In quantum mechanics, the wave function represents the state of a quantum system and contains all the information about its possible states and properties. The wave function evolves over time according to the Schrödinger equation, which describes the dynamics of quantum systems. However, when a measurement is made on a quantum system, the wave function undergoes a process known as wave function collapse or wave function reduction.
Wave function collapse occurs when a quantum system interacts with a measurement apparatus, an observer, or its surrounding environment. The collapse of the wave function results in the system transitioning from a superposition of multiple possible states to a single, definite state corresponding to the measurement outcome. This is often referred to as the "measurement problem" in quantum mechanics.
The exact mechanism and interpretation of wave function collapse are still subjects of debate and different interpretations exist. The most widely accepted interpretation is the Copenhagen interpretation, which states that the act of measurement causes an abrupt and random collapse of the wave function.
According to the Copenhagen interpretation, when a measurement is made, the wave function collapses into one of the eigenstates of the measured observable, with each eigenstate having a certain probability of being observed. The collapse is instantaneous and non-deterministic, meaning it is impossible to predict precisely which outcome will be obtained.
Other interpretations, such as the Many-Worlds interpretation and the Transactional interpretation, propose different explanations for wave function collapse. The Many-Worlds interpretation suggests that wave function collapse doesn't occur but rather the observer becomes entangled with the measured system, and the universe splits into multiple branches corresponding to different measurement outcomes. The Transactional interpretation introduces advanced and retarded waves to explain wave function collapse as a result of a transaction between the measurement apparatus and the system.
It's important to note that while wave function collapse is an essential aspect of measurement in quantum mechanics, the underlying process and interpretation are still actively studied and researched by physicists.