User:WalkingRadiance/Atomic Clock

An atomic clock is a clock that measures the frequency that atoms vibrate at. Atomic clocks are much more accurate than mechanical clocks because

Definition of the Second

The second was established as a base unit International System of Units in 1954, along with the kilogram as the unit of mass, the meter as the unit of length, the ampere as the unit of electric current, the kelvin as the unit of absolute thermodynamic temperature, the mole as a unit of amount of substance, and the candela as a unit of luminous intensity.

The old definition of the second was recommended by the CIPM in 1956 and ratified by the CGPM in 1960:

"The second is the fraction $\frac{1}{31556925.9747}$ of the tropical year for 1900 January 0 at 12 hours ephemeris time." The 1964 meeting of the CIPM issued the following recommendation for the second:

"The standard to employed is the transition between the hyperfine levels F=4, M=0 and F=3, M=0 of the ground state $^2S_{1/2}$ of the caesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz." The 13th meeting of the CGPM abrogated the tropical year definition of second with a new definition: "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.'" In 1970, the CIPM decided upon International Atomic Time: "International Atomic Time (TAI) is a coordinate time scale defined in a geocentric reference frame with the SI second as realized on the rotating geoid as the scale unit." The current definition of the second was reworded to make the new definition consistent with the kilogram, kelvin, ampere, and mole's new wording after the 2019 redefinition of the SI base units.

"'The second, symbol s, the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, $\Delta \nu_{Cs}$, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to $s^-1$" This definition implies the exact relation }}