Inconsistent Histories Revealed by Quantum Measurement A New Class of Paradoxes and their Implications Avshalom Elitzur and Shahar Dolev Bar-Ilan University.

Inconsistent Histories Inconsistent Histories Revealed by Quantum Revealed by Quantum

MeasurementMeasurement

A New Class of Paradoxes and A New Class of Paradoxes and their Implicationstheir Implications

Avshalom Elitzur and Shahar DolevAvshalom Elitzur and Shahar Dolev

Bar-Ilan UniversityBar-Ilan University

Overview:Overview:

• The RationaleThe Rationale• The three views concerning timeThe three views concerning time• The issue of time-asymmetry and The issue of time-asymmetry and

indeterminismindeterminism• Two types of QM experiments: Spatial Two types of QM experiments: Spatial

and temporal paradoxesand temporal paradoxes• Our strategyOur strategy• Inconsistent histories?Inconsistent histories?• Back to timeBack to time

The Rationale:The Rationale:

• QM challenges our basic notions of space QM challenges our basic notions of space and time. and time.

• Therefore, a better understanding of the Therefore, a better understanding of the quantum riddles will come from a deeper quantum riddles will come from a deeper account of spacetime.account of spacetime.

• Conversely, a better understanding of Conversely, a better understanding of spacetime might emerge from spacetime might emerge from investigating into quantum riddlesinvestigating into quantum riddles

Three Views of Time:Three Views of Time:

• ““Block Universe”Block Universe” • ““Becoming”Becoming”• ““Extreme Extreme Presentism”Presentism”

The Issue Of Time-The Issue Of Time-Asymmetry And Asymmetry And IndeterminismIndeterminism Run

Simulation!

Run Simulation!

The Issue Of Time-The Issue Of Time-Asymmetry And Asymmetry And IndeterminismIndeterminism

The Issue Of Time-The Issue Of Time-Asymmetry And Asymmetry And IndeterminismIndeterminism

Two Types Of QM Two Types Of QM Experiments:Experiments:

• Experiments presenting spatial Experiments presenting spatial peculiarities:peculiarities:

E-V Experiment

EPR Experiment

Two Types Of QM Two Types Of QM Experiments:Experiments:

• Experiments presenting temporal Experiments presenting temporal peculiarities:peculiarities:

Delayed Choice

HBT Experiment

Schrödinger’s Schrödinger’s catcat

• Aharonov’s and Cramer’s unifying theories: Aharonov’s and Cramer’s unifying theories:

• All type-A experiments are in fact type-B All type-A experiments are in fact type-B experiments. experiments.

• The problem: Block Universe again.The problem: Block Universe again.

Aharonov’s and Cramer’s Aharonov’s and Cramer’s proposalproposal

1. Offer

2. Confirmation

3. Negotiation

4. Handshakex

x ?

x

x?

Our Strategy:Our Strategy:

• Postpone the Quantum-classical Postpone the Quantum-classical Interaction.Interaction.

• Pursue the bomb ideaPursue the bomb idea• This was first taken up by Hardy. This was first taken up by Hardy.

Results:Results:

• The first result (Hardy, 1992): EPR formed by a The first result (Hardy, 1992): EPR formed by a single particle in an MZI:single particle in an MZI:

22112

1xxxx 2121

2

1xxxx

1. Particles in superpositions (but not entangled)

2. “Silent” Detector clicks

3. The particles become entangled

Results:Results:

• Second result (Hardy, 1992): a quantum Second result (Hardy, 1992): a quantum mechanical bomb more intriguing than EVmechanical bomb more intriguing than EV

1. Particle in a superposition

2. “Silent” Detector clicks

3. The particle must have “collapsed” into the crossing box

4. The photon must have gone through the opposite path!

Inconsistent Histories?Inconsistent Histories?

• A new class of paradoxes: When the A new class of paradoxes: When the measurement measures not only a measurement measures not only a state but an entire evolution, then state but an entire evolution, then – indeed sometimes an entire evolution indeed sometimes an entire evolution

seems to be formed;seems to be formed;– sometimes that evolution looks like a sometimes that evolution looks like a

Schrödinger cat with a history of a dead Schrödinger cat with a history of a dead cat but traces of a live one.cat but traces of a live one.

Inconsistent Histories?Inconsistent Histories?

• Non sequential behavior of the wave Non sequential behavior of the wave function:function:1. Particles in superposition

(but not entangled)

2. “Silent” Detector clicks

3. The middle particle was measured and found to have “collapsed” into the intersecting box

4. All other particles returned to their original superposition!

(Elitzur, Dolev, Zeilinger 2001)(Elitzur, Dolev, Zeilinger 2001)

… … or better call it: or better call it: RPERPE

Inverse EPR…Inverse EPR…

Inverse EPRInverse EPR

22112

1xxxx 2121

2

1xxxx

1. Particles in superposition (but not entangled)

2. “Silent” Detector clicks

3. The particles become entangled

Inverse EPRInverse EPR

21212

1xxxx 21 xx

• With an inconsistent history?With an inconsistent history?

1. To test non-locality, test for Bell Inequality

2. Use Spin measurement in 3 directions: x, y, and z

3. Spin x (“which box”) measurement allows only one history for the photon

4. Consequently, the entanglement disappears

Inconsistent Histories?Inconsistent Histories?

THIS SENTENCE HAS NEVER THIS SENTENCE HAS NEVER

BEEN WRITTEN BEEN WRITTEN

:-):-)

Back To TimeBack To Time

• Could there be a transactional model Could there be a transactional model in which spacetime itself is subject to in which spacetime itself is subject to dynamics?dynamics?