tific fields. As Weiss related, even Einstein in his final years, while engrossed in the search for a unified field theory, expressed interest in the MIT project to develop such clocks. If such devices could be perfected, one of their possible applications would be precise measurement of the effects of gravitation on time. This would help provide further confirmation of general relativity. Zacharias proudly introduced his project to Weiss.

“Jerrold said to me,” recalled Weiss, “that he had made himself a clock called the ‘fountain clock,’ which was a brand new idea involving tossing atoms high into the air and timing them. The idea was to get a long observation time on the atom. He kept telling me that if we could get the clock running, I would travel to the Jungfraujoch, a scientific observatory high in the Swiss Alps. He would be with his clock in the valley and we would measure the Einstein redshift. That’s what set the bee in my bonnet about relativity. But the clock didn’t work; it was a total failure.”

Nevertheless, Weiss’s interest in experimental tests of general relativity only grew. Obtaining a postdoctoral fellowship with Bob Dicke, he learned about attempts to measure gravitational radiation. “With Dicke I did something wacky,” continued Weiss. “I worked on a gravitometer to measure scalar waves [a hypothesized mode of radiation] hitting the Earth.”

Dicke, a master at cutting through thorny mechanical dilemmas, also instilled in Weiss the value of solid experimental design. Returning to MIT as a professor, Weiss embraced the teachings of his mentors and became one of the world’s leading experts in high-precision measurements of gravity.

The capstone of Weiss’s career is LIGO. Weiss developed the notion of using a special technique called laser interferometry to track minute movements of matter due to gravitational waves. Interferometry involves focused beams of light with well-defined frequencies (that is, laser beams) traveling along separate paths and then coming together again. The pattern created when the beams reunite provides precise information about the difference in path lengths.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement