Is Time a Human Construct?

When we ask “What time is it?” we’re not trying to pose a deep question. There is a universal assumption that a correct time exists, even though we might not know what it is at the moment. Most of us also believe that time is both unchangeable and uniform. An hour is an hour, whether you live in the United States or the United Kingdom.

It’s not true, however. Time is, and always has been, a human construct shaped by social interactions and customs.


Clocking Out

Life regulated by a clock is a foreign concept in certain countries. For example, in Burundi, meetings and obligations are scheduled according to certain events. If a person wants to arrange a morning appointment, they might specify “when the cows are out for grazing.”


The language of the Hopi tribe in northeastern Arizona has no past, present, or future; for them, time is not a series of distinct instances. Similarly, nomadic tribes in Afghanistan and Iran use the seasons to measure time, making it a cyclical event.

Allen Bluedorn, a University of Missouri management scholar, wrote, “What any group of people think about time ends up being a result of them interacting with each other and socialization processes.” In other words, time is a manifestation of social mores, just like fashion and technology.

When Time Began?

The U.S. national time standard didn’t come into effect until 1883, when the railroads adopted it to maintain shared timetables. Rather than a formal acceptance of an existing element, the adoption of national time struck Americans as revolutionary. The Washington Post likened it to the reformation of the calendar by Julius Caesar and later Pope Gregory XIII.

time zones

Prior to that event, cities and even smaller communities tended to observe their own local time. Many of them were firmly against the change, with the Boston Evening Transcript protesting, “Let us keep our own noon.” One Cincinnati newspaper editor huffing, “Let the people of Cincinnati stick to the truth as it is written by the sun, moon and stars.”1

The paper was reminding its readers—and the railroads—that seconds, minutes, and hours were not a natural phenomenon. Certain units of time, like days, months, and years were in sync with natural events, such as the earth’s movements. Anything else was too arbitrary and, in the case of the U.S. national time standard, too open to manipulation to be real.

Time as a Cultural Phenomenon

Even in societies that do live by the clock, not everyone shares the same concept of time. Americans are ultra-sensitive to timing, with their days consisting of one precisely scheduled event after another. Failure to be punctual is a sign of personal and professional weakness. For other cultures, notions of being early, late, or on time are not as rigid. In Brazil, people who are consistently late are regarded as being more successful than those who are always on time.

The presence of these subjective views and the historic resistance to the standardization of time indicates that time itself is not an independent and natural concept. It has been defined and developed to meet the needs and expectation of any given society. There are suggestions that the current era of globalization is bringing nations more closely together and may one day result in a global time standard, but it’s not likely. At least not without a lot more controversy than the U.S. railroad barons encountered in 1883.

1 Levine, Robert. A Geography of Time: The Temporal Misadventures of a Social Psychologist, or How Every Culture Keeps Time Just a Little Bit Differently. New York: BasicBooks, 1997. p.73

A Day on Another Planet

A day refers to the amount of time it takes for a planet to complete a single 360-degree rotation on its axis. On Earth, that’s 24 hours. But the other planets in the solar system rotate at faster or slower speeds, and their day lengths vary accordingly.



On Mercury, a single day amounts to 58 days and 15 hours Earth time. In contrast, the planet’s years are extremely short: only 88 Earth days. This is because Mercury moves more quickly around the sun, abbreviating its years, while its speed of rotation is slow enough to prolong its days.


Of all the planets in the solar system, Venus has the longest day. Its equivalent is 243 Earth days, while its year only consists of 224.7 days, essentially making its days longer than its years. The reason for the discrepancy is its slow rotation speed: while the velocity of the other planets have flattened their poles, Venus has not leveled out anywhere. It also rotates backwards, an oddity that some astronomers attribute to a massive impact with another planet billions of years ago.


A day on Mars, which is referred to as a ësol’, consists of 24 hours, 39 minutes, and 35 seconds, making its days similar to Earth time. This is one of many reasons why scientists asserted that plant and animal life could exist on the Red Planet, as Mars is also called. A Martian year lasts 686.98 Earth days, which translates to approximately 1.88 years.


Jupiter is the largest planet in our solar system, but it also happens to have the shortest day (9.9 Earth hours), because it rotates more quickly than any other body in the solar system. Its rapid rotation speed has caused extreme flattening at the poles and a bulging equator line.

Scientists had difficulty determining day length on Jupiter because it lacked surface features that could be used to calculate its rotational speed. At first storm centers were used, but Jupiter’s storms moved so rapidly that results were inconclusive. Rotational period and speed were finally determined by assessing radio emissions from the planet’s magnetic field.


The length of a Saturn day has proven to be extremely difficult to calculate, as the plant is a giant gas entity as opposed to terrestrial like Earth or Mars. The first estimation, which was attempted back in the 1980s, was 10 hours, 39 minutes and 24 seconds in Earth time. A second attempt delivered a result of 10 hours, 45 minutes, and 45 seconds. Using more advanced equipment in 2006, astronomers came up with a measurement of approximately 10 hours and 47 minutes. Some members of the scientific community assert that the length of a day on Saturn will never be known for certain.


A day on Uranus is the equivalent of 17 hours, 14 minutes, and 24 seconds on Earth. Because its axis is tilted to nearly 90 degrees, Uranus actually rotates on its side instead of spinning like a top. As a year progresses, one of its hemispheres faces the sun’s light while the other is in darkness for a complete season. What this means is that the planet’s days and seasons are one and the same. Day is as long as summer, and night is as long as winter.


