Einstein’s Next Theory of Gravity Could Have Recipe to Alleviate ‘Hubble Trouble’

A recent study explored teleparallel gravity and its potential to resolve the tensions surrounding the expansion of the universe in a way that general relativity cannot.

In the early 20th century, our understanding of the universe was turned on its head when Edwin Hubble’s observations revealed that the very fabric of the universe was stretching.

At the end of the same century, this knowledge was further complicated when two separate teams of scientists, observing distant supernovae moving away from Earth, discovered that the universe was not only expanding, but that the rate of expansion was accelerating.

The cause of this acceleration is a mystery and has been nicknamed “dark energy”; the best current explanation for this is a cosmological constant that accounts for a form of background energy called vacuum energy.

The rate at which the universe is expanding is known as the Hubble constant, which describes the proportionality between a galaxy’s distance from Earth and the rate at which it is receding.

This has been a headache for physicists because the two main ways of determining the Hubble constant are in huge disagreement. This problem is called the “Hubble tension,” and one way to explain it would be to extend our current best model of gravity, general relativity, proposed by Einstein in 1915.

Article published in a journal Dark Universe Physics Celia Escamilla Rivera, a cosmologist at the Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, and her co-researchers are trying to tackle dark energy and ease the strain on Hubble.

“We found that the use of gravity models goes beyond general relativity and new cosmological data sets [observations of distant quasars] we can face the Hubble strain and the dark energy problem on a local scale,” says Rivera.

“Using numerical and computational methods, we performed an analysis using different proposed models in ‘teleparallel gravity’ tested with two different cosmological samples that measured distances in the local universe.”

Teleparallel gravity is an alternative theory to the general theory of relativity, also invented by Einstein. This “other theory of gravity” uses a different recipe of equations to explain gravity without the curvature of space-time, and also tries to unify it with one of the other fundamental forces of the universe, electromagnetism.

“Recently, teleparallel gravity has been gaining popularity because of the promise that it could solve the cosmological problem related to the Hubble tension and could explain the nature of cosmic acceleration at late time without invoking the cosmological constant,” says Rivera.

Rivera and her colleagues tested the parameters of this alternative theory of gravity using two new data sets of distant and high-redshift quasars, bright regions at the heart of galaxies that are powered by the power of supermassive black holes, observed in ultraviolet, X-ray, and visible light.

“We are interested in this topic because teleparallel gravity is a good candidate for an alternative proposal to general relativity that solves various cosmological problems and also has some interesting theoretical properties,” concludes Rivera.

“It is of interest to a wider audience as we test alternative proposals to general relativity to better understand the universe, and to experts in the field it is an update on the state of the art on specific models in teleparallel gravity.” , also using relatively new samples of quasars at high redshifts.”