I Wheeler's delayed choice doesn't change the past

[zonde]

But in standard QED there are no causally connected spacelike separated events possible, and this is by construction.

How can QED say this is impossible when QED does not speak about individual events? Or I am missing something? In QT's minimal interpretation as given by Ballentine statistical nature of predictions is clearly stated. Is it somehow different in QED? Can QED go beyond that statistical nature and say something about individual realizations of experiment (except in some special cases where predicted probabilities approach 1)?

 

[vanhees71]

The commutator of local observables vanishes at space-like separated arguments identically. That's why actions at a distance (i.e., over space-like distances in Minkowski space) have probability 0, i.e., they don't happen with certainty!

 

[vanhees71]

The mystery has to do with ontology and ontology is always underdetermined by the formalism. Thus, more sophisticated experiments have not reduced the number of QM interpretations, indeed they have proliferated. Everyone picks their personal favorite and continues doing physics accordingly, i.e., everyone is using the same formalism and successfully fitting the same data, but offering different explanations afterwards. That's fine for the status quo, the book argues that to advance physics from the status quo (e.g., obtain quantum gravity and explain dark energy and dark matter data) we should consider moving to the "God's-eye view" per Wilczek. It's that simple.

For me the only mystery is why this is considered a mystery since the formalism tells us precisely what to expect, and that's what's empirically confirmed with high significance. You cannot expect more from any natural-science theory. It's about observable objective facts not some mysterious "ontology behind the phenomena".

 

[vanhees71]

The statement follows from the results of the cited papers (all of which I have checked). Nothing you've said here refutes that work.

The statement that the generators of boosts commute with the momentum operators (the generators of spatial translations) is wrong within standard non-relativistic QM, as shown already by Inönü and Wigner. For non-relativistic particles a vanishing mass doesn't make sense, because it doesn't lead to a physically interpretable quantum dynamics. For non-0 mass the commutator is
$$[\hat{K}_j,\hat{p}_k]=\mathrm{i} \delta_{jk} m \hat{1} \neq 0.$$
The group-representation theoretical reasons for this are quite obvious (see posting #78).

 

[Lord Jestocost]

The correlations are indeed there due to the preparation of the polarization-entangled biphoton state, and there's no assumption about causal effects between the later measurements necessary.

Maybe, as an experimental physicist, I don’t get the point when reasoning about “due to the preparation“. Does that mean that each entangled photon pair emerges from the source with, in effect, a set of pre-programmed, no longer modifiable, instructions for how each photon of the pair has to respond to a measurement on one of its observables?

 

[vanhees71]

Indeed, "due to preparation" means that the photon pairs have been created (today usually using parametric downconversion) in the polarization-entangled state. With appropriate "optical elements" you can produce the needed Bell states. I don't know, what you mean by "pre-programmed". The meaning of the state is very clearly given by Born's rule, and I don't know what you mean by "no longer modifiable". Of course, when the photons interact with something later, the state is modified. E.g., when the photon hits a detector usually it's absorbed and thus you have a state with this photon gone. So the state clearly changes through interactions. There are also no "instructions for how each photon of the pair has to respond to a measurement on one of its observables". The state of the single photon in the entangled pair is given according to the standard rules of QT by tracing out the other photon, i.e.,
$$\hat{\rho}_A=\mathrm{Tr}_{B} \hat{\rho}_{AB}=\sum_{j} |ij\rangle \langle ij |\hat{\rho}_{AB}|\langle kj \rangle \langle kj|.$$
For the "singlet state" you have
$$\hat{\rho}_{AB}=|\Psi \rangle \langle \Psi|, \quad |\Psi \rangle=\frac{1}{\sqrt{2}} (|HV \rangle-|VH \rangle),$$
and
$$\hat{\rho}_A=\frac{1}{2} \hat{1}.$$
I.e., the single photons in the entangled pair each are totally unpolarized, i.e., a polarizer in any direction let's the photon through with probability 1/2 and absorbs it with probability 1/2. There's nothing more known about the single photons than that.

 

[RUTA]

For me the only mystery is why this is considered a mystery since the formalism tells us precisely what to expect, and that's what's empirically confirmed with high significance. You cannot expect more from any natural-science theory. It's about observable objective facts not some mysterious "ontology behind the phenomena".

Do you understand why those who do wonder about the nature of reality (ontology) are mystified? Or is that why you're participating in such threads?

