Quantum mechanics is the branch of physics that studies the behavior of matter and energy in the presence of an observer. It is the foundation of modern physics and the theory of wave-particle duality.
In quantum mechanics, an object can exist in more than one state at a time. This means that it can be in two or more places at once, or it can have two or more properties at once. For example, an electron can spin in two opposite directions at the same time.
The behavior of a Quantum Mechanical system cannot be predicted with certainty. The best we can do is calculate probabilities for various outcomes. Even then, we can only make predictions about what we will observe; we cannot say for sure what is actually happening on a subatomic level.
Quantum mechanics has revolutionized our understanding of the universe and its workings. Its principles are essential to our understanding of how molecules and atoms interact with each other and with light, how transistors work, and how lasers emit their beams.