How time travel works?

In the runup to the return of Doctor Who, BBC America is pushing the boat out with new hour-long documentaries on the show, its characters, and science in the series. Before you wonder how long it takes to say "there isn't any really!" check out this clip with Steven Moffat talking wormholes alongside Michio Kaku Ph.D, Jim Al-Khalili Ph.D OBE, Maggie Aderin-Pocock Ph.D MBE, and Dallas Campbell from Bang Goes The Theory.