Observation of negative-frequency waves in a water tank: A classical analogue to the Hawking effect?

TL;DR

This paper reports the first direct observation of negative-frequency wave conversion in a water tank, serving as a classical analogue to black hole Hawking radiation, with higher-than-expected mode conversion.

Contribution

It provides experimental evidence of negative-frequency wave conversion in a water tank, illustrating a classical analogue to Hawking radiation.

Findings

Observed significant mode conversion from positive to negative frequencies

Higher conversion degree than theoretical predictions

Demonstrates water tank as an effective analogue for black hole horizons

Abstract

The conversion of positive-frequency waves into negative-frequency waves at the event horizon is the mechanism at the heart of the Hawking radiation of black holes. In black-hole analogues, horizons are formed for waves propagating in a medium against the current when and where the flow exceeds the wave velocity. We report on the first direct observation of negative-frequency waves converted from positive-frequency waves in a moving medium. The measured degree of mode conversion is significantly higher than expected from theory.