Microscopic Origin for the Apparent Uncertainty Principle Governing the Anomalous Attenuation of Third Sound

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Abstract
A macroscopic uncertainty principle has been invoked as an explanation for the anomalously high attenuation of third sound in certain thickness regimes of liquid-He films. The propagation criterion deduced from this idea appears to be in accord with experiment. We outline here a microscopic mechanism which gives rise to a large attenuation and which yields a propagation criterion essentially equivalent to the one proposed as a macroscopic uncertainty principle. We find that the nonlinearities inherent in the problem play the significant role in producing this attenuation.