Where is the flaw with predetermined entanglement state?

[stevendaryl]

I 'll try to say it in another way:
That is circular, because I allready had made the hypothesis (which is consistent with experiments) that $P_A=\frac{1}{2}$ so even if "the probability that B measures a photon if A measures a photon at 90" (lets name this $P_C$) is indeed zero, that does not make $P_B$ zero

What is your definition of P_B? I'm using P_B to mean the probability that Bob will detect a photon. That probability is not a fixed number, it depends on what other facts you know (such as whether Alice measured a photon).

 

[stevendaryl]

I am thinking something in the lines of:

$P_A(\alpha, \theta)$
$P_B(\beta, \kappa)$

where $\theta$ and $\kappa$ is the polarization angle of each photon such as
$\theta - \kappa = 0$
but
$(\theta+\kappa) \sim U([0,720])$ (aka random).

Because of the condition $\theta - \kappa = 0$ I think this does not violate locality

No, of course not. That's a hidden-variables theory of the form that Bell proved cannot explain the EPR correlations.

 

[LsT]

My definition of $P_B$ is "Probability that Bob detects a photon per photon "emited" (creation of entangled pair)

No, of course not. That's a hidden-variables theory of the form that Bell proved cannot explain the EPR correlations.

Care to make it more clear to me why this is the case?

 

[stevendaryl]

Care to make it more clear to me why this is the case?

That's exactly what Bell proved.

The claim is this: Let P(A,B, \alpha,\beta) be the probability that Alice will get result A and Bob will get result B, given that Alice's detector has setting \alpha and Bob's detector has setting \beta. For an EPR-type experiment, A = 0 or A=1, depending on whether Alice detects a photon, or not. Similarly for B. The prediction of QM for the two-photon case is:

P(A,B,\alpha,\beta) = \frac{1}{2} cos^2(\alpha - \beta) (if A = B) and P(A,B,\alpha,\beta) = \frac{1}{2} sin^2(\alpha - \beta) (if A \neq B)
(That's assuming perfect detection, and no spurious photons. I don't know how the formula should be adjusted to allow for detector mistakes)

We can say that the correlation P(A,B,\alpha,\beta) has a "local causal explanation" if there is some property, or variable \lambda characterizing the photon creation event such that the probabilities can be written as follows:

P(A, B, \alpha, \beta) = average over all \lambda of P_A(A, \alpha, \lambda) \cdot P_B(B, \alpha, \lambda)

Your hypothesis about \theta, \kappa is exactly of this form.

 

[LsT]

P(A,B,α,β)=P(A, B, \alpha, \beta) = average of λ\lambda of PA(A,α,λ)⋅PB(B,α,λ)P_A(A, \alpha, \lambda) \cdot P_B(B, \alpha, \lambda)

Your hypothesis about θ,κ\theta, \kappa is exactly of this form.

In my hypothesis, even if you consider the state $\lambda$, the probabilities $P_A$ and $P_B$ remain dependent. So you cannot do this.

 

[stevendaryl]

In my hypothesis, even if you consider the state $\lambda$, the probabilities $P_A$ and $P_B$ remain dependent. So you cannot do this.

Give me an actual probability function for P_A and P_B, and I will show you how it works.

You said that P_A depends on \alpha and \theta and P_B depends on \beta and \kappa. So isn't it the case that:

P(A \&B) = average over \theta of P_A(\alpha, \theta) \cdot P_B(\beta, \theta)

 

[LsT]

I post this just for completeness: ***

Definitions:
1. $P_A$ probability to detect a photon per photon emitted for Alice
2. $P_B$ " " for Bob
3. $H_1$ photon heading to Alice
4. $H_2$ photon heading to Bob
5. $\lambda =$ polarization angle of photon $H_1 =$ polarization angle of photon $H_2$
6. $\lambda \sim \cup([0, 360])$
7.$\alpha$ polarization angle of Alice's detector
8.$\beta$ polarization angle of Bob's detector

