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A project which challenges Einstein’s theory of gravity suggests there might be a flaw in the dominant force shaping our universe. If proven true, this discovery would call for a rewrite of every physics textbook. 

Experts at the ����ý are exploring whether gravity behaves differently on the largest distances in the cosmos than it does on the scale of humans and planets.

The project ‘Hi-COLA simulations of large-scale structure’ will develop simulations of the universe that help test ideas about dark energy, the hypothesised force driving the accelerating expansion of the universe. 

Professor Tessa Baker, from the University’s Institute of Cosmology and Gravitation, said: “To explore this idea, we need simulations that show how the universe might behave with different gravity laws. In these simulated universes, the dark matter behaves differently. It clumps together at varying rates, forming unique ‘cosmic webs’ akin to spider webs. Each web is distinct, with different-sized holes, shapes, and numbers of strands. These simulations help us see how gravity might really operate on the largest scales imaginable.”

Einstein's general theory of relativity has long reigned as our standard theory of gravity. It correctly predicts the detailed motions of planets, but also exotic phenomena such as gravitational waves - minute ripples in space itself, caused by collisions of black holes.

However, in 1999, Einstein's untouchable theory was thrown into doubt by observations of exploding stars: supernovae. These indicated that the expansion rate of the universe is accelerating, and this feature cannot be simultaneously reconciled with both general relativity and quantum theory.

Professor Baker explained: “An intriguing alternative is that Einstein's theory is not the last word in gravity. Could it be that gravity behaves differently on the largest distances in the cosmos? I was drawn to this question by the immense repercussions that the answer ‘yes’ would have. 

“As the fundamental force sculpting the universe, a flaw in our understanding of gravity would be a major shake-up at the core of physics and cause essentially every textbook on physics to be rewritten.”

Professor Baker’s work aims to answer this question by building computer simulations and mathematical tools that connect the latest developments in theoretical physics with the observations from astronomical telescopes. 

She said: “I can predict, for example, how the distribution of galaxies in the universe would change, if gravity behaves differently from general relativity. My work also allows us to use the first detections of gravitational waves - an experimental reality since only 2015 - which may hold the key to proving Einstein right or wrong.”

The aim of the project is to eventually produce results that match what could be observed by the , a major new ground-based telescope in Chile, starting in a couple of years. 

Making this connection would ultimately allow the data from Rubin to say if the true laws of gravity in the universe are 'standard' (like the ones we experience on Earth), or something very different. 

Professor Baker has held a University Research Fellowship from the Royal Society since 2019, which has been extended for another three years. The award of $640,000 supports Dr Baker and a postdoctoral research position, currently held by Dr Bartolomeo Fiorini.

Other colleagues working on this project include PhD student Ashim Sen Gupta, from Queen Mary University of London, and Dr Krishna Naidoo who will join the team in September from UCL.