Talk:Quantum entanglement/Archive 6

Archive 1

←

Archive 4

Archive 5

Archive 6

Archive 7

Prior to changing article

I am about ready to change the lead of this article. I've written a draft after carefully going over the Stanford article very carefully, and it now seems to me that the lead has some significant problems.

We need to make a distinction between what theory suggests and what reality may be. The present lead paragraph assumes the "naive" quantum mechanical picture. It implies that because theory tells us about states (which are, despite the natural language meaning of "state", not the characteristics of particles but assemblies of descriptions of those characteristics -- like talking about the statistics of births and deaths and the 3.1 persons per hundred thousand who died violent deaths rather than the real experiences of people who were born or who died) that is the end to what there is to know about the real world particles. In other words, the present discussion inappropriately mixes the abstract level of discourse with the concrete level of discourse. In doing so, it privileges quantum mechanical orthodoxy and gives the EPR people short shrift.

The article states that entanglement has been verified experimentally. If that statement means that particles that theory says are entangled will be found to have appropriately coordinated states when measured (opposing spins for entangled electrons, for instance), then that statement is true. If the statement is intended to affirm the truth of the theoretical interpretation that depicts each of two entangled particles as having superimposed and opposing characteristics (both electrons having both clockwise and counterclockwise spin, for instance) that will take on definite characteristics only once one of the particles is measured in regard to that characteristic (one electron then having clockwise and the other electron having counterclockwise spin, for instance), then the statement is not true. It is not true for two reasons: (1) It is contested by many scientists who hold a "hidden variable" interpretation or some other interpretation of theory and experimental facts that denies non-locality. (2) Nothing is ever proven true in science. It may be that there are hidden variables and no non-local changes. It may also be that there are no hidden variables and that we have to give up the "intuitively obvious" idea that there can be no "spooky action at a distance."

This stuff is really difficult to talk about because there is the level of the phenomena that physicists are trying to make predictions about, there is the level of abstract representation (theories, models, "convenient fictions"), and there is the level of interpretations that tries to tell us what the theory says about the reality that underlies phenomena. Keeping straight on what topics of discussion apply to what what levels of discourse is not easy. But I think I am ready to go.

I think it is possible, however, to say everything that needs to be said in plain English. Comments?P0M (talk) 12:46, 12 June 2011 (UTC)

Grandioso! I guess, you'll be the first to successfully say THAT in plain English. Till now it was usually believed that, sadly, the natural language is unable to express THAT (if only by a very long and tangled texts understandable mostly to those who already understands). Boris Tsirelson (talk) 17:28, 12 June 2011 (UTC)

Do not keep saying to yourself, if you can possibly avoid it, "But how can it be like that?" because you will get "down the drain", into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that. (Richard Feynman, "The character of physical law", Sect. 6, page 129.) Boris Tsirelson (talk) 17:52, 12 June 2011 (UTC)

I didn't say I'd make what happens make sense to people. Tercer is correct to say that some things that are or some things that have been stated in the article are not correct. It's enough for me that the article say what can be said without obfuscation, and that it not say things that are not true. What I would like, at this point, are corrections on anything I have said above -- while assuming good intentions on my part. P0M (talk) 19:47, 12 June 2011 (UTC)

Some points at which the first paragraph seems problematical

The text currently says:

Hence, if the system is composed of multiple particles, one of the particles cannot be fully described without also considering the other(s), even if the particles are separated by some distance. The simplest case of this would be when two particles, such as two electrons or two photons, have interacted and then separated.

1. This way of stating things makes it appear that only particles can be parts of a quantum system.

Ok. To make things simple, I think it's okay to give particles as an example, as long as it's clear it's only an example. Tercer (talk) 13:30, 17 June 2011 (UTC)

2. Saying that photons have "interacted" will puzzle most readers who already have some idea of what photons are. If photons can pass through each other without mutual influence, how are they believed to interact? I believe there are ways of accomplishing entanglement using special waveguide operations, but readers may need a link or something to make this idea of interaction understandable.

You're correct. Entangled photons can be generated (and are generated in countless optical experiments) through indirect interactions, mediated by a non-linear crystal; but I would prefer a simpler example in the lead. Tercer (talk) 13:30, 17 June 2011 (UTC)

The lead currently says:

For instance, when the spin of only one of the two entangled electrons is measured, the spin of the other immediately becomes determinate.

Readers are likely to interpret this statement as reflecting empirical fact rather than reflecting a quantum theoretical consequence. But if they do that then they will be taken aback by the hidden variable view that suggests that in some sense the spins were "always" whatever they are discovered by measurement to be.

Hmmm, better stay away from interpretation issues. I don't think any quantum physicist believes in hidden variables, they're just a very interesting model to be disproved. What quantum theory says is that when you measure the spin of one electron from an entangled pair, the spin of the other remains unknown. It only becomes determinate if the owner of the second electron knows the result of the measurement, and this is always false in the non-local scenarios. A way to state this that only sticks to experimental facts is

For instance, when the spins of a pair of entangled electrons are measured, they are always found to be strongly correlated.

"...becomes determinate if the owner of the second electron knows..." sounds totally solipsistic to me.P0M (talk) 14:33, 17 June 2011 (UTC)

Nevertheless, it is what quantum theory says. It sounds solipsistic only if you demand more of quantum theory than it is capable of giving. Quantum states are states of knowledge, not states of nature. In this example, let's say Alice and Bob share an entangled pair (a singlet), and Alice makes the measurement, and find that her spin is up. Then for Alice the state of Bob's electron will be spin down, whereas for Bob it will still be the probabilistic mixture of spin up and spin down until he finds out the result of Alice's measurement. Tercer (talk) 16:49, 17 June 2011 (UTC)

Bob does not necessarily know whether Alice has made a measurement, no? So he may just make his own measurement. He will then conclude that when Alice makes her measurement it must be be contrary to his.P0M (talk) 19:22, 17 June 2011 (UTC)

Also, that sentence is also assuming that the electrons are maximally entangled. It's a usual assumption, but that needs to be stated. Tercer (talk) 13:30, 17 June 2011 (UTC)

Being "maximally entangled" is going to be awfully hard to make meaningful to readers who do not know what "entangled" means.P0M (talk) 14:33, 17 June 2011 (UTC)

Yes, of course, I don't think that the best thing to do is to say this, but that we should avoid stating the conclusion that needs this assumption. Let me expand on this: The spin of the other electron becomes determinate only if the state is maximally entangled; if the state is not maximally entangled, it will still be in a superposition (dependent on the measurement outcome). Again, I don't think this belong in the lead, only that you should state this as an example, not a general truth. Tercer (talk) 16:49, 17 June 2011 (UTC)

3. The current text says:

Measuring the value of the spin of one disentangles the particles, and forces the other to take on its own, separate spin value.

This statement assumes the understanding of quantum events accepted by the Copenhagen group, so it prejudges the issues raised by EPR. It also uses the word "forces," which prejudges the issue of how the correlation of states occurs once one of the entangled things is measured.

The first part of the sentence is okay, "Measuring the value of the spin of one disentangles the particles". I think the rest you can just delete. It does not add information and assumes hidden variables. I think it will only confuse the reader. Tercer (talk) 13:30, 17 June 2011 (UTC)

I am working on a new first paragraph to try to avoid these problems.P0M (talk) 21:23, 16 June 2011 (UTC)

Nice one Patrick. Sorry I didn't get around to this befeore. Here is a suggested copyedit for you to consider. I have tried not to use the word "thing":

Quantum entanglement occurs when some objects (strictly, quantum systems), such as particles with mass like electrons or even larger entities such as "buckyballs," as well as particles without mass such as photons, originally interact physically and then become separated in such a way that each resulting object carries the same quantum mechanical description (state). This description is indefinite in terms of important factors such as position, momentum, spin, and polarization. When a measurement is made so that it causes one object to take on a definite value (e.g., clockwise spin), the other partner of this pair of entangled objects will at any subsequent time be found to have taken the complementary value (e.g., counterclockwise spin). There is then a correlation between the states of entangled pairs even though quantum mechanics depicts the states of both as indefinite until measured.

Physicists are in general agreement about this situation. However, there is a profound dispute about whether the objects that are being described by quantum mechanics already had their real values (e.g., clockwise spin or counterclockwise spin) set in some way at the instant they became separated, or whether the objects being described by the mathematically indeterminate equations were themselves as indeterminate as were their quantum mechanical descriptions. If the objects were truly indeterminate until one of them was measured, then the question becomes: "How can one account for the second object, that was at one point indefinite with regard to its spin, for instance, suddenly becoming definite in that regard, even though no physical interaction with the second object occurred, Also, if the two objects are sufficiently distant from each other, there could not even have been the time needed for the information measured from the first object to travel to the second object?" The answer to this question involves the issue of the Principle of locality, i.e., whether for a change to occur in something the agent of change has to be in physical contact (at least via some intermediary such as a field force) with the object that changes. The study of entanglement brings into sharp focus the dilemma between locality and the completeness or lack of completeness of quantum mechanics. Myrvin (talk) 13:42, 18 June 2011 (UTC)

I think that "thing" is better than "object" because "thing" (which originally meant a meeting or assembly) includes phenomena without mass. The Merriam-Webster on-line dictionary give a relevant example: "That sunset was the most beautiful thing I have ever seen." If "object" were substituted for "thing" in that sentence it would clearly be wrong. You can say, "Light if a funny sort of thing," but not "Light is a funny sort of object." P0M (talk) 16:05, 18 June 2011 (UTC)

Sorry P, I don't agree. "Thing" is just too vague and I think unencyclopedic. I agree the two words are not interchangeable; and the reason you can't substitute it in your sentences is because a thing is much wider than the objects you are describing. Anything can be a thing. It can be a concept for instance - we are dealing here with physical objects. The sunset isn't a physical entity - it's an event; and the sentence about light was thought up by someone who wasn't thinking of photons. Let's see what others think. Myrvin (talk) 19:32, 18 June 2011 (UTC)

Energy is not an object, so there's a problem there too.P0M (talk) 23:45, 18 June 2011 (UTC)

Entanglement exists also in vacuum fluctuations. What could be "object" or "thing" in this case? Boris Tsirelson (talk) 06:04, 19 June 2011 (UTC)

Surely energy photons can be called objects. Even a wave could be too. And don't vacuum fluctuations produce temporary objects? But you're the expert Boris, what word could be used? Maybe "entity"? I suspect we shall return to 'quantum system'. Myrvin (talk) 07:37, 19 June 2011 (UTC)

In the meantime, two definitions from Chambers dictionary:

object: a material thing; that which is thought of or regarded as being outside, different from, or independent of, the mind (as opposed to subject); that upon which attention, interest, or some emotion is fixed; a thing observed; an oddity or deplorable spectacle; that towards which action or desire is directed, an end; a thing presented or capable of being presented to the senses (as opposed to eject)

thing: a matter, affair, problem, point; a circumstance; a fact; an event, happening, action; an entity; that which exists or can be thought of; an inanimate object; a quality; a living creature (especially in pity, tolerant affection, kindly reproach); a possession; that which is wanted or is appropriate (colloquial)

So thing includes object, but is much too wide for these purposes. Myrvin (talk) 07:49, 19 June 2011 (UTC)

Even "thing" may not be broad enough to include "vacuum fluctuations." What, exactly, is entangled with what in these instances? The trouble with language is frequently that it needs to change to adapt to new circumstances.P0M (talk) 07:55, 19 June 2011 (UTC)

Exactly so: language needs to change! Giving once a course on quanta, I was forced to repeat several times each hour: "You see, all words I say are quite wrong; but equations I write are correct".

It takes years, to get used to the crazy quantum "world" (already a wrong word...) and to inevitably inappropriate words (since the natural language has no appropriate words for that). Thus, if the article (or the discussed part of the article) is not intended for experts, then it should treat only some relatively very simple cases, using words naively, and warn the reader, that it is far not the general case.

"What, exactly, is entangled with what in these instances?" --- The state is. Maybe you'd prefer a simpler explanation, but I intentionally took a "bad" example, probably not admitting simple words...

"And don't vacuum fluctuations produce temporary objects?" --- probably you understand this phrase correctly; but a newbie very probably will treat it very naively. A virtual particle is far from the thing usually called "object", and its existence is far from the thing usually called "existence".

Boris Tsirelson (talk) 09:22, 19 June 2011 (UTC)

A quote:

My complete answer to the late 19th century question ‘‘what is electrodynamics trying to tell us’’ would simply be this:

Fields in empty space have physical reality; the medium that supports them does not.

Having thus removed the mystery from electrodynamics, let me immediately do the same for quantum mechanics:

Correlations have physical reality; that which they correlate does not.

("What is quantum mechanics trying to tell us?" by N. David Mermin; Am. J. Phys. 66:9, September 1998, p.753)

Boris Tsirelson (talk) 11:09, 19 June 2011 (UTC)

Very well stated. Thank you.

