Energy condition respecting warp drives: The role of spin in Einstein-Cartan theory

Abstract: In this paper we study the so called "warp drive" spacetimes within the $U_{4}$ Riemann-Cartan manifolds of Einstein-Cartan theory. Specifically, the role that spin may play with respect to energy condition violation is considered. It turns out that with the addition of spin, the torsion terms in Einstein-Cartan gravity do allow for energy condition respecting warp drives. Limits are derived which minimize the amount of spin required in order to have a weak/null-energy condition respecting system. This is done both for the traditional Alcubierre warp drive as well as for the modified warp drive of Van Den Broeck which minimizes the amount of matter required for the drive. The ship itself is in a region of effectively vacuum and hence the torsion, which in Einstein-Cartan theory is localized in matter, does not affect the geodesic nature of the ship's trajectory. We also comment on the amount of spin and matter required in order for these conditions to hold.