Observation of the Thermal Casimir Force is Open to Question

TL;DR

This paper questions the experimental evidence for the thermal Casimir force, arguing that reported observations are inconsistent with existing data and models, and highlighting potential errors and misinterpretations in recent claims.

Contribution

It critically analyzes recent experimental claims of observing the thermal Casimir force, revealing inconsistencies with data and proposing that the plasma model aligns better with measurements.

Findings

Experimental errors are likely underestimated.

Data above 3 μm agree with the plasma model.

Inadequate proximity force approximation explains apparent Drude model agreement.

Abstract

We discuss theoretical predictions for the thermal Casimir force and compare them with available experimental data. Special attention is paid to the recent claim of the observation of that effect, as predicted by the Drude model approach. We show that this claim is in contradiction with a number of experiments reported so far. We suggest that the experimental errors, as reported in support of the observation of the thermal Casimir force, are significantly underestimated. Furthermore, the experimental data at separations above $3\,\mu$m are shown to be in agreement not with the Drude model approach, as is claimed, but with the plasma model. The seeming agreement of the data with the Drude model at separations below $3\,\mu$m is explained by the use of an inadequate formulation of the proximity force approximation.