So the problem cannot be solved so easily, no? I deliberately chose to use "thing" because it is such a mushy concept. It does not promise more precision in its intension than is actually there. To me what seems hardest for most people is the idea that Jill Bolte Taylor (author of My Stroke of Insight) expressed in a radio interview one time. She said something like this: "Language (conceptualization) is the tool by which we create our world, and by which we understand our world." The Universe is not a fabrication of our imaginations. It can very stubbornly refuse to behave the way we would think reasonable or desirable. We reach out with the creative faculties of our own minds (usually in cooperation with whatever society we were born into) and define (literally, give boundaries to) such things as "lichen." Later we discover that what we thought was one organism is a symbiotic coupling of two organisms. So we have to re-create a part of that picture. Or we have the idea of "empty gasoline storage tank," and a workman opens an inspection port to check the condition of the inside wall, but it is a thousand cubic meters of blackness, so he strikes a match in order to be able to see. He gets more photons than he wanted. The Universe can force us to give up our preconceptions, and we work better if we understand that we are using "models," "constructs," or "useful fictions" rather than going the Greek philosophical thing and imagining that there is a single ideal definition or concept or idea of "bear" and then lots of imperfect imitation bears in the world that humans perceive.

I tried to proceed from the concrete to the abstract. We can always look at lichen first, call it "a plant," and then bring it into the laboratory, put it under a microscope, and let students see what is under the surface that we perceive with our eyes. It is more instructive that way. For one thing it prepares students to understand that their "unalterable truths" about other groups of human beings, nasty spiders, horrible snakes, vicious bears, etc., etc. may need to be "deconstructed."P0M (talk) 17:37, 19 June 2011 (UTC)

P.S. I think one of the very positive things about Wikipedia is that it can make available to young people who have a genuine curiosity and scientific craving for answers a "best practices" path forward. When I was a junior in high school I got a copy of Philipp Frank's Philosophy of Science, and continue to reap benefits from it more than half a century later. It was not something that would ordinarily have come to the attention of a youngster in a farm community of 7,000. How I got to it involved a rather complex "bank shot" in the pool hall of life. Most other people my age likely were not as lucky as I was. But now young people wanting to know about "entanglement" can get an answer that is not the kind of complete nonsense that some of the stuff in "boys' books of science" purveyed back in the 1950s. If we do it right, we can prepare their minds to see the reasons for "the irreality of relata." ;-) P0M (talk) 17:49, 19 June 2011 (UTC)

Oh yes. The size of the "quantum" conceptual jump is terrible - even in comparison with the "relativity" conceptual jump! It is shocking, to revise space and time; but much more shocking, to revise the dichotomy of "possible" and "real".

No wonder that natural languages formed before the jump are in trouble after it. It is a wonder that the language of mathematics, also formed before the jump, works smoothly after it. I should be very proud of math; but I cannot explain to myself, why did it happen. (Sorry for being off-topic; I cannot resist...) Boris Tsirelson (talk) 19:19, 19 June 2011 (UTC)

Road to proof of "psychic" phenomena?

Would this Quantum entanglement stuff explain the supposed telepathic link between twins, and true lovers(2 hearts beating as 1)? Wireless, non-technological communication because 2 things did the exact same thing at the exact same time is what I get out of this. The quantum computer sound like a technological psychic network to me. — Preceding unsigned comment added by 99.252.114.222 (talk) 13:09, 21 June 2011 (UTC)

The phenomenon, in itself, would not give any grounds for communicating mentally -- any more than it gives hope for communicating with technological gadgets. John G. Cramer, a physicist, has been working for years on how one might somehow contrive to communicate using entangled particles, and it is not simple. (See http://www.analogsf.com/0612/altview.shtml) All the entanglement stuff depends on isolating each particle from random contacts with its environment, and that kind of isolation just does not happen in the brain.P0M (talk) 14:57, 21 June 2011 (UTC)

See also, http://cosmiclog.msnbc.msn.com/_news/2007/07/17/4350992-backward-research-goes-forward P0M (talk) 15:04, 21 June 2011 (UTC)

Bloated lead

Once again the lead to this article has become a well fattened beast ready to be roasted, carved and served to the various sections at the table.

The current lead is:

Quantum entanglement occurs when some things (particles with mass such as electrons or even larger things such as "buckyballs," particles without mass such as photons, etc.) originally interact physically and then become separated in such a way that each resulting thing carries the same quantum mechanical description (state), a description that is indefinite in terms of important factors such as position, momentum, spin, polarization, etc. When a measurement is made and it causes one object to take on a definite value (e.g., clockwise spin), the other part of this pair of entangled objects will at any subsequent time be found to have taken the complementary value (e.g., counterclockwise spin). There is then a correlation between the states of entangled pairs even though quantum mechanics depicts the states of both as indefinite until measured.

There is no question about this much of the picture, either in theory or in the laboratory. However, there is a profound dispute about whether the objects that are being described by quantum mechanics, in any case under discussion here, already had their real values (e.g., clockwise spin or counterclockwise spin) preset in some way at the instant they became separated, or whether the objects being described by the mathematically indeterminate equations were themselves as indeterminate as were their quantum mechanical descriptions. If the objects were indeterminate until one of them was measured, then the question becomes, "How can one account for something that was at one point indefinite with regard to its spin (or whatever is in this case the subject of investigation) suddenly becoming definite in that regard even though no physical interaction with the second object occurred, and, if the two objects are sufficiently far separated, could not even have had the time needed for such an interaction to proceed from the first to the second object?" The answer to the latter question involves the issue of locality, i.e., whether for a change to occur in something the agent of change has to be in physical contact (at least via some intermediary such as a field force) with the thing that changes. Study of entanglement brings into sharp focus the dilemma between locality and the completeness or lack of completeness of quantum mechanics.

In general, if a collection of things as described above, i.e., a system, is composed of multiple particles, one of the particles cannot be fully described without also considering the other(s), even if the particles are separated by some distance. In a system of entangled electrons, before a measurement is made it is impossible to describe their spins, and only the combined spin of the two-electron system is known. After the measurement of one of the electrons, the correlated spins of the two electrons become determinate. Measuring the value of the spin of one of them disentangles the particles, and forces the other to take on its own, separate spin value. This occurs even though the particles are now separated by arbitrarily large distances.

Entanglement can be measured, transformed, purified, and teleported. A quantum system in an entangled state can be used as a quantum information channel to perform tasks that are impossible for classical systems, and is also required to achieve the exponential speedup of quantum computation.

Research into quantum entanglement was initiated by the EPR paradox paper of Albert Einstein, Boris Podolsky and Nathan Rosen in 1935, and a couple of papers by Erwin Schrödinger shortly thereafter. Although these first studies focused on the counterintuitive properties of entanglement, with the aim of criticizing quantum mechanics, eventually entanglement was verified experimentally, and recognized as a valid, fundamental feature of quantum mechanics; the focus of the research has now changed to its utilisation as a resource for communication and computation.

That is 619 words. The rest of the article is only 2915 words. The lead section should not be a sixth of the article. So lets start carving.

I've carved out

In general, if a collection such as has been described above, i.e., a system, is composed of multiple particles, one of the particles cannot be fully described without also considering the other(s), even if the particles are separated by some distance. In a system of entangled electrons, before a measurement is made it is impossible to describe their spins, and only the combined spin of the two-electron system is known. After the measurement of one of the electrons, the correlated spins of the two electrons become determinate.

and I'm still working to reunify the text across the gap so created. Currently at 347 words. P0M (talk) 00:51, 5 July 2011 (UTC)

(1) Entanglement verses non-locality

This block of text:

If the objects were indeterminate until one of them was measured, then the question becomes, "How can one account for something that was at one point indefinite with regard to its spin (or whatever is in this case the subject of investigation) suddenly becoming definite in that regard even though no physical interaction with the second object occurred, and, if the two objects are sufficiently far separated, could not even have had the time needed for such an interaction to proceed from the first to the second object?" The answer to the latter question involves the issue of locality, i.e., whether for a change to occur in something the agent of change has to be in physical contact (at least via some intermediary such as a field force) with the thing that changes. Study of entanglement brings into sharp focus the dilemma between locality and the completeness or lack of completeness of quantum mechanics.

doesn't really add anything to the lead. The idea of hidden variables is already introduced in the text above this block. If this discussion is kept it needs its own section, which is currently alluded to but never actually covered, and some more work.

I agree that it could use its own section. The difference between entanglement and non-locality has been a source of controversy in this discussion, and the issue needs to be clarified to forestall confusion on the part of the general reader.P0M (talk) 17:21, 28 June 2011 (UTC)

(2) Duplicating text

The following two blocks try to describe the same thing:

Quantum entanglement occurs when some things (particles with mass such as electrons or even larger things such as "buckyballs," particles without mass such as photons, etc.) originally interact physically and then become separated in such a way that each resulting thing carries the same quantum mechanical description (state), a description that is indefinite in terms of important factors such as position, momentum, spin, polarization, etc. When a measurement is made and it causes one object to take on a definite value (e.g., clockwise spin), the other part of this pair of entangled objects will at any subsequent time be found to have taken the complementary value (e.g., counterclockwise spin). There is then a correlation between the states of entangled pairs even though quantum mechanics depicts the states of both as indefinite until measured.

In general, if a collection of things as described above, i.e., a system, is composed of multiple particles, one of the particles cannot be fully described without also considering the other(s), even if the particles are separated by some distance. In a system of entangled electrons, before a measurement is made it is impossible to describe their spins, and only the combined spin of the two-electron system is known. After the measurement of one of the electrons, the correlated spins of the two electrons become determinate. Measuring the value of the spin of one of them disentangles the particles, and forces the other to take on its own, separate spin value. This occurs even though the particles are now separated by arbitrarily large distances.

There is no reason to have both in the lead. We should combine and distill these blocks into one clear statement describing entanglement.

I wrote the top paragraph in the hope of saying everything that needed to be said, but I wanted to be conservative about chopping anything that might cover something I had missed. Decoherence seems to be the main thing to preserve, and I like the material in the footnote that I took from a paper by Max Tegmark and John Wheeler.P0M (talk) 17:21, 28 June 2011 (UTC)

More later after sleep.

Phancy Physicist (talk) 09:44, 28 June 2011 (UTC)

(3) "Objects" and "things"

I have read the above discussions about using "object or thing" and I wanted to address it explicitly here. I object to the use of both "thing" and "object" for the following reasons:

• While I agree with the idea of what is going on here, I don't think it belongs on wikipedia. Wikipedia is not the place to develop new terminology. I understand the philosophical argument. "Particle is not a sufficient term for things in the quantum realm." But why not use the more correct and commonly used term, "wave-particle or particle-wave". Both link to wave-particle duality.

• Using terms like "objects" or worse yet "things" opens up another can of worms. While it is true that photons, atoms and molecules are both things and objects, so are baseballs, dogs and airplanes. While in theory you can create two dogs to be quantum entangled, in reality it is, for all intents and purposes, impossible and even if you did manage to entangle something so large you could never keep the entanglement long enough to measure it due to the interactions with the surrounding environment.

• In the pursuit to be precise with the language and terminology, we have lost the idea of what entanglement is. All the talk with "objects" and "things" then the following examples and clarifications of what "objects" and "things" are in this context. The definition of entanglement has itself become entangled in the language and it doesn't need to be this way.

In summary, my solution is to use wave-particle instead of "object" or "thing". If it is unclear what a wave-particle is the reader can always click the link and find out.

(start philosophical side-note about the inequities of language)

For many things in this universe our language is insufficient to describe nature in all its wonder. You can tell someone that time passes at different rates based on your speed or that the stuff the universe is made of have both wave and particle properties at the same time but these basic descriptions lack the ability to convey an understanding of what is really going on.

The root of this lacking is simply our inexperience. When was the last time you traveled 5 hours in an hour? Or noticed the diffraction pattern in the breeze coming through your bedroom door. You haven't, because at the speeds and the scale we live our lives you never notice these effects.

It be like describing "snow" in a sub-Saharan language. I'm sure that you could manage to get the idea across but will really understand what snow is when you are done having never experienced snow? I have trouble describing snowfall in the Northern United States to someone from Florida that had seen a few snowflakes one day five years ago.

(end philosophical side-note about the inequities of language)

(4) Over all thought, "We have lost the forest somewhere in the trees"

Try to read the lead straight through and tell me if you can make it. I couldn't. I got lost and I am suppose to be an "expert" on Physics.

Conclusion

I don't want this section to sound like I am putting down all the hard work everyone has done. It is awesome that this article gets so much attention. I am just trying to take all that work and help "rein it in" so we get a great article that conforms better to the Wikipedia guidelines.

Phancy Physicist (talk) 19:43, 28 June 2011 (UTC)

Here is a starter trimmed version of the lead. I believe I have kept all the meat. It has 200 words. Let me know what everybody thinks.

Quantum entanglement occurs when wave-particles interact in such a way that each resulting wave-particle carries a quantum mechanical description that is correlated to the other even though quantum mechanics says that the states of both are indefinite until measured. The result of this correlation is that when a measurement is taken on one of the wave-particles (e.g., clockwise spin), a subsequent measurement of the made on the other part of this pair is found to have the complementary value of the first measurement (e.g., counterclockwise spin).

This behavior has been theoretically and experimentally shown and is accepted by the physics community. However there is some debate about the underlying mechanism that leads to this entanglement. The difference in opinion comes from whether one agrees with quantum nonlocality or a hidden variable theory.

Research into quantum entanglement was initiated by the EPR paradox paper of Albert Einstein, Boris Podolsky and Nathan Rosen in 1935, and a couple of papers by Erwin Schrödinger shortly thereafter. These first studies focused on the counterintuitive properties of entanglement, with the aim of criticizing quantum mechanics. The focus of the research on quantum entanglement has now changed to its utilization as a resource for communication and computation.

