Physicist Ginestra Bianconi proposes that gravity emerges from quantum information entropy, potentially uniting relativity and quantum mechanics while offering new insights into dark matter and dark energy.
A new theory proposes that gravity may emerge from quantum information entropy, offering a potential unification of quantum mechanics and general relativity. In a study published in Physical Review D, Ginestra Bianconi of Queen Mary University of London introduces an “entropic gravity” framework that derives the force of gravity from quantum relative entropy. By treating spacetime as a quantum system and leveraging tools from information theory, the approach connects two of physics’ most fundamental yet historically incompatible pillars.
This novel framework – aptly titled “Gravity from entropy” – recasts the equations of gravity in terms of information content. In essence, the work suggests that gravity may be understood as an emergent phenomenon arising from the difference in information between spacetime and matter. The theory matches Einstein’s familiar laws of gravity under normal conditions, but also predicts a tiny positive “cosmological constant” (a kind of built-in dark energy) that aligns with the observed accelerated expansion of the universe.
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The enduring quest for quantum gravity
For decades, uniting the physics of the very small with the physics of the very large has been one of science’s greatest challenges. Quantum mechanics governs subatomic particles, while Einstein’s general relativity describes gravity and the curvature of spacetime. But scientists are seeking a single framework that encompasses both – a quantum theory of gravity. Approaches like string theory and loop quantum gravity have been intensely explored, yet no consensus has emerged on how to reconcile quantum physics with gravity’s geometric description.
In 1973, Jacob Bekenstein proposed that black holes possess entropy proportional to the area of their event horizons. This idea bridged thermodynamics and gravity, suggesting that black holes are thermodynamic systems. Building on this concept, in 1995, Ted Jacobson demonstrated that assuming a relationship between entropy and the area of spacetime horizons allows one to derive Einstein’s gravitational equations as a thermodynamic “equation of state.”
In other words, gravity may emerge from the universe’s thermodynamic properties rather than being fundamental. More recently, theorists like Erik Verlinde have argued that gravity is an emergent force, arising “in the same way that temperature arises from the movement of microscopic particles,” with spacetime information playing the role of those particles. These ideas set the stage for treating spacetime and gravity as products of deeper informational or entropic principles, an approach that Bianconi’s new work takes to the next level.
An entropic approach to gravity and spacetime
Bianconi’s framework offers a fresh perspective by quantizing the fabric of spacetime itself. In this model, the metric of spacetime – the mathematical object that defines distances and curvature in general relativity – is treated as a quantum operator, analogous to a quantum state.
Matter fields (the particles and fields present in spacetime) also contribute to geometry: they define an “induced metric” that reflects how matter would curve spacetime. The crux of the theory is an entropic action defined as the quantum relative entropy between the spacetime metric and the matter-induced metric.
Quantum relative entropy is a concept borrowed from information theory that measures how one quantum state differs from another – here, it measures the “dissimilarity” between two descriptions of geometry.
In this representation, differences between the two curved surfaces correspond to an entropy measure, which effectively drives gravitational dynamics. By formulating gravity in this way, the model inherently links spacetime’s curvature with quantum information content from matter. The mathematical expression (top) encapsulates this entropy-based action, forming the basis for new gravitational field equations in the theory.
Varying this entropic action (using the principle of least action) yields modified Einstein field equations. Importantly, in the regime of weak fields and low energies, the new equations simplify to ordinary Einstein equations without a cosmological constant.
This means the familiar results of general relativity are recovered in everyday conditions – a necessary consistency check for any new gravity theory. However, at larger scales or higher energies, the theory diverges from classical Einstein gravity. The interplay of the two metrics and the entropic action naturally produces additional terms in the gravitational equations. Notably, it predicts the emergence of a small positive cosmological constant (a uniform energy density filling space) that isn’t put in by hand but emerges from the theory’s mathematics.
This emergent cosmological constant is especially interesting because its value can align with the measured acceleration of the universe’s expansion, addressing a major discrepancy in physics – the fact that quantum physics predicts a vastly larger vacuum energy than what we observe as dark energy.
A central innovation in Bianconi’s model is the introduction of the G-field, an auxiliary field that enters the action as a set of Lagrange multipliers (enforcing constraints in the theory). The G-field plays a crucial role in these modified gravity equations.
Intuitively, one can think of the G-field as a new ingredient woven into spacetime that adjusts how the entropic difference between metrics produces gravity. This field’s presence leads to the “dressed” Einstein–Hilbert action (the classical action for gravity) acquiring the small cosmological constant mentioned above. The resulting modified equations remain second-order (avoiding complicated higher-derivative terms), which could help mitigate potential instabilities.