Assumptions:
1. The photons are supposed to have a definite and real polarization that is defined the moment of pair creation
2. The probability $P_\delta$ that a single photon passes through a polarization filter is dependent only in their relative angle $\delta$, such as $P_\delta = 1$ IF $\delta < 45$ and $P_\delta = 0$ IF $\delta > 45$

$P_A = \cos^2(\alpha - \lambda)$

$P_B = \cos^2(\beta - \lambda)$

***
I just realized that the crucial assumtion 2 (I mention it for the first time...) that I have made from the beggining of this hypothesis in my mind, is wrong because its not in accordance with malus Law, and I can realize that without this, my hypothesis either falls under Bell's umbrella of local hidden variables or you cannot have perfect correlations. So I can consider my hypothesis wrong. Despite this I enjoyed this conversation, I have learned something and I hope that I was not too irritating. Thanks to everyone that aswered me.

 

[DrChinese]

I will show again, in my hypothesis, what happens at zero detectors angle difference:

A -> 0 1 0 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 1 0
B -> 0 1 0 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 1 0
C -> 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Here probability of Alice's Detection is 1/2 as is Bob's (as is always). And the perfect correlation is a fact. The probabilities here are related of course.

Yes, perfect correlations for 0 angle difference is explained by your local hypothesis. Unfortunately, that is one of the few settings that are.

Best to take A=0, B=120 and C=240 degrees as I have mentioned before. According to QM: P(A=B) = P(A=C) = P(B=C) = .25. Attempt to complete the example below where this is true and you will soon see the futility of the exercise.

A (000) -> 0 1 0 1 1 1 0 1 0 0 1 0 0 1 0 1 1 0 0 1 0
B (120) ->
C (240) ->

 

[LsT]

DrChinese I consider the matter settled, I have no reason to continue this, It was all about a wrong assumption of mine. See previous post. Thanks anyway.

 

[Carl B]

The spin states of the entangled photons could have been pre-determined from the beginning of the experiment, it requires simply that certain assumptions on which quantum physics is based are either untrue or misleading and you may not wish to consider this!
The first assumption I discuss is one of Dirac's. In his introduction to his theory of the Principles of Quantum Mechanics (Fourth Edition revised) he states that “Only questions about the results of experiments have real significance for the physicist.” and then “ The foregoing discussion about the result of an experiment with a single obliquely polarized photon incident on a crystal of tourmaline answers all that can be legitimately be asked about what happens to an obliquely polarised photon when it reaches the tourmaline. Questions about what decides whether the photon is to go through or not and how it changes its direction of polarisation when it goes through cannot be investigated by experiment and should be regarded as outside the domain of science... Nevertheless some further description is necessary in order to correlate the results of this experiment with the results of other experiments that might be performed with photons and to fit them into a general scheme. Such further description should be regarded, not as an attempt to answer questions outside the domain of science, but as an aid to the formulation of rules for expressing concisely the results of large numbers of experiments.”
Obviously when Dirac was formulating these statistical rules he was deeply concerned about the practicalities of making precise measurements on individual particles although he explicitly accepted that there may be deterministic rules guiding things.
All of quantum mechanics is now based on Dirac's derivation of statistical rules based on the idea that determinism is impossible to prove so we will adopt a statistical approach. When we interpret the sayings of physicists then, we should bear in mind that QM is only statistical because we do not have the fineness and gentleness of experiment to be able to conduct the experiment deterministically.

To then come to the issue of Bell's inequality which has been mentioned. Bell himself made the statement in a 1985 radio interview (from wiki) “There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the ‘decision’ by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster-than-light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already “knows” what that measurement, and its outcome, will be.”. I suggest that this super-determinism is excessive and that only individual photon exchanges need to be pre-determined, which would be the strict answer to what you ask, but it then begs follow on questions such as how such a 'local' (individual photon exchange) determinism maybe achieved in isolation from a more general non-deterministic environment and this is answered as follows:

There is no example of a photon existing independently and outside of an exchange between two atoms. The only way we can detect a photon is through its acceptance and incorporation into the structure of a receiving atom. Therefore we may consider a photon to be a singular exchange of an indivisible quantum of energy between two atoms. Over a large number of photons the pattern of distribution of those exchanges is then determined to fit a statistical pattern as described by what we know as electromagnetic waves. An exchange is a transaction or an instantaneous moment in time occurring between a giver and a receiver. I would suggest that at the moment of exchange of any photon its destination atom is known and 'agreed' with that destination.

