## Correlations and Entanglement swapping

For this week I want to do a pedagogical presentation of entanglement swapping, but I got busy with other things and tomorrow I'll go on vacation for a week in San Francisco, Lake Tahoe, and Yosemite National Park. Normally I would stay late to write the post, but this involves a lot of LaTeX and so I have to postpone this post. Sorry for the delay, I'll be back in a week.

1. Dear Florin,

On Lubos’ blog, TRF, one can find multiple examples of logical absurdities generated by his commitment of non-realism. The title of the post is “Socks and electrons are more analogous than Bellists pretend”.

Lubos tries here to provide an answer for my argument put forward on your blog in the comment section of the post “GHZ for die-hard local realists“. The argument is not new, being well known under the name “EPR-Bohm”.

Let’s just relax and see how Lubos gets entangled in absurdity after absurdity:

“The uncertainty principle is the actual reason why it's inconsistent in quantum mechanics to assume that the observables have their values before they're actually observed.”

“we may reinterpret the events right before this measurement and assume that the individual spins (just like sock colors) had these values, either ↑↓ or ↓↑, already right before the first measurement of an individual spin. But in quantum mechanics, due to the uncertainty principle, we mustn't do the same thing in the absence of an actual measurement. We're only allowed to assign sharp c-number values to observables that are actually measured and once they are measured.”

It should be clear from the quotes above that it is impossible, in his opinion, for the entangled particles to have a certain spin (up or down) before the measurement.

Not surprisingly, he is forced to accept that:

“On the other hand, in quantum mechanics, we must admit that the first spin (up/down) of an individual electron that we measure is created in the measurement itself. The reality – a particular c-number associated with the observable – wouldn't exist without the observation. The spin of the distant electron is therefore "determined" by our local measurement, too.”

Read carefully the quote above, because this is clearly a non-local phenomenon, and it is what the “Bellists” are arguing.

But he doesn’t admit it. His explanation follows:

“But as the sock analogy makes manifest, this "determination" doesn't require any superluminal or instantaneous influence because the spin of the remote electron wasn't strictly changed by the measurement of the spin of our local electron.”

Realy, Lubos? You say that the electron could not have had a spin up state. After the measurement it has a spin up state. It’s not that you were uncertain about the spin (if it was up or down), it is impossible for the particle to have been in either state. Sorry, no matter what you hope to achieve by placing the word “strictly” before “change” it’s not enough. At this moment you may go apologize to all “Bellists” out there.

1. I went to Lubos' blog and found just this; he is arguing that the individual spins do not exists in the entanglement (true), and then argues they come into existence with measurement. This is the case. Entanglement is a case of the "whole greater than the sum," for there are really no individual parts that ontologically exist in any way, but rather there is only the entire state. Lubos then says this is no different from classical mechanics --- Really?

Lubos is a case study in how the human brain "blows neurons" when it tries to make quantum physics translatable in classical or macroscopic terms. I don't write on Lubos' blog, finding it oriented largely towards a band of far right winged UR-fascists as himself, and not enjoyable. In fact I usually go there to see if he has found an article worth reading.

LC

2. LC:

"he is arguing that the individual spins do not exists in the entanglement (true), and then argues they come into existence with measurement."

He is also arguing the opposite. The measurement does not create the spins, it only changes the knowledge of the observer. He switches from one position to another hoping to maintain both non-realism and locality. Unfortunately for him it cannot be done. See the continuation of my original post below.

I think that one can understand QM as a statistical theory based on some underlying classical mechanism. Its non-intuitive aspect has been much exaggerated.

It is very difficult, if not impossible to get a fair treatment on Lubos' blog. He insults/bans anyone who disagree with him so that only his admirers remained. Even for the post I was discussing here, riddled with inconsistencies, he got a lot of appraisal for clarity.

