Sometimes the simplest questions are the deepest but hardest to answer.
Questions like:
How did the universe begin?
Is there a god who created and controls the universe?
If yes, then who created god?
If Big Bang really happened, What caused it to happen?
This is a brief explanation of How an immense universe can come out of nothing and I personally do believe in Big Bang Theory and don't want to discuss the second question.
About the origin of the universe, the big bang Theory states that our Universe Spontaneously Came Out of Nothing. In a fraction of a second, an explosion occurred about 14 billion years ago due to quantum fluctuations in unstable vacuum or Metastable false vacuum.
Unstable state is something incomplete and "NOTHING" itself is unstable. Spontaneous formation of universe needs two constituents or parts of "nothing" which are positive energy and negative energy and It's not a difficult idea to grasp that something negative and something positive sums up to zero (nothing) which means the net energy of whole universe is zero. In this way, it does not contradict with the Law of Conservation of Energy and a universe can actually come out of nothing.
The Positive energy is in the form of ordinary matter, light and anti-matter and Negative energy is in space. Negative energy is stored in the gravitational attraction that exists between all the positive-energy particles. The positive exactly balances the negative, so, ultimately, there is no energy in the universe at all.
Well the Big bang Theory is not just an idea but a theory with much evidence. Expanding universe and After Glow of Big bang that is presence of microwaves even here on earth are the main evidence of Big Bang.
