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Measurement Problem in Quantum Mechanics

The Schrodinger equation mathematically describing the evolution of quantum systems formalizes the dual nature of such systems, described as both wave and particle. The wave function evolves into a superposition of probable states, while measurements always find the system to be in just one physical state. Heisenberg's uncertainty principle limits our knowledge of state, in that we cannot simultaneously measure position and momentum of a quantum system (particle), but a measurement will always return a definite position or momentum, depending on which attribute is measured.

The Measurement Problem highlights the difference between probable system states and actual system states that are returned upon measurement of that system. Superpositions of probable states that are present in the unitary equation (Schrodinger) are never observed experimentally, as measurements always return a single state from among the probabilities. As illustrated in the famous thought experiment known as Schrodinger's Cat, the question of how the probabilities are converted into classical states - or, how the complex number weighted superpositions of all possible states are resolved into just one reality has led to several different and apparently incompatible interpretations of the wave-particle duality inherent in quantum mechanics.

Web Resources On Measurement Problem in Quantum Mechanics

Measurement in Quantum Theory
Wikipedia: Measurement Problem
The measurement problem

Book Resources On Measurement Problem in Quantum Mechanics

Speakable and Unspeakable in Quantum Mechanics by John Bell
Quantum Theory by David Bohm

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