crowded quantum information

[Eise]

Hi Joigus,

No, I do not want to take the deep dive into the principles of the so-called 'quantum teleportation'. AFAIK, Zeilinger was the first experimentally proving that it is possible. I do not quite understand it, and I will not spend my mind energy on that now. I mentioned it, because I suppose that Bangstrom's idea of 'identity swapping' comes from these experiments, and not from entanglement experiments 'an sich'. It is an application of entanglement.

[Mitcher]

I have re-read all this discussion with extreme interest and it seems that pretty much everything has been possibly said about non-locality, sometimes even a few times. There are obviously some competent and very patient people here taking the time to explain carrefully and i certainly do not intend to start it all again, however if the explanation for decoherence and a supposed non-locality is something as trivial as the analogy with the coin, the question that comes to mind is why did Einstein and followers up to this day had to use complicated notions as action at a distance, collapse of an unphysical wave function etc.. This is what puzzles me now and because I understood completely every objections made by Bangstrom here, given that I had exactly the same prejudices resulting from all my previous readings. Is it because those QM pionneers had not competely understood those phenomena ? Even today there seem to be quite a few opposed QM schools, local realism being just one of them. Is that part of the situation ?

[joigus]

1 hour ago, Mitcher said:

I have re-read all this discussion with extreme interest and it seems that pretty much everything has been possibly said about non-locality, sometimes even a few times. There are obviously some competent and very patient people here taking the time to explain carrefully and i certainly do not intend to start it all again, however if the explanation for decoherence and a supposed non-locality is something as trivial as the analogy with the coin, the question that comes to mind is why did Einstein and followers up to this day had to use complicated notions as action at a distance, collapse of an unphysical wave function etc.. This is what puzzles me now and because I understood completely every objections made by Bangstrom here, given that I had exactly the same prejudices resulting from all my previous readings. Is it because those QM pionneers had not competely understood those phenomena ? Even today there seem to be quite a few opposed QM schools, local realism being just one of them. Is that part of the situation ?

Here's the problem with the coins if you want to understand quantum mechanics with them. There is an observable with two possible outcomes, and the corresponding eigenstates. States are 2x1 matrices:

\[ \left|\textrm{heads}\right\rangle =\left(\begin{array}{c} 1\\ 0 \end{array}\right) \]

\[ \left|\textrm{tails}\right\rangle =\left(\begin{array}{c} 0\\ 1 \end{array}\right) \]

Yes-no questions are 2x2 matrices that satisfy that their square equals itself. In the case of heads/tails,

\[ \left(\textrm{heads?}\right)=\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right) \]

\[ \left(\textrm{tails?}\right)=\left(\begin{array}{cc} 0 & 0\\ 0 & 1 \end{array}\right) \]

Meaning of squaring the matrix (repeating the question):

\[ \textrm{Is it still heads?}=\left(\textrm{heads?}\right)\left(\textrm{heads?}\right)=\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right)\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right)=\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right) \]

\[ \textrm{Is it heads when state is "heads"?}=\left(\textrm{heads?}\right)\left|\textrm{heads}\right\rangle =\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right)\left(\begin{array}{c} 1\\ 0 \end{array}\right)=\left(\begin{array}{c} 1\\ 0 \end{array}\right)=\left(\textrm{yes}\right)\left|\textrm{heads}\right\rangle \]

Etc.

Incompatible questions. Suppose we introduce a question that's incompatible with the questions “is it heads/tails”?

\[ \left(\textrm{Euro?}\right)=\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right) \]

\[ \left(\textrm{Dollar?}\right)=\left(\begin{array}{cc} 0 & 0\\ 0 & 1 \end{array}\right) \]

But hang on. This looks like the same questions. Indeed. The new question, in the so-called Dollar/Euro representation, looks like this,

\[ \textrm{Is it Euro when state is "Dollar"?}=\left(\textrm{Euro?}\right)\left|\textrm{Dollar}\right\rangle =\left(\begin{array}{cc} 1 & 0\\ 0 & 0 \end{array}\right)\left(\begin{array}{c} 0\\ 1 \end{array}\right)=\left(\begin{array}{c} 0\\ 0 \end{array}\right)=0\left(\begin{array}{c} 0\\ 1 \end{array}\right)=\left(\textrm{no}\right)\left|\textrm{Dollar}\right\rangle \]

What's hopefully illuminating is asking the (Dollar/Euro) question in the (Heads/Tails) representation. Here's how QM does it:

\[ \left(\textrm{Euro?}\right)=\left(\begin{array}{cc} \frac{1}{2} & \frac{1}{2}\\ \frac{1}{2} & \frac{1}{2} \end{array}\right) \]

\[ \left(\textrm{Euro?}\right)\left(\textrm{Euro?}\right)=\left(\begin{array}{cc} \frac{1}{2} & \frac{1}{2}\\ \frac{1}{2} & \frac{1}{2} \end{array}\right)\left(\begin{array}{cc} \frac{1}{2} & \frac{1}{2}\\ \frac{1}{2} & \frac{1}{2} \end{array}\right)=\left(\begin{array}{cc} \frac{1}{2} & \frac{1}{2}\\ \frac{1}{2} & \frac{1}{2} \end{array}\right) \]

\[ \left(\textrm{Dollar?}\right)=\left(\begin{array}{cc} \frac{1}{2} & -\frac{1}{2}\\ -\frac{1}{2} & \frac{1}{2} \end{array}\right) \]

\[ \left(\textrm{Dollar?}\right)\left(\textrm{Dollar?}\right)=\left(\begin{array}{cc} \frac{1}{2} & -\frac{1}{2}\\ -\frac{1}{2} & \frac{1}{2} \end{array}\right)\left(\begin{array}{cc} \frac{1}{2} & -\frac{1}{2}\\ -\frac{1}{2} & \frac{1}{2} \end{array}\right)=\left(\begin{array}{cc} \frac{1}{2} & -\frac{1}{2}\\ -\frac{1}{2} & \frac{1}{2} \end{array}\right) \]

\[ \left(\textrm{Euro?}\right)\left(\textrm{Dollar?}\right)=\left(\begin{array}{cc} \frac{1}{2} & \frac{1}{2}\\ \frac{1}{2} & \frac{1}{2} \end{array}\right)\left(\begin{array}{cc} \frac{1}{2} & -\frac{1}{2}\\ -\frac{1}{2} & \frac{1}{2} \end{array}\right)=\left(\begin{array}{cc} 0 & 0\\ 0 & 0 \end{array}\right) \]

Wait a minute. What happens when the state is, eg, | heads 〉 , but we ask ( Euro? ) . Let's see,

\[ \textrm{Is it Euro when state is "heads"?}=\left(\textrm{Euro?}\right)\left|\textrm{heads}\right\rangle =\left(\begin{array}{cc} \frac{1}{2} & \frac{1}{2}\\ \frac{1}{2} & \frac{1}{2} \end{array}\right)\left(\begin{array}{c} 1\\ 0 \end{array}\right)=\left(\begin{array}{c} \frac{1}{2}\\ \frac{1}{2} \end{array}\right)=\frac{1}{2}\left|\textrm{heads}\right\rangle +\frac{1}{2}\left|\textrm{tails}\right\rangle \]

It mixes the answers in heads/tails. IOW, the coin is no longer heads. This all happens without me having even started talking about position. Space is even just one point for all I've claimed.

