Curious about an idea of a modified polariser to send signals with QE

[Nugatory]

man that's really mind-bending

Do remember that quantum mechanics is not a theory about what’s going on, it’s a theory about measurement results. QM says “these are the outcomes we’ll see if we look”, not “this is what is happening”.

 

[tade]

Do remember that quantum mechanics is not a theory about what’s going on, it’s a theory about measurement results. QM says “these are the outcomes we’ll see if we look”, not “this is what is happening”.

yeah that's true, though I was also thinking that Bell's theorem was to decide the issue of locality and spooky action at a distance

by the way just wondering is it you in your profile pic, at first glance I thought it was something like Hugh Laurie playing a physicist lol

 

[vanhees71]

Bell's theorem is about the properties of local realistic theories, where locality has the standard meaning of relativistic physics, i.e., that there cannot be causal connections between space-like separated events, particularly there cannot be a causal influence of one measurement at another measurement, where the measurement events (e.g., the registration of two photons at far-distant places by detectors) are space-like separated. "Reality" means that the theory assumes that all observables take always determined values, which may be unknown due to the inobservabality of some "hidden variables".

Now by construction the usual relativistic QFTs are "local", i.e., all operators representing local observables commute at space-like distance between their arguments. Particularly any such local observable operator commutes with the Hamilton density at space-like separated arguments, which implies that there cannot be FTL signals of any kind. At the same time these QFTs are not "realistic" in Bell's sense, because as any QT there's no "dispersion free state", i.e., in any state you may prepare any quantum system in there are observables that do not take a determined value. E.g., if you prepare a photon to be horizontally polarized in wrt. to some direction, it's polarization state wrt. another non-collinear direction is indetermined.

Bell's inequality, derived from the assumption of a "local realistic HV theory", is predicted to be violated within QT (including its realization of a relativistic local QFT), and thus the question, whether there's a local realistic HV theory that explains all observable facts or whether this is the case for QT can be decided by experiment, and this has been done over the last 40 years with the unanimous result that QT delivers the correct description, while any local realistic HV theory fails to do so. That's the content of the work of the three Nobel Laureats of this year.

 

[tade]

Bell's inequality, derived from the assumption of a "local realistic HV theory", is predicted to be violated within QT (including its realization of a relativistic local QFT), and thus the question, whether there's a local realistic HV theory that explains all observable facts or whether this is the case for QT can be decided by experiment, and this has been done over the last 40 years with the unanimous result that QT delivers the correct description, while any local realistic HV theory fails to do so. That's the content of the work of the three Nobel Laureats of this year.

 

[vanhees71]

I'm not sure, whether this statement is really what Clauser (or any other physicist working with quantum theory) wants to say, because of course Clauser very well understands quantum mechanics (and for sure also QT in general, i.e., including relativistic QFT), because he has been able to use it to plan and do his seminal experiment in relation to Bell's theoretical proposal. I think there's not more to understand about a physical theory than what it predicts for real-world observations of Nature, and if you even can use it to plan and do a very dedicated experiment testing its very foundations, that's proof of a very deep understanding of its implications.

What he perhaps means is the difficulty to understand that there's "irreducible randomness" in nature, i.e., that the outcome of the measurement of an observable which is indetermined due to the state the measured system is prepared in is not in some way predetermined but just unknown and how it comes that when measuring an observable we get a well-defined outcome although there's nothing predetermining this outcome, but that's precisely what QT implies and what this year's Nobel laureats (and many more) have unambigously demonstrated with their experiments. So it's not so much a lack of understanding of quantum theory as a scientific theory but the difficulty to accept this "irreducible randomness" implied by its formalism.

It's in the nature (pun intended) of the natural sciences that its methods tells us how nature behaves, even if this behavior is against our intuition based on our very limited experience of the "everyday world". For many people in the renaissance it was "incomprehensible" how it could be that the Earth moves around the Sun, which contradicts our experience that we and the Earth "are at rest" and the Sun moves in a very regular way.

 

[tade]

I'm not sure, whether this statement is really what Clauser (or any other physicist working with quantum theory) wants to say, because of course Clauser very well understands quantum mechanics (and for sure also QT in general, i.e., including relativistic QFT), because he has been able to use it to plan and do his seminal experiment in relation to Bell's theoretical proposal. I think there's not more to understand about a physical theory than what it predicts for real-world observations of Nature, and if you even can use it to plan and do a very dedicated experiment testing its very foundations, that's proof of a very deep understanding of its implications.

What he perhaps means is the difficulty to understand that there's "irreducible randomness" in nature, i.e., that the outcome of the measurement of an observable which is indetermined due to the state the measured system is prepared in is not in some way predetermined but just unknown and how it comes that when measuring an observable we get a well-defined outcome although there's nothing predetermining this outcome, but that's precisely what QT implies and what this year's Nobel laureats (and many more) have unambigously demonstrated with their experiments. So it's not so much a lack of understanding of quantum theory as a scientific theory but the difficulty to accept this "irreducible randomness" implied by its formalism.

