The largest three-dimensional map of the universe has been created by researchers at the Lawrence Berkeley National Laboratory in the United States, using the Dark Energy Spectroscopic Instrument (DESI). Clues from the cosmic evolution depicted in this map indicate that over time, dark energy appears to be diminishing. The findings of this study have been released on the preprint website arXiv.
Part of the largest three-dimensional map of the universe, showing the basic structure of matter. Image source: Claire Lamman/DESI collaboration
Twenty-five years ago, Adam Riess of Johns Hopkins University in the United States first discovered evidence for the existence of dark energy. He stated that the standard cosmological model, ΛCDM, suggests that the strength of dark energy should be static over time. "If this assumption holds true, it would be a very significant finding."
Dark energy is thought to be the reason for the accelerated expansion of the universe. If it is not static, it could have profound implications for our understanding of the origin, size, and ultimate fate of the universe. Riess suggested that this could mean "we will have to do some serious soul-searching about our understanding of gravity and fields."
Even the researchers at DESI are unsure about what the data indicating a recent possible weakening of dark energy might mean. They detect the strength of dark energy by measuring the large-scale structure and distribution of galaxies in the universe, illustrating how the universe expands over time. Subsequently, researchers combine this information with three sets of data on supernovae, which act as so-called "standard candles," determining the distance to cosmic objects based on their predictable brightness.
Surprisingly, all three supernova samples provide different answers regarding the rate of expansion of the universe over time. They all suggest that the influence of dark energy may have weakened in the recent billions of years, but the suggested magnitudes vary, leaving researchers uncertain how to interpret the data.
Kyle Dawson, spokesperson for DESI and professor at the University of Utah, pointed out that there are two supernova samples that disagree with each other, and they are very, very similar samples. So not knowing which one is correct, the truth may lie somewhere in between, but it seems that the real difference lies in how supernova researchers evaluate the data.
The sigma (σ) differences between models measure the likelihood of chance occurrences of similar conflicts between models. Riess noted that differences around 3σ are noteworthy indications, as discrepancies below this value are often likely just simple coincidences and do not typically excite researchers. The range of differences between ΛCDM and the combination of supernova and DESI measurements is between 2.5σ and 3.9σ.
Dark energy constitutes nearly 70% of the universe, so any misunderstandings about its nature could have broad implications for physics. However, to prove whether this error truly exists, more precise measurements will be needed in the coming years.
"If the findings are true, it will be the first real clue we've obtained in 25 years about the nature of dark energy," said Riess.
Related paper information: https://doi.org/10.48550/arXiv.1234.56789
