A modification of 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 foundation of our understanding of gravity. This theory has passed many experimental tests and is used to explain not only physics on 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 Universe is expanding at an accelerating rate, and while this does not necessarily contradict advanced ideas in general relativity, it is necessary to assume the existence of an entity called energy. black, a mysterious influence behind the accelerated expansion.
The origin of dark energy is currently unclear and understanding of its properties is still lacking. Therefore, 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 has been, to date, unobservable by any experimental means, is somewhat undesirable.
To remedy this shortcoming, a team of physicists from the Birla Institute of Technology and Science in Pilani, India, proposed to modify general relativity, making it more necessary to consider this mysterious form of energy for the theory to be consistent with the observable astronomical observations. The data.
Eliminate the need for dark energy
General relativity interprets gravity as a deformation of spacetime by particles and fields whose behavior is in turn affected by these changes in the geometry of spacetime. The two actors influence each other, which is similar to what happens in electromagnetism where an electric field modifies the trajectories of charged particles, which in turn modify the electric field. Einstein postulated a very specific way of 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 to study 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 observations necessitated the introduction of dark energy into the equations.
In the new study, physicists solved the equations of the alternative theory of gravity, called “torsional gravity squared”, and found that the rate of expansion of the Universe is better described by this theory than by the general relativity, even without the need to introduce “missing components” to general relativity in the form of dark energy.
Changing the way gravitational fields interact with matter in these equations has 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 dubbed “quintessence” without needing it.
Future studies of the dynamics of the expansion of the Universe will certainly make it possible to verify the theoretical results obtained here by physicists.
“The experiments are not planned yet, 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 there is still work to be done to determine whether their description of gravity is indeed correct. In addition to a global expansion rate, a robust theory of gravity must correctly account for other effects, such as fluctuations in matter density, which during cosmic evolution have led to the birth of stars, planets and galaxies.
“Future work includes the more detailed theoretical study of dark energy in our torsion squared F(J,T) gravity,” Arora concluded. “We plan to study other cosmological scenarios, including inflation, tensions in cosmological parameters, and perturbation analysis.”
Reference: Arora S., Bhat A., Sahoo PK, Squared f(T,T) Torsion Gravity and Its Cosmological Implications, Progress of Physics (2022), DOI: 10.1002/prop.202200162
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