Thunderbolts Forum v3.0

For almost three decades, astronomers have believed that the universe is expanding faster and faster and that the acceleration of this growth is constant over time—driven by a mysterious force they call “dark energy.” Last April a survey by the Dark Energy Spectroscopic Instrument (DESI) published hints that dark energy may not be as constant as they’d assumed, adding to a pile of concerns that are already threatening the standard model of cosmology. Today Nadathur and his DESI collaborators unveiled their follow-up results publicly at the American Physical Society’s Global Physics Summit and in multiple preprint papers, further validating the omen.

After nearly tripling the researchers’ collection of galaxy coordinates, the new DESI analysis provides the strongest evidence yet that the rate of cosmic expansion fluctuates—finally shedding some light on dark energy, which scientists think constitutes about 70 percent of everything in the universe.
Although the evidence still falls short of physicists’ benchmark for a “discovery,” experts say the new result leaves the standard model in dire straits. Making sense of an evolving dark energy would almost certainly involve amending the foundations of physics in order to unlock the true history and fate of our universe.

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The analysis seems to suggest that dark energy transforms over time—appearing a tad weaker today than Einstein’s prediction and a tad stronger in the early universe. This progression has implications for the ultimate destiny of the universe: a dark energy that is too strong could eventually rip apart all atoms, and one that is too weak could lure everything to crunch inward.

Fate aside, the changeable nature of dark energy would pose deep problems for fundamental physics today. An acceleration greater than that described by the cosmological constant evokes what cosmologists call “phantom energy,” which has an ever increasing density over time—something forbidden by our current understanding of gravity.

Assuming the results stand, this incongruence could spark an era of “chaos cosmology,” says Abazajian, who recently posted a preprint paper that showed how even the previous DESI results prefer a fluctuating dark energy. Reconciling this, he suggests, would require either uncovering an entirely new fundamental force or realizing that our universe has more than four dimensions. “No matter what, we are discovering new physics here,” Abazajian says. “There’s nothing in the standard physics that allows for an evolving dark energy.”