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canopic jug [soylentnews.org] writes:

SparkFun Electronics, known for open source designs and software libraries, has an article covering the history of time keeping [sparkfun.com], from the earliest archeological evidence like sundials and water clocks, through mechanical clocks, to the latest standards like Cesium-133 atomic clocks.

Atomic clocks function by measuring the precise frequency of microwaves needed to induce a particular energy state transition in atoms. The most common type of atomic clock today uses cesium atoms, specifically the transition between two energy states in the cesium-133 atom.

Cesium-133 is perfect for this application for a few reasons. It has one free electron in it's outermost energy level, which means it can be excited by a very specific and very regular frequency. It can also be vaporized at low temperatures, which is needed for the interior of the clock to work properly.

When cesium-133 atoms are exposed to microwaves of a very precise and consistent frequency, they undergo a predictable change in energy levels. The state of the atoms is detected inside the clock, and whether or not they are excited tells the clock if the microwave frequency is correct.

In simpler terms, atomic clocks do not actually count seconds, they create them. In the case of cesium atomic clocks, this frequency is exactly 9,192,631,770 cycles per second - a resonant frequency of cesium-133. This precise measurement is so reliable that in 1967, the International System of Units (SI) redefined the second based on this property of cesium-133.

Previously:
(2024) RIP: Inventor of NTP Protocol, That Keeps Time on Billions of Devices, Dies at Age 85 [soylentnews.org]
(2022) The New Yorker on NTP Software Maintenance [soylentnews.org]
(2015) OpenNTPD 5.7p1 Released [soylentnews.org]
(2014) What Time Is It? Time for Multiple NTP Vulnerabilities! [soylentnews.org]

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