# crowded quantum information

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9 hours ago, MigL said:

On the contrary, the only place we are dealing with actual physical experiments is at either end, where the observations are made; and the two observations are perfectly explainable by correlation.
At any point in between we have a mathematical abstraction that says the states are undefined, until said observations are made;  and that throws a wrench into the works.
Where is the reality in that intervening space ?

We are observing results in the field as data and not equations on paper.

There are some experiments dealing with the middle such as variations of the Wheeler delayed choice experiments. Correlation is an observation- not an explanation. It could serve as an explanation, as with “Bertelman’s sox” if the quantum identities could be demonstrated to be unchanging. This is not the case.

If the correlations are impossible to change, quantum teleportation would be impossible.

9 hours ago, MigL said:

For all intents and purposes, there is no reality until those observations are made.

The entanglement itself is the non-local part.

The experiments are planned, set up, and run and that is the reality before the observations are made.

9 hours ago, MigL said:

...thinking about war in the Ukraine and the Andromeda galaxy in the next instant, the probability of a coin flip showing heads is exactly the same in Ukraine as in Andromeda.

Is that your definition of non-locality ?

If a coin flip in Ukraine is random and a coin flip in Andromeda is also random and there is no correlation between them, the events are local.

But, if the coin flips are correlated such that the observation of one appears to affect the outcome of the other, the interaction is non-local.

9 hours ago, MigL said:

Is that what you would mean by the probabilities described by the mathematical wave function being non-local ?

The probabilities are in two different locations. That makes them local. The entanglement spans the two different locations simultaneously even though they are separated separated by space and time. That makes the entanglement itself non-local.

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56 minutes ago, bangstrom said:

If a coin flip in Ukraine is random and a coin flip in Andromeda is also random and there is no correlation between them, the events are local.

But, if the coin flips are correlated such that the observation of one appears to affect the outcome of the other, the interaction is non-local.

You keep saying this over and over, and it's just because you don't understand. It's not more true just because you repeat it.

Here (again):

The coins were made in Hamburg, and then taken to Ukraine and Andromeda. The results correlations are random whatever way you decide to toss them. Now, and here's the point, if you measure the same observable, the correlation is perfect. But if you measure incompatible observables, they're totally non-correlated.

You can't do that with coins. The correlations are strange, for sure. But because they were made in Hamburg the very same way, had you made the measurements in Hamburg at the very beginning, you would have found exactly the same correlations.

Edited by joigus
minor correction
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38 minutes ago, bangstrom said:

correlated such that the observation of one appears to affect the outcome of the other, the interaction is non-local.

Then you have to explain what the nature of that interaction is. Electromagnetic? Gravitational? You can't claim interaction and also say there is no claim of communication.

The underlying issue here is the notion that the particles have to communicate/interact with each other, because how do they "know" what state to be in after one is measured? But that's an error.  Since there's no information revealed by the measurement of the second particle, causality is not violated.

It's like the old joke about a vacuum dewar being the most amazing thing by keeping hot things hot and cold things cold, and the person asking "How does it know?" Not to ruin the joke, but: it's the wrong question to ask; the physics lies elsewhere.

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23 hours ago, joigus said:

You clarify the second point later, but I hope that doesn't mean 1) I cannot refer to quantum mechanics itself, in its closed mathematical form, in order to argue about what quantum mechanics itself means or implies. And 2) There's something about my statement of the EPR argument you don't agree with, but you reserve the right to bring it up later.

To 1). I completely accept what rolls out of the math of QM. I 'read' Leonard Susskind's Quantum Mechanics: The Theoretical Minimum, but somewhere halfway I had to give up on the math, but at least I can more or less follow the argumentation. Maybe I should now reread the relevant chapters again, with the present discussion in the back of my mind.

To 2): Ah, but I specified this immediate after that remark.

23 hours ago, joigus said:

"People say loosely, crudely, wrongly, that when you measure one of the photons it does something to the other one. It doesn't!! All that happens is you measure a property of one and you learn the corresponding property of the other one."