 

[RUTA]

The statement that the generators of boosts commute with the momentum operators (the generators of spatial translations) is wrong within standard non-relativistic QM, as shown already by Inönü and Wigner. For non-relativistic particles a vanishing mass doesn't make sense, because it doesn't lead to a physically interpretable quantum dynamics. For non-0 mass the commutator is
$$[\hat{K}_j,\hat{p}_k]=\mathrm{i} \delta_{jk} m \hat{1} \neq 0.$$
The group-representation theoretical reasons for this are quite obvious (see posting #78).

You're making the point for me. Clearly "Galilean boosts commute with spatial translations (time being absolute)" so in order to get the proper commutation relationship for QM, you need boosts that don't commute with spatial translations and for that you have to go to the Poincare group. That's Kaiser's point and yours.

 

[RUTA]

You attach physical meaning to convention. You can not blame reality for not respecting particular set of conventions.

The statement you quoted here is true and doesn't entail any interpretation. What you choose to believe ontologically about it can and does differ between different interpretations of QM.

 

[vanhees71]

You're making the point for me. Clearly "Galilean boosts commute with spatial translations (time being absolute)" so in order to get the proper commutation relationship for QM, you need boosts that don't commute with spatial translations and for that you have to go to the Poincare group. That's Kaiser's point and yours.

You don't need the Poincare group to get this result. You can get it from a careful analysis of the unitary ray representations of the Galilei group. Of course, it's equivalent to use the appropriate "deformation" of the Poincare group. I guess, I simply misunderstood your statement, and I think all in all we agree in this matter :-).

 

[vanhees71]

The statement you quoted here is true and doesn't entail any interpretation. What you choose to believe ontologically about it can and does differ between different interpretations of QM.

Of course, it's of high interest to understand all aspects of QT, including also the philosophical ones. It took me years to come to the conclusion that the "mystic approach" is simply due to an old-fashioned philosophical balast of the founding fathers, mostly Bohr and Heisenberg. Just taking the Born rule seriously for me resolves all problems, particularly the EPR problem (although the EPR paper is not reflecting Einstein's philosophical quibbles with QT very well; he's written a much clearer paper (Dialectica article in German):

http://onlinelibrary.wiley.com/doi/10.1111/j.1746-8361.1948.tb00704.x/abstract

I wonder, why this is still not accepted by many physicists and why modern textbooks still teach the confusing collapse hypothesis of some Copenhagen-interpretation flavors (admittedly that's not Bohr's fault, who, AFAIK, didn't include collapse in his version of the Copenhagen interpretation).

 

[Lord Jestocost]

It took me years to come to the conclusion that the "mystic approach" is simply due to an old-fashioned philosophical balast of the founding fathers, mostly Bohr and Heisenberg.

What the heck is that "mystic approach"? "Mystic" related to what? Related to 19th century physics? Related to some not pronounced implicit assumptions about "reality" which might merely based on your personal psychological predispositions? In case you don’t grasp Bohr’s and Heisenberg’s thinking, that’s your problem, but don’t coin the term “mystic” as a “killer argument”. Science should be based on arguments.

Listen, what Wheeler writes about Bohr:

“You tell me what isn’t the plan of physics, our friend rejoins. If you understand quantum mechanics so well, why don’t you tell we what is the plan of physics?
No one knows, we reply. We have clues, clues most of all in the writings of Bohr [23-25], but no answer. That he did not propose an answer, not philosophize, not go an inch beyond the soundest fullest statement of the inescapable lessons of quantum mechanics, was his way to build a clean pier for some later day’s bridge to the future.”

J. A. Wheeler in „Quantum Theory and Measurement“ (edited by John Archibald Wheeler and Wojciech Hubert Zurek), Princeton, New Jersey 1983, page 201

 

[bhobba]

What the heck is that "mystic approach"? "Mystic" related to what?

Related to someone like Dirac and even Einstein. Einstein and Bohr were good friends but in QM their approaches were different. Einstein would accuse Bohr of being 'mystical' - it was two different approaches. Actually Bohr wasn't too bad - he was more agnostic to it than a believer - others like Pauli, yes the great and rational Pauli, were worse. Worse still was the great Von-Neumann and Wigner that advocated the so called Princeton school based on the, it turns out to be wrong, but for reasons not known at the time, Von-Neumann's argument consciousness caused collapse:

See the attached document

As the above argues, correctly IMHO, even today we are still feeling the effects of those early years and it has been detrimental to understanding QM, especially at the beginner and even intermediate level. Fortunately books like Ballentine banish it, not that I agree 100% with Ballentine on every issue, but it is way more rational than others.

