About one hundred seconds after the big bang, the temperature would have fallen to one thousand million degrees, temperature inside the hottest stars.Do you know ,at this decreased temperature protons and neutrons would no longer have sufficient energy to escape the attraction of the strong nuclear force between protons and neutrons ,it means proton and neutron no longer remain separately and would have started to combine together to produce the nuclei of deuterium atoms( heavy hydrogen atoms), which contain one proton and one neutron . The deuterium nuclei then would have combined with more protons and neutrons to make helium nuclei, which contain two protons and two neutrons, and also small amounts of a couple of heavier elements, lithium and beryllium. One can also calculate that in the hot big bang model of Stephen hawking ,about a quarter of the protons and neutrons would have been converted into helium nuclei, along with a small  amount of heavy hydrogen(deuterium) and other elements. The remaining neutrons would have decayed into protons a positively charged , which are the nuclei of the ordinary neutral hydrogen atoms.

                  After this transformation, within only a few hours of the big bang explosion , the production of helium and other elements would have stopped tremendously fast. And  for the next million years or so, the universe would have just continued expanding till today , without anything much happening. Eventually , once the temperature had dropped to a few thousand degrees from earlier hot temperature , and electrons and nuclei no longer had enough energy to overcome the electromagnetic force of attraction between them for independent existence, they would have started combining to form new first originated atoms. The universe as  a would have continued expanding and cooling process, but in regions that were slightly denser than average condition, the expansion would have been slowed down by the extra gravitational attraction.

                                                                      This would eventually started the collapsing of matter by stopping the expansion in some region. During the collapsing of the matter, the matter outside these collapsing region would get the slanting pulling inwards resulting to the slight rotating of the particles. As the collapsing region got smaller and smaller, the spinning of matter got faster and faster like the tooth paste gel scattering on the surface of water. Thus in certain limit of the rotation of matters, the rotating force would have balance the gravitational force and would give birth to a disc like structure present day  galaxies. Whereas other non rotating region of universe give rise to the oval like structure called as oval galaxies. The oval galaxies have no rotating centre and shows no movement. As continues process of formation of galaxies, the hydrogen and helium gas collapse from the clouded form. Due to the heavy collapsing of the atoms , the internal core temperature rises extremely high , eventually triggering the nuclear fusion reaction. The nuclear fusion reaction process is the process of glowing of sun and the number of star. Likewise numbers of star were born. The continue nuclear fusion reaction will convert lighter hydrogen atoms into heavier helium atoms and ultimately the sun or star would forms a black hole, or supernova , or the white dwarf, or neutron star. Some of the heavy element formed during the nuclear fusion reaction get flown in gas forms and would be the raw material to give rise to the next generation star . Our sun is second or third generation star and contain nearly 2 % heavier atom. The lesser collected matter in the space give rise to the smaller bodies which started to revolves around the sun which are called the planets and satellite. Initially our planet earth is very hot , without atmosphere a magma ball. Later on gradual decrease of temperature give rise to different gases which became the shield of the gases around the earth called the atmosphere. The early atmosphere have no any oxygen, rather than plenty of harmful poisonous gases like hydrogen sulfide. Later on further decrease of the temperature would bring number of gradual changes of the molecules and finally the water molecules form. Then the water molecules collected to forms ocean. till there is no sign of life and the organic molecules. Then the continues evolution brings changes in the molecular composition of the atmosphere. During heavy lightening and thunders, the inorganic molecule changes into organic molecules which collected together to forms Coacervate . Coacervate continue to develops the genetic behavior to form the unicellular living organism on the surface of ocean. Then the  unicellular organism evolved to a multi-cellular organism and then to complex aquatic animals. Then aquatic animals evolved into terrestrial,areal, arboreal, amphibians  animals and soon. Thus animals are mammals, reptile, fish, birds and ultimately the human being.

Although having lot of series of discoveries about the origin of the universe , still Stephen Hawking leave number of the unanswered question to conduct the new research for new generation scientist

1) Why was the early universe so extremely hot ?

2) Why is the universe so uniform on a large scale or infinite? Why does it look the same at all points of space and in all directions and faces? In particular , why is the temperature of the microwave background radiation so nearly the same or equal when we look in different directions? It is a bit like asking a number of students an exam question or the test paper. If they all give exactly the same answer , you can be pretty sure they have communication with each other as the social networking. Yet , in the model described above, there would not have been time since the big bang for light to get from one distant region to another region very far ,even though the regions were close together in the early universe during the early bigbang. According to the theory of relativity, if light cannot get from one region to another, no other information can also passes. So there would be no way in which different regions in the early universe could have come to have had the same temperature as each other, unless for some unexplained reason they happened to start out with the same temperature and the condition.

3) Why did the universe start out with so nearly the critical rate of expansion that separates models and  that recollapse or reunion  from those that go on expanding forever , so that even now present day , ten thousand million years later, it is still expanding and expanding  at nearly the critical rate? If the rate of expansion one second after the big bang had been smaller by even one part in a hundred thousand millions  million , the universe would have early recollapsed before it ever reached its present size.

4) Despite the fact that the universe is so uniform , infinite and homogeneous on a large scale , it contains local irregularities , such as stars, galaxies and other heavenly bodies. These are thought to have developed from small differences or variation in the density of the early universe from one region to another. What was the origin of these density fluctuations?


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