Cosmic evolution

By Jayesh Giri

Our understanding of space has always been confined to an endless and infinite perspective whose termination is beyond our imaginations. The hypothetical view of it is also more or less the same. But let us imagine for a while that, like the creation and destruction each and every particle in this living "multiverse" (i.e. a combined form of all the other universes including ours), our universe also had a creation and it might undergo destruction in the near future.

Commonly we know cosmos as the endless and inestimable space but in general terms, cosmos is known as the universe with its multidimensions. Each and every dimension of the universe is the constituent of the cosmos. It seems odd that there existed no dimensions in this vast region of outer space before the creation of this universe. Time, which we regard as the fourth dimension of space was not even created.

Everything existed in absolute motion only. Now what we see is the universe, which is vast and much too versatile to read all its constituents. Who would have ever imagined that our universe was the size of a quark, which later on took the form of a super-atom? The quantum-string theory says it all. This super atom later on took the form of energy. Time was still not created viz. any forms of matter was not created yet. Slowly and progressively this single compact super atom changed into the super ball of energy. The intensity of the energy was concentrated into a closed spherical structure. This spherical configuration was nothing more than a highly compressed and resolute form of matter. This form of matter was so dense that a constant pressure of its own gravitational pull was experienced by the outer surface of the matter. After the matter reached its full repression, a huge explosion, which we know as, the "big bang" occurred some 20 billion years ago.

This outburst was worth the energy acquired by setting off a trillion atomic bombs which was enough to drive each and every matter of the universe spaced out even till now. Most of the cosmologists believe that our universe had been created five minutes after the big bang. The universe at this position was based upon three fundamental constants i.e. the speed of light, the universal constant of gravity and plank’s constant. This meant that time was one of the peculiar things to be created and its existence bought about many fundamental changes in the structure of the universe. New dimensions were created and the cosmic dust combined to form galaxies and clusters of stars inside them.

Before the moderation of the Big bang theory, many other theories dominated the fruition of our present universe. One of such theories was the ‘steady state theory’, which says that our universe never had a beginning and would never have an end. The universe was expanding and matter in the form of hydrogen was being continuously created out of nowhere to balance the density of matter in the universe. Since this theory failed to explain the phenomenon of the background radiation of the universe, it lost its favour to the big bang theory. The same was not the cause with the oscillating universe theory, which stated that universe in fact was expanding and at a certain point would cease its expansion and ultimately result in a retrenchment. It would then form a dense composition again and result in a huge outburst of matter and energy compiling another universe and the whole process would start all over again oscillating the universe again and again. Although these theories about the origin of the universe convey totally different ideas, they have one thing in common i.e. the expansion of the universe. In 1911 Edwin Hubble estimated that the universe was expanding and the velocity of recession of the galaxy directly was directly proportional to its red shift i.e.

V = H0r. Where H0 is Hubble’s constant and r is the red shift of the galaxy.

The value of H0 as proposed by Hubble is 20 km/sec per million light-years. Thus we come to the conclusion that the universe is expanding. The above theories are characteristically based upon this notion. Distant galactic structure as observed by the Hubble space Telescope. Our present universe came into being five minutes after the big bang, as we know it. How did the stars and the galaxies come into existence? As the big bang occurred the energy was blown out with tremendous dynamism. All the energy that was produced settled into the space in the form of cosmic dust, which we call the inter-galactic gases within a galaxy. The intricacy of the recently formed universe was diverse. The preliminary clouds within the galaxy contracted as a result of the pull towards the center of gravitation forming a protostar. The beginning of the conversion of hydrogen into helium in a protostar marks it as a genuine star; it is no longer a protostar.

A galaxy is not only constituted of stars, but also nebulae, planets and black holes. Some of the gas and dust within the galaxy still linger in the form of nebulae. Glowing accumulations of such gases have a very weak gravitational field; consequently they do not combine to form stars.

The death of the stars present in the universe brings about the formation of many unsuspected objects such as the neutron stars and the black holes. When the hydrogen present in the star completely burns into helium, the temperature of the star drops and it is no longer capable of counterbalancing the inward pull of its own gravity. Now the temperature of the star starts to increase due to the contraction of the helium core inside the star and it may reach up to 100000000 K. The helium nuclei start fusing together to form carbon atoms through the triple- alpha process and even other heavier metals. But a star of a relatively low mass soon runs out of helium and collapses into a white dwarf. When all the helium is consumed the cataclysmic collapse of the whole massive structure in the form of a supernova occurs. Such explosions can be equivalent up to the outburst of a trillion atomic c bombs. The core of the star is still filled with heavier elements like iron.

They start breaking into helium nuclei. The pressure is no longer enough to counteract the force of gravity hence the core collapses. The protons and the electrons collide with each other to form neutrons and neutrinos. The neutrinos (dark matter) escape where as the neutrons is squeezed into the center of the core as a result of its own gravitational pulls. Finally a stage known as the neutron degeneracy reaches where the neutrons cannot be packed more tightly. Now a neutron star is said to be formed. Einstein in his general theory of relativity predicted a region in outer space from where neither matter nor radiation can escape. If the matter left after a supernova explosion is very large then it collapses to a radius given by: - 2GM/c2.

Where G is the universal constant of gravity, M is the mass of the star and c is the speed of light. The gravitational field produced is so intense that it red shifts radiation as predicted by the general theory of relativity. As the mass contracts the radiation is continuously red shifted which is bent more and more. Eventually when the mass of the star is compressed up to a certain size the radiation from the star can no longer escape into the space. Hence a black hole is formed. Thus we can determine the ultimate faith of the universe. The universe may go on expanding as a result of the anti-gravity created by repulsive force of the dark matter. The stars present in the galaxies would get completely burned out. The galaxies would be so remote from each other that the cosmos would cease to exist as a unity.

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