Maps that preserve adjacency on the set of all invertible hermitian matrices over a finite field are characterized. It is shown that such maps form a group that is generated by the maps $A\mapsto PAP^{ \ast}$, $A\mapsto A^{ \sigma}$, and $A\mapsto A^{ -1}$, where $P$ is an invertible matrix, $P^{ \ast}$ is its conjugate transpose, and $\sigma$ is an automorphism of the underlying field. Bijectivity of maps is not an assumption but a conclusion. Moreover, adjacency is assumed to be preserved in one directions only. The main result and author's previous result [16] are applied to characterize maps that preserve the `speed of light' on (a) finite Minkowski space-time and (b) the complement of the light cone in finite Minkowski space-time.
Categories: math.RA