  In sum, the existing no-go results that use the first two degrees of  quantum involvement are not very convincing, and the third degree of  involvement is not mature enough to allow useful pronouncements.  There is, however, a rapidly growing literature on the possibility of time travel in lower-dimensional supersymmetric cousins of string  theory. For a review of these recent results and a discussion of the  fate of a time-traveller’s ambition in loop quantum gravity, see  Smeenk and Wüthrich (2010).