- Water down the Drain Leads to Black Holes in the Lab
Daniel S. Burgess
Archimedes, the famous story goes, cried, "Eureka!" and leapt from his overflowing bathtub, having discovered the principle of buoyancy. But the drain has much to offer, too. Physicists Ulf Leonhardt and Paul Piwnicki of the Royal Institute of Technology suggest in the Jan. 31 issue of Physical Review Letters that vortices or other rapid flows analogous to the swirl of water down the drain may enable researchers to model the relativistic effects of black holes.
Leonhardt explained that, as early as 1818, Augustin-Jean Fresnel predicted from theories of the luminiferous ether that a flowing medium will drag light with it. "For quite a long time we were rather puzzled and could not understand what is happening in moving media if one takes them seriously," said Leonhardt. "Then, suddenly, the picture emerged, and we realized the connection to gravity and curved space-time. This has come as a surprise."
The researchers demonstrated that, if a medium swirls more quickly than the speed of light through it, the vortex it forms can decelerate and trap light in much the same way as a black hole. If they could be created in the lab, these optical black holes would enable physicists to test such controversial concepts as Hawking radiation, the emissions by black holes theorized by Stephen W. Hawking. The problem is that no known materials display superluminal rotation without also forming a hollow core that is larger than the critical optical event horizon.
But recent efforts by Lene Vestergaard Hau of Harvard University in Cambridge, Mass., have dramatically slowed light with Bose-Einstein condensates, and they could produce the 1-cm/s speed limit required by Leonhardt and Piwnicki's model. Leonhardt also suggested that rotating alkali vapor could create a "weak" black hole that only traps light moving against its current, as may other techniques, including the creation of quantum vortices in Bose-Einstein condensates.
"I do not think that an earthly vortex has a realistic chance to become a hard black hole, but other flow patterns might do the job," he said. "One could conceive of using a real drain ... very similar indeed to a bathtub. This would probably help to generate hard black holes or even other interesting creatures of the zoo that general relativity has to offer."
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