In 1823, the Cauchy stress tensor was defined in three-dimensional geometric space as:
Fxx Fxy Fxz
Fyx Fyy Fyz
Fzx Fzy Fzz . . (1)
The Cauchy stress tensor is clearly incomplete because it does not contain time and must be modified to take the 4x4 form:
Fxx Fxy Fxz Fxt
Fyx Fyy Fyz Fyt
Fzx Fzy Fzz Fzt
Ftx Fty Ftz Ftt . . . (2)
Or,
∇2xx ∇2xy ∇2xz ∇2xt [U]
∇2yx ∇2yy ∇2yz ∇2yt [U]
∇2zx ∇2zy ∇2zz ∇2zt [U]
∇2tx ∇2ty ∇2tz ∇2tt [U] . . . (2*)
Where t is time in the 4-dimensional unit space xyzt.
and Fxy= ∇^2yx U(x,y,z,t). . ., etc.
This tensor is called the Cairo-Cauchy tensor to distinguish it from the steady-state Cauchy tensor.
Note that:
1- Formula 2 reduces to Formula 1 as dU/dt)partial approaches zero.
2- The stationary Cauchy tensor 1 cannot handle time-dependent cosmic events, unlike the Cairo Cauchy tensor 2.