Authors: Mirosław J. Kubiak
Comments: 7 Pages.
Until the early twentieth century, the three-dimensional space and one-dimensional time were considered separate beings. In 1909, German mathematician H. Minkowski connected together space and time into single idea, creating a new the four-dimensional spacetime.
In this paper we proposed the extension of this idea by the connection together the Minkowski four-dimensional spacetime and the mass density into the single idea, creating a new entity: the four-dimensional spacetime with the mass density.