It's in the nature (pun intended) of the natural sciences that its methods tells us how nature behaves, even if this behavior is against our intuition based on our very limited experience of the "everyday world". For many people in the renaissance it was "incomprehensible" how it could be that the Earth moves around the Sun, which contradicts our experience that we and the Earth "are at rest" and the Sun moves in a very regular way.

I think what Clauser means is that he finds it hard to comprehend that spooky action at a distance is real

 

[PeterDonis]

I think what Clauser means is that he finds it to comprehend that spooky action at a distance is real

Such statements don't say anything useful, because they're about the definitions of words rather than physics.

The physics is that the Bell inequalities are violated in experiments on entangled particles.

If you define "spooky action at a distance" to mean "the Bell inequalities are violated", then of course "spooky action at a distance" is "real" because the Bell inequality violations are real; they're right there in the data.

But then saying "spooky action at a distance is real" is just another way of saying "the Bell inequalities are violated". It conveys no additional information. But it has much greater potential for confusion because people are much more likely to read other connotations into "spooky action at a distance" than they are into "Bell inequality violations", and to be led into claims that are not justified by the physics, or to misunderstand what the physics actually says and does not say.

 

[tade]

Such statements don't say anything useful, because they're about the definitions of words rather than physics.

The physics is that the Bell inequalities are violated in experiments on entangled particles.

If you define "spooky action at a distance" to mean "the Bell inequalities are violated", then of course "spooky action at a distance" is "real" because the Bell inequality violations are real; they're right there in the data.

But then saying "spooky action at a distance is real" is just another way of saying "the Bell inequalities are violated". It conveys no additional information. But it has much greater potential for confusion because people are much more likely to read other connotations into "spooky action at a distance" than they are into "Bell inequality violations", and to be led into claims that are not justified by the physics, or to misunderstand what the physics actually says and does not say.

hmm I was thinking that the view is that the Bell inequalities are violated due to spooky action at a distance

 

[PeterDonis]

I was thinking that the view is that the Bell inequalities are violated due to spooky action at a distance

But that would require "spooky action at a distance" to be something other than "Bell inequality violations". What other something would that be? Look through the physics literature, and you will not find any such thing. You will find lots of vague talk, but nothing in the actual physics. The actual physics is just that the Bell inequalities are violated in measurements on entangled particles. That's it.

 

[tade]

But that would require "spooky action at a distance" to be something other than "Bell inequality violations". What other something would that be? Look through the physics literature, and you will not find any such thing. You will find lots of vague talk, but nothing in the actual physics. The actual physics is just that the Bell inequalities are violated in measurements on entangled particles. That's it.

Could that other something be the entanglement itself, even though no scientist has as of yet been able to delve deeper into how it might work

 

[PeterDonis]

Could that other something be the entanglement itself

Then you have just defined "spooky action at a distance" as "entanglement". Still doesn't give any useful information that we didn't already have.

 

[tade]

Then you have just defined "spooky action at a distance" as "entanglement". Still doesn't give any useful information that we didn't already have.

hmm well I was just thinking that Clauser still can't wrap his mind around spooky action, despite having just won a Nobel for it lol, as he was originally spurred by his desire to disprove quantum mechanics and prove Einstein correct
though I think that its pretty cool that the universe and nature turned out this way, the QM way

 

[PeterDonis]

he was originally spurred by his desire to disprove quantum mechanics and prove Einstein correct

I'm not sure what you mean by this. Einstein never said QM was incorrect. He only said it was incomplete. If Einstein could have read Bell's papers, he would have agreed at once that QM predicts that the Bell inequalities are violated, and he would have expected actual experiments to bear that out.

 

[tade]

I'm not sure what you mean by this. Einstein never said QM was incorrect. He only said it was incomplete. If Einstein could have read Bell's papers, he would have agreed at once that QM predicts that the Bell inequalities are violated, and he would have expected actual experiments to bear that out.

oh that's interesting, whether or not Einstein would have been hoping that the experimental results would conform to his "pair of gloves" analogous model, certainly that's what Clauser was hoping for

 

[PeterDonis]

certainly that's what Clauser was hoping for

Meaning, Clauser expected the experiments not to match the predictions of QM? Do you have a reference for that? I'm not aware of any physicist who expected that.

 

[tade]

Meaning, Clauser expected the experiments not to match the predictions of QM? Do you have a reference for that? I'm not aware of any physicist who expected that.

oh, as in, I'm not sure what he was expecting, though he was hoping that the results wouldn't match the predictions of QM

 

[PeterDonis]

he was hoping that the results wouldn't match the predictions of QM

"Hoping" in the sense of being saddened when the results did match the predictions of QM, I take it.

 

[tade]

"Hoping" in the sense of being saddened when the results did match the predictions of QM, I take it.

yeah exactly, as the screenshot above says, "I was again very saddened that I had not overthrown quantum mechanics"

 

[vanhees71]

I think what Clauser means is that he finds it hard to comprehend that spooky action at a distance is real

But within relativistic microcausal QFT by construction there are no spooky actions at a distance, only long-ranged correlations between parts of an entangled quantum system.

