Take a walk around the Caltech campus on any given day—save perhaps Ditch Day or commencement—and it is unlikely to reveal itself as a noisy place. However, step into any number of labs, and you can hear the sounds of science at work, from buzzing brain scanning technology to music-like signals from space, and many whirls, bleeps, and booms in between. It is impossible for us to embed all of those sounds into these pages, but here are just a few sounds and descriptions we could gather from a sampling of Caltech researchers…
“It sounds kind of like a cross between a car alarm and an angry squirrel, with some drums in the background.”
Ralph Adolphs, Bren Professor of Psychology and Neuroscience and professor of biology, describes the sound of the pulse sequence used for functional imaging of the human brain at Caltech’s Brain Imaging Center.
“We listen for changes in the separation of mirrors over the 4-kilometer length of each laser-interferometric detector. But thermal energy in the 0.4 millimeter diameter glass strings that hold up 40-kilogram mirrors also causes ringing sounds that we call ‘violin modes.’ And a hiss comes from the quantum nature of the light: fluctuations in the nothingness of empty space that interfere with our pure laser beam.”
Rana Adhikari, professor of physics, talks about noises from the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors. The aim of LIGO is to measure the stretching and squeezing of space-time. Scientists listen to the detector outputs—which are sometimes disturbed by things from the earth, such as earthquakes or traffic—using headphones.
“The tsunami causes the ionized gas that is out there to resonate — ‘sing’ or vibrate like a bell.”
Edward C. Stone, the David Morrisroe Professor of Physics, characterizes the sounds of “tsunami waves” that helped signal Voyager I’s entrance into interstellar space. These waves of pressure are caused by coronal mass ejections from the sun. Stone is the project scientist for the Voyager mission based at Caltech.
“Experiments in T5, one of the GALCIT Hypersonics Group facilities, begin with a siren… to alert the building. Sometimes it’s mistaken for an earthquake warning. A few seconds later the tunnel fires, accelerating gas to the velocities required to simulate planetary entry flows. The gun shot-like sound and vibrations can be heard and felt through the building.”
Joanna Austin, professor of aerospace, uses pistons and explosives in large test tunnels to compress gases. She studies the mechanics involved in compressible flows, which come into play in problems ranging from the logistics of a spacecraft’s entry into a planet’s atmosphere to the hows and whys of volcanic eruptions.
“My research literally includes the sound of waves crashing on the beach, the bubbling of a brook, and the crackling of glacial ice disintegrating as it flows into the ocean.”
Victor Tsai, assistant professor of geophysics, studies the seismic noise of ocean waves and rivers as well as glacier mechanics.