In a new study published in Physical Review D, Professor Ginestra Bianconi, Professor of Applied Mathematics at Queen Mary University of London, proposes a new framework that could revolutionize our understanding of gravity and its relationship with quantum mechanics.
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 behavior 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 with the spacetime metrics, this research could pave the way for a deeper understanding of gravity, quantum mechanics, and the cosmos itself.
Reference: Ginestra Bianconi, Gravity from entropy, Physical Review D (2025). DOI: 10.1103/PhysRevD.111.066001
