1. The physics of paradox John Ashmead

2. Physics of paradox www.timeandquantummechanics.com What is time? What is time? If no one asks me, I know. If I wish to explain it to one that asketh, I know not. — St. Augustine Questions are more important than answers. — Einstein

3. Physics of paradox www.timeandquantummechanics.com 6 questions Why is time a problem? What kinds of time are possible? Could we travel in time? What possible paradoxes might be created by time travel? Can we avoid the paradoxes? If we can, what would this mean?

4. Physics of paradox www.timeandquantummechanics.com Why is time a problem? At our level time goes one way, but laws of physics seem to go both ways In relativity, time is dynamic But in quantum mechanics, time is boring

5. Physics of paradox www.timeandquantummechanics.com In the world about us, the past is distinctly different from the future. More precisely, we say that the processes going on in the world about us are asymmetric in time, or display an arrow of time. Yet, this manifest fact of our experience is particularly difficult to explain in terms of the fundamental laws of physics. Newton’s laws, quantum mechanics, electromagnetism, Einstein’s theory of gravity, etc., make no distinction between the past and future - they are time- symmetric. -- Physical Origins of Time Asymmetry Halliwell, Pérez-Mercader, & Zurek

6. Physics of paradox www.timeandquantummechanics.com The twin paradox Alice’s ViewBob’s View Proxima Centauri Alice at Mission control Bob on spaceship Earth Proxima Centauri Alice at Mission control Bob on spaceship Earth

7. Physics of paradox www.timeandquantummechanics.com Black holes Alice Bob

8. Physics of paradox www.timeandquantummechanics.com Single slit experiment

9. Physics of paradox www.timeandquantummechanics.com Double slit experiment

10. Physics of paradox www.timeandquantummechanics.com Time goes step by step But space is uncertain

11. Physics of paradox www.timeandquantummechanics.com Uncertainty

12. Physics of paradox www.timeandquantummechanics.com Atoms

13. Physics of paradox www.timeandquantummechanics.com Relativity vs quantum Smooth Localized Predictable But time is dynamic How wonderful that we have met with a paradox. Now we have some hope of making progress. – Niels Bohr Relativity: Quantum mechanics: Quantized Fuzzy Uncertain But time is boring

14. Physics of paradox www.timeandquantummechanics.com kinds of time? Fleeting instant Block universe Massively parallel Spreadsheet

15. Physics of paradox www.timeandquantummechanics.com The Instant & Eternity You can’t step in the same river twice — Heraclitus [What exists] is now, all at once, one and continuous… — Parmenides

16. Physics of paradox www.timeandquantummechanics.com Parallel universes SymbolValueMeaning N 1,000,000,000,000,000,00 0, 000,000,000,000,000,000 (Douglas Adams Big) Ratio of fine structure constant to gravitational constant ε0.007Strong force Q1/100000Lumpiness of universe D3# of space dimensions Λ0.7Cosmological constant Ω1 Density of universe, compared to critical density

17. Physics of paradox www.timeandquantummechanics.com Coincidence, Mr Bond? It isn’t that much of a coincidence Or, we just got insanely lucky Or, there are a nearly infinite number of universes out there And, only those hospitable to intelligence life will have sentients asking, did we get insanely lucky?

18. Physics of paradox www.timeandquantummechanics.com And who can forget the fading photographs? Spreadsheet time

19. Physics of paradox www.timeandquantummechanics.com Could we travel in time? Wormholes Frame dragging The Large Hadron Collider

20. Physics of paradox www.timeandquantummechanics.com Wormholes A wormhole is two black holes stitched together with mathematical sutures Needs negative energy/mass “stuff” to stay open

21. Physics of paradox www.timeandquantummechanics.com Frame dragging

22. Physics of paradox www.timeandquantummechanics.com Looping thru a wormhole Future mouth Past mouth time space

23. Physics of paradox www.timeandquantummechanics.com possible paradox? “Why pick on grandfather? It seems that the only way to prove that time travel is impossible is to cite a case of killing one's own grandfather. This incessant murdering of harmless ancestors must stop. Let's see some wide-awake fan make up some other method of disproving the theory.” Grandfather paradoxes Bootstrap paradoxes Free will paradoxes

24. Physics of paradox www.timeandquantummechanics.com Grandfather paradox The quantum physics of time travel - Deutsch & Lockwood

25. Physics of paradox www.timeandquantummechanics.com Bootstrap paradox An engineer goes 30 years into the future, Reads some patents a later version of himself filed, Take the (information in) the patents back in time, And files them. Did the patents write themselves?

