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LIGO – The Road to Gold:  How it all began

At Caltech, the interest in gravitational waves began with a young professor of theoretical physics, Kip Thorne, who by the late 1960s began further exploring Einstein's predicted existence of such waves. As Thorne wrote in 1969:

According to general relativity, space and time make up a four-dimensional "space" (or manifold) called spacetime, which is curved. The curvature of spacetime is produced by its material content (galaxies, stars, planets, people). Experimentally, the curvature of spacetime shows up as gravity. In effect, gravity and spacetime curvature are one and the same thing. [Excerpt from Thorne's "Relativistic Astrophysics at Caltech: 1923-1969."]


Kip Thorne, 1969


Einstein's theory of general relativity also entailed that gravitational interactions produce waves, ripples in this spacetime. In the 1960s, physicists began building interferometers to detect such gravitational waves. In an interferometer, a beam of light is split into two rays which are sent off in different directions, reflected from mirrors, recombined, and ultimately projected onto a screen.  If the two rays have each been subject to the same forces, the pattern of light on the screen will be the same as if the beam shone on it directly; if, on the other hand, the rays have been subject to interference—such as a gravitational wave that subtly moved one mirror further away, so that one ray travelled further than the other—the combined pattern of light will appear different.


Drever’s simplified diagram, illustrating an optical cavity gravitational wave interferometer.


In 1968, Thorne established a research group here at Caltech, dedicated to working on the theory of gravitational waves. They also began a collaboration with Moscow State University professor Vladimir Braginsky and his experimental group. And by 1979, Caltech recruited Ronald Drever of the University of Glasgow (where Drever had developed a 10-meter prototype) to lead an experimental gravitational wave group here, together with Caltech physics professor Stanley Whitcomb, who came on board in 1980.


Shown above: May 18, 1976, Caltech's Alumni Seminar Day. Thorne discusses how, if gravitational waves could be detected and studied, how these waves could reveal what is happening inside quasars, black holes, and the cores of galaxies.


In 1980, the National Science Foundation decided to fund the construction of a Drever-Whitcomb 40-meter prototype interferometer at Caltech —as well as Rainer Weiss's 1.5 meter prototype at MIT. And by 1984, Caltech and MIT signed an agreement for the joint design and construction of LIGO, with administrative headquarters at Caltech under joint leadership by Drever, Weiss, and Thorne.


One arm of the 40-meter interferometer prototype made the cover of E&S in January 1983


Ronald Drever's 1983 article, "The Search for Gravitational Waves," discussed the history, theory, and problems regarding gravitational waves, and introduced the Caltech community to their prototype interferometric gravitational wave detector:

Caltech’s first prototype gravity wave detector, four years in planning and construction, is approaching completion in its initial form and is nearly ready for preliminary experiments.  The sensitive instrument, with 40-meter-long arms, is housed in its own temperature-controlled and vibration-isolated "building" attached to the north and west sides of the Central Engineering Services facility. . . . [If] this project —or any of the others around the world— do actually find gravitational waves, it could lead to a new window on the universe. . . . an entirely new area of astronomy would be opened up. [Excerpt from Drever’s January 1983 article.]


Stanley Whitcomb and Ronald Drever, with their prototype

When the LIGO construction proposal phase was initiated in 1987, Caltech physics professor Rochus Vogt was appointed Director of LIGO.  By 1989, Vogt, Drever, Fred Raab, Thorne and Weiss submitted their joint Caltech-MIT proposal to NSF. And construction of 2 sites was approved in 1990—the eventual sites being Hanford, Washington and Livingston, Louisiana.


Kip Thorne, Ronald Drever and Rochus Vogt in 1990, together with the 40-meter prototype


In 1994, Caltech’s physics professor Barry Barish became Principal Investigator, and would be appointed LIGO Director in 1997.  Under Barish's leadership, the final design stages, construction and commissioning of both LIGO sites was completed. And his creation of the LIGO Scientific Collaboration (LSC) would enable collaborators worldwide to participate in LIGO—which presently includes approximately 1000 scientists from 75 institutions and 15 nations.

Barry Barish, Linde Professor of Physics, Emeritus. 2005

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