The more detailed example should be listed in the body of the article.

Phancy Physicist (talk) 02:40, 29 June 2011 (UTC)

This paragraph looks fine to me except for the words "even though," which will make many readers think that the indefinite states somehow try to "take back" or "act against" the correlation. If I understand the intended meaning correctly, it is a matter of one thing being true even though ordinary expectations might make one dubious about its truth because of the indefinite states. "How can two things that are 'indefinite' in some respect also be 'correlated'?" My body is awake at this point, but my mind has yet to catch up, so I can't think of a way to reword the draft paragraph in this one respect.

Right that was the intent. I'll try again after sleep.

Phancy Physicist (talk) 09:51, 30 June 2011 (UTC)

One other thing, shouldn't it be "yielding, e.g., clockwise spin"? P0M (talk) 14:23, 29 June 2011 (UTC)

"Wave-particle" redirects to "Wave–particle duality", and no wonder: wave–particle duality exists, indeed, but "wave-particles" do not exist. At best, it is an unhappy term used in some popular speculations about quanta. If we want to use it, we should warn the reader that it is not a well-established notion of quantum theory. Boris Tsirelson (talk) 15:20, 30 June 2011 (UTC)

There is an older neologism, maybe no longer neo, which is "wavicle." I learned that word in the late 1950s, so maybe it counts as a word now. P0M (talk) 17:16, 30 June 2011 (UTC)

As far as I know, physicists never use ANYTHING like that. They speak about particles (or atoms etc) on one hand, and their wavefunctions on the other hand. And, significantly, a wavefunction depends on coordinates of all relevant particles. Thus, given for instance three entangled particles, and their wavefunction (of 9 coordinates), how many "wavicles" are there? Another example: three entangled spins, and their spin wavefunction (of 3 binary variables; coordinates are assumed irrelevant); how many "wavicles"? Boris Tsirelson (talk) 21:24, 30 June 2011 (UTC)

Was Arthur Eddington not a physicist then? See A.S. Eddington, The Nature of the Physical World, the course of Gifford Lectures that Eddington delivered in the University of Edinburgh in January to March 1927, Kessinger Publishing, 2005, p. 201. Memory goes bad after half a century, but I think George Gamow also used the term, unceremoniously attributing it to "some wag." P0M (talk) 01:26, 1 July 2011 (UTC)

In 1927 the situation was indeed much, much less clear than today. And no wonder! Boris Tsirelson (talk) 06:08, 1 July 2011 (UTC)

@Boris Tsirelson: I believe the answer is "depends on what you are concerned with". It could be 3 entangled protons but if you look more closely you would see 6 entangled quarks. The way you talk about the wave function, to me, makes it sound like the 3 particles "generate" the wave function, but the wave function is the particles.

I did not try to demonstrate my way to talk about it. Rather, the language of a usual article in Phys. Rev. (say). Boris Tsirelson (talk) 06:11, 1 July 2011 (UTC)

The tone somehow made me think it was saying that the wave function was a separate thing from the particle. I just wanted to let you know that was the impression I got and maybe someone else might read it that way.

Phancy Physicist (talk) 06:47, 1 July 2011 (UTC)

I see. But my point was rather, that (1) the wave function should not be thought of as a kind of a wave in the 3-dim space (it is not a function of 3 variables!), and (2), the wave function is neither "separate from the particle" nor "inseparable from the particle", since it relates to a multi-particle system, not at all to a single particle (or else we have no entanglement). Someone else might read "wavicles" in the way "one 3-dim wave per one particle", I bother. Boris Tsirelson (talk) 10:43, 1 July 2011 (UTC)

@POM: When I was trying to think of the alternatives I had heard, "wavicle" was one of them. However I thought that wavicle was even less formal then wave-particle or particle-wave. Am I wrong about that?

The term is used("We can scarcely describe such an entity as a wave or as a particle--perhaps as a compromise we had better call it a 'wavicle.'" -- Eddington), but the source I first saw it in (around 1956) discounted it a bit -- I think because of acknowledging it to be a word made up to try to deal with the shortcomings of more everyday terms like "particle" and "wave." I checked Google for "wave-particle" and only found it as a modifier for the noun "duality." I don't know how long it will take for the ordinary users of English to come up with a term that makes people avoid the unwanted implications of the terms we already have. I suspect that physicists who work with quantum effects on a regular basis have worked out their own modified understandings of "particle" and "wave," so they are not much motivated to develop better terminology.

I think the term "wavicle" has the advantage that it warns the ordinary reader not to be looking for some smaller version of a bullet, but maybe Wikipedia is not the place to break new ground.P0M (talk) 15:25, 1 July 2011 (UTC)

It is true that we talk about particles and wave functions depending on what is more convenient at the time but it is with the understanding that in reality things are like both waves and particles but neither. I would prefer to just say "particles" with the understanding that the definition of a "quantum mechanical" particle is different from a "classical" one. However there seemed to be a lot of concern with making that clear, so I suggested a term sometimes used in intro classes that helps get the point across quickly that they are different from a particle in the sense we experience everyday.

I believe it goes back to the lacking in language I mentioned above and is compounded by the guidelines of Wikipedia that say we should not introduce new terminology. I think wavicle will lead to more confusion, and a longer lead. And it appears particle-wave and wave-particle are not prominent enough terms.

What if we said something like this and forgo the whole issue:

Quantum Entanglement occurs when the quantum states in a system become correlated through interaction. For example, two electrons are generated in such a way that they have opposite spins. If the spin of one of the electrons is measured, giving a result of "spin up", then when the other electron's spin is measured the result will be "spin down".

This has the advantage of side stepping the issue of "picking the right word" while still being completely accurate. I think the example, as suggested in previous discussions, helps clarify the definition for the less quantum mechanically inclined. This is of coarse not meant to be an end-all, be-all definition but I think it is accurate and gets the main idea across.

Altogether now:

Quantum Entanglement occurs when the quantum states in a system become correlated through interaction. For example, two electrons are generated in such a way that they have opposite spins. If the spin of one of the electrons is measured, giving a result of "spin up", then when the other electron's spin is measured the result will be "spin down".

This behavior has been theoretically and experimentally shown and is accepted by the physics community. However there is some debate about the underlying mechanism that leads to this entanglement. The difference in opinion comes from whether one agrees with quantum nonlocality or a hidden variable theory.

How does that sound?

Phancy Physicist (talk) 01:52, 1 July 2011 (UTC)

It sounds like entanglement is just shared randomness. Two spins are correlated, just like two copies of today's newsletter in two different towns. But the main point is that this is beyond shared randomness. It is ridiculous that "This behavior has been theoretically and experimentally shown and is accepted by the physics community" if it is rather the behavior of the newsletter. Boris Tsirelson (talk) 05:32, 1 July 2011 (UTC)

Could you explain your objection a little more? I don't follow your point.

Phancy Physicist (talk) 06:12, 1 July 2011 (UTC)

"The philosopher in the street, who has not suffered a course in quantum mechanics, is quite unimpressed by Einstein-Podolsky-Rosen correlations /1/. He can point to many examples of similar correlations in everyday life." (The first phrase of the paper: J.S. Bell, "Bertlmann's socks and the nature of reality", Journal de Physique, Colloque C2, supplement au no. 3, Tome 42, mars 1981, page C2-41.) This article is written by Bell especially for explaining this point. Two particles were in contact, and now they share a random variable created in the time of the contact. Is it strange? Not at all. And of course, this "shared randomness" (the term is used in computer science, in communication complexity) cannot violate Bell inequalities. Quantum correlation can; in this sense it is stronger than classical. (Not that it exceeds 100%, of course.) Boris Tsirelson (talk) 10:28, 1 July 2011 (UTC)

Would changing it to something like this help?

Quantum Entanglement occurs when the quantum states in a system become correlated through interaction. When two states are entangled, the measurement of one state effects the value of the other state. For example, two electrons are generated in such a way that they have opposite spins. If the spin of one of the electrons is measured, giving a result of "spin up", then when the other electron's spin is measured the result will be "spin down".

Phancy Physicist (talk) 06:12, 1 July 2011 (UTC)

"measurement of one state effects the value of the other state" --- really? and what about no-signaling then? (Also, technically, it is a wrong use of the word "state"; here we have a state of the pair, not a pair of states.) Boris Tsirelson (talk) 10:33, 1 July 2011 (UTC)

@PP: The reason we started all this, is that a general reader couldn't understand the lead. I don't think that referring to 'quantum states' will help at all - not even with the link. I objected to 'things' as being too vague, but 'quantum states' is too techy - and didn't we have this some time before? Reading your suggested first line would make most people switch off immediately. I was fairly happy with 'wave-particle' - or better, your suggested 'particle-wave'. It maybe needs an example or two. And I think we decided 'system' doesn't work as being too vague too. Myrvin (talk) 08:42, 1 July 2011 (UTC)

Any kind of 'wave-particle' terminology is fundamentally misleading: it suggests that some wave in 3-dim space relates (in one sense or another) to each particle. But it does not! Rather, a single function of 3n variables relates (in one sense or another) to an n-particle system. In the absence of entanglement, this function boils down to n functions of 3 variables each. But is it the case under consideration here? Boris Tsirelson (talk) 10:55, 1 July 2011 (UTC)

@Tsirel: I want to make sure I understand you correctly. Are you objecting to "particle-wave" type terminology because you are afraid that people will think the wave properties mean a 3D wave and not a probability wave? What if we somehow worked in that it is a probability wave?

Myrvin: My objection to "things","objects",etc. is that those terms are too general. I would like what ever we end up with to clearly reflect that we are not talking about classical objects. I think "Quantum states","wavicles",wave-particles" all at least plant a flag saying "Not Classical!"

Phancy Physicist (talk) 21:42, 1 July 2011 (UTC)

Now I feel somewhat tired. You need not agree with my article on entanglement ([1] = [2]) and still, try the bibliography there; maybe you'll find something useful. Boris Tsirelson (talk) 11:32, 1 July 2011 (UTC)

Is entanglement vital to a quantum computer?

The paper "On the role of entanglement in quantum-computational speed-up" by Richard Jozsa and Noah Linden is used to support the statement that entanglement is "believed to be vital to the functioning of a quantum computer." The abstract of the paper actually states that "it is nevertheless misleading to view entanglement as a key resource for quantum-computational power." So, the reference cited does not support the article's statement and ought to be moved to a statement that it does support. User:Fartherred from 207.224.85.91 (talk) 23:49, 6 July 2011 (UTC)

Working on a compromise

There are three universes of discourse, and the general reader probably only operates in the first of them. The first is the everyday world of bullets, sound waves, etc. The second is the abstract world of quantum mechanics, the "math that does not lie." The third is the world of interpretation in which people try to "make sense of" the equations. The linguistic constructs used on the third level are linked to the linguistic constructs used on the first level via the math constructs used on the second level. In a sense, we are now trying to show the reader how the narratives proper to the third level apply to the narratives proper to the "common English" narratives. But we cannot depend on understandings constructed on the third level, arguments using third level concepts, to communicate meanings to readers who only have a naive first level narrative that explains their world to them. The task is to instruct readers who only have the terms and narrative proper to common English discourse. To do so we will succeed best if we use the terminology that produces the least chance of leading the reader astray. We should not expect to be able to say things correctly to people who have no basis to understand what we might say correctly. We should expect to say things incorrectly with the intent of leading the reader to a less naive understanding of the universe. (It is instructive to see how the Buddhist philosophers in the Prajñāpāramitā sūtras handle these situations, e.g., "As no individuals did the Buddha bring to enlightenmant countless multitudes of individuals.")P0M (talk) 15:25, 1 July 2011 (UTC)

I agree completely with POM's point. I think we all do. We have to trade accuracy with accessibility.

When I was in grade school they taught you that plants breath CO2 and exhale oxygen. This is of course wrong but in the end at least we kind of understood where our breathable air comes from. They traded understanding of the internal workings of a tree for understanding where the oxygen we use comes from.

It seems that our problem is that we haven't come to a consensus about what trades we are willing to make. So lets try a different approach. Try to make a list of the accuracies you are and aren't willing to trade for accessibility (in the lead) and state what you think is most important point the lead should get across. If you could add your "will"s,"wont"s and "important"s to my list and sign your last entry on each list. Also post any other comments in the usual fashion. That way we can all look at them side by side and compare.

Will Trade

• I don't really care what term we use for the "particles" as long it is clear that we are not talking about "classical ones".
• The idea that there isn't really two individual states any more.

Agreed. States are theoretical constructs, level two, and we talk about them on level three.P0M (talk)

• Any explicit mention of a probability wave, quantum states, quantum non-locality and hidden variable theories.

