Gravity waves hunting in quest to better understand the universe(Forwarded)

News Service
Cornell University
Ithaca, New York

Media Contact:
Susan S. Lang, Cornell News Service
(607) 255-3613

April 14, 2006

Eanna Flanagan hunts down gravity waves -- ripples in 'spacetime' -- in
quest to better understand the universe

By Thomas Oberst

Gravity is a familiar force. It's the reason for fear of heights. It
holds the moon to the Earth, the Earth to the sun. It keeps beer from
floating out of our glasses.

But how? Is the Earth sending secret messages to the moon?

Well, yes -- sort of.

Eanna Flanagan, Cornell associate professor of physics and astronomy,
has devoted his life to understanding gravity since he was a student at
University College Dublin in his native Ireland. Now, nearly two decades
after leaving Ireland to study for his doctorate under the famous
relativist Kip Thorne at the California Institute of Technology, his
work focuses on predicting the size and shape of gravitational waves --
an elusive phenomenon forecast by Einstein's 1916 Theory of General
Relativity but which have never been directly detected.

In 1974, Princeton University astronomers Russell Hulse and Joseph H.
Taylor Jr. indirectly measured the influence of gravity waves on
co-orbiting neutron stars, a discovery that earned them the 1993 Nobel
Prize in physics. Thanks to the recent work of Flanagan and his
colleagues, scientists are now on the verge of seeing the first gravity
waves directly.

Sound cannot exist in a vacuum. It requires a medium, such as air or
water, through which to deliver its message. Similarly, gravity cannot
exist in nothingness. It, too, needs a medium through which to deliver
its message. Einstein theorized that that medium is space and time, or
the "spacetime fabric."

Changes in pressure -- a thump on a drum, a vibrating vocal cord --
produce sound waves, ripples in air. According to Einstein's theory,
changes in mass -- the collision of two stars, dust landing on a
bookshelf -- produce gravity waves, ripples in spacetime.

Because most everyday objects have mass, gravity waves should be all
around us. So why can't we find any?

"The strongest gravity waves will cause measurable disturbances on Earth
1,000 times smaller than an atomic nucleus," explained Flanagan.
"Detecting them is a huge technical challenge."

The response to that challenge is LIGO, the Laser Interferometer
Gravitational-Wave Observatory, a colossal experiment involving a
collaboration of more than 300 scientists.

LIGO consists of two installations nearly 2,000 miles apart -- one in
Hanford, Wash., and one in Livingston, La. Each facility is shaped like
a giant "L," with two 2.5-mile-long arms made of 4-foot-diameter vacuum
pipes encased in concrete. Ultra-stable laser beams traverse the pipes,
bouncing between mirrors at the end of each arm. Scientists expect a
passing gravity wave to stretch one arm and squeeze the other, causing
the two lasers to travel slightly different distances.

The difference can then be measured by "interfering" the lasers where
the arms intersect. It is comparable to two cars speeding
perpendicularly toward a crossroads. If they travel the same speed and
distance, they will always crash. But if the distances are different,
they might miss. Flanagan and his colleagues are hoping for a miss.

Furthermore, exactly how much the lasers hit or miss will provide
information about the characteristics and origin of the gravitational
wave. Flanagan's role is to predict these characteristics so that his
colleagues at LIGO know what to look for.

Due to technological limits, LIGO is only capable of sensing
gravitational waves of certain frequencies from powerful sources,
including supernova explosions in the Milky Way and rapidly spinning or
co-orbiting neutron stars in either the Milky Way or distant galaxies.

To expand potential sources, NASA and the European Space Agency are
already planning LIGO's successor, LISA, the Laser Interferometer Space
Antenna. LISA is similar in concept to LIGO, except the lasers will
bounce among three satellites 3 million miles apart trailing the Earth
in orbit around the sun. As a result, LISA will be able to detect waves
at lower frequencies than LIGO, such as those produced by the collision
of a neutron star with a black hole or the collision of two black holes.
LISA is scheduled for launch in 2015.

Flanagan and collaborators at the Massachusetts Institute of Technology
recently deciphered the gravitational wave signature that results when a
supermassive black hole swallows a sun-sized neutron star. It is a
signature that will be important for LISA to recognize.

"When LISA flies we should see hundreds of these things," noted
Flanagan. "We will be able to measure how space and time are warped, and
how space is supposed to be twisted around by a black hole. We see
electromagnetic radiation, and we think it's probably a black hole --
but that's about as far as we've got. It will be very exciting to
finally see that relativity actually works."

But, he warned, "It may not work. Astronomers observe that the expansion
of the universe is accelerating. One explanation is that general
relativity needs to be modified: Einstein was mostly right, but in some
regimes things could work differently."

[Graduate student Thomas Oberst is a science writer intern at the
Cornell News Service.]

Related Information:

* Eanna Flanagan's Web site
http://www.astro.cornell.edu/people/...php?pers_id=99

IMAGE CAPTION:
[http://www.news.cornell.edu/stories/.../blackhole.jpg (4KB)]
A representation of how space is distorted by a small black hole in
orbit around a large black hole. This is the type of event that the
space-based gravitational wave detector, LISA (for Laser Interferometer
Space Antenna), hopes to detect. Copyright © Eanna Flanagan/Cornell
University