Andrei

3. I have verified all the quotes of mine and all of them are true, 100% accurate, important, compatible with each other, and compatible with reality. Let me assure you that if you see any problem in any of the sentences I wrote, it is due to your brain defect.

Some summary of these things is rewritten as a reply to Andrei at the bottom of this comment thread. I am afraid it makes no sense to respond many times because peabrains won't ever be able to understand these simple things, anyway.

4. There is a sort of physics Orwellian statement here. If you have an entanglement, say between spins or polarizations of photons, then the entire state is what has been prepared and is what is accessible to the experimenter. There really are no individual spins or polarizations. A measurement that is performed transfers the entanglement phase from the system to needle states, which by doing so means the spins or polarizations are now manifest or in a sense "created." Yet nowhere do you have both of these circumstances in one data set --- you can't have your cake and eat it too.

This means that the whole or total is not the sum of the parts. The whole can exist without any meaningful physical sense of the parts existing. From the meaning of a quantum bits it is evidence that quantum bits are conserved; for there is no inner information at all, but only the information of the entire state prior to observation and the individual state after observation with quantum entanglement phase shifted to needle states. This is hardly classical, and to say that it is classical just because it is what an observer experiences is maybe an emperor's new clothes idea. It is sort of a case of Orwell's double think, where two contradictory ideas are considered to be mutually compatible.

You do this with climate change, where you claim on your blog presumed data showing the coolest temperatures on record when everywhere else, such as NOAA etc, display just the opposite.

Quantum mechanics is a case of "whole not equal to sum of parts," and this is a mental difficulty comparable to over turning the idea of a god. The classical argument is that for something to be created you must have a creator, which of course gets into "turtles all the way down" once you ask who created the creator. QM similarly challenges our biases over what it means for something to exist and to be "composed" of other things. Some moments of reflection might also suggest that abolishing god(s) and the quantum abolition of the "whole = sum of parts" are somewhat related to each other.

5. To carry a bit further, I think Lubos' statements are a case of taking the meaning of "OR" in quantum mechanics and mistaking it for "AND."

6. To carry a bit further, I think Lubos' statements are a case of taking the meaning of "OR" in quantum mechanics and mistaking it for "AND."

2. But the gems continue to follow:

“Both individual spins were uncertain, just like both colors of the individual socks, and the measurement of the first spin just eliminated our uncertainty which may be thought of as residing in our head – just like in the case of the two socks.”

Here, Lubos changed his mind. The particles did have spins but the observer was uncertain about them. The uncertainty is only in the mind of the observer:

“So only our knowledge about the individual spins was changed, not the spins themselves.”

And also:

“When we learn about the individual spins, we are not remotely changing the two spins. We are just changing our knowledge from the ignorance (of individual spins/colors) to the knowledge”

Sorry, but you said earlier that the particle could not have had a spin, and the measured spin has been created at the time of the measurement. Because there was no spin to speak about there can be no knowledge about it either. You cannot acquire knowledge about something which does not exist.

I feel sad that an otherwise intelligent physicist can display such a complete ignorance of logical reason. This is not some subtlety but a gross logical error for which you would be laughed-out of a debate.

The resolution is simple. The particles have a certain spin before the measurement, but it is unknown. Only now all the talk about knowledge becomes meaningful.

The fundamental error comes from a confusion regarding uncertainty one should not expect from an ex-professor at Harvard. It doesn’t imply that the non-commuting observables cannot exist. Such an interpretation is falsified by the experiment involving two consecutive position measurements allowing the calculation, with a theoretically unlimited precision, of both position and momentum of the particle for the time between the measurements.

Andrei

1. There is absolutely no contradiction between any two of the statements I have made. All information about the state of Nature and physical objects in it is always defined relatively to an observer's perspective - and is obtained from observations. This is a basic principle of quantum mechanics.

So this applies to individual colors, uncertainty about them, correlations, and all other things. In the correlated/entangled experiments, the individual colors/spins are not measured at the beginning, so they're not determined. In QM, in fact, they have to be completely undetermined by the condition J_x=0 and by the uncertainty principle: it follows that J_1z and J_2z must be uncertain.

