Original: According to the prevailing scientific model of the universe, known as the Big Bang, the universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable universe was concentrated.
Simplified: The most used scientific model of the Universe is known as the Big Bang theory. The Universe expanded from a very hot, dense phase called the Planck epoch, in which all the matter and energy of the Universe was concentrated.