark Energy
When scientists discovered in the late 1990s that the Universe’s expansion is accelerating, they were surprised. Gravity should slow down expansion, yet galaxies were moving away from each other faster over time.
To explain this acceleration, scientists introduced dark energy — a mysterious component pushing the Universe apart.
The simplest explanation says dark energy has always remained constant. But recent observations, especially from the Dark Energy Spectroscopic Instrument (DESI), have suggested that dark energy may actually change.
DESI researchers studied the distribution of galaxies across the Universe and combined their results with measurements from the cosmic microwave background and exploding stars called supernovae.
The results are still not a confirmed discovery, but they show a possible hint that the Universe may not follow the simple ΛCDM model perfectly.
The Surprising Role of Neutrinos
Neutrinos are some of the strangest particles known to science. They are extremely light, have no electric charge, and interact very weakly with normal matter. Trillions of neutrinos pass through your body every second without you noticing.
For a long time, scientists thought neutrinos had no mass. But experiments later showed that they do have a tiny amount of mass.
Because neutrinos are present throughout the Universe, even small changes in their behavior could have a huge impact on cosmic evolution.
The new research suggests that neutrinos may interact with an unknown lightweight particle called a scalar field. This interaction could change the effective mass of neutrinos depending on the temperature and history of the Universe.
As the Universe expanded and cooled, these changing neutrino properties could create an energy effect that behaves like dark energy.
A New Idea About Gravity
To develop this theory, researchers used an alternative idea called Unimodular Gravity.
In Einstein’s general theory of relativity, energy and matter determine how space and time behave. The cosmological constant is usually treated as a fixed property of empty space.
But Unimodular Gravity provides a different perspective. It allows energy exchange between different parts of the Universe, meaning vacuum energy could have a more dynamic behavior.
In this model, neutrino interactions can create changes in the vacuum energy, producing a dark energy component that evolves over time.
Simply explained, instead of dark energy being a permanent feature of space, it could be influenced by the activity of tiny particles like neutrinos.
Two Different Dark Energy Possibilities
The scientists tested two versions of their model.
The first model involved one type of neutrino. In this case, dark energy changes slowly and increases toward the present time.
The second model included two types of neutrinos. This produced a more complex result.
In this version, dark energy could increase, reach a maximum at a certain point in cosmic history, and then decrease later.
This possibility is especially interesting because some recent observations suggest that dark energy may be weakening instead of staying constant.
If future observations confirm this behavior, it could mean that the Universe’s expansion is controlled by a much more complicated process than scientists expected.
Testing the Theory With Real Observations
To check whether their idea matches reality, the researchers compared their model with several modern astronomical datasets.
They used information from:
Supernova observations
Cosmic expansion measurements
Megamaser distance measurements
DESI galaxy mapping data
They studied different possible neutrino masses and calculated how strong the neutrino interaction would need to be.
Their results suggest that the interaction strength could be around 10¹² eV⁻².
If the interaction between neutrinos and the scalar particle is naturally strong, the mediator particle responsible for this interaction would need to be extremely light — around 10⁻⁶ electron volts.
Such a particle would be much lighter than most known particles and would belong to a group of hypothetical ultralight particles.
Could This Help Solve Other Cosmic Problems?
The idea is important because neutrinos are already connected to several mysteries in physics.
One major problem is the Hubble tension — the disagreement between different measurements of how fast the Universe is expanding.
Some scientists believe that unknown neutrino physics could help explain this difference.
If neutrinos can influence dark energy, they might provide a possible connection between two major puzzles:
Why is the Universe expanding faster?
Why do different measurements of the expansion rate disagree?
However, the current evidence is not enough to prove this theory. The preference for neutrino-driven dark energy is around the level of a scientific hint, not a confirmed discovery.
What Happens Next?
The researchers believe that future studies will need to examine how this model affects more detailed observations.
Scientists will need to study:
The cosmic microwave background
The formation of galaxies
The movement of matter across the Universe
The detailed behavior of neutrinos
These tests will help determine whether neutrinos are truly connected to dark energy or whether the Universe follows the simpler ΛCDM model.
The possibility that tiny neutrinos could influence the largest structures in the Universe is a remarkable idea.
For now, dark energy remains one of the biggest mysteries in science. But this research suggests that the answer may not only lie in distant galaxies or exotic cosmic forces — it may also be hidden inside some of the smallest particles in existence.
Reference: Alejandro Gil-Ocaranza, Josue De-Santiago, Mauricio Lopez-Hernandez, Jorge L. Cervantes-Cota, "Dark energy from neutrino interactions in Unimodular Gravity", Arxiv, 2026. https://arxiv.org/abs/2606.28488
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