What if you represent the outcome in the Dollar/Euro representation? You would obtain a state that's a linear superposition of \( \left|\textrm{Dollar}\right\rangle \) and \( \left|\textrm{Euro}\right\rangle \) –with a minus relative sign, if I remember correctly, but it would be a simple exercise to get the details. IOW: When the coin is “heads,” it's neither a Dollar, nor a Euro. You get me a coin that does that, and we would take the conversation from there with just coins.

Edited September 30, 2022 by joigus
Latex editing

[swansont]

1 hour ago, Mitcher said:

the question that comes to mind is why did Einstein and followers up to this day had to use complicated notions as action at a distance, collapse of an unphysical wave function etc..

You might recall that Einstein said god did not play dice with the universe. He did not embrace the probabilistic nature of QM, so hanging on to a classical notion that there must be an interaction between these particles isn't all that surprising to me.

The EPR paper was also well before the door closed on hidden variables, so this might play a part in the mindset.

[joigus]

1 hour ago, joigus said:

What if you represent the outcome in the Dollar/Euro representation? You would obtain a state that's a linear superposition of |Dollar〉 and |Euro〉 –with a minus relative sign, if I remember correctly, but it would be a simple exercise to get the details.

Correcting myself. You would obtain a state that's only 1/2 probability of being "Dollar"

If you ask the question Euro?, you obtain a state that's only 1/2 probability of being "Euro"

So, again, the conclusion is that when a state is "sharp" in one observable, it's "fuzzy" in non-compatible ones.

Just in case someone's doing the calculations and fixing on what I said too literally.

After all, projections are just an instrument to calculate probabilities, they don't tell you what happens to the quantum state after a measurement. This is very much in agreement with what seems to be the conclusion of the paper that @Eise posted:

Quote

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

with detectors that are moving with respect to each other at constant velocity. As I already said:

On 9/25/2022 at 12:40 AM, joigus said:

The only thing that looks non-local is Copenhagen's old projection postulate, that require you to kill off all the components of the wave function that are ruled out by a measurement. But it is incompatible with the Schrödinger equation. So people don't believe it anymore.

 

 

[hoola]

I have  breezed through the many pages of what I did not expect to see generated by my "crowded quantum" question, but the topic was not about "standard" QM and the normal questions associated to that, but the possibility of directly modifying specific particle pairs, thus creating a communications pathway by allowing an additional degree of freedom not present in normal matter, while at the same time not affecting normal entanglement properties of these prepared particles.  A sort of manipulation of larger clumps of matter can now be done with nanomaterials, and if all matter is composed of mathematics, why can't those basic building blocks someday be modified directly and alter reality at a "nanomathematical" (sub plankian) scale for specific purposes?

Edited October 1, 2022 by hoola

[joigus]

2 hours ago, hoola said:

I have  breezed through the many pages of what I did not expect to see generated by my "crowded quantum" question, [...]

IMO, all hell broke loose when you said,

On 9/9/2022 at 10:14 PM, hoola said:

it does seem that there is a faster than light signalling with quantum entanglement issues, but that it cannot transfer any signal other than the basics used to determine a static outcome.

(My emphasis.) You seem to insist on things like,

3 hours ago, hoola said:

thus creating a communications pathway by allowing an additional degree of freedom not present in normal matter,

Creating a communications pathway is precisely what is not possible. Also, all the degrees of freedom are present in normal matter and/or light. And then, you go on to say,

3 hours ago, hoola said:

while at the same time not affecting normal entanglement properties of these prepared particles.

If you use the channel so as to in any way break the coherence by interacting with it, the system is no longer entangled. In a manner of speaking, you have "selected" a subcomponent of the previous quantum state, thus destroying the richness of correlations it was packaging.

You also say the topic "is not about standard quantum mechanics." What other kind of quantum mechanics is it about?

When the system was prepared, it was correlated in any possible direction that you chose for the polarisers. If you set up a polariser, it is no longer entangled, but now you can predict something about the distant part. If you further deflect/filter any of the beams, it is no longer correlated at all, let alone entangled. What do you want to do with that?

Most anything you do ends up destroying the peculiar quantum correlations, and you get closer and closer to the classical description. Not totally, because you still see a binary observable, which is not covered by classical mechanics for spinning object. But you no longer have the effects of entanglement.

I hope that helps further clarify the discussion, but without us all getting muddled up into fantasy physics.

[bangstrom]

On 9/30/2022 at 6:11 AM, Eise said:

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.

This is a highly irregular statement. QM permits superluminal signaling, and ‘signaling’ is a word frequently used. The classical view does not permit superluminal signaling.

What are you saying about the superluminal nature of the transaction or non-signal signaling or whatever you choose to call it? The timing of the ‘whatever’ has been frequently measured in experiments to be superluminal so how can you claim superluminal is an illusion?

22 hours ago, joigus said:

Quantum teleportation' is a very bad name for what it actually is: 

What is quantum teleportation actually? If you tried to explain it before, that wasn't even close.

[joigus]

45 minutes ago, bangstrom said:

This is a highly irregular statement. QM permits superluminal signaling, and ‘signaling’ is a word frequently used. The classical view does not permit superluminal signaling.

What are you saying about the superluminal nature of the transaction or non-signal signaling or whatever you choose to call it? The timing of the ‘whatever’ has been frequently measured in experiments to be superluminal so how can you claim superluminal is an illusion?

What is quantum teleportation actually? If you tried to explain it before, that wasn't even close.

If a person who doesn't really understand English very well overhears a conversation in English, and hears the words "red herring" he may be at risk of thinking these people are talking about a rare species of fish.

That's similar to what's happening to you here. I'm sorry, you have proven to be a monumental loss of time to me.

Many posts ago I introduced an example designed to illustrate that even classical physics can mislead you to the wrong conclusion if you hear an argument and, loosely, poorly, wrongly, interpret it in terms of just the words, drawing loose inferences from them. You (1st) missed the point, and (2nd) offered an analysis of the physical example --totally wrong, by the way.

I'll finish with a clue for what may come next: Keep track of the phase changes in the components of the wave function, and the essential difference between closed quantum systems and open quantum systems, because I intuit that's what's confusing you, and many other people with you.

@Eisewas totally right when he said that the illusion of superluminal signals only appears because one wants to understand what is happening from a classical viewpoint.

I would add (repeat for the n^th time really) that there's a second possible source of illusion of superluminal character that comes from the (valid for-all-practical-purposes --FAPP--, but fundamentally flawed, in Bell's words) projection postulate.

 

1 hour ago, bangstrom said:

What are you saying about the superluminal nature of the transaction or non-signal signaling or whatever you choose to call it? The timing of the ‘whatever’ has been frequently measured in experiments to be superluminal so how can you claim superluminal is an illusion?

23 hours ago, joigus said:

I have two eyes. You have two eyes. The event that determined the astonishingly[?] precise correlation is far back in the past, somewhere in the pre-Cambrian seas, when the first animals developed eyes. You can measure the correlation between those facts with as much precision as you want here and in Andromeda. There is no limit to how "superluminal" this looks if you keep calling that a signal.

