Atomic wrist watches

The great book Longitude tells the story of the development of clocks that were accurate within very tight bounds under a wide range of sea-going conditions. In the late 1600's and early 1700's, clocks were so expensive that only the very rich could afford them -- even on land. That's why castle towers routinely showed a clock face: not only was it a gift of sorts to the surrounding inhabitants, it was a sure statement of the wealth of those in the castle.

Small clocks -- small enough to carry with you -- were even more expensive. They weren't available until the 1800's and well into the 1900's a small and accurate clock was still quite valuable. That was one reason why retirement gifts were often pocket watches (later, wrist watches) -- these were rare, expensive and something that a person was not likely to buy for himself or herself. A real gift.

The 21st century equivalent of "a good wrist watch" is on the horizon: an atomic clock small enough to fit inside a watch, a cell phone, a GPS hand-held unit. The technology is almost here:

Atomic clocks, which rely on the oscillations of atoms, not quartz crystals, are far more precise. But the smallest models currently on the market are about the size of a pack of cigarettes, bigger than most devices in which they might find a home. Now several researchers are developing tiny atomic clocks that could be made using standard semiconductor processes and slipped into cellphones, hand-held computers and Global Positioning System receivers.

"If you have a small, low-power clock available, all kinds of technologies or innovations will flow from it," said R. Michael Garvey, the chief technology officer at Symmetricom, a maker of atomic clocks. Mr. Garvey's company is among the research groups looking at miniature atomic clocks under a program funded by the military.

this article details their development.