A recipe for creating an optical black hole could soon be coming to a laboratory near you. Don't worry, it won't be sucking anything important into itself, except some slow-moving light and the curiosity of physicists.
The notion of creating an optical black hole, which could then be used to study the real thing and also perhaps answer other vexing theoretical questions, arose when Ulf Leonhardt put on his thinking cap and combined some old ideas with some new ones.
Leonhardt, of the Royal Institute of Technology in Sweden and at the University of St. Andrews in Scotland, worked with colleague Paul Piwnicki to develop the recipe.
A paper on the idea appears in the January 31 issue of the journal Physical Review Letters.
The researchers started with a theory, dating back to 1818, which says the effective speed of light is dragged down when it moves through a flowing medium, such as water. The change in effective velocity, however, is nearly inconsequential compared to the light's incredible speed. (Scientists already knew, by the way, that light moves more slowly through air and water than it does through a vacuum.)
More recent research, done last year, showed that a certain, extremely cold substance called a Bose-Einstein condensate, is able to slow the speed of light to less than that of a law-abiding motorist on the freeway.
Putting two ideas together
If a sufficiently rapid swirl of the Bose-Einstein condensate or similar material could be created, Leonhardt suggests, light inside the fluid could become trapped into the inescapable grip of the vortex, much like matter is thought to be trapped by a black hole in space.
"When the flow reaches the speed of light in the medium, the light will begin to loose maneuverability," Leonhardt said. "Similarly to fish swimming in a rapid stream that flows faster than the top speed of the fish, light is irresistibly carried away and spirals towards the vortex singularity. At a certain point, a return is not possible anymore."
This point of no return is what theorists call the event horizon.
Leonhardt says optical black holes created in the lab could be used to gain a better understanding of the general theory of relativity and the theory of quantum gravity. They might also be used to study Hawking radiation -- hypothetical emissions from evaporating black holes that are nearly impossible to observe because they are obscured by background radiation in the cosmos.
Leonhardt estimated the process, now only a theory, might be doable in five years or so.
Another group of researchers, led by Ignacio Cirac at Austria's University of Innsbruck, is working on creating a sonic black hole, whereby sound waves are trapped in certain areas of a moving fluid.
"Hopefully we can learn something about gravitational black holes, which cannot be created in the lab, by making experiments with optical or sonic black holes," Cirac said. "In fact, the equations describing the sound waves in a fluid are the same as the ones describing light propagation in a gravitational field."
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