Is quantum theory exact? Experiments confront theory

ABSTRACT:

According to the Schroedinger equation, the wave-function of a quantum system should not collapse during a quantum measurement. And yet, experiments suggest that the wave-function does seem to collapse! Why should there be this apparent disagreement between theory and experiment? One possible explanation is that the Schroedinger equation is not exact, but an approximation to a stochastic nonlinear model, known as Continuous Spontaneous Localization [CSL]. The nonlinearity becomes significant for macroscopic systems, and is responsible for the dynamical collapse of the wave-function during measurement. On the other hand, for microscopic systems, CSL reduces to the Schroedinger equation to an excellent approximation: this accounts for the extraordinary success of quantum theory. The CSL model is being subjected to rigorous constraints coming from astrophysics, cosmology, ongoing and planned laboratory experiments on molecular interferometry, optomechanics, and anomalous Brownian motion. The fundamental theoretical origins of  the phenomenological CSL model perhaps lie in the resolution of the so-called problem of time in quantum theory. 

[References: Models of wave-function collapse, underlying theories, and experimental tests, A. Bassi et al., Reviews of Modern Physics (2013, in press, arXiv.org:1204.4325); andarXiv.org:1212.0135]