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A LIGO Lecture for an Evening's Enjoyment

A LIGO Lecture for an Evening's Enjoyment

- Contributed by Dave Beckett

Barry Barish.On select Wednesdays during the school year, the Caltech campus offers a free lecture series on topics of leading-edge research currently underway at the institute. Named for the late Earnest C. Watson, who founded the series in 1922, these presentations are designed to inform interested members of the community about Caltech's works-in-progress. The range of subjects showcased can be as diverse as the institute's array of scientific research. Recent topics have included fuel cell development, plate tectonics, new voting technologies, superconductors, and planetesimals discovered at the rim of our solar system. On the first Wednesday of this past March, the subject on exhibit was the LIGO Laboratory and the speaker was LIGO's Director, Barry Barish.

Seen at right - LIGO Director Barry Barish.

Below - Caltech's Beckman Auditorium, scene of the Watson Lecture Series.

Barry Barish. The Watson Lecture Series is staged in the great 1100-seat rotunda of Caltech's Beckman Auditorium. This building, affectionately known as the "the giant wedding-cake" by campus pundits, lies at the edge of an inviting stretch of well-kept green lawn. Stout buildings border the grass on both long sides, creating an outdoor-amphitheater effect. This is the main approach to the Beckman Auditorium. On chilly autumn nights, there is a stillness and hush that settle in here, making you forget you're in the midst of a bustling city, in a school that never sleeps. On lecture evenings, the oval building and the cement steps leading to it are drenched by white spotlights, igniting a luminous beacon in the darkness. Nearby streets are clogged with arriving autos. Signs posted outside three-tier parking structures announce "Space Available" or the temper-triggering "Lot Full." Bicyclists and hurried pedestrians swerve to avoid each other's path. The audience is hastily assembling, in their jeans and their tee-shirts, in their dresses and their sports coats. Inside the building, cheerful ushers in uniform escort guests to their seats. People crane their necks this way and that to see who else is present, and a lively hubbub fills the theater. At 8:00pm sharp, the lights dim, the chatter subsides, and the speaker approaches the podium.

Barry Barish began his LIGO presentation with a brief overview of gravitational physics from Newton to Einstein. The tremendous achievements of Isaac Newton in mathematics and astronomy answered most of the questions then confronting 17th Century natural philosophers. His narrative on celestial mechanics stood as the dominant paradigm for our understanding of cosmology for hundreds of years. But telescopes of ever-increasing sensitivity began to find the subtlest flaws in this account. In particular it was revealed that the orbit of planet Mercury deviated minutely from the course predicted by Newton's theory. The discrepancy left observers baffled.

Along came a humble clerk from the patent office in Bern, Switzerland. In the opening years of the 20th Century, Albert Einstein completed an astonishing body of work in theoretical physics that would produce the first modification in centuries to Newton's mighty edifice--and eventually come to revolutionize our entire understanding of the universe. Einstein's General Theory of Relativity replaced the straight lines and Euclidean geometry of Newton's Universe with curved space, rolling paths, and arcs of light--warps all caused by the massive objects nestled in the fabric of space.

A corollary of Einstein's theory was the concept of gravitational waves. Any mass in space would produce curvature--the more mass, the more warp and the stronger the tug of its gravity. Soon Einstein reasoned that accelerating masses would produce so-called "gravitational waves," oscillating warps or "ripples" in the very fabric of space-time that broadcast outwards from their source at light speed. Infinitesimal in their long-range effects, these hypothesized waves were judged in Einstein's day as too weak ever to be measured. But in 1974, two radio astronomers, Russell Hulse and Joseph Taylor, discovered some potent evidence while studying the binary pulsar system PSR 1913+16. The two neutron stars in this system have been observed to be slowly spiraling inward toward union, a stellar embrace, and Hulse and Taylor have furnished calculations of stunning precision to show that the rate of the stars' orbital decay neatly coincide with the emission of gravitational waves predicted by general relativity.

