Simulation done on Einstein’s general theory of relativity may lead to answer why universe expands?

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The gravitational waves generated during the formation of structures in the universe is shown. The structures (distribution of masses) are shown as bright dots, gravitational waves by ellipses. the sizes of the ellipse is proportional to the amplitude of the wave and its orientation represents its polarization.

‘Universe is constantly expanding’, a statement that I hope all the astrophysicists and the cosmologists are familiar with. But the fascinating question lies in how does our universe evolve? We know that Universe merges everything that comes its way, but the topic of ‘evolution of universe’ is still a very enigmatic point in the vast field of cosmology.

But, with the discovery of Gravitational waves, all new kinds of coded simulation is going on in order to fully understand the formation of structures of the Universe. One such success is recently achieved by the physicists from the University of Geneva, where based on Einstein’s equations, they integrated the space-time rotation into their calculations and calculate the amplitude of gravitational waves, thus providing a new code of numerical simulation that offers a glimpse of the complex process of the formation of structures in the Universe.

Before the discovery of the gravitational waves, physicists studied the
formation of large-scale cosmological structures based on Newtonian gravitation. The principal of these codes hypothesizes that space itself does not change, it is said to be motionless, while time goes on. Thus, the Newtonian-based codes were applicable when the matter of the particles was moving very slowly (say about 300km per second).
However, the code failed to show accurate calculations when the speed of the matters was quite high. Moreover, the Newtonian numerical simulation does not describe dark energy’s fluctuations. Constituting 70% of the total energy of the Universe, it does not doubt that dark energy is responsible for the accelerated expansion of the Universe. Therefore, it was essential to find a new way to simulate the establishment of cosmological structures and sanction the study of these two phenomena.

Thus, Physicists from the University of Geneva successfully generated a code, named evolution and simulated the numerical codes based on Einstein’s theory of relativity. Unlike the Newtonian theory, the theory of relativity suggests that space and time are constantly changing. The most important advantage of this simulation is that now scientists can accurately calculate the fast-moving particles in space. The aim was to forecast the amplitude and the impact of gravitational waves and space-time’s rotation induced by the formation of cosmological structures.

To generate the code, the physicists analyzed a cubic part in space, consisting of 60 billion zones with each containing a particle. Thorough analyzing of particles was done with respect to their neighbors using an LATfield2 library which solves nonlinear partial differential equations. A supercomputer was also used to detect the motion of particles and calculate the metric (the measure of distances and time between two galaxies in the Universe) using Einstein’s equations. The calculations were then analyzed and compared to the Newtonian’s numerical simulation results. Finally, the effect of frame-dragging (the rotation of space-time) and gravitational waves was introduced by the formation of structure in the Universe.

It is the first time that frame-dragging and gravitational waves were being included in a numerical cosmological simulation. This operation opened a new way of testing the general theory of relativity as well as unlocking the mysteries behind Universe’s expansion.

NOTE: The above picture is copyrighted by Mr.Ruth Durrer of UNIGE.

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