Marking the Passage of Time: The Elusive Nature of the Concept

Nature presents us with few mysteries more tantalizing than the concept of “time.” Youngsters, today, might not think the subject worthy of much rumination: After all, one’s personal iPhone can conveniently provide the exact time at any location on our planet.


Human beings have long struggled with two fundamental questions regarding time:

  1. What are the fundamental units in nature used to express time? More simply, what constitutes one second of time? How is one second determined?
  2. How can we “accurately” measure time using the units chosen to express it?

The simple answers for those so inclined might be: We measure time in units of seconds, minutes, hours, and days, etc., and we have designed carefully constructed and calibrated clocks to measure time! That was easy, wasn’t it?

The bad news: Dealing with the concept of time is not quite that simple.
The good news: The fascinating surprises and insights gained from taking a closer, yet still cursory, look at “time” are well worth the effort to do so. To do the subject justice requires far more than a simple blog post – scholarly books, in fact – but my intent, here, is to illustrate how fascinating the concept of time truly is.

Webster’s dictionary defines time as “a period or interval…the period between two events or during which ‘something’ exists, happens, or acts.”

For us humans the rising and setting of the sun – the cycle of day and night is a “something” that happens, repeats itself, and profoundly effects our existence. It is that very cycle which formed our first concept of time. The time required for the earth to make one full revolution on its axis is but one of many repeating natural phenomena, and it was, from the beginning of man’s existence, uniquely qualified to serve as the arbitrary definition of time measurement. Other repeatable natural phenomena could have anchored our definition of time: For instance, the almost constant period of the earth’s rotation around the sun (our year) or certain electron- jump vibrations at the atomic level could have been chosen except that such technology was unknown and unthinkable to ancient man. In fact, today’s universally accepted time standard utilizes a second defined by the extraordinarily stable and repeatable electron jumps within Cesium 133 atoms – the so-called atomic clock which has replaced the daily rotation of the earth as the prime determinant of the second.

Why use atomic clocks instead of the earth’s rotation period to define the second? Because the earth’s rotational period varies from month to month due to the shape of our planet’s orbit around the sun. Its period also changes over many centuries as the earth’s axis “precesses” (a slowly rotating change of direction) relative to the starry firmament, all around. By contrast, atomic clocks are extremely regular in their behavior.

Timekeepers on My Desk: From Drizzling Sand to Atomic Clocks!

I have on my desk two time-keepers which illustrate the startling improvement in time-keeping over the centuries. One is the venerable hour-glass: Tip it over and the sand takes roughly thirty minutes (in mine) to drizzle from top chamber to bottom. The other timekeeper is one of the first radio-controlled clocks readily available – the German-built Junghans Mega which I purchased in 1999. It features an analog display (clock-hands, not digital display) based on a very accurate internal quartz electronic heartbeat: The oscillations of its tiny quartz-crystal resonator. Even the quartz oscillator may stray from absolute accuracy by as much as 0.3 seconds per day in contrast to the incredible regularity of the cesium atomic clocks which now define the international second as 9,192,631,770 atomic “vibrations” of cesium 133 atoms – an incredibly stable natural phenomena. The Junghans Mega uses its internal radio capability to automatically tune in every evening at 11 pm to the atomic clocks operating in Fort Collins, Colorado. Precise time-sync signals broadcast from there are utilized to “reset” the Mega to the precise time each evening at eleven.

I love this beautifully rendered German clock which operates all year on one tiny AA battery and requires almost nothing from the operator in return for continuously accurate time and date information. Change the battery once each year and its hands will spin to 12:00 and sit there until the next radio query to Colorado. At that point, the hands will spin to the exact second of time for your world time zone, and off it goes….so beautiful!

Is Having Accurate Time So Important?
You Bet Your Life…and Many Did!

