Spacetime

Spacetime is any mathematical model which fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams can be used to plot the motion and evolution of objects within this four-dimensional model. Spacetime is used in relativity to discuss the dimensions and functions of the universe. The term "spacetime" has its origin in the German Raumzeit coined by Hermann Minkowski in 1908. The translation of "spacetime" in Hebrew is מרחב-זמן (mirkhav-zman). In French, it is espace-temps, in Spanish, espacio-tiempo, and in Russian, пространство-время (prostranstvo-vremya). In classical mechanics, objects move in a flat, three-dimensional space, and time is treated as flowing uniformly and independently of the events that happen within it. Under this framework, time and space are independent of one another; this framework is a philosophical approach that had already been abandoned by the end of the 19th century with the rise of relativity. In the theory of special relativity, time can vary for different observers depending on their speed, leading to concepts such as time dilation, where a moving clock is measured to tick more slowly than a stationary one. General relativity further combines spacetime with gravity, showing that the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. This curvature of spacetime, calculated using the Einstein field equations, determines the path that objects in free fall follow. Time also has a gravitational rate effect: a clock that is deeper within a gravity well, or subject to a stronger gravitational field, will run slower than a clock that is in a weaker gravitational field: this effect is known as gravitational time dilation.