Is Time Travel Impossible?
Summary
PBS Space Time explores the theoretical possibilities of time travel, examining how special and general relativity permit concepts like tachyons, wormholes, and the Tipler cylinder. The episode discusses the physical requirements for these methods, such as negative energy or infinite structures, and addresses the resulting causality paradoxes. It concludes by reviewing arguments for and against the feasibility of backward time travel, noting that a definitive answer awaits a complete theory of quantum gravity.
Topics discussed
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Introduction: The desire for time travel
Einstein's relativity and the possibility of time travel
Special relativity: Time dilation and forward travel
Faster-than-light travel and backward time paths
Tachyons and imaginary mass
Transition to General Relativity and gravity
Wormholes as potential time machines
Requirements for stable, traversable wormholes
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Exotic matter and negative energy density
Energy conditions and the Alcubierre warp drive
The Tipler cylinder and closed time-like curves
Gödel universe and rotating black holes
Causality, paradoxes, and the grandfather paradox
Sponsors: SAP Concur, Subaru, and Sephora
Hawking's chronology protection and Novikov principle
Quantum gravity and the lack of observed time travelers
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Sponsor: Kuvasier Cognac
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