But then if this transaction is instantaneous the question then arises as to how the time-delay appears which gives rise to a speed associated with the photon's time of flight from source atom to destination atom. This question also has a complete answer but which would be a separate topic.

In conclusion I would say that it is possible for the spin of entangled photons to be pre-determined,there is no experiment or theory which precludes this possibility. In Dirac's words what you ask is “outside the domain of science”!

 

[ZapperZ]

In conclusion I would say that it is possible for the spin of entangled photons to be pre-determined,there is no experiment or theory which precludes this possibility. In Dirac's words what you ask is “outside the domain of science”!

But aren't the experiments that produced results that contradict classical realism actually are such experiments that are beginning to show evidence which preclude this possibility? Just a couple of weeks ago, we have the first ever demonstration of Wheeler's delayed choice experiments using single atoms (experiments using single photons have already been accomplished)[1].

And then there is a test of Leggett inequality, which has been shown to test realism, i.e .the notion that these measurements actually are already predetermined even before we measure them. There are now experiments showing that this inequality can be violated and thus, showing results that are incompatible with such realism.[2]

So I am not sure if you disagree with these experiments, disagree with their conclusions, or simply are ignoring them.

Zz.

[1] A.G. Manning et al., Nature Physics
[2] J. Romero et al., N. Jour. Phys. v.12, p.123007 (2010).

 

[stevendaryl]

...I would say that it is possible for the spin of entangled photons to be pre-determined,there is no experiment or theory which precludes this possibility.

The way I understand Bell's theorem, the "superdeterminism loophole" as applied to the case of Alice and Bob detecting photons in an EPR type experiment would require that Alice's and Bob's detector settings be pre-determined, in addition to the spins of the particles. The choice of settings can be based on absolutely anything: Alice might flip a coin to decide what setting to use, or might base it on who won a tennis game in Wimbledon, or whatever. So the superdeterminism loophole would end up requiring that absolutely everything about the universe be known ahead of time. So that's not just a small amount of pre-determinism. That's why Bell called it "super" determinism.

 

[Quantumental]

The way I understand Bell's theorem, the "superdeterminism loophole" as applied to the case of Alice and Bob detecting photons in an EPR type experiment would require that Alice's and Bob's detector settings be pre-determined, in addition to the spins of the particles. The choice of settings can be based on absolutely anything: Alice might flip a coin to decide what setting to use, or might base it on who won a tennis game in Wimbledon, or whatever. So the superdeterminism loophole would end up requiring that absolutely everything about the universe be known ahead of time. So that's not just a small amount of pre-determinism. That's why Bell called it "super" determinism.

I feel that Complete / Absolute / Total / Omni-determinism is a better word for it. SUPER sounds so.. weird. All it really is, is complete determinism. Which shouldn't be too hard to swallow if you already accept either Bohm or Many Worlds which is equally absolute in their determinism

 

[DrChinese]

The spin states of the entangled photons could have been pre-determined from the beginning of the experiment, it requires simply that certain assumptions on which quantum physics is based are either untrue or misleading and you may not wish to consider this!...
All of quantum mechanics is now based on Dirac's derivation of statistical rules based on the idea that determinism is impossible to prove so we will adopt a statistical approach. ... In Dirac's words what you ask is “outside the domain of science”!

Sorry, you want to have your cake and eat it too. You aren't going to be able to assert that is reasonable to assert pre-determination of outcomes, AND there are no instantaneous influences, AND hide in the refuge of Dirac's statements ("outside the domain of science"). Those of us who reject local realism make an assumption about what realism means, and that usually includes determination of the outcome of measurements INDEPENDENT of the choice of measurement settings. Clearly we DO consider this! If it is predetermined based on the observer's later choice of measurement settings... well, there are interpretations that support this already.

