Based on the usual mannequin of cosmology, that enlargement price must be the identical irrespective of the way you measure it. However in recent times, scientists have discovered that the enlargement price of the early universe and that of the more moderen universe differ by roughly 9 %.
That discrepancy, or rigidity, “has provoked heated debates within the cosmology group about whether or not this distinction may very well be attributable to systematic errors or whether or not it’s a sign of recent physics,” Teixeira and her co-authors wrote. Their mannequin posits that in a world the place darkish power and darkish matter work together, what gave the impression to be a disaster attributable to disparate enlargement charges as an alternative turns into one thing to be anticipated.
A Darkish Dimension
If darkish power and darkish matter do work together, it might imply that they’ve a typical origin, Khoury mentioned.
Ongoing work in string theory—the concept our universe, at its smallest, most elementary stage, is made up of vibrating strings—suggests a means these ideas could be linked. In 2019, constructing on the concept in string idea that darkish power is naturally varying, Vafa and two collaborators concluded that the mass of darkish matter particles may additionally differ over time. This led them to suggest in 2022 that darkish matter and darkish power might share a hyperlink with a so-called darkish dimension.
String idea posits the existence of six or seven additional dimensions along with our acquainted three dimensions of house and one in all time. All of those dimensions are regarded as as small as bodily attainable—near the Planck scale (10-35 meters)—however the researchers proposed that the darkish dimension may very well be considerably greater than the others—on the order of a micron (10-6 meters).
Gravitons, theoretical particles that impart the pressure of gravity, might leak into this enlarged darkish dimension. In the event that they did, they might decide up mass and develop into what are referred to as darkish gravitons. These large gravitons would reside at nighttime dimension, however their gravitational results may very well be felt in different dimensions, permitting them to meet the function that’s usually ascribed to darkish matter.
On this situation, “there’s a very pure coupling between darkish power and darkish matter,” mentioned Georges Obied, a physicist on the College of Chicago. Adjustments within the measurement of the darkish dimension would have an effect on each darkish power and darkish matter.
In a July 2025 paper, Obied and Vafa, together with Alek Bedroya of Princeton and David Wu of Harvard, discovered that the situation proposed in 2019 was in step with the DESI information. Their mannequin predicts that the energy of darkish power and the mass of darkish matter will lower over time and that the speed at which darkish power modifications might be proportional to its power density. As a result of astrophysical measurements inform us that the power density of darkish power is very small, “it received’t change quick,” Vafa mentioned.
“It’s not stunning that we didn’t see it till now,” he mentioned, as a result of the speed of change is so tiny. “We needed to wait all the age of the universe to detect one thing that small.”
