The concept of time being considered the fourth dimension in the context of physics and spacetime is derived from the development of Albert Einstein's theory of general relativity. Prior to Einstein's work, the prevailing view of physics was based on Isaac Newton's classical mechanics, which treated space and time as separate and independent entities.
Einstein's theory of general relativity revolutionized our understanding of gravity and proposed a new framework for describing the fabric of the universe, known as spacetime. According to general relativity, the presence of mass and energy warps or curves the fabric of spacetime, resulting in what we perceive as gravity.
In this theory, space and time are no longer considered as separate entities but rather as interconnected dimensions that constitute a unified fabric. Einstein's equations mathematically described how the curvature of spacetime is influenced by the distribution of mass and energy in the universe.
One crucial aspect of general relativity is that it treats time as an integral part of the four-dimensional fabric of spacetime. Just as we can move freely in three dimensions of space (up-down, left-right, forward-backward), we also move along the dimension of time. However, it is important to note that in this context, the term "dimension" refers to a coordinate direction, not the spatial concept of length, width, or height.
The idea that time is the fourth dimension arises from the mathematical framework of general relativity, where time is combined with the three dimensions of space to form a four-dimensional continuum. The equations of general relativity describe how objects move and interact within this four-dimensional spacetime, including the effects of gravity.
In summary, scientists concluded that time is the fourth dimension based on the mathematical formalism and predictions of Einstein's theory of general relativity, which treats space and time as interconnected dimensions within the fabric of spacetime.