The force of gravity has shaped the universe. The character of the pull has transformed the tiny differences in the amount of matter in the early universe into the vast filaments of galaxies that can be observed today. A new study using data from the
Dark Energy Spectroscopic Instrument (DESI) has mapped the growth of these structures over the past eleven billion years, and has produced the most accurate large-scale test of the force of gravity in history.
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.
Limits to Einstein’s theory of gravitation
The 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 comments that “these data allow us to study how quickly the largest structures in the cosmos have formed, to put limits to Einstein’s theory of gravitation on 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 “the results, for now, fit perfectly with the predictions of Einstein’s theory of general relativity”.
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.
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. 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 in the cosmos
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 and confirmation.
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 truly dazzling”. And he clarifies that “this is only the beginning because the project continues to obtain more data, which will greatly improve our current knowledge of gravity and dark energy”.
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 programme, is located at the top of Kitt Peak National Observatory’s Nicholas U. Mayall Telescope, which has a mirror with a diameter of four metres. 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 already analysing 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 a time-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 catalogues, notes that “the distribution of galaxies suggests the presence of dark matter and dark energy, which are largely a mystery to us. However, the precise measurements provided by DESI offer promising information on these fundamental questions about the universe”.
DESI collaboration
DESI receives funding from the following institutions: the US Department of Energy’s Office of Science and the Energy Scientific Computing Center (NERSC); the US National Science Foundation (NSF); the Division of Astronomical Sciences (AST), through a contract with the NSF National Optical Astronomy Observatory; the Science and Technology Facilities Council (STFC) in the United Kingdom; the Gordon and Betty Moore and Heising-Simons Foundations in the United States; the Commissariat à l'Energie Atomique et des Energies Alternatives (CEA) in France; the Mexico National Council of Science and Technology (CONACYT) in Mexico; the Spanish Ministry of Science, Innovation and Universities; and the member institutions of DESI.
The DESI collaboration is grateful to be allowed to conduct astronomical research on Du’ag on Kitt Peak, Arizona, a mountain of special significance to the Tohono O’odham Nation Indian reservation.
In Spain, the CIEMAT, the Institute of Space Sciences (ICE, CSIC), the ICCUB, the Institute of High-Energy Physics (IFAE), the Instiute of Theoretical Physics (IFT-UAM/CSIC), the Andalusia Institute of Astrophysics (IAA) Institute of Astrophysics of the Canary Islands (IAC) are participating.
The full list of participating institutions and further related information is shown on the DESI website.