# First universe modeling using Einstein's full theory of general relativity

Using software that incorporates all of the field theory equations developed by Einstein as part of his general theory of relativity, research teams from Europe and the United States have started developing a model of the universe that they claim will eventually provide the most precise and detailed representation of the cosmos ever created.

Incorporating two new independently-developed computer codes from a team comprising members from Case Western Reserve University and Kenyon College, Ohio, and a team formed by a collaboration between the Institute of Cosmology and Gravitation, Portsmouth, and the University of Catania, Italy, the new research aims to amalgamate a range of physical theoretical information to provide new insights into the nature of gravity and its effects on all of the objects in the universe.

The pair of new codes are also claimed to be the first to use the complete general theory of relativity to help explain why there is a clumping of matter in some areas of space, while there is a distinct dearth of matter in others.

Einstein's theory, despite being over 100 years old, is still the foremost and best theory of gravity that we have. However, despite reliably predicting a range of cosmological phenomena, including the groundbreaking proof of the existence of gravity waves, the general theory of relativity equations involved are so complex that, until now, physicists have had to use simplified versions of the theory when looking at the mechanisms at play in the entire universe.

The new codes, embedded in a new mathematical tool developed by the researchers and dubbed "Cosmograph" are said to be able to work with the complexities inherent in Einstein's equations to provide much more nuanced and detailed modeling than has ever been achieved before.

New Earth-based telescopes, such as the Event Horizon Telescope, and space-based instruments, like the James Webb Space Telescope, will produce a plethora of data over the next decade from future galaxy surveys that will be more accurate than ever before.

"To match this precision we need theoretical predictions that are not only equally precise, but also accurate at the same level," says Dr Marco Bruni, of the Institute of Cosmology and Gravitation, Portsmouth University. "These new computer codes apply general relativity in full and aim precisely at this high level of accuracy, and in future they should become the benchmark for any work that makes simplifying assumptions."

Developed independently by both sets of physicists whilst attempting to solve problems around whether small, close-proximity structures in the cosmos created effects that influenced larger structures at greater distances, the new codes indicated that their hypotheses were accurate, but varied greatly from a purely averaged model usually created to visualize the space-time structure of the universe.

As a result, it is this difference that affords the new method the ability to go further than a standard, simple model to one of greater complexity and deeper understanding that the researchers say differentiates their codes and subsequent computer simulations by leveraging the full force of the complex equations found in general relativity.

"No one has modeled the full complexity of the problem before," says Professor Glenn Starkman, a member of the American team of researchers. "These papers are an important step forward, using the full machinery of general relativity to model the universe, without unwarranted assumptions of symmetry or smoothness. The universe doesn't make these assumptions, neither should we."

The researchers realize that a lot more work will be required going forward to completely understand the significance of the contrast between simulations based on Einstein's general relativity equations and models produced using the current method of simplified assumptions. But they also know that methods such as theirs will help add greatly to our understanding of the cosmos.

"In the end, as always in physics, it will be the interplay between theory and observations that will further our understanding of the universe," said Dr Bruni.

The results of this research have recently been published in the journal *Physical Review D.*

Source: University of Portsmouth