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Bohm versus Everett

Bohm versus Everett. Lev Vaidman. 30.08.2010. 21st-century directions in de Broglie- Bohm theory and beyond. THE TOWLER INSTITUTE The Apuan Alps Centre for Physics Vallico Sotto, Tuscany, Italy. Hope:. Today’s physics explains all what we see. Big hope:.

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Bohm versus Everett

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  1. Bohm versus Everett Lev Vaidman 30.08.2010 21st-century directions in de Broglie-Bohm theory and beyond THE TOWLERINSTITUTE The Apuan Alps Centre for Physics VallicoSotto, Tuscany, Italy

  2. Hope: Today’s physics explains all what we see. Big hope: Today’s physics explains All. The quantum mechanical formalism does not provide physicists with a ‘pictorial’ representation: the ψ-function does not, as Schrödinger had hoped, represent a new kind of reality. Instead, as Born suggested, the square of the absolute value of the ψ-function expresses a probability amplitude for the outcome of a measurement. Bohr (SEP): Bohr and today’s majority of physicists gave up the hope I think, we should not. Bohm and Everett are candidates for a final theory.

  3. Bohm: All is and

  4. Everett: All is

  5. Everett: Allis Many-Worlds

  6. http://qol.tau.ac.il/TWS.html The Quantum World Splitter Choose how many worlds you want to split by pressing one  of the red dice faces.

  7. http://qol.tau.ac.il/TWS.html left right

  8. http://qol.tau.ac.il/TWS.html right

  9. World-splitter of Tel Aviv University

  10. World-splitter of Tel Aviv University

  11. World-splitter of Tel Aviv University

  12. All All is a closed system which can be observed

  13. All All is a closed system which might include an observer which can be observed

  14. What is ψ ? There is no sharp answer. Theoretical physicists are very flexible in adapting their tools, and no axiomization can keep up with them. But it is fair to say that there are two core ideas of quantum field theory. First: The basic dynamical degrees of freedom are operator functions of space and time- quantum fields. Second: The interaction of these fields are local in space and time. F. Wilczek(in Compendium of Quantum Physics, 2009) Bohm: At the end of the day, the only variables we observe are positions.

  15. Space is taken for granted

  16. Everett:

  17. Bohm:

  18. Bohm: All is and evolving according to deterministic equations • Everett: All is evolving according to deterministic equation

  19. A CENTURY AGO: All is particles evolving according to Newton’s equations Laplacian determinism

  20. Laplacian determinism TRIVIAL Observation Bohmian mechanics TRIVIAL Observation Everett Interpretation Observation HARD

  21. Laplacian determinism TRIVIAL Observation Bohmian mechanics TRIVIAL Observation Everett Interpretation Observation HARD

  22. Laplacian determinism TRIVIAL Observation Bohmian mechanics TRIVIAL Observation Everett Interpretation HARD Many parallel Observations

  23. What is “a world” in the Everett Interpretation ? many worlds Many parallel Observations world i Observation i An observer has definite experience. Everett’s Relative State World A world is the totality of (macroscopic) objects: stars, cities, people, grains of sand, etc. in a definite classically described state. is a Localized Wave Packet for a period of time The MWI in SEP

  24. What is our world in the BohmianInterpretation ? Observation We do not observe (experience)

  25. A tale of a single world universe The king forbade spinning on distaff or spindle, or the possession of one, upon pain of death, throughout the kingdom

  26. A tale of a single world universe The king forbade performing quantum measurements, or the possession of quantum devices, upon pain of death, throughout the kingdom Photomultipliers Geiger counters Stern Gerlach devices Beam splitters Down conversion crystals Quantum dots Quantum tunneling Photodiods …… The Quantum World Splitter

  27. A tale of a single world universe Quantum states of all macroscopic objects are Localized Wave Packets all the time Zero approximation: all particles remain in product LWP states Particles which do not interact strongly with “macroscopic objects” need not be in LWP states. Particles which make atoms, molecules, etc. can (and should be) entangled among themselves. Only states of the center of mass of molecules, cat’s nails etc. have to be in LWP states.

  28. A tale of a single world universe Quantum states of all macroscopic objects are Localized Wave Packets all the time of a cat! Observation TRIVIAL Almost the same as in Bohmian trajectories

  29. Two worlds universe This is a multiple worlds universe

  30. Two worlds universe

  31. A 0.9 0.1 Probability of what? B Bohm and Everett have no randomness so the concept of probability needs explanation Bohm – simple ignorance probability Everett – an illusion of probability due to ignorance of the decedents

  32. A A B B Bohmian Mechanics Ignorance probability: the observer does not know the initial Bohmian position

  33. A A B B Everett: Probability of what? Ignorant of what?

  34. A A B B Everett: Sleeping Pill Experiment Vaidman (1998) ISPS 0.9 0.1 Ignorance probability of the descendants A and B

  35. Only and can give this answer 0.9 What is the probability that you are in A? 0.9 A A B 0.9 0.1 What is the probability that you are in A? B

  36. 0.9 0.9 What is the probability that you are in A? What is the probability that you are in A? 0.9 A A B 0.1 B Since all the descendants yield the same answer we can relate it to me before the experiment. I put my bet for the descendants. They have probability. Thus, my bet is for a probabilistic event.

  37. What is the past of a quantum particle?

  38. Wheeler: The “past” and the “Delayed Choice” Double-Slit Experiment J.A. Wheeler 1978 The present choice of observation influences what we say about the “past” of the photon; it is undefined and undefinable without the observation. No phenomenon is a phenomenon until it is an observed phenomenon. My lesson: The “past” of the photon is defined after the observation

  39. Wheeler delayed choice experiment Wheeler: The photon took the upper path It could not come the other way

  40. Wheeler delayed choice experiment Bohm: The photon took the lower path

  41. Wheeler delayed choice experiment Wheeler: The photon took both paths Otherwise, the interference cannot be explained Bohm: The photon took one of the paths

  42. The past of a quantum particle can be learned by measuring the trace it left

  43. Wheeler delayed choice experiment Bohm: The photon took the lower path But the trace shows the upper path

  44. Wheeler delayed choice experiment Wheeler: The photon took both paths Otherwise, the interference cannot be explained Bohm: The photon took one of the paths The trace shows both paths

  45. Kwiat’s proposal

  46. Kwiat’s proposal Wheeler: The photon took the lower path It could not come the other way Bohm: The photon took the lower path The trace shows a different picture!

  47. What is “a world” in the many-worlds picture? world i Observation i is a Localized Wave Packet for a period of time • A world consist of: • "classical" macroscopic objects rapidly measured by the environment, • quantum objects measured only occasionally (at world splitting events), • weakly coupled quantum objects

  48. The two-state vector formalism expalnation The pre- and post-selected particle is described bythe two-state vector The outcomes of weakmeasurements are weak values

  49. One world • A world consist of: • "classical" macroscopic objects rapidly measured by the environment, • quantum objects measured only occasionally (at world splitting events), • weakly coupled quantum objects

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