One of the most asked questions has always been: How was the universe created? Many once believed that the universe had no beginning or end and was truly infinite. With the advent of the Big Bang theory, however , no longer could the universe be confidently considered infinite. The universe was forced to take on the properties of a finite phenomenon, possessing a history and a beginning. However, over the decades, there have been multiple interpretations of the Big Bang. In the standard interpretation of the Big Bang, which took shape in the 1960s, the formative event was not an explosion that occurred at some point in space and time — it was an explosion of space and time. In this view, time did not exist beforehand. Even for many researchers in the field, this was a bitter pill to swallow. It is hard to imagine time just starting: How does a universe decide when it is time to pop into existence?
In 2004 Sean Carroll and a graduate student of his, Jennifer Chen, came up with a much different answer to the problem of "before." In his view time's arrow, or time`s flow in only one direction, and time's beginning cannot be treated separately and are in fact cyclical: There is no way to address what came before the Big Bang until we understand why the before precedes the after. “Our universe has been evolving for 13 billion years,” Carroll says, “so it clearly did not start in equilibrium.” Rather, all the matter, energy, space, and even time in the universe must have started in a state of extraordinarily low entropy. That is the only way we could begin with a Big Bang and end up with the wonderfully diverse cosmos of today. Understand how that happened, Carroll argues, and you will understand the bigger process that brought our universe into being. In Carroll and Chen's theory, fluctuations in the dark-energy background trigger a crop of pocket universes from empty space which eventually go back to becoming empty spaces.
Yet another theory is put forth by rebel physicist Julian Barbour. According to Barbour in his 1999 book "The End of All Time," all possible configurations of the universe, every possible location of every atom, exist simultaneously. There is no past moment that flows into a future moment; the question of what came before the Big Bang never arises because Barbour's cosmology has no time. The Big Bang is not an event in the distant past; it is just one special place in a vast universe.