Do you understand now? Is that clear now? Will we be talking about this totally trivial point forever?

Edited October 1, 2022 by joigus
minor addition

[Eise]

2 hours ago, bangstrom said:

This is a highly irregular statement. QM permits superluminal signaling, and ‘signaling’ is a word frequently used. The classical view does not permit superluminal signaling.

OK, I will cite a few lines from Leonard Susskind's Theoretical Minimum: Quantum mechanics. First he makes a mathematical derivation, that is of course is over my head, but the end conclusion is clear:

Quote

Nothing that happens at Bob's end has any immediate effect on Alice's density matrix, even if Bob and Alice are maximally entangled. This means that Alice's view of her subsystem (her statistical model) remains exactly as it was. This remarkable result may seem surprising for a maximally entangled system, but it also guarantees that no faster-than-light signal has been sent.

With other words, QM does not need faster than light signals to explain entanglement, and QM obeys this speed limit. Recognise what Gell-Mann said in the video that Joigus linked.

Then Susskind presents a setup with two computers, that each for themselves simulate quantum spin measurements, which is not impossible, if the random generator is good enough. However, he shows that in order to simulate entanglement, a faster then light connection is needed.
 

Quote

But doesn't this mean that locality-violating information can be sent through the cable? It would, if Alice, Bob and Charly were allowed to do anything that non-relativistic classical systems can do, in other words, systems that permit signals to be instantly. But if the only operations that are allowed are those that simulate quantum operations, then the answer is no. As we've seen, quantum mechanics does not allow Alice's density matrix to be affected by Bob's actions.

   This is not a problem for quantum mechanics. It is a problem for simulating quantum mechanics with a classical boolean computer. That is the content of Bell's theorem: The classical computers have to be connected with an instantaneous cable to simulate entanglement.

(Italics in the original).

So now you can do three things:

• show that Susskind made an error in his math
• stick your head in the sand
• or accept what one of great QM specialists is saying here.

For me, I accept Susskind's, Gell-Manns (and Swansont's, and Joigus', and MigL's) position, even if I cannot follow the math. So I take the argument of authority. Such arguments are valid, when it is clear that Susskind and Gell-Mann are absolute 'quantum experts'. Just to give an idea of Gell-Mann: he predicted the existence of the Omega-minus particle, and is one of the fathers of the quark model of hadrons. I think for him this topic would be basic QM...

2 hours ago, bangstrom said:

The timing of the ‘whatever’ has been frequently measured in experiments to be superluminal so how can you claim superluminal is an illusion?

Because QM is right: the 'superluminal correlation' is only needed when you want to understand entanglement classically.

Edited October 1, 2022 by Eise
a few language errors

[hoola]

joigus....I agree that communication via entanglement is impossible now, only that a technical solution might change that in the future, and speculate that if the sub structure of everything is math, that is the key to achieve a technical solution. 

[joigus]

2 hours ago, hoola said:

joigus....I agree that communication via entanglement is impossible now, only that a technical solution might change that in the future, and speculate that if the sub structure of everything is math, that is the key to achieve a technical solution. 

I'm not looking for agreement. I'd rather you disagreed with me, or bangstrom, or any other, as long as you provided an argument for the particular point in QM where you see this possibility of superluminal communication, or instantaneous interaction, or what have you.

On what grounds do you agree that "communication via entanglement is impossible now"?

Are you saying that communication via entanglement will be possible without superseding QM with some other theory that is non-local?

Notice, please, what I'm not saying: I'm not saying that communication via a quantum channel --whether it involves entanglement or otherwise-- is impossible. It's only that whatever communication channel will be subject to the strictures of local, sub-luminal propagation. Unless we come up with a theory that substantially changes quantum mechanics, and ushers in a new era with the possibility of superluminal propagation. Such a new theory would also have to explain why we've never observed it so far. Then, it would have to explain: How come relativistic causality is not violated?

[Mitcher]

On 9/30/2022 at 6:41 PM, joigus said:

Here's the problem with the coins if you want to understand quantum mechanics with them. There is an observable with two possible outcomes, and the corresponding eigenstates. States are 2x1 matrices:

|heads〉=(10)

|tails〉=(01)

Yes-no questions are 2x2 matrices that satisfy that their square equals itself. In the case of heads/tails,

(heads?)=(1000)

(tails?)=(0001)

Meaning of squaring the matrix (repeating the question):

Is it still heads?=(heads?)(heads?)=(1000)(1000)=(1000)

Is it heads when state is "heads"?=(heads?)|heads〉=(1000)(10)=(10)=(yes)|heads〉

Etc.

Incompatible questions. Suppose we introduce a question that's incompatible with the questions “is it heads/tails”?

(Euro?)=(1000)

(Dollar?)=(0001)

But hang on. This looks like the same questions. Indeed. The new question, in the so-called Dollar/Euro representation, looks like this,

Is it Euro when state is "Dollar"?=(Euro?)|Dollar〉=(1000)(01)=(00)=0(01)=(no)|Dollar〉

What's hopefully illuminating is asking the (Dollar/Euro) question in the (Heads/Tails) representation. Here's how QM does it:

(Euro?)=(12121212)

(Euro?)(Euro?)=(12121212)(12121212)=(12121212)

(Dollar?)=(12−12−1212)

(Dollar?)(Dollar?)=(12−12−1212)(12−12−1212)=(12−12−1212)

(Euro?)(Dollar?)=(12121212)(12−12−1212)=(0000)

Wait a minute. What happens when the state is, eg, | heads 〉 , but we ask ( Euro? ) . Let's see,

Is it Euro when state is "heads"?=(Euro?)|heads〉=(12121212)(10)=(1212)=12|heads〉+12|tails〉

It mixes the answers in heads/tails. IOW, the coin is no longer heads. This all happens without me having even started talking about position. Space is even just one point for all I've claimed.

What if you represent the outcome in the Dollar/Euro representation? You would obtain a state that's a linear superposition of |Dollar〉 and |Euro〉 –with a minus relative sign, if I remember correctly, but it would be a simple exercise to get the details. IOW: When the coin is “heads,” it's neither a Dollar, nor a Euro. You get me a coin that does that, and we would take the conversation from there with just coins.

I find it extremely informative and interesting but I'am missing the point, what interest do we have in knowing if it's a dollar or an euro ? It could just be a medal with green/blue faces since we are only interested in knowing if the polarization of the photon or the electron is up or down. It was not me here who choosed this coin analogy but it was usefull in understanding that there is nothing causal in instantly determining the other face of the coin once we measured the first one. Now you got me confused i must say.

[joigus]

1 hour ago, Mitcher said:

I find it extremely informative and interesting but I'am missing the point, what interest do we have in knowing if it's a dollar or an euro ?

Just one:  _{No classical object will serve as an analogue of a quantum system.}

(Anti-emphasis.)

Don't tell anyone, apparently it's a secret, even if you repeat it 6 times.

Here they are:

On 9/30/2022 at 6:41 PM, joigus said:

IOW: When the coin is “heads,” it's neither a Dollar, nor a Euro. You get me a coin that does that, and we would take the conversation from there with just coins.

