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The End of the Time of Earth: Why Does the Leap Second Matter?

The views expressed are those of the author and are not necessarily those of Scientific American.


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Dial of the Prague astronomical clock. Creative commons. Click on image for license and information.

Ed Note: We have a guest today! AiP is pleased to host this post by Dr. Kevin Birth, who is a professor of anthropology at Queens College, CUNY and an expert on time. His forthcoming book, Objects of Time: How Things Shape Temporality (Palgrave Macmillan) discusses the hidden logics in clocks and calendars.

As a specialist in the study of time, I occasionally get asked about what I think of the so-called Mayan prophecy that the world will end in 2012. I guess people think that I’ll have some interesting insight into the cultural anthropology of time, and some special knowledge into the mysterious Mayan logics. Truthfully, it is not the Mayan logics that are mysterious, but our own. 2012 was almost a significant year in the cultural creation of time as we know it. Recently, those in charge of the global time system decided to defer to 2015 the ending of the time of Earth. Because of the timing of the debate over Earth’s time, it may come as a shock to those who expect some dismissive answer from an ivory-tower intellectual, but I think the Maya maybe were on to something.

The Mayan calendrical system consists of multiple cycles of different durations. Like a set of different-sized gears whirring together with gears completing their cycles at different times, it takes a long time for the Mayan system to return to a previous state. The Gregorian year 2012 marks a moment when this Mayan system will start over—the end of the old long count and the beginning of a new one. The Maya took such things very seriously, and as Professor Prudence Rice has demonstrated in her books, the ending of one cycle and beginning of a new one coincided with political transformations for the Maya.

The Maya are not alone in such a sensitivity. People in the European tradition are enamored of base-10 mathematics, so when the year 2000 approached, there was a great deal of hoopla over the number. Many saw it as the beginning of the new millennium, although, in truth, the millennium did not begin until 2001. Still, there seems to be magic in chronological numbers and their cycles.

But there is another thing going on in all these calendrical and chronological systems. Behind the curtain of these cycles are a set of logics that deal with some fundamental problems in time keeping. This is as true for us as it was for the Maya. First, the cycles of the moon, stars, and sun are not equivalent. Second, the revolution of the Earth around the sun is an awkward 365.242 days. Different cultures have come up with different solutions to this problem, and the Mayan calendar is just one of many such solutions. Our currently dominant calendar, implemented by Julius Caesar and tweaked by Pope Gregory the XIII, ignores sidereal and lunar cycles, and deals with the duration of the Earth’s orbit through leap years that add a day.

Whether it is ancient Maya or our contemporaries in 2012, most people have very little idea of how systems of time reckoning are created—we simply look at our clocks and calendars and believe them without recognizing the cabal of astronomers and/or priests that lurk behind the logics.   Through our objects of time, we rely on largely unknown experts to make sure that the trains and everything else run on a reliable time, and to ensure that we know when the airlines do not. All we need to know is how to read a clock and calendar, not how they work.

While almost everyone is familiar with the idea of the leap year, far fewer are aware that the Earth’s rotation is not uniform. It wobbles about with small deviations, and as a result, a international bureaucracy has been set up to keep our time system coordinated with the Earth’s foibles. In this bureaucracy, the International Earth Rotational Systems Service (IERS) has charted the Earth’s rotation and when necessary, made recommendations to the International Bureau of Weights and Measures (BIPM) to modify the international time keeping system by a second—a leap second. The BIPM receives time signals from atomic clocks distributed throughout the globe and then calculates what is called “coordinated time” based on these signals. This created, coordinated time is then set to the prime meridian, and sent back out to all those in the time signaling business as something called “Universal Coordinated Time” (UTC). It may be disconcerting to hear that time is created, but if one keeps in mind the theory of relativity, each point in space has its own unique time. From the perspective of relativity, a universal time is an illusion—but an illusion our society needs to function.

The BIPM creates time by following policies formulated by the Radiocommunications Sector of the International Telecommunications Union (the ITU-R). There are many technologies reliant on time, such as software and GPS, and these technologies do not work well with the Earth’s occasional hiccups and the irregular insertion or deletion of seconds from UTC. Since much software runs on a uniform time without leap seconds, to keep it coordinated with UTC requires software updates, and this gets expensive over time.

The recent consideration by the ITU-R to do away with leap seconds would have meant an end the time of Earth—in effect, the Earth’s cycles would no longer have a bearing on the time kept by clocks. In this culturally created system, the units of duration that define time for us are a choice of the ITU-R. A second is defined as 1/315,56,925.975 of the length of the tropical year for January 0, 1900 (in effect, December 31, 1899); a day as 86,400 of those seconds; a year as 365 or 366 (in a leap year) of those days. This decision would have meant our clocks are not tied to the Earth’s rotation, and our calendars are no longer associated with the Earth’s orbit—truly, the end of the time of Earth.

In an uncanny coincidence, this debate is unfolding at the end of the Mayan long count—the end of one time for the Maya and the beginning of a new one. A cataclysmic change that few will notice as global time ceases to refer to any single cycle but becomes entirely a cultural creation.

So maybe the time conscious Maya were right, but it is not the world that ends in 2012, only time as we knew it. However, since the decision has been delayed to 2015 it seems we have little to worry about, assuming we understand the Mayan calendar correctly (and that’s a big assumption).

Krystal D'Costa About the Author: Krystal D'Costa is an anthropologist working in digital media in New York City. You can follow AiP on Facebook. Follow on Twitter @krystaldcosta.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. MTHarden 1:55 pm 01/23/2012

    Can’t we pick a better day? Why December 31st, 1899? I mean sure Silvestre Revueltas was born that day but I hardly think that qualifies (HT Wikipedia). Why not a day with some significance to humanity, like 21 July 1969, or maybe July 16, 1945.

