Meaning of the word 'instantaneous'

[DrChinese]

Correct me if I'm wrong (always a safe assumption). Bell's mathematical statement assumes some underlying classical variable(s) are present which accounts for the correlation. In my classical example this variable would be the gyroscope axis direction. No such variables are allowed by the data on QM systems. From a QM viewpoint there is no issue as far as I can tell other than this annoys people who demand a classical resolution which experiments show can't be forthcoming.

... What does trouble me somewhat is the steady rain of QM experiments and papers which are worded to make the naive reader think otherwise WRT the usual QM.

The Bell proof does not demand any particular type of hidden variable - it could be a function, for example, or a set of functions. Simply calling it "quantum" does not resolve the issue.

The reason there are so many papers worded the way they are is that quantum non-locality can be demonstrated in so many ways - and is so fascinating. Note that quantum non-locality, the phase, is simply referring to the interaction between Alice and Bob (whatever mechanism that accomplishes such).

It may help you to know that it is possible to entangle objects which have never existed in a common light cone. And that can be done *after* they are measured. Quantum non-locality can take many unusual forms.

 

[vanhees71]

I clearly don't understand then. All I'm trying to convey is it is a quantum world, no more no less. This is classified (more like branded) as non-realistic world view. Then so be it. All evidence appears to support this non-realistic world.

Yes, of course, with overwhelming evidence the Bell inequalities are violated with overwhelming significance, and quantum theory is right. So we live in a quantum world. That's it. Case closed. We can switch back to physics in our discussion!

 

[Android Neox]

I know we go round and round on this, but, this statement isn't correct is it? Consider two Gyroscopes which are counter rotating which are separated using a torque free explosive device. These spins are correlated and require no information transfer and the situation is perfectly understandable. The problem arrises when the Gyroscopes are replaced with quantum ones. The very same experimental situation occurs in QM except the information is quantum mechanical, not classical. So, while we can think of each gyroscope carrying it's very own pointing direction we are forced by QM to consider each spin as carrying it's own state vector.

The "Action-at-a-Distance" interpretation of quantum entanglement requires simultaneity... the wavefunction collapse takes place instantly, across all of space, from the perspective of the observer that sees him/her-self as the one to make the first observation of part of the entangled pair.

Since Special Relativity requires non-simultaneity and action-at-a-distance requires simultaneity, I set up a thought experiment to highlight the issue:

 

[Paul Colby]

I set up a thought experiment to highlight the issue

My position is QM requires no additional "interpretation" so I may be boring to talk to. The measurements Bob and Alice do are independent. If either measures their particle they gain knowledge of the other's particle QM state. At this point I say so what? The wave function is more akin to a probability distribution and is only one mathematical piece of QM. The wave function doesn't make a noise when it "collapses".

As to what is observed in your EPR setup is Bob will measure 50% in the up state and 50% in the down state. What Alice will see is also 50% up and 50% down with the added knowledge that she has a particle by particle readout of what Bob will measure suitably inverted in her data. So, since Alice and Bob's measurements are isolated by the finiteness of c, we can conclude that the randomness Bob sees is not caused by an additional randomness introduced by his measurement device (provided it's aligned with Alice's). And, of course, Alice and Bob's roles are entirely reciprocal.

 

[DrChinese]

My position is QM requires no additional "interpretation" so I may be boring to talk to. The measurements Bob and Alice do are independent. If either measures their particle they gain knowledge of the other's particle QM state. At this point I say so what? The wave function is more akin to a probability distribution and is only one mathematical piece of QM. The wave function doesn't make a noise when it "collapses".

As to what is observed in your EPR setup is Bob will measure 50% in the up state and 50% in the down state. What Alice will see is also 50% up and 50% down with the added knowledge that she has a particle by particle readout of what Bob will measure suitably inverted in her data. So, since Alice and Bob's measurements are isolated by the finiteness of c, we can conclude that the randomness Bob sees is not caused by an additional randomness introduced by his measurement device (provided it's aligned with Alice's). And, of course, Alice and Bob's roles are entirely reciprocal.

Some of what you say is agreeable, some not so much.

QM needs no interpretation, the formalism is fine as is (as far as anyone knows). The randomness Bob sees is not caused by an additional randomness introduced by his measurement device. And Alice and Bob's roles are entirely reciprocal. But...

Alice and Bob's choice of measurements may be independent, but their outcomes are NOT. The case of the aligned measurements does not show that, as EPR discovered: it actually implies the existence of hidden variables (and a common cause).