But that is exactly what I think. Some years ago I had a thought exchange about this with Swansont. If I remember correctly, I defended that the only thing one can say something about is what the result of a measurement of the entangled partner will be. (Of course this is only valid when e.g. polarisers are in exactly the same position.) However, I am completely convinced that nothing physically changes. I think the reason I retracted to this point, is that there indeed are many descriptions of Bell-like experiments where is said something like "If the polarisation of one photon is measured, the other one immediately flips in the same direction." As if some 'Quantum God' already sees how the wave function changed,  before it is measured by a physical mortal. No, nothing flips, the only thing I can know for sure is what will be measured at the other end, if measured in the same polarisation direction.

Swansont and Gell-Mann (Swansont, correct me if necessary),and you make it already to 'reality' because under certain circumstances you can with 100% certainty predict what the other end will measure if the measurement is made with the same polarisers in the same direction.

But I have to confess, now I am getting confused myself. Thinking about this I could imagine superluminal communication, so there should be an error in my thinking here. It is easy to determine if a beam of light is polarised: just turn a polarisation filter in the direction that lets through the maximum of light intensity, and you know its polarisation directon. Now do the same with entangled photons located exactly between Geneva (for obvious reasons) and the Andromeda galaxy. In Geneva I measure a small stream of photons, with a polariser at 0o, and because the source of entangled photons is exactly in the middle, the entangled partner photons arrive there at the same time. The Andromedian measures in which direction they are polarised, and will also measure 0o. So it does not work with single photons, but with many it would work. I assume I am making some huge error here, but at the moment I do not see where. My mind-overflow alert is blinking red...

The one with the clearest explanation where my error lies, gets a free beer (entangled with the one I will drink then, so take care it does not spill over...).

I'll stop here for the moment, before my head explodes.

Never realised 'honest thinking' can hurt so much. Ah, how easier life would be if one could simply stick to an ideology!

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6 hours ago, joigus said:

You can't do that with coins. The correlations are strange, for sure. But because they were made in Hamburg the very same way, had you made the measurements in Hamburg at the very beginning, you would have found exactly the same correlations.

When two particles are entangled their quantum identities are random and indeterminate until one of the particles is measured. This instantly breaks the entanglement and their identities become determinate on both ends.

The identities will always be anti-correlated. For example, if two formerly entangled electrons are observed and one is found to be spin-up the other will be spin-down so their combined spins add up to zero. And the timing between the two events is instant even if the the events are light years apart. Instant action at a distance makes the observations non-local and no longer classical.

To go with the coin example, when one coin lands ‘heads’ the other will land ‘tails’ every time.

The events are ‘local’ if the measurement of one has no affect on the other. But they are non-local, in the case of entanglement, because the measurement of one particle instantly fixes the identity of the formerly entangled partner.

Here is a short video that explains entanglement and non-locality in greater detail.

3 hours ago, Eise said:

In Geneva I measure a small stream of photons, with a polariser at 0o, and because the source of entangled photons is exactly in the middle, the entangled partner photons arrive there at the same time.

A beam of polarized light can't be entangled because the first measurement breaks entanglement.  A polarizer at the source is that first measurement.

With entanglement, you can only measure one property of one particle at a time. The measurement of the first particle is random, as is the second, third etc.. Every particle can have a different polarization.

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38 minutes ago, bangstrom said:

Boy, I don't know. Could that be because it's classical?

There's no classical analogy of a bipartite system of electrons/photons. Swansont's example I had never heard before, but it illustrates perfectly that there's no such thing as two states. There's only one state. It also illustrates that there are states of the bipartite system that neither up nor down. So it also illustrates superpositions of sorts. That's what I like most about it, and I'll keep it in my toolkit.

It can't illustrate every aspect because coins are not quantum; they're classical.

45 minutes ago, bangstrom said:

When two particles are entangled their quantum identities are random and indeterminate until one of the particles is measured. This instantly breaks the entanglement and their identities become determinate on both ends.

Quantum identities? I don't know of any such thing. In fact, for all we know there isn't any such thing.

I would punish you for all you're saying to do quantum field theory in the Fock representation for the rest of eternity. Then you would understand!!!

It's actually more natural to describe a two-particle state in terms of the occupation number: This state is twice "busy."

These are difficult ideas, I'm not saying they come naturally to anybody.

