How did the whole world end up agreeing on what time it is?
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It started in the late 1800s
Atomic clocks invented in the 1950s
It was internationally agreed upon in the 1960s. There’s an entire history section on the UTC wiki page as well, if you’re interested.
It didn’t. That’s why we have time zones. If it did we would have star date like in star trek.
It was actually a long process, and started in the mid 1800s in the UK in an effort to synchronize train schedules. The widening use of the telegraph helped because before that, communication over long distances was done at the speed of horse (or train) and synchronizing time from city to city was not important. By 1880, Britain made the use of this synchronized train time official for the country. In 1883, the General Time Convention was widely adopted throughout the US and Canada, primarily because a common time was necessary for the nascent railroad industry – hard to make the trains run on time if you can’t agree on the time. This convention mirrored the earlier British convention and established time zones as well (using GMT as the prime meridian/reference for all time zones). Once these major countries agreed on a time convention (the adoption of the Greenwich Mean Time as the reference, and time zones utilizing GMT as their benchmark), one by one nearly all of the world’s nations adopted the same time convention.
At the [International Meridian Conference](https://en.wikipedia.org/wiki/International_Meridian_Conference?wprov=sfti1) held in 1884 in Washington DC, delegates from 26 countries met and decided that the imaginary line running through Greenwich in the UK would serve as the point for 0° longitude and everyone would offset their time from there.
Greenwich was selected because they had already figured out how to standardize the UK’s time against reference clocks for the sake of more efficient rail travel.
By locations of stars. Noon is when the sun reaches the highest point in the sky.
Eventually more stars were used (ephemerides.) Astronomers were very involved with this.
Then physicists got involved and learned a second can be defined by a constant found universally in nature–atoms. The second became the most precise SI unit as a result… so precise in fact that seconds needed to be added or removed on occasion (leap seconds) to avoid seasonal drift.
The speed of the rotation of the Earth pretty much sets what time of day it is. When the sun comes up is the start of the day, when it is over head is the middle of the day, when the sun goes down is the end of the day. Easy. There is no “agreement” there, that’s simple how the world is.
Dividing the day up into artificial increments. Well different civilizations did that in different ways. Methods of doing this spread (in historical times) through conquest. Basically a military adept colonizing/conquering empire comes in and takes over and says, “We don’t care how you divide the day up, this is how we do it and this is how you’re going to do it from now on.”
So someone like the Roman Empire comes through and regardless of how you divided the day up before, you now divide the day up into 12 increments. And it’s easy enough to use a sundial to do this.
At some point, probably alongside the invention of clocks, we divide the day up into 24 equal increments (rather than only dividing the day up into 12 increments based on the length of daylight). Clocks can easily keep track of this and the position of the sun is still enough to roughly determine what time of day it is by the hour (calibrating it as Noon = Sun directly over head).
Breaking the day up into more specific increments really isn’t a thing until watches come along and still pretty much a luxury.
For a majority of human history there was no agreement because there was never a need to agree on the time. Each settlement simply set its own time (e.g. via a church or clock toward). The idea that you needed to know what the time was in some other place would have been looked at as silly.
But when things like trains and long distance travel and communication come along, there then does become a need to know what time it is somewhere else. So now there is a pressure, a need, to determine “what time it is” all around the world. So we come up with time zones. But we can’t force anyone to accept them, they’re just an idea people voluntarily agree to. Now, given that we are still in the age of empires, this “agreement” comes pretty readily because most of the population and landmass of the world is under the political control of a handful of entities. But that basically sets people’s time at least within the hour. If you are in a given time zone, that determines what your hour is.
And that basically covers things for the most part up to today. We have time zones that people agree to because it is a useful tool for international travel and communication.
Please listen to the episode of “How It Began” podcast by “Brad C Harris,” titled “Measuring Time: The Hidden Mechanism of Modernity.” I don’t this subject cannot be explained better than the way he did.
A friend who worked in Ethiopia said there was a different time system used there. 12 hour days. So technically the whole world didn’t. Maybe there are other examples?
there was a great series on PBS a few years ago called “How we Got to Now” and one of the episodes focused on the standardization of time. Really interesting.
It’s hosted by the author of the same-named book, Steven Johnson
Pretty sure we didn’t, it’s 11:53am. I bet if you post what time it is there it won’t match up! (time zone aside)
Edit: stupid joke, by the time someone else posted it wouldn’t be the same…
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