Universe

Evolution of Universe

Some 15 billion years ago the universe emerged from a hot, dense sea of matter and energy. As the cosmos expanded and cooled, it spawned galaxies, stars, planets and life.

Introduction:

The physical universe is defined as all of space and time (collectively referred to as spacetime) and their contents. Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.The universe also includes the physical laws that influence energy and matter, such as conservation laws, classical mechanics, and relativity. While the spatial size of the entire universe is unknown, it is possible to measure the size of the observable universe, which is currently estimated to be 93 billion light-years in diameter.

There are several theories explaining the origin of the universe. But we will be discussing about the three major theories put forward by the scientists:

1. Big Bang Theory

2. Steady State Theory

3. Pulsating Theory

 

Big Bang Theory:

The Big Bang can also refer to the birth of the observable universe itself — the moment something changed, kick-starting the events that led to today. For most of human history, observers of the sky assumed it eternal and unchanging.

Georges Lemaitre first suggested the big bang theory in the 1920s, when he theorised that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble's observations that galaxies are speeding away from us in all directions.

The above picture represents the bright blue Earth looms over a star field that contains the oldest known planet in the Milky Way. The ancient planet is thought to be about 13 billion years old, a mere billion years younger than the estimated age of the universe. Its discovery, made using the Hubble Space Telescope, is evidence that planets began forming relatively soon after the big bang. 

Explanation of Big Bang : 

The best-supported theory of our universe's origin centers on an event known as the big bang. This theory was born of the observations of galaxies are moving away from our own at great speed in all directions, as if they had all been propelled by an ancient explosive force.

In the first 10^(-43) seconds of its existence, the universe was very compact, less than a million billion billionth the size of a single atom. It's thought that at such an incomprehensibly dense, energetic state, the four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—were forged into a single force. 

The major events that occurred in the universe is explained below pictorially:

 

Note : The other two theories are currently beyond our understanding at this point.