The measurement problem is a fundamental question in quantum mechanics that arises when attempting to understand the process of measurement and observation in the quantum realm. It refers to the apparent contradiction between the deterministic nature of the mathematical equations that describe quantum systems and the indeterministic nature of measurement outcomes.
In quantum mechanics, the state of a system is described by a mathematical object called a wavefunction. The wavefunction evolves over time according to Schrödinger's equation, which is a deterministic equation. However, when a measurement is made on a quantum system, the result is often probabilistic. This means that different measurement outcomes can occur with certain probabilities, rather than a single definite outcome.
The measurement problem asks how the probabilistic nature of measurement outcomes arises from the deterministic evolution of the wavefunction. In other words, how does the wavefunction "collapse" from a superposition of multiple possibilities to a single observed outcome?
There are several proposed interpretations and resolutions to the measurement problem, each with its own philosophical implications. The most common interpretation is the Copenhagen interpretation, which states that the wavefunction collapses upon measurement, but the exact mechanism of this collapse is not specified. Other interpretations include the many-worlds interpretation, which posits that the wavefunction never collapses but instead branches into multiple parallel universes, and the de Broglie-Bohm interpretation, which introduces hidden variables to explain the measurement process.
The measurement problem remains an active area of research and philosophical debate in quantum mechanics, and there is no universally accepted resolution at present.