Quantum Foundations
The smooth evolution of the wavefunction and the definite outcomes we observe sit uneasily together. What selects an outcome?
Current explanations
Interpretations differ radically: Copenhagen, many-worlds, pilot-wave, and objective-collapse all reproduce the predictions while disagreeing about what is real.
Research progress
Bell tests rule out local hidden variables; collapse models make testable deviations now being constrained, but no interpretation is empirically singled out.