UNIVERSE

Universe is the whole of all matter, energy, planets, galaxies and space. It is the totality of all the things that exist; creation; the cosmos. It is all space-time, matter, and energy, including the solar system, all stars and galaxies, and the contents of intergalactic space, regarded as a whole. It is from the Latin word "universum", the from neuter of universus, all together from unus, one + versus, last participle of vertere.

Theories of the Beginning of Universe

Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos today. This startling idea first appeared in scientific form in 1931 by Georges Lemaitre, a Belgian cosmologist and Catholic priest. He formulated the Big Bang and called it "hyphothesis of the primeval atom".

Steady State Theory is a view that the universe is always expanding but maintaining a constant average density, with matter being continuously created to form new stars and galaxies at the same rate that old ones become unobservable as a consequence of their increasing distance and velocity of recession. A steady-state universe has no beginning or end in time, and from any point within it the view on the grand scale-i.e., the average density and arrangement of galaxies - is the same. 

Cosmic Inflation Theory supports the Big Bang Theory. It is proposed by Alan Guth. It states that the early universe is a rapidly expanding bubble of pure energy. After the expansion and cooling a big bang occured, because of the extremely hot and dense condition of matter.












Source:

https://www.yourdictionary.com/universe
https://spiritsecret.com/root-of-the-universe/
https://www.space.com/25126-big-bang-theory.html
https://www.amnh.org/learn-teach/curriculum-collections/cosmic-horizons-book/georges-lemaitre-big-bang
https://www.britannica.com/science/steady-state-theory
https://www.thoughtco.com/steady-state-theory-2699310
https://www.universetoday.com/54756/what-is-the-big-bang-theory/
https://www.thoughtco.com/what-is-inflation-theory-2698852