What is smaller than a second?

Hint:A decimal prefix or decimal order-of-magnitude quantity is commonly combined with a base unit of time, such as a microsecond or a million years, to form an order of magnitude of time. In other circumstances, the order of magnitude is indicated, such as when a "second" or "year" is used. In other circumstances, the quantity name, such as "century," implies the base unit. The base unit is usually seconds or years.

Complete step by step answer:
Only a few scientific fields, such as observational astronomy and materials science, use metric units of time larger than the second, albeit this varies depending on the author. Minutes, hours \[\left( {3,600{\text{ }}s{\text{ }}or{\text{ }}3.6{\text{ }}ks} \right),\] days \[\left( {86,400{\text{ }}s} \right),\]weeks, months, and years (of which there are other variations) are generally employed for everyday use and most other scientific situations. Weeks, months, and years are highly variable units whose lengths are determined by the calendar used and are frequently irregular even when using a calendar, such as leap years versus ordinary years in the Gregorian calendar. Because it's unclear which version is being used, they're difficult to utilise against a linear and regular time scale like the one described by the SI.
The units which are smaller than the second are:
Milliseconds: ${10^{ - 3}}\,s$
Microseconds: ${10^{ - 6}}\,s$
Nanoseconds: ${10^{ - 9}}\,s$
Picoseconds: ${10^{ - 12}}\,s$
These are some units of time which are smaller than a second.

Note: The age of the universe, around \[13.8\] billion years since the Big Bang as estimated in the cosmic microwave background rest frame, is the biggest recognised length of time based on known scientific facts. The sum of those times is \[60\] decimal orders of magnitude. Metric prefixes go from \[1024{\text{ }}to{\text{ }}1024,{\text{ }}48\] decimal orders of magnitude, and they can be used with the metric base unit of second.