Ronald William Prest Drever, who cofounded the Laser Interferometer Gravitational-Wave Observatory (LIGO) with Kip Thorne and Rainer Weiss, died peacefully in Edinburgh, Scotland, on 7 March 2017. Known to his family as Ronald and to his colleagues as Ron, he was born 85 years earlier, on 26 October 1931, in the family home in Bishopton, just west of Glasgow.
Ron’s parents realized early on that he was different and special. He spent his childhood and adolescence tinkering with the electronics of the time. As a young adult, he made the first television set in Bishopton from war surplus items and junk, which allowed the family to view the Queen’s coronation in 1953.
Ron attended Glasgow University, where he received in 1953 a BSc in pure science and in 1958 a PhD in natural philosophy, with a thesis, supervised by Philip Dee, entitled “Studies of orbital electron capture using proportional counters.” Ron spent 1960–61 doing postdoctoral work under Robert Pound at Harvard University and then returned to Glasgow University as a lecturer. He ascended the academic ranks at Glasgow, becoming titular professor of physics in 1974 and a professor in 1979.
Before going to Harvard, Ron performed a fundamental test of the anisotropy of inertial mass produced by the concentration of mass at the center of the galaxy. The experiment, carried out in his family’s backyard, is a classic of cleverness and economy. It looked for a diurnal signal in the free precession of lithium-7 nuclei in Earth’s magnetic field; the diurnal effect comes from the change in the direction to the galactic center as Earth rotates. Ron reported a null result and set an upper limit on the anisotropic fraction of the proton’s inertial mass of 5 × 10−23, better by a factor of 200 than the results of a contemporaneous experiment by Vernon Hughes and colleagues at Yale University.
The Hughes–Drever experiment set the tone for Ron’s approach to experimental physics. As he recalled in a 2006 memoir,
A strong recollection for me of this work was how exciting it all was to do. A large part of this probably came from the knowledge that the sensitivity was better than anything of the kind known to have been done before, so there was a possibility, even if unlikely, that something quite unexpected and important might be discovered. And moreover a significant result might be found in a 24-hour run, without requiring extensive and time-consuming analysis. The fact that a positive result was not found did not significantly spoil the excitement—something quite new could have shown up.
Those of us who knew Ron can hear his Scottish lilt as he delights in having challenged the world to reveal its secrets, on the cheap, in his mother’s backyard, his wits against nature.
Beginning in the early 1970s, Ron and his research group at Glasgow turned their attention to the detection of gravitational waves. Their first effort used a pair of bar detectors akin to those pioneered by Joseph Weber at the University of Maryland. Each detector was split into two aluminum cylinders, bonded together by six stacks of piezoelectric transducers. Compared with other bar detectors, the split-bar configuration afforded a much higher bandwidth of good sensitivity. Searches for pulsed and periodic gravitational waves yielded no significant results, except for one tantalizing, three-millisecond coincidence, recorded on 5 September 1972, that shall forever remain tantalizing.
In the mid 1970s, Ron began thinking about detecting gravitational waves with laser-powered interferometers of the sort proposed and developed a few years earlier by Rainer Weiss of MIT and Robert Forward of Hughes Research Laboratories. In 1979 Kip Thorne persuaded Ron to head up an effort in that direction at Caltech. For the next five years, Ron split his time between Caltech and Glasgow before becoming a full-time professor of physics at Caltech in 1984. The period from the late 1970s to the late 1980s was the most productive of Ron’s career.
Weiss’s proposal imagined a Michelson interferometer with optical delay lines in the two arms to increase the gravitational-wave signal. Early experiments at Glasgow and at the Max Planck Institute for Physics and Astrophysics in Munich exposed the hazard of scattered light coupled to laser-frequency noise for a delay-line configuration. Ron’s solution was radical: Replace the delay lines with Fabry–Perot optical cavities. To make that work, Ron invented a scheme for locking a laser’s phase and frequency to an optical cavity. First implemented with John Hall of JILA and now called Pound-Drever-Hall (PDH) reflection locking, the scheme is a staple of optical-physics laboratories.
Ron charged ahead with ideas to exploit the power of nesting optical cavities. His first was power recycling, which increases the power in a Michelson run on a null fringe by placing a mirror between the laser and the Michelson’s input beamsplitter. His second, called resonant recycling, introduced the notion of placing additional optical elements in the dark output port of the interferometer; his student Brian Meers elaborated the approach into the form now in use, called signal recycling.
Those innovations of Ron’s—the Fabry–Perot Michelson (two names not juxtaposed before Ron put them together), PDH locking, and nested cavities for recycling—were implemented and developed at Caltech, Glasgow, and Munich (later Hannover). They are the basis for the optical design of the 4 km interferometers in the LIGO detectors in Washington State and Louisiana.
Ron lived for clever ideas to make experiments work. “Any new ideas?” was his habitual greeting. He was a friend, mentor, colleague, and inspiration to us and many others. Possessed of a unique, direct connection to the world of experimental physics, unmediated by theoretical modeling or analysis, he conceived innovations and inventions that eluded everyone else.
Ron was a genius in physics. His genius is imprinted on and is indispensable to the success of the LIGO interferometers.
