• Ashwini

GS3: The Big Bang

Updated: May 13, 2020

The Big Bang theory is a cosmological model of the present universe which describes the present state of our galaxy from its earliest known periods through its subsequent large-scale evolution. This model corroborated the expansion of the Universe from an initial state of very high density and high temperature, along with the possible explanation for different phenomenon observed such as the abundance of light elements, the cosmic microwave background (CMB) radiation and, the famous, Hubble’s law- the farther the galaxy is, the faster they are moving away from the Earth. When the observed conditions are extrapolated backwards in time using the known laws of physics, we reach the stage of singularity before a period of very high density.

When the extrapolated data are matched with the expansion rate of the universe, the Big Bang happened around 13.7 billion years ago, which is considered to be the age of the universe. According to this theory, all matter and energy- everything that now constitutes the Universe- was initially packed into an infinitesimally small point. The point exploded and the Universe began.

Of course, this is hard to believe, as nobody was there to present the testimony. However, with the help of the clever calculation of the noted observation the conclusion was made. During the first instant of existence, the Universe was so small, so dense, and so hot that it consisted entirely of energy. Within a few seconds, hydrogen atoms begin to form. Within 3 minutes, temperature had fallen below 1 billion degrees, and its diameter had grown to about 53 million km, hydrogen atoms coalesced to form helium atoms. Formation of new nuclei in the first few of time is called Big Bang nucleosynthesis (this happened before the existence of any star). New nuclei, which formed, constituted few protons and led to the genesis of element up to atomic number 5. In fact, all observations pointed that all the new atomic nuclei formed by Big Bang nucleosynthesis existed by the end of the first 5 minutes.

Eventually, the Universe became cool and chemical bonds began to bind atoms of certain elements together in molecules. With the further expansion of the Universe, it began cooling, atoms and molecules slowed down and accumulated into patchy clouds called nebulae. The earliest nebulae of the universe consisted almost entirely of hydrogen (74% by volume) and helium (24% by volume) gas.

Wondering, how then our planets came into existence? Stars? Moons? Check out the next part of this article. Till then, if you haven't checked our featured posts of Cosmology yet, click on the links below:

GS1: The Universe

GS2: The Milky Way


Essentials of Geology: Stephen Marshak

Principle of Physical Geology: Arthur Holmes

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