Another one:

On 9/27/2022 at 12:12 PM, joigus said:

You can't do that with coins. The correlations are strange, for sure. But because [...]

Another one:

On 9/27/2022 at 7:35 PM, joigus said:

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

Another one:

On 9/29/2022 at 2:45 PM, 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.

Another one --with icecream; maybe it's the concept of coin that's standing in the way, who knows:

On 9/30/2022 at 4:02 PM, joigus said:

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.

Another one:

On 9/21/2022 at 10:29 PM, joigus said:

The coin illustrates very well the indefinite nature of the intermediate states, but misses the correlations, and the fact that the state can be brought apart in the spatial components. The gloves cannot reproduce the total indefinition that characterises the state before a measurement is performed.

So we're at a loss for analogies really.

It really looks like I've said something about that before. Maybe I didn't and this is all a non-local, superluminal dream.

A coin (cat, gloves, icecream, etc.) has no states that are determined (elements of reality in Einstein's parlance) as to the Heads/Tails character, but a superposition of ·Euro/Dollar as to the "coinage" character, so it will never reproduce all quantum peculiarities. You couldn't, so it won't.

When will a classical analogue spell out the properties of quantum systems?:

No can do,

very problemo,

when Hell freezes over,

never happens,

when the cows get home and cook me dinner and sing me a lullaby...

So I'm sorry, no classical analogy.

You really must think quantum!!!!!!!!

 

Please, tell me it is clear now.

 

Yours truly,

Sisyphus

Edit:

x-posted with @NTuft

Edited October 1, 2022 by joigus
minor addition+link

[NTuft]

I do not think we can give Relativity a free-ride-along and hold to QM interpretations re: unitarity. Furthermore I think the reverence for R. is colouring any admissions for faster than light signaling, that R. is given here the preferred reference frame, but here in Speculations we should be free to drop it and say we want a preferred frame where particles are already moving at c and v>c is possible thereby opening up non-local interaction. I want to leave this by the way-side now and impart more in the state of matter in a singularity thread on this aspect.

But, to get to unitarity and strict locality...

On 9/24/2022 at 4:01 AM, joigus said:

[...]"Spooky" is not a physical term. If you paid even the slightest attention to the mathematical formalism of quantum mechanics, you would understand this perfectly, as both any "blips" of information, or any "blips" of energy would have to travel in the form of "blips" in the square of the absolute value of the wave function --or the square of the gradient too, in the case of energy. That's what the quantum dynamics doesn't allow to do superluminally.

Here, is this the squaring of the amplitudes, squaring of the Psi modulus, or multiplication by the complex conjugate?

On 9/24/2022 at 4:01 AM, joigus said:

[...]

EPR: If you can predict with absolute certainty the result of an experiment without in any way disturbing the system, there must be some element of reality underlying it. Quantum mechanics says that certain pairings of observables are incompatible, say A and B. If I can exploit a conservation law that's valid for at least one of them, say A, in a bipartite system (A₁+A₂ = constant) and measure A in part 1, and B in part 2, I can infer what the value of A₂ is without actually measuring it. I can, at the same time (within a space-like interval) measure B for 2, that is B₂, with as much precision as desired, and I would have proven that quantum description of reality is incomplete, because I would have the values of A₂ and B₂, which quantum mechanics declares as incompatible. In a nutshell: Either quantum mechanics is incomplete, or your wave function would have to be updated superluminally, to make this incompatible character of A and B persist. 

To quote wikipedia on Local Realism as mentioned by mitcher,

Quote

Local realism
Main article: Quantum nonlocality
In 1935 Albert Einstein, Boris Podolsky and Nathan Rosen in their EPR paradox theorised that quantum mechanics might not be a local theory, because a measurement made on one of a pair of separated but entangled particles causes a simultaneous effect, the collapse of the wave function, in the remote particle (i.e. an effect exceeding the speed of light). But because of the probabilistic nature of wave function collapse, this violation of locality cannot be used to transmit information faster than light. In 1964 John Stewart Bell formulated the "Bell inequality", which, if violated in actual experiments, implies that quantum mechanics violates either locality or realism, another principle, which relates to the value of unmeasured quantities (counterfactual definiteness). The two principles are commonly referred to as a single principle, local realism.

Experimental tests of the Bell inequality, beginning with Alain Aspect's 1982 experiments, show that quantum mechanics seems to violate the inequality, so it must violate either locality or realism. However, critics have noted these experiments included "loopholes", which prevented a definitive answer to this question. This problem may have been resolved during 2015 by Dr Ronald Hanson of Delft University, who performed what has been termed the first loophole-free experiment.[2] However, some loopholes might persist, like superdeterminism, with the result that the question may be fundamentally untestable.[3]

and on Counterfactual definiteness(CFD),

Quote

The dependability of counterfactually definite values is a basic assumption, which, together with "time asymmetry" and "local causality" led to the Bell inequalities. Bell showed that the results of experiments intended to test the idea of hidden variables would be predicted to fall within certain limits based on all three of these assumptions, which are considered principles fundamental to classical physics, but that the results found within those limits would be inconsistent with the predictions of quantum mechanical theory. Experiments have shown that quantum mechanical results predictably exceed those classical limits. Calculating expectations based on Bell's work implies that for quantum physics the assumption of "local realism" must be abandoned.[14] Bell's theorem proves that every type of quantum theory must necessarily violate locality or reject the possibility of extending the mathematical description with outcomes of measurements of measurements which were not actually made.[15][16]

Counterfactual definiteness is present in any interpretation of quantum mechanics that allows quantum mechanical measurement outcomes to be seen as deterministic functions of a system's state or of the state of the combined system and measurement apparatus. Cramer's (1986) transactional interpretation does not make that interpretation.[16]

So ths is the Cramer interpretation that bangstrom has repeatedly referenced, where he takes the opposite tack of what joigus seems to insist -- and will do away with CFD instead of locality. SD referenced seems to be SuperDeterminism. 

Quoting from Consistent Histories, as espoused by Murray Gell-Mann,

Quote

The consistent histories approach can be interpreted as a way of understanding which properties of a quantum system can be treated in a single framework, and which properties must be treated in different frameworks and would produce meaningless results if combined as if they belonged to a single framework. It thus becomes possible to demonstrate formally why it is that the properties which J. S. Bell assumed could be combined, cannot.

 

So I think there is no consensus here. Furthermore, I've read it that there is a growing consensus that both unitarity and locality are problematic. See, A jewel at the heart of quantum physics, "The amplituhedron, or a similar geometric object, could help by removing two deeply rooted principles of physics: locality and unitarity."

On 9/28/2022 at 3:24 AM, 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.

[...] 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. [...]

Well, I do not like your superpositin business. I think what needs examining is the Hilbert space where the unitarity of the Schrodinger equation. It's been said the Schrodinger equation exists to enforce unitarity. A loosening of unitarity mentioned in the article is isometry, which can be seen there to be equivalent to moving the 2-D complex plane to a 3-D sphere where the 'superposition' now has a new degree of freedom. 

It makes more sense to me that the Schrodinger equation requires the removal of measuring the phase of the wave, reducing/removing dimensionality for the sake of ease of calculations -- the shorthand you seem to use by saying the Wave equation is not a physical object. However, Heisenberg's matrices and density matrices preserve the phase aspect of the wave. There is a question posed by the amplituhedron, which is able to represent tremendous amounts of Feynmann diagrams. Is the mathematical basis of QM not accounting adequately for other dimensions, possibly confounded as hidden variables, and does QM treatment of time symmetry (unitarity) follow along behind R. space-time block universe or is there an alternative formulation?

 

On 9/24/2022 at 7:37 AM, joigus said:

Agreed. I would only add that, on top of all that, quantum systems force us to think in terms of amplitudes, which are meta-probabilistic, if I may be allowed to use the term. And we don't exactly know what amplitudes objectively represent. Behind all this confusion, lies the question of the interpretation of quantum mechanics, ie, the several implementations of the principles of quantum mechanics that make no difference as to the experimental results, while at the same time seem to have completely irreconcilable ontologies underlying them.

I think we can say that amplitude in a wave is like the magnitude, or the height displacement, but I'm sure you know that... Yes, what it represents objectively in QM seems to be a core issue.

On 9/24/2022 at 7:37 AM, joigus said:

I think the confusion of many people with such issues as "non-locality," "collapse of the wave function," "Schrödinger cats" (macroscopic superpositions, etc.) comes from the fact that we haven't, as yet, totally understood what amplitudes are representing, how to implement measurements in a non-ambiguous way, etc.

Again, to re-iterate, I think you are set upon dismissing non-locality but O.K., then you must get rid of CFD; and logically, I do not think one is superior to the other, but in this realm as understood by most perhaps our normal logic does not apply.

On 9/24/2022 at 7:37 AM, joigus said:

If I may be allowed to present a contention here --after all we are on the Speculations section-- is that we haven't totally understood the objective role that the gauge principle plays in all of this, but that's a topic for another --hopefully engaging-- thread.

Please, mind my use of "objectively represent" instead of "is."

Phew.

On 9/24/2022 at 2:50 PM, MigL said:

Mostly because a valid frame of reference for a photon ( emission/ absorption ) does not exist.
Much like non-locality involving superluminal communication/interaction.

R.+? We can't have a preferred ref. frame here?? 

On 9/26/2022 at 3:04 PM, bangstrom said:

Separability in space but not time is what makes the connection non-local. This is impossible in the classical model but possible for quantum correlations.

I think you mean Relativity, which is a classical model, but not necessary all classical models outlaw "action-at-a-distance", non-locality, faster than light comm., etc.

On 9/26/2022 at 3:04 PM, bangstrom said:

[...]

What you say may be true for Gell-Mann and Kracklauer to name one other claiming that QM is non-local but I don’t think that applies to Feynman. The Wheeler-Feynman Absorber theory had instant, non-local connections going both forward and backward in time preceding an actual EM transfer of energy. Feynman interpreted the transaction as a direct action between emitter and absorber.

As John Wheeler said, “I have always believed that electrodynamics is completely symmetric between events running both forward and backward in time. There is nothing fundamental in the laws that makes things run in only one direction. The one-way flow of events that is observed is of statistical origin. It comes about because of the large number of particles in the universe that can interact with each other.”

The W-F absorber theory never caught traction likely because they explained their theory by inventing swarms of photons moving at every possible speed, including all speeds in reverse, and taking every possible path between the sender and absorber of an EM signal.

The W-F Absorber theory survives today as John Cramer’s scrubbed clean version of the old theory.

[...]

The MWI and SD and likely Bohm’s double solution are not scientific in that they eliminate Popper’s “falsifiability” by vanishing any contrary evidence.

Unblemished locality of the wave function? The S. wave function itself functions non-locally.

 

I think of Feynmann's path-integral formulations to be an alternative to Schrodinger's wave or Heisenberg's matrix mechanics so someone please re-educate that stance if necessary. Also, I know you don't answer direct questions, but do please clarify for a short-cut: is Cramer's theory SD (SuperDeterminism)? Further, from reading here, the W-F absorber is very interesting, because I thought Feynmann in particular wanted to formulate time asymmetry, e.g. by looking at friction.

On 9/26/2022 at 6:27 PM, joigus said:

I think you mean non-separability in space. I haven't the foggiest idea what separability in time means, as separable or not is an attribute of the state that depends on how it factorises --or not-- in the particle-identity tags* (state)₁₂=(state)₁(state)₂ --separable-- or, as is the case for the singlet state (state)₁₂=(state)₁(state)₂-(state)₂(state)₁ --non-separable.

Once an inertial system is chosen, there's only one coordinate time.

Separability in time? Whether something is instantaneous. Of course it's doubtful we get that under R.

On 9/26/2022 at 6:27 PM, joigus said:

[...]

FW theory. This is a theory of classical (not quantum) electrodynamics in which Feynman, for reasons that were purely heuristic --see below--, wanted to dispose of the field altogether, and assume a direct interaction between charged particles that gave rise to a completely local, relativistically causal electrodynamics.

Google: "Heuristic hypothesis"

In this method Feynman, after a suggestion from Wheeler, imposed the condition that the force per unit charge (the field in disguise) be half-retarded and half-advanced. But of course, the final constriction is that the total solution from all the electrons in the universe propagated in a retarded way and be totally causal and local. Feynman found that he had to impose the condition that spatial infinity be a perfect absorber of EM radiation. Pretty weird, but it worked mathematically.

Observation: You can perhaps always introduce an interaction between pairs ab initio that is formally non-local, and then impose boundary conditions that restore locality --in this case, the perfect absorber at infinity. You can always have an infinite expansion in spatial derivatives of the interaction (and therefore, non-local) but you impose that the sum of all the infinitely many terms be local. You can play with that ad infinitum. It's just a change of variables.

In fact, I know of another perfect example in which the separation of variables makes locality non-manifest. The so-called MHV approach to solve quantum field theories.

The reason that we today do not believe that the WF model is telling us anything significant about non-locality is, of course, that we happen to know that the world is quantum, and not classical, on the one hand; and on the other hand, that the alleged non-locality has no observable consequences, because of reasons I've just explained. When you study quantum electrodynamics, you see very clearly that the advanced waves correspond to antiparticles, not to any bizarre waves propagating backwards in time.

If you're surprised by this mathematical fact, it's very understandable: In quantum field theory, if you want to have field variables that commute at space-like intervals --and therefore have a theory that preserves causality, and forbids superluminal propagation-- you actually need positrons. These are not actually waves propagating backwards in time, they're only degrees of freedom of the field for which the amplitudes have to be "interpreted" backwards, so to speak.

This is key to the Feynman prescription for the propagator. Feynman explains this point --not very clearly, I must say-- in this famous Dirac-Memorial conference --he starts at 10' 35'' with the words "now, here's a surprise":

<snip, needs review, my apologies...>

Here's the most revealing part of the transcript. Pay attention, please, to the words "apparently moving backwards in time."

So that's all there is to it in the quantum version. You need antiparticles if you want to guarantee locality and causality. Feynman, of course, never doubted locality and relativistic causality.

"You need antiparticles if you want to guarantee locality and causality". I think Dirac needed antiparticles because he needed unitarity?