On Neptune, a day translates to 16 hours, 6 minutes and 36 seconds on Earth. Since the planet is mainly gas, different parts actually rotate at varying speeds, a process known as differential rotation. Neptune’s equator zone takes around 18 hours to rotate, while the polar regions complete a cycle in 12 hours. Scientists attribute the large difference in rotational rate to Neptune’s winds, which can go up to 2,400 km/hour, making them the strongest in the solar system.

The Leap Second: a Jump in Time

Did you know? Leap seconds are adjustments made to Coordinated Universal Time (UTC) so that the UTC time standard, which is measured by atomic clocks and used for international timekeeping, can be synchronized with astronomical time to within 0.9 seconds.

The Earth’s rate of rotation around its axis is irregular, while atomic clocks are engineered to tick at the same speed for eons. The addition of leap seconds ensures astronomical time and UTC (otherwise known as Greenwich Mean Time) remain in accord.

earth rotation

The standard allows leap seconds to be applied at the end of any month, but so far all have been implemented on June 30 or December 31. Since their adoption in 1972, 25 leap seconds have been inserted, the last of which took place on June 30, 2012 at 23:59:60 UTC. The next one is scheduled for June 30, 2015 at the same time.

What’s in a Second?

The average day has 86,400 seconds, but atomic clocks do not define one second as 1/86,400 of the time it takes the Earth to travel around its axis. In atomic terms, one second is 9,192, 631,770 cycles of the standard Cesium-133 transition.

It’s an intricate calculation that’s incredibly precise, whereas the Earth’s rotation is slowing down over time, making the days irregular in length. An Earth day averages 0.002 seconds longer than the time tabulated by the atomic clocks. The result is a discrepancy of about one second every year and a half. Leap seconds ensure this discrepancy does not get too vast over time.

In theory, at least, leap seconds can be positive (with one second added) or negative (one second omitted), depending on the status of astronomical time results. All leap seconds have been positive so far, and the current pace of the Earth’s rotation makes it unlikely that a negative one will ever come into effect.

The Future of Leap Seconds

Some scientists want to abolish leap seconds, which would effectively redefine the way time is measured, but a consensus has yet to be reached on the subject. In 2012, attendees at the World Radiocommunication Assembly in Geneva scheduled a new vote on the matter for 2015.

Arguments against leap seconds include the following:

  • They are an anomaly, making them a cause for concern with safety-oriented real-time systems, such as air-traffic control programs that use satellite navigation.
  • Leap seconds are potential disruptions in computer systems that are closely synchronized with UTC.

2012’s leap second played havoc with LinkedIn, Reddit, Yelp, and other sites and applications. The Qantas Airlines computer system even went down for hours, forcing staff to check in passengers manually.

Coding for these apps and systems are based on UNIX, which appeared in 1970, before leap seconds came into effect. When the International Earth Rotation and Reference Systems Service, which maintains global time, signals to these computers that a certain minute has 61 seconds, Unix-based software systems become unstable.

Google developed a solution after the leap second of 2005 caused system issues. It slowly adds a couple of milliseconds to the clocks on its servers throughout the day of an impending leap second, which bypasses the security settings without triggering disaster.


Google’s fix has not been universally applied, and opponents of the leap second remain insistent that any time calibration benefits are overshadowed by the technological crises they cause. They point out that even if a leap second were applied every year, astronomical time would only be 16 minutes behind atomic schedule by 3015.

A Clockwork Strontium: The Future of Timekeeping

In early 2014, a new atomic clock was unveiled at JILA, a joint institute of the University of Colorado Boulder and the National Institute of Standards and Technology (NIST). This strontium atomic device, which set new world records for both stability and precision, has been heralded as a breakthrough in the science of timekeeping.

Atomic clocks keep time based on the frequencies of atoms. Their performance is measured by two primary metrics. The first is stability, or the variation of its speed. The second is precision, which is how closely the clock reaches the frequency at which its atoms oscillate between two energy levels.

First Atomic ClockThe first atomic clock was invented in 1949 at NIST (then known as the National Bureau of Standards) and, because of its accuracy compared to other timekeeping technologies, a new field of research evolved. Photo Credit: NIST.

According to NIST representatives, this clock is so precise that it can keep perfect time for 5 billion years. A small interior chamber contains strontium atoms suspended in a crisscross of laser beams.

When researchers ping them, they vibrate at lightning-quick frequency, turning the clock into a type of atomic metronome ticking out the seconds in tiny fractions.

Record Holder

It is the first clock to hold world records for both stability and precision since cesium fountain atomic clocks became available in the 1990s, and is around 50 percent more accurate than the previous record holder, which is NIST’s quantum clock. Because of its high performance level, it presently serves as the time and frequency standard for the United States.

Thomas O’Brian, who heads NIST’s Time and Frequency Division, said that the clock’s unprecedented ability will “not only lead to better use of things like GPS, but probably open up entirely new applications that I’m not even smart enough to think of yet.”

Technology That Underscores the Atomic Clock

Perfect timekeeping is essential for maintaining a lot of modern tools and conveniences, such as GPS, global telecommunications, and electrical grids. The technology that underscores the strontium atomic clock is so sensitive to gravity, magnetic fields, force, motion, electrical fields, temperature, and other phenomena that it could potentially be used to map the earth’s interior, or help locate underground water springs and other subterranean resources. If a network of these clocks were positioned in space, they could conceivably detect the gravitational waves generated by exploding stars and black holes.

JILA/NIST Fellow Jun Ye and the strontium lattice clock. credit: J. Burrus/NIST

The Next Time Standard?

National Institute of Standards and Technology scientists continue to develop next-generation atomic clocks using different atoms as a base: mercury, ytterbium, aluminum, and calcium. Although still in the experimental stage, these clocks have been showing rapid progress in their timekeeping ability, and each atom type has its own distinct advantages. At the very least, they may enable new technologies, and one might become the next time standard.