On the Beckman Auditorium stage, Barry Barish sat on the edge of a stool beside the podium, controlling the tempo of his slide-show presentation via keystrokes on a laptop computer. Having demonstrated the theory of gravitational waves, and offered some indirect evidence for their existence, he now announced the mission of the LIGO Laboratory: direct detection of these elusive waves and, by extension, fresh insights into the origin and composition of physical reality.

In what amounts to a global dragnet, the twin installations of the LIGO Laboratory, along with its partner observatories dotted across the earth, will work in tandem to seek out, capture and bring back these ripples to the laboratory for investigation. The Japanese gravitational-wave project, dubbed TAMA, was the first in operation. Two observatories in Western Europe, the Italian VIRGO project and the German/UK GEO 600 interferometer, are quickly heading toward completion. Another installation in Western Australia, AIGO, has finished construction. Plans are underway for the assembly of LISA, the space-borne Laser Interferometer Space Antenna, scheduled to begin operating in the next decade. And the LIGO Laboratory recently concluded its second Science Run, an event which established new limits on the scientific reach of a gravitational-wave interferometer.

Barish then provided some detailed descriptions of the LIGO instruments: how they work, their configuration and component parts, as well as charts mapping the interferometers' steadily-growing sensitivity. He next cited some of the dynamic stellar phenomena expected to be powerful sources of gravitational waves: supernovae, spinning binary pulsars, and binary neutron systems approaching coalescence. Here Barish explained that when the LIGO apparatus makes contact with one of these latter sources, the equipment is designed to translate its ripples into an audible signal for the benefit of the human monitor. This signal, said Barish, will sound something like a chirp, and he tapped a key on his laptop computer. A small blue speaker-icon appeared on the overhead screen and began to emit little floating musical notes. The notes were visible but not audible--no sound accompanied them. Obviously there was some tiny technical glitch. Thinking fast, Barish rebounded by turning to the rapt audience and giving them an impromptu, live chirp-simulation.

"Boop!" Barish said, delighting the crowd. "Boop! Boop! Boop!"

Funded by the National Science Foundation, the LIGO Laboratory is one of the most ambitious "big science" projects ever devised. Though chiefly focused on the detection and study of gravitational waves, it intends to further repay the confident investments put into it by developing into a world-class scientific research facility, with a web of alliances that envelopes the world. Leading this effort is the LIGO Scientific Collaboration, a gathering of over 400 associates from more than two-score institutions, all driven by the goal to fully capitalize on the science and technology that LIGO pioneers. Even now plans are afoot for the implementation of Advanced LIGO, a system of equipment and performance upgrades that will swell the interferometers' sensitivity by a factor of more than 10. The information thus gleaned will add a fresh new perspective on our vision of the universe.

Barish answers questions after his lecture. Ending his lecture, Barish arose from the stool and came around to face the audience. His lecture style throughout had been soft-spoken and low-key, as though wishing to keep himself well in the background and put the material on most prominent display. Now it was question time and he stood, candid yet demure, with his glance kept generally downward. The audience seemed invigorated by the 90 minute presentation, talkative and full of interest. A few people were clearly boggled by the notion of trying to reliably measure a fluctuation as intangible as 10-18, the size change of a motion LIGO must be able to detect. Replying, Barish wore a faint smile in sympathy with these skeptics. The technical challenges facing LIGO are indeed formidable, the science innovative, the aspirations enormous. Nevertheless, the research shows it can be done. The theory is tenable. Great resources of talent and energy have been marshalled, and vital equipment mobilized. Trail-blazing work has been performed in the areas of optics polishing, laser design, vacuum equipment, and seismic insulation. And LIGO's increasing approach to goal sensitivity shows that the prize is not beyond reach. The LIGO team and its associates know well the difficulty of the work before them. And they fully intend to accomplish it.

Exiting the stage, Barish was quickly surrounded by a cluster of avid listeners, still fascinated, brimming with curiosity, and eager to learn more. The evening's work had been a success.

See a video replay of Barry Barish's Watson Series Lecture.

View a Powerpoint or pdf version of his slide-show presentation.

Visit the Barry Barish Caltech Home Page.