In
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
, and in particular
relativity, an event is the instantaneous physical situation or occurrence associated with a point in
spacetime
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differ ...
(that is, a specific place and time). For example, a glass breaking on the floor is an event; it occurs at a unique place and a unique time. Strictly speaking, the notion of an event is an idealization, 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.
Upon choosing a frame of reference, one can assign coordinates to the event: three spatial coordinates
to describe the location and one time coordinate
to specify the moment at which the event occurs. These four coordinates
together form a
four-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 the
metric tensor
In the mathematical field of differential geometry, a metric tensor (or simply metric) is an additional structure on a manifold (such as a surface) that allows defining distances and angles, just as the inner product on a Euclidean space allow ...
, which allows for determining the
causal structure
In mathematical physics, the causal structure of a Lorentzian manifold describes the causal relationships between points in the manifold.
Introduction
In modern physics (especially general relativity) spacetime is represented by a Lorentzian ma ...
of spacetime. The difference (or interval) between two events can be classified into
spacelike,
lightlike and
timelike separations. Only if two events are separated by a lightlike or timelike interval can one influence the other.
See also
*
Relativity of simultaneity
In physics, the relativity of simultaneity is the concept that ''distant simultaneity'' – whether two spatially separated events occur at the same time – is not absolute, but depends on the observer's reference frame. This possib ...
References
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zh-yue:事件 (相對論)
Theory of relativity
Terms in science and technology