In relativity, an event is anything that happens that has a specific time and place in

spacetime In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualiz ...

. 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. The spacetime interval between two events:

(\text)^2 = \left \frac \right 2 -  \left \frac \right 2

is an invariant. 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

\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, sometimes Lorentz 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 vect ...

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 allows ...

, which allows for determining the

causal structure In mathematical physics, the causal structure of a Lorentzian manifold describes the possible causal relationships between points in the manifold. Lorentzian manifolds can be classified according to the types of causal structures they admit (''c ...

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

spacelike In mathematical physics, the causal structure of a Lorentzian manifold describes the possible causal relationships between points in the manifold. Lorentzian manifolds can be classified according to the types of causal structures they admit (''ca ...

lightlike In mathematical physics, the causal structure of a Lorentzian manifold describes the possible causal relationships between points in the manifold. Lorentzian manifolds can be classified according to the types of causal structures they admit (''ca ...

and

timelike In mathematical physics, the causal structure of a Lorentzian manifold describes the possible causal relationships between points in the manifold. Lorentzian manifolds can be classified according to the types of causal structures they admit (''ca ...

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 book '' The Logic of Modern Physics''. P. W. Bridgman (1927
The Logic of Modern Physics
@

Internet Archive The Internet Archive is an American 501(c)(3) organization, non-profit organization founded in 1996 by Brewster Kahle that runs a digital library website, archive.org. It provides free access to collections of digitized media including web ...

References

{{reflist zh-yue:事件 (相對論) Theory of relativity Point (geometry)

See also

References