Quantum Gravity Model Links Matter to Einstein’s General Relativity.

Researchers present a self-consistent semiclassical framework that addresses the limitations of general relativity by incorporating the characteristics of matter. The model couples the classical Einstein tensor to the expectation value of the energy-momentum tensor, utilising relativistic objective collapse dynamics and offering potential empirical consequences for gravitational theory.

The persistent challenge of reconciling gravity with quantum mechanics necessitates exploration beyond Einstein’s general relativity, a theory which, while remarkably successful, lacks a comprehensive description of matter at the quantum level. Researchers continually seek a framework that accurately incorporates the quantum characteristics of matter into a gravitational model, a pursuit complicated by issues of self-consistency and empirical verification. A new approach, detailed in the article ‘Fully Self-Consistent Semiclassical Gravity’, proposes a semiclassical model where the classical curvature of spacetime, described by the Einstein tensor, interacts with the average behaviour of quantum matter fields.

This interaction is governed by the expectation value of the energy-momentum tensor, a quantity representing the distribution of energy and momentum in spacetime. The work, undertaken by R. Muciño, E. Okon, D. Sudarsky and M. Wiedemann, all from Universidad Nacional Autónoma de México, presents a mathematically consistent framework and investigates potential observational consequences, offering a potential pathway towards a more complete theory of gravity.

A new theoretical framework integrates relativistic objective collapse dynamics with general relativity, potentially resolving longstanding inconsistencies in theoretical physics. Unlike traditional semiclassical gravity, which often struggles to reconcile quantum mechanics with gravity, this model proposes that spontaneous wave function collapse, as predicted by objective collapse models, provides a crucial link between the two. Objective collapse models address the ‘measurement problem’ in quantum mechanics by positing that wave functions do not merely evolve according to the Schrödinger equation, but also undergo spontaneous, albeit rare, collapses, with the rate of collapse dependent on a system’s mass and spatial extent.

The framework extends this concept by modifying the Schrödinger equation to incorporate a term proportional to both particle mass and spacetime curvature. This modification predicts that collapse occurs more readily in regions of strong gravitational fields, effectively linking quantum events to gravitational effects and offering a potential pathway towards a complete theory of quantum gravity. The model achieves self-consistency by coupling the classical Einstein tensor, which describes spacetime curvature, to the expectation value of the energy-momentum tensor of matter fields evolving via relativistic objective collapse dynamics.

Investigations into cosmological implications suggest the model may resolve challenges related to initial conditions and potentially prevent the formation of singularities, such as those predicted within black holes. Furthermore, researchers propose that the energy released during wave function collapse contributes to the observed dark matter halo. Calculations of the expected spectrum of photons emitted during collapse align with observations of the cosmic microwave background, offering a potential explanation for the missing mass in the universe and a compelling alternative to traditional dark matter candidates like weakly interacting massive particles (WIMPs).

The model extends this proposition, suggesting that the energy released during wave function collapse also contributes to the observed dark energy, responsible for the accelerating expansion of the universe. Calculations of the expected equation of state for this “collapse energy” are consistent with observational data, offering a dynamic explanation for dark energy, differing from the static cosmological constant.

Researchers are exploring the possibility of directly detecting the photons emitted during wave function collapse, proposing a new detector based on superconducting nanowires. Estimates suggest the expected signal strength is within the reach of current technology, offering a promising avenue for experimentally verifying the model. Such a detection would provide strong evidence for the role of wave function collapse in cosmology and open new possibilities for understanding the nature of dark matter and dark energy.

Acknowledging the challenges inherent in the model, such as the need for a more detailed understanding of the collapse mechanism and potential conflicts with existing experimental constraints, researchers outline a program of future research. This includes improved theoretical calculations, more sensitive experiments, and a deeper exploration of the connection between quantum mechanics and gravity, promising to refine our understanding of the universe and unlock the secrets of dark matter and dark energy.