Thanks
Bill

 

[bhobba]

why don’t you tell we what is the plan of physics?

I am surprised his old student and friend, Feynman, didn't see the fallacy of that - first you have to show physics has a plan.

Thanks
Bill

 

[.Scott]

I believe Hawking is exaggerating in telling us (page 83):
«...the Universe doesn't have just a single history, but every possible history, each with its own probability; and our observations of the current state affect its past and determine the different histories of the Universe, just as the observations of the particles in the double slit experiment affect the particles' past.»
Do you agree?

I may come closer to agreeing with this than most. If you follow the Multi World Interpretation (MWI) - in the sense that the universe is continuously spawning slightly different copies of itself that do not further interact, then I have no counter argument for you. Otherwise, consider this:

The first problem with "changing the past" is the notion of choosing an observation - acting independently of "predestination". Let's say that we have two copies of the universe, one where you (Alice) observe something at noon, the other where you observe something different at noon. Would it be safe to say that these universes were the same up until noon? That's certainly what we had in mind when we set up the experiment (notwithstanding that this experiment cannot actually be set up).

But when we test this in the only ways we can, we sometimes find a violation of the Bell inequality. Alice makes measurements "randomly", and when her choices and results are compared to those of Bobs, it appears that Alice mucked with the past. Of course, the results are symmetric, Alice can accuse Bob of mucking with the past as well.

But since we apparently only end up with a single copy of the past, whose to say that it has changed? And we have an equal problem with the future. Just as we can't duplicate the universe, we can't really inject information into it from "outside" either.

So if we allow ourselves to claim that either the present or the future are not specific, why should we treat the past any differently?

To a large extent, this is a matter of semantics. We can all agree on what restrictions QM places on experimental results. But when we go from the Math to the English language, we discover that English has ambiguities that are well tolerated in common affairs - but work poorly in describing the Physics.

Let me describe the Bell Inequality by moving "cause" into the future. Remember that the only purpose of this is to change the English semantics describing the QM results. I am not claiming that this is a "better" description - only a consistent one:

Both Alice and Bob make their measurement choices of the entangled particle independently. Since Alice did this based on a telescope facing the Northern sky and Bob did it based on the Southern sky, we presume that no information has yet been exchanged between them. But we will allow for an indefinite present, so Alice may not have measured the result, and if she did, it may be + or -. Similarly, Bob's may be any of the three as well. When they compare results, certain Alice/Bob combinations are inconsistent with QM and will not persist. They can be made to violate Bell's inequality without any FTL issue.

 

[DrChinese]

But since we apparently only end up with a single copy of the past, whose to say that it has changed?

I would argue that there is plenty of "evidence" there is more than one past. If light only goes in one path from source to detector, why is it possible to increase its intensity by blocking some paths (those providing destructive interference)? After all, this effect occurs even when photons are sent one at a time. Ditto with a suitable double slit setup. On the other hand, these particular setups are usually used as an example of the path integral approach. Which of course implies that the photon took all possible paths. (I placed "evidence" in quotes above because this should not be considered an absolute proof.)

My real point is that there is much we don't know about time. I'm not even sure if there is 1 past, 1 present, and/or 1 future - or many. And I'm not sure if time only flows in 1 direction, 2 directions (time symmetric), or in fact no direction (RBW)!

Mine is a minority position in this thread. However, these questions are far from settled scientifically.

 

[.Scott]

I would argue that there is plenty of "evidence" there is more than one past. If light only goes in one path from source to detector, why is it possible to increase its intensity by blocking some paths (those providing destructive interference)? After all, this effect occurs even when photons are sent one at a time. Ditto with a suitable double slit setup. On the other hand, these particular setups are usually used as an example of the path integral approach. Which of course implies that the photon took all possible paths. (I placed "evidence" in quotes above because this should not be considered an absolute proof.)

My real point is that there is much we don't know about time. I'm not even sure if there is 1 past, 1 present, and/or 1 future - or many. And I'm not sure if time only flows in 1 direction, 2 directions (time symmetric), or in fact no direction (RBW)!

Mine is a minority position in this thread. However, these questions are far from settled scientifically.

