Gravitational Measurements Fundamental Metrology And Constants

Proceedings of the NATO Advanced Study Institute, Erice, Italy, May 2-12, 1987

One of the exciting characteristics of metrology is its intimate relationship between fundamental physics and the leading edge of technology which is needed to perform advanced and challenging experiments and measurements. This title includes a set of lectures which present the relevant progress in Metrology.

The object of this NATO Advanced Study Institute was to pre sent a tutorial 'introduction both to the basic physics of recent spectacular advances achieved in the field of metrology and to the determination of fundamental physical constants. When humans began to qualify their description of natural phenomena, metrology, the science of measurement, developed along side geometry and mathematics. However, flam antiquity to modern times, the role of metrology was mostly restricted to the need of commercial, social or scientific transactions of local or at most national scope. Beginning with the Renaissance, and particularly in western Europe during the last century, metrology rapidly developed an international character as a result of growing needs for more accurate measurements and common standards in the emerging indus trial society. Although the concerns of metrology are deeply rooted to fundamental sciences, it was, until recently, perceived by much of the scientific community as mostly custodial in character.

The exchange between physics and metrology is always fascinating and exciting. Many are the open problems in physics that call for extremely precise standards, many are the advances in metrology made possible by a deep and assiduous study of the underlying physics. One has just to think of the enormous sophistication required in the measurements of some absolute quantities such as the Avogadro, the gas, or the gravitational constants. It is also worth noticing that not only the units of a metrological system are interrelated through the fundamental constants, but also the latter find their full significance when they are determined through the most exacting metrological experiments. Over the past decade many improvements took place and these are discussed in this book; from one side the old caesium SI second definition has found a new realisation, with the “fountain” approach, replacing the classical thermal atomic beam. The use of “cold” atom techniques, in which bunches of inert atoms are collected, slowed down, and cooled, has opened a number of new and unexpected avenues for metrology and fundamental constants; one of these possibilities being the atom interferometry. Another important “quantum jump” was the demonstration of the possibility of performing a direct frequency division in the visible, using ultra short femtosecond pulses. In addition, the possibility of “counting” electrons or photons gave a fundamental support to the development of single-electron capacitance standards and to new scenarios in the absolute calibration of photo-detectors.

The Newtonian constant of gravitation, G (often referred to as "big G"), is one of the most important of the universal fundamental physical constants. However, its value is the least well-determined of all such constants. This is because G is very difficult to measure reliably. Even though the gravitational force is responsible for star and galaxy formation on the massive scale of the universe, the force itself is minuscule on the tiny scale of the laboratory masses which must be used in the measurement. Consequently, its experimental value is prone to a high degree of inaccuracy. Moreover, it is the viewpoint of most physicists that G is not related to the other fundamental physical constants by any theory or understanding that is currently available. Therefore, it is thought that the value of G can only be obtained by measurement, and not from evaluating it in terms of other fundamental constants whose values are known with much greater precision and accuracy. The work presented in the book is an attempt to break through this mental barrier by demonstrating through numerical analysis that G is definitely related to the other fundamental constants. Consequently, it is possible to propose an exact value for G (to nine significant figures) that is obtainable from evaluation instead of from measurement.

An up-to-date description of progress and current problems with the gravitational constant, both in terms of generalized gravitational theories and experiments either in the laboratory, using Casimir force measurements, or in space at solar system distances and in cosmological observations. Contributions cover different aspects of the state and prediction of unified theories of the physical interactions including gravitation as a cardinal link, the role of experimental gravitation and observational cosmology in discriminating between them, the problem of the precise measurement and stability of fundamental physical constants in space and time, and the gravitational constant in particular. Recent advances discussed include unified and scalar-tensor theories, theories in diverse dimensions and their observational windows, gravitational experiments in space, rotational and torsional effects in gravity, basic problems in cosmology, early universe as an arena for testing unified models, and big bang nucleosynthesis.

Fundamental physical constants are used throughout the world by scientists and technologists in the course of every kind of theoretical and experimental research work. The book examines the present state of the measurement arts, and gives indications of likely future developments. This comprehensive and stimulating volume will certainly become a standard reference work in the field of measurement science for physicists, metrologists and workers in other physical science disciplines where a high accuracy of measurement is required.

Over the last decade of the 20th century, many improvements took place in the field of metrology and fundamental constants. These developments and improvements are discussed in this book. The old caesium SI second definition has found a new realization with the fountain approach, replacing the classical thermal atomic beam. The use of cold atom techniques, slowed down and cooled, has opened a number of unexpected avenues for metrology and fundamental constants, one of these possibilities being the atom interferometry. Another development was the demonstration of the possiblility of performing a direct frequency division in the visible, using short femtosecond pulses. Many other developments are also discussed.