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

pic 1
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.

Advertisements

Will the discovery of Gravitational waves ever help us detect the ripples of Big Bang?

 

pic 3

Detecting ripples in a space-time was not an easy task, after-all it took 50 years of trial and error, and 25 years perfecting a set of instruments so sensitive that could finally show a distortion in space-time millions of light years away. The discovery of gravitational waves have stirred the whole world of astronomy and have posed all sort of fascinating questions for astronomers regarding binary black-hole systems. Perhaps in a way it has opened a new field of gravitational physics which will revolutionize our understanding of the universe during its infancy.

The game has just started and now that we know how to measure gravitational waves, experiments like LIGO can be further enhanced to have a broader view of events happening in and around the cosmos that we have never been able to see before, such as mergers of super-massive black holes in the early universe. But the utmost question is that how far back can we really go? What about the gravitational waves that occurred moments after the big bang, will LIGO’s discovery help us catch those?

Let us take a step back in time, we are now in an era where the masses involved in the events are large by stellar standards, they are dwarfed by the super-massive black holes that scientists believe are present at the center of almost every galaxy. Our very own galaxy, the Milky Way, hosts a hole of about 4 million sun masses, detected through the motions of stars orbiting it.

There are yet a lot to discover about these super-massive black holes. We presently understand them through the immense amounts of electromagnetic radiation, like visible light and X-rays, produced by gas cascades into them. We know the likeliness of the process of formation of black holes, where some gasses are too slow and near and others are too fast and away for the black holes to capture it. So, the intriguing questions are that how could they get so big?

The answer could be that collisions between these super-massive holes helped to grow them, particularly when they were comparatively young and had not yet gained much gas. However, a collision between two super-massive black holes can probably only happen if the two galaxies hosting them collide and merge too. But these event is impossible to happen in the current time as because galaxies are far away from each other. But what if we go back in time, a time when the universe was much younger and the galaxies were very nearer to each other.

So detecting gravitational waves from such collisions means going back in time and analyzing the most distant galaxies giving us direct traces about how important these events were in growing super-massive black holes early in their lives and in turn unraveling the truth of mystery about the universe.

pic 2

But the collision of super-massive black-holes is not the end. The Big Bang, and particularly the eon of very rapid expansion dubbed inflation with enormous masses moving with almost light speed producing powerful gravitational waves are the goal we are looking forward to achieve. However, the most powerful signal comes from masses whose size is comparable to the scale of the universe itself. Since gravitational radiation has a typical wavelength larger than the masses emitting it, the “wavelength” of this radiation is itself similar to the entire size of the universe. So LIGO, or any other experiment that is smaller than the universe, will not be able to detect it.

The challenge is extremely difficult but a positive result could give evidence for the popular inflation theory, and offer explanations for several baffling features of the universe, such as why the distribution of matter is so standardized. Although finding such a signal is a colossal challenge, so was the direct detection of gravitational waves when first proposed half a century ago.

Can discovery of Gravitational waves unravel the mystery of quantum gravity?

With the discovery of gravitational waves, ripples in the fabric of space-time, scientists have finally been able to provide convincing evidence for the existence of black holes and confirming an enigmatic part of Einstein’s theory of relativity. The discovery is one of the most important climaxes of the century and may finally provide the fundamental understanding of the formation of the Universe.

pic 1

This article will not be related to gravitational waves fully, but will cover up another most important theory that has been the target of decades of study by physicists worldwide. If this idea is established, then the General Theory of Relativity can be combined with quantum mechanics eventually revolutionizing the field of subatomic particles.

Quantum gravity is a field of theoretical physics that deals with the force of gravity rendering to the principles of quantum mechanics, and where quantum effects cannot be ignored. Subatomic particles have different characteristics and some of them are quantized meaning they can only move or exist in particular whole number states. Many physicists believe gravitational waves are similarly quantized and are made up of individual quantum particles of gravity known as gravitons.

While there is no concrete proof of the existence of gravitons, quantized theories of matter may necessitate their existence. Some physicists believe that gravitons join together, forming gravitational waves that travel through space in the form of ripples. Like photons of light, gravitons are also considered massless and move at the speed of light.

In the center of black holes, effects of quantum gravity are predicted to be quite definite, however it is impossible to accumulate data from the events happening near a singularity. The scientists form LIGO (Laser Interferometer Gravitational Wave Observatory) used a set of instruments which was very sensitive, yet they could only identify a distortion in space-time, which is a thousandth the diameter of one atomic nucleus across a 4 km strip of laser-beam and mirror.

pic 2
LIGO Gravitational wave detected on Feb 11,2016

It is impossible for the LIGO detector or any advanced gravitational wave detector to detect a graviton in the space-time, leave alone proving the theory of relativity. But maybe in future a device so precisely modified is build, that it could finally detect the evidence of quantum gravity by examining the emission spectrum of energy surrounding the event horizons of black holes.

With LIGO , the astronomers have so far detected intangible ripples in space-time which is only the beginning of a new kind of physics. Further into the advancement of astronomical devices, they may come across other evidence of astrophysical theories such as cosmic strings, theoretical one-dimensional strings of energy, which may be there in the depth of space-time since the very beginning.

pic 3

The recorded data of the gravitational waves may also give the physicists to analyze the ripples in order to finally examine some evidence of gravitons which will eventually solve the mysterious puzzle of relativity theory. If the existence of gravitons is established, it could change the way of understanding gravity. Such a finding could suggest that other notions of gravity, such as string theory, could prove to be the basis of future work on the nature of gravity.

But until that time comes, the existence of gravitons are strictly theoretical.