The danger --of discussing these things forever-- comes from people who have only half-understood QM. You never see the end of it.

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Am I right to understand that these correlations only occur when thousands  of measurements  of entangled particles are taken?

It is a statistical outcome?

Or has this measurement been made with just 2 entangled particles and the outcome is predictable on each occasion?

Edited by geordief
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1 minute ago, geordief said:

Am I right to understand that these correlations only occur when thousands  of measurements  of entangled particles are taken?

Some aspects of correlations are manifest only when you do thousands upon thousands of experiments. But every single time the anti-correlation is exact --within the allowance of detectors noise.

It's like:

++-+-+--+-++-+- average = 0, sometimes +, sometimes - (random)

--+-+-++-+--+-+ average = 0, sometimes +, sometimes - (random)

See? Every column is one run of the experiment. Each row is observations for one particle.

But (+-)(+-)(-+)(+-)(-+)(+-)(-+)(-+)(+-)(-+)(+-)(+-)(-+)(+-)(-+) average = 0, every single time = 0

Does that help?

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1 hour ago, bangstrom said:

A polarizer at the source is that first measurement.

Then you have not understood my example. The source of the entangled photons lies in the middle between Geneva and Andromeda. No measurement is made there. The measurements are done in Geneva and Andromeda. No beer, sorry.

34 minutes ago, geordief said:

Or has this measurement been made with just 2 entangled particles and the outcome is predictable on each occasion?

To add to Joigus' reaction: the correlation is 100% if the polarisers are oriented in the same direction. So a single measurement would do the job (except no scientist would do it once, it could be accidental). However, the 100% correlation is not interesting, because it could just as well be explained by supposing the photons had their polarisation from the beginning. To show the stronger correlation, you must vary the orientation of the polarisers independently from each other. And that you can only do by doing many measurements, according Joigus' example. Only then the correlation turns out to be stronger than a classical theory, where the photons have a polarisation from the beginning.

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24 minutes ago, Eise said:

Then you have not understood my example. The source of the entangled photons lies in the middle between Geneva and Andromeda. No measurement is made there. The measurements are done in Geneva and Andromeda. No beer, sorry.

To add to Joigus' reaction: the correlation is 100% if the polarisers are oriented in the same direction. So a single measurement would do the job (except no scientist would do it once, it could be accidental). However, the 100% correlation is not interesting, because it could just as well be explained by supposing the photons had their polarisation from the beginning. To show the stronger correlation, you must vary the orientation of the polarisers independently from each other. And that you can only do by doing many measurements, according Joigus' example. Only then the correlation turns out to be stronger than a classical theory, where the photons have a polarisation from the beginning.

Absolutely. That's what's strange.

I've racked my brains in the past thinking about this. For example: Suppose the photons are some kind of "magic marbles" that have the property of responding to different colourful filters, but what they have in their innards is actually a simple-minded, totally stupid tag that says "yes" travelling in one direction, and a tag "no" traveling in the other direction, having actually nothing to do with their world of colourfulness. If you wanted to rule out something like that happening, you would have to go to non-parallel polarisers, and check whether they're giving correlated answers to uncorrelated questions, so to speak. I'm not sure that Alain Aspect did rule out that possibility, but I would be very surprised if he didn't. I'm not sure if my point is clear either.

If that were the case, we would all be as good as idiots, and Einstein would be laughing in his grave. I don't think for a moment that's the case, but it goes to prove the kind of logical maze this kind of thing gets us into.

5 hours ago, Eise said:

I'll stop here for the moment, before my head explodes.

Just now, joigus said:

and check whether they're giving correlated answers to uncorrelated questions, so to speak.

I don't think that would be consistent with quantum correlations either.

In fact, what I've just said is stupid, and now I remember the reason why.

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3 hours ago, joigus said:

Some aspects of correlations are manifest only when you do thousands upon thousands of experiments. But every single time the anti-correlation is exact --within the allowance of detectors noise.

It's like:

++-+-+--+-++-+- average = 0, sometimes +, sometimes - (random)

--+-+-++-+--+-+ average = 0, sometimes +, sometimes - (random)

See? Every column is one run of the experiment. Each row is observations for one particle.