On 9/26/2022 at 6:27 PM, joigus said:

Well, I'm sorry. It does. They all are quadratic expressions in the wave function, and satisfy local conservation law of energy, momentum, and angular momentum (both orbital and spin.) This is all mainstream. See below for local conservation of probability density and continuity equation, plus Wiki reference added.

What you're measuring there is a correlation that was there from the get-go. No wonder it "is superluminal" to you --and perhaps others who don't understand this particular point--, as it is not the speed of anything. I've told you before. The Book of Psalms is the same everywhere, not because different versions of it are communicating telepathically with each other, but because they were written long before the present time. Correlation is not causation, nor necessarily interaction.

You've got a point there, but that's not totally true. We always have our reliable good old Ockam's razor.

There are also TIQM (transactional interpretation of quantum mechanics), DH (decoherent histories approach), Nelson's SQM (stochastic quantum mechanics), etc. None of these models have been proven falsifiable, which is not the same as saying they are not falsifiable.

What's SD?

That is not correct. So local it is that a simple calculation from the Schrödinger equation allows you to derive the continuity equation for the square of the absolute value of the wave function. Probability satisfies the accepted paradigm of a local conservation law.

🤪

On 9/26/2022 at 6:27 PM, joigus said:

Probability flux getting out of surface = - time rate of variation of probability inside the surface

Totally dumbed down: No probability can get out of a volume without going through its surface. This is a theorem you can prove from the Schrödinger equation. Here it is:

https://en.wikipedia.org/wiki/Schrödinger_equation#Probability_current

I've tried to simplify the maths, but I can provide you a complete and detailed proof, if you're interested.

Wow, yes, more maths please. This I think is on track with the loosening of unitarity a la isometry: the normal constraint is to transitions that add to 1 on the (complex) unit sphere in (abstract) Hilbert space. It's been posited that the addition of 1 dimension, circle->sphere, is not going far enough in removing unitarity, but I think we need more math to, in effect, maintain the unitarity and the seemingly valid stochastic results while loosing it from a 2-D plane that facilitates the calculatons.

 

On 9/30/2022 at 8:24 AM, Mitcher said:

I have re-read all this discussion with extreme interest and it seems that pretty much everything has been possibly said about non-locality, sometimes even a few times. There are obviously some competent and very patient people here taking the time to explain carrefully and i certainly do not intend to start it all again, however if the explanation for decoherence and a supposed non-locality is something as trivial as the analogy with the coin, the question that comes to mind is why did Einstein and followers up to this day had to use complicated notions as action at a distance, collapse of an unphysical wave function etc.. This is what puzzles me now and because I understood completely every objections made by Bangstrom here, given that I had exactly the same prejudices resulting from all my previous readings. Is it because those QM pionneers had not competely understood those phenomena ? Even today there seem to be quite a few opposed QM schools, local realism being just one of them. Is that part of the situation ?

We might need to get into lattice gauges, Wick rotations; but I'm probably being unrealstic to peform like I know what I'm asking. It may tie in with the Amplituhedron, to speculate...

On 9/27/2022 at 6:08 AM, Eise said:

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.

Your quote from Gell-Mann:

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 0^o, 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 0^o. 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!

In keeping with your philosophical approach, I think we must establish first principles, and I for one do not have a handle on the basic math assumptions that underpin QM, so I strongly recommend you do not completely accept what rolls out, if you don't either. Second, if you like your experiment, I suggest that all you need is a preferred, objective and not-subjective translatable reference frame from the midpoint of where your experimental photons were released. You could look at Proper Time Geometry speculations by Carl Brennan on replacing SR with a different derivation coming from Lorentz's ether theory that does not have the second postulate of SR. But, i likely misunderstand your experimental problem.

13 hours ago, hoola said:

I have  breezed through the many pages of what I did not expect to see generated by my "crowded quantum" question, but the topic was not about "standard" QM and the normal questions associated to that, but the possibility of directly modifying specific particle pairs, thus creating a communications pathway by allowing an additional degree of freedom not present in normal matter, while at the same time not affecting normal entanglement properties of these prepared particles.  A sort of manipulation of larger clumps of matter can now be done with nanomaterials, and if all matter is composed of mathematics, why can't those basic building blocks someday be modified directly and alter reality at a "nanomathematical" (sub plankian) scale for specific purposes?

I think of modelling a system of particles akin to the "ropes" that bangstrom mentioned, but more like quantum harmonic oscillators whose entanglement exists in an extra-dimensional space currently not accounted for by local Hilbert space that underpins most QM formulations. 

9 hours ago, joigus said:

Creating a communications pathway is precisely what is not possible. Also, all the degrees of freedom are present in normal matter and/or light. And then, you go on to say,

Perhaps, but are they present in the mathematics?

9 hours ago, joigus said:

If you use the channel so as to in any way break the coherence by interacting with it, the system is no longer entangled. In a manner of speaking, you have "selected" a subcomponent of the previous quantum state, thus destroying the richness of correlations it was packaging.

You also say the topic "is not about standard quantum mechanics." What other kind of quantum mechanics is it about?

When the system was prepared, it was correlated in any possible direction that you chose for the polarisers. If you set up a polariser, it is no longer entangled, but now you can predict something about the distant part. If you further deflect/filter any of the beams, it is no longer correlated at all, let alone entangled. What do you want to do with that?

Most anything you do ends up destroying the peculiar quantum correlations, and you get closer and closer to the classical description. Not totally, because you still see a binary observable, which is not covered by classical mechanics for spinning object. But you no longer have the effects of entanglement.

I hope that helps further clarify the discussion, but without us all getting muddled up into fantasy physics.

I can't parse everything you bring, but, will you say you reject realism, since you hold locality?

8 hours ago, bangstrom said:

This is a highly irregular statement. QM permits superluminal signaling, and ‘signaling’ is a word frequently used. The classical view does not permit superluminal signaling.

Are you meaning to say SR classical view? Why do you say again classical does not permit superluminal? I thought it did, as others mentioned.

8 hours ago, bangstrom said:

What are you saying about the superluminal nature of the transaction or non-signal signaling or whatever you choose to call it? The timing of the ‘whatever’ has been frequently measured in experiments to be superluminal so how can you claim superluminal is an illusion?.

Please! Very specifically, even though you don't answer questions/requests, cite this material and it's interpretations!!!

7 hours ago, joigus said:

[...]

I'll finish with a clue for what may come next: Keep track of the phase changes in the components of the wave function, and the essential difference between closed quantum systems and open quantum systems, because I intuit that's what's confusing you, and many other people with you.

 

I hope you can see I've tried to keep track of multi-quotes. Please expound on this. Does closed vs. open have any relation to Wave equation/function vs. density/probablity Matrix mechanics?

7 hours ago, joigus said:

 

@Eisewas totally right when he said that the illusion of superluminal signals only appears because one wants to understand what is happening from a classical viewpoint.

Conversely, one denies superluminal signals by the assumption that a positive-valued probability distribution is the valid description, which is someone else's assertion I can't find reference to at the moment. 

