Schematics of the imagined trajectory of a virus (sfv) jumping from one species ( Xy ) to another ( Hs ). The figure is based on the assumption that a retrovirus experiences: (1) an Xy- component of the SB denoted the Index of Origin or IO; (2) at Hs the index of entry or IE. The path of such a retrovirus is analogous to the trajectory of an object cast from one planet's gravitational and atmospheric field into another's. The path of such a physical phenomenon is described by Einstein's field equations of gravitation (R
R = 8 T
, where R
is the Ricci Tensor, g
is the metric tensor, R is the Ricci scalar, and T is the all important Einstein's tensor) . Analogously, at the port of sfv exit from Xy (where SB is defined by the IO), sfv shedding is (1) enhanced by the two transmitting tensors (Tt) and (2) opposed by the five accepting scalars (At), as described in the text. The same forces acting in an opposing manner determine SB at the port of sfv entry (defined here by the IE).