Nº 7 2013 > The future of time
To abolish or not to abolish the leap second?
Modern times – Is the leap second history?
François Rancy, Director, ITU Radiocommunication Bureau
The international time-scale, Coordinated Universal Time (UTC), as defined by ITU, is used throughout the world and disseminated by radiocommunication systems. Recommendation ITU–R TF.460-6 on “Standard-frequency and time-signal emissions” is incorporated by reference in the Radio Regulations and provides the official definition of UTC.
Currently, UTC is used for a range of different purposes, from the minutes needed by the general public in adhering to timetables, to the synchronized nanoseconds required in the most demanding applications such as navigation through the global navigation satellite systems — for example the Global Positioning System (GPS), GLONASS and others on the horizon including Europe’s Galileo and China’s BeiDou.
A variety of systems using UTC have been developed over the past 40 years since the introduction of the leap second (1972), and some of these systems — for example for search and rescue services — are critical to human life. It has, therefore, been argued that the present definition of UTC should be maintained so that these systems can continue to operate as they do now. Another point that has been raised is that, if leap seconds are no longer used, the UTC time-scale will diverge from Earth rotation time. Apart from the affront to the common understanding of time by society at large, this may cause technical difficulties for specific applications including some used in astronomy.
In counterpoint, several arguments have been made for the adoption of a continuous reference time-scale, which would abolish the leap second. One is that the insertion of leap seconds is a costly process and reduces the reliability of systems that depend upon time. Pre-testing of equipment as well as correcting inevitable problems afterwards results in significant expenditure in terms of personnel as well as equipment. Furthermore, stopping all clocks in the world for one second in order to accommodate a leap second creates an ambiguous hiatus, where orderly processes such as precise time-stamping are disrupted. Also, the occasional nature of leap-second insertion is likely to cause significant technological problems to international infrastructure in years to come.
The ITU Radiocommunication Sector (ITU–R) is conducting studies on the feasibility of achieving a continuous reference time-scale for dissemination by radiocommunication systems. As part of the preparatory efforts for the World Radiocommunication Conference in 2015 (WRC-15), a special workshop organized by ITU and the International Bureau of Weights and Measures (BIPM) on 19-20 September 2013 in Geneva provided information to all stakeholders and raised awareness of the key issues and the different perspectives.
We are grateful to the authors of this special edition of ITU News for sharing their expertise and perspectives. Their combined knowledge offers a classic resource and reference on the science of timekeeping that will enrich and inform the ongoing debate on the future of time, and on whether or not to abolish the leap second..