Neutrinos, Dark Energy, and Einstein: DESI Maps the Universe’s Secrets

New analysis supports Einstein’s relativity and narrows neutrino mass ranges, hinting at evolving dark energy.

Gravity, the fundamental force sculpting the universe, has shaped tiny variations in matter from the early cosmos into the vast networks of galaxies we see today. Using data from the Dark Energy Spectroscopic Instrument (DESI), scientists have traced the evolution of these cosmic structures over the past 11 billion years. This research represents the most precise large-scale test of gravity ever conducted, offering unprecedented insights into the universe’s formation and behavior.

Introduction to DESI and Its Global Impact

DESI is an international collaboration of more than 900 scientists from over 70 institutions around the world, managed by the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). In this new study, scientists have found that gravity behaves as predicted by Einstein’s theory of general relativity. These results confirm the current model of the universe and narrow down possible theories of modified gravity, which had been proposed as alternative explanations for unexpected observations, such as the accelerating expansion of the universe, which is usually attributed to dark energy.

Testing Einstein’s General Relativity

Researcher Héctor Gil Marín, from the Faculty of Physics and the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), has co-led this new analysis and says that “these data allow us to study how fast the largest structures of the Universe have formed, to put limits to Einstein’s General Relativity theory at cosmological scales much larger than those of the solar system.” The researcher, who is also a member of the Institute for Space Studies of Catalonia (IEEC), adds that “for now, the results fit perfectly with the predictions of Einstein’s General Relativity theory.”

The study also provides a new upper limit on the mass of neutrinos, whose only elementary particles have not yet had their masses measured. Previous experiments revealed that the sum of the masses of the three types of neutrinos should be at least 0.059 eV/c² (for comparison, that of the electron is 511 000 eV/c²). The DESI results indicate that this sum should be less than 0.071 eV/c², which leaves a very narrow window for the possible values of the neutrino masses.

With only one year of data, DESI has achieved the most accurate global measurements of structure growth and has surpassed all previous results, which had taken decades of sustained effort.

The DESI collaboration has presented the new results in several scientific papers available in the arXiv repository. The complex analysis of the data used nearly six million galaxies and quasars located at distances ranging from one to eleven billion light-years from Earth.

Better Understanding of Gravity and Dark Energy

The results presented today are an in-depth analysis of data from the first year of DESI, which in April presented the largest 3D map of the Universe ever made and found some hints that dark energy may be changing over time. The results published then focused on a particular property of the spatial distribution of galaxies, known as baryon acoustic oscillations (BAOs). This new analysis incorporates all the information contained in the shape of the power spectrum and extends the scope of the above to extract more information from the data, allowing the distribution of galaxies and matter to be measured on different spatial scales. The study has required months of work and additional checks. As in the previous case, they have used a blind analysis technique that hides the results until the end, to mitigate any bias.

Eusebio Sánchez, a researcher at the Research Center for Energy, Environment and Technology (CIEMAT) who has collaborated in the analysis of the data, says that “the results obtained with the first year of DESI data are stunning.” And he clarifies that “this is only the beginning, the project is taking more data that will allow us to improve our current knowledge of gravity and dark energy.”

Future Prospects and Ongoing Research

DESI is a leading instrument capable of capturing the light from five thousand galaxies at once and determining their spectra. It was built and operated with funding from the US Department of Energy (DOE) Office of Science. DESI, as part of a US National Science Foundation (NSF) NOIRLab program, is located at the top of Kitt Peak National Observatory’s Nicholas U. Mayall Telescope, which has a mirror with a diameter of four meters. The experiment is currently in the fourth of its planned five years of data collection, and the goal is to have mapped some forty million galaxies and quasars by the end of the project.

The collaboration is currently analyzing data from the first three years and new results are expected to be presented in spring 2025, updating existing measurements of dark energy and the expansion history of the Universe. The results presented today are consistent with previous findings of a slight preference for an evolving dark energy, raising interest in the results of the current analysis.

Hui Kong, a postdoctoral researcher at the Institute for High Energy Physics (IFAE) who worked on the preparation of the galaxy catalogs, notes that “the distribution of galaxies suggests the presence of dark matter and dark energy, both of which remain a mystery to us. However, the precise measurements provided by DESI offer promising information on these fundamental questions about the universe.”

For more on this research:

• DESI Tests Einstein’s Theory of Relativity Across 11 Billion Years of Cosmic History
• Stunning Cosmic Map Confirms Gravity Theory Across Billions of Years
• Dark Energy May Be Evolving, Transforming Our View of the Universe
• How 5,000 Robotic Eyes Are Transforming Our View of the Universe

DESI Collaboration

DESI is supported by funding from a diverse group of institutions, including the US Department of Energy’s Office of Science, the Energy Scientific Computing Center (NERSC), and the US National Science Foundation (NSF). Additional contributions come from the NSF Division of Astronomical Sciences (AST) through a contract with the NSF National Optical Astronomy Observatory, the UK Science and Technology Facilities Council (STFC), the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, the French Commissariat à l’Energie Atomique et des Energies Alternatives (CEA), Mexico’s National Council of Science and Technology (CONACYT), the Spanish Ministry of Science, Innovation and Universities, and DESI’s member institutions.

The DESI collaboration conducts its research on Du’ag, located at Kitt Peak in Arizona, a site of deep cultural and spiritual importance to the Tohono O’odham Nation.

In Spain, several prominent institutions contribute to DESI, including the CIEMAT, the Institute of Space Sciences (ICE, CSIC), the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), the Institute of High Energy Physics (IFAE), the Institute of Theoretical Physics (IFT-UAM/CSIC), the Andalusian Institute of Astrophysics (IAA), and the Institute of Astrophysics of the Canary Islands (IAC).

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