If you expect anyone to respect your point of view, you must define predetermination in some manner we can relate to. Then we can choose whether or not that definition is worth consideration. Otherwise, your "predetermination" (as it currently sits) may as well read "xyz-ism". Please be aware that there are entanglement experiments in which particles are entangled that have never been in each others' light cones. I would challenge you to define "predetermination" in that light.

 

[Derek Potter]

If it is predetermined based on the observer's later choice of measurement settings... well, there are interpretations that support this already.

The transactional interpretation? Backwards causation - nasty stuff. "Hello Alice, I'm your photon. I believe you're busily setting your detector to 22.5 degrees? Bob's setting his to 45 right now. That's what I and my buddy have prepared ourselves for. I expect you're wondering how we knew? Simple! The Confirmation Wave which you are about to launch backwards in time converged on us just as we were being emitted a little while ago. No, you can't change your mind. That would be against the Novikov consistency criterion. Grandfather can rest in peace."

If you expect anyone to respect your point of view, you must define predetermination in some manner we can relate to. Then we can choose whether or not that definition is worth consideration. Otherwise, your "predetermination" (as it currently sits) may as well read "xyz-ism".
Please be aware that there are entanglement experiments in which particles are entangled that have never been in each others' light cones. I would challenge you to define "predetermination" in that light.

We are all brains in a vat fed with bogus sense data by the Lizard People.

 

[Derek Potter]

I feel that Complete / Absolute / Total / Omni-determinism is a better word for it. SUPER sounds so.. weird. All it really is, is complete determinism. Which shouldn't be too hard to swallow if you already accept either Bohm or Many Worlds which is equally absolute in their determinism

Determinism is not difficult to accept. Superdeterminism requires the entire universe to have been microscopically prepared at the Big Bang so that apparently random events are correlated to this day. There is a huge difference.

 

[zonde]

But aren't the experiments that produced results that contradict classical realism actually are such experiments that are beginning to show evidence which preclude this possibility?

I would say that idea of experimental results contradicting classical realism is so extraordinary that it's hard to take it seriously. Science takes realism for granted and if you consider possibility that realism is not acceptable then you just have to throw out all the science (and even more) and start from scratch (with philosophy). Additional problem is that such philosophical directions already have been explored and are not very popular.

 

[ZapperZ]

I would say that idea of experimental results contradicting classical realism is so extraordinary that it's hard to take it seriously. Science takes realism for granted and if you consider possibility that realism is not acceptable then you just have to throw out all the science (and even more) and start from scratch (with philosophy). Additional problem is that such philosophical directions already have been explored and are not very popular.

Then please scrutinize all those experiments and offer a formal rebuttal to them. Otherwise, all you have done is present an objection to them based on a matter of personal taste.

Zz.

 

[Derek Potter]

Then please scrutinize all those experiments and offer a formal rebuttal to them.

Even an informal rebuttal of just one would suffice!

 

[StevieTNZ]

But aren't the experiments that produced results that contradict classical realism actually are such experiments that are beginning to show evidence which preclude this possibility? Just a couple of weeks ago, we have the first ever demonstration of Wheeler's delayed choice experiments using single atoms (experiments using single photons have already been accomplished)[1].

And then there is a test of Leggett inequality, which has been shown to test realism, i.e .the notion that these measurements actually are already predetermined even before we measure them. There are now experiments showing that this inequality can be violated and thus, showing results that are incompatible with such realism.[2]

So I am not sure if you disagree with these experiments, disagree with their conclusions, or simply are ignoring them.

Zz.

[1] A.G. Manning et al., Nature Physics
[2] J. Romero et al., N. Jour. Phys. v.12, p.123007 (2010).

Remember the reference [2] rules out certain classes of non-local hidden variable theories; thus realism is still possible, e.g. Bohm Mechanics.