26. Physics of paradox www.timeandquantummechanics.com All you Zombies Never Do Yesterday What Should Be Done Tomorrow. If at Last You Do Succeed, Never Try Again. A Stitch in Time Saves Nine Billion. A Paradox May Be Paradoctored. The By-laws of time:

27. Physics of paradox www.timeandquantummechanics.com Free Will paradox "Ha! ha! ha! But you know there is no such thing as choice in reality, say what you like," you will interpose with a chuckle. "Science has succeeded in so far analyzing man that we know already that choice and what is called freedom of will is nothing else than--" But I repeat for the hundredth time, there is one case, one only, when man may consciously, purposely, desire what is injurious to himself, what is stupid, very stupid--simply in order to have the right to desire for himself even what is very stupid and not to be bound by an obligation to desire only what is sensible.

28. Physics of paradox www.timeandquantummechanics.com Tales of the time police

29. Physics of paradox www.timeandquantummechanics.com 2 Consistency principles Hawking: “The laws of physics do not allow the appearance of closed timelike curves.” Novikov: You can have closed timelike curves, and even travel along them. But if you go back in time, you can’t change anything that is already known.

30. Physics of paradox www.timeandquantummechanics.com Peres & Schulman “In any case where a signal from the future seems liable to tampering, either that signal will come through sufficiently muddled and unclear, or the overall system will otherwise conspire to subvert any schemes for tampering.” - Peres & Schulman, 1972 Peres & Schulman work with tachyons, hypothetical particles that travel faster than light. The catch is that faster than light to Alice is backwards in time to Bob. The cure - as always - is to look at the system as a whole, to adopt the block universe view & see that any paradoxical signals are self-canceling.

31. Physics of paradox www.timeandquantummechanics.com

32. Physics of paradox www.timeandquantummechanics.com Toy time machine According to our model, if you travel into the past quantum mechanically, you would only see those alternatives consistent with the world you left behind you. In other words, while you are aware of the past, you cannot change it. No matter how unlikely the events are that could have led to your present circumstances, once they have actually occurred, they cannot be changed. Your trip would set up resonances that are consistent with the future that has already unfolded. - Greenberger & Svozil

33. Physics of paradox www.timeandquantummechanics.com A market in time

34. Physics of paradox www.timeandquantummechanics.com A market in time Up Buy Down Sell Up Buy Bubble Crash &Sell Sell Buy 50% Sell50%

35. Physics of paradox www.timeandquantummechanics.com Paradox noise

36. Physics of paradox www.timeandquantummechanics.com Slippage The time machines here are subject to “slippage” There is always a bit of uncertainty as to where & when you will arrive And paradoxical trips are “flat out” In theory, history resists time travel which would cause the past to be altered by preventing visits to certain places or times. Typically the machine used for time travel will refuse to function, rendering the trip impossible. In other cases "slippage", a shift in the exact time target, occurs. The time-traveler arrives at the nearest place-and-time suitable for preventing a paradox; variance can be anything from 5 minutes to 5 years. - Wikipedia “If something unfortunate does happen, we can go back in time and pull [Kivrin] out before it happens, can’t we?” - Gilchrist “[Gilchrist] has no notion of how the net works, no notion of the paradoxes, no notion that Kivrin is there, and what happens to her is real and irrevocable.” - Dunworthy

37. Physics of paradox www.timeandquantummechanics.com What does this mean? What does paradox noise look like? Can you avoid it? Can you use it?

38. Physics of paradox www.timeandquantummechanics.com Crystallizing time

39. Physics of paradox www.timeandquantummechanics.com The impersonal subjective

40. Physics of paradox www.timeandquantummechanics.com Time in Time to come Everything not forbidden is compulsory. — Gellmann If at first an idea does not sound absurd, there is no hope for it. — Einstein The only way of discovering the limits of the possible is to venture a little past them into the impossible. — Clarke

41. Physics of paradox www.timeandquantummechanics.com Atropos -- aka fate #3 Time travel may be possible But if so, paradoxes will be self-canceling Whether the paradox is intended or not

42. Corporate sponsors The terminal alternative! Don’t get lost, take Oceanic! When “highly” improbable just isn’t improbable enough!

43. Physics of paradox www.timeandquantummechanics.com thanks! Ferne Welch Nathan Evans & Colleen Cahill Margaret Trebling Library of Congress & Capclave Philcon Physics of paradox www.timeandquantummechanics.com

44. Physics of paradox www.timeandquantummechanics.com References AuthorTitleYear ThorneBlack Holes & Time Warps1994 HawkingThe Illustrated a Brief History of Time1996 DaviesHow to Build a Time Machine2001 ToomeyThe New Time Travelers2007 KakuPhysics of the Impossible2008 CarrollFrom Eternity to Here2010 Goldberg & BlomquistA User’s Guide to the Universe2010