The dark energy pushing our cosmos apart may not be what it seems, researchers say

Faraway, ancient galaxies are giving researchers more hints that an enigmatic force called dark energy may not be what they believed. Astrophysicists know that the cosmos is being pushed apart at an accelerating rate and they have been baffled for decades over what could actually be speeding everything up. They theorize that a constant, powerful force is at play, one that fits well with the main mathematical model that describes how the cosmos behaves. But they are unable to see it and they don’t know where it actually comes from, so they call it dark energy. It is so colossal it is believed to make up nearly 70% of the universe — while ordinary matter like all the stars and planets and people make up just 5%.

But conclusions published earlier this year by an international research collaboration (DESI collaboration) of over 900 experts from around the globe yielded a huge surprise. As the researchers analysed how galaxies move they discovered that the force pulling or pushing them around did not seem to be constant. And the very same group published a new, broader set of analyses on Tuesday (19^th November 2024) that yielded a similar answer. “I did not think that such a result would happen in my lifetime,” said Mustapha Ishak-Boushaki (a cosmologist at the University of Texas at Dallas), who is part of the collaboration.

What is the DESI collaboration?

Termed the Dark Energy Spectroscopic Instrument, it employs a telescope southwest of Tucson, Arizona to create a 3D map of the cosmos over 11 billion years to see how galaxies have clustered across space and throughout time. That gives researchers information about how the cosmos evolved, and where it might be heading.

The map they are building would simply not make sense if dark energy were a constant force, as it is theorized. Instead, the energy seems to be altering or weakening over time. If that is really the case, it would upend astrophysicists’ standard cosmological model. It could mean that dark energy is very different than what experts thought — or that there may be something else altogether going on. “It’s a time of great excitement, and also some head-scratching and confusion,” said Bhuvnesh Jain (a cosmologist at the University of Pennsylvania), who is not involved with the research.

DESI collaboration’s latest finding points to a possible explanation from an earlier theory: that across billions of years of cosmic history, the cosmos expanded and galaxies clustered as Einstein’s general relativity predicted.