In a recent study that was published in Physical Review D, Queen Mary University of London Professor Ginestra Bianconi, offered a novel framework with the potential to completely alter knowledge of gravity and how it relates to quantum mechanics.
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. Image Credit: Queen Mary University of London
The study bridges the gap between Einstein's general relativity and quantum mechanics, two of the most fundamental but seemingly incompatible theories in physics, by introducing a novel method that derives gravity from quantum relative entropy.
The Challenge of Quantum Gravity
Physicists have been trying for decades to make sense of the differences between general relativity and quantum mechanics. General relativity explains the force of gravity on cosmic scales, whereas quantum mechanics controls the behavior of particles at the smallest scales. One of the most elusive objectives in contemporary science has been to bring these two frameworks together.
Professor Bianconi's research introduces a novel viewpoint by conceptualizing spacetime's metric, a fundamental element of general relativity, as a quantum operator. This groundbreaking method employs quantum relative entropy from quantum information theory to illustrate the relationship between spacetime geometry and matter.
The Role of Entropy and the G-Field
This research introduces a novel entropic action that measures the deviation between spacetime's metric and the metric generated by matter fields. This leads to revised Einstein equations, which converge with classical general relativity at low energies and curvatures. Importantly, the theory predicts a small, positive cosmological constant, aligning more accurately with observed cosmic acceleration than previous models.
A significant aspect of this theory is the introduction of the G-field, an auxiliary field functioning as a Lagrangian multiplier. This G-field is essential in the modified gravity equations and also provides a potential avenue for interpreting dark matter, the enigmatic substance that constitutes a large part of the universe's mass.
Wider Implications and Future Directions
The profound implications of this study lie in its potential to connect gravity with quantum information theory, offering a route to a unified theory of quantum gravity. Additionally, the G-field may unlock new understandings of dark matter, a long-standing cosmological mystery.
This work proposes that quantum gravity has an entropic origin and suggests that the G-field might be a candidate for dark matter. 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.
Ginestra Bianconi, Professor, Department of Applied Mathematics, Queen Mary University of London
Although further exploration is needed, this study represents a crucial step in humanity's understanding of the universe. Professor Bianconi's study, which uses a quantum view of spacetime and the entropy of spacetime metrics, challenges existing ideas and offers exciting new avenues for understanding gravity, quantum mechanics, and the cosmos.
Journal Reference:
Bianconi, G., (2025) Gravity from entropy. Physical Review D. doi.org/10.1103/PhysRevD.111.066001