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The space-time continuum is a mathematical model that joins space and time into a single idea. This space-time is represented by a model where space is three-dimensional and time has the role of the fourth dimension.
In Euclid's model of space, our universe has three dimensions of space, and one dimension of time. The actual number of dimensions in space-time is not fixed, but usually it means a four dimensional (three dimensions of space and one dimension of time). Some theories claim that there are more than four dimensions.
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 as gravity. 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 space-time 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.
Many people link space-time with Albert Einstein, who proposed special relativity in 1905. However, it was Einstein's teacher, Hermann Minkowski, who suggested space-time, in a 1908 essay. His concept of Minkowski space is the earliest treatment of 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 space-time (gravity) in general relativity. In general relativity, Einstein generalized Minkowski space-time to include the effects of acceleration. Einstein discovered that the curvature in his 4-dimensional space-time representation was actually the cause of gravity.
Edgar Allan Poe wrote an essay on cosmology titled 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.
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”.
Spacetime in quantum mechanics
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- Hermann 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).
- Einstein, Albert, 1926, "Space-Time," Encyclopedia Britannica, 13th ed.
- Poe, Edgar A. (1848). Eureka: an essay on the material and spiritual universe. Hesperus Press Limited. .
- Wells, H.G. (2004). The Time Machine. New York: Pocket Books. (pp. 5; 6)
- Lorentz H.A; Einstein, Albert; 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.