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
Dividing an hour into 60 parts was pretty common in the ancient world, because 60 is a number that divides evenly into many fractions – 1/3, 1/4, 1/2, 1/6. In fact this sexagesimal type of math was pretty common in the ancient world for this reason. Further dividing the minute into 60 seconds is just a logical progression of that. However, people in the pre-modern world would have used relative hours – that is, they counted twelve hours between sunrise and sunset and evenly divided them. This meant that hours were shorter in the winter and longer in the summer, so minutes and seconds would be longer and shorter as well.
It wasn’t until mechanical clocks that the period of the second became standardized as 1/60 of 1/60 of an hour (or 1/24 of the solar day).
The important question is … how long does a first last if the second lasts 1s?
Day split into 24h, one hour split into 60 minutes, one minute split into 60 seconds.
12 was a nice number.
60 was a nice number.
then someone thought to take some atom constant to define one second exactly the same for everyone and for eternity.
Imagine you have to take the train at 10 am. But if your clock says “10 am” at a different moment than the clock at the train station, you might miss the train.
This was how it used to be. People were late all the time, because my clock did give a different time than your clock.
Then, some very smart people in Paris thought it would be smart to make the time the same for everybody. And decided how long a second lasts.
Now people don’t come too late anymore.
[https://en.wikipedia.org/wiki/Metric_time](https://en.wikipedia.org/wiki/Metric_time)
*BTW I am not making this up, and it was worse than you might imagine: every city had it’s own “random” timezone, without much system like with the time zones we have now, it was pure chaos. You needed special tables to determine the time in the next city. It did not matter much until dirigibles and trains came along, hence I use trains as example.
Go back far enough and an hour wasn’t a consistent length. Romans divided daytime into 12 hours, so a winter hour was shorter than a summer one.
A very long time ago, people in Egypt decided to divide the daytime into 10 parts, and they added an extra part at the beginning and end of the daytime, so that’s 12 parts. They did this for nighttime too, so that’s 24 parts. Or hours.
But we needed a way to divide each of those hours again, so someone else from Afghanistan divided the hours into 60 minutes. Minute is what we call the time, but it also means something really small. Like “that ant is minute”. This person chose 60 minutes because 60 can be split by lots of other numbers, which makes it easier to count half a minute or a quarter of a minute.
So what about seconds? Well the same person that split hours into minutes (small parts) split it again into second minutes, the 2nd small part. Nowadays we just say seconds.
They didn’t all agree. other time systems exist, but the most commonly used option gets adopted until it becomes ubiquitous.
For example You could use metric time if you want. https://cable.ayra.ch/metric/
The second is defined by the amount of time it takes for the cesium atom to oscillate 9,192,631,770 times.
Everyone else has covered the history of sundials and other ancient methods of timekeeping. Fyi a primary driver of more accurate mechanical timekeeping was navigation in the age of sail. With the aid of a ship’s chronometer tracking the time of your nation’s prime meridian you can use the chronometer time of noon (when the sun is highest in the sky) at your current location to calculate longitude, and the angle of sun at noon at your current location and date to determine latitude. That allows you to determine with a decent degree of accuracy where you are on the globe even in the middle of the ocean.
The notion of doing geometry with a 360-degree circle had been around for a long time because it divided so well. A sundial marks the passage of time by drawing a circle, so the two ideas naturally went hand in hand. (Also note the mystical number 12 fits very nicely into a 360-degree circle.)
It’s important for science to have a universal standard so that experiments can be reproduced and recipes followed everywhere. In normal life, people could accept the measurement of a “yard” being “about as long as your arm,” or an hour being “about this much time,” and they rarely needed a measurement more precise than those. But science needs a more strict definition.
My old physics textbook tells me the original scientific definition of a “second” was 1/86,400 of a mean solar day, but it doesn’t tell me who came up with that. It sounds like something Copernicus or Galileo could have taken a stab at, probably Newton and his crowd, certainly. Once people figured out how to work with individual atoms, science was able to come with a really precise definition. The current definition of a second has to do with the amount of time it takes for a cesium atom to decay from one energy state to another. I guess that’s something people are able to measure with great accuracy and ease. Anyway, that’s what an “atomic clock” is.
You might be interested to know that things like the meter have similar scientific definitions. I think the meter is the measure of so many waves of a certain kind of laser light shot through a certain kind of gas. This is, again, apparently something scientists can count with ease. I can’t.
In the “What Might Have Been” department, when the metric system was formally adopted during the Age of Reason, the revolutionary French government also proposed a 400-degree circle with right angles of 100 degrees. They also proposed a standardized calendar with 30-day months and 10-day weeks. Both of those ideas make logical sense, but they didn’t catch on.
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