**Causal Classical Physics in Time Symmetric Quantum Mechanics**

**Published:**20 November 2017 by

**MDPI**in

**4th International Electronic Conference on Entropy and Its Applications**session

**Quantum Information and Foundations**

**Abstract:**

The letter (to be) submitted is an executive summary of our previous paper [3]. To solve the Einstein Podolsky Rosen "paradox" the two boundary quantum mechanics developed by Aharonov and coworkers [1] and others is taken as self consistent interpretation [2].

The difficulty with this interpretation of quantum mechanics is to reconcile it with classical physics. To avoid classical backward causation two "corresponding transition rules" are formulated which specify needed properties of macroscopic observations and manipulations. The apparent classical causal decision tree requires to understand the classically unchosen options. They are taken to occur with a "incomplete knowledge" of the boundary states typically in macroscopic considerations. The precise boundary conditions with given phases then select the actual measured path and this selection is mistaken to happen at the time of measurement. The apparent time direction of the decision tree originates in an assumed relative proximity to the initial state. Only the far away final state allows for classically distinct options to be selected from.

Cosmological the picture could correspond to a big bang initial and a hugely extended final state scenario. It is speculated that it might also under certain condition work for a big bang / big crunch world. In this case the Born probability postulate could find a natural explanation if we coexist in the expanding and the CPT conjugate contracting world.

References

[1] Yakir Aharonov, Peter G Bergmann, and Joel L Lebowitz. Time symmetry in the quantum process of measurement. Physical Review, 134(6B):B1410, 1964.

[2] Yakir Aharonov, Eliahu Cohen, and Tomer Landsberger. The two-time in-terpretation and macroscopic time-reversibility. Entropy, 19(3), 2017.

[3] Fritz W. Bopp. Time Symmetric Quantum Mechanics and Causal Classical Physics. Foundation of Physics, DOI:10.1007/s10701-017-0074-7, archiv:1604.04231, 2016.

**J.M. Isidro**

I enjoyed reading your paper. Please allow me one general comment. You may perhaps have read Roger Penrose's "The Road to Reality". Among many other things, Penrose defends the view that the initial state of our Universe was one of extremely low entropy, thus explaining the current (accelerated) expansion and, simultaneoustly, the existence of the arrow of time. I'm not sure how far this is consistent with Aharonov's "two-time formalism", in fact it seems to me that these two viewpoints (Penrose's and Aharonov's) are mutually excluding (though I am not taking sides). Penrose's cyclic cosmology resets the entropy to its initial low value at the Big Crunch, which coincides with the Big Bang of the next eon, So there is in fact no time-inversion symmetry at all, according to Penrose, this (apparent) symmetry being broken by gravitational effects.

I would appreciate your comments, if any.

Best regards

**Fritz Bopp**

My cosmology background has limitations and I did not read

Penrose bestseller.

A thermodynamic time arrow from an expanding dark sky is reasonable

and widely accepted. It is my understanding that except for boundary

effects gravity has no time direction. In quantum optic experiments

gravity can always be treated classical while radiation usually involves

decoherencing quantum fluctuations. Radiation of witnesses eventually

reaching the expanding dark sky seems therefore natural. In this way

even a radically far away final state can encode all quantum decisions.

It is understood that this assumption has far reaching conceptual

consequences. My dream is that Aharonov or Cohen listen in at this

conference. I would be very much interested how far they go along

regarding classical physics consequences.

**J.M. Isidro**

Many thanks for your comments.

If I understand correctly, classical general relativity is not time-symmetric (see, eg, D. Finkelstein, "Past-Future Asymmetry of the Gravitational Field of a Point Particle", Phys. Rev. 110 (1958) 965), but I stand to be corrected in case I'm wrong. In fact the whole issue of time symmetry in general relativity is somewhat tricky, due to the absence of a globally defined time coordinate (this is no longer the case in Minkowski space, of course). However, to the extent that one can talk about time-reversal symmetry within general relativity, it seems to me that the answer is negative: there is no such symmetry.

I mentioned Penrose because he stresses this point in his book, too (by the way: "The Road to Reality", although written for a general audience, is partly a compendium of previous scientific work of his (and others'). I don't know if it sold well or not, but I'd not call it a bestseller: it's no easy read at all!). Penrose stresses that any eventual theory completing or superseding quantum mechanics as we know it today must necessarily break time-inversion symmetry, possibly (or preferably, as he'd have it) by gravitational effects.

Many thanks for your opinions.

Best regards

**Fritz Bopp**

**Fritz Bopp**

not connected to boundaries. Even the not fully understood

dynamics of Black Holes can be described in a symmetric way.

(p.e.: "Black hole unitarity and antipodal entanglement", Gerard ’t Hooft

arXiv:1061.03447 ".... . Unitarity is a starting point; no other assumptions

are made. Region I and the diametrically opposite region II of the Penrose

diagram represent antipodal points in a PT or CPT relation, as was suggested

before. ....).

As soon as I get Penrose's book I will investigate whether GR can help to

understand how measurement results are encoded.

**Fritz Bopp**

If gravity could - in some limit - be equivalent to a spin 2 graviton theory (with probability=graviton*graviton(conjugate) ) the decoherencing through gravitons would seem also - to use his term - „for all practical purposes“ just like thermal radiation. If I understand Penrose's point, it is as gravity has no separate existence in two CPT conjugate parts it automatically decoherences.

There are two defenses:

1) Gravity might not do this.

2) The effect must be tiny. Quantum states (necessarily coherent) bound by gravity were experimentally observed. As long as the final state can still reflect all measurement choices nothing seems to change.

