According to physicists, space is commonly described as having three dimensions: length, width, and height. These dimensions are typically referred to as the x, y, and z axes, respectively, in a Cartesian coordinate system. This framework allows us to locate and describe the position of objects in three-dimensional space.
As for why time is referred to as the "fourth dimension," it is due to the concept of spacetime. In physics, spacetime is a unified four-dimensional framework that combines the three dimensions of space with the dimension of time. This idea was introduced by Albert Einstein in his theory of general relativity.
Einstein proposed that space and time are intertwined and cannot be considered separately. Instead, they form a single fabric, where the effects of gravity are described by the curvature of spacetime. In this framework, an event is described by its position in three-dimensional space and its occurrence at a particular moment in time.
To visualize this concept, one can think of spacetime as a four-dimensional grid or manifold, where each point represents an event in the universe. The three spatial dimensions correspond to the location of an event, while the fourth dimension represents the time at which the event occurs. This unified view of space and time led to the idea of time as the fourth dimension.
It is important to note that the term "fourth dimension" is more metaphorical than literal. Physicists use it to describe the integration of time into the fabric of spacetime rather than implying an additional spatial dimension.