archive: SETI [ASTRO] LSU Researchers Try To Catch A Gravity Wave

SETI [ASTRO] LSU Researchers Try To Catch A Gravity Wave

Larry Klaes ( lklaes@bbn.com )
Thu, 06 May 1999 15:24:11 -0400

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>Date: Thu, 6 May 1999 15:23:09 GMT
>From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>To: astro@lists.mindspring.com
>Subject: [ASTRO] LSU Researchers Try To Catch A Gravity Wave
>Sender: owner-astro@brickbat12.mindspring.com
>Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>
>News Service
>University Relations
>Louisiana State University
>Baton Rouge, LA 70803
>Phone: 225.388.8654 Fax: 225.388.3860
>
>News contact:
>Kristine Calogne, LSU News Service
>225 388-5985, kcalong@lsuvm.sncc.lsu.edu
>
>05/04/99
>
>LSU Researchers Try To Catch A Wave: LIGO Leading The Worldwide Search For
>Gravitational Waves
>
>They have never been seen. They have never been felt or measured. Their
>existence is nothing more than an educated guess. But two LSU researchers
>believe so strongly that they're out there, they have devoted their lives to
>catching a wave.
>
>A gravitational wave, that is.
>
>William Hamilton and Warren Johnson of the LSU physics and astronomy
department
>have been leading the nation for more than a decade in gravitational-wave
>detection technology. What began as one of Hamilton's early
gravitational-wave
>experiments nearly 30 years ago has evolved into LIGO -- a Laser
Interferometer
>Gravitational-Wave Observatory -- and has the eyes of the world's scientific
>community focused on LSU's researchers and their collaborators from MIT
and the
>California Institute of Technology.
>
>Located on a two-and-a-half-mile tract of land in Livingston Parish, LIGO
will
>house one of only two laser interferometers in the country and a handful
in the
>world. A laser interferometer is an elaborate light-beam and mirror system
that
>is used to detect gravitational waves. The $380-million project is funded
>primarily through the National Science Foundation and will be fully
operational
>by 2001. The goal is simple. Prove that gravitational waves exist.
>
>The existence of gravitational waves was predicted by Albert Einstein in
1915,
>but their effects have never been seen. Scientists believe gravitational
waves
>are the transmission of energy through the gravitational field, just as light
>and radio waves are the transmission of energy through the electromagnetic
>field. Theory states that gravitational waves send out vibrations that cause
>time and space to warp, slightly changing the distance between stationary
>objects. Proving their existence would enable scientists to better
understand such
>phenomena as the supernova, or the explosion of a star after it has used
up its
>fuel. Johnson said gravity is the engine that powers supernovas. Detecting
>gravitational waves could also prove the existence of black holes --
>concentrations of mass that are so great that the resulting gravitational
force
>is too powerful to let light escape.
>
>LIGO will gauge gravitational vibrations by measuring changes in the
distances
>between mirrors that hang from wires like pendulums two-and-a-half miles
apart.
>The interferometer is made up of a laser, a light-beam splitter, a group of
>mirrors and a light detector. The laser-light beam is first sent through the
>beam splitter, where it is divided into two beams. Those beams are then
bounced
>back and forth between four strategically placed mirrors. If the mirrors are
>spaced properly, the light reflections from two of the mirrors will cancel
out
>the reflections from the other two mirrors. Light is sent into the mirrors
but
>does not reflect back out. This is called "operating at a dark fringe."
>
>However, if gravitational-wave vibrations cause the distances between the
>mirrors to shift ever so slightly, the light will not be canceled out or
>interfered with and will reflect back out of the mirrors. The intensity of
that
>reflected light can be measured by the light detector to show the changes in
>distance. Johnson said changes in distance caused by gravitational waves
would
>be incredibly small -- less than 1/1,000 of the diameter of a proton.
Therefore,
>the larger the distance between the mirrors, the larger the fractional
change in
>that distance will be and the easier it will be to measure that change.
>Two-and-a-half miles is thought to be the optimum distance for performing
the experiment.
>
>The idea for the laser interferometer began in 1970 when Hamilton -- then a
>newly hired associate professor of physics at LSU -- developed an instrument
>that could detect the elusive gravitational wave. The instrument, which he
calls
>a "bar detector," is a 10-foot-long aluminum bar, measuring 2 feet in
diameter
>and weighing 5,000 pounds. The bar, like all solid objects, is made up of
atoms
>that are constantly jiggling because of normal movements and vibrations. If
>gravitational waves exist, they will also create vibrations that will
jiggle the
