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Overview          Basic framework            Main example                DiscussionRetrocausality – What Would it Take?   ...
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Overview   The block universe                           Basic framework    Knowledge and choice                           ...
Overview   The block universe                     Basic framework    Knowledge and choice                       Main examp...
Overview   The block universe                     Basic framework    Knowledge and choice                       Main examp...
Overview   The block universe                     Basic framework    Knowledge and choice                       Main examp...
Overview     The block universe                    Basic framework      Knowledge and choice                      Main exa...
Overview     The block universe                    Basic framework      Knowledge and choice                      Main exa...
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Overview     The block universe                                    Basic framework      Knowledge and choice              ...
Overview     The block universe                                    Basic framework      Knowledge and choice              ...
Overview     The block universe                      Basic framework      Knowledge and choice                        Main...
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Overview     The block universe                      Basic framework      Knowledge and choice                        Main...
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Overview     The block universe                                   Basic framework      Knowledge and choice               ...
Overview     The block universe                                    Basic framework      Knowledge and choice              ...
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Overview     The block universe                                             Basic framework      Knowledge and choice     ...
Overview     The block universe                  Basic framework      Knowledge and choice                    Main example...
Overview     The block universe                  Basic framework      Knowledge and choice                    Main example...
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Overview     The block universe                                    Basic framework      Knowledge and choice              ...
Overview     The block universe                                    Basic framework      Knowledge and choice              ...
Overview     The block universe                                             Basic framework      Knowledge and choice     ...
Overview   Classical Polarization 101                            Basic framework    Connection and control A              ...
Overview   Classical Polarization 101                              Basic framework    Connection and control A            ...
Overview   Classical Polarization 101                              Basic framework    Connection and control A            ...
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Overview        Classical Polarization 101                              Basic framework         Connection and control A  ...
Overview        Classical Polarization 101                              Basic framework         Connection and control A  ...
Overview        Classical Polarization 101                              Basic framework         Connection and control A  ...
Overview        Classical Polarization 101                              Basic framework         Connection and control A  ...
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LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
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LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
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LMPS Plenary 2011
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LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
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LMPS Plenary 2011
LMPS Plenary 2011
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LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
LMPS Plenary 2011
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LMPS Plenary 2011
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LMPS Plenary 2011

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LMPS Plenary 2011

  1. 1. Overview Basic framework Main example DiscussionRetrocausality – What Would it Take? Huw Price ∧ The University Alumni Huw Price Excellence Award 2011 Retrocausality – What Would it Take? 1/30
  2. 2. Overview Basic framework Main example Discussion1 Brief overview2 The basic framework3 The main example4 Some discussion Huw Price Retrocausality – What Would it Take? 2/30
  3. 3. Overview Basic framework Main example DiscussionThe issues 1 Could we have good scientific evidence for thinking that we can influence the past? 2 If so, what would such evidence look like? 3 Do we have any such evidence in fact? Huw Price Retrocausality – What Would it Take? 3/30
  4. 4. Overview Basic framework Main example DiscussionThe issues 1 Could we have good scientific evidence for thinking that we can influence the past? 2 If so, what would such evidence look like? 3 Do we have any such evidence in fact? Huw Price Retrocausality – What Would it Take? 3/30