Agreed. We can show that entangled particles share something is on level one, and we can introduce readers to the fact that when, e.g., we create two photons in any rough-and-ready way, we can't have any idea of what spin they will turn out to have, but that when we create in certain special ways we can have extraordinary knowledge of their spin. However, we will have to lead up to the probability waves, etc.P0M (talk)

• Phancy Physicist (talk) 21:42, 1 July 2011 (UTC)

Wont Trade

• something that shouts "Not Classical!" in the description.
• a lead under 250-300 words long
• Phancy Physicist (talk) 21:42, 1 July 2011 (UTC)

Most important point

• The fact that the values that are measured affect one another even though the values are not determined until measurement. This is the point I would like the casual reader to take away. Phancy Physicist (talk) 21:42, 1 July 2011 (UTC)

Corrected a typo.P0M (talk)

@POM: If you don't agree with the creation of a new section based on your post then please feel free to change it back. I was just hoping to take you point and run :)

The new section heading is fine. I agree with all of your points above. BTW, I think by his using "wavicle" Eddington tried to convey the idea that "it's not the kind of particle you would expect, nor is it the kind of wave you would expect, but it is in some ways analogous to both of those macro-world constructs." As a high school student, I did not find the use of that word created any misconceptions for me to have to tear down later. P0M (talk) 01:36, 2 July 2011 (UTC)

Phancy Physicist (talk) 21:42, 1 July 2011 (UTC)

Sorry to join the discussion so late. I hope I can still make useful comments.

• I agree with Phancy Physicist that the new lead is way too long, and liked his points to cut down.
• I find it completely unacceptable the use of "wave-particle", "wavicle", or any such neologism. They are not used by physicists, and aren't even defined in wikipedia! Where the confused reader will turn to for help? The precise term is quantum state; and I don't think it is too much to ask.

A quantum state is a mathematical model and/or a "convenient fiction." Furthermore, understanding it demands a fairly deep immersion in quantum mechanics, a qualification that the the inquiring non-specialist will not have. Talking about quantum states is an interpretation of the mathematics performed on equations that the non-specialist will neither know of nor understand. Interpretations of quantum theoretical expressions are problematical because they necessarily exceed the information available in the math. P0M (talk) 17:42, 4 July 2011 (UTC)

• I don't like the "most important point" of Phancy Physicist. If I understand it correctly, it is wrong. Keep in mind Tsirelson's comment: ""measurement of one state effects the value of the other state" --- really? and what about no-signaling then? (Also, technically, it is a wrong use of the word "state"; here we have a state of the pair, not a pair of states.)"

The question is how to account for the "correlations" that exceed Bell criteria in a universe that does not permit physical chains of action to exceed the speed of light. If Tsirelson only considers chains of action in space-time, then he is attacking a straw man. Nobody whom I know of asserts that there is a superluminal physical chain of action between measurement of particle A and the yet-to-be-measured particle B. P0M (talk) 17:42, 4 July 2011 (UTC)

Yet the phrase "measurement of one state effects the value of the other state" seems to say precisely that there is a causal relationship between the outcomes of the measurements. If you consider chains of action bounded by the speed of light, you don't get Bell correlations. If you consider superluminal chains of action, you're talking nonsense. The thing is that you do not account for the correlations, they are just there. In the words of Salart et al. "According to quantum theory, quantum correlations violating Bell inequalities merely happen, somehow from outside space-time, in the sense that there is no story in space-time that can describe their occurrence: there is not an event here that somehow influences another distant event there." http://arxiv.org/abs/0808.3316 Tercer (talk) 22:04, 4 July 2011 (UTC)

First, the word should be "affects," not "effects."

Second, the text says nothing about faster than light transmission through space-time.

Third, I made no nonsense claims about superluminal actions.

Schrödinger was upset with the implications of entanglement. At one time he considered it likely, or perhaps I should just say that he hoped, that the correlations of phenomena involved would disappear after the photons or whatever had been separated for a while. I gather that he gave up on that fond hope. The correlations being there, and (if Bell is correct) not any hidden variables, there is an obvious "why" question. If two experimenters intercept two unentangled photons, they would find no correlations between them except those consistent with individual chance, e.g., a probability of 0.25 that spins would match. Everyday experience prepares us for this result. I flip a coin and you flip a coin... We have our questions about how this kind of thing can happen (and our questions about whether the dice are loaded), but we feel o.k. with these results and do not ask for lots of reassurance. Schrödinger did not feel so comfortable with what theory predicted and experiment confirmed. The natural question is, "Why does measuring one photon change our expectations of what will be the results of measuring the other photon?" The fact that some group of researchers says correlations "merely happen" does not establish anything other than what they claim their opinions to be. The idea that "correlations happen" is a problematical affirmation. "Correlations are observed" would be o.k., but saying "correlations happen" is rather more like saying, "The magician flips this switch that I bought for him from Home Depot, and the light across the street turns on or off instantaneously. But it's just a correlation. Don't blame the magician. Things just happen." If the light going on and off without intervention on your part were in your bedroom, I think you would look for an explanation. The idea that "correlations... happen, somehow from outside space-time," is not well formed. If the correlations are themselves "outside space-time," then they are not subject to being observed. Clearly the surface meaning is not what the author intended. So it must be that he means that "correlations happen (i.e., get effected) somehow, outside of space-time."  And that is exactly correct, as far as I can tell.

Green, p. 117, says two things: "Physicists say that the spin results are correlated -- since the lists are identical -- but do not stand in a traditional cause-and-effect relationship because nothing travels between the two distant locations," and, "..there is a harmonious coexistence between special relativity and Aspect's results on entangled particles. In short, special relativity survives by the skin of its teeth. Many physicists find this convincing, but others have a nagging sense that there is more to the story." P0M (talk) 00:09, 5 July 2011 (UTC)

The authors of the paper mean what they say. Note that Green agrees precisely with them, perhaps with a less colourful language.

"The fact that some group of researchers says correlations "merely happen" does not establish anything other than what they claim their opinions to be." Now be careful. When a group of the best scientists of an area of research say something (in a published paper in a prestigious journal) about their area of expertise, well, I think it establishes something more than their opinion. I am making an argument from authority here, and I think it is entirely appropriate.

There are other authorities who disagree, no? Consider: Bell, Speakable and unspeakable in quantum mechanics, p. 152:

You might shrug your shoulders and say 'coincidences happen all the time', or 'that's life'. Such an attitude is indeed sometimes advocated by otherwise serious people in the context of quantum philosophy. But outside that peculiar context, such an attitude would be dismissed as unscientific. The scientific attitude is that correlations cry out for explanation.

P0M (talk) 03:39, 6 July 2011 (UTC)

Anyway, I think you are giving to much importance to the word "happen"; their point is that there is no causal relation between the outcomes of the measurements, so if you insist in finding one, it would have to be outside of space-time. Tercer (talk) 12:44, 5 July 2011 (UTC)

I only "insist" on noting that the only explanation, if there is anything to be said beyond only reporting the results in the empirical world, must be outside of space-time.P0M (talk) 16:47, 5 July 2011 (UTC)

It reminds me of the book "Veiled reality" by Bernard D'Espagnat. His conclusion is (as far as I remember): independent reality, if at all exists, is nearly unknowable; after centuries of research we know only few facts, mostly negative, and first of all, that it (the independent reality) is not situated in the space-time. Boris Tsirelson (talk) 18:21, 5 July 2011 (UTC)

Shades of[Lao Zi], [Zhuang Zi], and Kant. P0M (talk) 18:34, 5 July 2011 (UTC)

@Tercer: I agree that what I wrote is not strictly correct. But I don't see the problem you see I guess. As I said above some times it is better to know where oxygen comes from then how plants work. Is it really that important that the reader of the lead understand the idea that there is only one state not two? I think that the general idea of what entanglement is can be conveyed without explaining or knowing exactly how states work.

If we use "state" as the word but don't mention any explicit properties of those states would that be okay?

Is it not true that if you create two particles with maximally entangled spins over and over again and measure one but not both you will get a 50-50 distribution of spin-up vs spin-down? And when you measure both, one gives up and the other gives down every time. To me this is the main point I want people who don't read the whole article to take away from the lead. That the results of measurement will be correlated in some way when the particles are entangled. I was very careful not to say any thing about a signal being passed from one to the other. I thought what I wrote was clearly from an empirical point of view. "If you do the experiment this is what happens." How or why is too hard to approach and address in the lead.

Phancy Physicist (talk) 03:18, 5 July 2011 (UTC)

From my experience in teaching entanglement, everyone starts thinking that

(1) If you measure particle one to have spin up, this measurement instantaneously changes the state of the spin of the second particle to spin down.

I agree this is a problem. So you and Boris Tsirelson believe that the way I am talking about this makes it sound like the second state collapses instantaneously to spin down? Am I understanding you right? Would somehow explicitly saying that a "measurement" is required for the collapse to a single value clear this up?

How could this assertion by subjected to experimental test? P0M (talk) 20:49, 5 July 2011 (UTC)

Phancy Physicist (talk) 20:00, 5 July 2011 (UTC)

No, no collapse! Just say inseparable, and strongly correlated; an adequate explanation of this requires more space than is available in the lead. (I'm Tercer, decided to use my real name) Mateus Araújo (talk) 21:05, 6 July 2011 (UTC)

(2) Entanglement is just shared randomness.

We could explicitly say that entanglement is not just shared randomness, provide a link, and go into it deeper in the article. Would that be a sufficient solution?

Phancy Physicist (talk) 20:00, 5 July 2011 (UTC)

My preferred solution would be not to talk about 50-50, spin-up, spin-down, etc. Just say inseparability, and it can be used to show correlations stronger than classically possible, with a link to quantum nonlocality, and go into it deeper in the "concept" section. Mateus Araújo (talk) 21:05, 6 July 2011 (UTC)

So I think it is crucial to have a lead that does not contribute to these misunderstandings. I think the "If you do the experiment this is what happens" is the correct approach, but again, one must take care of what the reader will interpret; what you just said would make me think entanglement is just shared randomness. Tercer (talk) 12:53, 5 July 2011 (UTC)

Yes, I also bother about these points. Boris Tsirelson (talk) 15:49, 5 July 2011 (UTC)

• I think it is a very bad idea to discuss hidden variables in the lead. First of all, what it currently says is nonsense. Also, they are a technical point that will never help a naïve reader to understand entanglement. Tercer (talk) 03:07, 4 July 2011 (UTC)

All it says in the lead is, "the difference in opinion comes from whether one agrees with quantum nonlocality or a hidden variable theory." What about this sentence makes it "nonsense"?

The full sentence: "However there is some debate about the underlying mechanism that leads to this entanglement. The difference in opinion comes from whether one agrees with quantum nonlocality or a hidden variable theory." There is no mechanism leading to entanglement. See above point. Also, the author is confusing entanglement with nonlocality here; quantum nonlocality is the mysterious correlations, entanglement is the inseparability of the states that are needed to demonstrate nonlocality. Also, there is no debate about hidden variable theories being credible; they are a model to refute, not a plausible model of nature. I do not know any physicist that believes hidden variables Tercer (talk) 22:04, 4 July 2011 (UTC)

Careless mistake in wording. Sorry.P0M (talk) 00:57, 5 July 2011 (UTC)

Yeah that is all messed up. I was trying piece together what was there in a better way. But as I said above I am okay with removing any mention of hidden-variables or quantum non-locality.

Phancy Physicist (talk) 03:18, 5 July 2011 (UTC)

There are now two alternative versions of the lead. They may both be better than the current lead. Please critique these versions in a constructive way. P0M (talk) 17:42, 4 July 2011 (UTC)

Two? They seem to be a bit lost in the discussion. If you could gather them, I'd be happy to comment. Tercer (talk) 22:04, 4 July 2011 (UTC)

Cross-talk with another universe, sorry. See the alternative version below Conclusion above.P0M (talk) 00:35, 5 July 2011 (UTC)

Comparing the following three opinions I wonder: if we accept all the three then, is it possible to say even a word about entanglement to "the general reader"? Or do we reject at least one of these three? Which one?

(1) "There are three universes of discourse, and the general reader probably only operates in the first of them. The first is the everyday world of bullets, sound waves, etc. The second is the abstract world of quantum mechanics, the "math that does not lie." The third is the world of interpretation in which people try to "make sense of" the equations."

(Very well stated!)

(2) "quantum nonlocality is the mysterious correlations, entanglement is the inseparability of the state needed to demonstrate nonlocality"

Another case where it depends on what "is" is?

Correlations are found in the first universe of discourse. They are the matches that we find in certain lab experiments. Non-locality is a very general characterization that humans make in the face of experiences that do not meet the expectations that we carry with us from the macro world. Some researchers use non-locality to explain why in the double-slit experiment the photon goes through slit A but behave differently than it would if slit B were closed -- despite the fact that slit B is at a place remote and physically separated from the slit that the photon travels through. Non-locality amounts to an assertion that the separation of some events in three dimensional space does not necessarily mean that these events are isolated in all the ways that we would expect from ordinary experience.

