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…Travel Possible? Is Time… FTL Travel and Time Travel: Science or Science Fiction? Barak Shoshany Perimeter Institute January 13, 2020 McMaster University Hamilton, Ontario, Canada Please feel free to ask questions throughout the lecture! About Me Education • BSc, Mathematics & Physics, Tel Aviv University (Israel) • MSc & PhD, Theoretical Physics, Perimeter Institute (Canada) Research •Classical and quantum gravity •Discrete & continuous spacetime structures (PhD thesis) •Causality and its violations (side projects) Other Scientific Activities •Teaching mathematics & physics •Science outreach •Online Q&A on Quora.com Hobbies •Music composition •Board games •Role-playing games (D&D, etc.) Based on Available at https://scipost.org/SciPostPhysLectNotes.10 Outline General Spacetime and Curvature and Causality Relativity matter geodesics Faster- The expansion Warp Drives Wormholes than-Light of the universe Travel Quantum Is FTL The energy FTL travel limitations on conditions and requires Travel negative their violations “exotic” matter Realistic? energy Paradoxes and FTL travel = proposed Conclusions Time Travel time travel resolutions General Relativity Spacetime and Causality General Relativity in 60 Seconds Spacetime tells Matter tells matter how to spacetime how move to curve The geodesic equation: Einstein’s equation: 1 푥ሷ 휎 + Γ휎 푥ሶ 휇푥ሶ 휈 = 0 푅 − 푅푔 = 푇 휇휈 휇휈 2 휇휈 휇휈 Curvature and Geodesics Faster-than-Light Travel The Expansion of the Universe Warp Drives: Expansion Warp Drives: Light Cones Warp Drives: View from the Bridge Wormholes Visualization of a Wormhole Is FTL Travel Realistic? Strong Energy Condition Gravity is always attractive; geodesics converge The Weak Energy Condition Energy Observers measure non-negative energy Conditions density Null Energy Condition The SEC and WEC also apply to massless particles Cosmological constant Violates the SEC Known Violations of Classical scalar fields (e.g. Higgs) the Energy Violate the SEC Conditions in Can violate the WEC and NEC Nature Quantum fields Violate the SEC, WEC, and NEC The Casimir Effect (uncharged) Violate the second law of thermodynamics What Can Create a perpetual motion machine You Do with Uncover black hole singularities Exotic Matter? Travel faster than light Travel back in time Warp Drives and Exotic Matter Wormholes and Exotic Matter + DEFOCUSING The Quantum Inequalities Longer = weaker Positive > negative Quantum interest Time Travel Time Travel from FTL Travel Time Travel Paradoxes Bootstrap •An effect is its own cause Paradoxes •Something is created from nothing •Something happens if and only if it Consistency does not happen Paradoxes •Variations of the grandfather paradox Example of a Consistency Paradox A More Concrete Example Proposed Resolutions to the Paradoxes The Hawking Chronology • The Universe does not allow time travel Protection Conjecture • Quantities always diverge The Novikov Self- • The Universe must be consistent, no matter what Consistency Conjecture • The Postselected Quantum Time Travel Model • The Universe branches when time travel occurs Multiple Timelines • Deutsch’s Quantum Time Travel Model My paper: arXiv:1911.11590 Introduced a hybrid of Novikov and multiple timelines. If enough exotic matter can be created, then faster-than-light travel and time travel could be possible in our universe. For more information, please see: Conclusions https://scipost.org/SciPostPhysLectNotes.10 arXiv:1911.11590 Thank you for listening! Any questions?.
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