Contains research objectives and summary of research.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E)National Aeronautics and Space Administration (Grant NGR 22-009-359)M.I.T. Cabot Solar Energy Fun

Davidson, A.

Ezekiel, Shaoul

Muehler, D. J.

Owens, D. Kingston

Ryan, T. J.

Weiss, Rainer

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XIII. GRAVITATION RESEARCHAcademic Research StaffProf. R. WeissProf. S. EzekielGraduate StudentsD. J. MuehinerT. J. RyanRESEARCH OBJECTIVES AND SUMMARY OF RESEARCHThe research effort in this group is in the field broadly labeled experimental rela-tivity, in particular, experiments related to the gravitational interaction and mea-surable consequences of cosmological models.Specific Research Activities1. Balloon-borne far infrared radiometer experiment designed to measure the 3'Kisotropic black-body background that is alleged to be a remnant of the cosmological"Big Bang." The radiometer was flown in a successful flight on September 29, 1969and again on November 20, 1969. The last flight, however, ended in a catastrophewith the total loss of the apparatus. Preliminary results of the first flight indicate that(i) in the region between 6 cm-1 and 20 cm-1 the radiation does not follow a black-bodyspectrum, and (ii) the radiation by atmospheric water above an altitude of 39 km is nota problem in the experiment. At present, we plan to construct a new radiometer muchas the original one, and also a low-resolution spectrometer to cover the same frequencyspectrum.D. J. Muehlner, R. Weiss2. Long-term frequency stabilization of the Argon laser using a resonance absorp-tion excited in a molecular beam as a primary reference. This project is the continuationof an experiment that uncovered a match between a resonance absorption in moleculariodine and one of the lines of the Argon ion laser. The present effort is on investigationof the short-term stability of the Argon ion laser. Another part of this project isan experiment to observe saturated absorption by iodine in an intracavity absorptioncell.T. J. Ryan, S. Ezekiel3. Gravitational vs atomic clock experiment to test the strong principle of equiva-lence, in particular, to search for evidence for the Brans-Dicke scalar gravitationalinteraction which violates the strong principle. In this experiment an atomic oscillatorand a gravitational oscillator are both placed in a space vehicle. One measures thenumber of axis crossings of the atomic oscillator per axis crossing of the gravitationalThis work was supported in part by the Joint Services Electronics Programs (U. S.Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E), andin part by the National Aeronautics and Space Administration (Grant NGR 22-009-359),and the M. I. T. Cabot Solar Energy Fund.QPR No. 96(XIII. GRAVITATION RESEARCH)field as the space vehicle travels through varying gravitational potentials, for example,from Earth to Jupiter. If the strong principle is satisfied, the ratio of axis crossingsis an invariant. But if the Brans-Dicke theory is correct, the ratio changes by a fewparts in 108 between Earth and Jupiter. The design that was considered was a super-conducting suspension of a triangular distribution of masses. This was the subject of aMaster's thesis in instrumentation by Michael G. Blitch. There are still some major,but not necessarily murderous, problems in the design. Further work continues withthe collaboration of the M. I. T. Measurement Systems Laboratory and P. K. Chapmanof the N. A. S. A. Manned Flight Space Center, in Houston, Texas.4. A gravitational wave antenna to look for evidence of gravitational radiation bythe Crab Nebula pulsar. Our intention is to use a pair of masses separated by a longdistance, say, at first of the order of tens of meters. The separation of the masses ismeasured interferometrically. The interferometer output is used in a digital servo sys-tem to couple the masses such a way that it makes a very high Q resonator at twice thepulsar frequency.A. Davidson5. Index of refraction and birefringence of a magnetic field. If the theoretical workof T. Erber (Nature, No. 4770, p. 25, 1961) is correct, it may now be possible withpulsed magnetic fields and phase-locked lasers to observe vacuum polarization effects.D. K. OwensQPR No. 96

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