That’s precisely the aim of DESI: to obtain exact measurements of the perceived size of these cosmic bubbles (both nearby and distant) by establishing the distances to galaxies and quasars spanning 11 billion years. This information can then be analyzed in segments to discern how rapidly the universe was expanding at various moments throughout history, allowing for improved models of the influence of dark energy on that expansion.
An Increasing Trend
The results from the previous year were derived from a comprehensive analysis of one year’s worth of data collected from seven distinct epochs in cosmic history. This dataset includes 450,000 quasars, the largest number ever compiled, achieving a record-breaking precision for the most distant period (between 8 to 11 billion years ago) at 0.82 percent. While there was a general alignment with the Lambda CDM model, some subtle deviations emerged when the initial results were integrated with findings from other studies, including cosmic microwave background radiation and Type Ia supernovae.
These deviations implied that dark energy might be diminishing over time. In terms of statistical confidence, the findings represented a 2.6-sigma level when DESI’s data was combined with CMB datasets. The incorporation of the supernovae data raised these levels to 2.5-sigma, 3.5-sigma, or even 3.9-sigma, depending on the specific supernova dataset utilized.
It is critical to integrate the DESI data with other independent measurements because, as DESI co-spokesperson Will Percival from the University of Waterloo puts it, “we seek consistency. All different experiments should yield the same conclusions regarding the matter present in the universe today and the rate at which it is expanding. It is not sufficient for all experiments to align with the Lambda-CDM model yet produce differing parameters. That simply does not suffice. Merely stating that it aligns with Lambda-CDM isn’t adequate; it has to be consistent with Lambda-CDM and provide the same parameters for the model’s fundamental properties.”
These recent findings encompass the first three years of collected data, covering nearly 15 million galaxies and quasars. Once again, the DESI data alone was consistent with the Lambda CDM model, indicating that dark energy remains constant. However, once combined with other datasets—from CMB, supernovae, and weak gravitational lensing studies—strong indications emerged suggesting that dark energy might be evolving over time. The confidence level ranges from 2.8 to 4.2 sigma, depending on the dataset combinations—just shy of the five-sigma criterion.
This may appear to the average person as a gradual progress, but the truth is more intricate. “The DESI data itself is not just incremental,” says Percival. “We now have three years of data instead of just one. This is meaningful, not solely because of the expanded area but because we have increased the overlap. Our survey method involves constructing plates in the sky, and after three years, rather than just one, we’ve filled in significantly more of these overlaps. Therefore, our data is far more complete, as we have reached the full depth we anticipate achieving over more areas. As a result, our BAO measurements are significantly improved, ranging from two to three times better, depending on the balance between area and depth.”
