Big Bang theory is a scientific explanation of the birth of the Universe. It’s more a topic of wonder than just being a topic of physics. Even on a calm dark night when we look up in the star studded sky and feel ultimate peace, least are we concerned that each and every particle of this Universe at that very moment is tremendously moving away from each other. Yes, in each passing moment, the Universe is expanding and we being parts of it are moving away from each other. This concept is what is known as the Big bang.
In 1929, Edwin Hubble discovered that the Universe is expanding at enormous speed and this has set science in revolution. The Big bang event is supposed to have occurred some 13.75 billion years ago. At that circumstance, he realized that there must have been an instant of time, when the Universe was just a point source of energy. The Universe was born in a single event called the BIG BANG! There has been a misconception about the Big bang, that it, it is thought to be an explosive event which is not true. Rather it is a violent ‘Expansion’.
Prior to the Big Bang, the concentrated Universe was supposed be dense and hot and had tremendous high temperature. As a result it started expanding obeying laws of physics and then after certain amount of expansion, the temperature becomes lower due to distribution of heat uniformly between the expanded mass. The sudden lowered temperature caused condensing of energies to form sub-atomic particles like protons, neutrons and electrons. As time went on the Universe cooled further and gave birth to neutrons, protons and combination of both to make deuterium which is an isotope of hydrogen. Thus the Universe much before the formation of starts and planets was filled with clouds of hydrogen plasma. It absorbs the thermal radiation of the universe.
Eventually the recombination was enhanced further when the temperature reached a point which influences these recombination processes and finally the recombination gave birth to electrically neutral atoms. No sooner did neutral atoms were formed, than the Universe became transparent. This is because the free charged electrons scattered light energy, absorbed thermal radiation and the Universe appeared opaque. So after the universe became transparent, the photons that were scattered by the free charged electrons now can travel freely. This phenomenon is called photon decoupling. The photon decoupling left an afterglow post occurrence of Big Bang is known as the Cosmic Background radiation.
Today this expansion of Universe, various measurements and metrics on the topic concerned are carried on using the NASA spacecraft such as the Hubble Space Telescope and the Spitzer Space Telescope. During the Big Bang, there occurred a burst of expansion which is scientifically termed as inflation. When this inflation took place, the universe filled up with various unknown unstable energy whose nature is still not known. The primordial energy is supposed to be a result of the quantum noise which was evident when the universe was dense and concentrated.
A lot of advanced revolutionary observations have been achieved regarding the Big Bang Theory but the primary questions remain unanswered. How long will this expansion of Universe continue? Will it expand forever or stop with a Big Crunch. What is it that caused this Big Bang and Big Crunch (If it happens)? Will the source of thrust be ever revealed?