The Big Bang Theory is a cosmological model that explains the large-time scale evolution of the observable universe. The model explains how Universe evolved and expanded from an initial point with extremely high temperature and density to how we observe it today. The Universe expanded from this point of singularity where known laws of space and time break down and quantum interactions hold. This model is the most widely accepted as the model explaining the evolution of the Universe among Astrophysicists, Astronomers, and Mathematicians.

Big Bang Model offers a comprehensive explanation for a broad range of observed criteria in the Universe, like Cosmic Background Radiation, large-scale structure of the observable Universe, expansion of the Universe, and abundance of light elements i.e. Hydrogen and Helium. This theory is compatible with the Hubble’s Law- the phenomena that farther the galaxies- the faster they will be moving away from each other.

Space and Time were born at the time of big bang and therefore, known laws of physics came into existence at the time of Big Bang. Therefore, any event which may have occurred before the Big Bang would not affect any event of the modern Universe as time itself came after the Big Bang. Careful analysis of the expansion rate of the Universe and detailed measurements spot the Big Bang to have occurred at 13.8 billion years ago, which is thus accepted as the age of the Universe.

Features of the Model

The model depends on 2 major assumptions-

  1. The universality of physical laws = This assumption states that all parts of the Universe are subjected to the same laws of nature that we find here on Earth. This was the underlying assumption of General relativity.
  1. Cosmological Principle = This principle suggests that on large scales the Universe is homogeneous and isotropic.

These assumptions have been tested separately and results gathered from experiments have agreed with the theoretical results.

The first assumption was tested by calculating and analyzing observations of the Universe showing the largest possible deviation of the fine structure constant over the age of the Universe to be of the order of. 

Also, the large-scale structure of the Universe appears isotropic as viewed from Earth. If it is isotropic, then one can derive the cosmological principle from the simple Copernican principle, which states that there is no preferred observer or vantage point. The cosmological principle has therefore been calculated to an order of via observations of the temperature of the CMB. The Universe at the has been measured to be homogenous with an upper bound of the order of 10% inhomogeneity.

Written by-Sukhjit Singh

He is a student currently pursuing B.Sc. Mathematics honors from SGTB Khalsa College, Delhi University. He aims at developing multiple skills by taking up exciting projects and wants to be a professor in Mathematics.