ORIGIN OF UNIVERSE
The origin of the universe dates back to around 15 billion years. Our universe originated as a dense cloud of gas that expanded rapidly outwards. It was made up of a hydrogen and a small amount of helium. In the beginning, the stars and the planets were absent. The first stars came into existence when the universe was around 100 million years old. The universe was created during a cosmic explosion called the big bang that occurred between 10 to 20 billion years ago. Before the big bang, all matter that exists in the present day universe was condensed into a tiny area. After the explosion, the matter scattered as dust, cloud, or, mist all around.
Big bang theory of origin of universe
•In 1927, Georges Lemaitre, a Belgian mathematician and catholic priest, first proposed that the universe had originated from the Big Bang explosion. In 1929, Edwin Hubble was the first to observe that the Universe was continuously expanding. The observation provided the foundation for the Big Bang Theory. Recent calculations prove that the primary products of the Big Bang were hydrogen and helium. Later, the heavier elements were produced within the stars
General theory of relativity
•The General Theory of Relativity was proposed by Albert Einstein in 1916. In this Einstein included the effect of gravitation on the shape of space and the flow of time. The theory states that gravity pulling in one direction is equivalent to acceleration in the opposite direction, and both are equivalent to curvature of space. •
•The Steady-State Theory is an alternative theory about the origin of the universe . This theory fills the gaps left in the Big Bang Theory. Fred Hoyle, Hermann Bondi, and Thomas Gold proposed the Steady-State Theory in 1948. The theory states that matter is being created continuously at the rate of hundreds of atoms per year. It also states that although the universe is expanding, its appearance and the density does not change with the passage of time.
•The Pulsating Theory states that the universe is pulsating or expanding and contracting alternately. According to this theory, the current expansion of the universe will stop at a certain point of time by gravitational pull if the total mass of the universe is more than a certain value. Once the expansion stops, it will start contracting again. After contraction to certain size, an explosion will occur and the universe will start expanding again. This alternating expansion and contraction makes the pulsating universe.
•The Inflation Theory was propounded by Alan Guth , Andrei Linde , Paul Steinhardt , and Andy Albrecht. It states that during the formation of the universe, there was a period when the universe expanded very fast leading to the Big Bang. During this period, the energy density of the universe was dominated by a cosmological constant term that later decayed and produced all the matter and radiation present in the universe today.