Build a white hole in your kitchen sink

A white hole is the opposite of a black hole in that matter can only come out of a white hole and never penetrate it’s event horizon from the outside. It turns out that you can make a simple hydrodynamic analogy in your sink with exactly the same mathematical description as a white hole. Experimenters have shown for the first time that this truly is a white hole in the sense that nothing can penetrate from the outside.

You can make a white hole, the reverse of a black hole, in your kitchen sink. The needle in this picture is creating a Mach cone downstream of it.

You can make a white hole, the reverse of a black hole, in your kitchen sink. The needle in this picture is creating a Mach cone downstream of it.

To make a white hole in your sink all you need to do is run water at a high enough speed that it carves out a circle around where it hits the sink. The circle is a shockwave where water from the outside is moving too slowly to be able to penetrate any further upstream.

In the photo, there is a needle stuck into the stream, showing what is called a Mach cone. Mach cones form behind anything moving at supersonic speeds, and it is the Mach cone hitting you that you hear as a sonic boom when a supersonic plane flies overhead.

One of the predictions about a white hole is that Mach cones should form around objects inside the hole with the angle of the Mach cone getting greater until you get to the very edge where it forms a right angle. Testing these angles is the process the experimenters used to show that the white hole analogy holds up exactly.

As the needle is placed further out, the Mach cones get wider until the reach a right angle at the event horizon and then disappear outside the event horizon.

As the needle is placed further out, the Mach cones get wider until the reach a right angle at the event horizon and then disappear outside the event horizon.

In this series of images, the needle is placed at different distances out from the source of water and you can see the angle getting larger as it moves toward the boundary and then outside the boundary there is no Mach cone, as predicted.

Knowing that the mathematics and properties of white holes really do stand up, it seems that these hydrodynamic systems could be more useful than previously thought in understanding the behavior of black holes, which are just white holes run in reverse.

Ref: Phys. Rev. E 83, 056312 (2011)

Posted May 13th, 2011 in Uncategorized.

2 comments:

  1. RD Padouk:

    This is excellent – one of the most elegant home experiments I have ever seen. The “white-hole” concept also reminds me of the “negative pressure” rooms they use in hospitals for those very susceptible to airborne illness.

  2. Josh:

    A very nice experiment indeed. However, the description in the blog (which was correct in the paper) with the accompanying picture is misleading – when the fluid speed equals the speed of sound, the opening angle (2theta) should be 180degrees (hence theta=90degrees).

    What happens is that the opening angle in figure b will continue to expand up to 180degrees at the boundary (the authors probably didn’t choose this photo as it would be see in the presence of the jump, but they do measure it in the paper).

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