Tuesday, July 22, 2003


Dava Sobel’s book, “Longitude” was a great introduction to the importance of exact knowledge of the time of day. For anyone reading this who did not read the book (hard to imagine), lots of lives were lost a sea in the 18th century because ship crews didn’t know exactly where they were after long sea voyages. Latitude was relatively easy to calculate from celestial observations, but longitude had to be calculated from the time at which celestial events occurred. Unfortunately clocks were not good enough to accurately measure time, especially when subjected to the harsh conditions on sea voyages in the ships of the time. Sobel tells the story of how the first marine chronographs were created to solve the problem.

At the beginning of the 19th century, overland travel was slow, and information traveled with people. On land there was no apparent need for clocks in different towns to be synchronized accurately, (except perhaps for the port towns). Then came the railroad. Two trains traveling in different directions on the same track had to keep schedules so that they didn’t try to occupy the same piece of track at the same time. Towns along the railroad had to keep the same time. In the United States, the U.S. Naval Observatory took on the responsibility of setting the standard time in the country.

(As an aside, I have always wanted to, but never have visited the old Naval Observatory, although I have worked within walking distance for many years. It sits near the State Department, on a site overlooking the Potomac river, not far from the National Academy of Science’s main building. Many of the great astronomical discoveries of the 19th century were made there, and one would think it would be a major tourist attraction for a certain kind of “knowledge geek”, but it seems almost totally ignored.)

In the middle ages in Europe, church bells calling people to prayer served for scheduling purposes, as did calls to prayer in the Moslem world. The 19th century saw the development of mass production. In the home craft shop, scheduling was easy, and people tended not to work fixed schedules. The factory introduced the need for people to work fixed shifts to attend to the machines. The industrialization of office work, that stemmed from the need to coordinate national businesses (built on the technological foundations of mass production and mass transportation) contributed to the scheduling of work. (Indeed, for Americans and many Europeans, one of the more difficult aspects of working in developing nations comes from the different cultural expectations about time and scheduling; perhaps poor countries, lacking the centuries of experience with industrial schedules have not made the same cultural changes vis a vis timekeeping as have OECD countries.)

As the 19th century progressed, clocks were standardized by signals sent via telegraph. By the 20th century, more accurate time was sent nationwide by radio from the standard clocks in Washington.

Today’s Washington Post has an article by Monte Reel describing the master timekeeper in the United States. Still in the Naval Observatory, the function is the responsibility 27 scientists who monitor 50 atomic clocks. The average time of those clocks is used to synchronize 12 atomic clocks located across the country. Every month, the International Bureau of Weights and Measures in Sevres, France compares the U.S. time with that from 50 other national timekeepers, and sets “Universal Time”, the global standard. Accuracy is measured in hundreds of a trillionth of a second per day!

Why is the accuracy so important? Certainly some of the applications are military, smart bombs and missiles depend on global positioning data, which in turn depends on accurate time measurements. But GPS has lots of important civilian applications as well. Cell phones send packets of data that are time stamped, and the time stamps have to be consistent and accurate. Packet switching networks also depend on time stamps on the packets, and one assumes that the time stamps also have to be accurate.

This blog is about “knowledge for development”. The point of today’s entry is that knowledge of things often taken for granted, like the exact time, is important for a knowledge society. While most of use could not care less if our watches are off by a minute or two, and indeed many deliberately keep their watches inaccurate, modern society includes activities that depend on widely shared knowledge of time with accuracy better than a billionth of a second per day!

In the United States and Europe, very highly specialized teams of experts operate expensive equipment to assure this accuracy. Poor countries don’t have the capacity, and indeed some regions of significant geographical size don’t have such facilities.

In short, it is dangerous to extrapolate from everyday experience in thinking about the knowledge society. Timekeeping has become ever more accurate and important in the last three centuries. Most of us operate our quotidian lives on 19th century time, but 21st century economies are based on widely shared knowledge of time accurate to billionths of a second per day!

No comments: