Time

"The trouble is, you think you have time."

~ Jack Kornfield

The first math lesson on this website is about units. My favorite unit is that of time. I have always been fascinated with the concept of time. From an early age my mom would tell me that time didn't exist—it's a manmade construct.

When Did Time Begin?

Since prehistoric times, humans have measured time. The Sun, Moon, stars and planets all play crucial roles in time keeping. It is said that the oldest star map is a carving of the constellation of Orion on a mammoth tusk, dated 32,500 years old. While the carving does bear some resemblance to the constellation, and it is certainly a great carving, there is debate about whether or not it was truly meant to be a star map.

The oldest known sun dial was used by the Egyptians, around 1500 BC. While it was a useful device for dividing the day into equal parts, it was useless at night. Candle clocks, water clocks and hourglasses were all used to measure the passage of time.

Lunar and Solar Cycles

The Moon and Sun are the two most prominent celestial bodies in our sky. Ancient peoples observed the movements of these two bodies and used them to keep time. The problem was that the two cycles don’t match up. Roughly speaking, the lunar cycle is 29.5 days and the solar cycle is 365.2 days. 365.2 divided by 29.5 is 12.4. That’s a messy number. That fraction of a day adds up over time, requiring an extra day be added to the calendar every four years—known as a leap year.

The solution is to find a period that is a common multiple of the months (lunar cycle) and years (solar cycle.) That is, we want a whole number of months to fit nicely inside a year. Such a number does not exist. Cultures throughout history have strived to find the best approximation possible. It was this desire to align the lunar and solar cycles that led to the creation of the calendar.

Do You Have A Minute?

The Egyptian sundial divided the daylight hours into 12 equal parts. Since summer days are longer than winter days, each summer hour was longer than a winter hour. A water clock was used around 1400 BC to keep time at night. One example was found that divided the night into 12 equal parts. 12-hour days, 12-hour nights—we have our 24-hour clock.

The division of hours into 60 minutes, and minutes into 60 seconds originates from the mapping of the Earth with lines of latitude and longitude. Greek astronomers divided a circle into 60 parts (utilizing a sexagesimal system invented by ancient Babylonians) to create lines of latitude. Lines of longitude were created, running north-to-south, encompassing 360 degrees. So, 360 degrees was divided into 60 equal parts, called minutes (from the Latin partes minutae primae, or first minute) and each of those minutes was divided into 60 parts, called seconds (partes minutae secundae, or second minute).

Does Time Exist?

Was my mom right? Is time just a manmade construct? It would seem so. Certainly, we see the physical representaions in sunrises and sunsets; the changing of the seasons; the lengths of the days; the precession of the equinoxes. But just as certainly, we all experience the same interval of time, as measured on a clock, in different ways. The last hour of work before the weekend drags on for you, while your neighbor, who’s getting ready to work the weekend night shift, perceives that hour as flying by all too quickly. The four years spent in high school seem an eternity to the child, while to the parent the years are over in the blink of an eye.

To quote Albert Einstein, “Time is an illusion.”

For The Interested Reader

Fixed-length hours were not common until the invention of the mechanical clock in the 1300s. Until then, the hours varied in length with the seasons.

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