Scientists propose lab-grade black holes

One day, scientists may create the ultimate tempest in a teapot — an artificial black hole in a millimeter-long gadget. Such laboratory-grade black holes may illuminate enigmatic physical properties of their wild galactic counterparts, all from the safety of a lab bench, a study to appear in Physical Review Letters suggests.

“For black holes, we just don’t understand the physics at all,” says physicist William Unruh of the University of British Columbia in Vancouver, Canada, who was not involved in the new study. The prospect of conducting actual experiments on systems resembling black holes is exciting, he says. “Belief is not the same as doing an experiment.”

Mysterious black holes were originally thought to gobble up everything around them, including light (hence the name). But in the 1970s, British physicist Stephen Hawking predicted that because of quantum effects, these voracious monsters should emit photons. Right on the brink of the black hole, these photons “are so energetic that they go beyond what we understand,” says study coauthor Miles Blencowe of Dartmouth College in Hanover, N.H. Such emitted photons, known as Hawking radiation, have not yet been caught in the wild, nor have they been simulated in an experiment, leaving knowledge of their basic properties — and existence — in limbo.

In the new study, the researchers propose using a series of tiny, cold superconducting devices called SQUIDs in a linear, train-track–shaped arrangement to create a black hole analog. “But unlike a black hole out in space, we know the physics of this system,” says study coauthor Paul Nation, also of Dartmouth College.

Particles inside a black hole’s boundary, called the horizon, get sucked into the depths of the black hole, while particles outside the horizon can escape. Blencowe likens the horizon to a steep waterfall, where a fish above the drop can swim at normal speeds, but once a fish hits the fast-flowing water in the waterfall, it is swept down into the water below.

Similarly, the proposed system also creates a horizon, in the form of an electromagnetic wave that moves across the device in response to a magnetic pulse. Photons behind this horizon are trapped, while photons ahead of it move normally. By detecting and studying the photons that emerge from the device, researchers hope to have a better idea of what happens to particles near the edge of a black hole, both those that escape and those that are pulled in.

Changing the strength of the horizon-creating magnetic pulse may create conditions that fluctuate, making a system that simulates “shaking spacetime,” Nation says. Watching how photons behave in such a quantum system may answer some basic questions about the quantum nature of gravity, he says.

Building the new system has many challenges. “All of these experiments have a long way to go before they’ll deliver their promise,” comments Unruh, who has proposed a black hole analog that relies on sound waves.

Nation says that stringing together the 4,000 or so SQUIDs needed to create the artificial black hole would be a difficult endeavor. The largest string built so far is only 400 units long. Another hurdle to creating this system is designing a detector sensitive enough to catch single photons that would have a frequency much lower than that of visible light. “People are close to making a detector, but technically, it hasn’t been done,” says Nation.

Web edition : Thursday, August 13th, 2009


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