Regarding the first reference, I sent my go-to-physics Professor this link -- http://phys.org/news/2015-05-quantum-theory-weirdness.html -- and they replied:

I’m not sure I agree 100% with the rather unsophisticated ontology of the last part of this…

"It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,"

…but I guess we see once again that what can be said about reality is contextual;and somehow arranged to be self-consistent within the context.

So not every physicist can agree with the interpretation of a particular experiment.

 

[DrChinese]

I feel that Complete / Absolute / Total / Omni-determinism is a better word for it. SUPER sounds so.. weird. All it really is, is complete determinism. Which shouldn't be too hard to swallow if you already accept either Bohm or Many Worlds which is equally absolute in their determinism

Superdeterminism - under any name - is ridiculous. Just try to formulate in a scientific (and falsifiable) manner and you will see just how so!

For example: if all interactions are superdetermined and local and realistic (the reason superdeterminism was invented), then every particle in the universe must carry a complete copy of its "answer" to every measurement (question) possible - with every other particle in the universe to which it ever has or will interact. That is because entanglement can be swapped from particle X to particle Y and you never know which particle might be entangled with what other particle. Basically you are talking about an infinite amount of information being stored locally in every particle in the universe. Of course that information is "hidden" because there is no other evidence of it.

 

[zonde]

Then please scrutinize all those experiments and offer a formal rebuttal to them. Otherwise, all you have done is present an objection to them based on a matter of personal taste.

Where did you get I have objections against these experiments? I have objections against your interpretation of these experiments. Besides my objections are not strict - I presented a way how one can still hold to this viewpoint. In particular one can become a philosopher who does not trust his senses an leave science to those who believe in realism.
As I understand you earn for your living by doing experimental physics, right? So becoming a philosopher who does not trust his senses would be quite extraordinary turn for you, I believe. So I don't quite understand your position. You can't have your cake and eat it too.

 

[stevendaryl]

I would say that idea of experimental results contradicting classical realism is so extraordinary that it's hard to take it seriously. Science takes realism for granted and if you consider possibility that realism is not acceptable then you just have to throw out all the science (and even more) and start from scratch (with philosophy). Additional problem is that such philosophical directions already have been explored and are not very popular.

I sort of agree with you, that a lot (most? all?) of science is done with an implicit idea of a universe external to us that we are learning about through experiment and observation. However, a more limited view of science is that it is about making predictions, of the form: If I perform such and such an experiment, I will get such and such result. That limited view of science doesn't require realism.

 

[stevendaryl]

Where did you get I have objections against these experiments? I have objections against your interpretation of these experiments. Besides my objections are not strict - I presented a way how one can still hold to this viewpoint. In particular one can become a philosopher who does not trust his senses an leave science to those who believe in realism.
As I understand you earn for your living by doing experimental physics, right? So becoming a philosopher who does not trust his senses would be quite extraordinary turn for you, I believe. So I don't quite understand your position. You can't have your cake and eat it too.

The sort of anti-realism suggested by violations of Bell's inequalities doesn't amount to rejecting experimental results. Instead, it amounts to rejecting the idea that there is a definite "state of the world" outside of experimental results.

 

[ZapperZ]

Where did you get I have objections against these experiments? I have objections against your interpretation of these experiments. Besides my objections are not strict - I presented a way how one can still hold to this viewpoint. In particular one can become a philosopher who does not trust his senses an leave science to those who believe in realism.
As I understand you earn for your living by doing experimental physics, right? So becoming a philosopher who does not trust his senses would be quite extraordinary turn for you, I believe. So I don't quite understand your position. You can't have your cake and eat it too.

Please note that that was not MY interpretation. If you read those papers that I referenced to, there is a clear reference to realism and what they are testing. The Leggett inequality was formulated with that in mind! That is why I said that if you disagree with that, you should be the one doing the rebuttals to those papers!

I don't get this reference to philosophy. If anything, you were the one who was arguing this based on philosophy. YOur post in #67 contains no physics, only personal preference. The fact that "realism", as defined within this context, can actually be tested experimentally means that it has been brought out of philosophy and into physics, the very same way the EPR paradox was brought out of philosophical argument and into physics when John Bell formalize its test. So if you have issues with this, let's see you rebut, say, Leggett's formalism.

