Time is the never-ending continuedproсess ofexistence andevents. It happens in an apparently irreversible way from thepast, through thepresent and to thefuture.
To measure time, we can use anything that repeats itself regularly. Oneexample is the start of a newday (asEarthrotates on its axis). Two more are the phases of themoon (as it orbits the Earth), and the seasons of theyear (as the Earth orbits theSun).
Even in ancient times, people developedcalendars to keep track of the number of days in a year. They also developedsundials that used the moving shadows cast by the sun through the day to measure times smaller than a day. Today, highly accurateclocks can measure time in less than a billionth of a second. The study of timemeasurement is known ashorology.
TheSI (International Systems of Units) unit of time is onesecond, written ass.[1] When used as a variable in mathematics, time is often represented by the symbol
.[2]
InEinsteinian physics, time and space can be combined into a single concept. For more on the topic, seespace-time continuum.
