Ronald William Prest Drever 26 October 1931 – 7 March 2017
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Ronald William Prest Drever 26 October 1931 – 7 March 2017 Professor Ronald Drever was co-founder, with Kip Thorne and Rainer Weiss, of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which in September 2015 made the first direct observation of gravitational waves. Seven months after Drever’s death Thorne and Weiss shared the 2017 Nobel Prize for Physics for LIGO’s innovation and success. Ronald was born on 26 October 1931 in Bishopton, Renfrewshire. His father (George Douglas Drever) had, following distinguished Army service in WWI in Mesopotamia and the North-West Frontier, been awarded a medical scholarship. His GP training took him to Northumberland, where he met, and in 1929 married, Mary (Mollie) Matthews, following which he set up as a GP in Bishopton. Ronald started school at Glasgow Academy at the age of five in 1936. He hated school, largely due to a severe and persistent writing difficulty. However, he showed an early talent for creative design and construction, developing expertise in using Meccano, mirrors, magnets and electric motors. The outbreak of war in 1939 interrupted his education, and he transferred to the local school in Bishopton before returning to Glasgow Academy in 1943 (with his younger brother Ian). With the war still on, this involved the young boys travelling alone to and from Glasgow in the black-out, having to flash a tiny torch to stop the bus. At the Academy his mathematical and scientific skills were well recognized, and he won prizes in Mathematics and Physics in his 5th and 6th years. He also learned how to design and construct electronic equipment and constructed a TV set at home, on which his family watched the Coronation in 1953 (see image above). Ronald attended Glasgow University from 1950, gaining in 1953 a First in pure science and in 1958 a PhD in natural philosophy, supervised by Professor Philip Dee, with thesis title “Studies of orbital electron capture using proportional counters.” As a Research Fellow, Drever performed a fundamental test for a putative anisotropy of inertial mass due to the concentration of mass at the center of our Galaxy. The experiment, carried out at home in his family garden, is a classic of cleverness and economy. It looked for a diurnal signal in the free precession of lithium- 7 nuclei in the Earth’s magnetic field; the diurnal effect would come from the change in the direction to the galactic center as Earth rotates. Using this deceptively simple and apparently crude apparatus Drever carried out what has been called “the most precise null experiment ever performed” (Max Jammer, 2000, Princeton UP). He set an upper limit on the anisotropic fraction of the proton’s inertial mass of 5 x 10−23, better by a factor of 200 than the limit obtained in a sophisticated contemporaneous experiment at Yale by Hughes and colleagues. The reputation acquired by this experiment enabled Drever to obtain a visiting fellowship at Harvard University in 1960–61. There he worked under Robert Pound, who had recently made the first terrestrial measurement of the gravitational red shift of light predicted by Einstein nearly fifty years earlier. Drever returned to Glasgow University, with a lectureship from 1961. He became an accomplished and popular teacher. He would use items from the large collection of devices and components in his Bishopton garage to make demonstration experiments. One of the Honours students he supervised was Jocelyn Bell, who famously went on to discover pulsars (and to become RSE President). Between 1968 and 1972 Drever was a consultant scientist at AERE Harwell, working on Cerenkov and fluorescence observations relating to supernovae and pulsar emissions and other astronomical observations. During one of these trips, he heard Joseph Weber present his claim of discovering gravitational waves. A pulse of gravitational waves will stretch lengths in one direction while shrinking those in a perpendicular direction, or vice versa. The differential change is very small, even for the strongest feasible astronomical sources. Weber’s idea was that such a pulse might excite a measurable reverberation in a massive metal cylinder. His claims of successful detection were highly controversial (and later discredited), but Drever was immediately engaged and challenged by the problem of the detection of gravitational waves. His drive, skills and experimental vision enabled him to rapidly develop at Glasgow, along with Dr Jim Hough, a world- class prototype split bar detector system. From the early 1970s, however, Rainer Weiss and others began to consider measuring gravitational-wave length changes directly using laser interferometry. If a light beam is split, sent along two orthogonal there-and-back paths and then recombined, any differential length change in the paths will cause a phase shift between the two return beams. Even small phase shifts