New data hint dark energy varies, sparking theories of a linked dark sector and hidden dimension

Measurements by the Dark Energy Spectroscopic Instrument revealed that the strength of dark energy changed over cosmic time, reaching a maximum roughly 2 billion years ago before weakening. This challenges the assumption of a fixed cosmological constant and has revived theories that dark energy and dark matter influence each other. Physicists including Tim Tait, Justin Khoury, Meng-Xiang Lin and Mark Trodden have built models where the energy density of dark energy and the mass of dark matter evolve together, sometimes invoking a dark-sector analogue of quantum chromodynamics.

String-theory researchers such as Cumrun Vafa and Georges Obied suggest the two could share a “dark dimension” of micron size, allowing gravitons to acquire mass and act as dark matter. Their framework predicts a slow, proportional decline of both dark components, which could also ease the Hubble tension between early- and late-universe measurements. Preliminary astrophysical tests, like searches for enhanced tidal tails in galaxy encounters by Marc Kamionkowski and Michael Kesden, have not ruled out the predicted interaction strength. Ongoing observations may soon provide empirical checks on these unified dark-sector scenarios.