Time is one of the seven fundamental physical quantities in the International System of Units (SI). While we use hours, days, and years in daily life, science requires a stricter, universally accepted standard.
Atomic clocks, which use the vibrations of atoms to measure time, are so incredibly accurate that they will not lose or gain a single second even over 100 million years.
The SI unit of time is the Second, denoted by the lowercase letter s.
Whether you are measuring the speed of a car (m/s) or the frequency of a wave (Hz = 1/s), the second is the absolute foundational unit of time in Physics.
While the second is the official SI unit, other units are accepted for use with the SI system because they are so common:
Historically, a second was defined as 1/86,400 of a mean solar day. However, because the Earth's rotation is slightly irregular, scientists redefined it in 1967 using atomic physics: One second is officially defined as the time it takes for a Cesium-133 atom to vibrate exactly 9,192,631,770 times.
No. Even though it has the word 'year' in it, a **light-year is a unit of Distance**. It is the distance that light travels in the vacuum of space in one Earth year.
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