New DESI Observations Line Up with What Theory of General Relativity Predicts

Astronomers using the Dark Energy Spectroscopic Instrument (DESI), a state-of-the-art instrument mounted on NSF’s Nicholas U. Mayall 4-m telescope at Kitt Peak National Observatory, have mapped how nearly 6 million galaxies cluster across 11 billion years of cosmic history. Their results provide one of the most stringent tests yet of Albert Einstein’s general theory of relativity.

“General relativity has been very well tested at the scale of solar systems, but we also needed to test that our assumption works at much larger scales,” said Dr. Pauline Zarrouk, a cosmologist at CNRS and the Laboratory of Nuclear and High-Energy Physics.

“Studying the rate at which galaxies formed lets us directly test our theories and, so far, we’re lining up with what general relativity predicts at cosmological scales.”

In their new study, Dr. Zarrouk and colleagues found that gravity behaves as predicted by Einstein’s general theory of relativity.

The result validates our leading model of the Universe and limits possible theories of modified gravity, which have been proposed as alternative ways to explain unexpected observations, such as the accelerating expansion of our Universe that is typically attributed to dark energy.

The complex analysis used nearly six million galaxies and quasars and lets researchers see up to 11 billion years into the past.

Today’s results provide an extended analysis of DESI’s first year of data, which in April made the largest 3D map of our Universe to date and revealed hints that dark energy might be evolving over time.

The April results looked at a particular feature of how galaxies cluster known as baryon acoustic oscillations (BAO).

The new analysis broadens the scope by measuring how galaxies and matter are distributed on different scales throughout space.

The study also provided improved constraints on the mass of neutrinos, the only fundamental particles whose masses have not yet been precisely measured.

Neutrinos influence the clustering pattern of galaxies very slightly but this can be measured with the quality of the DESI data.

The DESI constraints are the most stringent to date, complementing constraints from laboratory measurements.

The study required months of additional work and cross-checks. Like the previous study, it used a technique to hide the result from the scientists until the end, mitigating any unconscious bias.

“This research is part of one of the key projects of the DESI experiment — to learn about the fundamental aspects of our Universe at large scales, such as matter distribution and the behavior of dark energy, as well as fundamental aspects of particles,” said Dr. Stephanie Juneau, an astronomer at NSF’s NOIRLab and a member of the DESI Collaboration.

“By comparing the evolution of the matter distribution in the Universe with existing predictions, including Einstein’s theory of general relativity and competing theories, we’re really tightening the possibilities on our models of gravity.”

“Dark matter makes up about a quarter of the Universe, and dark energy makes up another 70%, and we don’t really know what either one is,” said Mark Maus, a Ph.D. student at Berkeley Lab and the University of California, Berkeley.

“The idea that we can take pictures of the Universe and tackle these big, fundamental questions is mind-blowing.”

The DESI Collaboration shared their results today in several papers at arXiv.org.