Yes, keeping accurate time is far more important than not arriving late for your doctor’s appointment! The fleets of navies and the world of seagoing commerce require accurate time…on so many different levels. In 1714, the British Admiralty offered the then-huge sum of 20,000 pounds to anyone who could concoct a practical way to measure longitude at sea. That so-called Longitude Act was inspired by a great national tragedy involving the Royal Navy. On October 22, 1707, a fleet of ships was returning home after a sojourn at sea. Despite intense fog, the flagship’s navigators assured Admiral Sir Cloudisley Shovell that the fleet was well clear of the treacherous Scilly Islands, some twenty miles off the southwest coast of England. Such was not the case, however, and the admiral’s flagship, Association, struck the shoals first, quickly sinking followed by three other vessels. Two thousand lives were lost in the churning waters that day. Of those who went down, only two managed to wash ashore alive. One was Sir Cloudesley Shovell. As an interesting aside, the story has it that a woman combing the beach happened across the barely alive admiral, noticed the huge emerald ring on his finger, and promptly lifted it, finishing him off in the process. She confessed the deed some thirty years later, offering the ring as proof.

The inability of seafarers to navigate safely by determining their exact location at sea was of great concern to sea powers like England who had a great investment in both their fleet of fighting ships and their commerce shipping. A ship’s latitude could be quite accurately determined on clear days by “shooting” the height of the sun above the horizon using a sextant, but its longitude position was only an educated guess. The solution to the problem of determining longitude-at-sea materialized in the form of an extremely accurate timepiece carried aboard ship and commonly known ever since as a “chronometer.” Using such a steady, accurate time-keeper, longitude could be calculated.

For the details, I recommend Dava Sobel’s book titled “Longitude.” The later, well-illustrated version is the one to read. In her book, the author relates the wonderfully improbable story of an English country carpenter who parlayed his initial efforts building large wooden clocks into developing the world’s first chronometer timepiece accurate enough to solve the “longitude problem.” After frustrating decades of dedicated effort pursuing both the technical challenge and the still-to-be-claimed prize money, John Harrison was finally able to collect the 20,000 pound admiralty award.

Why Mention Cuckoo Clocks? Enter Galileo and Huygens

Although the traditional cuckoo clock from the Black Forest of Germany does not quite qualify as a maritime chronometer, its pendulum principle plays an historical role in the overall story of time and time-keeping. With a cuckoo clock or any pendulum clock, the ticking rate is dependent only on the effective length of the pendulum, and not its weight or construction. If a cuckoo clock runs too fast, one must lower the typical wood-carved leaf cluster on the pendulum shaft to increase the pendulum period and slow the clock-rate.

No less illustrious a name than Galileo Galilei was the first to propose the possibilities of the pendulum clock in the early 1600’s. Indeed, Galileo was the first to understand pendulum motion and, with an assistant late in life, produced a sketch of a possible pendulum clock. A few decades later, in 1658, the great French scientist, Christian Huygens, wrote his milestone book of science and mathematics, Horologium Oscillatorium, in which he presented a detailed mathematical treatment of pendulum motion-physics. By 1673, Huygens had constructed the first pendulum clock following the principles set forth in his book.


In 1669, a very notable scientific paper appeared in the seminal English journal of science, The Philosophical Transactions of the Royal Society. That paper was the first English translation of a treatise originally published by Christian Huygens in 1665. In his paper, Huygens presents “Instructions concerning the use of pendulum-watches for finding the longitude at sea, together with a journal of a method for such watches.” The paper outlines a timekeeping method using the “equation of time” (which quantifies the monthly variations of the earth’s rotational period) and capitalizes on the potential accuracy of his proposed pendulum timekeeper. The year 1669 in which Huygens’ paper on finding the longitude-at-sea appeared in The Philosophical Transactions preceded by thirty-eight years the disastrous navigational tragedy of the British fleet and Sir Cloudesley Shovell in 1707.

As mentioned earlier, John Harrison was the first to design and construct marine chronometers having the accuracy necessary to determine the longitude-at-sea. After many years of utilizing large balanced pendulums in his bulky designs, Harrison’s ultimate success came decades later in the form of a large “watch” design which utilized the oscillating balance-wheel mechanism, so familiar today, rather than the pendulum principle. Harrison’s chronometer taxed his considerable ingenuity and perseverance to the max. The device had to keep accurate time at sea – under the worst conditions imaginable ranging from temperature and humidity extremes to the rolling/heaving motion of a ship at sea

The Longitude Act of 1714 specified that less than two minutes of deviation from true time is required over a six-week sea voyage to permit a longitude determination to within one-half degree of true longitude (35 miles at the equator). Lost time, revenue, and human lives were the price to be paid for excessive timekeeper inaccuracies.