Zz.

 

[stevendaryl]

Superdeterminism - under any name - is ridiculous. Just try to formulate in a scientific (and falsifiable) manner and you will see just how so!

For example: if all interactions are superdetermined and local and realistic (the reason superdeterminism was invented), then every particle in the universe must carry a complete copy of its "answer" to every measurement (question) possible - with every other particle in the universe to which it ever has or will interact. That is because entanglement can be swapped from particle X to particle Y and you never know which particle might be entangled with what other particle. Basically you are talking about an infinite amount of information being stored locally in every particle in the universe. Of course that information is "hidden" because there is no other evidence of it.

I agree with you that superdeterminism is unpalatable as a physical theory, but it wouldn't necessarily require infinite information stored in every particle. Instead, superdeterminism could be achieved through ordinary determinism plus very fine-tuned initial conditions.

 

[Quantumental]

I agree with you that superdeterminism is unpalatable as a physical theory, but it wouldn't necessarily require infinite information stored in every particle. Instead, superdeterminism could be achieved through ordinary determinism plus very fine-tuned initial conditions.

But why is it then unpalatable? We live in a infinite ocean of somethingness. Is it really that hard to accept that everything is fine tuned at the beginning?

 

[stevendaryl]

But why is it then unpalatable? We live in a infinite ocean of somethingness. Is it really that hard to accept that everything is fine tuned at the beginning?

Yes. Fine-tuning is like explaining something by "it's just a coincidence".

 

[Quantumental]

Yes. Fine-tuning is like explaining something by "it's just a coincidence".

Not really. Check out Gerard 't Hoofts proposals

 

[stevendaryl]

Not really. Check out Gerard 't Hoofts proposals

If we're talking about the same thing, I feel the same way about his proposals. Are you talking about his classical model for quantum mechanics?

 

[Derek Potter]

I sort of agree with you, that a lot (most? all?) of science is done with an implicit idea of a universe external to us that we are learning about through experiment and observation. However, a more limited view of science is that it is about making predictions, of the form: If I perform such and such an experiment, I will get such and such result. That limited view of science doesn't require realism.

Actually even such a prediction assumes the onticity of the formula - otherwise it can't refer to real observations.
EPR does not require the rejection of realism, it requires the rejection of direct realism. In other words our view of the universe needs to be modified drastically but, very importantly, we can still think of it as real.
From what I've hear of it, the Leggett inequality violations confirm that the issue is a particular view of reality, that a system has a unique and definite state. That little dent in common-sense seems here to stay.

 

[StevieTNZ]

From what I've hear of it, the Leggett inequality violations confirm that the issue is a particular view of reality, that a system has a unique and definite state. That little dent in common-sense seems here to stay.

The Leggett inequality only rules out certain classes of non-local hidden variables. Therefore realism is still possible, as it does not rule out Bohmian Mechanics.

The inequality I want tested is the Leggett-Garg inequality, which tests macro-realism. But if Bohmian Mechanics and QM give the same predictions, then realism could still be viable even if the inequality is violated.

 

[Derek Potter]

The Leggett inequality only rules out certain classes of non-local hidden variables. Therefore realism is still possible, as it does not rule out Bohmian Mechanics.
The inequality I want tested is the Leggett-Garg inequality, which tests macro-realism. But if Bohmian Mechanics and QM give the same predictions, then realism could still be viable even if the inequality is violated.

I do not follow the logic of that. If (and it's a big if) LG violation only rules out some classes and doesn't rule out BM then that does not mean realism is back on the table.

I'm not at all sure BM is realist in the required sense anyway. Sure there is a real wave and a real particle, but what of superpositions? The particle is like a predetermined collapse riding along with the wave, but how does BM cope the fact that Alice and Bob have not yet decided what basis to use? That's a genuine question, by the way. I suspect I know the answer - it doesn't - but I don't actually know.

