Scientists in New Zealand are said to have solved one of astronomy's greatest mysteries by proving that dark energy - a force thought to drive the universe's expansion - does not actually exist.
Researchers from the University of Canterbury have proposed a radical new theory that challenges decades of astronomical understanding.
In a new paper published in Monthly Notices of the Royal Astronomical Society Letters, the team have argued that the effect of gravity on time itself provides the answer astronomers have been seeking for decades.
Dark energy has long been a placeholder term used by scientists to explain why the universe appears to be expanding at an accelerating rate.
The concept gained prominence in 1998 when the Hubble Space Telescope revealed that the universe was expanding much faster than theory predicted
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It is commonly thought to be a weak anti-gravity force, making up approximately two-thirds of the mass-energy density of the universe.
The concept gained prominence in 1998 when the Hubble Space Telescope revealed that the universe was expanding much faster than theory predicted.
Recent measurements from the James Webb Space Telescope have further complicated matters, showing the gaps between galaxies are growing eight to 12 per cent faster than expected.
No one has ever directly seen or measured dark energy, making it one of astronomy's most perplexing mysteries.
Lead author Professor David Wiltshire explains: "Our findings show that we do not need dark energy to explain why the Universe appears to expand at an accelerating rate."
The team's alternative 'timescape' model takes into account how time moves more slowly in gravitational fields, such as the one around Earth.
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Their research arrives at a crucial moment, as scientists face growing uncertainty around the current "standard model" of the universe, which traditionally assumed that the universe consisted of ordinary matter, invisible dark matter, and dark energy as a constant outward force.
The timescape model has proposed that a clock on Earth would move 35 per cent slower than one floating in the cosmic voids between galaxy superclusters, which means that whilst Earth completes one 24-hour day, a clock in space would already show 8:00 am the next morning.
Over the universe's lifetime, this effect becomes dramatic. Billions more years have passed in the voids between galaxies than at the heart of the Milky Way.
Even with a steady expansion rate since the Big Bang, these time differences mean the spaces between galaxies have grown much more than expected - creating what appears to be acceleration.
The research team validated their theory by studying Type Ia supernovae - exploding white dwarf stars whose brightness can be used to measure cosmic distances.
Looking ahead, the European Space Agency's Euclid satellite, launched in July 2023, could definitively prove the theory correct
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By comparing the supernovae's brightness with their speed moving away from Earth, scientists could calculate how much the universe has expanded since the explosions occurred.
The timescape model proved superior at predicting the supernovae data compared to traditional theories.
Looking ahead, the European Space Agency's Euclid satellite, launched in July 2023, could definitively prove the theory correct.
This would require at least 1,000 high-quality supernovae observations, potentially settling one of space's greatest mysteries by decade's end.
Wiltshire added: "We now have so much data that in the 21st century we can finally answer the question - how and why does a simple average expansion law emerge from complexity?"
