In his theory of special relativity, Einstein showed that the very idea of simultaneity--of two events occurring at the same time in different places--is flawed. Simultaneity is all relative, Einstein argued; it depends on your perspective or, technically, your reference frame. Yet we at NOVA note the passing of Norman Ramsey, the physicist whose work led to the most accurate timekeeping devices in history, with special poignancy due to a personal sense of simultaneity; we are just about to begin our exploration of time in tonight's episode of The Fabric of the Cosmos.

Norman Ramsey shared the 1989 Nobel Prize in physics for his contributions to the invention of the hydrogen maser and the cesium atomic clock. Ramsey began working on atomic spectroscopy, a way of discovering the structure of atoms by analyzing the wavelengths of light that they release and absorb, at Columbia University in the late 1940's. He then moved to Harvard and in 1949 invented a new way to measure the frequency of photons released by atoms and molecules with even greater accuracy. In 1960, Ramsey contributed to the invention of the hydrogen maser, which was also put to use as a timekeeping device. Ramsey literally helped redefine time, not as something to be measured by the motion of Earth and Sun, but to be "ticked off" by the vibrations of an atom.

Today's best atomic clocks are so accurate that they won't gain or lose a second for the next 138 million years. Atomic clocks are critical to GPS and modern communications; they help radio astronomers see the universe with pinpoint precision; and ironically, they have even been used to confirm Einstein's ideas about the plasticity of time. Ramsey did not at first realize that his work would have these far-reaching applications. In fact, as recounted by The New York Times, he once said, "I didn't even know there was a problem about clocks initially. My wristwatch was pretty good."

For more about Ramsey's work, we recommend coverage from: