Big Bang Theory
பெருவெடிப்பு கொள்கை
Do not confuse the origin of the universe with the origin of life. The Big Bang explains the physical universe, not abiogenesis. If you conflate these, you lose marks in the Evolution chapter.
The idea
The Big Bang theory attempts to explain the origin of the universe as a singular huge explosion unimaginable in physical terms. The universe expanded, temperature came down, and gases condensed under gravitation to form galaxies.
Why it matters
It provides a scientific framework for the origin of matter, space, and time, setting the stage for the formation of stars, planets, and eventually life.
NEET lens
The Big Bang theory posits a singular, massive explosion of unimaginable physical scale. As the universe expanded, temperatures dropped, allowing gases to condense under gravitational force. This process ultimately formed the galaxies. Remember: expansion led to cooling, which led to condensation.
Introduction
The Big Bang theory explains the origin of the universe as a single huge explosion, unimaginable in physical terms, about 20 billion years ago (as given in NCERT).
Core concept
After the Big Bang the universe expanded and the temperature came down. Hydrogen and helium formed sometime later. The gases condensed under gravitation and formed the galaxies of the present-day universe. In the solar system of the Milky Way galaxy, the Earth formed about 4.5 billion years ago. There was no atmosphere on early Earth; water vapour, methane, carbon dioxide and ammonia released from molten mass covered the surface. UV rays from the sun broke water into hydrogen and oxygen; the lighter H2 escaped. Oxygen combined with ammonia and methane to form water, CO2 and others; the ozone layer formed. As it cooled, water vapour fell as rain to fill depressions and form oceans. Life appeared about 500 million years after the formation of Earth, i.e. almost four billion years back.
Go deeper
These conditions — a reducing atmosphere with energy from lightning and UV — set the stage for chemical evolution and the origin of life.
From Class 10
The universe began with a massive explosion and has been expanding ever since; Earth formed much later as part of our solar system.