The idea of "entanglement" grew out of Einstein's trying to see the consequence of discourse universe two equations. He was therefore operating in the third universe of discourse when he stated what would be found were quantum mechanics correct, and that that his stated prediction has consequences applicable to the first universe of discourse. On that first, empirical, level, we see consequences of certain methodologies used in the laboratory to produce twinned particles. It's interesting to speculate on how researchers would have responded if they had discovered the correlations in the lab before a theoretical rationale had been offered for them. Quantum mechanics does provide a quantum theoretical description of the evolution of state(s) as two photons are produced by the sacrifice of one photon (or by other means), and these mathematical representations can be clarified by people operating on the third level, as Einstein did in his debates with Bohr et al. Entanglement, as seen in empirical studies, does not depend on theory. It is a real-world consequence of the preparation of certain experiments. It might be explained in a variety of ways. The "inseparability of the state" that quantum theoretically describes two or more linked particles serves to explain entanglement. "These twinned particles behave contrary to macro world expectations because they are entangled." Non-locality, on the other hand, is "demonstrated" by many kinds of experiments, but as far as I know there are just opinions on how pair members that are physically remote can be somehow relevant to what happens to each other. P0M (talk) 08:14, 5 July 2011 (UTC)

"...Einstein... was therefore operating in the third universe of discourse when he stated what would be found were quantum mechanics correct, and that prediction has consequences applicable to the first universe of discourse." --- really? As far as I know, Einstein died two years before the first "consequence applicable to the first universe of discourse" was found (by Bell). Thus, if we relegate all Bell-related topics to "nonlocality" then we have nothing to say on the first level. Boris Tsirelson (talk) 10:04, 5 July 2011 (UTC)

Sorry, "that" has two interpretations in my sentence. I meant that if his ideas (second and third level) about quantum mechanics turned out to be correct, then humans would see unexpected phenomena in empirical research. I did not mean to say: "Quantum theoretical predictions had consequences relevant to the entanglement issue which would be subject to investigation on the empirical level."P0M (talk) 15:39, 5 July 2011 (UTC)

I would have to see a revised version of (2) to decide whether there is anything that actually contradicts (1) or (3).

(3) "A quantum state is a mathematical model and/or a "convenient fiction.""

I personally have no doubt that there is something in reality to which a quantum state stands as a map. Human-made maps are inherently problematical. "Quantum states" belong on discourse level two. I think Tercer was the first one of us to make this point explicitly. I don't see any conflict with (1). I'd have to see a revised (2) to comment further.P0M (talk) 08:14, 5 July 2011 (UTC)

Boris Tsirelson (talk) 06:19, 5 July 2011 (UTC)

I don't think I get your point, professor Tsirelson. For me, it is nigh hopeless to agree on a definition of entanglement and strategy of explanation different from the technical notion of entangled state; in this view, Bell correlations would only be a motivation to study it, not a manifestation of the phenomenon. Are you proposing we do something more? Tercer (talk) 12:35, 5 July 2011 (UTC)

That is, you prefer to reject (1) and therefore not to make the lead understandable to "the general reader". OK, this is one of the possible decisions. As far as I understand, Patrick0Moran prefers to reject (revise, he wrote) (2), that is, to write something Bell-related here (POM, do I understand you correctly?). OK, this is another possible decision. I did not propose a decision. My proposal was rather, to choose a decision explicitly, in order to better understand each other. (I did my decision in my article,[3] = [4], but that article is not suitable to Wikipedia, - too much OR by synthesis etc.) Boris Tsirelson (talk) 15:37, 5 July 2011 (UTC)

But wait, Tercer, you just wrote ""If you do the experiment this is what happens" is the correct approach"; that is, you want to speak the first level language! "What happens in the experiment" surely is not a change of a quantum state! You also emphasize "not a shared randomness", therefore you rely on Bell! Now I don't think I get your point... Boris Tsirelson (talk) 15:53, 5 July 2011 (UTC)

I'm not saying it's easy, and that I'm not guilty of making the confusion myself. But I'm talking about shared randomness as a resource, and in this sense it can be compared to entanglement. So the Bell correlations are what you get with this resource that you don't with shared randomness, useful to illustrate the difference.

"What happens in experiment" was my answer to Phancy Physicist, on how to describe the Bell correlations without talking about causal relations between the outcomes of the measurement.

The rejection of (1) does not imply making the lead impossible to understand to "the general reader", it only stops us telling the whole story. What I say when I'm trying to teach entanglement to someone is always that you can't attribute states to the individual subsystems involved, only the whole system has a well-defined state. I then give the example of the spin of a pair of electrons, and rephrase the above statement as "you can't fully describe the system by only considering separately the properties of the individual electrons". They seem to mostly get it. In this way I don't give a precise definition of state, I don't say why you can't attribute states to the individual subsystems, I don't talk about mixed states, etc., but most importantly I don't say anything wrong, and if the reader wants to pick up another source to learn entanglement, he will succeed.

(1) is a statement of principal regarding how the article should be written, not some kind of a draft of content. It is saying that there is a foundation level, a math level, and a speculation level, and that it makes no sense to start the average well-informed reader on the speculation level. P0M (talk) 05:35, 8 July 2011 (UTC)

But I think you did reveal the point of contention between the editors: we need to make an explicit decision. I see that in your article (very good, by the way) you did not took a decision: you tried to cover all aspects/definitions of entanglement. But by doing that your article became very hard for the layperson (especially the section "Empirical entanglement"), and it became impossible to separate entanglement from nonlocality (or quantum pseudo-telepathy, for that matter. As a sidenote, I like it very much, despite the non-serious name).

So to defend my opinion: doing anything different from it would make the article very complicated, and use a definition of entanglement different from what you'll find in quantum theory textbooks. Also, we already have a good quantum nonlocality article, which takes my view. (I'm Tercer, decided to use my real name) Mateus Araújo (talk) 20:44, 6 July 2011 (UTC)

I cannot accept (2) because I don't understand the English used in it.

(2) "quantum nonlocality is the mysterious correlations, entanglement is the inseparability of the state needed to demonstrate nonlocality"

because to me it says (taking out modifiers, etc.) (a) quantum nonlocality is correlations. (b) entanglement is inseparability. I have no intention or desire at all to bring in Bell inequalities, especially in the lead. I've already tried to explain why I find (2) incomprehensible above. P0M (talk) 17:02, 5 July 2011 (UTC)

Well, this is a question to Tercer. Probably my poor English (I am not a native English speaker) hides from me some problem with that formulation. To me it looks clear enough (even if a bit "unofficial"). Thus I am unable to help. Boris Tsirelson (talk) 18:07, 5 July 2011 (UTC)

Maybe he meant "is related to the question of" or "is used to explain" when he said "is." I didn't realize you were quoting him, so I didn't see the entire context before.P0M (talk) 18:40, 5 July 2011 (UTC)

So, you assumed I quote you in (1) but not others in (2) and (3)... :-) Boris Tsirelson (talk) 19:07, 5 July 2011 (UTC)

I plead nolo contendere.P0M (talk) 00:53, 6 July 2011 (UTC)

Well, I am not a native english speaker as well, and I can't see what's unclear about my sentence. I can write it again with other words: entangled states are states that can't be written as products of states of the subsystems (inseparability), and quantum nonlocality is the violation of local causality, that is, the strong correlations shown through the violation of a Bell inequality. Mateus Araújo (talk) 20:53, 6 July 2011 (UTC)

O.K., I get the idea, but nonlocality is not correlation. It is one thing that might be a condition for explaining correlations that cannot be otherwise explained. So would it be acceptable to you to say: If a change of any kind at x, y, z, t is reflected by a correlated change at some "distant" point, x', y', z', t', and there is no explanation possible for a c or sub-c transaction in the interval t'-t, then the correlation may be attributed to nonlocality"? P0M (talk) 06:18, 8 July 2011 (UTC)

(Unindent)
The problem with:

"Quantum nonlocality is the mysterious correlations, entanglement is the inseparability of the state needed to demonstrate nonlocality."

is not a language problem. It is a problem of words and their referents. When you say "x is Y" in English you frequently indicate that an individual (or individuals), x..., are members of a set called Y. If you were going to make a Venn diagram then you would have a large rectangle for the universe, a big circle for Y, and a little circle (or circles) for x, x',...

You could avoid using Venn diagrams and talk about intensions and extensions, i.e., the definitions used and the range of things that fit those definitions. Then the questions become: (I) what are the intensions and extensions of (i) quantum nonlocality, (ii) mysterious correlations, (iv) entanglement, and (v) entanglement, and (II) how do these intensions and/or extensions equate? What makes an "x" a "Y" according to these intensions and extensions?

So, going back to the Venn diagrams, inside the Universe rectangle you would have a large circle for "correlations," a smaller circle within that for "mysterious," and within that there could be even smaller circles for subsets of mysterious correlations. Now to this set of sets you (linguistically) bring a potential set member called "quantum nonlocality." "Quantum nonlocality" is itself a set -- even if it turns out to be a set with only one number. Do you intend to convey the idea that the membership of the "quantum nonlocality" set is identical to the membership of the "mysterious correlations" set? Or is this set going to overlap part of the "mysterious correlations" set, there being some mysterious correlations that have nothing to do with quantum nonlocality? Or maybe you were imprecise in formulating the original sentence and it really should be the other way around because the instances of "quantum nonlocality" are more numerous than the instances of "mysterious correlations." In other words, maybe there are some kinds of quantum nonlocality that have nothing to do with correlations.

Again, we could look at the intensions of "quantum nonlocality" and of "mysterious correlations." How are the definitions of "quantum nonlocality" and of "mysterioius correlations" such that they have the same extensions?

Going on to "entanglement is the inseparability of the state needed to demonstrate nonlocality," the problems are rather more severe. Which is intended:
(a) "Entanglement is inseparability (of a certain kind).
(b) "Entanglement is a state (of a certain kind).
In other words, I can read this statement as:
(a') "Entanglement is the inseparability (of the state )[that is] needed to demonstrate nonlocality),
(b') "Entanglement is the (inseparability ([that is] needed to demonstrate nonlocality) of) the state,
(b) "Entanglement is the inseparability of [some] state AND Entanglement is needed to demonstrate nonlocality.
It is o.k. to be vague if the person you are communicating with already knows what you are talking about. At a certain time in my life I could have walked into my mother's home and said, "She is moving back." Mother would have known exactly what I meant. Nobody outside the family could have done anything but speculate about what I meant. That is the position I find myself in with regard to (2).

My guess would be that you intended to say:
(for "quantum nonlocality is the mysterious correlations")
"Quantum nonlocality is the refutation by the Universe of the human-created 'law' that says that things have to be in physical touch (at least via some chain of causation in 3-dimensional space and in time) for certain phenomena to be observed because empirical experience shows that correlations among distant relata do occur and we cannot explain them if the 'only in physical touch law" is in effect."

(for "entanglement is the inseparability of the state needed to demonstrate nonlocality")
"Entanglement is a kind of relationship between relata that must be set up in order to demonstrate nonlocality, and it involves those relata having a single, co-possessed, state."

If you are tearing your hair out because I so badly represent your original intention, I apologize. However, it has taken me one hour and forty minutes to try to "parse" these phrases and to select among multiple possibilities of interpretation.

The implications of these two paraphrases, put back together, have some interesting consequences: You need entanglement to account for nonlocality, and if you accept nonlocality you need to abandon the "in touch" rule. To me, this linked set of conditions does not get us in trouble with the well substantiated claim that actions through three-diminsional space cannot go faster than the maximum speed (i.e., c). But, again, all of these words are constructions that I have placed on your words with the benefit of a great number of preconceptions I bring to the conversation that other readers may not share.P0M (talk) 23:23, 6 July 2011 (UTC)

Addition of superposition idea to the lead

J-Wiki has added information that entanglement is a form of quantum superposition to the lead. I think that such highly technical references should be placed much later in the article. They will tend to flood the beginning reader with information s/he cannot understand, and therefore create an obstacle to understanding. Quantum superposition is on the third level where people say things in English about the "equations that don't lie" on the second level. I think it is better to keep to the concrete in the beginning. Once the empirical factors of entanglement have been introduced, the article can tell readers that there are equations that describe and predict the regularities of these empirical factors. Following that the article can discuss what various authorities have ventured to tell others about what these equations indicate about the nature of reality.P0M (talk) 03:33, 8 July 2011 (UTC)

Although the term "quantum superposition" may be quite technical, per the manual of style, use of such terms in intros is acceptable if they are essential and appropriately handled.

In general, specialized terminology and symbols should be avoided in an introduction. Mathematical equations and formulas should not be used except in mathematics articles. Where uncommon terms are essential to describing the subject, they should be placed in context, briefly defined, and linked. The subject should be placed in a context with which many readers could be expected to be familiar. For example, rather than giving the latitude and longitude of a town, it is better to state that it is the suburb of some city, or perhaps that it provides services for the farm country of xyz county. Readers should not be dropped into the middle of the subject from the first word; they should be eased into it. ( http://en.wikipedia.org/wiki/Wikipedia:MOSINTRO )

In the case of entanglement, I think it is necessary to refer to superposition to adequately describe what it is, and it is implicitly defined by the current wording. To avoid its use would be like avoiding use of the word "utensil" in the intro to the article "spoon", or avoiding some other generic noun for which the subject of an article is a particular example. Also, it's not much more technical than the term "quantum entanglement", so if someone is motivated to learn about entanglement, learning a bit about superposition should not be an excessive burden for them. However, I do think it would be better if the word could somehow be de-emphasized by artfully placing it later in the lead paragraph.J-Wiki (talk) 13:47, 9 July 2011 (UTC)

Recap

Isn't this what our discussions boil down to at present?

(1) "There are three universes of discourse, and the general reader probably only operates in the first of them. The first is the everyday world of bullets, sound waves, etc. The second is the abstract world of quantum mechanics, the "math that does not lie." The third is the world of interpretation in which people try to "make sense of" the equations."

