Black holes not black after all (Forwarded)

Press Office
University of St Andrews
St Andrews, Scotland

Contact:
Fiona Armstrong, Press Officer
01334 462530 / 462529

Monday, 12 May 2008

Black holes not black after all

International scientists have used flowing water to simulate a black hole,
testing Stephen Hawking's theory that black holes are not black after all.

The researchers, led by Professor Ulf Leonhardt at the University of St
Andrews and Dr Germain Rousseaux at the University of Nice, used a water
channel to create analogues of black holes, simulating event horizons.

An event horizon is the place in the channel where the water begins to
flow faster than the waves. The scientists sent waves against the current,
varied the water speed and the wavelength, and filmed the waves with video
cameras. Over several months the team painstakingly searched the videos
for clues. They wanted to see whether the waves show signs of Stephen
Hawking's famous prediction that the event horizon creates particles and
anti-particles.

Professor Ulf Leonhardt, from the School of Physics and Astronomy,
explained, "It is probably impossible to observe the Hawking radiation of
black holes in space, but something like the radiation of black holes can
be seen on Earth, even in something as simple as flowing water."

Black holes resemble cosmic drains where space disappears like water going
down a plughole. Space seems to flow, and the closer one gets to the black
hole, the faster it flows. At the event horizon space appears to reach the
speed of light, so nothing, not even light, can escape beyond this point
of no return.

The experiments were carried out at the Genimar laboratory near Nice which
houses a 30-metre-long water channel with a powerful pump on one end and a
wave machine on the other. The normal business of Genimar is testing the
environmental impact of currents and waves on coasts or the hulls of
French submarines, but the scientists turned the machinery to testing
black holes.

The team demonstrated that something as simple and familiar as flowing
water might contain clues of the mysterious and exotic physics of black
holes. In a forthcoming paper in New Journal of Physics, the scientists
report observed traces of "anti-waves" in their videos.

Professor Leonhardt continued, "Flowing water does not create
anti-particles, but it may create anti-waves. Normal waves heave up and
down in the direction they move, whereas anti-waves do the opposite.

"We definitely have observed these negative-frequency waves. These waves
were tiny, but they were still significantly stronger than expected.
However, our experiment does not completely agree with theory and so much
work remains to be done to understand exactly what happens at the event
horizon for water waves."

Images and videos can be downloaded from
http://www.genimar.fr/htmlfr/genimar.html

ENDS

NOTE TO EDITORS:

The researchers are available for interview:

Professor Ulf Leonhardt
University of St Andrews
+44-1334-463115 / +44-777-0701348

Dr Germain Rousseaux
Université de Nice Sophia Antipolis
Research associate at CNRS
+33-4-92-07-60-29 / +33-4-92-07-60-30 / +33-6-74-41-10-58

Andrew Yee wrote:
An event horizon is the place in the channel where the water begins to
flow faster than the waves. The scientists sent waves against the current,
varied the water speed and the wavelength, and filmed the waves with video
cameras. Over several months the team painstakingly searched the videos
for clues. They wanted to see whether the waves show signs of Stephen
Hawking's famous prediction that the event horizon creates particles and
anti-particles.


So these scientists used water flowing down a drain from a bathtub to
pretend ... er,... simulate a black hole? I do that quite often too. :-)

Yousuf Khan