My point is that this is semantics. We know what the Math says - it's just a matter of how it is described in common English terms.
And I would not say that there is a single right way to describe it. If you decide you want only a single history, you can find other ways to make the Math work.

 

[zonde]

My point is that this is semantics. We know what the Math says - it's just a matter of how it is described in common English terms.
And I would not say that there is a single right way to describe it.

It's not enough to know what math says. In science we want to test it experimentally. And there are certain assumptions that have to be satisfied for us to test it experimentally. One is that cause and effect has to produce factual records for us to analyze them at a later time. Another is that we assume experimenter has some ability to determine experimental conditions FAPP independently from the relationship he is testing.
So if we propose different pasts that produce the same factual records there is no way in principle how we could ever falsify existence of multiple pasts.
And if we propose retrocausal relationships where effect comes before cause we have paradoxical situation where experimenter can not determine the conditions of cause based on records about observed effect.

So even so there no single right way how to describe the math, there certainly are unscientific ways how to describe the math. So I can't agree it's just semantics.

 

[vanhees71]

I am surprised his old student and friend, Feynman, didn't see the fallacy of that - first you have to show physics has a plan.

Thanks
Bill

Sure, physics has a plan, as nearly any endeavor of men. The plan is to investigate and describe as good as we can the reproducible phenomena in a quantitative way, no more no less. That's why I call Bohr's and Heisenberg's approach "mystic". They want to find something "behind the phenomena", an explanation of the world so to say. That's not the purpose of the natural sciences however but belongs to the "complementary" other part of human experience, namely emotions and particularly religion. Of course, both realms of human experience are equally important, but it's as important to keep them strictly separated.

 

[Fra]

(1)

That's fine for the status quo, the book argues that to advance physics from the status quo (e.g., obtain quantum gravity and explain dark energy and dark matter data)

Do you by this mean that the rational behind these "interpretational discussions" - as contrasting to fruitless discussions that aim to make no difference to current theory - is a process of trying to improve the understanding of the theory in a bigger context IN ORDER to figure out what is the most plausible way to generalize or modidy the theory to allow solving the open questions? Then I fully agree.

Thus, if one participates in these discussions holding the viewe that the status quo is all we need, and there may be open questions but to which the foundational issue has no relevance, then it is a rational conclusion that the discussions are somewhat meaningless. A researcher thinking like this, thinks of the unlike thinkers as perpahs irrational philosophers that only talk.

But if one has the opinion (all researchers have their own opinions) that the open questions, are very likely to related to some of the foundational issues then it is rather irrational to ignore these things. A researcher thinking like this, may view the unlike thinkers as ostriches, not wanting to look at the real problems simply because they are too hard. And it simply feels better to reject these questions.

(2) About the mysticism of QM. I rather always found it to be a mystery WHY so much people keep confusing the idea of observer or context dependent information, with the completely off topic discussion about human brain and consciousness. As far as I know Bohr never comitted this mistake, but others did, and those who did was most probably also the people that kept misinterpreting Bohr, making his probably insightful views dirty.

Observer dependence, subjective probabilities or context dependent inferences has imo NOTHING mystical over it? It is rather and extremely rational information processing picture? This has absolutely nothing to do with humans or consciossness.

In this respect Bohr was probably more clear than others that in instead of insisting that the experiment requires and "observer" which can by some be misinterpreted to mean a conscious human, he said it requires a CLASSICAL measurement device, as that is the "conditional reference" required to formulate questions and experiments. But the meaning is similar if you only think about it. the reason for instead talking about observers, is in the extension where you want to generalize these ideas to thinkings that was not existing at Bohrs time.

/Fredrik

 

[bhobba]

Sure, physics has a plan, as nearly any endeavor of men. The plan is to investigate and describe as good as we can the reproducible phenomena in a quantitative way, no more no less. That's why I call Bohr's and Heisenberg's approach "mystic". They want to find something "behind the phenomena", an explanation of the world so to say. That's not the purpose of the natural sciences however but belongs to the "complementary" other part of human experience, namely emotions and particularly religion. Of course, both realms of human experience are equally important, but it's as important to keep them strictly separated.

I agree with you, but the question is does it need a plan at all. Its science - that's enough IMHO - no more needs to be said. Is science a plan? Yes - but is it any different than the plan of any science - conjecture, experiment, conjecture, experiment - and so on.

