| The LIGO
Sixty Students Tour LIGO 40m Lab
Sixty 6th-grade students were gathered outside of the Caltech Millikan library, enjoying their lunch. The group had come from John Muir Elementary School to visit both the Seismology (Seismo) Lab as well as LIGO's 40m prototype lab. The students had finished at the Seismo Lab and were now anxiously awaited the next leg of their Caltech tour. With lunch finished, we made our way across campus toward the 40m. As we walked, I spoke with Jessica, Tammy and Amy, and quizzed the girls about what they had learned so far. Behind us followed the chaperones, teachers Ms. Madonissian and Ms. Sharp, with the remainder of the enthusiastic youngsters. When asked why Caltech was chosen for a tour, Ms. Madonissian explained, "We want to reinforce our studies of plate tectonics, earthquakes and other ground vibrations." At last we reached the 40m prototype, which struggles against vibrations constantly. We arranged the youngsters in groups of twenty, each led in turn through the lab by Alan Weinstein and Dennis Ugolini.
Dennis eloquently put LIGO on an elementary level. "We want our mirrors to stay very still even though the ground is shaking everything at a range of frequencies. So we hang the mirror from a thin wire to make a pendulum. We then bolt this pendulum to a table, and sit the table on top of a layer of rubber springs. These springs sit on another table, which sits on another layer of springs, and so on. Each pendulum and spring has a resonance frequency at which it likes to vibrate; the more the shaking frequency is above this resonance, the less the pendulum or spring will move. So we try to set the resonance frequencies as low as possible, so that by the time the shaking reaches the mirror, there is barely any motion at all."
Other aspects of the interferometer were highlighted, from the complicated optical layout of the laser table, to scores of electronics boards and cables. Questions from the young audience ranged from the basic ("How much does all this cost?") to the more fanciful ("If there were a hole in the tube, would we all get sucked inside?"). The tour ended with another happy group filled with knowledge about LIGO.