In quantum mechanics, wavefunction collapse refers to the process by which a quantum system — which exists in a superposition of multiple possible states — reduces to a single, definite outcome when it is measured or observed.
The Superposition Principle:
Before measurement, a quantum particle (like an electron or photon) doesn’t have a single, definite state. Instead, it exists in a superposition — a combination of all the possible states it could be in. This is described by its wavefunction, a mathematical function that encodes the probabilities of finding the particle in each possible state.
What Is Wavefunction Collapse?
When a measurement is made:
- The wavefunction “collapses” from its superposition to a single state.
- Only one outcome is observed, even though many were possible before the measurement.
- The act of measurement itself plays a critical role — without observation, the system remains in superposition.
For example, in the famous double-slit experiment, if no one observes which slit the particle goes through, it behaves like a wave and creates an interference pattern. But if you measure which slit it goes through, the wavefunction collapses to a definite path, and the interference disappears.
Interpretations:
- Copenhagen Interpretation: Wavefunction collapse is real and triggered by observation.
- Many-Worlds Interpretation: There is no collapse — instead, all possible outcomes happen in parallel universes.
- Objective Collapse Theories: Collapse happens spontaneously at certain scales or energy levels, without measurement.
Why It Matters:
Wavefunction collapse highlights the deeply probabilistic nature of quantum physics and challenges our classical understanding of reality. It raises profound questions about the role of the observer, the nature of reality, and how information becomes definite in a fundamentally uncertain world.
This concept is central to understanding quantum behavior, quantum computing, and the boundary between quantum and classical physics.