Just what’s a second, just? . The question was open to interpretation ever since the first long case grandfather clocks began marking off seconds from the mid-seventeenth century and introduced the concept into the world at large. The answer, simply, is that a second is 1/60th of a moment, or 1/3600 th of one hour. But that is simply pushing the question down the road a little. In the end, what is a hour? . That answer is connected to the best means of time keeping ancient civilizations had, the motion of the Earth throughout the heavens. The quantity of time it can take for the Earth to turn once around its axis, or for it to rotate about the sun, is pretty stable, and also for much of human history, it sufficed as a method of marking the passage of time.
Days, hours, minutes, they are only derivatives of planetary movement. Not Enough Time. Today, however, when computers execute operations in the speed of 4 billion cycles per second, we are in need of a better measure. The rotation of Earth, and its orbit, change slightly with time. Earth’s rotation, for instance, is slowing slightly. So measuring a second based on rotation would mean a second would get gradually longer with time. Eventually, we could not compare the second of today to the second of yesterday.
Therefore, to pin down a really timeless measure of a second, scientists in the 50s devised a better clock, one based not on astronomical processes, But also about the movement of the fundamental bits of atoms, whose subtle vibrations would be, for all intents and purposes, locked in for eternity. Today, one second is defined as 9, 192, 631, 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. That is a mouthful. That number seems arbitrary because each definition of a second has by necessity been based on the one which came before.
We have gotten better at pinning down the exact span of a second, however it still has its origins in early astronomical observations. The 2nd today, the one engraved in cesium, is based on a collection of observations of the Earth’s orbit from the astronomer Simon Newcomb between 1790 and 1892. It had been known as the ephemeris second, and was just a fraction of a year, as characterized by Newcomb’s tables. When scientists moved to their new atomic clock, in 1967 they calibrated it with his measurements. When hit by a laser, the single electron in a cesium atom’s outermost shell will cycle back and forth between two states, known as a hyperfine transition. It may be magnetically aligned in either the same direction as the atom’s nucleus, or the contrary direction, and under a laser’s beam, it is going to flip back and forth between both of these States quickly at a pace that has never changes.