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  2. 2. Dick Jacobson 2:35 pm 01/23/2012

    Leap seconds should be scheduled 10 or 20 years in advance. This would solve the problem faced by software and hardware developers who cannot build a reliable leap-second table because they have only six months’ advance warning. The predictions of leap seconds might be inaccurate by a few seconds, but this is of concern only to astronomers and operators of Earth-observing satellites, who could make the necessary adjustments.

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  3. 3. jtdwyer 4:15 pm 01/23/2012

    While the variabilities of Earth’s rotation likely prevents scheduling leap seconds long in advance, that mission critical software does not allow for the introduction of leap seconds is simply a failure of requirements analyses.

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  4. 4. David N'Gog 4:50 pm 01/23/2012

    Is there really any significance to “real” time as in our rotational time being completely in sync with time keeping down to the second?

    It will take 200 years before we are off by an hour. By which time, “space” surely will make us rethink our time keeping anyway- and if not- just do a leap-hour in 200 years time- or not at all- civilization will have time to adjust to the fact that 11am is then “midday”… why bother resetting the clocks every time we’re off by a second?

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  5. 5. rhodinsthinker 8:32 pm 01/23/2012

    315,56,925.975 has commas in wrong. 31,556,925.975 gives 31,556,925.975 / 86,400 = 365.242198785 mean solar days in the year January 0 1900.

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  6. 6. ash5353 10:49 pm 01/23/2012

    Time is just an abstract concept created by carbon based life forms to monitor their on going decay.

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  7. 7. Bloodnok 2:02 pm 01/24/2012

    A general comment: The advertising sidebar, apparently sponsored by an oil company, leaves out the only option that will put fossil fuels out of business.
    That option is the nuclear breeder reactor.

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  8. 8. Bloodnok 2:06 pm 01/24/2012

    A question about leap seconds: is it really true that the Earth’s angular momentum, which is being transferred to the Moon in its orbit, by the tides (perhaps including the subterranean molten regions?) is doing so at an irregular, unpredictable rate?

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  9. 9. frankcrawford 6:41 am 01/25/2012

    In regard to Bloodnok’s question, yes, over short time periods (geologically speaking) it is unpredicable. The vagaries of currents within the mantle mean that the crust and core can and do rotate at slightly different rates.

    In fact, while the discussion is about adding leap seconds, most recently the crust has been speeding up and we were close to having to remove a second to keep things lined up. It has since slowed down again.

    On a different point, this article was not particularly informative, as there was too much about the mythical 2012 and the Mayan calendar and little about the real effects of the issue.

    The whole concept of a time standard that is constant for even a few decades let alone a few hundred years is yet to be obvious. Atomic clocks are not and have not been stable even since their introduction, with numerous corrections to their actual result going on. The process for measuring a time period is take measurements with your clock, take another measurement at a later stage and subtract the difference. This does not change no matter if we use UTC or GMT.

    The question is how to measure from an arbitrary point in the past and even with atomic clocks, the time is taken as an average of a number of atomic clocks, after an event and adjusted back to the original point.

    The insertion of a “leap second” for any device is also a misnomer, since every clock, no matter how accurate, needs continual adjustment for any systematic or random drift.

    Finally, the concept of time measurement having an absolute starting point is a human artifact and should remain so. The vast majority of the population reset their internal clock every morning, yet there have been riots in the past when time measurements (i.e. calendars) have changed. Even now, try getting into a discussion with the general public about when midnight is on New Year’s Eve and explain how this will drift over a period so midnight was not during the night!

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  10. 10. Donzzz 10:27 pm 01/26/2012

    A “Leap Second” is added by our official time keepers every so often. The reason for adding a leap second is that the planet does not rotate exactly once every 24 hours (86,400 seconds). The rotation actually takes 86,400.002 seconds so that each day this little difference builds up between the atomic clock and the earth’s rotation relative to the stars. All leap seconds so far have been positive. http://novan.com/mind.htm

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  11. 11. iWind 5:23 am 02/7/2012

    Software and hardware can pretty much be split in two categories.

    The first – almost all the IT in existence – which does not rely on leap-second accurate time-keeping, and is in no way affected by the introduction of leap seconds. It keeps coordinated with UTC not by software updates but by regularly synchronizing with time servers.

    The second category is the few pieces of equipment that do rely on such accurate time-keeping and is constantly being updated with accurate data from atomic clocks – most of it probably incorporates atomic clocks. This is all obviously designed to be capable of handling leap seconds, or it would have failed to function long ago. The most glaringly obvious example is GPS, which definitely can handle it – as well as far more complicated aspects of diverging time.

    No costs at all are incurred for the first category, and no appreciable costs are incurred for the second. The main costs involved are with keeping track of the Earths rotation, which would be done anyway, and the real anthropological question is, “why is there a little group of engineers so upset about the idea of a leap second in their calculations, that they have decided to make an issue of it, and to invent problems to justify dissociating international time keeping from it’s human rationale?”

    Indeed, even if the leap second were to be abandoned, it would give no cost reduction at all – not only because all equipment would still have to be designed for leap seconds in case they or something similar were re-introduced, or you would suddenly have billions of dollars worth of useless equipment in orbit, because you decided to save fifteen minutes wages for a programmer, but even more because you would then need to compensate for the drift between time standards which must by necessity occur when you abandon the common frame of reference. Welcome to the leap-microsecond!

    There’s no need to end the Time of Earth.

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