But (+-)(+-)(-+)(+-)(-+)(+-)(-+)(-+)(+-)(-+)(+-)(+-)(-+)(+-)(-+) average = 0, every single time = 0

Does that help?

Yes it helps.

Next stop I will be a particle physicist

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11 hours ago, Eise said:

So a single measurement would do the job (except no scientist would do it once, it could be accidental).

A small correction to this: correlation always only shows up statistically.

10 hours ago, joigus said:

If you wanted to rule out something like that happening, you would have to go to non-parallel polarisers, and check whether they're giving correlated answers to uncorrelated questions, so to speak. I'm not sure that Alain Aspect did rule out that possibility, but I would be very surprised if he didn't.

It is my understanding that this is already accounted for in Bell's unequality: QM measurements cannot be reproduced by introducing any local hidden variables. I think 'hidden' is the keyword here.

Compared to the Clauser et al experiment, Aspect changed the polarisers after the photons left the source, and also did this so fast that it was impossible for the measurement devices to communicate, i.e. they were spacelike separated.

BTW, I am still sitting on my problem...:

16 hours ago, Eise said:

The one with the clearest explanation where my error lies, gets a free beer (entangled with the one I will drink then, so take care it does not spill over...).

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4 hours ago, Eise said:

A small correction to this: correlation always only shows up statistically.

I agree. That's why the statement that decoherence is instantaneous I find very suspicious. The correlation with parallel magnets/polarisers you would start seeing very soon: (+,-), (+,-), (-,+), (+,-), (-,+)...

Every once in a while you would get a (-,-) or a (+,+) that are atributable to noise.

4 hours ago, Eise said:

It is my understanding that this is already accounted for in Bell's unequality: QM measurements cannot be reproduced by introducing any local hidden variables. I think 'hidden' is the keyword here.

Yes, you're right. It's just that when you think too much about this, you end up considering stupid ideas. Bell's theorem excludes even the possibility that the hidden variables are not correlated at all with spatial directions. They could be correlated with whatever you like... As long as they're yes-no variables --no superpositions of yes-no-- they satisfy Bell's inequality, and therefore QM violates them.

20 hours ago, Eise said:

To 2): Ah, but I specified this immediate after that remark.

I noticed. I'm paying a lot more attention to this thread than previous discussions we had, because of my interest on it, and because I think I can contribute more significantly.

Edited by joigus
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23 hours ago, swansont said:

The underlying issue here is the notion that the particles have to communicate/interact with each other, because how do they "know" what state to be in after one is measured? But that's an error.  Since there's no information revealed by the measurement of the second particle, causality is not violated.

Causality may not be violated but the cause and effect is instant and not mediated by a direct physical contact and that makes the interaction non-local.

I like to visualize entanglement as something like a game of tug-of-war. If the rope breaks, the participants all fall but in opposite directions so their directions of fall are anti-coordinated. There is no need to communicate that one side has fallen to the left for the other side to know they should fall to the right. Both sides respond to their local loss of equilibrium.

A connection by rope is a classical connection and the break in that connection can not be transmitted through the rope any faster than light speed so the timing of events is space-like or slower. On the other hand, a connection by entanglement is instant and simultaneous at all points in space. This never happens at the macro level but it is possible at the particle level.

With entanglement, the break, and loss of entanglement at both ends are all simultaneous. The conventional explanation for the quantum identities of entangled particles is that their identities are in a state of superposition. Their polarities are both horizontal and vertical and their spins are both up and down like Schroedinger’s dead and alive cat.

Superposition is difficult to visualize. I prefer to think that entangled particles lie on opposite ends of a common wave function such that when one particle is a the peak of the wave the other is at the trough. This explains how they can be constantly anti-coordinated. And, when entanglement is lost their identities drop out as determinate but anti-coordinated depending upon whether they happen to be at the peak or the trough end of the wave when it was lost.

On 9/27/2022 at 5:12 AM, joigus said:

Here (again):

The coins were made in Hamburg, and then taken to Ukraine and Andromeda. The results correlations are random whatever way you decide to toss them. Now, and here's the point, if you measure the same observable, the correlation is perfect. But if you measure incompatible observables, they're totally non-correlated.

