Creation of Matter in a Noncommutative Universe

TL;DR

This paper introduces a noncommutative geometric framework using groupoids that unifies Mach's principle and Wheeler's geometrodynamics, leading to matter creation from geometry and new solutions to Einstein's equations.

Contribution

It develops a noncommutative algebraic generalization of geometry that naturally incorporates matter creation from geometric degrees of freedom.

Findings

Derived generalized Einstein equations with additional matter-like terms.

Found two exact solutions demonstrating matter creation from geometry.

Showed that matter can emerge purely from geometric degrees of freedom in this framework.

Abstract

The dark matter and dark energy problem, that is now dominating the research in cosmology, makes the question of the origin of mass-energy content of the universe more urgent than ever. There are two philosophies regarding this question: according to Mach's principle it is matter that generates geometry of space-time, and according to Wheeler's geometrodynamics some configurations of space-time geometry are to be interpreted as its material content. Neither of these philosophies has led to success. In the present paper, we show that there exists an algebraic generalisation of geometry that reconciles, in a sense, these two seemingly opposite standpoints. The geometry is constructed with the help of a noncommutative algebra of smooth functions on a groupoid and its derivations. The groupoid in question has a nice physical interpretation: it can be regarded as a space of Lorentz rotations. In this way, Lorentz symmetries are inherent to the generalised geometry of space-time. We define the action for this geometry and, by varying it, obtain generalised vacuum Einstein equations (for a simplified model). It turns out that these equations contain additional terms (with respect to the standard vacuum Einstein equations) which are naturally interpreted as the components of the energy-momentum tensor. Matter is thus created out of purely geometric degrees of freedom. We find two exact solutions (for even more simplified case). We argue that the creation of matter, being a global effect, makes the contrast between Mach and Wheeler philosophies ineffective.