The Evolution of TAI and UTC

Abstract

The development of modern precision time-keeping has followed the emergence of various new and demanding practical requirements; it has been made possible by international co-operation and by taking full advantage of many advances in science and technology. Initially progress was achieved in the establishment of a unified system of time reckoning based on astronomical observations. More significant changes resulted from the need for improved accuracy in the measurement and control of frequency; this called for a more precise definition and superior techniques for the realization of the unit of time. Atomic time soon replaced astronomical time in a wide range of applications. Space flight navigation and world-wide communication systems brought stringent demands for time scales of the highest attainable uniformity, readily accessible for daily operational use. In this rapidly-changing situation, a major role was played by the Bureau International de 1'Heure, on the basis of advice received from the relevant scientific unions and related inter-governmental organizations. The present systems of TAI and UTC appear to meet current needs, but we are working near the limit of our capabilities. The accelerating pace of development leaves no room for complacency.