New Experimental Test of Special Relativity

Abstract

The relative frequency stability of two beamtype maser oscillators is used to test the dependence of the velocity of light on velocity of the frame of reference with considerably more precision than has been obtained from experiments of the Michelson-Morley 1 type. Expressed in terms of an ether, the maximum ether drift is shown to be less than 1/1000 of the earth's orbital velocity.The experiment, which was performed at the Watson Laboratory, involves comparison of the frequencies of two masers 2 having their beams of NH 3 molecules traveling in opposite directions. Miller 3 has analyzed this case and given the change in frequency of a beam-type maser due to ether drift, assuming the molecules in the beam to have a velocity u with respect to the cavity through which they pass, and the cavity to have a velocity v with respect to the ether. The shift may be simply discussed by assuming that, if v is zero, radiation is emitted perpendicularly to the molecular velocity so that there is no Doppler shift. If the cavity and beam are then transported at velocity v through the ether in a direction parallel to u, radiation must be emitted by the molecules slightly forward at an angle 6 =7r/2 -v/c with respect to u. The fractional change in frequency due to the Doppler effect is then e = u/c cos0 or uv/c 2 due to motion through the ether, assuming that the proper molecular frequencies are unchanged by such motion 0 For a thermal molecular velocity of 0.6 km/sec and for the earth's' orbital velocity (30 km/sec), € -2 x 10 ~1 0 . The difference in frequency due to the above effect between two masers with oppositely directed beams would be 2ev, or about 10 cps for v equal to 23 870 Mc/sec, the NH 3 inversion frequency.Although uv/c 2 is of second order in the velocities, it is of first order in the velocity of the cavity, or of the laboratory, with respect to the ether Q The present experiment measures the entire effect with a rather small fractional error, which affords a particularly small upper limit to v since this quantity enters in first order, rather than in second order as in the Michelson-Morley experiment. A somewhat similar term would occur in the latter experiment if the interferometer used were transported by a plane of speed u, and interference fringes were compared for two opposite directions of flight.Two maser oscillators with oppositely directed beams were mounted with necessary auxiliary equipment on a rack which could be rotated about a vertical axis. The beat frequency between the two oscillators was adjusted to about 20 cps and recorded continuously. After approximately one minute of recording with the maser axes oriented in an east-west direction, the apparatus was rotated 180° and the beat frequency recorded in the new position.The change in beat frequency, on the basis of an ether drift, should be 4ev, or about 20 cps. Sixteen such comparisons were made during a period of about 20 minutes. These were repeated about once per hour during a time somewhat longer than 12 hours, so that the earth's rotation...

Robert Dicke and the naissance of experimental gravity physics, 1957–1967

“…Historians might see room for closer examination of this situation and, I expect, many other aspects of how empirical gravity physics grew. (Gordon, Zeiger, and Townes 1955); Møller (1957) acknowledged "stimulating discussions" with Townes "on problems of general relativity in connection with the maser;" and a year after that Townes's group published a variant of the Kennedy-Thorndike aether drift experiment (Cedarholm, Bland, Havens, and Townes 1958; as discussed below in Sec. 6.2).…”

“…Since they do not report problems with reproduceability as the Earth rotates and moves around the Sun we may take it that their bound in equation ( 10) bounds the coupling parameter to < ∼ 10 −8 for the hyperfine structure lines. Cedarholm, Bland, Havens, and Townes (1958) used ammonia beam masers for an aether drift test based on Møller's (1956Møller's ( , 1957 considerations of how atomic clocks might test relativity. The experiment compared the frequencies of two masers with ammonia beams that moved in opposite (antiparallel) directions at beam velocity u 0.6 km s −1 .…”

“…The fractional change of frequency when the system was rotated by 180 • was bounded to ∆ν/ν < ∼ 10 −12 , in trials repeated for a year (Cedarholm and Townes 1959). Møller (1957) and Cedarholm et al (1958) argued for the expression in equation ( 11), without the parameter , from a consideration of the Doppler effect on radiation reflected by the walls of a resonant cavity moving through an effective aether. But it seems best to follow Turner and Hill (1964) in going directly to the model in equation ( 11), including , as a fitting function.…”

“…High energy physics papers often acknowledged support from military agencies. In experimental gravity physics the development of the maser used in the Cedarholm et al (1958) aether drift test (Sec. 6.2) was supported "jointly by the Signal Corps, the Office of Naval Research, and the Air Research and Development Command."…”

URSI National Committee Report: Commission 1. Radio Measurement Methods and Standards

“…In closing, a sort of Michelson-Morley experiment using ammonia masers is worthy of mention [Cedarholm et al, 1958]. Two masers with oppositely directed beams were compared and turned with respect to the earth's motion.…”