Objective collapse models and their experimental tests

4 problems

• Bounds on colored and dissipative collapse models

  Open

  If the collapse noise has a 'color' (it stops above some frequency) or the collapse loses energy to a finite effective temperature, the X-ray bounds weaken greatly. Low-frequency tests with heavy oscillators then become the main probes.

• Test of gravity-related collapse in the Diosi-Penrose model

  Partially resolved

  Penrose proposed that a mass in a superposition of two places decays in a time of about $\hbar$ divided by the gravitational energy of the difference between the two mass arrangements. Detecting or excluding this needs massive superpositions or very quiet detectors.

• Does any parameter window of white-noise CSL remain viable?

  Partially resolved

  The best-studied collapse model, continuous spontaneous localization (CSL), has two numbers: how often collapse happens and over what distance. In 2025 a dark-matter detector excluded the originally proposed values; the question is whether any values remain that still collapse visible objects fast enough.

• A Lorentz-covariant collapse model for interacting quantum fields

  Partially resolved

  Collapse models are written for slow particles. Versions consistent with special relativity exist for a fixed number of distinguishable particles, but not for quantum fields, where particles are created and destroyed and continuous-collapse versions produce unlimited energy.