Groundbreaking new findings are challenging the existence of dark energy, based on research that suggests the uneven structure of the universe could provide an alternate explanation for its accelerating expansion.
A long-hypothesized repulsive force that overcomes gravity and accounts for the increasing rate of expansion of our universe, the mysterious “dark energy” astrophysicists believe to be affecting the universe at the largest scales remains elusive.
Now, a new theory dubbed the “timescape” model presents an alternative: that the observed acceleration of our universe is not the result of an unseen force in the cosmos, but could instead arise from the irregular distribution of matter within it.
The model, developed by a research team at the University of Canterbury in Christchurch, New Zealand, challenges long-held assumptions about the supposed invisible force driving the acceleration of cosmic expansion, and could potentially help astronomers resolve several anomalies that have long perplexed cosmologists.
Questioning Dark Energy’s Existence
Although long accepted as a fundamental force behind one of astronomy’s greatest mysteries, dark energy’s existence remains theoretical. The concept of a mysterious invisible force was initially introduced to help account for phenomena that the standard model of physics currently cannot explain.
However, many scientists have acknowledged the persistent inconsistencies the theory presents, which include what astronomers call the “Hubble tension,” where observed predicted rates of cosmic expansion differ from those proposed by models that conform to the standard model.
Enter the Timescape
Now, researchers led by Professor David Wiltshire have proposed a bold alternative: that based on observations of light curves produced by supernovae, the universe’s expansion may not, in fact, be uniform.
According to Wiltshire and his colleagues, the universe unfolds in a “lumpy” manner, which arises from variations in the distribution of gravity with relation to different cosmic structures. The uneven distribution of the universe’s matter would exert a significant influence on the surrounding spacetime in very dense regions where galaxies exist, while having little effect on vast empty regions of the cosmos.
The resulting effect, Wiltshire proposes, creates the illusion of accelerating expansion that has long puzzled astronomers.
“Dark energy is a misidentification of variations in the kinetic energy of expansion,” explained Professor Wiltshire in a statement. “Our findings show that we do not need dark energy to explain why the Universe appears to expand at an accelerating rate.”
Because of the accumulation of matter in certain regions of space, time passes close to 35% more slowly than it does in empty cosmic voids where little matter is found. The new research by Wiltshire and his team suggests that over periods of billions of years, the resulting discrepancy would allow far more significant expansion in the void regions, which make up most of the universe’s large-scale structure.
This, the researchers say, can account for the perceived acceleration, and offers a better fit for the discrepancies that have long perplexed astronomers, all without any need for invisible dark energy.
Comparing Theories and Future Research
According to the standard Lambda Cold Dark Matter (ΛCDM) model, dark energy represents a weak anti-gravity force, which constitutes close to two-thirds of the Universe’s energy density.
Although this model can account for why observations of supernovae cause them to appear to be further away than they should be if expansion is occurring uniformly throughout the universe, recent measurements obtained with the Dark Energy Spectroscopic Instrument (DESI) since 2021, along with other sources of high-precision data, all point to the likelihood that the ΛCDM might be too simplistic to fully account for the Universe’s complex structure.
However, implementing tests for the timescape model will require robust observational data. In July, the launch of the European Space Agency’s Euclid satellite marked a promising advancement toward obtaining such data, as it is expected to provide insights that will likely be critical for gauging the new theory.
By examining the characteristics of more than 1,000 supernovae, the required amount of observational data could potentially be obtained to help verify the timescape model. Fortunately, Wiltshire and the University of Canterbury team have worked in collaboration with the Pantheon+ team to analyze 1,535 supernovae already, which which they say yields very promising evidence in support of the new theory.
Going forward, additional observations from Euclid and other sources, which include the forthcoming launch of NASA’s Nancy Grace Roman Space Telescope, may be able to provide essential data that may help to confirm the timescape theory’s validity, and thereby help to resolve one of cosmology’s greatest unresolved debates.
“With new data, the Universe’s biggest mystery could be settled by the end of the decade,” Wiltshire said.
The team’s research was recently detailed in a new paper by Wiltshire, along with co-authors Zachary G Lane, Antonia Seifert, and Ryan Ridden-Harper, titled “Cosmological foundations revisited with Pantheon+” that appeared onDecember 19, 2024, in Monthly Notices of the Royal Astronomical Society.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.