One of the reasons for 1979 Nobel Prize for physics is "for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles". While the strict "unified theory" cannot be existed, there is only "partial and temporary unified theory so far". Applying least square method, "partial and temporary unified electromagnetic theory so far", "partial and temporary unified gravitational theory so far", "partial and temporary unified theory of four fundamental interactions so far", and "partial and temporary unified theory of natural science so far" can be established. In this way, the theory of everything to express all of natural laws, described by Hawking that a single equation could be written on a T-shirt, is partially and temporarily realized in the form of "partial and temporary unified variational principle of natural science so far".