Waves and currents: Hawking radiation in the hydraulics laboratory?

ABSTRACT: This paper discusses experiments performed to test an analogy between Hawking radiation (the process by which black holes radiate energy) and the propagation of water waves against an adverse current. A streamlined obstacle was placed in a flume to create a region of high velocity. Long waves generated downstream of the obstacle were blocked by this region and converted to a pair of short waves. The group velocities of both the converted waves were downstream, but one of the converted waves retained an upstream phase velocity, whereas the other had a downstream phase velocity. These waves are shown to be analogous to Hawking radiation.