The universe has been expanding for almost 14 billion years, and with it, its total entropy—a measure of disorder—has been growing. This seems natural: the second law of thermodynamics states that entropy in an isolated system does not decrease. However, in a new paper published in Physical Review D, physicist and mathematician Ginestera Bianconi from Queen Mary University of London offers a fresh perspective on this problem. According to her "Gravity from Entropy" (GfE) theory, entropy per unit volume can even decrease, opening an unexpected path to the emergence of cosmic structures.
Bianconi's idea is to derive gravity from entropic action. She considers spacetime and matter on an equal footing, using Geometric Quantum Relative Entropy (GQRE). This is a measure of the difference between the metric of real spacetime and the "metric induced by matter." Gravity here emerges not as a fundamental force, but as a consequence of the informational interaction between geometry and matter. In the limit of low energies and small curvatures, the theory smoothly transitions into Einstein's classical equations, but adds important nuances.
Recently, Bianconi and her colleagues delved deeper into the thermodynamics of this model. They showed that universes within the GfE framework allow for a thermal description: temperatures and pressures arise locally, obeying the first law of thermodynamics. The total entropy of such universes does not decrease over time—in full agreement with the second law. Meanwhile, the GQRE relative entropy per unit volume does not increase, which is natural for a relative quantity. However, the total volume of the expanding universe increases, and this allows for a reconciliation of the global increase in entropy with the local emergence of order: galaxies, stars, complex structures.
Imagine the early universe—hot, dense, almost homogeneous. As it expands, space stretches, and the temperature drops. In the classical picture, the entropy per comoving volume remains approximately constant (as in the adiabatic expansion of a gas), but the total entropy increases due to irreversible processes: the formation of stars, black holes, and dissipation. The new theory adds that gravitational interaction itself has an entropic nature. This provides a dynamic effective dark energy term that depends on an auxiliary G-field and remains positive, helping to explain the accelerated expansion of the universe without parameter tuning.
The theory is still young and requires further testing, including quantization and comparison with observations. But it already offers an elegant bridge between thermodynamics, gravity, and cosmology. Instead of seeing entropy only as an inevitable path to heat death, we find in it a mechanism that allows the universe to "self-organize" against the backdrop of a general increase in disorder.
Bianconi's work reminds us how deeply information, geometry, and physics are intertwined. Perhaps it is through entropy that we will one day understand why spacetime behaves the way it does, and how the complexity we observe arises from the chaos of the Big Bang. This is not a revolution that refutes Einstein, but a natural development of ideas that invites us to look at old questions from a new angle. And while astronomers study distant galaxies, theorists continue to search for the very informational "building blocks" from which gravity is constructed.
