Physicists say dark energy ‘doesn’t exist’ so can’t be pushing ‘lumpy’ cosmos apart

One of the biggest ambiguities in science—dark energy—doesn’t in fact exist, according to scientists looking to solve the riddle of how the cosmos is expanding. Their analysis has been published in the open access journal MNRAS Letters (Monthly Notices of the Royal Astronomical Society: Letters).

For the past 100 years, physicists have assumed in general that the universe is growing equally in all directions. They used the concept of dark energy as a placeholder to explain unknown physics they couldn’t basically understand, but the contentious theory has always had its issues. Now a team of astronomers and physicists at the university of Canterbury in Christchurch, New Zealand are challenging the existing state of affairs, utilising improved analysis of supernovae light curves to show that the cosmos is expanding in a far more varied, “lumpier” way.

The newly emerged evidence supports the “timescape” model of cosmic expansion, which doesn’t have a necessity for dark energy because the differences in stretching light aren’t the resultant of an accelerating cosmos but instead a consequence of how we attune time and distance. It proposes that gravity slows time, so an ideal clock ticks faster in empty space than inside a galaxy.

The model proposes that a clock in the Milky Way would be roughly 35 percent slower compared to the same one at an average spot in large cosmic voids, meaning billions more years would have passed by in voids. This would in turn permit more expansion of space, making it seem like the expansion is getting quicker when such vast empty voids grow to dominate the cosmos.

Professor David Wiltshire, leader of the study, said, “Our findings show that we do not need dark energy to explain why the universe appears to expand at an accelerating rate. Dark energy is a misidentification of variations in the kinetic energy of expansion, which is not uniform in a universe as lumpy as the one we actually live in.” He further added, “The research provides compelling evidence that may resolve some of the key questions around the quirks of our expanding cosmos. With new data, the universe’s biggest mystery could be settled by the end of the decade.”

Dark energy is usually thought to be a weak anti-gravity force which acts independently of matter and makes up about 2/3^rd of the mass-energy density of the cosmos. The standard Lambda Cold Dark Matter (ΛCDM) model of the cosmos needs dark energy to explain the observed acceleration in the rate at which the universe is expanding.