Physical-Review-Letters and Seventh-Marcel-Grossmann Relativity-Gyro Papers

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The PRL Paper

Around 1990 it became clear that a version of the Relativity-Gyroscope Experiment which used an Autocollimator to read out the gyro spin axis combined with a pure Unsupported Gyroscope could improve the accuracy of the Relativity-Gyro Experiment by about a factor of 10,000 over a version which used a SQUID to read out the London Moment.

In 1995 a short version of the Relativity-Gyro paper was published in Physical Review Letters detailing these improvements.

Benjamin Lange, A High-Accuracy Gyro Test of General Relativity and the Search for a Massless Scalar Field, Physical Review Letters, Vol. 74, No. 11, March 13, 1995, p. 1904.

To get a copy of this article, go to the link, PRL Paper (PDF).

There are many reasons for the improvements, and these are detailed in the Physical Review D Gyro Paper. The three principal ones are that the noise level of an Autocollimator is about 20,000 times lower than the SQUID/London Moment combination, the annual aberration of star light does not prevent the gyro being used as the attitude reference improving roll averaging of gyro drift by about 1000, and two satellites in counter-rotating orbits can almost eliminate proper motion of the reference star as a source of error.

In 1993 an explanation was published of why a scalar field (which apriori should be as large as the tensor field) was so small. General Relativity is an attractor for Scalar-Tensor gravity driving it toward General Relativity as the Universe expands. See T. Damour and K. Nordtvedt, PRL70, 15, 2217, (1993) and PRD48, 8, 3436, (1993). Not only did they explain why a scalar field was so small, but they gave estimates of its values. These estimates were in a range which made a high-accuracy version of the Relativity-Gyro experiment especially important. Later, more accurate, calculations of this effect, however, have shown that it can be much smaller than originally believed; making a high-accuracy Equivalence-Principle experiment even more important.

The MG7 Paper

As the PRL paper was being published, the theory of General Relativity as an attractor for scalar fields (ibid.) was extended to include dilaton fields (T. Damour and A. M. Polyakov, Nucl. Phys. B423, 532, (1994)). One of the results of this extension was that the Eddington Parameter, gamma, and a violation of the Equivalence Principle were related. If this relation is correct, a test of the Equivalence Principle is a much more accurate measurement of the existence of a scalar field than the gyro experiment. In fact, present limits on any violation of the Equivalence Principle are within an order of magnitude of the best possible gyro measurement. For this and many other reasons, a high-accuracy test of the Equivalence Principle is very important.

At the 1994 Seventh Marcel Grossmann Conference at Stanford, a paper was given which integrated these new results into the scientific significance of a high-accuracy gyro experiment.

B. Lange, The Scientific Significance of a Long-Lifetime High-Accuracy Version of the Relativity-Gyro Experiment with Altitude-Change Capability (PDF), pp. 1538-1541, Seventh Marcel Grossmann Meeting, Proceedings, Ed. Robert T. Jansen, G. Mac Keiser, Remo Rufini, World Scientific, (24-30, July, 1994).