For decades, dark energy has been one of the most enigmatic concepts in physics, introduced to explain the accelerated expansion of the Universe. This mysterious force, often described as an “antigravity” effect, was thought to make up approximately 70% of the Universe’s total energy density. However, new research challenges this assumption, proposing a groundbreaking explanation rooted in the behavior of gravity and the nature of time.

The concept of dark energy emerged to reconcile observations of distant supernovae. These celestial explosions appeared farther away than expected if the Universe’s expansion were consistent with a purely gravitational model. Physicists theorized that a repulsive force, dubbed dark energy, was driving the acceleration. This idea became a cornerstone of the ΛCDM (Lambda Cold Dark Matter) model, the standard framework for cosmology.

However, recent observations have raised questions about the accuracy of this model. The “Hubble tension”, for instance, reveals discrepancies between the current expansion rate of the Universe and its inferred early expansion from the Cosmic Microwave Background (CMB). Additionally, data from advanced instruments like the Dark Energy Spectroscopic Instrument (DESI) suggest that the ΛCDM model struggles to account for evolving patterns in cosmic structures.

Dark energy not exist
This graphic offers a glimpse of the history of the Universe, as we currently understand it. The cosmos began expanding with the Big Bang but then around 10 billion years later it strangely began to accelerate thanks to a theoretical phenomenon termed dark energy. Credit: NASA

Researchers at the University of Canterbury, led by Professor David Wiltshire, offer an alternative explanation that removes the need for dark energy altogether. Their timescape model proposes that the appearance of an accelerating Universe is an illusion caused by the uneven effects of gravity on time.

The theory hinges on a key principle of Einstein’s general relativity: gravity can distort the flow of time. In regions of space with strong gravitational fields, such as galaxies, time runs more slowly compared to vast, empty voids in the cosmos. These differences in time dilation mean that clocks in galactic regions would measure billions of years less than clocks in cosmic voids.

This uneven flow of time affects how we perceive the Universe’s expansion. Light traveling through these “grumpled” structures appears stretched in a way that mimics accelerated expansion, even though the Universe may simply be expanding at different rates in different regions.

Using an improved analysis of supernova light curves, the researchers have shown that the Universe’s expansion is far less uniform than previously believed. This non-uniformity supports the timescape model, which interprets these variations as natural consequences of gravitational time dilation rather than evidence of dark energy.

Dark energy not exist
This graphic shows the emergence of a cosmic web in a cosmological simulation using general relativity. From left, 300,000 years after the Big Bang to right, a Universe similar to ours today. The dark regions are void of matter, where a clock would run faster and allow more time for the expansion of space. The lighter purple regions are denser so clocks would run slower, meaning under the “timescape” model of cosmology that the acceleration of the Universe’s expansion is not uniform. Credit: Hayley Macpherson, Daniel Price, Paul Lasky / Physical Review D 99 (2019) 063522

When first tested in 2017, the timescape model offered a slightly better fit than the ΛCDM model, but with recent observations—including data from over 1,500 supernovae cataloged by the Pantheon+ collaboration—it now provides “very strong evidence” for a foundational shift in cosmological understanding.

The European Space Agency’s Euclid satellite and NASA’s Nancy Grace Roman Space Telescope are poised to play pivotal roles in testing the timescape model further. By collecting high-quality data from thousands of supernovae and other cosmic phenomena, scientists aim to distinguish definitively between the ΛCDM model and its alternatives.

As Professor Wiltshire notes, the timescape model could resolve some of the most pressing anomalies in modern cosmology, including the Hubble tension. If validated, it would revolutionize our understanding of the Universe, revealing that its apparent acceleration is a profound artifact of the interplay between gravity, time, and structure.

In the coming years, this research may bring us closer to answering one of the Universe’s most profound mysteries: the true nature of its expansion.

SOURCES

Royal Astronomical Society

Antonia Seifert, Zachary G Lane, Marco Galoppo, Ryan Ridden-Harper, David L Wiltshire, Supernovae evidence for foundational change to cosmological models, Monthly Notices of the Royal Astronomical Society: Letters, Volume 537, Issue 1, February 2025, Pages L55–L60, doi.org/10.1093/mnrasl/slae112

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