GPQ-Bridges: Bridging Gravity to Quantum Mechanics through Probability: from theory to cosmology and nuclear physics experiments and back

The quest for a theory capable of describing both the microscopic and macroscopic realms is on the verge of a paradigm shift. At the center of this shift lies one of the longest-standing debates in the foundations of quantum mechanics: the nature of wave-function collapse, i.e. the “measurement problem”. On one hand, the pioneering work of Diósi and Penrose has inspired the development of gravitational decoherence mechanisms within the context of quantum gravity, reproducing the structure of the master equation for the density operator. On the other hand, various efforts to reconcile quantum mechanics with gravity are increasingly drawing on mathematical tools from probability theory and functional analysis. These efforts aim to reformulate gravity so that it can coexist with quantum mechanics within a unified probabilistic framework. Complexity is naturally integrated into this approach, as it involves processing information via probability distributions incorporating stochastic methods. Probability theory—deeply rooted in phenomenology and anchored in measurement theory—also provides a conceptual bridge to the rich domain of stochastic gradient flows. These are applicable across a wide range of contexts, including astrophysics, particle and nuclear physics, cosmology, quantum collapse, artificial intelligence, and even quantum finance. This probabilistic framework also offers a novel pathway to understand gravity as a theory emergent in the infrared regime. Simultaneously, targeted experiments, particularly in atomic and nuclear physics, are placing increasingly stringent constraints that started to shape the development of these theories. Within this broad and evolving context, the GPQ-Bridges Workshop aims to foster dialogue on the complex relationship between experimental and theoretical investigations of collapse models. What role does the physics of complexity may play in collapse models and phenomena undergoing relaxation toward equilibrium? What insights can atomic, nuclear and particle physics offer into the nature of quantum collapse? These questions lie at the heart of our interdisciplinary workshop.