We all experience time. If you’re interested, reading this may feel like it takes 5 seconds when in reality it actually takes 30 seconds. This defines the concept of relativity. Every individual may experience time differently based on the given circumstances. However, more often than not, relativity is attributed to motion. From Einstein, we know that the faster one moves, time slows relative to a stationary individual. Eventually, time stops once you reach the speed of light, indicating that photons perceive their birth and death instantaneously. But what dictates time? How do we know time actually slowed down and isn’t due to malfunctioning clocks?
Before the 1960s, the second had been defined as 1/86400 of the time it takes for the Earth to complete a full rotation. The logic here is that since there are 24 hours a day, 60 minutes an hour, and 60 seconds a minute, there are 86400 seconds throughout the day. Therefore, a second is just 1/86400 of 24 hours. Though this portion is true, we cannot directly connect this to the time it takes for the Eart to rotate. As some may know, Earth’s rotation does not always take 24 hours to complete, and in fact does not always take the same amount of time. Based on the previous system for time, scientists quickly realized that certain events on Earth could slow the rotation speed, which threw off our international clock. Earthquakes, tsunamis, and other natural disasters were able to slow the spin by fractions of a second, but these fractions eventually add up.
After this fault was discovered in the current system, scientists looked for a more static form of measuring a second. The answer lies in the most fundamental unit of life: the atom. Specifically, we use the cesium atom to measure time. Under light with a frequency of 9,192,631,770 Hz, cesium’s valence electron jumps energy levels 9,192,631,770 times thus defining the SI unit of a second. Fundamentally, this model is superior to the previous one not only due to its incredible accuracy but also the fact that it can be used to measure time anywhere in the universe and is not dependent on observing the Earth. This gives scientists a, quite-literal, universal model to measure time without discrepancies.
