If one follows the model of space that Euclid had, our universe has three dimensions of space, and one dimension of time. By combining space and time into a single manifold, physicists have simplified a good deal of theory, as well as described in a simpler way, the workings of the universe at both the levels of the very large (supergalactic) and very small (subatomic).
Wherever an important quantity of matter exists, it bends the geometry of spacetime. This results in a curved shape of space-time that can be understood asgravity. The white lines on the picture on the right do not represent the curvature of space, but instead represent the coordinate system imposed on the curved spacetime which would be rectilinear(straight and uncurved) in a flat spacetime where there is no mass.
In classical mechanics, the use of spacetime is optional, as time is independent of mechanical motion in the three dimensions of Euclidean space. When a body is moving at speeds close to the speed of light (relativistic speeds), time cannot be separated from the three dimensions of space as time then depends on how close to the speed of light the object is moving.
The origins of this 20th century scientific theory began in the 19th century with fiction writers. Edgar Allan Poe stated in his essay on cosmology titled Eureka(1848) 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. 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.”
Albert Einstein's 1905 theory of special relativity is the beginning of the concept of spacetime, but the first mathematical theory of spacetime was proposed by one of his teachers, the mathematician Hermann Minkowski, in a 1908 essay. His concept of Minkowski space is the earliest treatment of space and time as two aspects of a unified whole, the essence of special relativity. The idea of Minkowski space also led to special relativity being viewed in a more geometrical way, this geometric viewpoint of spacetime being important in general relativity too. The 1926 thirteenth edition of the Encyclopedia Britannica included an article by Einstein titled "space-time".
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