  As a concrete example of these concepts, consider the \((1 +  1)\)-dimensional Misner spacetime (see   Figure 1)  which exhibits some of the causal features of Taub-NUT spacetime, a  vacuum solution to Einstein’s gravitational field equations. It  satisfies all three of the conditions discussed above. It is  temporally orientable, and a time orientation has been singled  out—the shading in the figure indicates the future lobes of the light cones. To the past of the partial Cauchy surface  \(\Sigma_0\) lies the Taub region where the causal structure  of spacetime is as bland as can be desired. But to the future of  \(\Sigma_0\) the light cones begin to “tip over,”  and eventually the tipping results in CTCs in the NUT region.