Thanks
Bill

 

[.Scott]

It's not enough to know what math says. In science we want to test it experimentally. And there are certain assumptions that have to be satisfied for us to test it experimentally. One is that cause and effect has to produce factual records for us to analyze them at a later time. Another is that we assume experimenter has some ability to determine experimental conditions FAPP independently from the relationship he is testing.
So if we propose different pasts that produce the same factual records there is no way in principle how we could ever falsify existence of multiple pasts.
And if we propose retrocausal relationships where effect comes before cause we have paradoxical situation where experimenter can not determine the conditions of cause based on records about observed effect.

So even so there no single right way how to describe the math, there certainly are unscientific ways how to describe the math. So I can't agree it's just semantics.

All that is required by the scientific method is that hypothesis be testable and that experiments be reproducible. Causation is a human characterization of events. We have an ingrain notion that we are able to influence the future. This presumption is completely independent of whether we live in a deterministic universe or not.
When we model a system, we often tend to put it into cause/effect terms - with the cause and effect events having a time-like relation and the cause preceding the effect. And QM can often be cast into those familiar terms. But QM doesn't intrinsically work that way. QM applies limits to the entire experiment - and across the entire duration of the experiment.

At the end of the experiment, we have results, we have analysis of the results, and we have a story about those results. For example, we have results that show a violation of the Bell inequality. On analysis we see that the results are consistent with our Mathematical model (QM). Then we make up a story about how our experiment worked - and that usually includes the construction of a list of events in time-like sequence which each causing the next.

I agree that the cause/effect way of looking at things is very useful - and I do not oppose it. But we need to recognize that cause and effect are in the man, not in the nature. QM is the science, cause/effect is part of our technology.

 

[zonde]

All that is required by the scientific method is that hypothesis be testable and that experiments be reproducible. Causation is a human characterization of events. We have an ingrain notion that we are able to influence the future. This presumption is completely independent of whether we live in a deterministic universe or not.

Yes, everything is right. But I'm not sure why you switched from causation to determinism in the last sentence. They are different things. Maybe you perceive them as equivalent?

When we model a system, we often tend to put it into cause/effect terms - with the cause and effect events having a time-like relation and the cause preceding the effect. And QM can often be cast into those familiar terms. But QM doesn't intrinsically work that way. QM applies limits to the entire experiment - and across the entire duration of the experiment.

Well, if you mean that QM makes statistical predictions then yes, it complicates things a bit. But other than that cause and effect still applies to QM. And I have no idea what do you mean by "QM doesn't intrinsically work that way". And surely we can split experiment with large ensemble into two sub experiments with half as big ensembles and still describe them with QM.

At the end of the experiment, we have results, we have analysis of the results, and we have a story about those results. For example, we have results that show a violation of the Bell inequality. On analysis we see that the results are consistent with our Mathematical model (QM). Then we make up a story about how our experiment worked - and that usually includes the construction of a list of events in time-like sequence which each causing the next.

The story part goes beyond minimal QM.

I agree that the cause/effect way of looking at things is very useful - and I do not oppose it. But we need to recognize that cause and effect are in the man, not in the nature. QM is the science, cause/effect is part of our technology.

I agree that cause and effect are in the man. But all of the science is in the man just as well.
And I would not say that cause/effect is part of our technology unless by technology you mean all the things we have got by birth and by our upbringing.

 

[RUTA]

(1)
Do you by this mean that the rational behind these "interpretational discussions" - as contrasting to fruitless discussions that aim to make no difference to current theory - is a process of trying to improve the understanding of the theory in a bigger context IN ORDER to figure out what is the most plausible way to generalize or modidy the theory to allow solving the open questions? Then I fully agree.

Thus, if one participates in these discussions holding the viewe that the status quo is all we need, and there may be open questions but to which the foundational issue has no relevance, then it is a rational conclusion that the discussions are somewhat meaningless. A researcher thinking like this, thinks of the unlike thinkers as perpahs irrational philosophers that only talk.

But if one has the opinion (all researchers have their own opinions) that the open questions, are very likely to related to some of the foundational issues then it is rather irrational to ignore these things. A researcher thinking like this, may view the unlike thinkers as ostriches, not wanting to look at the real problems simply because they are too hard. And it simply feels better to reject these questions.
/Fredrik

Yes, that sums up my attitude and many in foundations of physics, e.g., Smolin. But, in defense of my colleagues who are not motivated to seek new physics in this fashion, I certainly can’t say they’re wrong to ignore these concerns. As you say, “all researchers have their own opinions.”