 

[atyy]

I do not follow the logic of that. If (and it's a big if) LG violation only rules out some classes and doesn't rule out BM then that does not mean realism is back on the table.

I'm not at all sure BM is realist in the required sense anyway. Sure there is a real wave and a real particle, but what of superpositions? The particle is like a predetermined collapse riding along with the wave, but how does BM cope the fact that Alice and Bob have not yet decided what basis to use? That's a genuine question, by the way. I suspect I know the answer - it doesn't - but I don't actually know.

BM is realist in the sense that it solves the measurement problem in the most boring way possible.

BM deals with the preferred basis problem by assuming that position is the only thing one measures.

 

[atyy]

But why is it then unpalatable? We live in a infinite ocean of somethingness. Is it really that hard to accept that everything is fine tuned at the beginning?

No. It is not unpalatable (people say these things, but it's not scientific). Rather, it is impractical, because we cannot write down such a theory. So basically, we have already done all the research we can on superdeterminism. The open questions are, if we cannot write down the true theory of everything (say superdeterminism or whatever), are there intermediate steps in theory we can take that will make sense to us in the traditional scientific framework? Maybe the answer is no. However, Bohmian Mechanics shows that it is too early to give up, and there's probably room to explore the other openings allowed by Bell, such as retrocausation and many-worlds.

 

[Derek Potter]

BM is realist in the sense that it solves the measurement problem in the most boring way possible.
BM deals with the preferred basis problem by assuming that position is the only thing one measures.

Really? What does entanglement look like in a position basis?

 

[atyy]

Really? What does entanglement look like in a position basis?

It's the same as in QM.

The idea is that we can measure momentum by measuring position - we just cannot do it measure the canonically conjugate position at the same time. But we can use a different position to indicate momentum. For example, in the double slit experiment, the momentum of the particle just after the slit can be read by its position at a distant screen.

Also, QM doesn't say that a particle cannot have a trajectory. It says that a particle cannot have position and momentum simultaneously. So we can just choose to have particles with position but no momentum.

 

[stevendaryl]

Really? What does entanglement look like in a position basis?

In this paper, the EPR experiment for spin-1/2 particles is analyzed from the point of view of Bohmian mechanics.

http://www.tau.ac.il/~vaidman/lvhp/m115.pdf

 

[Derek Potter]

It's the same as in QM.

The idea is that we can measure momentum by measuring position - we just cannot do it measure the canonically conjugate position at the same time. But we can use a different position to indicate momentum. For example, in the double slit experiment, the momentum of the particle just after the slit can be read by its position at a distant screen.

Also, QM doesn't say that a particle cannot have a trajectory. It says that a particle cannot have position and momentum simultaneously. So we can just choose to have particles with position but no momentum.

OK. However that just covers the particle position. I was more interested in the wave, which never collapses and therefore, I assume, propagates nonlocaly - in a space of 6 or more dimensions. It would seem - please correct me if I'm wrong - that the wavefunction/pilot wave for the two particles together cannot be a function of the two separate waves. So we are back to the wave of A not existing on its own but only being defined in relation to the wave of B. Which is the very definition of non-realism. Is that correct?

 

[atyy]

OK. However that just covers the particle position. I was more interested in the wave, which never collapses and therefore, I assume, propagates nonlocaly - in a space of 6 or more dimensions. It would seem - please correct me if I'm wrong - that the wavefunction/pilot wave for the two particles together cannot be a function of the two separate waves. So we are back to the wave of A not existing on its own but only being defined in relation to the wave of B. Which is the very definition of non-realism. Is that correct?

If you are talking about Leggett's definition of realism, which is a technical one, I don't know.

 

[zonde]

Please note that that was not MY interpretation. If you read those papers that I referenced to, there is a clear reference to realism and what they are testing.

I read very carefully your reference about Wheeler's delayed-choice experiment with helium atoms. I could not find anything similar to your statement.
The best bet would be this:
"Wheeler's thought experiment is important since it tries to force a classical view of reality on to a quantum system."
It is quite a stretch by itself and yet it does not go as far as your statement.

