Desktop Black Hole Possibly on the Horizon

Date:23 January 2001

Two teams of scientists recently announced they can bring light to a halt, and that finding may speed up little-known efforts to create a desktop black hole.

What was little more than a distant dream a week ago -- an experiment to create a laboratory system that simulates the physics of a black hole -- might now be done within five years, says one researcher. Others, while excited about the implications of the new work, are skeptical about applying it to the study of one of nature's most enigmatic objects.Strictly speaking, black holes are only theoretical, but experts are nearly certain they exist. Nothing else accurately describes the observed effects of gravity on matter and energy that surround suspected black holes.

But it's hard to examine what you can't see.

Hiding the evidence

A black hole's immense gravity accelerates nearby matter and energy, which spirals inward and eventually reaches the speed of light. At that speed, the incoming stuff crosses a so-called "event horizon," a sphere beyond which events cannot be seen because nothing, not even light, comes back out.

It's as though a hole were punched in the very fabric of space and time.So researchers are left to pick at the bones of information that swirl around the edges of suspected black holes. In the lab, it's even tougher.

"Doing experiments with real gravity is extremely difficult," says Matt Visser, a black hole theorist at Washington University in Saint Louis. "And doing experiments with real black holes is possibly inadvisable."

So Visser and some colleagues, along with a handful of other groups, have been working to create what they call an "analog" to a black hole. Such a desktop experiment would trap light in a vortex and replicate at least some of the behavior of a real black hole -- without all the matter-gobbling density and its attendant danger.

Seeing the light

The ability to control light is a key. And two research groups have just mastered that seemingly impossible task by creating what they describe as optical molasses.

Both groups, working separately with slightly varied techniques, used atoms in a chilled gas to trap light, store it briefly and then release it again. Information about the light was imprinted on the atoms and iced for up to a millisecond -- an eternity in the world of light-speed. Then, using a special laser, the information was reassembled and the light continued on its way.

Physicists called the work a significant step toward a greater understanding of the properties of light. Practical applications, including faster computing, could still be years away.

Meanwhile, Visser said the experiments make desktop black holes that much more attainable.

"The stopping of light is an extremely helpful step towards building analog black holes," Visser told SPACE.com. Before last week's announcement he would have put the time frame for creating one at five to 10 years, but "now I'd say less than five years."

Visser cautioned that remaining technological hurdles are "highly nontrivial." And if a simple analog black hole is developed, it could take a few more years to develop a sophisticated version that would answer a broader range of questions.

And the questions are huge.

Lots to learn

Theorists expect that the normal laws of nature, described by Einstein's theory of relativity, break down inside a black hole.

Once inside the event horizon, for example, nothing can prevent matter and energy from collapsing. So everything inside a black hole is reduced to a singular point in time and space -- a point of infinite density. No one knows for sure what goes on in a world where space and time are turned to mush.

Einstein's theory also does not explain the quantum world, a place ruled by the smallest particles -- atoms and even more basic units from which they are made.

Possible answers

Another researcher said Friday that desktop black holes, sometimes called optical or sonic black holes, could help resolve some of the longstanding puzzles in physics.

"The aim of these experiments would be to study the quantum properties of light or sound in these artificial black holes," said Ulf Leonhardt of the University of St. Andrews. "The observations from such experiments could help to resolve some of the conflict between general relativity and quantum theory."

Leonhardt has been working with colleague Paul Piwnicki for years to develop a recipe for a desktop black hole. They published their idea a year ago in the journal Physical Review Letters. At the time, they said it might be five years before they could turn the idea into a working model.

The scheme is similar to the work announced last week, in which light was frozen in its tracks, but with a twist.

Leonhardt would not need to stop light cold, but rather get it moving slower than a special vapor through which the light passes.

Get a sufficiently rapid swirl of material going, Leonhardt figures, and 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.

Leonhardt likens the idea to fish approaching a waterfall.

"The flow of the stream increases the closer [they get] to the waterfall," he explains. "A point is reached where the flow of the stream is faster than the speed at which…fish can swim. The fish become trapped in the flow and can move only in one direction -- they have no chance of escape."

No simple task

Michael Fleischhauer, a theoretical physicist at the University of Kaiserslautern, Germany, worked with a team from Harvard-Smithsonian Institute for Astrophysics to bring light to a halt in one of the studies announced last week.

"Light in moving media has some very interesting formal similarities with general relativity," Fleischhauer told SPACE.com. "The study of the former will certainly help our understanding of the latter."

But Fleischhauer was not sure that the present technique can be used to create an optical black hole.

As far as the recent experiments are concerned, Mikhail Lukin of the Harvard-Smithsonian Center for Astrophysics said, "Unfortunately, the technique we described and demonstrated will probably have no implications for relativity and black hole studies."

Visser, the Washington University theorist, does emphasize that laboratory black holes would not function identically to the real variety, as predicted by relativity. Instead, they would only be analogous to real black holes but would, if all goes well, simulate some of their properties.

"The stopping of light tells us that we can make light arbitrarily slow," says Visser, "which means that even a little bit of flow in the gaseous fluid used in the [recent light-stopping] experiments should be enough to set up an 'analog horizon.'"

Visser has an additional caution: No one knows how much will actually be revealed by a desktop black hole.

"The main issue will be just how much of the physics of real black holes can be replicated by these analog systems," Visser said. "The more exact the analogy, the more excited the general relativity community will be."