A study reveals how the universe builds complex structures while obeying the laws of thermodynamics.
For decades, cosmologists faced a major paradox. The second law of thermodynamics states that entropy always increases. This usually implies a relentless growth of disorder. Yet, cosmic history shows the rise of highly ordered structures like galaxies, stars, and life.
Now, research by Professor Ginestra Bianconi from Queen Mary University of London provides an answer. Published in Physical Review D, the study utilizes a framework called Gravity from Entropy (GfE).
The Core Discovery
The GfE theory shifts how we view cosmic expansion. By analyzing the universe through statistical mechanics, the research shows a dual thermodynamic behavior:
- Total entropy increases over time.
- Local volume expands continuously.
- Entropy density decreases per unit volume.
This dropping local entropy density clears the path for complex, ordered structures to emerge locally without violating universal thermodynamic laws.
How Gravity Emerges from Information
The GfE framework builds upon 1970s black hole thermodynamics established by Jacob Bekenstein and Stephen Hawking. It treats gravity not as a fundamental force, but as an emergent phenomenon.
- Information tension: Gravity stems from geometric differences between physical metrics and matter fields.
- Intrinsic warmth: Spacetime geometry possesses an inherent thermal nature.
- Dark energy: The theory naturally generates a dynamical dark energy term.
Bridging the Gaps in Physics
While still a theoretical model, GfE offers a mathematical bridge between general relativity, quantum mechanics, and cosmology. It opens new paths to explain how cosmic irreversibility coexists with the intricate architecture of our universe.
Deep Dive: The Quantum Geometric Relative Entropy
The mathematical backbone of the Gravity from Entropy (GfE) theory rests on treating spacetime metrics and matter fields symmetrically. In traditional General Relativity, matter is essentially attached to a fixed geometric stage. Conversely, GfE evaluates the mutual information shared between two distinct metrics:
- The physical metric: Represents the true, underlying Lorentzian spacetime geometry.
- The induced metric: Generated directly by matter fields and localized cosmic curvature.
The difference in information between these metrics is calculated via the Quantum Geometric Relative Entropy (QGRE). The theory operates on the principle that these two metrics naturally pull toward each other. This minimization of informational tension matches Einstein’s equations at large cosmic scales but provides different, testable mechanics at high energies.
An Anti-Reductionist View of Space
Professor Bianconi’s approach challenges standard reductionist views in quantum gravity. Instead of attempting to break gravity down into individual, isolated point particles, the GfE model prioritizes geometry as a holistic, integrated system.
- No horizons required: Unlike earlier entropic gravity models proposed by Eric Verlinde or Ted Jacobson, GfE does not require a holographic horizon to function.
- Volumetric nature: The thermodynamic properties emerge locally from the fundamental volume elements of spacetime itself.
- Intrinsic temperature: In isotropic Friedmann–Robertson–Walker (FRW) universes, space behaves like a statistical mechanic fluid with its own intrinsic temperature and pressure profiles.
The Emergence of Dark Energy
One of the most notable outcomes of the GfE framework is how it handles the accelerating expansion of the universe. Traditional cosmology relies on inserting a static cosmological constant by hand to account for dark energy. Under the GfE action, a dynamical dark energy term emerges naturally as a Lagrange multiplier.
This emergent field acts directly as internal energy within the system’s localized first law of thermodynamics. Because this dark energy term is dynamical and shifts beyond weak gravitational limits, it opens up realistic opportunities for astrophysicists to test the validity of the GfE theory through upcoming cosmic observations.
Scientific Reference:
Bianconi, G. (2026). Thermodynamics of the gravity from entropy theory. Physical Review D. DOI: 10.1103/26kn-thgp
