Dark energy may be losing energy: explaining strange behavior express
In the late 1990s, astronomers including Saul Perlmutter discovered that the universe is expanding at an accelerating rate. The cause was dubbed dark energy — an invisible force stretching the cosmos. For a long time, it was thought to be constant, but fresh data from the DESI telescope, which studies millions of galaxies via their light, showed: around 6 billion years ago dark energy changed its behavior, crossing a critical threshold beyond which its influence becomes even stranger. Physicists described this field like a pendulum. In a standard model, a pendulum meets no resistance and swings forever. But if you put it in a very thick fluid, it starts losing energy due to friction. Similarly, dark energy experiences an ultra-weak ‘friction’ that dissipates its energy and makes the expansion of the universe accelerate differently. No exotic hypotheses — just a natural energy loss. Previously, such a transition would have doomed the universe to a ‘Big Rip’ — a catastrophic end, but the subtle friction cancels this scenario.
Original abstract
as written by the authors arXiv:2606.04886
DESI results preferring an evolving dark energy component that appears to cross the phantom-divide in the recent past has raised a lot of interest in exploring the nature of dark energy. We present here a simple dissipative dark energy scenario that can explain both the evolving nature of dark energy as well as its crossing of the phantom-divide without invoking any pathological phantom-like dynamics for the quintessence field. We show that even weak dissipation of the quintessence is enough to explain the current DESI observations.
The density of dark energy is so tiny that within the volume of Earth, it would amount to just a couple of kilograms — yet on cosmic scales, it determines the fate of the universe.