More than 200 years ago Benjamin Franklin coined the now famous dictum that equated passing minutes and hours with shillings and pounds. The new millennium--and the decades leading up to it--has given his words their real meaning. Time has become to the 21st century what fossil fuels and precious metals were to previous epochs. Constantly measured and priced, this vital raw material continues to spur the growth of economies built on a foundation of terabytes and gigabits per second.

An English economics professor even tried to capture the millennial zeitgeist by supplying Franklin's adage with a quantitative underpinning. According to a formula derived by Ian Walker of the University of Warwick, three minutes of brushing one's teeth works out to the equivalent of 45 cents, the compensation (after taxes and Social Security) that the average Briton gives up by doing something besides working. Half an hour of washing a car by hand translates into 4.50.

This reduction of time to money may extend Franklin's observation to an absurd extreme. But the commodification of time is genuine--and results from a radical alteration in how we view the passage of events. Our fundamental human drives have not changed from the Paleolithic era, hundreds of thousands of years ago. Much of what we are about centers on the same impulses to eat, procreate, fight or flee that motivated Fred Flintstone. Despite the constancy of these primal urges, human culture has experienced upheaval after upheaval in the period since our hunter-gatherer forebears roamed the savannas. Perhaps the most profound change in the long transition from Stone Age to information age revolves around our subjective experience of time.

By one definition, time is a continuum in which one event follows another from the past through to the future. Today the number of occurrences packed inside a given interval, whether it be a year or a nanosecond, increases unendingly. The technological age has become a game of one-upmanship in which more is always better. In his book Faster: The Acceleration of Just About Everything, James Gleick noted that before Federal Express shipping became commonplace in the 1980s, the exchange of business documents did not usually require a package to be delivered absolutely positively overnight. At first, FedEx gave its customers an edge. But soon the whole world expected goods to arrive the next morning. When everyone adopted overnight mail, equality was restored, Gleick writes, and only the universally faster pace remained.

Simultaneity

THE ADVENT of the Internet eliminated the burden of having to wait until the next day for the FedEx truck. In Internet time, everything happens everywhere at once--connected computer users can witness an update to a Web page at an identical moment in New York or Dakar. Time has, in essence, triumphed over space. Noting this trend, Swatch, the watchmaker, went so far as to try to abolish the temporal boundaries that separate one place from another. It created a standard for Internet timekeeping that eliminated time zones, dividing the day into 1,000 increments that are the same anywhere on the globe, with the meridian at Biel, Switzerland, the location of Swatch's headquarters.

The digital Internet clock still marches through its paces on the Web and on the Swatch corporate building in Biel. But the prospects for it as a widely adopted universal time standard are about as good as the frustrated aspirations for Esperanto to become the world's lingua franca.

Leaving gimmickry aside, the wired world does erase time barriers. This achievement relies on an ever progressing ability to measure time more precisely. Over the aeons, the capacity to gauge duration has correlated directly with increasing control over the environment that we inhabit. Keeping time is a practice that may go back more than 20,000 years, when hunters of the ice age notched holes in sticks or bones, possibly to track the days between phases of the moon. And a mere 5,000 years ago or so the Babylonians and Egyptians devised calendars for planting and other time-sensitive activities.

Early chronotechnologists were not precision freaks. They tracked natural cycles: the solar day, the lunar month and the solar year. The sundial could do little more than cast a shadow, when clouds or night did not render it a useless decoration. Beginning in the 13th century, though, the mechanical clock initiated a revolution equivalent to the one engendered by the later invention by Gutenberg of the printing press. Time no longer flowed, as it did literally in a water clock. Rather it was marked off by a mechanism that could track the beats of an oscillator. When refined, this device let time's passage be counted to fractions of a second.

The mechanical clock ultimately enabled the miniaturization of the timepiece. Once it was driven by a coiled spring and not a falling weight, it could be carried or worn like jewelry. The technology changed our perception of the way society was organized. It was an instrument that let one person coordinate activities with another. Punctuality comes from within, not from without, writes Harvard University historian David S. Landes in his book Revolution in Time: Clocks and the Making of the Modern World. It is the mechanical clock that made possible, for better or worse, a civilization attentive to the passage of time, hence to productivity and performance.

Mechanical clocks persisted as the most accurate timekeepers for centuries. But the past 50 years has seen as much progress in the quest for precision as in the previous 700 [see A Chronicle of Timekeeping, by William J. H. Andrewes, on page 46]. It hasn't been just the Internet that has brought about the conquest of time over space. Time is more accurately measured than any other physical entity. As such, elapsed time is marshaled to size up spatial dimensions. Today standard makers gauge the length of the venerable meter by the distance light in a vacuum travels in 1-299,792,458 of a second.

Atomic clocks, which are used to make such measurements, also play a role in judging location. In some of them, the resonant frequency of cesium atoms remains amazingly stable, becoming a pseudo-pendulum capable of maintaining near nanosecond precision. The Global Positioning System (GPS) satellites continuously broadcast their exact whereabouts as well as the time maintained by onboard atomic clocks. A receiving device processes this information from at least four satellites into exact terrestrial coordinates for the pilot or the hiker, whether in Patagonia or Lapland. The requirements are exacting. A time error of only a millionth of a second from an individual satellite could send a signal to a GPS receiver that would be inaccurate by as much as a fifth of a mile (if it went uncorrected by other satellites).