Einstein and Special Relativity: Speeding Clocks that Run Slow

Albert Einstein revolutionized physics in 1905 with his special theory of relativity. Contrary to the assumptions of Isaac Newton, relativity dictates that there is no absolute flow of time in the universe – no master clock, as it were. An experiment will demonstrate what this implies: Two identical cesium 133 atomic clocks (the time-standard which defines the “second”) will run in virtual synchronization when sitting side by side in a lab. We would expect that to be true. If we take one of the two and launch it in an orbital space vehicle which then circles the earth at 18,000 miles per hour, from our vantage point on earth, we would observe that the orbiting clock now runs slightly slower than its identical twin still residing in our lab, here on earth. Indeed, upon returning to earth and the lab after some period of time spent in orbit, the elapsed time registered by the returning clock will be less than that of its twin which stayed put on earth even though its run-rate again matches its stationary twin! In case you are wondering, this experiment has indeed been tried many times. Unerringly, the results of such tests support Einstein’s contention that clocks moving with respect to an observer “at rest” will always run slower (as recorded by the observer) than they would were they not moving relative to the observer. Since the constant speed of light is 186,000 miles per second based on the dictates of relativity, the tiny time dilation which an orbital speed of 18,000 miles per hour would produce could only be observed using such an incredibly stable, high resolution time-source as an atomic clock. If two identical clocks passed each other traveling at one-third the speed of light, the “other” clock would seem to have slowed by 4.6%. At one-tenth the speed of light, the “other” clock slows by only 0.5%. This phenomena of slowing clocks applies to any timekeeper – from atomic clocks to hourglasses. Accordingly, the effect is not related to any construction aspects of timekeepers, only to our limitation “to observe” imposed by the non-infinite, constant speed of light dictated by relativity.

For most practical systems that we deal with, here on earth, relative velocities between systems are peanuts compared to the speed of light and the relativistic effects, although always present, are so small as to be insignificant, usually undetectable. There are important exceptions, however, and one of the most important involves the GPS (Global Positioning System). Another exception involves particle accelerators used by physicists. The GPS system uses earth-orbiting satellites traveling at a tiny fraction of the speed of light relative to the earth’s surface. In a curious demonstration of mathematical déjà vu when recalling the problem of finding the longitude-at-sea, even tiny variations in the timing signals sent between the satellites and earth can cause our position information here on earth to off by many miles. With such precise GPS timing requirements, the relativistic effect of time dilation on orbiting clocks – we are talking tiny fractions of a second! – would be enough to cause position location errors of many miles! For this reason, relativity IS and must be taken into account in order for the GPS system to be of any practical use whatsoever!

Is it not ironic that, as in the longitude-at-sea problem three centuries ago, accurate time plays such a crucial role in today’s satellite-based GPS location systems?

I hope this post has succeeded in my attempt to convey to you, the reader, the wonderful mysteries and importance of that elusive notion that we call time.

Finally, as we have all experienced throughout our lives, time is short and….



2 thoughts on “Marking the Passage of Time: The Elusive Nature of the Concept

  1. You are going to be so jealous when I tell you that I will be visiting the Greenwich Observatory with all of the “wonderful time machines” and will be standing on the International Dateline – one foot on each side – just 3 weeks from Saturday. Can’t wait! Been there before and it fascinates me. Maybe I was a British sailor in another life! ha! Thanks for the interesting read. Reminds me of my PHYSICS FOR TEACHERS class at Cal Poly 🙂

    On Thu, Apr 7, 2016 at 11:32 AM, Reason and Reflection wrote:

    > Alan posted: “Nature presents us with few mysteries more tantalizing than > the concept of “time.” Youngsters, today, might not think the subject > worthy of much rumination: After all, one’s personal iPhone can > conveniently provide the exact time at any location on our pl” >

    • You are so right, Miz Fiz, I am very envious! How lucky are you? I wanted to add to the post some info on Greenwich, but did not want to get too lengthy. As you know, the observatory opened in 1676, being commissioned by King Charles II to advance the cause of astronomy…with an eye to solving the longitude problem. Greenwich is high on my list of future destinations. Take some good pictures to bring back, and have fun straddling the prime meridian!

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