A stranger hands you an antique pocket watch; decades later you invent time travel and hand it to your younger self. Who built the watch? This episode uses that bootstrap paradox to open a tour of temporal paradoxes, from Lossev and Novikov’s 1992 classification of self-existing objects and information as jinn, and their argument that environmental interaction lets a looping object escape the entropy problem, to Sergei Krasnikov’s point that a watch with no origin is no stranger than matter from the Big Bang.

The hosts then flip to consistency paradoxes, including the grandfather paradox and the Hitler paradox that erases its own motivation, and Joseph Polchinski’s billiard ball fired through a wormhole. Modal logic, Norman Swartz’s debate with Bradley Dowden, and the Novikov self-consistency principle lead to Kip Thorne’s glancing-blow solution. Newcomb’s paradox raises the free will problem, the many-worlds interpretation offers an escape, and Stephen Hawking, David Deutsch and Allen Everett’s cosmic-blender objection complicate it, before Kurt Godel suggests the passage of time itself may be an illusion.

• Jinn of the first kind versus jinn of the second kind
• Why a time traveler can only do what did happen, even at the Titanic’s wheel
• Infinite self-consistent trajectories for Polchinski’s billiard ball
• The branching tree, not the highway exit, as the right picture of many worlds
• Godel’s rotating universe and past, present and future existing at once