Revised theory of gravity doesn’t predict a Big Bang

Lisa Zyga in PHYSORG:

The Big Bang theory has formed the basis of our understanding of the universe’s origins since it was first proposed in 1927 by Georges Lemaitre. And for good reason: the theory is supported by scientists’ latest observations and experiments, and is based on Einstein’s widely accepted theory of general relativity. But scientists are always on the lookout for any evidence that might suggest an alternative to the Big Bang. The latest in this area of research comes from astrophysicists Maximo Banados and Pedro Ferreira, who have resurrected a theory of gravity from the early 20th century and discovered that a modified version of the theory may hold some surprises.

In a recent study published in , Banados and Ferreira have reconsidered the theory of gravity proposed by Arthur Eddington, a contemporary of Einstein. Eddington is perhaps best known for his trip to the Island of Principe on the west coast of Africa in 1919, where during a solar eclipse he observed that the Sun’s gravity does indeed bend starlight, providing one of the earliest confirmations of general relativity.

Although Eddington played a significant role in developing general relativity, during the following decades he became more interested in finding a theory to unify gravity and  – a task that is still being studied today. In 1924, Eddington proposed a new “gravitational action” as an alternative to the Einstein-Hilbert action, which could serve as an alternative starting point to general relativity. In astrophysics, a gravitational action is the mechanism that describes how gravity can emerge from space-time being curved by matter and energy. However, Eddington’s theory of gravity only worked for empty space and didn’t include any source of energy such as matter, making it an incomplete theory.

Since Eddington’s proposal, scientists have attempted various ways of including matter into the theory, although they have run into problems. In this study, Banados and Ferreira have tried a new way to extend the theory to include matter by using a gravitational action called the Born-Infeld action.

In their analysis, the scientists found that a key characteristic of Eddington’s revised  is that it reproduces Einstein gravity precisely in the vacuum conditions (with no matter), but it produces new effects when matter is added. Due to this characteristic, the revised theory has implications especially for high-density regions, such as in the very early Universe or within a black hole. For instance, the theory predicts a maximum density of homogeneous and isotropic space-time, which could have implications for black hole formation.

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