Scientists reconstruct gravity to better understand the universe

November 10, 2022

ASimon Fraser University physicist led an international team of scientists in reconstructing the laws of gravity—to gain a better understanding of how they work in the larger universe.

The study, published in Nature Astronomy and featured in The Conversation, explored whether modifying General Relativity could help resolve some of the open problems of cosmology.

SFU Professor Levon Pogosian says that, while laws of gravity as laid out by Newton and Einstein work well in our solar system, there are still questions around how they work beyond it.

“The gaps in our understanding appear when we when we try to apply these laws to the entire universe,” says Pogosian, who also organizes biennial international conferences on Testing Gravity at the SFU Harbour Centre in Vancouver.

“To describe the universe using Einstein’s theory we need to introduce dark matter and dark energy – two ingredients that together make up 95 percent of the universe and whose nature we do not understand. Moreover, different ways of measuring the rate of cosmic expansion appear to give different answers – a serious problem in cosmology known as the Hubble Tension.”

The standard model of cosmology is based on General Relativity, which describes gravity as the curving or warping of space and time that bends the pathways along which light and matter travel. The authors considered modifications to the expansion of the Universe, to the way gravity affects light, and to the way it affects matter. Using a statistical method known as the Bayesian inference, the team reconstructed the three types of modifications simultaneously for the first time.

The scientists’ reconstruction to test Einstein’s theory in the outer-reaches of space was carried out by examining new observational data from satellites and ground-based telescopes that measure the expansion of the universe and the shapes and distribution of distant galaxies. 

“What we found was that current observations are getting good enough to test General Relativity over cosmological distances,” says Pogosian. “We also saw interesting hints of possible departures from Einstein’s prediction, which, if confirmed with future data, could pave the way to resolving some of the open challenges in cosmology.

“But, at the same time, we found that it's very difficult to solve the Hubble Tension even by extending our theory of gravity. As the era of precision cosmology is unfolding, we are on the brink of learning about gravity on cosmological scales with high precision.”

One exciting prospect is that in a few years’ time we’ll have a lot more data from new probes, says professor Kazuya Koyama, from the Institute of Cosmology and Gravitation at the University of Portsmouth in the UK. “This means that we will be able to continue improving the limits on modifications to General Relativity using these statistical methods.”