Journey through Big Bang

From my friends I got to know that while reading Big Bang theory they mix up different stages of Big Bang and end up knowing many things without proper sequence and understanding. To ease understanding I divided the theory in different stages with timeline.

The prevailing model for the evolution of the Universe is the Big Bang theory. It is considered to be "birth" of universe. The Big Bang model states that the earliest state of the Universe was extremely hot and dense and that it subsequently expanded. The Big Bang model accounts for observations such as the correlation of distance and redshift of galaxies, the ratio of the number of hydrogen to helium atoms, and the microwave radiation background.

TIMELINE of universe

Why big bang?

In 1929, from analysis of galactic redshifts, Edwin Hubble concluded that galaxies are drifting apart, important observational evidence consistent with the hypothesis of an expanding universe. In 1965, the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang model.

The beginning  (0 to 10 seconds)

·         PLANCK EPOCH : The universe begin from the initial hot, dense state is called the Planck epoch, a brief period extending from time zero to one Planck time unit of approximately 10^-43 seconds. During the Planck epoch, all types of matter and all types of energy were concentrated into a dense state, where gravitation is believed to have been as strong as the other fundamental forces, and all the forces may have been unified.

·         INFLATION  : Since the Planck epoch, the Universe has been expanding to its present form, possibly with a very brief period of cosmic inflation which caused the Universe to reach a much larger size in less than 10^-32 seconds.

·         quark, hadron, and lepton EPOCHS: After the Planck epoch and inflation came the quark, hadron, and lepton epochs. Together, these epochs encompassed less than 10 seconds of time following the Big Bang

Big Bang nucleosynthesis ( 10 sec to 20 min )

 As the Universe expanded and cooled, elementary particles existed in combinations. Thus, in the early part of the matter-dominated era, stable protons and neutrons formed, which then formed atomic nuclei through nuclear reactions. This process, known as Big Bang nucleosynthesis, led to the present abundances of lighter nuclei, particularly hydrogen, deuterium, and helium. Big Bang nucleosynthesis ended about 20 minutes after the Big Bang, when the Universe had cooled enough so that nuclear fusion could no longer occur.

Photon epoch (20 min to 380,000 years )

At this stage, matter in the Universe was mainly a hot, dense plasma of negatively charged electrons, neutral neutrinos and positive nuclei. This era, called the photon epoch, lasted about 380 thousand years.

Recombination ( 0.38 to 100 million years  )

Eventually, at a time known as recombination, electrons and nuclei formed stable atoms, which are transparent to most wavelengths of radiation. With photons decoupled from matter, the Universe entered the matter-dominated era. Light from this era could now travel freely, and it can still be seen in the Universe as the cosmic microwave background (CMB).

Formation of Star ( 0.1 to 9.8 billion years  )

After around 100 million years, the first stars formed; these were likely very massive, luminous, and responsible for the reionization of the Universe. Having no elements heavier than lithium, these stars also produced the first heavy elements through stellar nucleosynthesis. The Universe also contains a mysterious energy called dark energy; the energy density of dark energy does not change over time.

Dark-energy-dominated era (9.8 billion to today)

After about 9.8 billion years, the Universe had expanded sufficiently so that the density of matter was less than the density of dark energy, marking the beginning of the present dark-energy-dominated era. In this era, the expansion of the Universe is accelerating due to dark energy.

In Short……

The Big Bang theory is the prevailing cosmological model describing the development of the Universe. Space and time were created in the Big Bang, and these were imbued with a fixed amount of energy and matter .As space expands, the density of that matter and energy decreases. After the initial expansion, the Universe cooled sufficiently to allow the formation first of subatomic particles and later of simple atoms. Giant clouds of these primordial elements later coalesced through gravity to form stars.