Supercomputer simulations of galaxies have shown that Einstein's theory of general relativity may not be the only way to explain how gravity works or how galaxies form.
Physicists at Durham University, UK, simulated the cosmos using an alternative model for gravity – the f (R) gravity, a so-called chameleon theory.
The images generated by the simulation show that galaxies similar to our Milky Way could still form in the Universe even with different laws of gravity.
The results show the viability of chameleon theory – so called because it changes behavior depending on the environment – as an alternative to the General Theory of Relativity for explaining structure formation in the universe.
Research could also contribute to a better understanding of dark energy – the mysterious substance that accelerates the rate of expansion of the universe.
The results were published in Nature Astronomy .
General The theory of relativity was developed by Albert Einstein at the beginning of the 20th century to explain the gravitational effect of large objects in space, for example to explain the orbit of mercury in the solar system.  05] It is the foundation of modern cosmology, but also plays a role in everyday life, for example in the calculation of GPS positions in smartphones.
Scientists already know from theoretical calculations that chameleon theory can reproduce the success of the General Theory of Relativity in the Solar System
The Durham team has now shown that this theory enables the formation of realistic galaxies such as our Milky Way and general relativity very large cosmological scales can be distinguished.
Research co-principal author Christian Arnold, Durham The University's Computer-Aided Cosmology Institute said: "Chameleon theory allows us to modify the laws of gravity so that we can test the effects of gravitational changes on galaxy formation. ” Chamäleontheorie “, könnten unser Denken über die Gravitation verändern ” title=”Computer generated images showing a disk galaxy from a modified gravity simulation are available. Images show (right side of image, in red-blue color) the gas density within the disk of the galaxy with the stars shown as bright dots. The left side of the images show the force changes in the gas within the disk, where the dark central regions correspond to standard, General Relativity-like forces and the bright yellow regions correspond to enhanced (modified forces). Images show views of the simulated galaxy from above and the side. Credit: Christian Arnold/Baojiu Li/Durham University.”/>
Computer-generated images, ” Chamäleontheorie “, könnten unser Denken über die Gravitation verändern ” title=”Computer generated images showing a disk galaxy from a modified gravity simulation are available. Images show (right side of image, in red-blue color) the gas density within the disk of the galaxy with the stars shown as bright dots. The left side of the images show the force changes in the gas within the disk, where the dark central regions correspond to standard, General Relativity-like forces and the bright yellow regions correspond to enhanced (modified forces). Images show views of the simulated galaxy from above and the side. Credit: Christian Arnold/Baojiu Li/Durham University.”/>
The images show (right side of the picture, in red-blue color) the gas density within the disk of the galaxy, the stars being shown as bright points .The left side of the pictures shows the force changes in the gas inside the disk, with the dark central areas corresponding to the standard forces, the general relative forces and the bright yellow areas of the amplified (modified forces) .The pictures show views of the simulated galaxy from above and from the side Arnold / Baojiu Li / You rham university.
"Through our simulations, we have shown for the first time that even if you change gravity, the formation of disk galaxies with spiral arms will not be prevented.
" Our research definitely does not mean that General Theory of Relativity is wrong, but it shows that explaining the role of gravity in the evolution of the universe is not the only way to explain it.
The researchers studied the interaction between gravity in chameleon theory and supermassive black holes located at the center of galaxies.
Black holes play a key role in the formation of galaxies because of the heat and the material that make up the galaxy release them by swallowing the surrounding matter, burn gas needed to form stars, and effectively stop star formation.
The amount of heat spilled out by black holes changes due to gravity, which affects the formation of galaxies.  However, the new simulations showed that galaxies still exist, even taking into account the gravitational change caused by the application of chameleon theory.
General relativity also has consequences for understanding the accelerating expansion of the universe.
Scientist g allow this expansion to be driven by dark energy, and the Durham researchers say their results could be a small step toward explaining the properties. "In General Theory of Relativity, scientists explain the accelerated expansion of the universe by creating a mysterious form of matter called dark energy – the simplest form of this may be a cosmological constant whose density is a constant in space and time.
"Alternatives to a Cosmological Constant Explaining the Accelerated Expansion by Modifying the Law of Gravity, as f (R) Considering the low knowledge of the dark energy, gravity is also considered to be widely used."
The Durham researchers expect that their results can be verified by testing gh observations with the Australia-based and South Africa-based Telescope Square Kilometer Array (SKA), with which observations are due to begin in 2020.
SKA will be the world's largest radio telescope and will challenge Einstein's Theory of General Theory How the first stars and galaxies formed after the Big Bang, and help scientists understand nature or dark energy.
Video: 100 years of gravity
Christian Arnold et al., Realistic Simulations of Galaxy Formation in F (R) -modified Gravitation, Nature Astronomy (2019). DOI: 10.1038 / s41550-019-0823-y
Supercomputershows & # 39; Chameleon Theory & # 39; could change our thinking about gravity (2019, July 8)
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