Gravity from entropy: A radical new approach to unifying quantum mechanics and general relativity

Diagrammatic representation of the entropic quantum gravity action. The action for gravity is given by the quantum relative entropy between the metric of the manifold and the metric induced by the matter field and the geometry.

The study, titled Gravity from Entropy, introduces a novel approach that derives gravity from quantum relative entropy, bridging the gap between two of the most fundamental yet seemingly incompatible theories in physics: quantum mechanics and Einstein’s general relativity. 

The challenge of quantum gravity 

For decades, physicists have struggled to reconcile the principles of quantum mechanics with those of general relativity. While quantum mechanics governs the behaviour of particles at the smallest scales, general relativity describes the force of gravity on cosmic scales. Unifying these two frameworks has been one of the most elusive goals in modern science. 

Professor Bianconi’s work offers a fresh perspective by treating the metric of spacetime, a key concept in general relativity, as a quantum operator. This innovative approach uses quantum relative entropy, a concept from quantum information theory, to describe the interplay between spacetime geometry and matter. 

The role of entropy and the G-field 

The study introduces a new entropic action, which quantifies the difference between the metric of spacetime and the metric induced by matter fields. This approach leads to modified Einstein equations that, in the low coupling regime i.e. low energies and small curvature, reduce to the classical equations of general relativity. However, the theory goes further, predicting the emergence of a small, positive cosmological constant – a value that aligns with experimental observations of the universe’s accelerated expansion much better than for other pre-existing theories. 

A key feature of the theory is the introduction of the G-field, an auxiliary field that acts as a Lagrangian multiplier. The G-field not only plays a crucial role in the modified equations of gravity but also opens the door to new interpretations of dark matter – a mysterious substance that makes up a significant portion of the universe’s mass but has yet to be directly observed. 

Wider implications and future directions 

The implications of this research are profound. By linking gravity to quantum information theory, the study provides a potential pathway to a unified theory of quantum gravity. Moreover, the G-field could offer new insights into the nature of dark matter, a long-standing puzzle in cosmology. 

"This work proposes that quantum gravity has an entropic origin and suggests that the G-field might be a candidate for dark matter,” explains Professor Bianconi. “Additionally, the emergent cosmological constant predicted by our model could help resolve the discrepancy between theoretical predictions and experimental observations of the universe’s expansion."

While further research is needed to fully explore the implications of this theory, the study represents a significant step forward in the quest to understand the fundamental nature of the universe.  

Professor Bianconi’s work challenges conventional wisdom and opens up exciting new avenues for exploration. By treating spacetime as a quantum entity and leveraging the power of entropy associated to the spacetime metrics, this research could pave the way for a deeper understanding of gravity, quantum mechanics, and the cosmos itself.