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The Dark Energy Spectroscopic Instrument (DESI) has been successfully installed on the Mayall Telescope located at Kitt Peak. This instrument plays a crucial role in exploring the mysteries of our universe.
Since its inception during the Big Bang, our universe has been in a constant state of expansion. For many years, the prevailing belief among cosmologists was that this expansion was gradually slowing due to the gravitational pull of matter. It was thought that eventually, gravity would halt or even reverse this expansion.
However, a significant breakthrough came in 1998 with observations of supernovae that revealed the universe is not just expanding, but that this expansion is accelerating. This surprising discovery led scientists to introduce the concept of dark energy, a mysterious repulsive force that drives galaxies apart. For 25 years, the assumption was that this force remained constant, a fixed characteristic of space responsible for the accelerated expansion observed. It has since become an integral part of our standard cosmological model.
Recent revelations from two significant cosmological surveys — the Dark Energy Spectroscopic Instrument (DESI) survey and the Dark Energy Survey (DES), released on March 19 — challenge this longstanding belief. They contribute to a growing array of evidence suggesting that dark energy may actually vary over time rather than remain static.
Related: Supernova survey hints dark energy could be changing
Indications of Change
Stephanie Juneau, an astronomer at NSF’s NOIRLab and a member of the DESI data team, remarked, “Initially, we thought we would provide high-precision measurements confirming the constancy of dark energy. Discovering any hints of deviation was a significant surprise.”
The emerging evidence does not stem from a single dataset; rather, it arises from a growing consensus across independent measurements. DESI researchers constructed a three-dimensional map featuring nearly 15 million galaxies and quasars, the most detailed spectroscopic map of the universe created to date. On its own, the DESI data does not contradict the standard cosmological model; however, when combined with other observations, such as data from the cosmic microwave background, supernova studies, and gravitational lensing, inconsistencies start to surface.
Moreover, the scientists at DES have identified similar anomalies over six years of observations, suggesting that the standard model may not encompass the full picture of our universe.
Mustapha Ishak-Boushaki, a theoretical astrophysicist at the University of Texas at Dallas and co-chair of the working group analyzing the DESI data, expressed, “What is most compelling is that evidence is emerging from various independent sources. It’s improbable for all these different datasets to lead to the same incorrect conclusion.”
Related: Are the percentages of dark matter and dark energy stable?
A Dynamic Force
The notion that dark energy might not be a constant force introduces a significant paradigm shift within modern physics. In Einstein’s equations, the cosmological constant Lambda (Λ) is thought to represent the force exerted by dark energy, illustrating accelerated expansion. Quantum field theory also suggests that even in a vacuum, energy should exist — referred to as vacuum energy. While this is a strong candidate for dark energy, theoretical predictions indicate that vacuum energy should exert a force approximately 40 orders of magnitude greater than what astronomers currently observe.
Ishak-Boushaki stated, “If dark energy is treated as a cosmological constant, it has often been viewed as a theoretical dead end. The gap between theoretical predictions and actual measurements is famously known as an embarrassing difference we cannot justify.”
However, if dark energy is indeed evolving over time, this could reconcile the discrepancy between its measured minimal value and the vacuum energy predicted by quantum theory. Such a variable dark energy would allow astronomers to explore new theoretical models, including modifications to gravitational theory and evolving energy fields throughout cosmic history.
“With DESI, we have begun to perceive clearer insights,” Ishak-Boushaki remarked. “There is renewed hope that we are looking at something fundamentally different. While we don’t yet have a precise understanding, we are opening doors to newfound discovery.”
With dark energy constituting approximately 70 percent of the universe, establishing that it changes over time could dramatically reshape our understanding of cosmic evolution. A constant cosmological model leads to a scenario wherein the universe expands indefinitely, ultimately reaching a state sometimes referred to as heat death or the Big Freeze. On the other hand, dynamic dark energy could result in varied outcomes, ranging from decelerated expansion to a catastrophic Big Rip that disintegrates galaxies, stars, and even atomic structures.
The current level of statistical certainty surrounding the combined results stands at approximately 4.2 sigma, nearing the 5-sigma benchmark required for a scientific finding to be widely accepted. Such statistical confidence suggests the likelihood of the results being mere chance is less than one in a million.
“For researchers like myself who have dedicated 25 years to this pursuit, this outcome was beyond our expectations,” Ishak-Boushaki commented.
The Path Ahead
Despite this encouraging data, researchers caution that the implications remain speculative. Clarification on whether dark energy is indeed changing, and the factors influencing such an evolution, is crucial.
Jessie Muir, a cosmologist at the University of Cincinnati and a member of both DES and DESI teams, stated, “I’m not ready to declare the end of the standard cosmological model. My excitement is cautious; it represents an area for ongoing research and careful analysis.”
The subsequent years will be essential for further investigation into these preliminary findings. DESI intends to continue its data collection through 2026, aiming to map over 50 million galaxies and quasars to potentially elevate the evolving dark energy signal to the 5-sigma discovery threshold. Additionally, researchers plan to validate their findings against new instruments and experiments, including the Vera C. Rubin Observatory’s Legacy Survey of Space and Time and NASA’s Nancy Grace Roman Space Telescope. These advanced tools will empower scientists to explore deeper into the cosmos than ever before, facilitating groundbreaking inquiries into the nature of dark energy.
“This is an opportunity to revisit fundamental questions. We have the potential to uncover the true essence of our universe,” Juneau concluded. “There is an immense reservoir of new discoveries awaiting us.”
Source
www.astronomy.com