The fact that "realism", as defined within this context, can actually be tested experimentally means that it has been brought out of philosophy and into physics

You can of course use the same word in physics as used in philosophy but it's confusing and I would say it's attempt to do philosophy disguised as physics.

Say we use some "word" in one sense. I redefine the "word" in different sense and falsify it in this second sense. Then I claim that "word" is falsified while the "word" is generally understood in first well established sense and is obviously not falsified in that first sense. Do you see the fallacy?

 

[ZapperZ]

Fact check: what do you think is the definition of "realism" as used here in theses PHYSICS papers and the one being addressed in Leggett inequality?

Zz.

 

[zonde]

However, a more limited view of science is that it is about making predictions, of the form: If I perform such and such an experiment, I will get such and such result. That limited view of science doesn't require realism.

In some idealized sense your argument is valid but ... scientific model contributes to knowledge of society when you can share it (communicate it), share results of experimental tests, repeat experiments and such things. It all relies on realism.
Besides new model would most certainly rely a lot on existing knowledge in order to make predictions (experimental equipment, design of experiment). Can you review all existing knowledge in light of some non-realistic model? Say we have arrived at existing knowledge by throwing out non-realistic models. You can't really review all discarded models.

 

[Derek Potter]

If you are talking about Leggett's definition of realism, which is a technical one, I don't know.

Nothing so specific. I'm just groping towards understanding what a real but non-local model could mean. I don't seem to be getting very far. No matter, I'll brush up on BM after I've fixed the measurement problem in MWI At least I have an idea of what I'm up against now, thanks.

 

[zonde]

Fact check: what do you think is the definition of "realism" as used here in theses PHYSICS papers and the one being addressed in Leggett inequality?

There is no definition of realism in paper about Wheeler's delayed choice experiment as word "realism" is not used there at all.
I don't know about Leggett inequalities but I suppose it's some sort of realism that requires that particle observables are determined by non-contextual variables (and that allows non-locality).

 

[ZapperZ]

Then maybe, BEFORE you attack, that you understand the definition that has been used when we talk about "realism" in physics AND in the context that of this topic. I had been explicit in invoking the Leggett formalism here, which I thought was sufficient to clarify the exact definition of what I was referring to. To hear now that you didn't even bother to figure that out and yet were quick to criticize on it is ridiculous.

In case you are too lazy to look, these things have been posted elsewhere already:

https://www.physicsforums.com/threads/recent-noteworthy-physics-papers.127314/page-4#post-1599072
https://www.physicsforums.com/threads/recent-noteworthy-physics-papers.127314/page-2#post-1307660

Zz.

 

[zonde]

Then maybe, BEFORE you attack, that you understand the definition that has been used when we talk about "realism" in physics AND in the context that of this topic. I had been explicit in invoking the Leggett formalism here, which I thought was sufficient to clarify the exact definition of what I was referring to. To hear now that you didn't even bother to figure that out and yet were quick to criticize on it is ridiculous.

Let me repeat this particular question:

Say we use some "word" in one sense. I redefine the "word" in different sense and falsify it in this second sense. Then I claim that "word" is falsified while the "word" is generally understood in first well established sense and is obviously not falsified in that first sense. Do you see the fallacy?

 

[atyy]

Nothing so specific. I'm just groping towards understanding what a real but non-local model could mean. I don't seem to be getting very far. No matter, I'll brush up on BM after I've fixed the measurement problem in MWI At least I have an idea of what I'm up against now, thanks.

BM is realistic in the common sense classical physics way. There is a subtlety as to whether the "wave function" in BM is real or not, since there is more than one wave function, but to start we can ignore that. BM is nonlocal in the sense that the wave function in QM is nonlocal, since it is in Hilbert space. The position of a particle depends on the wave function, so it is nonlocal. Basically, QM itself is nonlocal, if the wave function is taken to be real. BM takes over this nonlocality and solves the measurement problem by introducing hidden variables, so that there is naive reality and an observer is not required to determine what is real.

 

[Drakkith]

Thread locked, pending moderation.