Bianconi Proposes Gravity from Entropy

Professor Ginestra Bianconi Proposes Gravity from Entropy

Reconciling Cosmic Structure with the Second Law

Modern cosmology has long grappled with a fundamental tension: while the second law of thermodynamics dictates that the universe should move toward increasing disorder, the actual history of the cosmos shows the opposite trend. Einstein famously stated that The second law of thermodynamics occupies a unique position among the laws of Nature, reflecting his conviction that it is among the most fundamental principles of physics and unlikely to be overthrown. The second law states that the total entropy of an isolated system tends to increase over time, a principle often associated with the growth of disorder.

Einstein’s Second Law and the Growth of Cosmic Complexity

Over 13.8 billion years, matter has organized itself into increasingly complex structures, including galaxies, stars, planets, and life. Explaining how this growing complexity can coexist with the continual rise of entropy remains an unresolved problem. According to the research, the standard answer—that the universe’s growing volume provides room for both global disorder and local order—has always gestured at a resolution without providing one from within the field equations of gravity.

Professor Bianconi’s work addresses this by distinguishing between the universe’s total entropy and its entropy density. As the universe expands, total disorder rises in compliance with the second law, but the entropy per unit volume—the density within a fixed patch of space—actually decreases. This local drop in density provides the necessary thermodynamic headroom for gravity to pull matter into clumps. Galaxies are not violations of the second law; they are its local expression in an expanding geometry.

Jacob Bekenstein and Stephen Hawking’s Quantum Geometric Relative Entropy

Gravity as Information: The GfE Framework

The GfE theory shifts the definition of gravity away from a fundamental force or the curvature of spacetime. Instead, it describes gravity as a form of “bookkeeping”—the universe’s running tally of a mismatch between two geometric descriptions of the same place. Gravity emerges from the information-theoretic tension between the true spacetime metric and the metric induced by matter fields and curvature.

The theory relies on the Quantum Geometric Relative Entropy (QGRE) to quantify this geometric mismatch. The GfE Lagrangian is given by this QGRE between the two metrics. This approach builds upon the foundational 1970s work of Jacob Bekenstein and Stephen Hawking, which established that black holes possess entropy and emit thermal radiation. These discoveries suggested a deep relationship between spacetime, information, and thermodynamics.

GfE Model Predictions for Dynamical Dark Energy

Predicting Dark Energy and Future Observations

One of the most significant features of the GfE model is its behavior at high energy levels. While the theory reduces to General Relativity for low energies and small curvature, it deviates from it beyond the weak limit. Interestingly, beyond the weak limit, the GfE equations include the emergence of a dynamical dark energy.

The research offers a mathematically precise resolution to the puzzle of how the universe builds structure while growing more disordered. By exploring the thermodynamic properties of the Gravity from Entropy theory, Bianconi shows that while the total entropy of the Universe increases in time, the entropy per unit volume decreases, leaving open new interpretations for the emergence of local structures.