# Principle of least decoherence for Newtonian semi-classical gravity

## TL;DR

This paper introduces a principle of least decoherence to select a unique semi-classical gravity model in the Newtonian regime, aligning with Penrose's spontaneous decoherence proposal and highlighting potential new phenomena at submillimeter scales.

## Contribution

It proposes a principle of least decoherence to uniquely determine semi-classical gravity models, connecting them to Penrose's spontaneous decoherence and collapse theories.

## Key findings

- The resulting model matches Penrose's gravity-related spontaneous decoherence.
- The principle of least decoherence selects a unique model among many.
- Potential new phenomena are suggested at submillimeter gravity scales.

## Abstract

Recent works have proved that semi-classical theories of gravity needed not be fundamentally inconsistent, at least in the Newtonian regime. Using the machinery of continuous measurement theory and feedback, it was shown that one could construct well behaved models of hybrid quantum-classical dynamics at the price of an imposed (non unique) decoherence structure. We introduce a principle of least decoherence (PLD) which allows to naturally single out a unique model from all the available options; up to some unspecified short distance regularization scale. Interestingly, the resulting model is found to coincide with the old --erstwhile only heuristically motivated-- proposal of Penrose and one of us for gravity-related spontaneous decoherence and collapse. Finally, this letter suggests that it is in the submillimeter behavior of gravity that new phenomena might be found.