 Like nonrelativistic quantum theory, of which it is a version, Bohmian mechanics is not compatible with special relativity, a central principle of physics: Bohmian mechanics is not Lorentz invariant. Nor can it easily be modified to accommodate Lorentz invariance. Configurations, defined by the simultaneous positions of all particles, play too crucial a role in its formulation, with  the guiding equation  defining an evolution on configuration space. (Lorentz invariant extensions of Bohmian mechanics for a single particle, described by the Dirac equation (Bohm &amp; Hiley 1993; Dürr et al. 1999) or the Klein-Gordon equation (Berndl et al. 1996; Nikolic 2005), can easily be achieved, though for a Klein-Gordon particle there are some interesting subtleties, corresponding to what might seem to be a particle traveling backwards in time.)