Description
Title: A healthier stochastic semiclassical gravity: world without Schrödinger cats
Abstract: Semiclassical gravity couples classical gravity to the quantized matter in the mean-field approximation, which is problematic for two reasons. It ignores the quantum fluctuation of matter distribution, and it violates the linearity of the quantum dynamics. The first problem can be mitigated by allowing stochastic fluctuations of the geometry, but the second problem lies deep in quantum foundations. Restoration of quantum linearity requires a conceptual approach to
hybrid classical-quantum coupling. Studies of the measurement problem and the quantum-classical transition point to a solution. It is based on a postulated mechanism of spontaneous quantum monitoring plus feedback. This approach eliminates Schrödinger cat states, takes quantum fluctuations into account, and restores the linearity of quantum dynamics. Such conceptually ’healthier’ semiclassical theory exists in the Newtonian limit, but its relativistic extension hits a wall. The long-known obstacles lie in quantum foundations.