You can't do that with coins. The correlations are strange, for sure. But because they were made in Hamburg the very same way, had you made the measurements in Hamburg at the very beginning, you would have found exactly the same correlations.

We must have a different understanding of what you mean by, "Now, and here's the point, if you measure the same observable, the correlation is perfect. But if you measure incompatible observables, they're totally non-correlated.

Does this mean you can measure only all 'heads' or all 'tails' as the observable and find them coordinated. Or, you can measure only 'heads' here and 'tails' there and find them non-coordinated"?

I don't see where your measurements are not classical. And what does having been made in Hamburg have to do with it?

1 hour ago, joigus said:

I agree. That's why the statement that decoherence is instantaneous I find very suspicious. The correlation with parallel magnets/polarisers you would start seeing very soon: (+,-), (+,-), (-,+), (+,-), (-,+)...

The timing between the first observation as either + or - instantly determines what the second will be. That is the part that is instantaneous. The identities as either + or- is random at the time of observation but it was not fixed from the start as with the gloves in boxes.

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1 minute ago, bangstrom said:

Causality may not be violated but the cause and effect is instant and not mediated by a direct physical contact and that makes the interaction non-local.

If you're going to call it an interaction you need to identify the interaction and retract your claim that there is no communication. Otherwise it's a hand-waving misrepresentation of the science, and you're claiming something without defending it.

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1 hour ago, bangstrom said:

We must have a different understanding of what you mean by, "Now, and here's the point, if you measure the same observable, the correlation is perfect. But if you measure incompatible observables, they're totally non-correlated.

Does this mean you can measure only all 'heads' or all 'tails' as the observable and find them coordinated. Or, you can measure only 'heads' here and 'tails' there and find them non-coordinated"?

No. One thing is the outcome = result = eigenvalue = + or -

Another thing is the observable = experimental question = Hermitian operator = polarization direction

Let's go step by step, please, because otherwise this is going to take forever.

Any discussion that doesn't contemplate this essential difference is meaningless

+ for $$\sigma_x$$ has nothing to do with + for $$\sigma_y$$, even thought they're both "plus."

If I just say "yes," are you able to tell what this is the answer to, if I don't tell you the question?

If we agree on that at least, then maybe we can proceed from there.

Edited by joigus
minor correction
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11 hours ago, swansont said:

If you're going to call it an interaction you need to identify the interaction and retract your claim that there is no communication. Otherwise it's a hand-waving misrepresentation of the science, and you're claiming something without defending it.

You may call it a “communication” and I have no problem calling it a communication but officially it is not a communication because one qubit of information does not cross the threshold of being a communication since nothing intelligible can be understood from one qubit of information as defined by those working on quantum computers.

Apparently, at the particle level, one qubit of information is all it takes for an ‘intelligible communication’ among other particles since particles ‘know’ how to respond. It may look like a communication to you and me but it is not officially defined as such.

I suspect it may look like a ‘communication’ to the quantum computer people as well but if they call it a communication that puts their view at odds with Einstein’s Second Postulate about nothing being able to travel faster than light.

If you and I agree to call it a communication, that puts us on the wrong side of the second postulate because it has been measured as a faster than light ‘communication’. That is OK by me.

11 hours ago, joigus said:

No. One thing is the outcome = result = eigenvalue = + or -

Another thing is the observable = experimental question = Hermitian operator = polarization direction

Let's go step by step, please, because otherwise this is going to take forever.

Any discussion that doesn't contemplate this essential difference is meaningless

+ for σx has nothing to do with + for σy , even thought they're both "plus."

If I just say "yes," are you able to tell what this is the answer to, if I don't tell you the question?

If we agree on that at least, then maybe we can proceed from there.

If I understand this so far, your coin example is local, (but not classical) in Hermitian space.

But I see it as both local and classical in my observable space or Euclidean space, Newtonian space, Hamiltonian space, or

Minkowsky space.

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13 hours ago, bangstrom said:

If I understand this so far, your coin example is local, (but not classical)

The coin example is Swansont's. It is local. It reproduces one interesting aspect of quantum mechanics, which is superpositions: Until we measure, the coin is neither up nor down.