**Giacomo D'Ariano**

Non causal variation of QT are under analysis by our group, Caslav Bruckner's one in Vienna, and other groups, but these theories are different from QT.

I would like to see a proposition coming from Yakir's which is falsifiable, and is not causal.

**Fritz Bopp**

Also it has to be admitted without an a-causal (macroscopic) prediction the 2 boundary theory lacks falsifiability. The observation of a change in the emission probability (affecting the initial state preparation) by devices felt later on might help. The merit of the 2 boundary theory is simplicity on a fundamental level.

The transition to something like classical physics is then of course not simple, but - and this is the central point - conceivable.

**Fritz Bopp**

Is there a problem I overlooked to attribute the the decision usually attributed to

measurement jumps to the chosen final state?

Aharonov's two boundary quantum mechanics largely aims for a better

understanding of the structure of QM. However in the Entropy paper

("The Two-Time Interpretation and Macroscopic Time-Reversibility"

Yakir Aharonov, Eliahu Cohen and Tomer Landsberger) it is said:

"The two-state vector formalism motivates a time-symmetric interpretation of

quantum mechanics that might solve the measurement problem. ...."

Is something wrong with my understanding that he and his coauthors

also consider a two boundary quantum physics a possible interpretation?

The resurrection of something like causality in macroscopic physics

involves daring assumptions. I there a really serious problem

(i.e. a "No_Go" theorem) or a more reliable formalism to describe the

transition?

**Fritz Bopp**

**Fritz Bopp**

Is there a problem I overlooked to attribute the the decision usually attributed to

measurement jumps to the chosen final state?

Aharonov's two boundary quantum mechanics largely aims for a better

understanding of the structure of QM. However in the Entropy paper

("The Two-Time Interpretation and Macroscopic Time-Reversibility"

Yakir Aharonov, Eliahu Cohen and Tomer Landsberger) it is said:

"The two-state vector formalism motivates a time-symmetric interpretation of

quantum mechanics that might solve the measurement problem. ...."

Is something wrong with my understanding that he and his coauthors

also consider a two boundary quantum physics a possible interpretation?

The resurrection of something like causality in macroscopic physics

involves daring assumptions. I there a really serious problem

(i.e. a "No_Go" theorem) or a more reliable formalism to describe the

transition?

Three questions - I hoped to get reactions - are:

Is there a problem I overlooked to attribute the the decision usually attributed to

measurement jumps to the chosen final state?

Aharonov's two boundary quantum mechanics largely aims for a better

understanding of the structure of QM. However in the Entropy paper

("The Two-Time Interpretation and Macroscopic Time-Reversibility"

Yakir Aharonov, Eliahu Cohen and Tomer Landsberger) it is said:

"The two-state vector formalism motivates a time-symmetric interpretation of

quantum mechanics that might solve the measurement problem. ...."

Is something wrong with my understanding that he and his coauthors

also consider a two boundary quantum physics a possible interpretation?

The resurrection of something like causality in macroscopic physics

involves daring assumptions. I there a really serious problem

(i.e. a "No_Go" theorem) or a more reliable formalism to describe the

transition?

**Fritz Bopp**

**Giacomo D'Ariano**

quantum mechanics that might solve the measurement problem. ...."

Did it solve it? Which problem? The fact that QT predicts probabilities and it is inherently probabilistic?

I formulated causality in a simple way:

"If one performs two experiments A and B in cascade on the same system, the probability distribution of experiment A does not depend on the choice of experiment B."

This is falsifiable, and has been never falsified!

There are two theorems that are iff condition for the causality:

1) there can be no signalling without interaction

2) every state preparation can be achieved deterministically

If you believe in reversibility of actual physics (the one that you see in the lab) try to revert the process from the measurement outcome back to the original quantum state...

Causality never resurrect, because it never died.

**Fritz Bopp**

If you apply usual QT to the ellipsoid described in the paper causality is violated. There are Quantum Optics experiment which make it extremely difficult not to accept it violated (backward causation). I understand that this conclusion is not widely followed and that causality is usually taken as a basic pillar of our knowledge. Nevertheless the aim to investigate the situation in which causality is violated - if a very fundamental level is considered - seems worthwhile.

Without causality there is no need to restrict the ontology of fields or wave functions. Inversely, if we - disliking alternatives - want to consider fields as real objects, Einstein-Podolsky-Rosen tells us that causality has to be broken.

After a measurement - whatever this means if the universe is taken as a closed system - the not measured part of the wave function suddenly disappears in what looks like a statistical process. In the two boundary concept the unmeasured state would evolve to be orthogonal to the final state and without overlap not contribute in the two boundary world. As the final state can not be known it is seen as statistical.

The two boundary universe is a completely consistent picture. That the fate of all Schroedinger cats ect. is enshrined in the final state is clearly a daring assumption and serious estimates might question it. The paper contains arguments why it should work in our cosmic situation.

The problem with the two boundary concept is how the usual macroscopia we know is restored. Concepts how this could work is the main part of the paper.

**Giacomo D'Ariano**

Concretely, my question is:

Can you provide a reference of experimental falsification my causality postulate, namely:

"If one performs two experiments A and B in cascade on the same system, the probability distribution of experiment A does not depend on the choice of experiment B."

Do you have an experiment in optics, where changing the output experiment B produces a different probability distribution for experiment A?

If this happens, then Quantum Theory as formulated by von Neumann is falsified, since my causality statement is a theorem following his axioms.

**Fritz Bopp**

G. Alber, J. Z. Bernád, M. Stobinska, L. L. Sánchez-Soto, and G. Leuchs QED with a parabolic mirror Phys. Rev. A 88, 023825 – Published 14 August 2013

The emission probability is changed by mirrors felt after the emission.