  Sider (2002, 119–20) endorses Smith’s second objection. Dowe (2003) criticises Smith’s first objection, but agrees with the second, concluding overall that time travel has not been shown to be improbable. Ismael (2003) reaches a similar conclusion. Goddu (2007) criticises Smith’s first objection to Horwich. Further contributions to the debate include Arntzenius (2006) and Smeenk and Wüthrich (2011, §2.2). For a different argument to the same conclusion as Horwich’s—that time travel is improbable—see Ney (2000).