Explaining the accelerating expansion of the Universe without dark energy

A modification to the theory of general relativity makes it consistent with observable astronomical data without the need for dark energy.

Since its completion in 1915, einstein’s theory of general relativity has been the basis of our understanding of gravity. This theory has passed many experimental tests and is used to explain not only physics at the scale of planets, stars, and galaxies, but even the evolution of the cosmos as a whole. However, it has some shortcomings.

Recent astronomical observations have shown that the yourthe universe is expanding a tan acceleration rateAnd although this does not necessarily contradict the ideas expounded in general relativity, it is necessary to assume the existence of an entity called dark energy, a mysterious influence that drives the accelerated expansion.

Currently, the origin of dark energy is unclear and an understanding of its properties is still lacking. Thus, for many physicists, for whom simplicity and minimalism are often important criteria for the validity of a scientific theory, the inclusion of a substance or entity that, to date, has not been observable by any experimental means, it is something undesirable.

To remedy this shortcoming, a team of physicists from the Birla Institute of Technology and Science in Pilani, India, have proposed modifying general relativity, making it no longer necessary to consider this mysterious form of energy for the theory to be consistent with the astronomical observable. . data.

Eliminate the need for dark energy

General relativity interprets gravity as a deformation of space-time by particles and fields whose behavior is in turn affected by these changes in the geometry of space-time. Both actors influence each other, which is similar to what happens in electromagnetism, where an electric field changes the paths of charged particles, which in turn change the electric field. Einstein postulated a very specific way for how this subtle mutual influence of geometry and matter occurs, and changing the details of this interaction is what the authors of the new study proposed.

The equations of a theory of gravity can be applied to various physical situations, such as studying the geometry of the entire Universe as it evolved after the Big Bang. Using these, one can find the rate at which space is expanding and compare the solution to observational data. The requirement that the solution of Einstein’s equations be consistent with the observations required the introduction of dark energy into the equations.

In the new study, the physicists solved the equations of the alternative theory of gravity, called “torque gravity squared,” and found that the expansion rate of the Universe is better described by this theory than by general relativity, even without the need to introduce “missing components” to general relativity in the form of dark energy.

Modifying how gravitational fields interact with matter within these equations resulted in a change in the influence of matter on the geometry of spacetime, an effect similar to that of hypothetical types of dark energy termed “quintessencewithout the need for them.

Future studies of the dynamics of the expansion of the Universe will certainly help to verify the theoretical results obtained here by physicists.

“Experiments are not yet planned, but theoretical validation of our theory can be done with observational data,” said Simran Arora, one of the study’s authors.

Despite the encouraging results, the physicists note that more work still needs to be done to determine if their description of gravity is correct. In addition to a general rate of expansion, a robust theory of gravity must correctly explain other effects, such as fluctuations in the density of matter, which during cosmic evolution led to the birth of stars, planets, and galaxies.

“Future work includes the more detailed theoretical study of dark energy in our squared torsion F(you,T) gravity”, concluded Arora. “We plan to study other cosmological scenarios, including inflation, stresses on cosmological parameters, and perturbation analysis.”

Citation: Arora S., Bhat A., Sahoo PK, Torsion gravity f(T,T) squared and its cosmological implicationsPhysics Progress (2022), DOI: 10.1002/prop.202200162

Feature image credit: Miriam Espacio on Unsplash

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