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{{mergefrom|Space-time continuum}}
[[File:GPB circling earth.jpg|thumb|300px|An illustration of the space-time curvature caused by Earth.]]

'''Spacetime''' is a model in [[physics]] that joins the three [[dimension]]al space and one dimensional [[time]] into the idea of [[space-time continuum]]. Combining these two ideas helped [[physicist]]s to make many laws of physics easier to understand, and to explain how the universe works on the big level (e.g., [[star]]s) and small level (e.g., [[atom]]s).

The actual number of [[dimension]]s in spacetime is not fixed, but usually spacetime means a four dimensional (three dimensions of space and one dimension of time) spacetime. Some other theories claim that there are more than four dimensions.

== Historical origin ==
Many people link spacetime with [[Albert Einstein]] who found [[special relativity]]. However, it was Einstein's teacher, [[Hermann Minkowski]], who suggested this idea. He hoped this new idea would clarify the theory of special relativity. It was Einstein, though, who discovered the curvature of spacetime (gravity) in [[general relativity]].

==Spacetime in Special Relativity==
[[File:World line.svg|Thumb|right]]
The idea of spacetime originated from the concept of ''Minkowski spacetime''. Minkowski spacetime is a 4-dimensional [[manifold]] that is the arena of every event in the universe. To the right, a 3-dimensional analogy of 4-dimensional Minkowski spacetime is given. Time is taken to be the vertical axis, and the two spacial dimensions are the forward-backwards and left-right axes. In reality, there are four dimensions, but this concept is virtually impossible to visualize. 

Minkowski spacetime is only accurate at describing [[constant velocity]]; this means the velocity cannot change at any period in time (acceleration is dealt with in general relativity). Minkowski spacetime also allows for visualizations of the [[Lorentz transformations]], [[time dilation]], and [[Lorentz contraction]] without the algebraic equations. 

==Spacetime in general Relativity==
In general relativity, Einstein generalized Minkowski spacetime to include the effects of [[acceleration]]. Einstein discovered that the curvature in his 4-dimensional spacetime representation was actually the cause of [[gravity]].  If you graph accelerated motion on a typical x-and-time coordinate system, you will end up with some form of curve; never a straight line. Einstein felt that this was a deep connection between the nature of spacetime and acceleration. Via his [[equivalence principle]], he showed that a curve in generalized spacetime would result in the effects of gravity. 

== Spacetime in quantum mechanics and disagreements ==
In [[general relativity]], spacetime is thought as smooth and continuous. However in the theory of [[quantum mechanics]], spacetime is not always continuous.

[[Category:Physics]]⏎
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