What I've said is that no classical analogue can reproduce quantum mechanical correlations. So no coin, dice, gloves, cats, or whatever other classical mechanism can reproduce quantum correlations to their full extent.

This is, in some sense, like a house of cards. If you remove one feature, the whole "quantum peculiarity" falls apart, and you get something in contradiction with actual physics. I gave an example before: If you removed randomness in a way that you could force a sequence of data --that would be an interaction; that would be writing a message--, while keeping the quantum correlations, and the validity of QM everywhere else, you would be able to exploit exact correlations for parallel polarisers to send superluminal signals, because the far-away observer would be reading the negative image of your message. Of course, that's impossible.

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1 hour ago, joigus said:

What I've said is that no classical analogue can reproduce quantum mechanical correlations. So no coin, dice, gloves, cats, or whatever other classical mechanism can reproduce quantum correlations to their full extent.

I was breeding on a similar, precise way to formulate what we really learn from Bell-like experiments.

• In the first place, we learn that the predictions of QM are correct. (I suppose that is the reason that Feynman threw Clauser out of his office.)

Secondly, nearly the same formulation you used:

• No system, based on classical physics, can reproduce all predictions of QM.

Only if you would introduce 'action at a distance', one could. But we know this is classically impossible, because of SR.

@bangstrom: I think there is a rather clear experiment that shows that the correlation between the 2 distant measurements cannot be causal. And 'not being causal' implies:

• no communication is taking place between the two measurements, no superluminal signals
• none of the more or less equivalents of causality: effect, action, interaction, etc. applies.

Now this is the experiment: in a Bell like experiment the distances of the detectors are exactly equal. So, assuming we use a photon/polarisation experiment, int the rest frame of the source of entangled photons, the photons will arrive at exactly the same time. Further, the detections are spacelike separated, so even light is not fast enough to reach the other detector (maybe superfluous, because using photons in the experiment it would be impossible anyway. We measure the correlations, which of course are exactly as QM says they will be.

Now imagine 2 other observers: one is travelling in the direction of the first detector to the second, the other observer in exactly the opposite direction. For both observers, the detections do not occur at the same time. For Observer 1 Detection 1 will be the first, for Observer 2 Detection 2 will be first. However, SR demands 'conservation of direction of causality'. It cannot be that for Observer 1 Detection 1 causes Detection 2, and for Observer 2 Detection 2 causes Detection 1. Same holds of course for all other 'disguises of causality': communication, effect, interaction etc. This leaves us with the only other option, correlation. And as Detection 1 and 2 are outside their respective light cones, this correlation must have its origin somewhere else: the source of the entangled photons. 2 photons just leaving the entanglement source are of course in the light cones of Detection 1 and 2.*

And this is what Swansont has already repeated a few times: the photons are correlated direct at the beginning.

It is only when we look at it with a classical view, it seems we need 'action at a distance'. (That sounds like Joigus)

A bit against Joigus and Swansont, I would 'cry out': "yes, but we, as macroscopic human beings, live in a classical world!"

And therefore we are astonished about these results. But this is nothing new: QM is astonishing. But that is nothing new. Citations, just from my head:

Bohr: Who is not astonished about QM, has not understood QM.

Feynman: I do not understand QM.

* An actual experiment, not exactly like the one I described, but I assume equivalent, was indeed done:

Quote

We report on a new kind of experimental investigations of the tension between quantum nonlocally and relativity. Entangled photons are sent via an optical fiber network to two villages near Geneva, separated by more than 10 km where they are analyzed by interferometers. The photon pair source is set as precisely as possible in the center so that the two photons arrive at the detectors within a time interval of less than 5 ps (corresponding to a path length difference of less than 1 mm). One detector is set in motion so that both detectors, each in its own inertial reference frame, are first to do the measurement! The data always reproduces the quantum correlations, making it thus more difficult to consider the projection postulate as a compact description of real collapses of the wave-function

Bold by me, of course. Joigus, do you still not want to earn a beer?

Edited by Eise
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2 minutes ago, Eise said:

Bold by me, of course. Joigus, do you still not want to earn a beer?

Of course I do. Give me some more time, please. Thanks for the reference.

