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…Travel Possible? Is Time…

…Travel Possible? Is Time…

FTL Travel and Travel: or ?

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, , Perimeter Institute (Canada)

Research •Classical and quantum •Discrete & continuous structures (PhD thesis) • 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 geodesics

Faster- The expansion Warp Drives 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 resolutions Spacetime and Causality General Relativity in 60

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 Is FTL Travel Realistic? Strong

Gravity is always attractive; geodesics converge

The Weak Energy Condition

Energy Observers measure non- Conditions density

Null Energy Condition

The SEC and WEC also apply to massless 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

(uncharged) Violate the law of

What Can Create a machine You Do with Uncover singularities Exotic

Matter? Travel faster than light

Travel back in time Warp Drives and Wormholes and Exotic Matter

+ DEFOCUSING The Quantum Inequalities

Longer = weaker

Positive > negative

Quantum interest Time Travel Time Travel from FTL Travel

Time Travel

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 Example of a Consistency Paradox

A More Concrete Example Proposed Resolutions to the Paradoxes

The Hawking • 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 • 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?