7 hours ago, joigus said:

I would add (repeat for the n^th time really) that there's a second possible source of illusion of superluminal character that comes from the (valid for-all-practical-purposes --FAPP--, but fundamentally flawed, in Bell's words) projection postulate.

 

I have two eyes. You have two eyes. The event that determined the astonishingly[?] precise correlation is far back in the past, somewhere in the pre-Cambrian seas, when the first animals developed eyes. You can measure the correlation between those facts with as much precision as you want here and in Andromeda. There is no limit to how "superluminal" this looks if you keep calling that a signal.

Do you understand now? Is that clear now? Will we be talking about this totally trivial point forever?

https://en.wikipedia.org/wiki/Principle_of_locality#Quantum_mechanics

https://en.wikipedia.org/wiki/Counterfactual_definiteness

 

S.E. “literal purpose in life is to enforce unitarity,”, from QuantaMagazine article on Amplituhedron

[NTuft]

correction post-edit time:

1 hour ago, NTuft said:

A loosening of unitarity mentioned in the article [*this other article: Physicists Rewrite a Quantum Rule that Clashes with our Universe ]is isometry,

I appreciate the heads/tails dollar\euro quantum money business and various other efforts.

Quote from second article, both cite work by: Arkani-Hamed, N., et al.

Edited October 1, 2022 by NTuft

[bangstrom]

13 hours ago, Eise said:

For me, I accept Susskind's, Gell-Manns (and Swansont's, and Joigus', and MigL's) position, even if I cannot follow the math. So I take the argument of authority. Such arguments are valid, when it is clear that Susskind and Gell-Mann are absolute 'quantum experts'. Just to give an idea of Gell-Mann: he predicted the existence of the Omega-minus particle, and is one of the fathers of the quark model of hadrons. I think for him this topic would be basic QM...

If you are looking for an argument form authority, I suggest you broaden sources. From my reading of the literature, non-locality is largely settled science and contrary views are far from the mainstream.

[bangstrom]

8 hours ago, NTuft said:

Furthermore I think the reverence for R. is colouring any admissions for faster than light signaling, that R. is given here the preferred reference frame, but here in Speculations we should be free to drop it and say we want a preferred frame where particles are already moving at c and v>c is possible thereby opening up non-local interaction. 

I see no contradiction between R. and v>c with the exception of Einstein's Second Postulate which is a provisional statement and not a law of physics. We still have c in the body of R. and Maxwell's equations where it is a universal dimensional constant and not a speed.

8 hours ago, NTuft said:

On 9/28/2022 at 5:24 AM, bangstrom said:

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. [...]

Well, I do not like your superposition business.

 If you read my quote, I don't like it either.

8 hours ago, NTuft said:

Also, I know you don't answer direct questions

I have no objections to answering direct questions and spend much doing the same.

8 hours ago, NTuft said:

...is Cramer's theory SD (SuperDeterminism)?

I have never considered Cramer’s theory to have anything to do with Superdetermism. My understanding is that SD considers the past and future to be like a movie in the projector and there is nothing we can do to alter our fates. In SD there is no such thing as free will.

I don’t know if Cramer has ever stated his opinion about free will but his theory does imply a non-Newtonian sense of time much like the ‘Block Universe’ but I don’t find that to be necessarily deterministic.

8 hours ago, NTuft said:

Are you meaning to say SR classical view? Why do you say again classical does not permit superluminal? I thought it did, as others mentioned.

I am not aware of anything superluminal in the classical view with the exception of the recessional velocities of the very distant galaxies.

8 hours ago, NTuft said:

Please! Very specifically, even though you don't answer questions/requests, cite this material and it's interpretations!!!

This is not the newest experiment and the Chinese have done it better since but here is one citation from Eise.

 https://archive-ouverte.unige.ch/unige:37034

Experimental test of nonlocal quantum correlation in relativistic configurations

 

In this experiment, a type of Bell test was performed near Geneva. Pairs of entangled photons were generated at a central location S and sent through fiber optic cables to widely separated locations:  A and B. Detectors at A and B measured the polarity of the incoming photons simultaneously (< 5 ps) and found them to be anti-correlated.

The intuitive explanation is that the polarities were present from the start and remained so until their detection. This possibility was ruled out by the violation of The Bell inequality so the old question becomes, 'How did the second photon to be detected 'know' it should be anti-correlated to the first if was detected before a light speed signal travel from one detection point to the other to 'inform' it of the polarity of the first?  

The < 5 ps was a far shorter time than a light speed signal could travel the distance between A and B so something superluminal appeared to be happening.

Edited October 2, 2022 by bangstrom
My citation didn't work. It works now

[MigL]

6 hours ago, bangstrom said:

How did the second photon to be detected 'know' it should be anti-correlated to the first if was detected before a light speed signal travel from one detection point to the other to 'inform' it of the polarity of the first?

Because the probability distribution for the separated states was encoded in the common wave function shared by entangled particles.
How many times does this probabilistic view have to be repeated, before you stop thinking classically ?

 

In the mentioned experiment in Geneva, given a large enough separation, the question could arise as to which of the two particles' entangled states decoheres first ( SR considerations ).
If the wave function does not encode states as probabilities, how do we know which particle is communicating/signalling/Qbitting ( or whatever you choose to call the interaction today ) with the other to ensure the observed anti-correlation ?

Or are you fine with violating causality for macroscopic events ( observer experiments ) also ...

[bangstrom]

3 hours ago, MigL said:

How many times does this probabilistic view have to be repeated, before you stop thinking classically

The random probability is lost at the instant the first measurement is made and I understood that many years ago.

What about my view do you think is “classical”?

3 hours ago, MigL said:

In the mentioned experiment in Geneva, given a large enough separation, the question could arise as to which of the two particles' entangled states decoheres first ( SR considerations ).
If the wave function does not encode states as probabilities, how do we know which particle is communicating/signalling/Qbitting ( or whatever you choose to call the interaction today ) with the other to ensure the observed anti-correlation ?

Which came first has been done in other experiments and that is how we know the first observation matters.

In the Geneva experiment, they made the timing of events as close to instant as possible on both ends to measure the speed of decoherence. It made no difference which came first.

3 hours ago, MigL said:

Or are you fine with violating causality for macroscopic events ( observer experiments ) also ...

Entanglement and violating causality may well be two different things. In the past I considered entanglement at the macro level to be impossible but some experimenters have claimed to have achieved entanglement at the level of Buckey balls and even tardigraves. I will wait for the experiments to discover how far up the scale entanglement can go.

Edited October 2, 2022 by bangstrom
Added the question about classical.

[Eise]

19 hours ago, NTuft said:

In keeping with your philosophical approach, I think we must establish first principles, and I for one do not have a handle on the basic math assumptions that underpin QM, so I strongly recommend you do not completely accept what rolls out, if you don't either.

I am not aware of any QM physicist who would not agree with Susskind's position:

• Nothing that Bob does has any FTL influence on Alice's side. QM does not allow for such interactions. 
  If you know of FTL interactions (i.e. FTL causal relationships allowed by QM), let me know. This would mean that the direction of cause to effect is agreed upon by all observers.
• Bell's theorem says that no classical theory can replicate all predictions of QM

If you have any serious references, please post them.

