Precision Measurement and Fundamental Constants II

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It seems a pity, in this day and age of camera-ready copies, almost instant printing and so on, that the Second International Conference on Precision Measurement and Fundamental Constants, which was held in June 1981 at the National Bureau of Standards in Gaithersburg, should have the publication of its proceedings delayed for more than three years. This is not to say that the appearance of this publication will not be welcomed by those working in the various fields of precision measurement. The necessarily slow pace with which metrology advances means that many of the techniques and ideas reported in these Proceedings are still relevant to those actively involved in precise measurements. If the past is to be any guide, we can expect the third PMFC conference to be held in the early l990s: until then the current proceedings will, no doubt, act as a source of stimulation in the furtherance of our knowledge of the techniques of precision measurement and the fundamental constants.The topics covered by the Conference were many and varied and this itself speaks for the current vitality of the subject and the vigour with which metrology is being pursued. The Proceedings contain papers on atomic clocks, spectroscopy, X-ray interferometry, quantum electrodynamics, elementary particles, gravitation and relativity. Measurements of the Fundamental Constants claiming accuracies of 0.001 ppm for the Rydberg constant, 0.3 ppm for the ratio of the neutron to proton magnetic moments, 2 ppm for the farad, about 0.005 ppm for kilogram metrology, 1 ppm for the ampere, 0.01 ppm for a 100 mV voltage standard, 1 ppm for the ratio of h/e and 60 ppm for that least well known of the fundamental constants, the Newtonian constant of gravitation, to quote but a few, are reported in these Proceedings. Whether the published values of these and the other constants given in the Proceedings will stand the test of time remains to be seen.The techniques involved in these determinations seem to be as many and as varied as the topics themselves. They include, to mention but three, the utilization of the Josephson junction, the quantized Hall resistance, and that instrument known to all schoolboy physicists, the torsion pendulum. In particular, the application of the quantum Hall effect to the determination of the fine-structure constant and to electrical resistance standards is one of the most remarkable developments in metrology in recent years. Although the effect was discovered only a short while before PMFC II, these Proceedings include eight papers devoted to it and its applications and, of course, many more have appeared since. The impact of the quantum Hall effect will certainly be considerable, not only in metrology, but also in solid state physics. It is to be expected that the proceedings of PMFC III will, in due course, reflect this. Noteworthy also for their impact on precision spectroscopy during the decade between PMFC I and II are the techniques of Doppler-free two-photon transitions and the methodology for trapping a single ion.Not all the papers, however, are devoted to reports of hard measurement. Many consist of progress reports of experiments in hand at the time of the Conference. It would be interesting to know just how many of these have been completed in the four years since the Conference took place. And of these, it would be more interesting still to learn which of them achieved the accuracies that their authors had, optimistically perhaps, hoped for. A few of the papers are purely speculative, an example being the suggestion by Faller and Bender for a space-borne gravitational-wave detector. Their suggestions involve a laser device with baseline lengths of the order of 106 km. If the authors are to launch this experiment they will need powerful friends in high places to find the necessary funding.But to return to earth and to the comments made at the beginning of this article: may this reviewer make two pleas on behalf of all those who, in the fullness of time, will find themselves delving not into the proceedings of PMFC II but of PMFC III? Firstly, will future editors of these conferences please avail themselves of modern printing technology to ensure that future proceedings appear with far less tardiness than that which was experienced with PMFC II. Secondly, and finally, will future editors please publish, at the beginning of each volume, a table of new determinations of physical constants reported in the body of the conference proceedings, together with their uncertainties and the names of the authors responsible. This would be of considerable assistance to the busy reader who wishes to separate papers giving details of hard measurement from those which are either progress reports or are purely speculative in nature.