![]() A scale factor, c (conventionally called the speed-of-light) relates distances measured in space with distances measured in time. Mathematically, spacetime is a manifold, which is to say, it appears locally "flat" near each point in the same way that, at small enough scales, a globe appears flat. That line is called the particle's world line. The series of events can be linked together to form a line which represents a particle's progress through spacetime. The path of a particle through spacetime can be considered to be a succession of events. ![]() Although it is possible to be in motion relative to the popping of a firecracker or a spark, it is not possible for an observer to be in motion relative to an event. Unlike the analogies used in popular writings to explain events, such as firecrackers or sparks, mathematical events have zero duration and represent a single point in spacetime. An event is represented by a set of coordinates x, y, z and t. ![]() A position in spacetime is called an event, and requires four numbers to be specified: the three-dimensional location in space, plus the position in time (Fig. 1). In the Cartesian coordinate system, these are called x, y, and z. In ordinary space, a position is specified by three numbers, known as dimensions. : 214–217 General relativity also provides an explanation of how gravitational fields can slow the passage of time for an object as seen by an observer outside the field. In the context of special relativity, time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer. Furthermore, it assumes that space is Euclidean it assumes that space follows the geometry of common sense. Classical mechanics assumes that time has a constant rate of passage, independent of the observer's state of motion, or anything external. Non-relativistic classical mechanics treats time as a universal quantity of measurement which is uniform throughout space, and separate from space. ![]() This interpretation proved vital to the general theory of relativity, wherein spacetime is curved by mass and energy. In 1908, Hermann Minkowski presented a geometric interpretation of special relativity that fused time and the three spatial dimensions of space into a single four-dimensional continuum now known as Minkowski space. However, space and time took on new meanings with the Lorentz transformation and special theory of relativity. Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its description in terms of locations, shapes, distances, and directions) was distinct from time (the measurement of when events occur within the universe). Spacetime diagrams are useful in visualizing and understanding relativistic effects such as how different observers perceive where and when events occur. In physics, spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. ![]()
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