N.B. This statement stands as a principle for structuring our article. It is not intended as a draft or outline for content. For the general reader we need to start on the concrete level and then say that there are equations that describe/predict the strange behavior observed in the lab, and beyond that there are attempts to make sense of what the math tells us about the universe that we would not otherwise know about.P0M (talk) 05:38, 8 July 2011 (UTC)

(2a) (Reworded, see my attempts to get the set theory stuff right above) Entanglement is a phenomenon characterized by correlations that go beyond the level of "shared randomness" (e.g., pulling ones socks for the day at random from a laundry bag and (almost) always getting an unmatching pair) to the level of obligatory correlations that exceed the laws of chance. This kind of correlation can be demonstrated in an ordinary undergraduate physics lab, but how to explain it is problematical. In the second, abstract QM, realm, the equations that work for us are single expressions (called "states") that apply to both members of an entangled pair. A state expression, in mathematical form, is such that when it applies to still-entangled photons both clockwise and counterclockwise spins are indicated (the spins are said to be "in superposition"), and when one or the other photon is measured for spin the equations take two individual forms. The new state expression for the photon that just got measured is made to reflect whatever spin was discovered for it, which is quite appropriate and seems easy to understand. However, the new state expression for the remaining photon cannot correctly assume a form indicating the same spin as the spin discovered for its twin. Explaining this well confirmed experimental result solely in terms of the equations is impossible as there is no calculation implicit within the quantum theoretical account laid down so far that would yield the changed result. As far as the math is concerned, then, the state expression does not change. However, it is also known that conservation of spin holds, so if the total spin was originally 0, a balance of clockwise and counterclockwise spin, when one photon assumes a definite clockwise or counterclockwise spin, then there would be an imbalance (defeating conservation) if the second photon exhibited the same spin.

Symbolically I guess we could handle this by saying:

QS_{superposition} = QS_{superposition}

and

QS _{resolved as clockwise} = QS _{resolved as counterclockwise}

(2b) It was anticipated by Einstein, and has been demonstrated repeatedly in the lab, that the "mysterious correlation" is established without the mediation of processes occurring in three dimensional space and time, and can be demonstrated by measuring the spin of the second photon at any time after the first photon is measured. The empirical, realm one, facts are perfectly straightforward, but the reason why the two photons can maintain their correlations despite being separated in space and time is not at all clear. As Einstein pointed out, explaining these correlations puts in question the idea that things must be in touch via physical processes that propagate through space at a velocity limited by c.

(3) "A quantum state is a mathematical model and/or a "convenient fiction.""

I think I've included this idea by indirect reference above.

I have now re-read all the intricate discussions above, and I think I have all the major parts in the right places. I think that the question regarding the original (1), (2), (3) set was whether we had to reject any of them. I originally could not answer, but now that I have reworded (2) I would accept all of these alternatives. However, that is only my opinion. What do others think? Matteus originally wanted to get rid of (1), but I think he took it as a statement about what content ought to be. My intention was to say something about the three different kinds of perspectives one can bring to the question of what entanglement is, and to say that the average well-informed reader has to be approached through the first way of knowing -- because that is all s/he has before we provide the additional content needed to begin understanding the equations and the interpretations of the equations.

I think it is possible to explain in the lead what will be the "realm 1" knowledge to be gained in the lab about entanglement, to state that the correlations noted can be mapped with appropriate quantum theoretical equations, and at least adumbrate the arguments about what these two kinds of results seem to imply and how some people hoped to get around the consequences that they felt uncomfortable with. I don't think we need to go into what Bell inequalities are, at least not in the lead. P0M (talk) 06:58, 8 July 2011 (UTC)

I am happy that J-Wiki has removed the word 'originally' - I didn't understand why it was there. I think the words "electrons, molecules even as large as "buckyballs", photons, etc., " are rather weak, but it took us ages to get to that! Myrvin (talk) 09:04, 8 July 2011 (UTC)

I took a look at how Brian Greene handled things, and took my lead from the fact that he always seemed to ease into things and never (?) had a generic term for what could be entangled. P0M (talk) 02:09, 9 July 2011 (UTC)

The lead is now down to 326 words. P0M (talk) 02:25, 9 July 2011 (UTC)

Buckyballs

This talk page has been rather quiet of late. May I stir things up by questioning the mention of buckyballs in the lead. They are not spoken of again in the rest of the article and there is no citation (nor anything in the buckyballs article} to provide evidence that such large molecules can undergo entanglement. I understand that they provide a possible upper bound for the scale of those things that can undergo QE, but there ought to be some more words to justify the assertion. Also, does it mean that there are entangled water and CO₂ molecules out there? Myrvin (talk) 12:14, 26 July 2011 (UTC)

Your question makes me wonder what the lower known limit in size is. I used the mention of buckyballs as a part of the implicit definition of the "things" that can get entangled.

The existence of other entangled molecules surely is possible. The only problem, and not a big one, would be to try to prepare entangled molecules and then test whether they are actually in that state. Maybe the way to look at the size issue would be to calculate the difficulty of preventing decoherence as volume and/or mass increases. How, for instance, did Zeilinger et al. prepare entangled "buckyballs and other large molecules" and then keep them from getting "disentangled" by being hit by a random mote of dust or whatever for long enough to do their experiment?

Suppose that somebody piloted a spaceship at a black hole in such a way that mass bending of space would give an equal probability of the ship following a geodesic to the left or the right and around the black hole. Where would the spaceship "show up" to observers on the other side of the black hole? If the spaceship did not "show up" before the two paths converged on the far side of the black hole, then the psi-wave for the spaceship would presumably interfere with itself, and the spaceship might "show up" at different places depending on whatever it is that "collapses" a psi-wave. This scenario might make a good science fiction plot, but to me it seems very unlikely that the spaceship could go any distance after it entered the "two equally likely paths" region before hitting something and "materializing" as a single spaceship on one path or the other. That's my extremist way of thinking about the upper size limit of quantum entanglement experiments.

I found a couple citations for the article.P0M (talk) 14:08, 26 July 2011 (UTC)

I think that if they're going to be mentioned at all, it should not be in the first sentence of the article. Entanglement is a general feature of QM and applies to everything. What subset of things can be usefully or verifiably entangled is another question altogether. In my opinion the first sentence of this article is horrendous. Isocliff (talk) 01:18, 27 July 2011 (UTC)

As an amusing side-note, if we knew an upper limit on the size of entangled objects then wouldn't that effectively ruin the MW Interpretation? This would be in stark contrast with the fundamental theorem of interpretations of quantum mechanics: "If there exists a question whose answer unilaterally and convincingly favours one interpretation over another, then one can never have a full answer to that question". Also known as Mermin indeterminacy. --Sabri Al-Safi (talk) 14:36, 14 October 2011 (UTC)

Sure. These things were discussed repeatedly long ago (see e.g. here). But do not confuse an upper limit on the size of entangled objects with an upper limit on the size of things can be usefully or verifiably entangled by humans. Boris Tsirelson (talk) 15:23, 14 October 2011 (UTC)

Bell states - complementary value???

"When a measurement is made and it causes one member of such a pair to take on a definite value (e.g., clockwise spin), the other member of this entangled pair will at any subsequent time[5] be found to have taken the complementary value (e.g., counterclockwise spin)"

I think this sentence is false. If the system is in one of the Φ Bell states, it will not take the complementary value but the same value as the other member of this entangled pair. --Schiefesfragezeichen (talk) 15:50, 22 August 2011 (UTC)

The QM formalism can accommodate either possibility, although the possibility in which the partner-system collapses into the "complementary" state is the one most often realized in practice. Its true that this could be made more clear, and more general, but the statements not wrong by itself. Isocliff (talk) 19:51, 22 August 2011 (UTC)

Well, let's say the statement is not true in its generality. I agree with you - it needs revision. --Schiefesfragezeichen (talk) 16:04, 29 August 2011 (UTC)

So we need a better term than "complementary". "Corresponding"? P0M (talk) 03:38, 2 December 2011 (UTC)

Instantaneous communication without entanglement

Need a little more clarification for laymen: Is instantaneous communication/quantum correction between non-entangled particles nonexistent? Theoretically, can that happen without entanglement?Mastertek (talk) 15:07, 23 October 2011 (UTC)

QM does not discuss deterministic (non-entangled) particles. Other parts of physics (such as special relativity) prohibit instantaneous (faster than light) communication. David Spector (talk) 22:10, 29 November 2011 (UTC)

Anything that involves a process that propagates from atom to atom, molecule to molecule, billiard ball to billiard ball, etc. is limited by the speed of light. In our daily lives we treat things like steel rods as though they are absolutely incompressible and rigid. If you pull on the handle of a steel fishing rod you expect the tip of the rod to move at exactly the same time. But the reality is that the steel rod is composed of many components that are joined in a way analogous to the connections from car to car on a long train. When a locomotive starts to move a train down the track you can hear when the slack is taken up between the engine and the first car, then when the slack is taken up between the first car and the second car, and so on. If you send a radio message, your voice is mapped onto a radio signal that goes forth at the speed of light and is then retranslated into sound waves in radio receivers that pick up your message. That's about as fast as you can ever hope to get something you do here to cause a change somewhere else.

If what you mean by communication is "transmitting a message through space by some physical process," then no communication is instantaneous. Light is much faster than any other transmission modality, and yet it is limited to about 300,000 kilometers per second

The unexpected thing about entangled particles is that two entangled particles act as though they have an absolutely rigid connection "between" them. Or, actually, it is more like the two particles are two ends of one rigid bar. So when something happens with one end it is happening to the other end too -- with no delay in time because there is no "taking up slack chain of action" such as would happen with a freight train starting up. The problem for comprehending this mystery is that there is no physical connection between what we have been thinking about as the two ends of a rigid rod. But what I have said above is only an analogy.

The way humans have learned to talk about this stuff that seems to have the fewest problems with it is to say that when two photons or other particles are entangled they share the same state. There is something about them that is one and the same. Where is it? That's a question like Vimalakirti would give a smart answer to. Our ideas of location in space and time evidently do not apply to "states." The state of two entangled particles is shared and is the same with itself until something happens that requires that one entangled particle "materialize" or "show up" as having one spin or the other spin, one polarization or the other polarization, etc., itc. When the entangled particles, which have been isolated from the universe we all share for a while, come back into touch with the universe because of, e.g., running into a wall, then one of them has to decide that it is, e.g., spin positive. When that happens the other one will no longer be both spin positive and spin negative either, and it will have to take the other choice available. Then there is no longer a single shared "state" but, instead, there are two different states.

Entanglement is extremely unsettling to physicists because it upsets their ordinary idea that when something is changed here and something else changes, accordingly, there, it is because some causal interaction has passed (at the speed of light or less) between them. In the case of entanglement, measuring something here (making it reveal whether it is spin up or spin down, or making it reveal some other such characteristic here in this lab) results in a determination of what must be revealed when a second measurement is made "over there." P0M (talk) 03:35, 2 December 2011 (UTC)

A clarification (?)

The following sentence has been added:

Although the "effect" of quantum entanglement appears to exceed the speed of light, there is no violation of special relativity or causality which declares that information cannot be transferred faster than the speed of light.

How can an "effect" not be paired with a cause? Is the word put in scare quotes in the quoted sentence because of this very question?

How can causality get violated? A description, even a highly abstract and tightly organized description such as a theory, cannot be violated. A description is not a law of heavenly commandment. Einstein postulated that the speed of light is the highest speed that can be achieved by anything and that it has a constant value. It follows from that postulate that anything that moves through the space-time continuum will not exceed c. So any transmission of a force from one place to another will not exceed that speed. If "information" means a physical sign of some state of affairs such that a decision on what to do about the state of affairs can be validly based on the presence of the sign, then the assertion is that such a physical state of affairs (a morse-code radio transmission for instance) cannot reach its recipient at any speed faster than c. Isn't that all that is at stake here? It is known (1) that one kind of thing that happens in the universe is that forces move through space at c, (2) that a change in something at one place in space-time will transmit a change to something at some other place in space-time, (3) so a change will always occur at a location d distance away at a time equal or greater to t=c/d. If the first event is called a cause and the second event is called an effect, then the effect will always occur at a time t=c/d or later than the cause.

As for entanglement, either nothing at all is happening to the quantum states of entangled entities after they have separated, or something very interesting is happening. First, if causation involves priority in space-time, then there is no causation involved between the entangled pairs. The change in state of one member of an entangled pair involves a change in state of the other member at the same time. If we look at the interaction between the measuring apparatus and the entangled twin particles, then the idea of causation is preserved if the measuring apparatus goes into operation at some time t and the entangled particles change state at some time t+1.

If we conceptualize the experiment in somewhat different terms, then the measuring apparatus goes into operation at time t=1, the measuring apparatus acts only on one of the entangled twin particles, and the fact that the first of the entangled twin particles changes state somehow determines how the second of the twin particles does or will at the time of measurement change state in a way that is "correlated" to that of the first.

If it is true that in the beginning entangled particles each have a superposition of states, then, whether you call it causation or something analogous to causation, it becomes necessary to understand how the two particles coordinate their changes of phase even across astronomical distances.P0M (talk) 21:20, 25 November 2011 (UTC)

"It follows from that postulate that anything that moves through the space-time continuum will not exceed c." Language must be used carefully so we understand what is being said and so that the tool of mathematics (which is precise) can be used. There are lots of things that move through space and time that exceed a velocity of c. The only speed limitation imposed by nature is on information and matter, and that limitation applies to observations in an inertial frame of reference.

