Professor Ulf Leonhardt
University of St Andrews
01334 463115
ulf@st-andrews.ac.uk

Physicists in the UK are planning pioneering experiments to create tiny, artificial black holes in the laboratory which will be able to suck in light or sound waves. The researchers hope that the desk-top black holes will provide important information about the fundamental behaviour of matter and energy and help to resolve some of the apparent contradictions that lie at the heart of theoretical physics.

The foundations for the experiments are currently being developed by Professor Ulf Leonhardt and his team at the University of St Andrews, with funding from the Engineering and Physical Sciences Research Council.

In space a black hole is formed when a star collapses in on itself. Because of its hugely concentrated mass it has an extremely high gravitational pull. To escape from a black hole, matter or energy would need to travel at a velocity greater than that of light "something which is not possible. "This makes a black hole a perfect trap," says Professor Leonhardt.

For physicists black holes are particularly interesting because they meet at the boundary of the two ways of describing the fundamental nature of the Universe: quantum theory, which describes the behaviour of matter and energy at the subatomic level, and relativity, which accounts for the behaviour of matter and energy at the large scale, including gravity. There are apparent conflicts between these two descriptions of Nature and the researchers at St Andrews hope that their experiments could help to open new avenues of investigation to help develop suitable theories for"quantum gravity."

"We believe we may be able to create an experimental system using moving fluids in which it is possible to suck in either light waves or sound waves, similar to a black hole," says Professor Leonhardt. If sound or light waves are introduced into the a fluid that is moving faster than the waves, then it may be possible to trap the waves, creating in effect a small black hole.

"A useful analogy is of fish swimming in a stream that is approaching a waterfall," says Professor Leonhardt. "The flow of the stream increases the closer it gets to the waterfall. A point is reached where the flow of the stream is faster that the speed at which the fish can swim. The fish become trapped in the flow and can move only in one direction " they have no chance of escape"

The trick is to reduce the speed of the waves. "If you take a vapour of certain types of atom at very low temperatures and pass laser light into it, the vapour's properties can become altered. If a second laser light is then shone into the vapour, this light propagates extremely slowly "a matter of only tens of centimetres a second."

This phenomenon, called electromagnetically induced transparency, has been studied closely at St Andrews. "If the vapour can then be made to flow at a rate faster than the velocity of the light waves travelling within it, you then have a situation similar to the fish in the stream," says Professor Leonhardt. "The light could effectively become trapped."

Another possible system could involve a small cloud of atoms being held in a doughnut configuration by a laser beam with a hollow cylindrical section. It is possible to accelerate the atoms at one point in the ring of vapour. At ultra-low temperatures sound waves can be passed into the system. The speed of sound in these conditions is very low, less than that of the moving vapour. This could be a way of creating a "sonic black hole".

"The aim of these experiments would be to study the quantum properties of light or sound in these artificial black holes," says Professor Leonhardt. "The observations from such experiments could help to resolve some of the conflict between general relativity and quantum theory. One or two groups around the world are working on similar systems and it looks as though this could be the start of a new field in physics."

EPSRC reference no: GR/R09534 (physics)

Also see:

http://www.st-and.ac.uk/'www_pa/group/quantumoptics/
Click Light in Moving Media

Home page of Artificial Black Holes
(Analog models of general relativity):
http://www.physics.wustl.edu/'visser/Analog/