Science: Evidence that dark energy weakens over time
Quanta magazine reports about a line of research on dark energy that I know all of us have been following very closely:
Is Dark Energy Getting Weaker? New Evidence Strengthens the Case.
Computer-simulated flight through the Dark Energy
Spectroscopic Instrument’s (DESI’s) new map of millions of galaxies
Cosmologists have mapped billions of years of cosmic expansion
based on the new data and analysis
Last spring, a team of nearly 1,000 cosmologists announced that dark energy — the enigmatic agent propelling the universe to swell in size at an ever-increasing rate — might be slackening. [But that] was tentative and preliminary. Today, the scientists report that they have analyzed more than twice as much data as before and that it points more strongly to the same conclusion: Dark energy is losing steam.
Portions of the newly mapped universe by two observatories
15 million galaxies spanning 32 billion light-years of space[1]
(I think: Top: Southern sky DES (Dark Energy Survey) galaxy map
Bottom: Northern sky DESI (Dark Energy Spectroscopic Instrument) galaxy map)
If the evidence of evolving dark energy holds up as more data accrues — and this is not guaranteed — it would upend cosmologists’ understanding of our ultimate destiny. Dark energy that has a constant density and pressure would doom our cosmos to expand for all time until unbridgeable gulfs separate every particle from all the others, snuffing out all activity. But dark energy that evolves makes alternative futures possible. “It challenges the fate of the universe,” said Mustapha Ishak-Boushaki, a cosmologist at the University of Texas at Dallas and DESI team member. “It’s game-changing.”
DESI is the black cylinder in the photo
is mounted on the Mayall Telescope atop Kitt Peak in Arizona
Where DESI’s first year of data contained six million galaxies, the three-year data set spans nearly 15 million. The team again identified the spherical shells of galaxies and again reconstructed the last 10 billion years of cosmic expansion — this time, with even greater resolution.
DESI has about 5,000 robotic eyes that swivel toward
distant galaxies each collecting light independently
(That's a lot of eyeballs 👀👀👀👀!)
DESI reported last spring that the combined data sets diverged from what the Lambda-CDM model would predict by as much as 3.9 “sigma,” a measure of statistical significance. Now that figure has ticked up to 4.2 sigma. Assuming that the researchers have not made a mistake, this number means that the odds are only about 1 in 30,000 [~0.00003%] that Lambda-CDM** is the correct model of the cosmos. That’s roughly as likely as flipping a coin 15 times and getting 15 heads in a row. [Analysis: Geez, that's not very likely]**Lambda is the Greek symbol used for Einstein’s cosmological constant, and CDM stands for cold dark matter. Lambda-CDM predicts that dark energy is constant (cannot get stronger or weaker), but DESI survey data strongly indicates that prediction is false, dark energy is weakening and maybe new physics is afoot!The unblinking robotic eyes on Kitt Peak will continue to stare out across the universe and into the past, catching photons for a third (and final) cosmic map. This one will include 50 million galaxies and could take shape by late 2026 or early 2027. Later this year, the DES** collaboration plans to publish observations of how galaxies and matter have clustered over the eons, a process that reflects the tug-of-war between gravity’s pull and dark energy’s push. Their results should further clarify whether dark energy is running out of steam.** The DES (Dark Energy Survey) is being conducted in the Southern Hemisphere at the Víctor M. Blanco Telescope in Chile
Víctor M. Blanco Telescope (center)
Footnote:
1. For those interested, how can the universe, which is about 13.8 billion years old be mapped out to 32 billion light years back in time? That's because cosmic expansion stretched everything out. The universe is expanding, stretching space itself over time. This means that light emitted from distant objects long ago has been traveling for less time than the current distance to those objects due to ongoing expansion of the universe during the light’s journey. So for example, a galaxy whose light took 11 billion years to reach us is now ~32 billion light-years away because space expanded while the light was en route to Earth. DESI and DES use baryon acoustic oscillations (BAOs) as standard rulers to analyze incoming data. In essence, BAOs are fossilized sound waves from the early universe. They can be used as “rulers” to measure cosmic distances. These wave patterns act as fixed reference points to track how space has stretched over time. Current data sets indicate that the observable universe’s radius is ~46.5 billion light-years due to expansion.
1st draft submitted March 9, 2025
Λ is the Greek letter lambda
ΛCDM = LambdaCDM
By Germaine: Dark energy exemplified, getting weaker all the time
