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[[File:GPB circling earth.jpg|thumb|280px|An illustration of the spacetime curvature caused by Earth.]]

'''Spacetime''' or  '''space–time''' is a [[mathematical model]] that joins [[Space (physics)|space]] and [[time]] into a single idea called a '''continuum'''. This [[4D|four-dimensional]] continuum is known as [[Minkowski spacetime|Minkowski space]]. 

Combining these two ideas helped [[cosmology|cosmologists]] to understand how the universe works on the big level (e.g. [[galaxies]]) and small level (e.g. [[atom]]s).

In non-relativistic [[classical mechanics]], the use of [[Euclidean space]] instead of space–time is good, because time is treated as universal with a constant rate of passage which is independent of the state of motion of an observer. 

But in a [[Theory of relativity|relativistic]] universe, time cannot be separated from the three dimensions of space. This is because the observed [[Rate (mathematics)|rate]] at which time passes depends on an object's [[velocity]] relative to the observer. Also, the strength of any [[gravitational field]] slows the passage of time for an object ''as seen by an observer outside the field''.
== Further aspects ==
[[File:spacetime curvature.png|thumb|right|250px|Two-dimensional analogy of spacetime distortion]] 

Wherever [[matter]] exists, it bends the [[geometry]] of spacetime. This results in a curved shape of spacetime which can be understood as [[gravity]]. The white lines on the picture on the right represent the effect of [[mass]] on spacetime.

In [[classical mechanics]], the use of spacetime is optional, as time is independent of motion in the three dimensions of Euclidean space. However, when a body is moving at speeds close to the [[speed of light]] ([[theory of relativity|relativistic speeds]]), time cannot be separated from the three dimensions of space. Time, from the point of view of a stationary observer,<ref>Einstein, Albert and Infeld, Leopold 1938. ''The evolution of physics: from early concept to relativity and quanta''. Cambridge University Press.</ref> depends on how close to the speed of light the object is moving.<ref name=Einstein26/>
== Historical origin ==
Many people link spacetime with [[Albert Einstein]], who proposed [[special relativity]] in 1905. However, it was Einstein's teacher, [[Hermann Minkowski]], who suggested spacetime, in a 1908 essay.<ref>[[Hermann Minkowski]], [http://de.wikisource.org/wiki/Raum_und_Zeit_(Minkowski) "Raum und Zeit"], 80. Versammlung
Deutscher Naturforscher (Köln, 1908). ''Physikalische Zeitschrift'' '''10''' 104-111 (1909) and ''Jahresbericht der Deutschen Mathematiker-Vereinigung'' '''18''' 75-88 (1909).  For an English translation, see Lorentz et al. (1952).</ref> His concept of [[Minkowski space]] is the earliest to address space and time as two aspects of a unified whole, which is the essence of [[special relativity]]. He hoped this new idea would clarify the theory of special relativity. 

Minkowski spacetime is only accurate at describing [[constant velocity]]. It was Einstein, though, who discovered the curvature of spacetime ([[gravity]]) in [[general relativity]]. In general relativity, Einstein generalized Minkowski spacetime to include the effects of [[acceleration]]. Einstein discovered that the curvature in his [[4D|4-dimensional]] spacetime representation was actually the cause of gravity. 

The 1926 thirteenth edition of the ''[[Encyclopedia Britannica]]'' included an article by Einstein titled "space–time".<ref name=Einstein26>[[Albert Einstein|Einstein, Albert]], 1926, "[http://www.britannica.com/EBchecked/topic/1987141/Albert-Einstein-on-Space-Time Space-Time,]" ''Encyclopedia Britannica'', 13th ed.</ref>
== Literary background ==
[[Edgar Allan Poe]] wrote an essay on cosmology titled ''[[:en:Eureka:_A_Prose_Poem|Eureka]]'' (1848) which said that "space and duration are one".  This is the first known instance of suggesting space and time to be different perceptions of one thing.  Poe arrived at this conclusion after approximately 90 pages of reasoning but employed no [[mathematics]].<ref>{{cite book| last = Poe| first = Edgar A.| authorlink= Edgar Allan Poe| title = Eureka: an essay on the material and spiritual universe | publisher = Hesperus Press Limited| date = 1848| location = | pages =| url =| doi =| isbn=1-84391-009-8 }}</ref>  

In 1895, [[H.G. Wells]] in his novel, ''The [[Time Machine]]'', wrote, “There is no difference between Time and any of the three dimensions of Space except that our consciousness moves along it”. He added, “Scientific people…know very well that Time is only a kind of Space”.<ref>{{cite book| last = Wells| first = H.G.| authorlink = H.G. Wells| title = The Time Machine | publisher = Pocket Books| date = 2004| location = New York| pages = | url =| doi =| id = }} (pp.&nbsp;5; 6)</ref>
== Spacetime in quantum mechanics ==
In [[general relativity]], spacetime is thought of as smooth and continuous. However, in the theory of [[quantum mechanics]], spacetime is not always continuous.

== Spacetime Media ==
<gallery widths='160px' heights='100%' mode='traditional' caption=''>
File:Observer in special relativity.svg|Figure 1-1. Each location in spacetime is marked by four numbers defined by a [[frame of reference]]: the position in space, and the time, which can be visualized as the reading of a clock located at each position in space. The 'observer' synchronizes the clocks according to their own reference frame.

File:Minkowski Diagram from 1908 'Raum und Zeit' lecture.jpg|Figure 1–4. Hand-colored transparency presented by Minkowski in his 1908 ''Raum und Zeit'' lecture

File:Spacetime Diagram of Two Photons and a Slower than Light Object.png|Figure 2–1. Spacetime diagram illustrating two photons, A and B, originating at the same event, and a slower-than-light-speed object, C

File:Standard configuration of coordinate systems.svg|Figure 2-2. Galilean diagram of two frames of reference in standard configuration

File:Galilean and Spacetime coordinate transformations.png|Figure 2–3. (a) Galilean diagram of two frames of reference in standard configuration, (b) spacetime diagram of two frames of reference, (c) spacetime diagram showing the path of a reflected light pulse

File:ModernPhysicsSpaceTimeA.png|Figure 2–4. The light cone centered on an event divides the rest of spacetime into the future, the past, and "elsewhere"

File:World line.png|Figure 2–5. Light cone in 2D space plus a time dimension

File:Relativity of Simultaneity Animation.gif|Figure 2–6. Animation illustrating relativity of simultaneity

File:Spacelike and Timelike Invariant Hyperbolas.png|Figure 2–7. (a) Families of invariant hyperbolae, (b) Hyperboloids of two sheets and one sheet

File:Spacetime diagram of invariant hyperbola.png|Figure 2–8. The invariant hyperbola comprises the points that can be reached from the origin in a fixed proper time by clocks traveling at different speeds
</gallery>
== Related pages ==
{{Wikibooks|Special Relativity}}
* [[Continuum (theory)]]
* [[Dimension]]
* [[Manifold]]
== References ==
{{Reflist}}
* Lorentz H.A; [[Albert Einstein|Einstein, Albert]]; [[Hermann Minkowski|Minkowksi, Hermann]] and Weyl, Hermann 1952. ''The principle of relativity: a collection of original memoirs''. Dover.
*Lucas, John Randolph 1973. ''A treatise on time and space''. London: Methuen.

[[Category:Relativity]]
[[Category:Basic physics ideas]]