 

[vanhees71]

Then you have just defined "spooky action at a distance" as "entanglement". Still doesn't give any useful information that we didn't already have.

Yes, and entanglement is a property of the state, i.e., of the preparation procedure on a quantum system and as such it does not describe interactions but correlations and that's why, within relativistic microcausal QFT, there's no violation of causality, because the correlations are not due to some "spooky action at a distance" (i.e., a faster-than-light influence among two space-like separated "measurement events").

 

[tade]

But within relativistic microcausal QFT by construction there are no spooky actions at a distance, only long-ranged correlations between parts of an entangled quantum system.

though i think there's the question of how they get correlated at a long-range within a very short duration, for example the lower bound of the "entanglement speed" being 10,000c

 

[vanhees71]

They get correlated through the preparation procedure. E.g., to have two photons in an entangled state you can use parametric downconversion and select only entangled pairs, i.e., these two photons moving in different directions are all the time entangled until they are detected, and the detection events can be as far as you like. As long there's no interaction of the photons on their way to the detector you'll just measure the strong correlations (of their polarization) which are there all the time since the photons have been created.

 

[tade]

these two photons moving in different directions are all the time entangled until they are detected, and the detection events can be as far as you like. As long there's no interaction of the photons on their way to the detector you'll just measure the strong correlations (of their polarization) which are there all the time since the photons have been created.

hmm that does sound like spooky action at a distance lol

 

[vanhees71]

Why should this be spooky action at a distance? The photons have been created by a local action, e.g., when using parametric down-conversion the interaction of a laser beam with a BBO.

 

[tade]

Why should this be spooky action at a distance? The photons have been created by a local action, e.g., when using parametric down-conversion the interaction of a laser beam with a BBO.

as in, hmm, maybe you can elaborate on the part about the photons being all the time entangled

 

[vanhees71]

You create two photons in an entangled state, like
$$|\Psi \rangle=\frac{1}{\sqrt{2}} [\hat{a}^{\dagger}(\vec{p}_1,h=1) \hat{a}^{\dagger}(\vec{p}_2,h=-1) -\hat{a}^{\dagger}(\vec{p}_1,h=-1) \hat{a}^{\dagger}(\vec{p}_2,h=1)]|\Omega \rangle.$$
If neither of the photons interact with anything, they stay in this state forever.

 

[tade]

You create two photons in an entangled state, like
$$|\Psi \rangle=\frac{1}{\sqrt{2}} [\hat{a}^{\dagger}(\vec{p}_1,h=1) \hat{a}^{\dagger}(\vec{p}_2,h=-1) -\hat{a}^{\dagger}(\vec{p}_1,h=-1) \hat{a}^{\dagger}(\vec{p}_2,h=1)]|\Omega \rangle.$$
If neither of the photons interact with anything, they stay in this state forever.

oh i see, and i was thinking that if both are measured in quick succession, as both are entangled, there could be the spooky action at a distance

 

[PeterDonis]

there could be the spooky action at a distance

This phrase is meaningless unless you define what, in the actual math, it corresponds to. So far we have had two possible definitions: violation of the Bell inequalities, and entanglement of the two photons. Neither of these seems to be what you mean, but you seem unable to give any other definition. If that is the case, there is probably no point in continuing this thread, since the actual physics has already been discussed in some detail.

 

[tade]

This phrase is meaningless unless you define what, in the actual math, it corresponds to. So far we have had two possible definitions: violation of the Bell inequalities, and entanglement of the two photons. Neither of these seems to be what you mean, but you seem unable to give any other definition. If that is the case, there is probably no point in continuing this thread, since the actual physics has already been discussed in some detail.

maybe another notion would be one photon sending info to the other photon instantaneously across a great distance

and i would also like to ask about taking a look at any literature on the the maths and mechanics of the situation at the moment when the wave encounters the molecules of the polariser, the interaction of the target particle with the polariser molecules, like the photon-polariser interactions at the quantum-molecular level, or also the maths of the transition when and as the wavefunction is collapsing as it encounters and interacts with the molecules of the polariser

though yeah i think some of the parts might not have existent literature as of yet

 

[PeterDonis]

maybe another notion would be one photon sending info to the other photon instantaneously across a great distance

I said something in the actual math. I did not say whatever your imagination can dream up.

i would also like to ask about taking a look at any literature on the the maths and mechanics of the situation at the moment when the wave encounters the molecules of the polariser, the interaction of the target particle with the polariser molecules, like the photon-polariser interactions at the quantum-molecular level, or also the maths of the transition when and as the wavefunction is collapsing as it encounters and interacts with the molecules of the polariser

This is well beyond the scope of a single PF thread. Basically you are asking for a complete course in quantum measurement techniques and solid state physics.

The thread topic has been sufficiently discussed and personal speculation is off limits here at PF. Thread closed.