Universe

The Universe is all of spacetime and everything that exists therein, including all planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy.Encyclopaedia Britannica Wikipedia
he concept of Universe's shape, creation and working is under much conjecture and speculation and can never be fully researched in the lifetime of the mankind's existence.
==How big is the Universe?==
Throughout history, humans have used a variety of techniques and methods to help them answer the questions 'How far?' and 'How big?' Generations of explorers have looked deeper and deeper into the vast expanse of the universe. And the journey continues today, as new methods are used, and new discoveries are made. 
The size of the Universe is unknown; it may be infinite. The region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years, based on where the expansion of space has taken the most distant objects observed.
==Expanding Universe==
In the 1920s, Edwin Hubble used the 100" telescope (2.5 meters) at the Mount Wilson Observatory in California to detect variable stars in nebulae. He discovered that the stars he observed had the same characteristic variations in their brightness as a class of stars called Cepheid Variables. Earlier, astronomer Henrietta Levitt had shown there was a precise correlation between the periodic change in brightness of a Cepheid Variable and its luminosity. Hubble was able use this correlation to show that the nebulae containing the variable stars he observed were not within our own Galaxy; they were in external galaxies far beyond the edge of our Milky Way.
Hubble determined the distances to the galaxies and the velocities that they were moving at, relative to Earth. From this, he discovered an amazing thing: the farther galaxies were away from us, the faster they were moving away from us. In other words, the Universe was expanding.
==Age of Universe==
According to research, the universe is approximately 13.8 billion years old. Scientists can determine the age of the universe using two different methods: by studying the oldest objects within the universe and measuring how fast it is expanding. 
== References ==