Inrelativity, anevent is anything that happens that has a specific time and place inspacetime. For example, a glass breaking on the floor is an event; it occurs at a unique place and a unique time.^[1] Strictly speaking, the notion of an event is anidealization, in the sense that it specifies a definite time and place, whereas any actual event is bound to have a finite extent, both in time and in space.^[2][3]

Thespacetime interval between two events:$${\displaystyle (\text{interval}{)}^2={\left[\frac{\text{event time}}{\text{separation}}\right]}^2-{\left[\frac{\text{event space}}{\text{separation}}\right]}^2}$$

is aninvariant.^[4]: 9

An event in the universe is caused by the set of events in its causal past. An event contributes to the occurrence of events in its causal future.

Upon choosing a frame of reference, one can assign coordinates to the event: three spatial coordinates${\displaystyle \overrightarrow{x}=(x,y,z)}$ to describe the location and one time coordinate${\displaystyle t}$ to specify the moment at which the event occurs. These four coordinates${\displaystyle (\overrightarrow{x},t)}$ together form afour-vector associated to the event.

One of the goals of relativity is to specify the possibility of one event influencing another. This is done by means of themetric tensor, which allows for determining thecausal structure of spacetime. The difference (or interval) between two events can be classified intospacelike,lightlike andtimelike separations. Only if two events are separated by a lightlike or timelike interval can one influence the other.

P. W. Bridgman found the event concept insufficient for operational physics in his bookThe Logic of Modern Physics.^[5]

• Relativity of simultaneity

• Theory of relativity
• Point (geometry)

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