There is a mathematical analogy between the propagation of fields in a general relativistic space-time and long (shallow water) surface waves on moving water. Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. Similar arguments predict the same effect near wave horizons in fluid flow. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process.

 

The project is a joint-collaboration between the School of Mathematics at the University of Nottingham (Nottingham, UK) and the University of British Columbia (Vancouver, Canada):
  Silke Weinfurtner (School of Mathematics, University of Nottingham)

  Matt Penrice (ICTP, Trieste, Italy)

 

External collaborators:

  Bill Unruh (Department of Physics & Astronomy, UBC, Vancouver, Canada)

  Greg Lawrence (Department of Civil Engineering, UBC, Vancouver, Canada)

  Ted Tedford (Department of Civil Engineerin, UBC, Vancouver, Canada & ICTP/SISSA, Trieste, Italy)

  

 

 

The results of our experiments, that attest for the first detection of Hawking radiation in a table-top experiment, are published in:

 

 

Popular science articles about our experiments:

 

 

Below you will find a brief description of the effective spacetime, and a summary of our key results obtained so far.

 

Experiments at Civil and Mechanical Engineering Laboratories Building (Rusty Hut),
The University of British Columbia (UBC),
Vancouver,
(Canada).
Classical aspects of Hawking radiation verified in analogue gravity experiment

Hydrodynamic simulation of black hole evaporation process

Drawing of experimental apparatus
Drawing of experimental apparatus

The experimental apparatus used in our experiments: (1) holding reservoir, (2) pump and pump valve, (3) intake reservoir, (4) flume, (5) obstacle, (6) wave generator, and (7) adjustable weir.

Experimental setup from the side
Experimental setup from the side

Ted is adjusting the camera used for the surface wave detection method.

Experimental setup back end of flume
Experimental setup back end of flume

Matt is working on the PC operating our high resolution camera. The red dye (Rhodamine) in combination with our light sheet is used to record the free surface.

Obstacle illuminated by laser light
Obstacle illuminated by laser light

PIV setup: Laser light sheet with tracer particles emerged in water.

Effective horizons. (above) The propagation of for example sound waves in a convergent fluid flow exhibiting sub- and supersonic flow regions are depicted. The dashed (red) black / white lines, separating the sub- and supersonic regions, indicate the location of the acoustic black/white horizon. From the left to the right the flow velocity is speeding up and slowing down again. (left) The blocking of surface waves on the effective white hole horizon can be seen in our video taken from our experimental setup.

Effective horizons
Positive & negative norm modes

Pair-creation process. (left) Hawking predicted the pair-creation of positive and negative 'energy' (more accurately 'norm') particles at the black hole horizon. (right) In our experiment we observed this process at the effective (white hole) horizon. To demonstrate this further, we filtered for the positive (below left) and negative (below right) energy/norm modes. 

positive energy

negative energy

positive energy

negative energy

horizon

effective horizon

Boltzmann spectrum

Thermal hypothesis. Hawking also predicted at the ratio between negative to positive norm modes follows a Boltzmann distribution determined by the surface gravity at the horizon. We plotted on the left the logarithm of the this ratio, and as predicted it is following a Boltzmann distribution. In an independent mesurement we were able to directly measure the effective surface gravity, and it is in agreement with the value of the Boltzmann spectrum (i.e. the slope of the curve presented in the image to the left).