What Is Quantum Theory (2026): Understanding the Rules Behind Quantum Reality What Is Quantum Theory (2026) Quantum theory describes how energy and matter behave at atomic and subatomic scales—where particles act like waves, and certainty disappears into probability. In 2026, it remains the foundation for technologies from quantum computing to post-quantum cryptography . TL;DR Summary Definition: Quantum theory explains how particles behave as both waves and discrete quanta of energy. Why it matters: It powers quantum computing, secure communication, and new materials design. Key principle (2026 view): Reality is probabilistic—measurement defines outcomes. Next frontier: From physics labs to hybrid AI–quantum systems and quantum-secure infrastructure. 1) The Core Principles Wave–Particle Duality: Light and matter behave as both waves and particles. Superposition: Systems exist in mu...