A lot happens in 24 hours.
Your heart beats around 100,000 times.
150 to 200 species of animals become extinct.
Lightning strikes earth 8.6 million times.
Astronauts aboard the International Space Station
will see 16 sunrises and 16 sunsets.
About 367,200 babies will be born
and about 151,600 people will die.
So yeah, a lot goes on in just 24 hours.
But why is a day divided in 24 hours in the first place?
Who decided how we would calculate it?
Today, time is tucked away in our pockets,
just an unlock button away.
It drives our technology,
with atomic clocks being responsible for
precise GPS location services
and speedy internet search results.
Our ancestors, on the other hand,
didn’t have it that easy.
Time for them was written in the stars,
in the sunrise and sunset,
in the moon’s waning and waxing.
So how did we go from looking up to celestial bodies
to looking down at our phones for time?
What other time-keeping methods did ancient humans
use before watches and clocks became ubiquitous?
And what the heck is an atomic clock?
You’re watching Explore Mode and today,
we are diving into time,
and how humans developed technologies to measure it.
Let’s start with celestial bodies.
Early civilizations like the Egyptians
used the moon’s phases
to determine the length of a month.
In prehistoric Europe, humans built stone rings called
recumbent stone circles that would frame and track
the moon in each of its phases.
It’s believed they were built for ritualistic purposes.
Then we have the creation of the sundial.
A device that shows the time using the sun's shadow
depending on its position in the sky.
The earliest archeological evidence of a sundial
was found in the Valley of Kings in Upper Egypt in 2013
and it dates back to 1500 BCE.
A larger version of the sundial is the obelisk,
which was used to mark
the summer and winter solstices.
While Egyptians, Romans and Greeks
were using sundials to keep track of time,
people in Asia were using candles and incense sticks.
Candle clocks worked as follows:
Each candle had markings on its sides indicating
the passage of a certain period of time
so as the candle burned you could calculate
how much time had expired.
The first reference to candle clocks
dates back to 520 AD in a poem
written by Chinese thinker You Jiangu,
who seemed to use them for study sessions.
Similar to candle clocks,
early evidence of incense clocks takes us back to China
6th century China to be exact.
Different incense sticks would indicate
the passing of time depending on
how quickly they burned.
Some sticks had different aromas
for each hour that passed
and others had weights attached at different sections
that would drop as the incense burned.
But incense clocks stuck around well after
we had developed watches and pendulum clocks.
Until 1924, in Japan, geishas would count
how many incense clocks had been burned
during their services to charge their customers.
Egyptians divided their sundials into 12 parts
for each hour of the day from dusk to dawn.
Although sundials were quite accurate for their time,
they had one very evident disadvantage.
They were practically useless
during overcast days and at night.
But back to the 12 hour day division.
So 12 hours for day time, 12 hours of the night time.
That’s 24 hours a day, no surprise there.
But why then is each hour divided into 60 minutes
and each minute into 60 seconds?
Well, that has to do with a numerical system
that is still used today.
Time for an Express Explore Explanation.
Start the Clock.
The Sexagesimal system takes us
back to ancient Mesopotamia.
It is a numerical system based on the number 60
that was developed by the Sumerians
and later adopted by the Babylonians.
They developed it by dividing parts of their fingers
into single units, and units of 12.
Here’s how it worked.
Take a look at the palm of your hands.
Notice that each of your fingers is divided
into three sections.
Using their thumbs to count,
the Babylonians realized they could count up to 12
for each section on each finger of one hand:
3 x 4 = 12.
The five fingers on the other hand
each represented a dozen.
So 12 x 5 = 60.
Also, 60 is divisible by
1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30,
making it an easy number to split
for a civilization with no calculators.
This system is used nowadays to divide
time, angles, geographical coordinates
and it is the mathematical base
for astronomical coordinate systems.
In order to bypass the “no sunlight” conundrum,
the Egyptians needed another method of timekeeping
and so, they developed the water clock.