But at almost any other settings, the actual results do not display outcome independence. And the formalism itself demands outcome dependence without consideration of time or distance. For example, entangled photon polarization coincidence is a function of the difference in Alice and Bob's measurement settings (theta). And the correlation is too tight for independence to exist (that's from Bell).

 

[Paul Colby]

And the correlation is too tight for independence to exist (that's from Bell).

Bell's statement of independence doesn't accommodate a QM world. Game over.

 

[DrChinese]

Bell's statement of independence doesn't accommodate a QM world. Game over.

I think it is more that the quantum mechanical world we live in does not feature observer independence. An observer's choice of measurement here is somehow connected to an outcome there, where distance and time interval are not a factor.

 

[Paul Colby]

I think it is more that the quantum mechanical world we live in does not feature observer independence. An observer's choice of measurement here is somehow connected to an outcome there, where distance and time interval are not a factor.

In a QM world observations are always dependent on the observer. For an isolated spin 1/2 system the outcome of a measurement must depend on the measurement made. That this works even non-locally is amazing, yes but completely understandable if one is willing to concede QM as fundamental. Many here can't or won't make that jump. Bell's statement has a classical bias that is actually wrong given the data.

 

[DrChinese]

In a QM world observations are always dependent on the observer. For an isolated spin 1/2 system the outcome of a measurement must depend on the measurement made. That this works even non-locally is amazing, yes but completely understandable ...

Use of the word "isolated" is somewhat ambiguous to me in this context. I might re-phrase: For an isolated system of an entangled pair of spin 1/2 particles, outcome correlations are dependent on the the observers of each. "That this works even non-locally is amazing, yes but completely understandable..."

 

[newjerseyrunner]

Wouldn't it be different depending on if you're in the context of QM or GR? Would these be correct?

In QM instantaneous is any delta in time that is less than the precision allowed by the uncertainty principal.
In GR, it's completely non-sensical since there can be disagreement between observers in the flow of time.

 

[Paul Colby]

Use of the word "isolated" is somewhat ambiguous to me in this context.

isolated as in single non-entangled spin. Spin component depends on the measurement direction

 

[DrChinese]

isolated as in single non-entangled spin. Spin component depends on the measurement direction

Somehow that's what I thought you meant. So I am glad I clarified. The same applies in an entangled 2 particle system; the outcomes are consistent with the measurement choices of both observers. They are not independent as you keep trying to imply.

 

[Paul Colby]

They are not independent as you keep trying to imply.

They are correlated, how is it I implied otherwise? They are independent in that Bob and Alice's measurements may be made in either order in a way that doesn't interact with the other. Alice's measures doesn't effect or in anyway cause Bob's outcome. Alice's data merely determines the single particle QM state of Bob's particle. This is a fact that is true independent of Bob's chosen measurement. For arbitrarily aligned measurements It does so in a way that upsets Bell's concept of "dependence" which fails to hold in QM.

 

[DrChinese]

They are independent in that Bob and Alice's measurements may be made in either order in a way that doesn't interact with the other. Alice's measures doesn't effect or in anyway cause Bob's outcome. Alice's data merely determines the single particle QM state of Bob's particle. This is a fact that is true independent of Bob's chosen measurement.

Alice's measurement choice apparently affects Bob's outcome (by placing Bob into a eigenstate compatible to Alice's), or alternately Bob's measurement affects Alice's outcome - or some mixture of both. The QM prediction does not support any other variables, and requires both choices to explain the results.

That may be the same as what you say in your last 2 sentences, not sure.

 

[votingmachine]

I think people are not viewing this thread (especially the expert ones)

OK. I ask in a different way.

What does instantaneous mean?

1. No time lag.

2. A very-very-very small time lag.

This would be easy, hopefully...

I would say the first, no time lag.

That should not bother anyone. If I hold a ball in my hand and let go, it INSTANTANEOUSLY begins to accelerate downward (it was all along, but my hand stopped the process). There is no time lag between the removal of my restraining force, and the beginning of acceleration. There is no "road-runner-coyote" moment where the coyote pauses, and then falls.

I'm going to say that the electron emitting a photon instantaneously does not bother me. That does not mean the PROCESS is proven to take no time. But the entire process is invisible. If there is an energetic electron, and later a less energetic electron and a photon, there is no intermediate state (that we see) of an electron forming a photon from its decreasing energy. We see the kinetic energy being (continuously) formed, from gravitational potential energy, in the falling ball. But we don't see the (quantum) photon energy being formed from electron-state energy.

