Gravity is the most familiar of nature’s forces. It keeps our feet planted on the ground and dictates the movements of planets and stars. Yet, even so, gravity remains one of the greatest mysteries in physics.
In their quest to understand the fundamental forces of the universe, scientists have gotten stuck on gravity. While the other forces — electromagnetism, the strong nuclear force, and the weak nuclear force — have been successfully described by quantum mechanics, gravity has resisted joining this framework, and stubbornly so.
In a new study, Ginestra Bianconi of Queen Mary University of London presents a bold reinterpretation of gravity. Instead of treating it as a fundamental force, Bianconi suggests that gravity arises from entropy—a measure of disorder in a system. In this formulation, the very fabric of spacetime and the presence of matter may be dictated by the principles of information theory and statistical physics.
Quantizing Gravity
Here’s the thing that has been bugging physicists for years. We have two descriptions of the Universe that work perfectly well: General Relativity and quantum physics. Too bad they don’t work together.
In all the years scientists have been rigorously testing these frameworks, we’ve never found a single observation or made a single experimental measurement that’s conflicted with either Einstein’s General Relativity (the theory of gravity) or with the Standard Model’s predictions from quantum field theory.
Quantum field theory describes three of the four fundamental forces of nature, electromagnetism, and the strong and weak nuclear forces, through the exchange of force-carrying particles, like photons for electromagnetism. Yet gravity, the weakest but most pervasive of the four, refuses to fit into this scheme.
Attempts to quantize gravity have run into deep mathematical trouble. In quantizing, scientists describe it as a field with a corresponding force-carrying particle, the hypothetical graviton. However, when physicists try to calculate interactions at extremely high energies, such as those near the center of a black hole or at the beginning of the universe, the equations explode into infinities. General relativity and quantum mechanics appear to be fundamentally incompatible. That’s a big issue in physics because something glaring is missing.
A New Kind of Gravity
In her new paper, Bianconi attempts to resolve this age-old inconsistency by treating gravity in a novel way. The physicist suggests that the geometry of spacetime — the very stage on which the universe’s events unfold — can be described by a quantum operator that encodes entropy. In simpler terms, the fabric of spacetime itself could be thought of as a kind of quantum object, with its own entropy.
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This idea is not entirely new. Physicists have long speculated that gravity might have a thermodynamic origin, inspired by the discovery that black holes have entropy and emit radiation. But Bianconi’s work takes this a step further, proposing a concrete mathematical framework that links the geometry of spacetime to the entropy of quantum fields.
In this new framework, spacetime is described by two metrics: the traditional metric that defines its geometry, and a second metric induced by matter fields. The interplay between these two metrics is captured by an entropic action — a mathematical expression that quantifies the relationship between them. This action is based on the concept of quantum relative entropy, a measure of how different two quantum states are.
Bianconi proposes a modified version of Einstein’s equations, the mathematical foundation of general relativity. In the limit of low coupling — where the interaction between matter and spacetime is weak — these modified equations reduce to the familiar Einstein equations with zero cosmological constant.
The G-field
The researcher introduced an auxiliary field called the G-field, which acts as a set of Lagrange multipliers — a tool in physics used to impose constraints. This way, the entropic action can be rewritten as a dressed Einstein-Hilbert action, the standard form of the equations of general relativity, but with an emergent cosmological constant. This constant, which describes the accelerated expansion of the universe, arises naturally from the G-field and is small and positive—consistent with observations of the universe’s expansion.
One of the biggest mysteries in modern astrophysics is dark matter, an invisible substance that appears to make up the bulk of the universe’s mass. Bianconi speculates that the G-field may play a role in explaining dark matter’s effects. If gravity arises from an entropic process rather than a fundamental force, then the missing mass problem in galaxies could be a consequence of how entropy governs the interplay between spacetime and matter.
“This work proposes that quantum gravity has an entropic origin and suggests that the G-field might be a candidate for dark matter,” explains Professor Bianconi. “Additionally, the emergent cosmological constant predicted by our model could help resolve the discrepancy between theoretical predictions and experimental observations of the universe’s expansion.”
What Comes Next?
Of course, this is just all theory. One major challenge is determining whether this entropic gravity model can make predictions that differ from general relativity in ways that can be tested experimentally.
For now, Bianconi’s work is a bold idea, one that could reshape our understanding of the cosmos.
As physicists delve deeper into these mysteries, with each new theory, we come closer to understanding the fundamental nature of reality.
The findings appeared in the journal Physical Review D.