New research challenges Einstein's predictions on cosmic expansion

New research is challenging long-held assumptions about the universe's expansion and the behavior of gravitational wells, suggesting that Einstein's theories may not fully explain cosmic phenomena at the largest scales. A team of researchers from the University of Geneva (UNIGE) and Toulouse III – Paul Sabatier has analyzed data from the Dark Energy Survey, revealing slight discrepancies between observed gravitational wells and Einstein's predictions, which vary depending on different periods in cosmic history.

The French-Swiss team examined 100 million galaxies at four distinct points in cosmic history: 3.5, 5, 6, and 7 billion years ago. Their findings indicate that 6 to 7 billion years ago, gravitational wells were as deep as Einstein predicted. However, in more recent times, about 3.5 to 5 billion years ago, these wells were slightly shallower than expected. This period coincides with the beginning of the universe's accelerated expansion, a phenomenon that remains one of the great enigmas of modern physics.

"We discovered that in the distant past—6 and 7 billion years ago—the depth of the wells aligns well with Einstein's predictions. However, closer to today—3.5 and 5 billion years ago—they are slightly shallower than predicted by Einstein," said Isaac Tutusaus, assistant astronomer at the Institute of Research in Astrophysics and Planetology (IRAP/OMP) at Université Toulouse III and the study's lead author.

The universe's accelerated expansion challenges our understanding of physics and the cosmos. The recent findings from the Dark Energy Survey could exhibit an incompatibility with Einstein's theories, prompting scientists to explore whether his equations are still valid at the edge of the universe. The research results show that Einstein's predictions have an incompatibility of 3 sigma with measurements, which draws significant interest from the scientific community and justifies the need for additional research.

"Our results show that Einstein's predictions have an incompatibility of 3 sigma with measurements. In the language of physics, such an incompatibility threshold arouses our interest and calls for further investigations," said Nastassia Grimm, postdoctoral researcher in the Department of Theoretical Physics at UNIGE and co-author of the study. The incompatibility, she said, is not large enough, at this stage, to invalidate Einstein's theory. "For that to happen, we would need to reach a threshold of 5 sigma. It is therefore essential to have more precise measurements to confirm or refute these initial results, and to find out whether this theory remains valid in our universe, at very large distances."

The discrepancy raises questions about the validity of Einstein's theories when applied to phenomena occurring on cosmic scales. Rather than focusing solely on matter distribution, the research team used the Dark Energy Survey data to directly measure the distortion of space and time, enabling them to compare their findings with Einstein's predictions.

In Einstein's theory of general relativity, space-time is described as a flexible and deformable surface that curves around massive objects, creating gravitational wells. When light passes through this warped surface, its path bends according to the shape of space-time, an effect known as gravitational lensing, similar to the effect of a glass lens. Observing gravitational lensing provides insights into the components, history, and expansion of the universe.

Since its first measurement in 1919 during a solar eclipse, observations of gravitational lenses have proven to be key tools for studying the distribution of matter in the universe and exploring its expansion. The 1919 measurement confirmed Einstein's theory, which predicted a light deflection twice as large as that predicted by Isaac Newton.

The team is preparing to analyze new data from the Euclid space telescope, launched a year ago. As Euclid observes the universe from space, its measurements of gravitational lensing will be significantly more precise. Euclid is expected to observe about 1.5 billion galaxies within the six years of the mission. Its precision in observing gravitational lenses will allow researchers to look even further back in time and rigorously test Einstein's equations.

Scientists are hopeful that the Euclid space telescope will provide much more detailed measurements. However, to definitively refute Einstein's theory, it would be necessary to reach a 5-sigma threshold, which would require even more precise data. The researchers believe that the answer to two phenomena—the acceleration of the universe and the slower growth of gravitational wells—may be the same: gravity could operate under different physical laws at large scales than those predicted by Einstein.

Sources: Der Standard, Phys.org, Science Daily, Science

This article was written in collaboration with generative AI company Alchemiq