My understanding if the models is that the electron is sufficiently "wavy" that it does not behave like a particle (a "ball"), and move from place "A" to place "B". There is a moment it is at "A" and a subsequent moment it is at "B", with ambiguity about how, when, and if there is a transition. In general, the electron cannot be in between, and in general the mass-energy of the electron is conserved. Something that cannot have a path between "A" and "B", and yet goes from "A" to "B", probably goes instantaneously.

 

[votingmachine]

One could construct a classical version of EPR using two counter rotating gyroscopes. A small explosive device separates the two. Sometime later you measure one gyroscope and, as if by magic, in an instant, you predict the direction of the unmeasured one. Clearly, no non-local interaction is needed to account for this astounding fact. What sticks in peoples craw is the quantum nature of the observables not the correlation.

Now, in regard to the photon emission, how exactly is the time of emission to be known?

That is not correct. The classical model you describe does not match the results of Bell-type experiments. It is definitely true that you can deduce complete set properties about paired classical objects by measuring one. The thing that Bell-type experiments SHOW and PROVE is that you cannot deduce complete set properties about paired quantum objects similarly.

What sticks in the craw is that the property sets are not deducible, not that they are deduced at a distance.

 

[Paul Colby]

That is not correct. The classical model you describe does not match the results of Bell-type experiments.

Never said or attempted such. I gave a classical example which shows how priorly prepared information (which in the classical case is a vector direction) can exhibit correlation for space like separations. It does so quite trivially. The analogous QM example (two particles possessing angular momentum) also shows correlation for the very same reasons, however, because of the QM nature of the problem fails to meet Bell's classical statement. In the QM situation one should view the outcome of one measurement as discovering the one-particle Hilbert space state vector of the other particle. Since the measurements are space like separated there is no interaction in the sense that they share a hamiltonian interaction term. One should not view QM measurement as an interaction or cause.

 

[DrChinese]

I gave a classical example which shows how priorly prepared information (which in the classical case is a vector direction) can exhibit correlation for space like separations. It does so quite trivially. The analogous QM example (two particles possessing angular momentum) also shows correlation for the very same reasons, however, because of the QM nature of the problem fails to meet Bell's classical statement. In the QM situation one should view the outcome of one measurement as discovering the one-particle Hilbert space state vector of the other particle. Since the measurements are space like separated there is no interaction in the sense that they share a hamiltonian interaction term. One should not view QM measurement as an interaction or cause.

There are a lot of things wrong with the above. There is no quantum mechanical sense in which "the analogous QM example (two [entangled] particles possessing angular momentum) " features separated, independent systems - even in the Bohmian interpretation (which features explicit nonlocality).

Much of what you say implies that you do not understand Bell, or simply reject it. Bell's no-go proof applies to local realistic theories, which QM is not. However, it certainly highlights why there can be no analogy to classical systems to explain the correlations. You can't have it both ways. You either accept Bell (and reject classical analogies), or you don't. Give up locality or give up realism (or both).

 

[Paul Colby]

ou either accept Bell (and reject classical analogies), or you don't.

I totally and completely reject all classical analogies. I'm totally understand the correlations as a QM effect. People are fond of quoting Feynman "no one understands QM". Here this should read, no one will allow you to claim to understand QM.

 

[Paul Colby]

There are a lot of things wrong with the above. There is no quantum mechanical sense in which "the analogous QM example (two [entangled] particles possessing angular momentum) " features separated, independent systems - even in the Bohmian interpretation (which features explicit nonlocality).

How so?

You're claiming that when Bob measures +z particle he can't conclude that Alice's particle is in the $\vert -z\rangle$ state??

 

[votingmachine]

Never said or attempted such. I gave a classical example which shows how priorly prepared information (which in the classical case is a vector direction) can exhibit correlation for space like separations. It does so quite trivially. The analogous QM example (two particles possessing angular momentum) also shows correlation for the very same reasons, however, because of the QM nature of the problem fails to meet Bell's classical statement. In the QM situation one should view the outcome of one measurement as discovering the one-particle Hilbert space state vector of the other particle. Since the measurements are space like separated there is no interaction in the sense that they share a hamiltonian interaction term. One should not view QM measurement as an interaction or cause.

You lost me there. I don't see how that squares with:

One could construct a classical version of EPR using two counter rotating gyroscopes.

The problem with the results of EPR-Bell experiments is that they explicitly rule out the presence of a complete description. Classical systems have property sets that can be explicitly described. The entangled particles do not. If you try to use a pair of classical objects in an EPR-Bell experiment, you get different results, as the objects DO have explicit property sets. That is the distinguishing difference, that the results are different and rule out explicit and complete property sets.

