In 1915, Albert Einstein published his pioneering theory of general relativity, which describes the nature of gravity and its effect on large objects in space. Since then, his work has formed the basis for scientists’ understanding of our universe.
But, despite its importance, general relativity is not the only explanation for how gravity works. In fact, several scientists have proposed alternative theories over time, although it should be noted that none of them is consistent with the experimental data exposed by the Theory of General Relativity.
The fifth force
Now, a team of scientists from the University of Durham (UK) has published a study in the journal Nature Astronomy that suggests that one of these alternative theories, known as gravity F (R) or “chameleon theory”, could really explain how gravity works in some situations.
It is an alternative theory to Einstein’s general relativity. In this theory, in addition to the standard gravitational force, there is an additional force, called the ‘fifth force’ since it is different from the other four types of fundamental interactions.
For their study, the team carried out advanced simulations with supercomputers, which showed that galaxies could form in a universe where the principles of the chameleon theory apply.
“What we have discovered is that realistic galaxies like our Milky Way can form, with the observed properties, even with the complicated behavior of the fifth force. It also shows that the chameleon theory can make certain different predictions about the evolution of the large-scale structures in the universe from general relativity “, explains Baojiu Li, co-author of the work.
Thus, according to this alternative model that states that gravity can change its behavior in relation to the environment, it does not mean that Einstein was wrong, but that perhaps there is no single way to explain these cosmic events.
The latest findings could have significant implications for our understanding of phenomena such as black holes and the role they play in galaxy formation, as well as the nature of so-called “dark energy,” the mysterious force or substance that scientists use to explain the accelerated expansion of the universe.
Black holes
The researchers looked at the interaction between gravity in the Chameleon Theory and supermassive black holes that are located at the center of galaxies.
Black holes play a key role in galaxy formation because the heat and material they expel by swallowing surrounding matter can burn the gas needed to form stars, stopping star formation.
The amount of heat expelled by black holes is altered by changing gravity, which affects the way galaxies form. However, the new simulations showed that even taking into account the change in gravity caused by the application of the chameleon theory, galaxies could still form.
“General relativity has been very successful in explaining many phenomena, and it is one of the foundations of modern cosmology,” Li said. “However, one thing that has been puzzling to cosmologists is the observational evidence that the expansion of the universe is accelerating .”
“Therefore, one has to assume that there are other , hitherto undetected materials present in the universe that accelerate its rate of expansion. The so-called cosmological constant is one of the simplest possibilities, but its origin and value have proven to be difficult to explain, which motivates other alternative explanations, such as dark energy, “Li clarifies.
“This study is the first time that it shows that an alternative theory of gravity, despite its complicated gravitational force behavior, can still create realistic galaxies. Studies like this will help us verify the feasibility of a theory, as well as identify places where we can test different theories of gravity using future observational data. Of course, much more work is needed to reach a final conclusion, “Li concludes.
AKA
The next step for this team of scientists is to test their findings using real-world experimental data. However, they will have to wait to carry out this research until next year’s opening of the Square Kilometer Array or SKA of South Africa and Australia, which will be the largest radio telescope in the world and which will begin observations in 2020.
SKA aims to challenge Einstein’s theory of general relativity, observe how the first stars and galaxies formed after the Big Bang, and help scientists understand the nature of dark energy.
Referencia: Christian Arnold et al, Realistic simulations of galaxy formation in f(R) modified gravity, Nature Astronomy (2019). DOI: 10.1038/s41550-019-0823-y
Crédito imagen: Christian Arnold/Baojiu Li/Durham University.
