Quantum theory, or quantum mechanics, is a fundamental theory in physics that describes the behavior of matter and energy at the smallest scales, such as atoms and subatomic particles. It represents a significant departure from classical physics and introduces concepts that are often counterintuitive. Here are some key aspects of quantum theory: Overall, quantum theory provides a comprehensive framework for understanding the behavior of matter and energy at the smallest scales, fundamentally reshaping our understanding of the physical world and leading to numerous technological and theoretical advancements.