 

[.Scott]

I agree that cause and effect are in the man. But all of the science is in the man just as well.
And I would not say that cause/effect is part of our technology unless by technology you mean all the things we have got by birth and by our upbringing.

By technology I meant everything we invent to change our environment. Once we believe we have a working model of the universe (Science), we often use that model to improve our situation. When we invent new technology, we are tapping into our intrinsic cause/effect method of thinking - one that presumes we are able to change the future.

 

[.Scott]

Yes, everything is right. But I'm not sure why you switched from causation to determinism in the last sentence. They are different things. Maybe you perceive them as equivalent?

They are related. If you presume determinism, then seeing the past as a function of the future is no great challenge. Without determinism, you are presuming that decisions are being made from "outside" the universe - and the tendency is to view this new information as affecting only the future.

 

[vanhees71]

By technology I meant everything we invent to change our environment. Once we believe we have a working model of the universe (Science), we often use that model to improve our situation. When we invent new technology, we are tapping into our intrinsic cause/effect method of thinking - one that presumes we are able to change the future.

Well, and I think engineering, i.e., the functioning of all our technology is a strong hint that evidence-based science, which hinges in its very foundations on the assumption that causality holds true, really "works" (even in the literal sense). I dare to doubt that any philosophical speculations have brought anything like this for the development of mankind (to the better or worse, one must of course admit) as science (physics, chemistry, biology, which are the input for the more applied sciences like engineering, chemical industry, and medicine and agriculture, respectively).

 

[.Scott]

Well, and I think engineering, i.e., the functioning of all our technology is a strong hint that evidence-based science, which hinges in its very foundations on the assumption that causality holds true, really "works" (even in the literal sense). I dare to doubt that any philosophical speculations have brought anything like this for the development of mankind (to the better or worse, one must of course admit) as science (physics, chemistry, biology, which are the input for the more applied sciences like engineering, chemical industry, and medicine and agriculture, respectively).

Yes. It certainly works. As I said earlier, I do not oppose it at all. I only note that "works" (as you are using it here) is an anthropocentric assessment.

 

[RUTA]

It's not enough to know what math says. In science we want to test it experimentally. And there are certain assumptions that have to be satisfied for us to test it experimentally. One is that cause and effect has to produce factual records for us to analyze them at a later time. Another is that we assume experimenter has some ability to determine experimental conditions FAPP independently from the relationship he is testing.
So if we propose different pasts that produce the same factual records there is no way in principle how we could ever falsify existence of multiple pasts.
And if we propose retrocausal relationships where effect comes before cause we have paradoxical situation where experimenter can not determine the conditions of cause based on records about observed effect.

So even so there no single right way how to describe the math, there certainly are unscientific ways how to describe the math. So I can't agree it's just semantics.

zonde sums up nicely what bothers some people about delayed choice experiments. Again, it’s not the physics per se, the physics works beautifully (theory and experiment agree nicely), it’s the implications for one’s view of reality. When physics contradicts your view of reality you have three choices: live with contradiction, reject the physics, or amend your view of reality. We’re seeing all three of these responses on this thread. In our book, we advocate the third option, i.e., moving from the “ant’s-eye view” to the “God’s-eye view” of reality. Delayed choice is particularly tough for dynamical explanation in the mechanical universe (“ant’s-eye view”) for the reason that zonde describes here. That’s why Zeilinger’s delayed choice experiment (cited earlier) is the first experiment we present and discuss in our chapter on QM. As I stated earlier, no amount of formal analysis dispells the challenge presented by zonde here — the ramafications of my choice occurred before my choice was made. How can that be? QM just doesn’t care about “freely made choices,” so live with it, reject QM, or change your view of reality.

 

[vanhees71]

Well, if I have some prejudices about "reality" (I usually do not use this word anymore in physics discussions because the philosophers spoiled any definite meaning of that word), then empirical objective reproducible facts help to get rid of these prejudices. The predicted possibility of delayed choice (by Wheeler using quite simple foundations of QT which can be easily explained to students in the QM 1 lecture) is confirmed by many high-precision experiments in various forms (mostly with photons but also with other systems). So instead of hinging on classical prejudices we should accept the empirical facts related to the predictions of QT (but not more!). As a physicist you cannot really simply reject QM (or rather QT since one has to include relativistic QFT here). For that it's too successful a description of nature. So, as I said above, rather change your view of "reality" (reality for me is simply any reproducible objective observational fact).