The Dark Energy Spectroscopic Instrument (DESI) was engineered to make precise measurements of the apparent size of cosmic bubbles, ranging from those nearby to those 11 billion years away, through determining the distances to galaxies and quasars. This data enables scientists to analyze how the universe’s expansion rate varied at different times in the past, thus aiding in modeling the influence of dark energy on that expansion.
In the previous year, DESI’s results were derived from a year’s data across seven segments of cosmic time, encompassing 450,000 quasars—the largest collection of its kind. The precision achieved for the furthest epoch, spanning 8 to 11 billion years ago, was a record 0.82 percent. While these findings generally supported the Lambda Cold Dark Matter (Lambda CDM) model, combining these initial results with data from other research, including cosmic microwave background radiation and Type Ia supernovae studies, revealed some subtle discrepancies.
These discrepancies indicated that dark energy might be weakening. The confidence in these results reached a 2.6-sigma level when DESI’s data was combined with cosmic microwave background datasets. This confidence increased to between 2.5-sigma and 3.9-sigma when supernovae data were included, depending on the dataset employed.
Combining DESI data with other independent measurements is crucial to ensuring consistency, as noted by DESI co-representative Will Percival from the University of Waterloo. He emphasized the importance of achieving uniform results across different experiments concerning the current amount of matter in the universe and the universe’s expansion rate. Disparate findings would undermine the Lambda-CDM model’s validity, underscoring the need for consensus not only with Lambda-CDM but also regarding the model’s fundamental properties.
The latest findings encompass data gathered over a three-year period, involving nearly 15 million galaxies and quasars. Once more, DESI data alone aligned with the Lambda CDM model, indicating constant dark energy. However, combining this data with other datasets—from cosmic microwave background, supernovae, and weak gravitational lensing studies—suggests changes in dark energy over time. Confidence levels ranged from 2.8 to 4.2 sigma, nearly reaching the five-sigma threshold.
To an average observer, these findings might seem like incremental advancements, but the situation is more nuanced. According to Percival, the DESI data is markedly not incremental; the expansion from one to three years of data collection is significant. This is not merely due to expanded coverage but also due to improved overlaps in the survey area. Over three years, more overlaps have been filled, resulting in a more comprehensive dataset that reaches the expected full depth in more regions. Consequently, the Baryon Acoustic Oscillation (BAO) measurements have improved substantially, enhancing by a factor of two to three depending on the balance between area and depth.
