Who, how and when decided to count to a second and was like “Yup. This is it. This is a second. This is how long a second is. Everybody on Earth will universally agree that this is how long a second is and use it regardless of culture, origin, intelligence or beliefs”?
In: 1035
I would suggest a read of “the history of measurements” by James Vincent. Really delves into the history of measurements like this and is actually a really interesting read. I was dubious but it kept me captivated for hours.
Blame the Babylonians. Babylonian mathematics used a base 60 system which means they were all about dividing things into 60 parts. One exception is the division of the day into hours. For whatever reason, they thought 12 daylight hours and 12 hours of night made more sense than splitting the while day 60 ways. For what it’s worth, 12 is 1/5 of 60. Anyway, hours get divided into 60 minutes and each minutes is in turn divided into 60 seconds. As a result, a second is the length it is because it was originally defined as 1/86,400 of a day. Today, a second is more rigorously defined as a specific number of vibrations of a cesium atom but the period of time is still essentially the same
Dividing things by 12 and 60 were very common in early civilisations because these numbers can be easily divided by others. 12 can be divided by 1, 2, 3, 4, 6 and 12; and 60 can be divided by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60.
They’re highly divisible numbers. Thats another reason why there are 360 degrees in a circle – it’s highly divisible.
So it’s not surprising modern Western timekeeping has its mathematical roots in ancient Babylonian astronomy, who were familiar with the divisibility of these numbers, and divided the movement of the Sun across the ecliptic into degrees, then into minutes and further into seconds (though not by these names).
The “day”, of course, is was naturally divided into two logical and useful periods – day and night.
And once again, the original time piece – the sundial – was the projection of a shadow from the sun on a circle.
Useful days, sunrise to sunset, were then formally divided by the ancient Greeks into 12 parts (and nights into three or four watches). That was usually accurate enough for the practical needs of the day. Divisions of the night into similar periods of 12 hours came later.
But, more accurate times were needed for specific purposes, so these hours were divided by ancient Rome, as the Babylonians did with astronomical time, into first divisions of 60 minutes, from the Latin “minutus” meaning “made small”.
Then, these first minute divisions were further divided into 60 second divisions, which gives us “seconds”; literally the second small part of an hour.
The actual length of a second of course, varied based on the latitude and time of year, because of the tilt of the earth making the daylight hours longer in summer and shorter in winter. Modern timekeeping standardises this so it remains constant.
Seconds last a “second” because if you divide a standard revolution of the Earth into 24 hours, then these hours into first divisions of 60 minutes, then each of these minutes into second divisions of 60 seconds each. These numbers were chosen because of their practicality and divisibility.
All units are like this – not just the second. People / scientists have got together and defined all units based on something.
I remember when I was little me and my cousin who was also little were staring at a clock for some reason waiting for the digital time to tick up one. And he said “ok any second now”
And I remember saying well yeah any second now, as there only seconds left in a minute. We both laughed and laughed. I feel like it was a profound thought for our age
We all just agreed. Just like the metric system, we agree a meter is a meter, a kilogram is a kilogram. Even places that don’t use the metric system, a foot is a specific fraction of a meter and a pound is a specific number of kilograms.
We also defined a second as a specific number of oscillations of a cesium atom, a meter as the distance light travels in a specific number of oscillations of a cesium atom, etc so you can determine these measurements anywhere in the universe.
The second was actually defined well before the other units in the metric system. When the metric system was created, they tried to make metric time, 10 hours in a day with 100 minutes with 100 seconds, but this didn’t catch on.
By “well before,” I mean the metric system was established in 1795, whereas the second was first conceived by the Babylonians (who used a base 12 counting system, hence 24 hours in a day, 60 minutes, and 60 seconds, as well as 360° in a circle). The first mechanical clocks were built on this system in the 14th century, and we could get an accurate measurement of a second by the late 16th century.
I want to add to all the good answers with a recommendation. Riley Knight did two episodes on the History of Clocks in his Half-Arsed History Podcast. [https://halfarsedhistory.net/2020/05/31/episode-101-the-history-of-clocks-part-1/](https://halfarsedhistory.net/2020/05/31/episode-101-the-history-of-clocks-part-1/) The podcast is a really fun listening experience if you like casually presented history.
A lot of ancient civilizations did things in groups of 12. This is a really easy number grouping when you need to split things up into groups (you can do groups of 2, 3, 4, or 6 easily while 10 things can only easily be shortly into groups of 2 or 5), and there are a lot of interesting coincidences related to 12.
If you use the phases of the moon to track a year, then you have around 12 cycles to a year. If you teach the number of days in a year, 365 is pretty close to 360 which is 12×30 (several ancient calendars had 12 30-day months and then a 5-day period at the end of the year that doesn’t fit inside those months). This is one reason why there are 360 degrees in a complete rotation–it’s pretty close to the number of days in a year and it’s a multiple of 12.
So it turns out if you split the day rotation into two 12s (12 night hours and 12 daylight hours) and then make those hours equal lengths, and then split those hours into 5 12s (5×12 being 60), and then split *those* into 5 12s, the amount of time that represents is a second.
Some people think that a counting system based around 10 is more intuitive since we have 10 fingers, but it’s a purely cultural thing that we count each finger as 1. In the Babylonian fingerer counting system for example, [they didn’t count their fingers but their finger segments for each finger other than the thumb](https://www.earthdate.org/episodes/how-10-fingers-became-12-hours#:~:text=Babylonians%20also%20used%20their%20hands,times%20five%20fingers%20is%2060.), which means they would count to twelve on one hand.
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