4 minutes ago, Eise said:

A bit against Joigus and Swansont, I would 'cry out': "yes, but we, as macroscopic human beings, live in a classical world!"

I'm aware of it. I didn't want to bring that up just yet. The peculiar epistemological position of quantum mechanics is that it postulates a different mechanics, but makes constant reference to a limiting regime that's not really in its formalism --it cannot be obtained as an assymptotic limit, but only through analogy--. But, in fact, you put it there from the very beginning as a hidden assumtion at some points. Classical mechanics appears in quantum mechanics only as a shadowy figure. Very much like melody in music. Perhaps we will be able to discuss it later. Or open a new thread about that specific question.

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14 hours ago, Eise said:

13 hours ago, Eise said:

@bangstrom: I think there is a rather clear experiment that shows that the correlation between the 2 distant measurements cannot be causal. And 'not being causal' implies:

• no communication is taking place between the two measurements, no superluminal signals
• none of the more or less equivalents of causality: effect, action, interaction, etc. applies.

Why do you say the experiment near Geneva rules out the superluminal nature of entanglement?

There may be something 'causal' about the simultaneous loss of entanglement but it is not causal in the classical sense where a direct physical interaction is required. It is "spooky action at a distance."

Zeilinger's work with quantum teleportation demonstrates a superluminal transaction where an action at the source of an entanglement instantly- that is much too fast to measure- affects the observation at the other end.

14 hours ago, Eise said:

And this is what Swansont has already repeated a few times: the photons are correlated direct at the beginning.

I have also repeated numerous times that the particles have been correlated from the beginning. This is not the question.

The correlated identities are not fixed from the start as with the gloves in boxes analogy where the left and right handed anti-correlation remains fixed from the start to finish such that the box with the right hand glove has always had the right hand glove and the box with the left hand glove has always had the left hand glove. This is the classical assumption.

The tests of Bell’s inequalities suggest that more combinations are possible in QM than with the classical physics when more than a single pair of possibilities are considered. Think of boxes with left or right handed gloves that can also be red or blue. The possibilities are still anti-coordinated so you can never have two left handed gloves or two red gloves but there is no way of knowing which box is which, or if they have always remained the same.

The conventional explanation is that the identities of the particles are both in a state of superposition with both gloves simultaneously being both left/right and red/blue identities like Schroedinger’s dead/alive cat until the first measurement is made and then their identities become determinate but always anti-coordinated. This defies our classical visualization. I think there must be a better explanation but the superposition explanation does work.

In short, Bertlmann’s socks may always be anti-coordinated pink and blue but you never know if they were on his feet the same way all day or if rotated them about occasionally. Tests of Bell’s inequalities suggest that particle identities may be coordinated but their identities are not necessarily the same from the start. They are indeterminate until the first measurement is made.

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1 hour ago, bangstrom said:

Why do you say the experiment near Geneva rules out the superluminal nature of entanglement?

Because in this experiment, there is no direction all observers can agree upon. Detection1 can be the first for one observer, while for another observer Detection2 is the first. So there is no superluminal signal from one detection to the other, because a signal always has a direction. Hiding behind the vague word 'nature' does not help you.

1 hour ago, bangstrom said:

This defies our classical visualization

Yep. Nature is not obliged to follow our capabilities to visualise how this happens; our visualisations are classical, per definition. The superluminal signal is only necessary if you want to reproduce entanglement with classical means.

I scanned through Susskind's Theoretical Minimum about QM: he is making this argument very precise. Classically you would need direct action at a distance; QM does not. I would suggest to read this book.

1 hour ago, bangstrom said:

The correlated identities are not fixed from the start as...

Stop using the word 'identities', this is very imprecise. I assume you mean properties. If not explain what you mean with 'identity' in this context.

2 hours ago, bangstrom said:

Zeilinger's work with quantum teleportation demonstrates a superluminal transaction where an action at the source of an entanglement instantly- that is much too fast to measure- affects the observation at the other end.

Zeilinger would not agree with you, because your use of the word 'affects', which is just another way of saying 'one measurement causes a change at the remote side'.

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2 hours ago, Eise said:
5 hours ago, bangstrom said:

Why do you say the experiment near Geneva rules out the superluminal nature of entanglement?