When a measurement of the individual spins J_1z and J_2z takes place, they will be found anticorrelated - because the "relative spin" was known from the beginning (the anticorrelation was perfectly guaranteed at every moment since the decay of the original particle). However, the individual spins j_1z and j_2z only become specific c-numbers when the first one of these two is actually measured. When it's done, this "birth of classical information" must be interpreted exactly as it was in classical physics, and one may say that the individual spins always existed but the observer was just ignorant about them.

This particular reconstruction of the history would have led to wrong predictions if the spins j_1x and j_2x were measured instead but it's OK - for these other types of measurements, a different reconstruction that is analogous to a classical one would be OK. These two ways of study the 2-electron systems are not compatible with each other but it's totally OK because they are Bohr-complementary or, equivalently, using e.g. Gell-Mann's language, they take place at different branches of the history. Whenever the measurements are actually done, the birth of the particular individual bits for the spins/colors may be understood as an observer's learning about some information that has existed from the beginning.

2. LM:

“All information about the state of Nature and physical objects in it is always defined relatively to an observer's perspective - and is obtained from observations. This is a basic principle of quantum mechanics.”

This is irrelevant for the EPR-Bohm setup as this experiment can be performed by a single observer. Nevertheless, I disagree that this is a “principle of quantum mechanics”. It is nowhere to be found in QM postulates, and it is not what Bohr or Heisenberg believed.

“When a measurement of the individual spins J_1z and J_2z takes place, they will be found anticorrelated - because the "relative spin" was known from the beginning (the anticorrelation was perfectly guaranteed at every moment since the decay of the original particle).”

It is possible that the observer did not know that the source produces entangled particles (the source could be defective), so he didn’t know what to expect.

“However, the individual spins j_1z and j_2z only become specific c-numbers when the first one of these two is actually measured. When it's done, this "birth of classical information" must be interpreted exactly as it was in classical physics, and one may say that the individual spins always existed but the observer was just ignorant about them.”

Sure, but you have clearly said that those values were CREATED during measurement. You need to decide what your working hypothesis is. Are those values created at the time of measurement or were they there before?
You keep switching between those two logical incompatible scenarios, claiming that they are both true. Sorry, but this is absurd. You just cannot have them both.

I notice your use of the word “may”: “one MAY say that the individual spins always existed”. Why don’t you have the courage to say what you think? Do you believe that statement to be true or not? Did the individual spins existed or not? I predict that you will not answer this question because it would force you to choose between non-realism and locality. If the individual spins existed before measurement you have realism, if not, you have non-locality.

“This particular reconstruction of the history would have led to wrong predictions if the spins j_1x and j_2x were measured instead”

This is not true. The statistics used in Bell’s theorem, are only true for naïve classical theories like non-interacting billiard balls. Contextual local realistic theories, like classical electrodynamics, do not allow you to deduce those wrong predictions. So, you are avoiding the only reasonable answer (the spins had those values all the time) for nothing.

“These two ways of study the 2-electron systems are not compatible with each other but it's totally OK because they are Bohr-complementary or, equivalently, using e.g. Gell-Mann's language, they take place at different branches of the history.”

Bohr complementarity is logically consistent, while your view is not. Bohr insisted that a measurement induces an uncontrollable disturbance on the system under observation. I find this view perfectly acceptable and in agreement with (properly understood) classical realism.

Andrei

3. We seem to be in the Bohr-Einstein debates circa 1930 all over again. Really much of this has been sorted out, and Lubos appears to be requiring that the "OR" of quantum complementarity with respect to entanglements or nonlocality be an "AND."

This appears to bother some people, and even 't Hooft has gone off into this sort of lala land. The difference is that Lubos denies there is nonlocality by requiring a quantum "AND" while 't Hooft accepts nonlocality and argues for nonlocal signalling that is entirely opposite what Lubos says. It would be amusing if the two were put in a room to debate this one out!

