In the early 20th century, our understanding of the universe was turned on its head when observations made by Edwin Hubble revealed that the very fabric of the cosmos was stretching.
At the close of the same century, this realization was made even more complicated when, by observing distant supernovas as they move away from Earth, two separate teams of scientists discovered that not only is the universe expanding, but this rate of expansion is accelerating.
The cause of this acceleration is a mystery and has been given the placeholder name "dark energy"; the best current explanation for it is the cosmological constant that accounts for a form of background energy called vacuum energy.
The rate of the expansion of the universe is known as the Hubble constant, which describes the proportionality between the distance of a galaxy from Earth and the velocity by which it recedes.
This has been a headache for physicists because the two major ways of determining the Hubble constant are in vast disagreement. This issue is dubbed the "Hubble tension," and one way to explain it would be by extending our current best model of gravity, general relativity, posited by Einstein in 1915.
A paper published in the journal Physics of the Dark Universe by Celia Escamilla Rivera, a cosmologist at Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, and her co-researchers, attempts to tackle dark energy and relieve the Hubble tension.
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