In a groundbreaking study recently published in Physical Review D, Professor Ginestra Bianconi, a leading figure in applied mathematics at Queen Mary University of London, has proposed a revolutionary framework that could fundamentally change our understanding of gravity and its relationship to quantum mechanics. The research, titled “Gravity from Entropy,” introduces a new theoretical perspective that bridges the longstanding gap between quantum mechanics and Einstein’s general relativity—two of the most influential yet seemingly incompatible theories in modern physics.
The Quantum Gravity Conundrum
For decades, physicists have faced one of the most profound challenges in the field of theoretical physics: how to reconcile quantum mechanics, the theory that governs the behavior of particles at microscopic scales, with general relativity, which describes the gravitational force acting on massive bodies at cosmic scales. These two theories, though both extraordinarily successful in their respective domains, are built on fundamentally different principles, making it extremely difficult to unify them into a single, comprehensive theory.
The quest for a theory of quantum gravity—one that can describe both the quantum properties of matter and the curvature of spacetime due to gravity—has remained elusive. While general relativity has been remarkably effective in explaining phenomena such as the behavior of black holes and the expansion of the universe, quantum mechanics has led to unprecedented successes in describing the behavior of particles, atoms, and subatomic forces. Yet, when physicists attempt to combine these two theories into one framework, they encounter numerous inconsistencies, including the breakdown of classical concepts of spacetime and energy at the quantum level.
Professor Bianconi’s Innovative Approach
Professor Bianconi’s new approach offers an exciting possibility of bridging the divide between quantum mechanics and gravity. Rather than treating gravity as a force mediated by a classical field, as is traditionally done in general relativity, Bianconi’s framework treats the metric of spacetime itself as a quantum operator. This subtle but important shift in perspective opens up an entirely new way of thinking about the relationship between spacetime and the particles that inhabit it.
At the heart of the study is the concept of quantum relative entropy—a central idea from quantum information theory that measures the difference between two quantum states. In the context of Professor Bianconi’s framework, relative entropy is used to describe the interplay between the geometry of spacetime and the distribution of matter. This allows the creation of a new entropic action, which quantifies the discrepancy between the spacetime metric dictated by general relativity and the spacetime geometry influenced by the presence of matter fields.
In this framework, gravity is not treated as an inherent force or field, but rather as an emergent phenomenon that arises from the entropic properties of spacetime itself. This novel approach provides a fresh perspective on how gravity can be derived from quantum mechanical principles, potentially leading to a more complete understanding of both quantum mechanics and general relativity.
Gravity from Entropy: Implications and Predictions
One of the most remarkable aspects of Professor Bianconi’s work is the introduction of a new term, the G-field, which serves as an auxiliary field in the modified equations of gravity. The G-field acts as a Lagrangian multiplier, playing a crucial role in determining how spacetime behaves at different scales. This new field is expected to have far-reaching implications, particularly in relation to the ongoing puzzle of dark matter.
Dark matter, which is believed to make up around 85% of the universe’s mass, is invisible to current detection methods because it does not interact with light. Its existence has been inferred from gravitational effects on visible matter, but it remains one of the most profound mysteries in cosmology. In Bianconi’s framework, the G-field could potentially serve as a candidate for dark matter. This idea proposes that the G-field, while invisible like dark matter, could exert gravitational effects similar to the mysterious substance, offering a potential explanation for the elusive phenomenon.
Another significant consequence of this framework is the prediction of an emergent cosmological constant, a value that accounts for the accelerated expansion of the universe. General relativity’s original equations do not provide a natural explanation for this expansion, and previous models have struggled to align theoretical predictions with experimental observations. Bianconi’s approach, however, leads to the prediction of a small, positive cosmological constant that more closely matches current observational data. This could resolve the discrepancy between theory and observation and provide a more satisfactory explanation for the accelerated expansion of the cosmos.
Entropy, Spacetime, and the Future of Quantum Gravity
At the core of Bianconi’s proposal is the concept of entropy, a measure of disorder or randomness in a system. In classical thermodynamics, entropy is a fundamental concept, and its role in quantum systems has been explored in great detail. In this new framework, entropy is used as a tool to understand the geometry of spacetime itself. By associating spacetime geometry with quantum relative entropy, Bianconi’s theory treats gravity as an emergent property, much like temperature or pressure can be considered emergent properties in thermodynamic systems. This innovative approach suggests that gravity, rather than being a fundamental force in its own right, might be a consequence of the microscopic, quantum mechanical behavior of spacetime and matter.
The potential for this framework to unify quantum mechanics with gravity is immense. If gravity is indeed an emergent property derived from quantum information, it may be possible to describe the gravitational interaction at both the macroscopic (cosmic) and microscopic (quantum) levels using the same set of principles. This could lead to a unified theory of quantum gravity, which has been one of the most elusive goals in modern physics.
Furthermore, by linking gravity with quantum information theory, Professor Bianconi’s research could offer new insights into some of the most pressing questions in contemporary physics, such as the nature of black holes and the behavior of the universe at its earliest stages. For example, understanding the quantum nature of gravity could lead to new approaches in studying the “quantum foam” that is believed to exist at the smallest scales of spacetime, potentially unlocking the mysteries of the Big Bang and the very fabric of the universe.
Wider Implications for Dark Matter and Cosmology
The connection between the G-field and dark matter is another key implication of Professor Bianconi’s research. Dark matter is one of the most perplexing phenomena in modern astrophysics and cosmology. Although it cannot be directly observed, its presence is inferred from its gravitational effects on visible matter. Several candidate particles have been proposed for dark matter, including weakly interacting massive particles (WIMPs) and axions. However, none have been definitively detected.
By suggesting that the G-field could represent a form of dark matter, Professor Bianconi’s framework opens up new possibilities for understanding this mysterious substance. If the G-field does indeed have properties that mimic dark matter, it could provide a direct link between the quantum nature of gravity and the large-scale structure of the universe. This would not only help explain the missing mass of the universe but also potentially lead to new methods for detecting dark matter in the future.
Moreover, the predicted emergence of a positive cosmological constant could have profound implications for our understanding of the universe’s expansion. Current observations suggest that the universe is expanding at an accelerating rate, driven by a force known as dark energy. However, the origin of dark energy and its relationship to the cosmological constant remains unclear. Bianconi’s framework, by predicting an emergent cosmological constant, could offer a new approach to understanding the nature of dark energy and its role in shaping the evolution of the universe.
More information: Ginestra Bianconi, Gravity from entropy, Physical Review D (2025). DOI: 10.1103/PhysRevD.111.066001