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The Deep(est) Paradox of Physics: Exploring the Arrows of Time in Nature

Discover why physics is time-symmetric while nature is not, and delve into the seven arrows of time that distinguish the past from the future. Explore concepts such as the memory arrow, electromagnetic arrow, quantum arrow, black hole arrow, cosmological arrow, kaon arrow, and entropy arrow.

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The Deep(est) Paradox of Physics: Exploring the Arrows of Time in Nature

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  1. Tony Rothman

  2. Deep(est) Paradox of Physics: Physics is Time Symmetric Nature is Not

  3. Fundamental Theories of Physics Don’t Care Which Way Time Goes • Newtonian Physics • Electromagnetism • Relativity • Quantum Mechanics

  4. Nevertheless, Nature Cares

  5. Roger Penrose lists seven ways in which Nature distinguishes past from future,seven “arrows of time”

  6. Seven Arrows of Time Memory Arrow Electromagnetic Arrow Quantum Arrow Black Hole Arrow Cosmological Arrow Kaon Arrow Entropy Arrow

  7. Memory only works backwards (We don't remember the future) 1. Memory Arrow

  8. 2. Electromagnetic Arrow Electromagnetic Causes Precede Effects

  9. 3. Quantum Arrow Wave Functions “Collapse” But Don’t “Uncollapse”

  10. 4. Black Hole Arrow Black Holes Exist But White Holes Don’t (Apparently)

  11. 5. Cosmological Arrow We live in an expanding universe, not a contracting one. Would time change direction if universe started contracting?

  12. 6. Kaon Arrow Kaon decay not time symmetric Ko ππ In a time-reversed world this particle decays at a different rate than in our world!

  13. CPT theorem “Charge-Parity-Time” Change electric charge of all particles in world (Change all particles to antiparticles);Reflect it in mirror;Run time backwards: New world is indistinguishable from old

  14. Princeton 1964 Experiment: Kaon decay not invariant under CP-reversal Must also change under T-reversal

  15. 7. Entropy Arrow Entropy always increases (second law of thermodynamics)

  16. Question: Are arrows independent? Hawking: Memory and entropy arrows linked (Requires energy to read one bit, increases entropy by certain amount)

  17. Rothman to Penrose: One arrow arbitrary; only six independent signs.

  18. Sudarshan to Rothman: All particle decay CPT invariant but Irreversible: Particle-decay arrow. Rothman to Rothman: Temperature dependent?

  19. Entropy Entropy can be thought of as waste heat generated in any realistic process “Disorder” in a system

  20. Second Law:Entropy of a system always increases under realistic (“irreversible”) process Only law of nature that exhibits direction of time!

  21. “Thermodynamic system”:System with lots of particles(Gas)Obeys second law But individual particles obey Newtonian physics

  22. Central Paradox:Gas is a thermodynamic system;obeys second law.But if gas particles individually obey time-symmetric Newtonian physics, how canarrow of time arise?

  23. Boltzmann attempts to deriveincrease of entropy from Newtonian PhysicsH-Theorem

  24. Loschmidt Strikes Back

  25. Boltzmann goes to probabilistic theory An ordered deck of cards becomes disordered on shuffling

  26. Gibbs strikes back

  27. Another Problem: Entropy should not alwaysbe equated with disorder

  28. Prigogine’s Solution: Second Law is fundamental. Can’t derive. Chaotic systems manifest irreversible Behavior. Entropy increase tied up with chaos

  29. Objection: Chaotic systems are time-symmetric. If a system is chaotic into the future, it is also chaotic into the past

  30. Conclusion: To date no satisfactory explanation for direction of time

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