Superpositions of allowed (quantum) states exist at specified times and places. They refer to tiny phenomena, such as elementary particles, or to larger phenomena that share a quantum state, such as superfluid helium or superconductivity of electricity. There is no evidence that particles (which can be observed) coordinate anything faster than c. Such evidence would contradict the speed limit c on information propagation. However, wave functions, which describe the way that superposition states change in space and/or time, can extend throughout a region of space-time and appear to reflect sophisticated coordination between actions happening at far-away times and places. Wave functions may appear to violate causality, but such apparent violations are illusions appearing only in observable values, not in the wave functions themselves, which are always consistent with respect to the entire system involved.

QM does not violate causality. However, it may predict that there is a finite possibility that the fluid in a cup may overcome gravity and leave the cup. In real life, the only way that happens is if the fluid is in a macroscopic quantum state, such as can happen with liquid helium. It doesn't happen with water, so our common experience is not violated by QM.

Many QM experiments challenge us, and seem like magic tricks, because the rules of quantum reality are not the rules we are familiar with in daily life. We live in an intermediate scale of size, temperature, time intervals, etc., where Newtonian mechanics applies very accurately. Consequently, we live by "common sense" physics. It is no surprise that we try to coerce the reality revealed by experiment in other size and temperature (etc.) regimes to "make sense" to us. However, physics objectively reveals the truth of various regimes, fearless and independently of our common sense physics. Even Einstein seemed to find QM unnatural--he felt that QM must be very incomplete; it could not be true as it stands. Yet, subsequent theory and experiment has upheld even the earliest results in QM, such as double-slit interference, strange though they seem to us. David Spector (talk) 15:37, 2 December 2011 (UTC)

The word "effect" was put in scare quotes in the article, which makes it "o.k." I guess. But it is also true, as you say, that "language must be used carefully so we understand what is being said." That is why I objected to the supposed clarification.P0M (talk) 16:28, 2 December 2011 (UTC)

I see your point about this small issue, but all these QM articles are just a starting point, particularly for the general public who don't realize how their very limited experience in time, temperature, pressure, gravity, electrical current, etc. ill prepares them to understand the remarkably dramatic range of the description of reality that is being developed by science. Even scientists find it difficult to expand their common sense beyond our familiar classical regime, as you can see in the inconsistent or argumentative comments they make on any physics forum when articles are published on results in QM, cosmology, special relativity, etc.

And all this tumult is as nothing compared to the coming insights when philosophy has its turn, and the Absolute, changeless Self is finally identified subjectively through the experimental mental procedure known as transcending (about which there is as yet no WP article due to the near-monopoly on this knowledge held by the Transcendental Meditation organization). We are about to discover that we, as the human race, are missing an entire necessary state of consciousness (in addition to waking, dreaming, and deep sleep). I'm thinking this paradigm transformation may begin happening as early as five or ten years from now. The importance to society will be undeniable from the standpoint of the beneficial health effects alone. Wait until you see the difficulty the general public will have getting used to such ideas, again seeming to be in contradiction with common sense. Having been prepared by the mind-expanding vistas opened by QM, physicists may be, as a group, alert early adopters of transcending. Stranger things have happened. Sorry for the digression. David Spector (talk) 18:22, 2 December 2011 (UTC)

Entangling macroscopic diamonds at room temperature

Editors here will want to use:

• "Entangling macroscopic diamonds at room temperature". Science. 334 (6060): 1253–1256. 2 December 2011. doi:10.1126/science.1211914. {{cite journal}}: Unknown parameter |authors= ignored (help); Unknown parameter |laysummary= ignored (help)
• http://www.sciencemag.org/content/334/6060/1253/suppl/DC1 supplementary materials]

Enjoy!LeadSongDog come howl! 16:44, 2 December 2011 (UTC)

Yes, I enjoy! Boris Tsirelson (talk) 06:38, 13 December 2011 (UTC)

Where are 3-particle experiments !?!?!?

There are 3-particle versions of the 2-particle entanglements. Yet I see no mention of them here! Surely you all know whereof I speak -- I came here to find the name. :smack: Jamesdowallen (talk) 17:55, 4 January 2012 (UTC)

There is a wikipedia page for Multipartite Entanglement, albeit a very messy one - http://en.wikipedia.org/wiki/Multipartite_entanglement --Sabri Al-Safi (talk) 18:25, 11 January 2012 (UTC)

Confusing sentence

Somebody tried to improve the following sentence by adding "i.e. one" in parentheses. The sentence didn't make sense before, and the addition only makes more obvious how strange it is:

In general, a bipartite pure state ρ is entangled if and only if one, meaning both (i.e. one), of its reduced states are mixed states.

If anybody understands what the intended meaning is, please reword.P0M (talk) 21:17, 12 December 2011 (UTC)

It should mean that the following three conditions (on a bipartite pure state) are equivalent: (a) it is entangled; (b) at least one of its reduced states is mixed; (c) both of its reduced states are mixed. Let a native English speaker formulate it nicely... Boris Tsirelson (talk) 06:33, 13 December 2011 (UTC)

I think the English is fine, but I am having trouble with seeing how to put this in formal logic because it appears to be tautological in that both its reduced states being mixed makes it impossible that at least one of its reduced states is not mixed. So what is the use or function of (b)?

To me it looks like:

"A bipartite pure state ρ is entangled." ↔ ("At least one of its reduced states is mixed."∨"Both of its reduced states are mixed.")

Maybe you are saying:

"A bipartite pure state ρ is entangled."&("At least one of its reduced states is mixed."∨"Both of its reduced states are mixed.")

I guess the word "equivalent" is puzzling to me in your formulation. If you replace ∨ with & above, then (b) is unneeded because (c) means: (b) & "Any other of its reduced states must be mixed."ll

So I still need some help.P0M (talk) 16:01, 14 December 2011 (UTC)

I know that you are not a mathematician. :-) Condition (c) is (seemingly) stronger than Condition (b). That is, (c)→(b) evidently. But it does not mean that (b)→(c) evidently! Thus, it does not mean that (b)↔(c) evidently. Nevertheless I claim that (b)↔(c); this is not evident (at least for non-experts) but true. And so, finally, the claim is (a)↔(b)↔(c). Boris Tsirelson (talk) 18:47, 14 December 2011 (UTC)

Thank you. I think I now know what needs to be said. In this case, formal logic is of greater use than ordinary English.P0M (talk) 19:43, 14 December 2011 (UTC)

Formal logic, really? For a wide audience? Or maybe just say: ..."in fact, it cannot happen that one of the two reduced states is mixed while the other is pure" (or something like that). (I mean, it cannot happen for a bipartite pure state; for a bipartite mixed state it can happen, of course.) Boris Tsirelson (talk) 21:21, 14 December 2011 (UTC)

So it is true that you really do read minds! I was about to ask you for an instance of a false case.

Above, I proposed:

Both its reduced states being mixed makes it impossible that at least one of its reduced states is not mixed,

and you just said:

It cannot happen that one of the two reduced states is mixed while the other is pure"

I fail to see how these two statements are different. "Pure" means "not mixed," no?

Maybe I am missing something in the context, either the experimental context or the theoretical context, that separates the following two statements temporally: "(b) at least one of its reduced states is mixed; (c) both of its reduced states are mixed." I can understand that one might determine the status of two reduced states in sequence, but does that have some significance in the way that the order of operations in matrix multiplication has a significance not relevant to ordinary multiplication?P0M (talk) 04:55, 15 December 2011 (UTC)

No, it is about a single bipartite state, at a single instant; the time is not relevant.

Yes, "pure" means "not mixed".

Sure, "Both its reduced states being mixed makes it impossible that at least one of its reduced states is not mixed" (which is a bit of pure logic, irrespective of any physics).

But the trivial statement above does not exclude the (seemingly possible) case of one pure and one mixed. Right? Both the assumption and the conclusion are violated in this case; so what? Boris Tsirelson (talk) 06:41, 15 December 2011 (UTC)

Indeed, so what?

Above you said: "Condition (c) is (seemingly) stronger than Condition (b). That is, (c)→(b) evidently. But it does not mean that (b)→(c) evidently! Thus, it does not mean that (b)↔(c) evidently. Nevertheless I claim that (b)↔(c); this is not evident (at least for non-experts) but true. And so, finally, the claim is (a)↔(b)↔(c)."

(c)→(b) is o.k., logically at least. In fact it is a tautology. We need the facts, however.
(c)→(b) does not mean that (b)→(c), but on the other hand it does not exclude the possibility either. We need the facts to evaluate further.
Neither of those sentences mean that (b)↔(c), but on the other hand if it turns out that (c)→(b) and (b)→(c) are both true representations (not destroyed theories or old wives tales), then (b)↔(c). At this point we are only considering how things would work out just looking at the functions of logical connectives. Saying (b)↔(c) means that at least one of its reduced states is mixed if and only if both of its reduced states are mixed. And then working backwards you want to work in the statement "The bipartite pure state is entangled," making the whole thing:
"The bipartate pure state is entangled if and only if at least one of its reduced states is mixed if and only if both of its reduced states are mixed."
That sentence is incompatible with the statement that "One reduced state of the bipartate pure state is pure and another reduced state of the bipartate pure state is mixed."
So far we are only looking at empty schemata. We may have a clearer idea than before what what empirical evidence we would need to further evaluate these assertions, but that has to come from the laboratory. We might find a case of some bipartate pure state with a pure reduced state and a mixed reduced state. Logic does not tell us whether in that case entanglement would be exhibited. But if it turned out that way, then the earlier assertion that both reduced states have to be mixed would be fatally challenged, no?
Maybe we need a simple list of what the conditions are that are consistent with entanglement, and what the conditions are that are not consistent with entanglement.P0M (talk) 09:16, 15 December 2011 (UTC)

I am afraid I miss your point (after all, the whole matter is very simple), but I try to reply. The mathematical theory of pure bipartite states proves that it cannot happen that one reduced state is pure and the other mixed. The same theory proves that in the case of pure reduced states entanglement is absent, while in the case of mixed reduced states entanglement is present. (Do not ask me what happens in the case of one pure and one mixed, or else I'll ask you whether or not 4<5 in the case of 2+2=7.) All that holds irrespective of any experiments (except for the fact that the whole theory is ultimately experiments-based, of course).

Moreover, the notion of entanglement (as presented here, unlike my article on CZ) is not formulated on the empirical level. It is about theory, not experiment. True, this entanglement sometimes has (very important) empirical implications. But it is not defined in empirical terms. Boris Tsirelson (talk) 10:38, 15 December 2011 (UTC)

And here is an elementary counterpart.

The following three conditions on a parallelogram ABCD are equivalent:

(a) its area equals AB times BC;

(b) at least one of its four angles is right;

(c) all the four angles are right.

Yes, as simple as this is! Boris Tsirelson (talk) 11:25, 15 December 2011 (UTC)

Thank you.P0M (talk) 16:49, 15 December 2011 (UTC)

entanglement and physical interaction

I suggest to change the introductory sentence, in order to define the entanglement without mentioning the physical interaction. I say this in the light of measurement-based entanglement protocols, which use path-erasure. Now I don't have time, but if no one objects, I will proceed with this idea Oakwood (talk) 22:25, 23 December 2011 (UTC)

"Attempts to talk around the phenomenon" section

The "Attempts to talk around the phenomenon" section has no references and reads like original research. Should probably either be removed or reworded (with citations added). I'm not sure the section adds any real value to the page so unless people care terribly or are willing to fix it I vote for just deleting it. Medlefsen (talk) 20:35, 25 January 2012 (UTC)

Some clarification about the definition in the first sentence

The first sentence states "...properly described by the same quantum mechanical description (state), which is indefinite in terms of important factors..."
Can someone kindly clarify, what "indefinite" means in this context? It would be much appreciated if someone explains how it is "indefinite", taking the example of one of the Bell states. BotCyborg (talk) 14:25, 21 August 2012 (UTC)

Yes, these are quite strange formulations. "each resulting member of a pair is properly described by the same quantum mechanical description (state)" – no, the pair has a state; each member has the corresponding marginal, mixed state, but this is hardly meant in this phrase; and why "the same" state? Also: "their shared state is indefinite until measured" – no, the state of the pair usually is a pure state, in no way "indefinite"; of course, a measurement changes it, but this is not specific to entanglement; a quantum measurement in general changes a state. Boris Tsirelson (talk) 17:35, 21 August 2012 (UTC)

Concept

I removed the stuff about the effects of entaglement travelling at thousands of times the speed of light. The second reference certainly doesn't say that, since it's looking at the situation if there were a preferred frame.Sylvia (talk) 08:53, 29 October 2012 (UTC)

I have undone MrOllie's edit that reversed the change I made above, because he has not responded to my edit to his talk page. Sylvia (talk) 03:35, 1 November 2012 (UTC)[

The following statement: "However, quantum entanglement does not enable matter to convey genuine information beyond the relativistic speed limit of normal spacetime.[9]" Is not correct.

[9] The article referenced - "Quantum teleportation achieved over record distances" - states in no uncertain terms: And although part of the transfer happens instantaneously, the steps required to read out the teleported quantum state ensure that no information can be communicated faster than the speed of light.

