Albert Einstein's prediction of gravity has been confirmed by an international team of researchers exploring how this fundamental force operates on cosmic scales. Scientists, including astrophysicists from the University of Portsmouth, used the Dark Energy Spectroradiometer (DESI) to map the clustering of nearly 6 million galaxies over a period of 11 billion years. Their detailed analysis of DESI's first year of data is one of the most rigorous tests of Einstein's general theory of relativity on such a massive scale, providing crucial insights into how gravity shapes the universe.
Albert Einstein's predictions about how gravity works have been verified on a cosmic scale.
An international team of researchers has studied the effects of gravity on cosmic scales, and their findings support Albert Einstein's predictions about how gravity works.
Dark energy spectrometer (
A complex analysis of DESI's first year of data provides one of the most rigorous tests yet of how general relativity and gravity behave on cosmic scales.
Observing galaxies and their clustering over time reveals how the structure of the universe grew, allowing DESI to test modified gravity theory - an alternative explanation for the accelerating expansion of the universe.
DESI is managed by the U.S. Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab). Institutions participating in DESI in the UK include:
Analysis of the expansion structure of the universe
By studying how galaxies clump together over time, researchers have discovered patterns that reveal how the structure of the universe evolved.
This allowed DESI scientists to test modified gravity theory - an alternative explanation for the accelerating expansion of the universe, often attributed to dark energy.
They found that galaxies clump together in a way that matches our standard gravity model and Einstein's predictions.
The result validates leading models of the universe and limits possible modified gravity theories that have been proposed as alternatives to explain unexpected observations such as the expansion of the universe.
Research collaborations and insights
Several universities in the UK are involved in DESI's latest research results, including the University of Portsmouth, Durham University and University College London.
Today, the DESI collaboration team published multiple papers on the online repository arXiv to share their research results.
The new analysis was carried out by a team led by Dr Seshadri Nadathur, Associate Professor at the Institute of Cosmology and Gravitation at the University of Portsmouth.
Dr Nadatur said: "The data we collect with DESI allows us to measure subtle patterns in how galaxies clump together. What's really exciting is that we can use these patterns not only to measure how fast the universe is expanding, but even to test our understanding of gravity itself! General relativity holds up pretty well so far, but we're seeing some surprises when it comes to dark energy."
Explore fundamental physics questions
Nathan Findlay, a PhD student at the University of Portsmouth, also led some of the work to quantify some of the uncertainties in the analysis. "It's incredible what we can learn about dark matter, dark energy, the history and destiny of the universe, and even a correct theory of gravity - all of these fundamental questions in physics - with these data from DESI," he said. "I'm very excited to be a part of it."
Testing gravity on a cosmological scale
Dr. Pauline Zarrouk, a cosmologist at the Laboratory for Nuclear and High Energy Physics (LPNHE) of the French National Center for Scientific Research (CNRS), co-led the new analysis.
Dr Zaluk, who was a postdoctoral researcher at the Institute of Computational Cosmology at Durham University and is now an academic visiting scholar at the Institute: "General relativity has been well verified on the scale of the solar system, but we also need to verify whether our assumptions are valid on larger scales.
"Studying the rate at which galaxies form allows us to directly test our theory, and so far we are consistent with the predictions of general relativity on cosmological scales."
Neutrino mass and galaxy clustering
Detailed analysis of the DESI data, led by Durham University researchers Dr Willem Elbers and Professor Carlos Frenk, provides a new upper limit on the mass of neutrinos.
Neutrinos have a minimal effect on galaxy clustering patterns, but this can be measured by the quality of the DESI data. Neutrino Laboratory experiments set a lower limit for neutrino masses; notably, the galaxy distribution in DESI set an upper limit for this mass, which is now very close to the lower limit, with a value of about one ten millionth of the electron's mass.
Durham University is a key member of the DESI collaboration and also designed and built the fiber optic system to deliver light to DESI's spectrometer. Durham University scientists also conducted supercomputer simulations of the universe, which were crucial in interpreting DESI's data.
Professor Carlos Frenk, a member of the DESI team and from the Institute of Computational Cosmology at Durham University, said: "General relativity is one of the most elegant and profound theories in physics. It is truly remarkable that the universe seems to conform to its precepts, and it is a testament to the brilliance of Einstein and the brilliance of the astronomers who devised methods to test it."
"Equally remarkable, DESI sheds light on the long-standing mystery of the mass of neutrinos. These tiny elementary particles have very little mass, but the gravity they collectively produce affects the movement and clustering of galaxies in space. The unprecedented size and mass of the DESI data set make it possible to detect such tiny effects, which is exciting for cosmologists and particle physicists alike."
DESI's contributions to physics and cosmology
DESI contains 5,000 fiber-optic "eyes," each of which can collect the light of a galaxy in 20 minutes. UCL researchers, also a key member of the DESI collaboration, helped design, assemble and build DESI's optical correctors - six lenses, the largest of which are 1.1 meters in diameter, that focus light onto the "eye".
In April this year, DESI created the largest three-dimensional map of the universe to date and revealed clues about how dark energy may evolve over time.
The April analysis looked at a special feature of the galaxy cluster called baryon acoustic oscillations (BAO). The new analysis, called a "full-scale analysis," broadens the scope of the analysis to extract more information from the data, measuring how galaxies and matter are distributed at different scales throughout space.
Like previous studies, today's findings use a technique that doesn't reveal the results to scientists until the end, reducing any unconscious bias.
More information about this discovery
DESI is a cutting-edge instrument capable of capturing the light of 5,000 galaxies simultaneously. It is designed, built and operated with funding from the U.S. Department of Energy's Office of Science.
DESI is located in Arizona and is installed on the Nicholas U-Mayor 4-meter telescope at Kitt Peak National Observatory and is part of the National Science Foundation's NOIRLab program. DESI is a five-year survey now in its fourth year, with the goal of collecting data on approximately 40 million galaxies and quasars by the end of the project.
The collaborative team is currently analyzing data collected during the first three years of the survey and plans to release updated measurements of dark energy and the expansion history of the universe by spring 2025. Today's expanded results are consistent with earlier findings suggesting that dark energy is evolving, further raising expectations for the next phase of analysis.
DESI's collaborators knew that their research was being conducted on Iolkam Du'ag (Kitt Peak), which has profound cultural significance to the Tohono O'odham people.
Compiled from /ScitechDaily