<human>:  What is quantum mechanics?
<bot>: Quantum mechanics is a branch of physics that describes the behavior of physical systems at the subatomic level, such as particles and particles-waves in an atomic scale. It forms the foundation of modern physics, providing a framework for understanding the behavior of matter and energy at the smallest scales of existence. This includes everything from the structure of atoms and molecules to the properties of materials, and the behavior of fields, energy, and particles in the universe.