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 r ...

, 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

\vec = (x,y,z)

to describe the location and one time coordinate

t

to specify the moment at which the event occurs. These four coordinates

(\vec,t)

together form a

four-vector In special relativity, a four-vector (or 4-vector) is an object with four components, which transform in a specific way under Lorentz transformations. Specifically, a four-vector is an element of a four-dimensional vector space considered as a ...

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, 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 m ...

of spacetime. The difference (or interval) between two events can be classified into

spacelike 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 differen ...

lightlike In mathematical physics, Minkowski space (or Minkowski spacetime) () is a combination of three-dimensional Euclidean space and time into a four-dimensional manifold where the spacetime interval between any two events is independent of the inert ...

and

timelike 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 differen ...

separations. Only if two events are separated by a lightlike or timelike interval can one influence the other.

References

{{reflist zh-yue:事件 (相對論) Theory of relativity Terms in science and technology

See also

References