You're right of course that I cannot evaluate the correctness of Susskind's calculations. But for this kind of situation, there is only one option for me: wait, and see if this is (will be) a well established viewpoint of the physics community at the long term.

As you call my approach 'philosophical', I would like to tell what my position is: in QM we have come at the limit of our, human, epistemological possibilities. We can measure particles arriving at a detector, measure some of their properties (but not all of them at the same time), or we can measure wave properties in the collective behaviour of many particles. These are physical, measurable results. But the wave function is not physical: we cannot measure it in itself. We cannot measure it (any experiment measuring the phase of the wave function? Or when it flips due to entanglement with a remote measurement?). It is part of a recipe to predict quantum events, but only in terms of probabilities. The wave function itself is not a physical object.

Earlier I compared it with the use of the imaginary i. AFAIK QM cannot be done without it. It is not just shorthand to make some calculations easier, as it is in the description of classical wave mechanics. And this imaginary i stares you in the face in the Schrödinger equation! (Just to be honest, I read somewhere (I think it was in the blogs of Sabine Hossenfelder) that much of QM can be done without imaginary numbers, but not everything).

At least I find it funny that a function is taken as a physical object. That its name is still a 'function' is at least suspicious. That is also the reason I cannot take MWI seriously. It heaves the existence of the wave function from a mathematical tool to physical reality. That is metaphysics.

13 hours ago, bangstrom said:

If you are looking for an argument form authority, I suggest you broaden sources. From my reading of the literature, non-locality is largely settled science and contrary views are far from the mainstream.

OK, give some of the same caliber as Gell-Mann and Susskind, that base their position on established mathematics of QM. Not of some metaphysical interpretation of it. (I found nothing of the kind in Susskind's book, just descriptions of experiments and mathematical derivations).

1 hour ago, bangstrom said:

In the past I considered entanglement at the macro level to be impossible but some experimenters have claimed to have achieved entanglement at the level of Buckey balls and even tardigraves.

I think you are confusing entanglement with plain superposition. I also know of experiments where they succeeded in doing double-split experiments with buckey-balls, and producing interference. Not with tardigrades. But if you have a source, let us know.

[MigL]

3 hours ago, bangstrom said:

Which came first has been done in other experiments and that is how we know the first observation matters.

Except that relativity tells us you cannot always know which came first, as there is no preferred frame.

[joigus]

2 hours ago, bangstrom said:

In the past I considered entanglement at the macro level to be impossible but some experimenters have claimed to have achieved entanglement at the level of Buckey balls and even tardigraves. I will wait for the experiments to discover how far up the scale entanglement can go.

This is by far the most ridiculous thing you've said so far on this thread.

You're being the mouthpiece of some fat-ass crackpottery, my friend. Through no fault of your own perhaps, just by constantly ignoring the physics involved.

Really?, quantum coherent superpositions of order 10²⁴ -plus individual electrons, protons, neutrons and photons making up a tardigrade, --I guess that's what you mean-- which is an animal that has dissipative processes constantly going on in its body?

Now for buckyballs --I guess that's what you mean-- those are fullerene particles very common in interstellar soot, so I'm guessing it's possible in principle, like in the case of silicon atoms, although extremely difficult. I already gave you a reference to macroscopic superpositions of bunches of silicon atoms, but again you missed it.

Give us the reference to your Schrödinger water bears, please. I wanna have a good laugh.

21 hours ago, NTuft said:

Here, is this the squaring of the amplitudes, squaring of the Psi modulus, or multiplication by the complex conjugate?

Not only the square of the amplitude ψ∗ψ , but the probability current, which is conserved locally, as an exact theorem of quantum mechanics.

[Mitcher]

23 hours ago, joigus said:

So I'm sorry, no classical analogy.

You really must think quantum!!!!!!!!

 

Please, tell me it is clear now.

As I said the coin analogy was not mine, i forgot who spoke of it first here but from what i understood it was only to clarify that nothing non-local would be at play when measuring two (anti)correlated particles apart from each others. It was not to modelize the wavefunction or anything, it was to explain that nothing magic happens when measuring one part of two opposite parts : one know immediately what it is even before measuring it. If i got that wrong then i suppose it means that non-locality is a QM feature after all ?

15 hours ago, bangstrom said:

I am not aware of anything superluminal in the classical view with the exception of the recessional velocities of the very distant galaxies.

A sure sign something is seriously flawed in the model but that's truly personal.

23 hours ago, joigus said:

When will a classical analogue spell out the properties of quantum systems?:

When one says that a photon is a particle and a wave at the same time it's an analogy one can comprehend, at least intuitively. I see no problemo with this.

[bangstrom]

11 hours ago, Eise said:

OK, give some of the same caliber as Gell-Mann and Susskind, that base their position on established mathematics of QM. Not of some metaphysical interpretation of it. (I found nothing of the kind in Susskind's book, just descriptions of experiments and mathematical derivations).

I could cite any number of authorities who find entanglement and non-locality as valid. This is the mainstream view since it has been established experimentally. The burden of proof is on the person, you, making the extraordinary position.

I can name one more who might agree with Gell-Mann and Susskind and that is A.F. Kracklaurer.

Can you name another?

11 hours ago, Eise said:

I also know of experiments where they succeeded in doing double-split experiments with buckey-balls, and producing interference. Not with tardigrades. But if you have a source, let us know.

That’s a great idea for a new experiment. I can supply the tardigrades.

If you pass a single particle through a single slit, it produces an interference pattern due to diffraction.If you pass a single particle through a double slit it produces a double slit interference. If you try again with 3,4 or 5 slits, you get increasingly complex interference patterns.

How does a single particle passing through multiple slits ‘know’ how many slits are to its left or right so it can land in the proper position with the appropriate pattern? There must be something non-local going on.

 

9 hours ago, MigL said:

Except that relativity tells us you cannot always know which came first, as there is no preferred frame.

Experimentally it is possible to select a detector to make the first measurement. The timing is much like it is done at the track.

9 hours ago, joigus said:

This is by far the most ridiculous thing you've said so far on this thread.

Give us the reference to your Schrödinger water bears, please. I wanna have a good laugh.

This is serious physics. I suspect next year this will announced as a winner of the Ig Nobel prize.

https://arxiv.org/abs/2112.07978

Entanglement between superconducting qubits and a tardigrade

K. S. Lee, Y. P. Tan, L. H. Nguyen, R. P. Budoyo, K. H. Park, C. Hufnagel, Y. S. Yap, N. Møbjerg, V. Vedral, T. Paterek, R. Dumke

Quantum and biological systems are seldom discussed together as they seemingly demand opposing conditions. Life is complex, "hot and wet" whereas quantum objects are small, cold and well controlled. Here, we overcome this barrier with a tardigrade -- a microscopic multicellular organism known to tolerate extreme physiochemical conditions via a latent state of life known as cryptobiosis. We observe coupling between the animal in cryptobiosis and a superconducting quantum bit and prepare a highly entangled state between this combined system and another qubit. The tardigrade itself is shown to be entangled with the remaining subsystems. The animal is then observed to return to its active form after 420 hours at sub 10 mK temperatures and pressure of 6×10−6 mbar, setting a new record for the conditions that a complex form of life can survive.