Have you ever thought about the origin of universe? How did everything happen? Why are we in the way we are? And the things, why are they in the way they are?

From the dawn of human history, these are the major things about which our ancestors as well as we have been thinking about. The steady model which used to be widely accepted suggests the existence of eternal universe without beginning. The aroma of curiosity has travelled from the evolution of human being to the present through gene. From the large number of models of universe, “Big Bang” has the highest number of evidences. Big bang is a theory that highlights the origin of universe from a single point, smaller than atom around 14 billion years ago. The cosmos before big bang exists outside our past light cone which is why it’s not a matter of our concern. As famous astrophysicist as well as author Carl Sagan says, “Somewhere, something incredible is waiting to be known”, universe that originated after the big bang, in which we are residing is desperate to get explored.

Expanding Universe and the notion of big bang

With the advent of Newton’s universal law of gravitation, the belief of static universe had to be discarded but the strong belief of people in the static universe didn’t make it do so.Einstein modified his theory of relativity to support static universe but  Alexander Friedmann, didn’t see it possible for universe to be static. Friedmann had predicted that the speed at which the galaxies are moving apart from us is directly proportional to the distance from us.

Edwin Hubble in 1929 A.D discovered the Hubble’s law by the analysis of red shifted light. He found that the speed of recession of a galaxy is proportional to its distance from us. Hubble’s law was exactly in favor of Friedmann’s prediction who had predicted the universe to be expanding. With the Hubble’s law, revolution was experienced by astronomy. The big bang model of the universe was accepted and the steady theory had to end.

Cosmic Microwave Background Radiation

Big bang was a flash of radiation. After the origin of universe from big bang, it was immensely hot, dense and dark. The plasma from big bang was a black body and absorbed as well as emitted the radiation. The density of the plasma didn’t allow the escaping of the light energy from big bang. As the universe, started to expand, it cooled. The wavelength of the light increased owing to the expansion of universe being the microwave radiation. This radiation was accidentally trapped by two communication engineers Arno Penzias and Robert Wilson in 1965. COBE launched in 1990s proved the CMBR to be uniform. WIMP with one of the most complex path to space gave us the variation of density of matter in universe for formation of stars and galaxies. Planck, is the latest mission for the further analysis of CMBR.The three pictures below show the universe after 38,000 years of big bang in CMBR from COBE, WIMP and Planck respectively.



Different events after big bang are responsible for the formation of present universe in the way it is. The major events that took place after big bang is summarized below:

  1. Initial expansion of the universe initiated 14 billion years ago from a singularity.
  2. The temperature of the universe was about 1032K, at T=10-43s and the average energy per particle was about 1019 GeV. All the laws of physics were made possible at that moment of time.
  3. Temperature decreased at T=10-35 to 1027 K and average energy to about 1o14 GeV.The universe had undergone a tremendously rapid inflation increasing the size by a factor of about 1030.
  4. At t=10-32s the universe was a mixture of quarks, leptons and meditating bosons.
  5. At t=-6s the temperature was about 1013K and typical energies were 1GeV. At this time quarks began to bind together to form nucleons and anti-nucleons. Also, there were still enough photons of sufficient energy to produce nucleon-anti nucleon pairs to balance the process of nucleon anti nucleon annihilation.

6.At t=1 min the universe had cooled enough so that the protons and neutrons in colliding, can stick together to form the low mass nuclei H2,He3,He4 and Li7 the predicted relative abundance of these nuclides are just what we observe in the universe today.

  1. At t=300,000 years, the temperature had fallen to about 104K and electrons can stick to bare nucleus when they collide forming atoms. Atoms of H and He under the influence of gravity begin to clump together, starting the formation of stars and galaxies. Early supernovas spewed out the various elements heavier than helium that later became incorporated in other stars and in their satellite planets. Living things developed on at least one of these planets and quite possible on a great many others as well, which brings us to present.




Author : Shilpa Bhandari is a high school graduate from Pentagon International College,Kathmandu.She loves science and believes in power of Science communication . She is passionate about astronomy and Physics as a whole. She has also been blogging since 2014. Follow her on twitter : @77parasian