  5. 5. Overview Basic framework Main example DiscussionThe issues 1 Could we have good scientific evidence for thinking that we can influence the past? 2 If so, what would such evidence look like? 3 Do we have any such evidence in fact? Huw Price Retrocausality – What Would it Take? 3/30
  6. 6. Overview Basic framework Main example DiscussionThe issues 1 Could we have good scientific evidence for thinking that we can influence the past? 2 If so, what would such evidence look like? 3 Do we have any such evidence in fact? Huw Price Retrocausality – What Would it Take? 3/30
  7. 7. Overview Basic framework Main example DiscussionStructure of the talk 1 Simplifying assumptions – making the issue as simple as possible, by setting aside various metaphysical complexities. (Would the complexities make a difference? Maybe, maybe not, but let’s consider the simple case first!) 2 The central example – showing how some of the distinctive correlations of QM can commit us to retrocausality, in the defined sense. (The argument depends on three further assumptions, which – though not incontestable – are far from implausible. Thus it shows how, in accepting those assumptions, we might take ourselves to have discovered retrocausality.) 3 Discussion. Huw Price Retrocausality – What Would it Take? 4/30
  8. 8. Overview Basic framework Main example DiscussionStructure of the talk 1 Simplifying assumptions – making the issue as simple as possible, by setting aside various metaphysical complexities. (Would the complexities make a difference? Maybe, maybe not, but let’s consider the simple case first!) 2 The central example – showing how some of the distinctive correlations of QM can commit us to retrocausality, in the defined sense. (The argument depends on three further assumptions, which – though not incontestable – are far from implausible. Thus it shows how, in accepting those assumptions, we might take ourselves to have discovered retrocausality.) 3 Discussion. Huw Price Retrocausality – What Would it Take? 4/30
  9. 9. Overview Basic framework Main example DiscussionStructure of the talk 1 Simplifying assumptions – making the issue as simple as possible, by setting aside various metaphysical complexities. (Would the complexities make a difference? Maybe, maybe not, but let’s consider the simple case first!) 2 The central example – showing how some of the distinctive correlations of QM can commit us to retrocausality, in the defined sense. (The argument depends on three further assumptions, which – though not incontestable – are far from implausible. Thus it shows how, in accepting those assumptions, we might take ourselves to have discovered retrocausality.) 3 Discussion. Huw Price Retrocausality – What Would it Take? 4/30
  10. 10. Overview Basic framework Main example DiscussionStructure of the talk 1 Simplifying assumptions – making the issue as simple as possible, by setting aside various metaphysical complexities. (Would the complexities make a difference? Maybe, maybe not, but let’s consider the simple case first!) 2 The central example – showing how some of the distinctive correlations of QM can commit us to retrocausality, in the defined sense. (The argument depends on three further assumptions, which – though not incontestable – are far from implausible. Thus it shows how, in accepting those assumptions, we might take ourselves to have discovered retrocausality.) 3 Discussion. Huw Price Retrocausality – What Would it Take? 4/30
  11. 11. Overview Basic framework Main example DiscussionStructure of the talk 1 Simplifying assumptions – making the issue as simple as possible, by setting aside various metaphysical complexities. (Would the complexities make a difference? Maybe, maybe not, but let’s consider the simple case first!) 2 The central example – showing how some of the distinctive correlations of QM can commit us to retrocausality, in the defined sense. (The argument depends on three further assumptions, which – though not incontestable – are far from implausible. Thus it shows how, in accepting those assumptions, we might take ourselves to have discovered retrocausality.) 3 Discussion. Huw Price Retrocausality – What Would it Take? 4/30
  12. 12. Overview Basic framework Main example DiscussionStructure of the talk 1 Simplifying assumptions – making the issue as simple as possible, by setting aside various metaphysical complexities. (Would the complexities make a difference? Maybe, maybe not, but let’s consider the simple case first!) 2 The central example – showing how some of the distinctive correlations of QM can commit us to retrocausality, in the defined sense. (The argument depends on three further assumptions, which – though not incontestable – are far from implausible. Thus it shows how, in accepting those assumptions, we might take ourselves to have discovered retrocausality.) 3 Discussion. Huw Price Retrocausality – What Would it Take? 4/30
  13. 13. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion Interventionism1 Brief overview2 The basic framework The block universe Knowledge and choice Why not retrocausality? Interventionism3 The main example4 Some discussion Huw Price Retrocausality – What Would it Take? 5/30
  14. 14. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismThe block universe Huw Price Retrocausality – What Would it Take? 6/30
  15. 15. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismThe block universe [Images: Scientific American/Bryan Christie Design] Huw Price Retrocausality – What Would it Take? 6/30