>atoms in the bar and actually change the length of the bar minutely. In other
>words, gravitational energy would alter the physical structure of the bar.
>
>The tricky part, though, is isolating the bar to cut down on normal
vibrations.
>Much of Hamilton's and Johnson's work over the years has been to devise a
way to
>hang the bar from its middle by a special cable that is supported from
above by
>steel and rubber. In addition, the scientists keep the bar cooled to 4
degrees
>above absolute zero, since normal vibrations increase with the temperature.
>
>Once Hamilton and Johnson invented a way to hang the bar, they had to come up
>with a super-sensitive means of measuring it for changes. Several years
ago an
>LSU graduate student, Norbert Solomonson of Tacoma, Wash., solved the
dilemma by
>building an accelerometer -- a device that measures the acceleration of the
>atoms in the bar, thereby detecting minute changes in its length that
could be
>caused by gravitational waves.
>
>Hamilton said that, from the beginning, student involvement in the project
was
>crucial. When he began the experiment in 1970, he set up a laboratory with
four
>LSU freshmen helping him. Since then, he has worked with numerous other
>undergraduate, graduate and post-doctoral students. Hamilton said one of the
>most interesting aspects of his work is that everybody participating in the
>experiment is always learning.
>
>"People tend to identify teaching with someone standing in front of a
classroom,
>but the great thing about a university is that a lot of teaching goes on in a
>completely different setting," Hamilton said. "I would not have guessed that
>this project would have taken so many years, but an awful lot of students
have
>worked on this and received their degrees."
>
>The laser interferometer concept, developed by researchers at MIT and the
>California Institute of Technology, takes the bar-detector technology a step
>farther. With the help of LSU Chancellor Emeritus James Wharton and the
>Livingston Parish Economic Development Council, Johnson obtained the land in
>Livingston Parish for LSU and submitted one of 18 site proposals to the LIGO
>national board. Two sites were chosen -- the Livingston site and another in
>Hanford, Wash. Each location will have a wave-detection observatory and will
>compare results to ensure correct findings. MIT researcher Joseph Giaime, who
>will join the LSU physics faculty in August, will have a major role in
building
>the interferometer, and Hamilton and Johnson will serve as advisers to the
>project. California Institute of Technology professor Mark Coles, an adjunct
>professor of physics at LSU, will run the observatory. Before the advent
of the
>laser interferometer, Hamilton's aluminum bar was considered the best
>gravitational-wave detector in the world.
>
>LSU's bar detector is the only one in America, although Stanford
University had
>one briefly, but it was destroyed in the 1989 San Francisco "World Series"
>earthquake and was never rebuilt. The only other bar detectors in the
world are
>in Italy, where several university groups have been exchanging information
with
>Hamilton and Johnson for years, and in Perth, Australia, where one of
Hamilton's
>post-doctoral students from LSU has carried on the work.
>
>In spite of all this technology, gravitational waves remain just a concept.
>Johnson said LIGO is important because the more advanced equipment has a
better
>chance of detecting waves. But he admits that, although the scientific
community
>believes gravitational waves exist, it is possible that they don't. But the
>gamble doesn't dissuade the researchers.
>
>"There are two ways to do science," Johnson said. "You can experiment on
readily
>accessible things, or work on some long-term project like this one. We got
into
>this because the scientific payoff -- if we succeed -- is so great that it's
>worth spending our whole careers on it," Johnson said of himself and
Hamilton.
>"If we don't find anything, it will be disappointing, but there's no way to
>discover things like this without spending many years developing the
technology.
>It's worth it to me -- I don't have any regrets."
>
>Johnson said developing the bar detector has been fascinating in itself,
and the
>team has conducted numerous experiments with the bar to prove that it is a
>capable detector. Although the laser interferometer's improved sensitivity
may
>soon prove the bar detector obsolete, both Johnson and Hamilton said they
will
>continue to work with the bar, at least for a while, because LSU will be the
>only place in the world to have both a laser interferometer and a bar
detector
>-- a unique situation that will allow for some experiments and comparisons
that
>cannot be done elsewhere. Also, the bar detector is their baby.
>
>"The personal payoff is knowing that we really can build this boat," Johnson
>said. "Whether there's a new world on the other side of the ocean, we don't
>know, but we're going to sail anyway. The journey alone is enough for me.
That's success."
>
>