I will put my arguments to rest at this point I think. Continued arguments are not likely to lead to much and Lubos has already resorted to ad hominem comments on his blog.

4. Let me just say that I've quick-read all those comments and it would be a waste of time to reply to individual sentences because 99% of them are completely illogical and wrong crap and you're just two irrelevant cranks who would have been banned on this blog a long ago if Mr Moldoveanu cared about some standards at least infinitesimally.

3. LM:

“The uncertainty principle is the actual reason why it's inconsistent in quantum mechanics to assume that the observables have their values before they're actually observed.”

“one may say that the individual spins always existed but the observer was just ignorant about them.”

Take those quotes to anyone with some grasp of logic, expect him to lough for a fiew minutes and ask him to explain to you the rules of logical consistency.

"Let me just say that I've quick-read all those comments and it would be a waste of time to reply to individual sentences because 99% of them are completely illogical"

From someone utterly ignorant about logic this sounds almost like a compliment.

"you're just two irrelevant cranks who would have been banned on this blog a long ago if Mr Moldoveanu cared about some standards at least infinitesimally"

This is the reason your blog doesn't contain interesting debates. You have nourished there just a bunch of yes-men and rejected valuable people like 't Hooft. Great strategy!

Andrei

4. Wow, 13 comments on a non-existent post. I read them but no time to reply, I will drive today to lake Tahoe. Ans I only want to give the fake Mark Twain quote: the coldest winter for me was a summer in San Francisco. What a cold weather here.

1. In part this is an extension of Musser's guest post on Lubos' blog. The problem in part is there are some serious people who can't ignore him. There are a range of people that Lubos has condemned as communist agent provocateurs, or complete idiots, including sean Carroll who Lubos repeatedly excoriates. Of course his favorite person to dump on is Smolin, who I do not agree with on some things, but there are a couple of works he has done that I think are fine. He recently has a bit on Fotini, who did some ideas about graph theory with loop variables (a not entirely unreasonable topic to look at even if it might be wrong) who Lubos completely rakes over the coals as being some immoral trollop. Being condemned by Lubos in some sense actually puts you in with good company.

This is in line with borderline personality disorder BPD. Such people have a very white vs black view of the world, and to be in their favor you have to conform virtually 100% to their world view. Any deviation and the BPD person will respond histrionically or with great hostility. BPD people display an absolute intolerance for people with ideas, opinions or outright facts that diverge from their world view. This can include their image of a person they are in a relationship with, and in fact most often this happens. BPD people are pure misery to be in any relationship with, I know for I have been there and done that. I am a bit of an expert at spotting BPDs.

The other two main personality disorders are narcissistic personality disorder, which a certain orange colored baboon running for US President has, and anti-social personality disorder or psychopathy. All personality disorders occur with a range of severity. About 5% of people have one of these, about 1% have one of these seriously, and with .1% are dangerously afflicted. These three overlap some, and the all share a diminished lack of empathy. Psychopathy is the worst on that front. A BPD can exhibit empathic deficits as well, and Lubos yesterday condemned the fact the Italian navy rescued some 1600 refugees in the Mediterranean. What the hell should they have done? Sit back and watch them drown, maybe laughing at it? Sheesh, this and related posts clearly demonstrate an empathic deficit.

Some signs of personality disorders are unreasonable explosive anger, an inability to maintain a relationship with others, whether professional, friendships or intimate and familiar, and a tendency to adhere to or join extremist groups and ideas. Often people who join religious cults or political groups of an extreme nature have some underlying mental dysfunction or illness. Lubos was let go from Harvard in part as I understand because almost nobody could stand him. He explosively responds to things on his blog, often peppered with four letter words, and his politics is really very extreme --- though becoming less so as the world slouches more towards fascism these days.

LC