Big Bang Model

Basics

The Big Bang Model is the prevailing cosmological model that explains the origins and development of the universe.
It posits that the universe began from an extremely hot and dense state, approximately 14 billion years ago, and has been expanding ever since.
The term “Big Bang” was actually coined by British astronomer Fred Hoyle, and it was initially intended to mock the concept.

The universe started from a singularity, a point of infinite density and temperature.
In the very early stages, it is believed that four fundamental forces - gravity, electromagnetism, and the weak and strong nuclear forces - were unified. As the universe expanded and cooled, these forces separated.
A few minutes after the Big Bang, it is believed that protons and neutrons started to form atomic nuclei in a process called primordial nucleosynthesis. This lead to the creation of light elements such as hydrogen and helium.
Approximately 380,000 years later, electrons combined with these nuclei to form atoms, in an era known as recombination. This allowed light to travel throughout the universe, marking the start of the Cosmic Microwave Background (CMB) radiation.
The period following recombination was dark, with no stars or galaxies; it is thus called the “Dark Ages”. It ended when the first stars began to form.

Hubble’s Law: The observation by Edwin Hubble that galaxies are moving away from us in every direction. This notion supports the idea that the universe is expanding.
Cosmic Microwave Background (CMB) Radiation: The afterglow of the Big Bang. It was discovered unexpectedly by two American radio-astronomers, Arno Penzias and Robert W. Wilson, in 1965.
Abundance of Light Elements: Hydrogen and Helium are the two most abundant elements in the universe, consistent with predictions from the Big Bang Theory.

The Big Bang Theory cannot explain what triggered the initial expansion of the universe or what occurred before the Big Bang.
There are some unresolved issues in the theory, such as the “Horizon problem” and the “Flatness problem”.
The Big Bang Theory predicts the existence of dark matter and dark energy, mysterious substances that we have not yet detected directly.