Closed timelike curves in superfluid $^{3}$He
  It is shown that the curved spacetime induced in a thin film of superfluid $^{3}$He-A by the presence of symmetric vortices with the unbroken symmetry phase, admits the existence of closed timelike curves through which only superfluid clusters formed by anti-$^{3}$He atoms can travel and violate causality. 
Pedro F. Gonzalez-Diaz (IMAFF,CSIC,Madrid), Carmen L. Siguenza (Univ.   CEU, San Pablo)