Einstein’s other theory of gravity could have the recipe to alleviate ‘Hubble problems’

A recent study explored teleparallel gravity and its potential to resolve the tension 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 upside down when observations by Edwin Hubble revealed that the fabric of the cosmos was stretching.

At the end of the same century, this realization was made even more complicated when two separate teams of scientists discovered, by observing distant supernovae as they moved away from Earth, that not only was the universe expanding, but also that the rate of expansion was increasing. .

The cause of this acceleration is a mystery and has been given the temporary name “dark energy”; the best current explanation for this is the cosmological constant responsible 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 its rate of retreat.

This is a headache for physicists, because the two main ways of determining the Hubble constant have major disagreements. This issue is called the ‘Hubble tension’, and one way to explain it would be to extend our current best model of gravity, general relativity, which was posited by Einstein in 1915.

An article published in the magazine Physics of the dark universe by Celia Escamilla Rivera, a cosmologist at Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, and her fellow researchers, aims to tackle dark energy and alleviate the Hubble strain.

“We discovered this by using gravity models that extend beyond general relativity and new cosmological data sets [observations of distant quasars] we can deal with the Hubble tension and the dark energy problem on a local scale,” says Rivera.

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

Teleparallel gravity is an alternative theory to the general theory of relativity, also devised by Einstein. This ‘other theory of gravity’ uses a different recipe of equations to explain gravity without the curvature of spacetime, and also attempts to reconcile it with one of the other fundamental forces of the universe, namely electromagnetism.

“Recently, teleparallel gravity has been gaining popularity due to the promise that it could solve the cosmological problem involving the Hubble tension and explain the nature of late cosmic acceleration without invoking a 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 highly redshifted quasars, the bright regions at the heart of galaxies powered by feeding supermassive black holes, observed in ultraviolet, X-ray radiation. and visible light.

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

“For a wider audience it is interesting because we test alternative proposals to general relativity to better understand the universe, and for experts in the field it is an update on the state of the art on specific models in teleparallel gravity, also involving relatively new quasar samples at high redshifts are used.”