Alas For Time Travel: The Leap Second Stands In Its Way

When one considers time travel, it is wise to become aware of a set of agencies and policies that are responsible for keeping our clocks on time, and of the consequences of their policies for surfing the chronoscape. A small policy change can cause all sorts of problems.

The current system that ensures that clocks run on time involves coordination between the International Earth Rotation and Reference Systems Service (IERS), the International Bureau of Weights and Measures (BIPM), and the Radiocommuncation Sector of the International Telecommunications Union (ITU-R). The IERS charts the Earth’s movements, the BIPM takes signals from atomic clocks distributed around the globe in order to define a precise clock time, and the ITU-R sets policies and standards. Right now these institutions are engaged in the debate over the future of the leap second.

The use of leap seconds has kept our highly precise atomic time standards in sync with the Earth’s tendency to wobble and create slight irregularities in its rotation. But since leap seconds do not come at regular intervals, they cannot be programmed into software and left alone. Instead, whenever there is a leap second, the time architecture of all time-sensitive software applications must be adjusted. This creates confusion and problems for some systems—enough for there to be a powerful case to eliminate the leap second and go to a time standard decoupled from the Earth’s movement.

One constituency has not been addressed in this debate—either because there is nobody in this constituency, or because they are all presently elsewhen. This constituency is that of time travelers. So I am going to imagine, for a moment, that the resolution to eliminate the leap second has passed—and that the following has appeared in some future Tor.com blog:

O woe to time travelers. Their lot is about to get more difficult.

As any experienced time traveler knows, this type of journey is not merely through time, but also through space. Everything in the universe is in motion, and if you simply travel in time while staying in one spot, then you stay in that spot while everything else is in motion. This has rather ugly results. For instance, if you wanted to travel back to chat with Cicero (rather chatty fellow), and you merely set your coordinates in time, then you’d most likely find yourself in empty space because the Earth isn’t where it used to be in Cicero’s time.

So, in traveling in time, you must know where the Earth was for the moment you are traveling to, and you should know where your goal location is in relationship to the Sun—the Earth is spinning, after all. What’s the point of going to chat with Cicero if you end up in the middle of the Pacific because you did not account for the Earth’s rotation? Glug, glug, glug.

Here’s the rub: to travel successfully, you need to know two kinds of time. One kind of time has to do with the timing of Earth’s relationship to other celestial bodies. This has to do with orbit, rotation, and the movement of the entire solar system through space. The other kind of time has to do with the precise measure of duration. Even if you get your space coordinates right, if you get the duration only slightly wrong, you may find yourself plummeting through the atmosphere or someplace underneath the Earth’s crust.

Alas For Time Travel: The Leap Second Stands In Its Way

Another thing to keep in mind is that the time on your clock does not match the time of the Earth’s rotation. Because the Earth is a tilted rotating orb moving through space, the relationship between a rotation to the same point in relationship to the Sun and a 360-degree rotation is a bit complicated. This is why for many years clock time was known as mean time and set to Greenwich Mean Time—it’s an average of the length of day. Up until now, the relationship between mean time and apparent solar time has been represented with a handy formula known as the equation of time.

These two different times need to be reconciled. As Newton pointed out in his Principia Mathematica, the Earth is not a particularly good timekeeper. It wobbles about, and while these wobbles do not have that serious an effect on mean solar time, they accumulate over time to lead to serious differences. The further backwards or forwards in time you travel, the more you must worry about these wobbles. For the past century or so, these differences have been charted with sufficient accuracy to be of use, but before that you can only estimate, and with regard to the future, since we’re dealing with a wobble rather than a regular pattern, it is risky going too far forward. One really should stop frequently to check what the current stage of the Earth’s wobbliness is.

But as I said, the lot of time travelers is about to get more difficult. Ever since the beginning of the 21st century, there have been those pushing to dismantle the time services that kept clock time (known as Universal Coordinated Time or UTC) and mean solar time coordinated. This practice resulted in the use of leap seconds to keep both time scales synchronized. Since the leap seconds were well-documented and announced, the careful time traveler could take them into account when making calculations. But recently, UTC has been decoupled from mean solar time. To avoid confusion, UTC continues to be signaled but the difference between UTC and mean solar time has to be sought out.

What this means is that you can no longer rely on the equation of time when making your time traveling plans. Basically, you can’t trust your gauges any longer, and have to think for yourself.

Not that I’m against thinking for yourself. One part of me thinks that our time system has for too long cultivated ignorance of its underlying algorithms in its users. It was too easy to just look at the clock and know the time without knowing how that time was determined. But this is now, at least temporarily, going to change. So in your first ventures into the past or future using this new time regime, use caution, and double and triple check your calculations, and don’t trust your software, old gauges, or old clocks.

Except for the fantasizing about time travel, this situation is not too far from the truth. The objects we use to tell time are full of hidden algorithms based on choices made in the past. For instance, the 24-hour day is an inheritance from the Egyptians, the 60 minutes in an hour from the Sumerians, the calendar from the Romans and adjustments by Pope Gregory XIII, mean time is a product of the Enlightenment, atomic timekeeping is not that old, and even more recently, atomic timekeeping was adjusted to take into account Einstein’s theory of relativity. My book Objects of Time: How Things Shape Temporality discusses this state of affairs and explores some of its consequences, as well as discussing how life works under other systems of reckoning time.


Kevin K. Birth is a professor of anthropology at Queen’s College, CUNY and a member of the International Society for the Study of Time. His previous book, Any Time is Trinidad Time (1999), was the subject of a 2002 article in Scientific American. Objects of Time: How Things Shape Temporality is out this month from Palgrave.

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