 

[DrChinese]

How so?

You're claiming that when Bob measures +z particle he can't conclude that Alice's particle is in the $\vert -z\rangle$ state??

They are part of a single quantum mechanical system while entangled. They are not independent systems. That is QM orthodoxy (the formalism). There was no definite value for Alice's z prior to Bob's measurement (assuming he measures first).

 

[Paul Colby]

There was no definite value for Alice's z prior to Bob's measurement (assuming he measures first).

True of all QM measurements and systems entangled or not.

 

[Paul Colby]

You lost me there. I don't see how that squares with:

You're reading way more into my statements than is there. Two counter spinning Gyroscopes taped together with duct tape are a classical analog of two spin-1/2 particles in an $S=0$ state. The Gyroscopes are a classical example. The spin-1/2 particles are a QM example. Ones classical, the other quantum mechanical. Clear?
Both exhibit correlations when separated, yes? The QM violates Bell because Bell's formulation of the problem presupposes classical degrees of freedom. We all agree on this as far as I can tell.

 

[votingmachine]

I'm not sure what you are saying ... I may well be reading something into it.

Somehow it sounds to me that you are presenting two gyroscopes with a single spin property as an identical experiment as the EPR experiments. And it isn't. If you calculate the results of measurements and calculate the correlations, you won't get the same results. If you don't get the same results, it is not an analogy, not a model.

Sorry if that is a complete misread.

 

[TimeLord]

As to the meaning of the word instantaneous, my interpretation is that it means that cause and effect are separated by no more than one Planck time.

And unless we are completely wrong about photons being the fastest anything can propagate in normal space/time then that is the least time that any event can take place in.

 

[DrChinese]

You're reading way more into my statements than is there. Two counter spinning Gyroscopes taped together with duct tape are a classical analog of two spin-1/2 particles in an $S=0$ state. The Gyroscopes are a classical example. The spin-1/2 particles are a QM example. Ones classical, the other quantum mechanical. Clear?
Both exhibit correlations when separated, yes? The QM violates Bell because Bell's formulation of the problem presupposes classical degrees of freedom. We all agree on this as far as I can tell.

Bell explicitly assumes that Alice's choice of measurement basis does not affect Bob's outcome, and vice versa. But that is not true with the QM formalism, something that had actually been missed previously. So... no, you are not clear and I don't agree at all with your assessment as you are saying quite the opposite. The observers' relative choices and the resulting correlations are relevant, so they cannot be considered separated. They are quantum nonlocal, whereby separation in space and time are not a factor. Alice, Bob, and the 2 entangled particles form a context.

 

[Paul Colby]

So... no, you are not clear and I don't agree at all with your assessment as you are saying quite the opposite.

I'm always willing to learn if you have the stamina. So help me out. Bob's result on a given particle determines the particle state Alice's particle will be in. Knowing this state, Bob may predict within the ability of QM Alice's outcome. There is nothing in the formalism, however, to suggest that Alice's measurement on said particle would not have yielded the very same result even if Bob's measurement was never made. In fact, all the data would suggest Bob's measurement doesn't have an affect. So in what sense can one claim that Bob's measurement affects or changes Alice's?

a. But that is not true with the QM formalism, something that had actually been missed previously.

This would indicate I truly don't understand. Yet, what in the above is wrong?

 

[DrChinese]

There is nothing in the formalism, however, to suggest that Alice's measurement on said particle would not have yielded the very same result even if Bob's measurement was never made. In fact, all the data would suggest Bob's measurement doesn't have an affect.

There is EVERYTHING that indicates it does! The problem is you are looking at VERY special cases that cloud your viewpoint - same angle on both sides. You must look at the other cases that tear your idea down.

1. Consider a pair of Type I PDC entangled photons, these will have the *same* polarization (measured at any given angle). Consider their polarization at 3 angles: 0, 120 and 240 degrees. In this case, anytime Alice and Bob pick different angles (of the 3), there is a 25% chance of a match. That's because the relative difference (theta) of their measurement angles is always 120 degrees. cos^2(120 degrees) is 25%. If you look at the permutations, you will see that this value cannot be arrived at by ANY mechanism other than the outcome being dependent on *both* angles. It cannot be independently arrived at. If you do a series of trials and hand pick numbers that make it be 25%, you will realize you have cheated and knew the other's choice. So that defeats your premise. You MUST work it through to see this.

2. Same as above, with this twist: the photons can be entangled after they have already been detected. And by they way, they were never even in contact during their existence. This cannot be explained by saying "oh it's just a quantum analogy to the gyroscopes and Bell doesn't apply". Obviously there is quantum nonlocality, which as I said is not limited by time or space separation.

