General relativity, formulated by Albert Einstein in 1915, revolutionized our understanding of gravity. According to this theory, spacetime is not a fixed arena where all physical processes take place, but a dynamic entity whose shape responds to the movement, interaction, and transformation of particles and radiation.
Einstein’s theory not only changed our concept of space, time, and gravity on the theoretical level, but by providing many testable predictions and explained many observed phenomena, such as time dilation in a gravitational field, the deflection of light rays by massive bodies, the formation of black holes, and even the expansion of the Universe throughout its evolutionary course.
However, this extraordinary and successful theory has its limitations. In the context of the expansion of the Universe for example, when we use the “mathematical machinery” of general relativity to theoretically “rewind” the history of the Universe back to its very beginning, we end up with the Big Bang singularity, in which the densities of matter and energy are infinitely large.
The entirety of physics’ history has taught us that infinities do not exist in the natural world. When they arise in calculations, this is an indication that the theory is not completely correct and must be modified to eliminate them, replacing them with finite, albeit large, quantities.
A non-singular birth
It is this search that a recent study published in the Progress of Physics has reported on. In their paper, a team of theoretical physicists from India and Brazil were able to change the equations of Einstein’s theory in such a way that the state of the Universe, at the moment of its birth, appears to be non-singular.
The study retains the interpretation of gravity as a deformation of spacetime, as proposed by Einstein, but modifies the mechanisms by which matter moving in space causes this deformation.
As a result, their predictions regarding the evolution of the Universe almost exactly match those made by general relativity (and observational data), except for the moment of the Big Bang, in which the infinite density of matter that arises in Einstein’s theory are replaced by a finite quantity.
In addition to resolving the paradox of the Big Bang singularity, their modified theory of gravity seems able to solve another problem of general relativity: the problem with dark energy.
Dark energy, which accounts for 70% of the energy in space, is a necessary inclusion in general relativity order to align theory with the observed accelerated expansion of the Universe.
This mysterious entity has never been observed or replicated in any laboratory experiments, and its origins and nature remain murky. Understandably, dark energy has been a source of concern and intrigue for scientists for many years.
This is why the findings of the current study may be substantial as it explains the observed expansion rate of the Universe without the need to introduce any type of unobservable energy.
Although the results are encouraging, the scientists indicate they still have a lot of work to do to confirm whether their theory of gravity is indeed more accurate than general relativity. To do this, precise predictions about the dynamics of the expansion of space and other processes that took place are necessary.
The authors also hope that their modified gravity will be able to solve the mystery of dark matter, which, like dark energy, has not yet been detected in any experimental study, and was discovered only through its gravitational effect on other fields and particles.
The team say they are planning to analyze this interaction in their theory, and, hopefully, will be able to explain the observational data.
Reference: B.S. Gonçalves, P.H.R.S. Moraes, B. Mishra, Cosmology from Non-Minimal Geometry-Matter Coupling, Progress of Physics (2023). DOI: 10.1002/prop.202200153.
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