  16. 16. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismThe block universe [Images: Scientific American/Bryan Christie Design] Huw Price Retrocausality – What Would it Take? 6/30
  17. 17. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in the future. Given the block universe, this is ignorance about how the future actually is. It relies on hypotheticals, not counterfactuals: If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). Huw Price Retrocausality – What Would it Take? 7/30
  18. 18. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in the future. Given the block universe, this is ignorance about how the future actually is. It relies on hypotheticals, not counterfactuals: If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). Huw Price Retrocausality – What Would it Take? 7/30
  19. 19. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective Choice-dependent ignorance E(A) E(-A) Outcome As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in Time the future. Given the block universe, this is ignorance Act about how the future actually is. It relies on hypotheticals, not counterfactuals: A/-A? If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). me Huw Price Retrocausality – What Would it Take? 7/30
  20. 20. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective Choice-dependent ignorance E(A) E(-A) Outcome As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in Time the future. Given the block universe, this is ignorance Act about how the future actually is. It relies on hypotheticals, not counterfactuals: A/-A? If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). me Huw Price Retrocausality – What Would it Take? 7/30
  21. 21. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective Choice-dependent ignorance E(A) E(-A) Outcome As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in Time the future. Given the block universe, this is ignorance Act about how the future actually is. It relies on hypotheticals, not counterfactuals: A/-A? If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). me Huw Price Retrocausality – What Would it Take? 7/30
  22. 22. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective E(A) Outcome As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in Time the future. Given the block universe, this is ignorance Act about how the future actually is. It relies on hypotheticals, not counterfactuals: A If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). me Huw Price Retrocausality – What Would it Take? 7/30
  23. 23. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective E(-A) Outcome As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in Time the future. Given the block universe, this is ignorance Act about how the future actually is. It relies on hypotheticals, not counterfactuals: -A If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). me Huw Price Retrocausality – What Would it Take? 7/30
  24. 24. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismChoice ignorance: the agent’s perspective E(A) Outcome As I decide how to act, I’m ignorant about what I will do. Will I do A or -A? When I decide I’ll know, but not before! My ignorance extends to whatever I take to depend on my choice . . . normally in Time the future. Given the block universe, this is ignorance Act about how the future actually is. It relies on hypotheticals, not counterfactuals: A If I (actually) do A, then E(A) If I (actually) do -A, then E(-A). me Huw Price Retrocausality – What Would it Take? 7/30
  25. 25. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Choice-dependent ignorance Why can’t my zone of choice-dependent E(A) E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? Time Act A/-A? me Huw Price Retrocausality – What Would it Take? 8/30
  26. 26. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Choice-dependent ignorance Why can’t my zone of choice-dependent E(A) E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? Time Act A/-A? me Huw Price Retrocausality – What Would it Take? 8/30
  27. 27. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Choice-dependent ignorance Why can’t my zone of choice-dependent E(A) E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? Time Act A/-A? Known past me Huw Price Retrocausality – What Would it Take? 8/30
  28. 28. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Why can’t my zone of choice-dependent E(A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? Time Act A Known past me Huw Price Retrocausality – What Would it Take? 8/30
  29. 29. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Why can’t my zone of choice-dependent E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? Time Act -A Known past me Huw Price Retrocausality – What Would it Take? 8/30
  30. 30. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Choice-dependent ignorance Why can’t my zone of choice-dependent E(A) E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? It can’t include the ‘known’ (or knowable) past, of course, because that conflicts Time with ignorance (I could ’bilk’) – but why should the entire past be assumed Act ‘knowable’, for these purposes? A/-A? This is what I mean by ‘retrocausality’. Known past Our question: What would it take to show that our choice-dependent me ignorance extends into the past? Huw Price Retrocausality – What Would it Take? 8/30