can be measured very accurately, and the longer the paths the bigger the phase shift, in principle. In contrast, bar detectors have obvious practical size limits. Drever began to experiment with optical detection systems, eventually building a laser interferometer system with ten-metre arms (then world-leading) in the Glasgow department. In LIGO, the orthogonal paths are 4 km long (which would stretch from Ronald’s Bishopton garden almost to Dumbarton Castle, with the orthogonal arm reaching beyond the Erskine Bridge!). One cannot measure optical phase shifts over kilometer paths unless the laser source has a sufficiently stable phase (or frequency). Drever conceived a modulation technique to lock a laser’s frequency to a resonance of a (small) mechanically-stable optical cavity. He successfully implemented the idea with Hough at Glasgow and, to even higher precision, with John Hall at NBS in Boulder, Colorado. The technique, now known as the Pound-Drever-Hall method, has become standard across optical physics. Hall shared the Nobel Physics prize in 2005. The effective length of an optical gravitational-wave detector can be enhanced by sending the beam to and fro many times, rather than just twice. Such multi-pass interferometer systems were used in all the early systems, but they proved unexpectedly noisy, largely due to scattering cross- talk between the multiple beams. Drever proposed to use Fabry-Perot cavities instead. They also benefit from an effective length much longer than the physical length, but with much-reduced scattering noise. Furthermore, the Pound-Drever-Hall technique can be used to lock the Fabry-Perot to the source laser! Once so locked, any gravitational-wave perturbation can be read out as the control signal needed to maintain lock. This, in essence, is how LIGO is actually configured today. As Rainer Weiss says in his Drever obituary: “I disagreed with (Ron) about the use of optical cavities; it turned out he was right.” (Nature April 2017.) During this period Drever ascended the academic ladder, becoming titular professor of physics in 1975 and a full professor in 1979. His creativity and accomplishments were attracting notice, however, and when Kip Thorne launched an experimental gravitational-wave initiative at Caltech, Drever was chosen to lead it. From 1979 to 1984 he did so part time, retaining his Glasgow post and using the long flights between the UK and California to fill notebooks with ideas and sketches for experiments. At Caltech he built and commissioned a 40 m interferometer system. Progress in both Glasgow and Caltech was good, but no gravitational-wave events were being detected. In 1982 indirect evidence was reported, when it was shown that the orbital characteristics of a binary pulsar was in excellent agreement with calculations which included gravitational-wave emission. These waves would be much too weak to detect directly on Earth, however. Everything pointed to a need to increase the size, as well as the sensitivity, of the laser interferometers, leading to a proposal for a kilometer-scale system, in fact two such systems, in order to be able to use coincidence-detection to improve the accuracy and certainty with which candidate events could be validated. A multi-million-dollar Caltech-MIT proposal was developed from 1984 and put to NSF, with Drever, Thorne and Weiss as scientific leaders. As this scheme developed into the actual LIGO system, the search for gravitational-waves became “Big Science”, akin to a CERN or NASA project. Ronald Drever described his scientific approach as in the tradition of Ernest Rutherford: “The key thing, which I had been taught, was to do things very fast: don’t try to do accurate experiments; do rough experiments very, very quickly. Just do them as fast as you can — don’t care if they don’t work. Learn as much as you can, very, very quickly, until you find out how to do it right. And the last thing you do very carefully, but the key thing is to move very fast at early stages — this was quite against the grain.” (Caltech Oral History 1997). This approach is the polar opposite of Big Science, where everything has to be meticulously planned and reported. Drever was obliged to go full-time at Caltech, and his laboratory was later incorporated into the LIGO project. Robbie Vogt was appointed LIGO project director in 1987, and was successful in driving LIGO through the fund-raising process, in establishing sites, and implementing construction of the huge 4 km interferometer systems. Vogt sought to control every aspect of LIGO, including even conference presentations. The incompatibility of this with Drever’s philosophy and approach became ever more evident, and in 1992 Vogt removed Drever from the LIGO project. Over the next few years Caltech was found to have violated Drever’s academic freedom, and was required to make reparation. Vogt was himself replaced in 1994 by Barry Barish, who eventually shared the 2017 Nobel Prize with Thorne and Weiss.