The fundamental nature of gravity remains one of the most profound questions in physics, and researchers are increasingly exploring the idea that spacetime itself may not be fundamental, but rather emerges from deeper underlying principles. Andrea Addazi from Sichuan University and the Laboratori Nazionali di Frascati INFN, working with colleagues, investigates this concept of ‘pre-geometric’ gravity, proposing that spacetime and gravity arise from the spontaneous breaking of a larger symmetry governing the universe. This work demonstrates how a carefully constructed gauge theory, initially lacking a defined spacetime structure, dynamically generates a metric through symmetry breaking, successfully reproducing key features of Einstein’s General Relativity, including the observed Planck mass and a small cosmological constant. Importantly, the team’s analysis reveals a connection between these pre-geometric models and established approaches to quantum gravity, such as Loop Quantum Gravity, potentially offering a new pathway towards a complete theory of gravity and the universe’s origins.
Emergent Gravity From Symmetry Breaking Models
This document details a theoretical framework for emergent gravity, where gravity isn’t a fundamental force, but arises from the spontaneous breaking of a gauge symmetry in a pre-geometric phase, a phase where spacetime as we know it doesn’t yet exist. The authors explore two specific models, the MacDowell-Mansouri and Wilczek formulations, and demonstrate that standard General Relativity and a cosmological constant naturally emerge through this symmetry breaking. The framework also offers potential solutions to the cosmological constant problem and connects to approaches like Loop Quantum Gravity. The Planck mass isn’t a fundamental parameter, but emerges from the combination of parameters within the pre-geometric model. This framework provides a potential solution to the cosmological constant problem, with a large Higgs field suppressing the cosmological constant through a see-saw relation. The authors also propose a pre-geometric analogue of the Wheeler-DeWitt equation, opening a path to quantizing the pre-geometric theory and addressing the problem of time in quantum gravity. This approach offers an alternative to string theory for quantum gravity, potentially resolving the cosmological constant problem and bridging classical General Relativity with quantum gravity approaches. It opens new avenues for research in quantum gravity, cosmology, and fundamental physics, proposing a bottom-up approach where spacetime and gravity emerge from more fundamental building blocks.
Emergent Spacetime from Symmetry Breaking Confirmed
Scientists have demonstrated emergent gravity, revealing how spacetime geometry and the gravitational field can arise from the spontaneous symmetry breaking of a larger gauge symmetry. This work explores a pre-geometric paradigm where a manifold initially lacks a metric structure, constructing spacetime from more fundamental components. The team formulated gauge theories based on the de Sitter and anti-de Sitter groups, triggering symmetry breaking with an internal vector field that dynamically generates a spacetime metric. Experiments utilizing the MacDowell-Mansouri and Wilczek models successfully reproduced the Einstein-Hilbert action, the foundation of general relativity, alongside a dynamically generated cosmological constant.
The observed Planck mass emerges from a see-saw mechanism dependent on the symmetry-breaking scale, while the small observed value of the cosmological constant is naturally explained by this mechanism. The research demonstrates that the pre-geometric theory possesses three physical degrees of freedom, corresponding to a massless graviton and a massive scalar particle. Integrating out the massive scalar, the Arnowitt-Deser-Misner Hamiltonian of General Relativity is obtained, establishing a direct connection between pre-geometric theories and canonical gravity approaches like Loop Gravity. This breakthrough delivers a pre-geometric Wheeler-DeWitt equation, opening new avenues for exploring quantum gravity from a fundamentally different perspective. The Levi-Civita symbol successfully generates a Riemannian metric structure and recovers the Einstein Equivalence Principle without presupposing a prior spacetime metric.
Gravity Emerges From Broken Symmetry Naturally
This research establishes a framework for understanding gravity as an emergent phenomenon, arising from the spontaneous breakdown of symmetry within a pre-geometric theory, where spacetime itself is not fundamental. Scientists demonstrate that established models, including the MacDowell-Mansouri and Wilczek formulations, dynamically generate the Einstein-Hilbert action and a cosmological constant when a larger symmetry is broken, indicating that geometry emerges from a more fundamental structure. The resulting Planck mass is not a pre-defined constant, but emerges naturally from the parameters of this pre-geometric theory. A noteworthy achievement is the explanation for the observed smallness of the cosmological constant, which arises through a natural “see-saw” mechanism dependent on the scale of symmetry breaking.
The team’s Hamiltonian analysis confirms the theory’s consistency, revealing the expected number of physical degrees of freedom, a massless graviton and a massive scalar, and demonstrating a reduction to the standard Arnowitt-Deser-Misner Hamiltonian of General Relativity after symmetry breaking. Further research is needed to fully explore the implications of this framework, particularly regarding the challenges of quantizing the pre-geometric theory and addressing potential operator ordering issues.