Quantum theory, also known as quantum mechanics, is a fundamental theory in physics that provides a mathematical framework to describe the behavior of particles and systems at the quantum level. It explains various "quantum" phenomena through a set of principles and mathematical equations.
At its core, quantum theory departs from classical physics by introducing the concept of wave-particle duality and the uncertainty principle. Here are a few key principles of quantum theory and how they explain "quantum" things:
Wave-Particle Duality: Quantum theory describes particles, such as electrons or photons, as having both wave-like and particle-like properties. This means that particles can exhibit wave-like behavior, such as interference and diffraction, as well as particle-like behavior, such as being localized at a specific position. The wave-particle duality is explained by the wavefunction, a mathematical function that describes the quantum state of a particle or system. The wavefunction encodes the probability distribution of finding a particle in a particular state or position.
Superposition: Quantum theory allows for the existence of superposition, where a particle or system can be in multiple states or configurations simultaneously. This means that a particle can exist in a combination of different states until it is measured or observed, at which point it "collapses" into a single state. Superposition is mathematically described by the linear combination of wavefunctions.
Quantum Entanglement: Quantum theory introduces the concept of entanglement, where two or more particles become correlated in such a way that the state of one particle cannot be described independently of the others. Entangled particles exhibit a phenomenon known as non-locality, where changes to one particle instantaneously affect the state of the other, regardless of the distance between them. Quantum entanglement has been experimentally verified and plays a crucial role in various applications, including quantum information and communication.
Uncertainty Principle: The uncertainty principle, formulated by Werner Heisenberg, states that there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be known simultaneously. This principle arises from the wave-particle duality and implies that there are inherent limits to the predictability of quantum systems.
Quantum theory explains the behavior of "quantum" things through these principles and the associated mathematical formalism. By applying the principles and equations of quantum theory, physicists can make predictions and understand a wide range of phenomena, including the behavior of atoms, the nature of subatomic particles, the functioning of quantum computers, and more.