Here’s how they worked:
Egyptians would fill a bowl-shaped container with water.
Said water had a spout at the bottom
which would allow for water
to flow out into another container.
It had 12 markings on the inside,
each line representing the passing of an hour.
As the water flowed out,
they would compare the water level with the markings
to determine how much time had passed.
The problem with this type of water clock
was that it didn't provide an accurate representation
of the passage of time.
You see, as the container emptied out,
pressure of the water would lessen,
making the water run more slowly by the end.
Enter Ctesibius,
an inventor and mathematician from Alexandria,
and the man now regarded as the inventor
of the first real clock.
Between 270 BC and AD 500,
he figured that instead of measuring time
based on the outflow of water,
he would measure the consistent inflow of it.
It worked pretty much in the same way
except that instead of measuring
how much a container had emptied,
he would measure the rise of the water level
as the liquid steadily flowed into the container.
Unbeknownst to Ctesibius,
he had created the first, albeit quite rudimentary,
mechanical clock.
For many years, the perfected water clock
was the most accurate timekeeping device.
That is until proper mechanical clocks appeared.
The first people to build large mechanical clocks were
Catholic monks.
They needed precise timekeeping devices
to schedule chores and prayers within the monastery.
According to historian Thomas Woods,
the first recorded clock was built
by the future Pope Sylvester II for
the German town of Magdeburg, around the year 996.
Then came the inventions of Christian Huygens,
a Dutch physicist, mathematician, astronomer,
and inventor who, using theories from
none other than Galileo Galilei,
created the technology behind the pendulum clock
and the springs in the pocket watch.
Pocket watches were the first to be mass-produced
allowing everyone and their mother
to be able to keep time in their pockets.
Clocks today are more precise than they have ever been.
Seconds are no longer measured
with the swing of a pendulum.
They are measured with crystals and atomic particles.
Time for an Express Explore Explanation,
start the clock.
With pendulum clocks,
one swing of the pendulum equates to one second.
This is how you calculated time.
But pendulums depend on a lot of external factors
to maintain a constant swing,
so a more precise form of frequency
was needed to create more accurate clocks.
That’s where the quartz comes in.
Check your wristwatch or whatever timepeace you own.
If it says quartz,
it means that your device is powered by a crystal.
The quartz is a clear mineral
made of silicon and oxygen (SiO2)
that vibrates at a very precise frequency
whenever it is zapped with electricity.
Quartz crystals are fashioned into resonators
in the shape of a tuning fork and put inside timepieces
where they’re receiving constant electric signals.
A piece of quartz resonates at
32,768 pulses per second.
Indicating that whenever the quartz
reached that amount of pulses,
a second had passed.
But although quartz clocks are fairly accurate,
they’re still not the most precise form of timekeeping.
Quartz crystals vibrate at different frequencies
depending on whether they’re in
warm or cool environment
making them gain or lose a few seconds.
What can be more precise than the oscillation
of a crystal being electrocuted?
Atoms.
Cesium-133 atoms to be precise.
See, Cesium-133 atoms resonate between
different energy states at an extremely stable frequency.
A quality that is imperative for precise timekeeping.
So, in 1967
the National Institute of Standards and Technology
declared that the official measurement of a second
is equivalent to 9,192,631,770 oscillations
of a Cesium atom’s resonant frequency.
And that is still the standard used today.
Timekeeping devices nowadays not only help us
to determine our work schedule or set up our alarms.
They are an integral part of the technology
we see all around us.
GPS satellites have at least
two caesium and rubidium atomic clocks onboard
in order to calculate the time delay of signals
and provide an accurate reading of a location.
In December 2018, scientists
at the National Institute of Standards and Technology
developed two clocks using 1,000 atoms
of the element ytterbium in grids of lasers.
These clocks are so precise that
they can show the effects of gravity on Earth,
helping us measure the space-time continuum.
So far this is the most precise form of timekeeping,
but a new technology might emerge in the next decade,
or century or millenia ...
who knows,
only time will tell.
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