The fate of the Universe depends on the balance between matter and dark energy, the fundamental ingredient that drives its accelerating expansion. New results from the Dark Energy Spectroscopic Instrument (DESI) use the largest 3D map of the universe ever built to characterize the influence of dark energy on the expansion of the universe over the past 11 billion years. This study shows hints that dark energy, previously thought to be a cosmological constant, may evolve in unexpected ways.
DESI is an international experiment involving over 900 participants from more than 70 institutions around the world, and it is led by the US Department of Energy's Lawrence Berkeley National Laboratory (United States). The collaboration published its findings in multiple papers submitted to the ArXiv digital repository and in a presentation at the American Physical Society Global Physics Summit in Anaheim, California.
"The results we have obtained are very interesting", says Andreu Font-Ribera, IFAE scientist and member of the DESI team that developed the study. "It seems that we are on the verge of a change of paradigm for our models of the Universe, and this is very exciting", he notes.
Alone, he DESI data are consistent with the standard model of the universe, ΛCDM (where CDM stands for cold dark matter and Λ represents the simplest explanation of dark energy, where it behaves like a cosmological constant). However, when combined with other measurements, there are growing indications that the impact of dark energy may be weakening over time. This suggests that models other than the commonly accepted one may provide a better explanation of cosmic evolution. Such other measurements include the light left over from the dawn of the universe (the cosmic microwave background or CMB), exploding stars (supernovae) and distortions in the propagation of light caused by gravity (weak gravitational lensing).
"In my opinion, it is still too early to claim categorically that we have discovered an evolving dark energy", says Eusebio Sánchez, a science researcher at CIEMAT, who has participated in the analysis of the data. "However, the fact that different independent projects are observing similar results makes the situation particularly interesting".
So far, the preference for a changing dark energy has not reached "5 sigma", the statistical convention used in physics that sets the threshold needed to consider whether a measurement is considered a discovery. Analysis of different combinations of the DESI data with the CMB and several sets of supernovae finds a range between 2.8 and 4.2 sigma (a 3 sigma event has a 0.3% chance of being a statistical fluctuation, but many 3 sigma events in physics have disappeared as more data have been collected). The analysis has used a double-blind technique that hides the results until the end, mitigating any unconscious bias in the data.
