Colloquium: Kleppner Charts|
'How Physics Got Precise'
To Professor Daniel Kleppner, one 19th century development marked
the turning point in the precision of physics.
"For me, the breakthrough was the invention of the Michelson Interferometer
by A.A. Michelson in 1883," says Kleppner, the Lester Wolfe Professor of
Physics at MIT. "The interferometer made it possible to measure distances
to a small fraction of the wavelength of light. Since a meter typically has
a million wavelengths, the resulting precision is enormous."
Kleppner examines the evolution of precision measurements, from the King's thumb to the atomic clock and beyond, in "How Physics Got Precise," the Fermilab Colloquium presentation on Wednesday, January 19 at 4 p.m. in Wilson Hall's 1 West conference room. Kleppner sets the stage with the impressive accuracy of time measurement in early civilizations.
"The Babylonians, about 7000 B.C., and Hipparchus in Egypt, about 150 B.C., knew the length of the year to about 5 minutes," Kleppner says. "The length was found by telling the time of the day of the equinoxes over a long time. If you estimate it to one hour, which is pretty easy, and keep count of the days between equinoxes for twelve years, you have the length of the year to five minutes. Tycho Brahe, in 1600, knew the length of the year to about three seconds."
Kleppner also offers another surprise for post-modern time measurement, involving the re-introduction of human-made or human-related "artifacts."
"For a new generation of atomic clocks," he says, "time keeping could be so precise that the effects of the local gravitational potentials on the clock rates would be important. This would force us to re-introduce an artifact into the definition of the second-specifically, the location of the primary clock."