New Cosmology Model Suggests Patchy Expansion of the Universe

• A Hungarian research team has proposed a new cosmological model in which the universe’s accelerating expansion can be explained without invoking dark energy.
• The approach assumes that the cosmos is not perfectly homogeneous but made of many independently expanding regions.
• Their model may also ease the long‑standing Hubble tension while remaining consistent with key astronomical observations.

Rethinking Cosmic Expansion

A group of Hungarian researchers led by astrophysicist Péter Raffai from Eötvös Loránd University has introduced a theoretical framework that challenges one of modern cosmology’s central assumptions. The standard Lambda–CDM model treats the universe as homogeneous and isotropic on large scales, an idea that has successfully explained the cosmic microwave background, galaxy distributions and many other observations. According to this model, cosmic expansion initially slowed due to gravity but began accelerating roughly 5–6 billion years ago because of an unknown component called dark energy. Although dark energy is widely accepted, its physical nature remains one of the biggest mysteries in physics.

The standard model also faces a persistent difficulty known as the Hubble tension. Measurements of the universe’s expansion rate from the early cosmos, such as those derived from the cosmic microwave background, consistently yield lower values than those obtained from nearby galaxies and supernovae. This discrepancy has resisted explanations based on measurement errors and has become one of the most debated issues in cosmology. The new Hungarian model offers a potential way to address this tension without modifying early‑universe physics.

Their proposal, called the inhomogeneous Einstein–de Sitter model (iEdS), assumes that the universe is not perfectly uniform. Instead, it consists of many regions with different densities and spatial curvatures, each evolving partly independently. These regions do not need to fill space seamlessly, but they must occupy most of the cosmic volume. The interaction between their individual expansion rates produces a global behaviour that differs from homogeneous models.

Patchy Structure and Its Consequences

In the iEdS framework, dense regions with positive curvature expand more slowly. By contrast, low‑density regions with negative curvature expand more rapidly and gradually dominate the total cosmic volume. Over time, this shift causes the average curvature of the universe to become increasingly negative. Such behaviour does not occur in homogeneous models, where curvature remains fixed.

This evolving curvature has important implications for cosmic expansion. A universe with constant negative curvature eventually settles into a steady expansion rate once matter becomes less influential. In the iEdS model, however, curvature grows more negative as matter’s role diminishes. This combination leads to a temporary phase of accelerated expansion, even though no dark energy is present. The acceleration arises naturally from the differing evolution of the regions rather than from a new form of energy.

The model predicts that this acceleration does not continue indefinitely. As the universe evolves, the expansion rate gradually approaches a uniform pace again. This behaviour contrasts with the standard model, where dark energy drives perpetual acceleration. The iEdS approach therefore offers a fundamentally different explanation for the observed expansion history.

Another notable consequence concerns the cosmic horizon. In the standard model, accelerated expansion creates a boundary beyond which light can never reach us. The iEdS model, lacking permanent acceleration, does not produce such an impenetrable horizon. In principle, the entire universe could become observable over extremely long timescales, and distant regions might even be reachable.

Compatibility With Observations

Despite its unconventional assumptions, the iEdS model does not discard the successful elements of modern cosmology. It preserves the early‑universe processes described by the Lambda–CDM framework, including the formation of the cosmic microwave background, the synthesis of light elements and the possible inflationary phase. These features ensure that the model remains consistent with well‑established observations from the universe’s first moments.

The researchers report that their model can reproduce several key cosmological measurements. These include the structure of the cosmic microwave background, the pattern of baryon acoustic oscillations and the brightness of Type Ia supernovae. Importantly, the model accommodates these observations without generating the Hubble tension. According to their calculations, the universe’s age in this framework is 13.67 billion years, only about one percent lower than the value inferred from the standard model.

The scientific community has responded positively to the work. The team’s paper has been accepted for publication in *Physical Review D*, a respected international journal in theoretical physics. This acceptance suggests that the model will receive further scrutiny and comparison with other cosmological approaches. Future studies may explore whether additional observations can distinguish between the iEdS model and the standard cosmological framework.

The idea that cosmic inhomogeneities might influence large‑scale expansion has appeared in earlier theoretical discussions, but it has rarely been developed into a model capable of matching observations. The Hungarian team’s work stands out because it provides a mathematically consistent framework that aligns with multiple datasets while offering a fresh perspective on dark energy and the Hubble tension. As new astronomical surveys deliver increasingly precise measurements, models like iEdS may play a growing role in interpreting the universe’s behaviour.