How do we know exact time? Do we all copy one clock and if so, how do we know it is correct?
In: Technology
All the world’s base clocks are coordinated with each other. That’s why UTC is called Coordinated Universal Time. The base clocks communicate with each other all the time, making small adjustments to move the time as represented in the group forward consistently. UTC is based on TAI (International Atomic Time) a weighted average of hundreds of atomic base clocks located all around the world. It’s coordinate by the BIPM ([International Bureau of Weights and Measures](https://www.bipm.org/en/bipm/tai/ )), a group of scientists.
Yes the atomic clock. And through astrology and mapping the sun is how all our time is based. Earth is slowing down by like 10,000ths of a second gradually. The time keepers at the international earth rotation services account for this.
The main way to tell the clock is by using an atomic clock, there are different around the world, the us uses one in colorado iirc, eu uses one somewhere in germany. Theyre cesium based, as we define a second as the time elapsed between 9.192631770 x 10 9 wobbles (dont know the way to explain this in english, sorry xD) between two levels a cesium atom.
And the easy way to say why its correct is because we choose to collectively say that its correct. There is no “actual time” in the universe.
well, yes, we have atomic clocks and satellites measuring the orbit of the earth and we can copy the calculation to get an exact time But is this time correct?
Basically, where ever you live, the sun is as high in the sky as it will get all day at one exact moment in the afternoon. That moment, that is the time of day, no matter how you measure it.
How long is a second? It should be based on some physical thing we can measure that happens regularly.
Up until about 50 years ago, measurement of time was based on astronomy (the motion of the Earth, which causes day/night and seasons).
There are small disturbances in the motion of Earth from other planets, and from things like tides. Once you build precise enough clocks, you notice that astronomical things aren’t good measurements, because they have irregular tiny disturbances.
Since sometime in the 1960’s, time is based on measuring how fast certain kinds of atoms vibrate. This is a physical process that can be measured extremely precisely.
Anyone with certain kinds of science knowledge and enough money can build an atomic clock. The US, some other governments, and some science labs have their own atomic clocks. Many of them put their clocks’ timing signal on the Internet. The US government’s timing system [for example](https://www.usno.navy.mil/USNO/time/master-clock/precise-time-and-the-usno-master-clock) has a couple dozen atomic clocks of multiple different kinds that are used to guard against the possibility of one being wrong.
Time in the sense we usually think about it is a human invention. We “know” the exact time because we have agreed to a definition of what units to use, and when to start counting from. Asking “What time is it?” is like asking “How far away are we?”. The answer depends entirely on what reference point you are measuring from, and what units you define to use.
Most people consider this to be the year 2020 AD, but this counting method was derived from a decision made by the Catholic Church many centuries ago. People from non-Christian cultures may not consider it to be the year 2020. For instance, in the Hebrew calendar it is the year 5780. In the Chinese traditional calendar, it is the year 4718. In North Korea, it is the year 109. These calendars don’t necessarily have the same 365 day year, or consider January 1 to be the first day of the year.
The most widely used standard for time is based on “Greenwich Mean Time”. This is based on the time in Greenwich England. At the time this standard was created, England was the scientific capital of the world, so it made sense that the standard for time would be based in England.
Most of the world is now synchronized to atomic clocks. This is done over the internet, or using radio signals broadcast from different radio stations all over the world. In the United States, the timing radio station is located in Colorado. The atomic clocks in each country are synchronized together.
There is an international standards body that defines the length of one second. This used to be cased on the amount of time it takes earth to rotate, but it is now based on precise measurements of atoms vibrating, which is constant (the earth’s rotation actually varies over time).
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