Because in this experiment, there is no direction all observers can agree upon. Detection1 can be the first for one observer, while for another observer Detection2 is the first. So there is no superluminal signal from one detection to the other, because a signal always has a direction. Hiding behind the vague word 'nature' does not help you.

Yes, but that is from the human perspective.

From the perspective of the experiment which is what I was referring to, the timing of events with clocks on both ends timed of the loss of entanglement as superluminal.

2 hours ago, Eise said:

Yep. Nature is not obliged to follow our capabilities to visualise how this happens; our visualisations are classical, per definition. The superluminal signal is only necessary if you want to reproduce entanglement with classical means.

A superluminal signal is not possible by classical means. I don't know if you could even call it a 'signal' because it is instant at all points and has no direction.

2 hours ago, Eise said:

Stop using the word 'identities', this is very imprecise. I assume you mean properties. If not explain what you mean with 'identity' in this context.

I agree ‘properties’ is a better term but ‘identities’ is the term I first encountered in my readings on the topic and I think even Zeilinger now speaks of ‘identity swapping’.

2 hours ago, Eise said:

Zeilinger would not agree with you, because your use of the word 'affects', which is just another way of saying 'one measurement causes a change at the remote side'.

Good point but what word would you suggest?

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1 hour ago, bangstrom said:

Yes, but that is from the human perspective.

Yes, and you are human. And humans do not have the ability to visualise what is 'really going on'. That is why you have a problem here. As any other human. But QM is unambiguous: the measurements are local, but correlated.

1 hour ago, bangstrom said:

A superluminal signal is not possible by classical means. I don't know if you could even call it a 'signal' because it is instant at all points and has no direction.

I think your postings are scattered with 'signal', 'cause', 'affect', 'action' etc. In QM superluminal signals are also impossible. The illusion of a superluminal signal only appears because one wants to understand what is happening from a classical viewpoint.

1 hour ago, bangstrom said:

A superluminal signal is not possible by classical means. I don't know if you could even call it a 'signal' because it is instant at all points and has no direction.

Correct. So there is no signal, and it is superluminal?

Reminds me of a bonmot of Pauli about Dirac's atheism: there is no God, and Dirac is his prophet.

1 hour ago, bangstrom said:

I agree ‘properties’ is a better term but ‘identities’ is the term I first encountered in my readings on the topic and I think even Zeilinger now speaks of ‘identity swapping’.

I assume this is in the context of 'quantum teleportation'. Quantum teleportation is based on entanglement, but it is a good trick, made possible on the basis of entanglement.

1 hour ago, bangstrom said:

Good point but what word would you suggest?

Correlation. That is what we (if I may speak for Joigus, Swanson and MigL...) are calling it all the time.

Edited by Eise
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2 hours ago, Eise said:

I assume this is in the context of 'quantum teleportation'. Quantum teleportation is based on entanglement, but it is a good trick, made possible on the basis of entanglement.

'Quantum teleportation' is a very bad name for what it actually is: The possibility that QM affords you to select certain pairings of flavour (by drafting people with different sensibilities for different flavours) of a "magic icecream" that was prepared in Hamburg (so all its properties have been cooked up back there and then) in such a way that, if someone tastes it in Andromeda later, and other person tastes it in Australia, (and both have analogous taste receptors) and it tastes of vanilla, it will taste the opposite (whatever that means) to the person tasting it at Andromeda. But if you choose people with different sensory receptors, the flavours will be completely uncorrelated. Strange flavour properties for a classical icecream, right? Sure.

The argument is a bit involved, granted. But if the whole setup was prepared in Hamburg, so that the strange flavour correlations were already present there, how is this mess --whatever it implies-- telling you anything at all about locality? If the x-position has been factored out of the problem, how can it be the case that it's telling you anything about the x position?

If ever anyone were capable of making an icecream with non-commutative flavours, it would be obvious to us all where the real crux of the matter is. Because that's so far removed from our intuition, it will never happen.

The problem with quantum mechanics, the real thing that's difficult to wrap your head around is that a perfectly defined vanilla-flavoured piece of icecream is made of equal parts of chocolate and anti-chocolate.

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