# A cosmic shadow on CSL

## TL;DR

This paper examines the CSL model's application to cosmology, revealing that natural density choices conflict with current cosmic microwave background measurements and laboratory experiments.

## Contribution

It demonstrates the incompatibility of the CSL model with cosmological observations when applying natural density contrasts.

## Key findings

- Most natural density contrasts conflict with CMB data
- Laboratory experiments further constrain CSL parameters
- Cosmological application of CSL faces significant challenges

## Abstract

The Continuous Spontaneous Localisation (CSL) model solves the measurement problem of standard quantum mechanics, by coupling the mass density of a quantum system to a white-noise field. Since the mass density is not uniquely defined in general relativity, this model is ambiguous when applied to cosmology. We however show that most natural choices of the density contrast already make current measurements of the cosmic microwave background incompatible with other laboratory experiments.