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Why is the Universe's expansion speeding up? This question has baffled scientists for over 25 years since its discovery. Addressing it requires re-examining fundamental physics, particularly Einstein's general relativity. Researchers from the University of Geneva (UNIGE) and the Universite Toulouse III - Paul Sabatier have compared Einstein's theoretical predictions with empirical data from the by Robert Schreiber
Berlin, Germany (SPX) Nov 12, 2024
Why is the Universe's expansion speeding up? This question has baffled scientists for over 25 years since its discovery. Addressing it requires re-examining fundamental physics, particularly Einstein's general relativity. Researchers from the University of Geneva (UNIGE) and the Universite Toulouse III - Paul Sabatier have compared Einstein's theoretical predictions with empirical data from the Dark Energy Survey, revealing slight deviations that shift over different eras of cosmic history. These observations, published in *Nature Communications*, suggest potential limits to Einstein's theories for explaining universal-scale phenomena.
Einstein's theory visualizes the Universe as a flexible sheet that distorts with the presence of matter, forming what are known as "gravitational wells." Light passing through these wells is bent by gravity, a concept known as "gravitational lensing." The first observational evidence of this phenomenon came during the solar eclipse of 1919, where light bending matched Einstein's predictions, showcasing how both space and time deform.
Testing these principles at the Universe's vast reaches is a current focus for cosmologists who aim to quantify matter density and understand the acceleration of cosmic expansion. Utilizing data from the Dark Energy Survey, which maps the shapes of millions of galaxies, the UNIGE and Toulouse III team explored gravitational distortions and their alignment with Einstein's models.
"Until now, Dark Energy Survey data have been used to measure the distribution of matter in the Universe. In our study, we used this data to directly measure the distortion of time and space, enabling us to compare our findings with Einstein's predictions,' said Camille Bonvin, associate professor at UNIGE's Department of Theoretical Physics.
The analysis of 100 million galaxies at four distinct cosmic ages - 3.5, 5, 6, and 7 billion years ago - revealed intriguing insights. "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,' explained Isaac Tutusaus, assistant astronomer at IRAP/OMP and lead author of the study.
This period is also notable for the acceleration of the Universe's expansion. A connection between the recent shallower wells and this acceleration could suggest that gravity functions differently on large scales compared to Einstein's model.
"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. But this incompatibility 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,' highlighted Nastassia Grimm, a postdoctoral researcher at UNIGE and co-author of the study.
The upcoming analysis of data from the Euclid space telescope, launched a year ago, promises to provide more refined measurements. With Euclid's ability to observe around 1.5 billion galaxies over six years, researchers anticipate improved insights into space-time distortions and a deeper probe into the fabric of Einstein's equations.
Research Report:Measurement of the Weyl potential evolution from the first three years of dark energy survey data
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University of Geneva
Understanding Time and Space