The Big Bang

It is always a mystery about how the universe began, whether if and when it will end. Astronomers construct hypotheses called cosmological models that try to find the answer. There are two types of models: Big Bang and Steady State. However, through many observational evidences, the Big Bang theory can best explain the creation of the universe.
The Big Bang model postulates that about 15 to 20 billion years ago, the universe violently exploded into being, in an event called the Big Bang. Before the Big Bang, all of the matter and radiation of our present universe were packed together in the primeval fireball -- an extremely hot dense state from which the universe rapidly expanded. The Big Bang was the start of time and space. The matter and radiation of that early stage rapidly expanded and cooled. Several million years later, it condensed into galaxies. The universe has continued to expand, and the galaxies have continued moving away from each other ever since.…