Quantum Mechanics is simply a group of theories that offer math models explaining how physical phenomena works at microscopic size or atomic and subatomic levels. There are many theories that explain how the universe exists via quantum mechanics, from the original cloud atoms to the alternate realities existing all at the same time proposition. And there are math models that define all of these theories too. From 30 years ago, atoms no longer spin around an orbital. They are a micro cloud of everything and everywhere giving solid and more to our universe.