Description

Ali Javan, left, and Charles H. Townes working on an experiment measuring variation in length and velocity in relation to the Special Theory of Relativity at the Round Hill Field Station.

Original caption: "A research team headed by M.I.T. Provost C. H. Townes (right) recently set up two helium-neon masers in what was formerly a wine vault at M.I.T.'s Round Hill Field Station, South Datmouth, Massachusetts, in an experiment aimed at checking one consequence of the Special Theory of Relativity -- namely, variation in length with velocity. The wine vault, built into rock, was selected because of its relative freedom from distorting vibrations. The masers were mounted at right angles -- one parallel to, and one perpendicular to the earth's orbital velocity vector -- on a rotatable table suspended from the ceiling by airplane shock cords that further shield the experiment from vibrations. Maser beams were reflected simultaneously into a photocell that, in turn, mixed the beams and produced a beat -- or difference -- frequency. As the table rotated and the masers changed position with respect to the earth's orbital velocity, one might expect a change in the transit time of light between the two mirrors, if this were not compensated by relativistic changes in the length of the masers. These changes, although far too tiny for ordinary measurement techniques, were detectable through changes in the beat frequency. The technique used can detect changes in optical path lengths as small as about one thousandth of an atomic diameter. The experiment provided a precision method of checking the laws of relativity. At left is Associate Professor Ali Javan, who jointly with Townes has set up a laboratory for fundamental research on masers at M.I.T. The work is associated with the M.I.T. Research Laboratory of Electronics and the M.I.T. Spectroscopy Laboratory. Round Hill is a 278-acre estate formerly owned by the late E. H. R. Green and willed to M.I.T as a research station in 1948."