Advances in precision timekeeping continue apace. In fact, in the next few years clockmakers may outdo themselves. They may create an atomic clock so precise that it will be impossible to synchronize other timepieces to it [see Ultimate Clocks, by W. Wayt Gibbs, on page 56]. Researchers also continue to press ahead in slicing and dicing the second more finely. The need for speed has become a cornerstone of the information age. In the laboratory, transistors can switch faster than a picosecond, a thousandth of a billionth of a second [see From Instantaneous to Eternal, on page 24].

A team from France and the Netherlands set a new speed record for subdividing the second, reporting in 2001 that a laser strobe light had emitted pulses lasting 250 attoseconds--that is 250 billionths of a billionth of a second. The strobe may one day be fashioned into a camera that can track the movements of single electrons. The modern era has also registered gains in assessing big intervals. Radiometric dating methods, measuring rods of deep time, indicate how old the earth really is.

The ability to transcend time and space effortlessly--whether on the Internet or piloting a GPS-guided airliner--lets us do things faster. Just how far speed limits can be stretched remains to be tested. Conference sessions and popular books toy with ideas for the ultimate cosmic hot rod, a means of traveling forward or back in time [see How to Build a Time Machine, by Paul Davies, on page 14]. But despite watchmakers prowess, neither physicists nor philosophers have come to any agreement about what we mean when we say tempus fugit.

Perplexity about the nature of time--a tripartite oddity that parses into past, present and future--precedes the industrial era by quite a few centuries. Saint Augustine described the definitional dilemma more eloquently than anyone. What then, is time? he asked in his Confessions. If no one asks me, I know; if I want to explain it to someone who does ask me, I do not know. He then went on to attempt to articulate why temporality is so hard to define: How, then, can these two kinds of time, the past and the future be, when the past no longer is and the future as yet does not be?

Hard-boiled physicists, unburdened by theistic encumbrances, have also had difficulty grappling with this question. We remark that time flies as we hurtle toward our inevitable demise. But what does that mean exactly? Saying that time races along at one second per second has as much scientific weight as the utterance of a Zen koan. One could hypothesize a metric of current flow for time, a form of temporal amperage. But such a measure may simply not exist [see That Mysterious Flow, by Paul Davies, on page 6]. In fact, one of the hottest themes in theoretical physics is whether time itself is illusory. The confusion is such that physicists have gone as far as to recruit philosophers in their attempt to understand whether a t variable should be added to their equations [see A Hole at the Heart of Physics, by George Musser, on page 12].

The Great Mandala

THE ESSENCE OF TIME is an age-old conundrum that preoccupies not just the physicist and the philosopher but also the anthropologist who studies non-Western cultures that perceive events as proceeding in a cyclical, nonlinear sequence [see Clocking Cultures, by Carol Ezzell, on page 42]. Yet for most of us, time is not only real, it is the master of everything we do. We are clock-watchers, whether by nature or training.

The distinct feeling we have of being bookended between a past and a future--or, in a traditional culture, being enmeshed in the Great Mandala of recurring natural rhythms--may be related to a basic biological reality. Our bodies are chock-full of living clocks--ones that govern how we connect a ball with a bat, when we feel sleepy and perhaps even when our time is up [see Times of Our Lives, by Karen Wright, on page 26].

These real biorhythms have now begun to reveal themselves to biologists. Scientists are closing in on areas of the brain that produce the sensation of time flying when we're having fun--the same places that induce the slow-paced torpor of sitting through a monotone lecture on Canadian interest-rate policy. They are also beginning to understand the connections between different kinds of memory and how events are organized and recalled chronologically. Studies of neurological patients with various forms of amnesia, some of whom have lost the ability to judge accurately the passage of hours, months and even entire decades, are helping to pinpoint which areas of the brain are involved in how we experience time [see Remembering When, by Antonio R. Damasio, on page 34].

Recalling where we fit in the order of things determines who we are. So ultimately, it doesn't matter whether time, in cosmological terms, retains an underlying physical truth. If it is a fantasy, it is one we cling to steadfastly. The reverence we hold for the fourth dimension, the complement of the three spatial ones, has much to do with a deep psychic need to embrace meaningful temporal milestones that we can all share: birthdays, Christmas, the Fourth of July. How else to explain the frenzy of celebration in January 2000 for a date that neither marked a highlight of Christ's life nor, by many tallies, the true millennium?

We will, nonetheless, continue to celebrate the next millennium (if we as a species are still around), and in the meantime, we will fete our parents golden wedding anniversary and the 20th year of the founding of our local volunteer fire department. Doing so seems to be the only way of imposing hierarchy and structure on a world in which instant messaging, one-hour photo, express checkout and same-day delivery threaten to rob us of any sense of permanence.