Key findings: Dark matter and dark energy hints
Beyond unifying quantum information with gravity, the “gravity from entropy” study offers insights into two of cosmology’s biggest puzzles: dark matter and dark energy. Dark matter is the name given to the unseen mass theorized to make up the majority of matter in the universe – astronomers infer it must exist because galaxies rotate and cluster as if influenced by far more gravity than visible matter alone can provide.
Estimates have suggested dark matter constitutes up to roughly 80–85% of all matter in the cosmos, yet decades of searches have not yielded a single confirmed dark matter particle. In Bianconi’s entropic gravity model, the newly introduced G-field might offer an alternative explanation for these “missing” masses. The G-field in effect adds an extra source of gravity in the equations, and the study suggests this field “might be a candidate for dark matter” itself.
In other words, what we call dark matter could be an emergent aspect of spacetime entropy dynamics rather than a swarm of unknown particles – a bold proposal that echoes other emergent gravity ideas, but now grounded in a specific quantum information framework.
Meanwhile, dark energy – often associated with the cosmological constant – is thought to be the driver of the universe’s accelerating expansion. In standard cosmology, dark energy is an enigmatic uniform energy (or vacuum energy) that pushes space apart. One of the most crucial issues in theoretical physics is why the cosmological constant (dark energy density) observed is so incredibly small yet positive, defying straightforward quantum predictions. The entropic gravity theory provides a fresh angle on this: it predicts an emergent cosmological constant term that is naturally small and positive.
In certain theoretical frameworks, such as those of Schlatter (2021) and Diaz-Saldana et al. (2023), terms arising from entropy-based actions that depend on fields like the G-field are not arbitrary adjustable parameters; instead, they emerge naturally from the equations once such fields are included. Studies by Zamora and Tsallis (2019) and Chagoya et al. (2022) suggest that these values could potentially align with experimental observations of cosmic acceleration more closely than in many prior theories. If validated, this approach might help resolve longstanding discrepancies between theoretical expectations and observed reality regarding the universe’s expansion rate.
In short, a theory initially devised to unite quantum mechanics and gravity also appears to naturally address dark matter and dark energy – an interesting convergence of problems that are usually considered separate.
Broader implications and next steps
The implications of deriving gravity from entropy reverberate across fundamental physics. By linking gravity to quantum information theory, Bianconi’s research provides a novel pathway toward a unified theory of quantum gravity.
Rather than quantizing gravity in the traditional sense (which treats Einstein’s geometric theory as fundamental), this approach suggests gravity itself emerges from deeper quantum informational underpinnings. This perspective resonates with a broader movement in theoretical physics that views spacetime and gravity as emergent. For instance, studies in recent years have indicated that spacetime and gravity might emerge from the entanglement structure of an underlying microscopic quantum system.
Bianconi’s work adds to that idea by using the language of quantum relative entropy to derive gravitational dynamics from first principles.
If this entropic gravity framework holds up under further scrutiny, it could mark a significant shift in how we understand the universe. It provides a cohesive narrative where information and entropy become just as fundamental as particles and forces – gravity would essentially be the “information force.” This could allow for new connections between areas like quantum computing/information science and cosmology.
The theory’s built-in explanations for dark matter and dark energy also mean it will attract interest from cosmologists; for example, the G-field’s effects might be probed indirectly by seeing if the theory can reproduce the detailed observed properties of galaxies, galaxy clusters, or the cosmic microwave background without traditional dark matter. While the theory incorporates entropic principles, further research will be needed to explore how it fully integrates with quantum mechanics—particularly how to quantize the new entropic action—and to determine whether the G-field leaves any observable signatures that could distinguish this theory from standard dark matter models.
As with any radical proposal, healthy skepticism will drive thorough examination of this new framework. The concept of gravity emerging from entropy isn’t entirely without precedent – Jacobson’s thermodynamic derivation and Verlinde’s emergent gravity ideas laid important groundwork – but Bianconi’s implementation via quantum relative entropy is unique. Researchers will need to assess if this theory can be made compatible with all known observations and whether it plays nicely with quantum principles (for instance, does it resolve known paradoxes or create new ones?). The good news is that the modified equations reduce to known physics in the appropriate limit, and they remain mathematically well-behaved (second-order), which lends credibility to the framework.
“Gravity from entropy” represents a bold step toward unifying the laws of nature by viewing gravity through the lens of information. It not only strives to bridge the gap between quantum mechanics and general relativity, but it also provides fresh insight into what might constitute the dark components of our universe. As scientists continue to probe the boundaries between quantum theory, gravity, and information, ideas like this inject new energy into one of science’s grandest quests. While further work is needed to fully flesh out and test this entropic gravity theory, it stands as an exciting example of how rethinking fundamentals can lead to potential breakthroughs in understanding the cosmos.
This article was created with the assistance of artificial intelligence and thoroughly edited by FirstPrinciples staff and scientific advisors.
