Something seems Wrong with Dark Energy, Scientists Say

Envision sitting in the center of a firework that has just about exploded. After the initial flash of light and heat, sparks fly off in every direction, with some streaming together into sizzling filaments and others fading hastily into cold, ashy oblivion. After a moment further, the smoke is all that is left—the echo, if you will, of the firework’s big bang.

Now perceive the firework is the cosmos, which scientists believe began with a similar explosion. While the firework’s expansion is driven by a chemical reaction, the expansion of the universe comes from the energy of empty space itself. From where we sit, it appears as if the universe is expanding in every direction, faster and faster at every moment.

This spring scientists proclaimed that something is wrong with the fireworks. For the first time since the discovery of dark energy (the enigmatic force that is accelerating our cosmic fireworks show), astrophysicists think we may be on the verge of something new. Two prominent dark energy surveys meant to measure the nature of this force found signs of weakening of dark energy over time.

“If it is true, it is a big deal,” says Licia Verde (a theoretical cosmologist at the Institute of Cosmos Sciences of the University of Barcelona and a member of the collaboration reporting the oddity). “But as usual, extraordinary claims require extraordinary proofs.”

Dark energy was anticipated to be a constant force in the cosmos, as unchanging and dependable as the forward march of time. If the new results are right, it is variable after all. “its mega important,” says Paul J. Steinhardt (a cosmologist at Princeton University), who did not work on the data, adding that this is only true if the outcomes hold up to scrutiny. “But it’s still early days.”

The news is based on an amalgamation of two dark energy studies, termed the Dark Energy Spectroscopic Instrument (DESI) and the Dark Energy Survey (DES), with a third set of preexisting data. The DESI experiment measures galaxies and sound waves from the early universe, and DES measures distant supernovae. The third component measures the cosmic microwave background (CMB)—the smoke ring of the cosmic firework.

DES bore new findings back in February, and DESI came out with fresh results in April. The DESI data fashioned a detailed three-dimensional map of the cosmos. It showed that galaxies appear to be spread apart less than they should be if dark energy’s role was unchanging through cosmic time. Perched on Kitt Peak in Arizona, the DESI telescope measures the positions of millions of galaxies as they were between 12 billion and two billion years ago. Astrophysicists compared these observed galactic locales against where galaxies are anticipated to be based on dark energy predictions and saw the lack of expected spreading.

A far bigger surprise came when cosmologists amalgamated the DESI galaxies, DES’s supernovae and the cosmic microwave background. The map of reality started to drift apart from theory. Theorists have been buzzing since: if the outcomes are true, a bedrock assumption of cosmology is erroneous. Researchers might have to discard the widely held idea that dark energy is a “cosmological constant”—a static element of the cosmos. “If the cosmological constant is wrong, all bets are off about what’s right,” says Adam G. Riess (a cosmologist at Johns Hopkins University), who shared the 2011 Physics Nobel Prize for the discovery of dark energy and did not work on the new results.