 

[Paul Colby]

There is EVERYTHING that indicates it does! The problem is you are looking at VERY special cases that cloud your viewpoint - same angle on both sides. You must look at the other cases that tear your idea down.

I need to go through your post carefully to be certain I do understand. This may take time. That said, I don't think you are reading what I'm saying (yes I'm aware of the reciprocal issue). I'm very much not assuming anything about Alice's measurement or the angle of her SG in the above. Once Bob knows the QM state of Alice's particle, he may predict the statistical outcome of Alice's measurements. I have consistently said this to no effect. I also asked a question which is not negated by any angle assumptions you think I'm making. In what sense has Bob's measurements been shown to effect Alice's? The answer appears to be not at all in the example I've given. I think the rebuttal to this will be the Bell relation which assumes a classical probability relation which is simply wrong, expects otherwise.

Let me ponder your photon case and I'll get back to you.

 

[DrChinese]

I need to go through your post carefully to be certain I do understand. This may take time. That said, I don't think you are reading what I'm saying (yes I'm aware of the reciprocal issue). I'm very much not assuming anything about Alice's measurement or the angle of her SG in the above. Once Bob knows the QM state of Alice's particle, he may predict the statistical outcome of Alice's measurements. I have consistently said this to no effect. I also asked a question which is not negated by any angle assumptions you think I'm making. In what sense has Bob's measurements been shown to effect Alice's? The answer appears to be not at all in the example I've given. I think the rebuttal to this will be the Bell relation which assumes a classical probability relation which is simply wrong, expects otherwise.

Let me ponder your photon case and I'll get back to you.

If you do not already know what I am talking about (regarding angle settings), then you definitely have a few things to learn. You may as well be denying that the squares of the sides of a right triangle have a relationship to the hypotenuse. This is what Bell discovered that had been overlooked by EPR and everyone else for decades.

Bell merely assume about the same as you do - that there is outcome independence (also parameter independence but that is another story). There isn't. The statistics would be different if there were. The fact is, Bob does NOT know anything about Alice's measurement basis when he makes his. That is the experimental situation. So how does he know to have an outcome consistent with Alice?

 

[Paul Colby]

So how does he know to have an outcome consistent with Alice?

I don't see a problem here. By symmetry both Alice and Bob's result happen on each particle independently of the other. For non-aligned SG the statistics are then dictated by the single particle particle state deduced by Bob's (or Alice's) measurement. With or without this additional information neither Alice or Bob's measurements are changed or affected by the outcome of the others measurement (or lack of one). My understanding is that Bell disqualifies a classical mechanism for correlation which is good because it's a QM world according to all experiments to date. So, why is it people feel compelled to accept the Bell criterion as an accurate description of how the world should work? The fact that it doesn't work that way would seem to make my somewhat traditional QM views even more warranted.

 

[Paul Colby]

The long digression on Bell was undertaken when it was suggested that the EPR was an example of something happening instantaneously. The goal of my side of this discussion was to point out that while Bob may learn something about Alice's particle neither experimenter causes or affects the other "instantaneously". This appears to be a fact in the sense that one like myself defines cause or affect. This is not an issue I should try to resolve here.

 

[nortonian]

Once Bob knows the QM state of Alice's particle, he may predict the statistical outcome of Alice's measurements.

I have been following this discussion and think the differences may hinge on the question of what can be known about a system?

Classical measurements assume the possibility of perfect knowledge of a system, while QM measurements allow only knowledge of the wave function. If we try to say that Bob can predict Alice's statistics once he performs measurements on his own system then aren't we trying to turn a QM measurement/experiment into a classical one by going backward in time to obtain information? After all, the polarization angle depends on the photons not how we measure it.

 

[Paul Colby]

If we try to say that Bob can predict Alice's statistics once he performs measurements on his own system then aren't we trying to turn a QM measurement/experiment into a classical one by going backward in time to obtain information?

I'm not aware of attempting any such classical ploy. Knowing Alice's single particle wave function permits Bob to "predict" the statistics of Alice's measurement. This is all my arguments relied on. I think it's note worthy that Alice's and Bob's concept of the wave function (after Bob's measurement) of each particle are completely different, yet they both get the expected statistics based on that knowledge. Multiple wave functions may be assigned by multiple experimenters to a given system based on their knowledge. Wave functions are by no means unique in this sense.

In any event knowledge or information is not a cause in this case that is instantaneously conveyed.