  31. 31. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Choice-dependent ignorance Why can’t my zone of choice-dependent E(A) E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? It can’t include the ‘known’ (or knowable) past, of course, because that conflicts Time with ignorance (I could ’bilk’) – but why should the entire past be assumed Act ‘knowable’, for these purposes? A/-A? This is what I mean by ‘retrocausality’. Known past Our question: What would it take to show that our choice-dependent me ignorance extends into the past? Huw Price Retrocausality – What Would it Take? 8/30
  32. 32. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismWhy not backwards? Choice-dependent ignorance Why can’t my zone of choice-dependent E(A) E(-A) Outcome ignorance extend into the past, as well as the future . . . so that my decision hypotheticals look like this? It can’t include the ‘known’ (or knowable) past, of course, because that conflicts Time with ignorance (I could ’bilk’) – but why should the entire past be assumed Act ‘knowable’, for these purposes? A/-A? This is what I mean by ‘retrocausality’. Known past Our question: What would it take to show that our choice-dependent me ignorance extends into the past? Huw Price Retrocausality – What Would it Take? 8/30
  33. 33. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismInterventionism Assuming determinism, ignorance about my choice is bound to imply ignorance about something in my own past. I’ll ignore this, and assume an ‘interventionist’ model of agency – i.e, that our actions come from ‘outside’ the systems we consider. (Cf. Pearl) So the only issue is this one: what would it take to convince us that this is actually the right model of our situation? Huw Price Retrocausality – What Would it Take? 9/30
  34. 34. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismInterventionism Assuming determinism, ignorance about my choice is bound to imply ignorance about something in my own past. I’ll ignore this, and assume an ‘interventionist’ model of agency – i.e, that our actions come from ‘outside’ the systems we consider. (Cf. Pearl) So the only issue is this one: what would it take to convince us that this is actually the right model of our situation? Huw Price Retrocausality – What Would it Take? 9/30
  35. 35. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismInterventionism Choice-dependent ignorance E(A) E(-A) Outcome Assuming determinism, ignorance about my choice is bound to imply ignorance about something in my own past. I’ll ignore this, and assume an ‘interventionist’ model of agency – i.e, Time that our actions come from ‘outside’ the systems we consider. (Cf. Pearl) Act So the only issue is this one: what would A/-A? it take to convince us that this is actually the right model of our situation? me Huw Price Retrocausality – What Would it Take? 9/30
  36. 36. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismInterventionism Choice-dependent ignorance E(A) E(-A) Outcome Assuming determinism, ignorance about my choice is bound to imply ignorance about something in my own past. I’ll ignore this, and assume an ‘interventionist’ model of agency – i.e, Time that our actions come from ‘outside’ the systems we consider. (Cf. Pearl) Act So the only issue is this one: what would A/-A? it take to convince us that this is actually the right model of our situation? me Huw Price Retrocausality – What Would it Take? 9/30
  37. 37. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismInterventionism Choice-dependent ignorance E(A) E(-A) Outcome Assuming determinism, ignorance about my choice is bound to imply ignorance about something in my own past. I’ll ignore this, and assume an ‘interventionist’ model of agency – i.e, Time that our actions come from ‘outside’ the systems we consider. (Cf. Pearl) Act So the only issue is this one: what would A/-A? it take to convince us that this is actually the right model of our situation? me Huw Price Retrocausality – What Would it Take? 9/30
  38. 38. Overview The block universe Basic framework Knowledge and choice Main example Why not retrocausality? Discussion InterventionismInterventionism Choice-dependent ignorance E(A) E(-A) Outcome Assuming determinism, ignorance about my choice is bound to imply ignorance about something in my own past. I’ll ignore this, and assume an ‘interventionist’ model of agency – i.e, Time that our actions come from ‘outside’ the systems we consider. (Cf. Pearl) Act So the only issue is this one: what would A/-A? it take to convince us that this is actually Known past the right model of our situation? me Huw Price Retrocausality – What Would it Take? 9/30
  39. 39. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control B1 Brief overview2 The basic framework3 The main example Classical Polarization 101 Connection and control A Quantum Polarization 101 Connection and control B4 Some discussion Huw Price Retrocausality – What Would it Take? 10/30
  40. 40. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe classical case (right) L=0 R=0 Photon Beam L=1 τL R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR Malus’ Law: IntensityR=1 = cos2 (τ − σR ), IntensityR=0 = sin2 (τ − σR ) Huw Price Retrocausality – What Would it Take? 11/30
  41. 41. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe classical case (right) L=0 R=0 Photon Beam L=1 τL R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR Malus’ Law: IntensityR=1 = cos2 (τ − σR ), IntensityR=0 = sin2 (τ − σR ) Huw Price Retrocausality – What Would it Take? 11/30
  42. 42. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe classical case (left) L=0 R=0 Beam Photon L=1 τR R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR ‘T-reversed’: IntensityL=1 = cos2 (τ − σL ), IntensityL=0 = sin2 (τ − σL ) Huw Price Retrocausality – What Would it Take? 12/30
