Black hole analog experiment?

Question

This question is directed mostly at people giving lectures on black holes, but input by other physicists or students is very much appreciated.

Do you know a good (home)-experiment with a black hole analog (such as water in a bathtub) that allows to discuss most of the pertinent concepts and features of a black hole?

To clarify what I mean by 'good' let me provide what I consider as a good experiment with a white hole analog (see exercise 2.2 in this exercise sheet), namely a hydraulic jump.

This experiment allows you to discuss in very simple terms what a white hole is (the white hole region is visibly distinct from the exterior because of their different water depths). It is also quite easy to show experimentally that you cannot send information into the white hole (in the form of shallow water wave excitations aka 'ripplons'). Moreover, the white hole exhibits some interesting features in the near horizon region (see the concentric rings in the picture on the back of the exercise sheet). Most importantly, this experiment can be done basically by anyone - there is no need for access to lasers, waveguides, Laval nozzles, supersonic flow etc.

The purpose of the hydraulic jump experiment is to provide a pedagogic introduction to white holes. I would like to have a comparable (non-Gedanken-)experiment available to introduce black holes.

Answer 1

This is a water flow analogy with a black hole. Take a fish tank filled with guppies and put a large drain or siphon in the tank. This opening has to be big enough to set up a decent water flow. When the water starts flowing the fish will generally swim against the current. Assume all the guppies are the same size and generally swim at the same speed.

Then the rate they flow is a vector sum of the water flow and the swimming velocity in the absence of water flow. This will provide a visual model for how photons move in spacetime. The flow of water is a model for the flow of spacetime points. The guppies represent photons (modulo the fact they change direction at will), and the guppies within some approximate radius will tend to be taken up by siphon.

Answer 2

How deep do you want the analogy to go? If you just want some region of a fluid where information cannot escape, all you need to do is pump liquid out of the volume quickly enough that you get fluid flows speeds that exceed the speed of sound in the fluid. I don't know how easy it is to do this and not make the flow completely turbulent, and it would only be an analogy, as a "swimmer" with sufficient strength could overcome the flow, but the basic idea of water signals not being able to escape would be present.