  43. 43. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe classical case (left) L=0 R=0 Beam Photon L=1 τR R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR ‘T-reversed’: IntensityL=1 = cos2 (τ − σL ), IntensityL=0 = sin2 (τ − σL ) Huw Price Retrocausality – What Would it Take? 12/30
  44. 44. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThinking about connection and control L=0 R=0 Beam L=1 R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR 1 Polarization as a ‘local’ mechanism 2 What we can wiggle Huw Price Retrocausality – What Would it Take? 13/30
  45. 45. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThinking about connection and control L=0 R=0 Beam L=1 R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR 1 Polarization as a ‘local’ mechanism 2 What we can wiggle Huw Price Retrocausality – What Would it Take? 13/30
  46. 46. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThinking about connection and control L=0 R=0 Beam L=1 R=1 τ σL σR us 1 Polarization as a ‘local’ mechanism 2 What we can wiggle Huw Price Retrocausality – What Would it Take? 13/30
  47. 47. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThinking about connection and control L=0 R=0 Beam L=1 R=1 τ σL σR us 1 Polarization as a ‘local’ mechanism 2 What we can wiggle Huw Price Retrocausality – What Would it Take? 13/30
  48. 48. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  49. 49. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  50. 50. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  51. 51. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  52. 52. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  53. 53. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  54. 54. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left? L=0 R=0 Beam L=1 R=1 τ σL σR us Suppose we control the left polarizer angle, σL , but not the input beams – the Demon of the Left controls those. Can we control the polarization of the output beam, τ ? No! The Demon can make τ whatever He likes, by choosing the appropriate input intensities. (The Demon can ‘counteract’ our wiggles, in other words.) Huw Price Retrocausality – What Would it Take? 14/30
  55. 55. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BNature as the Demon of the Right L=0 R=0 Beam L=1 R=1 τ σL σR us Similarly, suppose we control the right polarizer angle, σR , but not the output beams – Nature controls those. Can we control the polarization of the input beam, τ ? No. Nature absorbs our wiggles in changes in the output intensities, and τ doesn’t change. (So no retrocausality here!) Huw Price Retrocausality – What Would it Take? 15/30
  56. 56. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BNature as the Demon of the Right L=0 R=0 Beam L=1 R=1 τ σL σR us Similarly, suppose we control the right polarizer angle, σR , but not the output beams – Nature controls those. Can we control the polarization of the input beam, τ ? No. Nature absorbs our wiggles in changes in the output intensities, and τ doesn’t change. (So no retrocausality here!) Huw Price Retrocausality – What Would it Take? 15/30
  57. 57. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BNature as the Demon of the Right L=0 R=0 Beam L=1 R=1 τ σL σR us Similarly, suppose we control the right polarizer angle, σR , but not the output beams – Nature controls those. Can we control the polarization of the input beam, τ ? No. Nature absorbs our wiggles in changes in the output intensities, and τ doesn’t change. (So no retrocausality here!) Huw Price Retrocausality – What Would it Take? 15/30
  58. 58. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BNature as the Demon of the Right L=0 R=0 Beam L=1 R=1 τ σL σR us Similarly, suppose we control the right polarizer angle, σR , but not the output beams – Nature controls those. Can we control the polarization of the input beam, τ ? No. Nature absorbs our wiggles in changes in the output intensities, and τ doesn’t change. (So no retrocausality here!) Huw Price Retrocausality – What Would it Take? 15/30
  59. 59. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BNature as the Demon of the Right L=0 R=0 Beam L=1 R=1 τ σL σR us Similarly, suppose we control the right polarizer angle, σR , but not the output beams – Nature controls those. Can we control the polarization of the input beam, τ ? No. Nature absorbs our wiggles in changes in the output intensities, and τ doesn’t change. (So no retrocausality here!) Huw Price Retrocausality – What Would it Take? 15/30
  60. 60. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BNature as the Demon of the Right L=0 R=0 Beam L=1 R=1 τ σL σR us Similarly, suppose we control the right polarizer angle, σR , but not the output beams – Nature controls those. Can we control the polarization of the input beam, τ ? No. Nature absorbs our wiggles in changes in the output intensities, and τ doesn’t change. (So no retrocausality here!) Huw Price Retrocausality – What Would it Take? 15/30
  61. 61. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe quantum case (right) L=0 R=0 Photon Photon L=1 τL R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR QM Malus’ Law: ProbR=1 = cos2 (τ − σR ), ProbR=0 = sin2 (τ − σR ) Huw Price Retrocausality – What Would it Take? 16/30
  62. 62. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe quantum case (right) L=0 R=0 Photon Photon L=1 τL R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR QM Malus’ Law: ProbR=1 = cos2 (τ − σR ), ProbR=0 = sin2 (τ − σR ) Huw Price Retrocausality – What Would it Take? 16/30
  63. 63. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe quantum case (left) L=0 R=0 Photon Photon L=1 τR R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR ‘T-reversed’: ProbL=1 = cos2 (τ − σL ), ProbL=0 = sin2 (τ − σL ) Huw Price Retrocausality – What Would it Take? 17/30
  64. 64. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BThe quantum case (left) L=0 R=0 Photon Photon L=1 τR R=1 τ Polarizing cube Polarizing cube set at angle σL set at angle σR ‘T-reversed’: ProbL=1 = cos2 (τ − σL ), ProbL=0 = sin2 (τ − σL ) Huw Price Retrocausality – What Would it Take? 17/30
  65. 65. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BConnection and control again L=0 R=0 Photon L=1 τL R=1 Polarizing cube Polarizing cube set at angle σL set at angle σR 1 Polarization as a local mechanism – intuitively, τL is just whatever ‘beable’ connects changes on the left to changes on the right. (Let Realism be the assumption that here is some such beable.) 2 What we can wiggle? Huw Price Retrocausality – What Would it Take? 18/30
  66. 66. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BConnection and control again L=0 R=0 Photon L=1 τL R=1 Polarizing cube Polarizing cube set at angle σL set at angle σR 1 Polarization as a local mechanism – intuitively, τL is just whatever ‘beable’ connects changes on the left to changes on the right. (Let Realism be the assumption that here is some such beable.) 2 What we can wiggle? Huw Price Retrocausality – What Would it Take? 18/30
  67. 67. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BConnection and control again L=0 R=0 Photon L=1 τL R=1 Polarizing cube Polarizing cube set at angle σL set at angle σR 1 Polarization as a local mechanism – intuitively, τL is just whatever ‘beable’ connects changes on the left to changes on the right. (Let Realism be the assumption that here is some such beable.) 2 What we can wiggle? Huw Price Retrocausality – What Would it Take? 18/30
  68. 68. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BConnection and control again L=0 R=0 Photon L=1 τL R=1 Polarizing cube Polarizing cube set at angle σL set at angle σR 1 Polarization as a local mechanism – intuitively, τL is just whatever ‘beable’ connects changes on the left to changes on the right. (Let Realism be the assumption that here is some such beable.) 2 What we can wiggle? Huw Price Retrocausality – What Would it Take? 18/30
  69. 69. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BConnection and control again L=0 R=0 Photon L=1 τL R=1 σL σR us 1 Polarization as a local mechanism – intuitively, τL is just whatever ‘beable’ connects changes on the left to changes on the right. (Let Realism be the assumption that here is some such beable.) 2 What we can wiggle? Huw Price Retrocausality – What Would it Take? 18/30
  70. 70. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BConnection and control again L=0 R=0 Photon L=1 τL R=1 σL σR us 1 Polarization as a local mechanism – intuitively, τL is just whatever ‘beable’ connects changes on the left to changes on the right. (Let Realism be the assumption that here is some such beable.) 2 What we can wiggle? Huw Price Retrocausality – What Would it Take? 18/30
  71. 71. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  72. 72. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  73. 73. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  74. 74. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  75. 75. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  76. 76. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  77. 77. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating the Demon of the Left L=0 R=0 Photon L=1 τL R=1 σL σR us Again, suppose we control the left polarizer, σL , but not the input photons – the Demon of the Left controls those. Can we control τL ? Yes! . . . so long as the Demon has to put the photon on one channel or other (the Discreteness assumption). In this case, τL = σL or τL = σL + π/2. So we can’t fix τL completely, but we can restrict it to just two possibilities. Huw Price Retrocausality – What Would it Take? 19/30
  78. 78. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  79. 79. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  80. 80. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  81. 81. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  82. 82. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  83. 83. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  84. 84. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  85. 85. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30
  86. 86. Overview Classical Polarization 101 Basic framework Connection and control A Main example Quantum Polarization 101 Discussion Connection and control BDefeating Nature on the right L=0 R=0 Photon L=1 τL , τ R R=1 σL σR us Suppose we control the right polarizer, σR , but not the output beams – Nature controls those. Can we control some property τR of the input beam? Yes, on two assumptions: (1) Time-symmetry: if τL exists, so does τR (with T-reversed rules); (2) Discreteness: Nature has to put the output photon on one channel or other. Then τR = σR or τR = σR + π/2 – we can’t fix τR completely, but we can restrict it to two possibilities. (Retrocausality!) Huw Price Retrocausality – What Would it Take? 20/30

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