This statement confirms what has already been established by experiments with entangled particles (and theoretically projected) that they do "instantaneously" share information i.e. faster than speed of light. This has been sadly muddled here and will mislead many people in thinking the state change is not instantaneous.

It's unfortunate that the referenced article uses the word "instantaneously" because the word really has no place in physics. It is not a covariant concept and no reasonable meaning can be attached to it except in the special case of measurements made in the same reference frame. Sylvia (talk) 04:42, 6 December 2012 (UTC)

The evidence for non-locality and "instantaneity" is overwhelming, as was predicted by early quantum physicists. There have been many experiments confirming that two entangled photons - without being able to send signals to each other - react to each other's situation instantaneously and regardless of distance. This has been firmly established with empirical evidence backed up by solid scientific research. There is no place in physics for scientists who remain biased against empirical evidence. User:Jamenta — Preceding unsigned comment added by 71.198.153.153 (talk) 02:34, 7 December 2012 (UTC)

I draw a distinction between non-locality, which is demonstrated by experiment together with Bell's theorem, and the notion of instantaneity, which is a problematical concept involving the notion that things happen at the same time. Things that happen at the same time in one frame of reference happen at different times in others, unless they are colocated in space. The article already points out that the correlations remain intact even when the measurements are made in reference frames where the order of measurements depends on the observer's reference frame. If something happens instantaneously from the perspective of one observer, it is nothing like instantaneous from the perspective of the other, yet there is no way of perferring one observer over the other. The word "instantaneous" gets bandied about in popular descriptions of this process, but it doesn't work, isn't part of the science, and should be omitted from the article, lest it further mislead the reader. Sylvia (talk) 23:55, 7 December 2012 (UTC)

Empirical evidence as such shows rather that they are unable to send signals to each other. In combination with some classical principles it shows also that they react to each other's situation instantaneously and regardless of distance. Boris Tsirelson (talk) 07:33, 7 December 2012 (UTC)

What was horridly misleading to the reader was the state of the 2nd paragraph in this article, before much needed alterations were made (by myself) - to more accurately reflect the current knowledge and evidence in regards to the quantum entanglement phenomena. Although one might quibble about the definition of "instantaneity" - it should have been sufficient to have made it clear from the beginning, the most prominent empirical facts that have been uncovered by the entanglement phenomena i.e. the lack of any known physical signals, and the process of change occurring faster than the speed of light. In addition, the Copenhagen interpretation is not the last word on the measurement problem - and yet the second paragraph text also implicitly (by omission) misled in this regard. Were one not to know any better, upon first reading the original text, one could have easily assumed that the quantum entanglement phenomena fell into the category of classical physics - which the quantum physics world has long left behind for decades. Jamenta (talk) 09:11, 9 December 2012 (UTC)

Well, the Copenhagen interpretation is not the last word on the measurement problem. But do you think that your phrase "the collapse must be caused by the consciousness of the observer" is the last word? Just consciousness? Not decoherence, Many-worlds interpretation, Consistent histories etc? Boris Tsirelson (talk) 12:32, 9 December 2012 (UTC)

Decoherence does not address the cause of the quantum wave function collapse or attempt to explain the measurement problem. Jamenta (talk) 21:34, 9 December 2012 (UTC)

Since the quantum wave function never collaspes and the entire universe is entangled, that's a good thing. Hcobb (talk) 22:55, 9 December 2012 (UTC)

Although it is remarkable how the quantum-entangled particles are somehow aware of each other's state, regardless of distance (and likely time), unfortunately, the collapse of either particle is subject to Heisenberg's uncertainty, and therefore seems uncontrollable. Although maybe on a meta-scale with statistical results of all collapsing entangled particles, FTL communication might be possible? Jamenta (talk) 20:10, 10 December 2012 (UTC)

Particles do not collapse. And that's a good thing. If the electrons in say Lithium collapsed into these hypothetical point particles, what would keep them from dropping down to a one-s-three orbital configuration, without constant FTL links between them? Hcobb (talk) 20:44, 10 December 2012 (UTC)

Whatever. You're doing exactly what the original text in this article did, intentional misinformation, mis-characterizing what people are saying. By the way COBB - particles do not exist in actuality until after the wave function collapse. Before that - there is nothing. ZIP. NADA. I know - you can't wrap yourself around that. You still got particles orbiting like we're in some kind of 4th grade physics class. Jamenta (talk) 01:14, 12 December 2012 (UTC)

The Universal wavefunction never collapses. Take for one concrete example, the electron orbit. (The thing that keeps Concrete from collapsing.) These electron wave functions are stable for at least four billion years (for example the Earth), or even 13.4 billion years (the rest of everything). If wave functions don't collapse in the lifetime of the Universe (Look, no Hydrinos!), then why would anybody fear zombie kittens? Hcobb (talk) 03:09, 12 December 2012 (UTC)

Sorry, two slit experiment has been well established for nearly half a century or more. I suggest you read a few more physics books and snap out of your Newtonian zombie funk. Jamenta (talk) 03:13, 10 January 2013 (UTC)

About collapse by consciousness, see Wigner's friend. Boris Tsirelson (talk) 08:07, 12 December 2012 (UTC)

You don't need consciousness or many worlds. Particle physics can't enforce Fermi–Dirac statistics without FTL radio (How do the three electrons in Lithium coordinate NOT all dropping down into the lower energy 1s orbital together, without FTL links between these tiny particles?) Since particles don't exist and aren't needed, let's move Particle physics to Wavepacket physics. Hcobb (talk) 12:12, 12 December 2012 (UTC)

Surely, classical particles do not exist. Quanta of fields exist (not classically, of course), and are usually called particles. Boris Tsirelson (talk) 18:50, 12 December 2012 (UTC)

Challenging "the collapse must be caused by the consciousness of the observer"

It cites von Neumann's Mathematical Foundation of Quantum Mechanics. I searched inside the book for the word "consciousness" (or any superstring of it) using Google Books and it returned nothing. http://books.google.com.ec/books?id=JLyCo3RO4qUC&q=+consciousness#v=onepage&q=consciousness&f=false

I'm removing it unless someone cites the page where von Neumann claims it. 190.131.114.134 (talk) 17:15, 22 December 2012 (UTC)

I have put the section back and have included numerous additional references. Please do not excise unless you plan to concretely discredit the references I have provided, other than a spurious and ridiculous argument that since Von Neumann never used the word "consciousness" he never implied it. Many physicists have worked on the well-known Quantum mind-body problem which Von Neumann logically posed, and the question remains valid today. Jamenta (talk) 03:04, 10 January 2013 (UTC)

And now the lead is inconsistent. "When a measurement is made and it causes one member of such a pair to take on a definite value..." — but wait, what causes this? A measurement itself (that is, a special interaction with an apparatus), or consciousness (a special interaction between the apparatus and someone)? Boris Tsirelson (talk) 11:17, 10 January 2013 (UTC)

The final measuring apparatus is the non-physical consciousness of the observer (i.e. von Neumann chain.) It cannot be a physical measuring device since it too is subject to the universal wave function Jamenta (talk) 18:48, 12 January 2013 (UTC)

Which is entirely appropriate given the number of interpretations that now exist, and also given that the Copenhagen Interpretation has lost ground in the last decade while the Von Neumann Interpretation and variations of it have become more prominent. Jamenta (talk) 18:20, 12 January 2013 (UTC)

Hmmm... But did you read the next section on this page? Boris Tsirelson (talk) 19:33, 12 January 2013 (UTC)

Yes I did. But the way the article was originally written, one would have assumed very early on that the Copenhagen Interpretation was the most superior, dominate interpretation (which is not true - it has been losing ground recently.) In addition, the original text misled in regards to the now well substantiated phenomena of non-locality, and the FTL information exchange (using layman's terms.) Both should be highlighted early in this article, as both are the most significant discoveries of quantum entanglement. In addition, there is no reason to dismiss John Von Neumann - perhaps the greatest physicist of the last century outside of Albert Einstein. His work is solid, and is the basis of the Von Neumann intepretation, and has grown in significance over time, given the prominence of consciousness studies and the "hard" mind-body problem that continues to be the subject of a growing body of scientific and psychological research today. Jamenta (talk) 00:20, 13 January 2013 (UTC)

Do you really accept the consequences noted below? Do you really want to rewrite the article accordingly? It seems, you rather avoid taking them seriously. Boris Tsirelson (talk) 06:50, 13 January 2013 (UTC)

If you wish to refute John Von Neumann - be my guest. So far, you haven't even scratched the surface. Jamenta (talk) 08:16, 16 January 2013 (UTC)

And you did not address at all any one of the two my "Consequences". Well, I see that we cannot interact successfully. Fortunately, I am not responsible for the content of Wikipedia. Maybe some day more competent and numerous editors will join; maybe not. Happy editing. Bye. Boris Tsirelson (talk) 11:38, 16 January 2013 (UTC)

I agree with Boris Tsirelson, philosophical interpretations and speculations published in humanities journals do not belong here, there is a separate article for them: http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics.

I have provided absolutely solid references to the few sentences I provided. The original article referenced the Copenhagen Interpretation (which you will not just find in "humanity journals") nor will you find the Von Neumann Intepretation "speculation" that will be found in "humanity journals". What does not belong here is this kind of reasoning and an unwillingness to explain to me why the references I provide are invalid. Please do. Jamenta (talk) 09:48, 22 January 2013 (UTC)

I'll remove them, please don't reverse until a consensus is reached in the talk page for their reinclusion. 89.43.152.3 (talk) 11:35, 20 January 2013 (UTC)

Will reinsert original text. Clearly no consensus will be reached if you are unwilling to recognize the references I provide (which I suspect is the real problem here.) The interpretations are valid positions in Quantum physics (they are not philosophical speculation.) I am willing to be reasonable if you can show me how the citations I provide are invalid. The citations I give and statements made are supported by some of the leading quantum physicists in the world. Please refute. Jamenta (talk) 09:18, 22 January 2013 (UTC)

Wikipedia is not a forum for discussion about the merits of different arguments, it's based on consensus. We can talk about it here, but you cannot insert your personal point of view in a article until such a consensus is reached. I'll remove it again, please refrain from reinserting the paraghraph until more editors will agree that it belong here. Mihaiam (talk) 17:36, 24 January 2013 (UTC)

Please refrain from removing the valid text without sufficient reason. I have provided solid citations to articles and books - including references to other supporting sections of Wikipedia on the given statements (which apparently you and your buddies have not removed from Wikipedia.) Consensus is not you - or whomever you can find down the hall from your office - arbitrarily discounting reasonable text that has been provided citations - including other Wikipedia pages. You have provided no valid reason why my statement is false and once again - the Von Neumann and Copenhagen Interpretations are well known in quantum physics. To argue otherwise is to pretend ignorance. Jamenta (talk) 03:19, 26 January 2013 (UTC)

If you remove text without challenging the citations I will continue to reinsert the references to the Von Neumann and the Copenhagen Interpretations, since they are well known and solidly supported in the Quantum Physics community despite your unscientific prejudice toward them. Jamenta (talk) 03:28, 26 January 2013 (UTC)

Please review Wikipedia edit policy and selfrevert rather than making changes opossed to the consensus reached here. http://en.wikipedia.org/wiki/Wikipedia:BRD Mihaiam (talk) 09:36, 26 January 2013 (UTC)

Please review Wikipedia policy if you wish to arbitrate. I have provided solid citations for my statements in GOOD FAITH. There is no controversy regarding either the Copenhagen or the Von Neumann Interpretations in Quantum Physics. I have provided solid references to books and other Wikipedia web pages. Jamenta (talk) 15:54, 26 January 2013 (UTC)

Wikipedia is build on consensus, not faith. There are a lot of controversies regarding your interpretation presented in the apropiate article, please move your contribution there. http://en.wikipedia.org/wiki/Quantum_mind/body_problem Mihaiam (talk) 17:50, 26 January 2013 (UTC)

Wikipedia is built on good faith, of which you are not practicing. There is no controversy that the Copenhagen or Von Neumann Interpretations exist, and they are still cited today - and it is ABSOLUTELY REASONABLE and valid they be mentioned regarding quantum entanglement. In fact this article references Interpretations a few paragraphs further down - but you have not excised these references - you are only focused on my statements - in an abusive harassing manner. You say Wikipedia is based on consensus - but consensus is not your intention - you simply want to excise the text and have provided no reasonable rationale why my citations are invalid. This is clear because I have requested REPEATEDLY that you provide a valid reason why the citations I provide are no good (or the Interpretations provided are not related to Quantum Entanglement.) Instead, you have entirely ignored my repeated requests here, and therefore, you are not acting in good faith. Consensus is not you unilaterally removing someone's text repeatedly. Consensus is when we both agree. So far you have provided zilch reason (or straw man reasons) why you're being an asshole. Jamenta (talk) 04:05, 27 January 2013 (UTC)

Your contribution is giving undue weight to a particular interpretation. It is not consensus building to insist on making changes despite several editors objections. Please refrain from making personal remarks and selfrevert the undue changes. Mihaiam (talk) 08:08, 27 January 2013 (UTC)

Collapse by consciousness? Face the consequences!

If we take the "collapse by consciousness" viewpoint then:

• Consequence 1.

In famous experiments with entanglement (Aspect's, and other), thousands of entangled pairs are created and measured, each pair during a microscopically short time; no human observes individual results in real time (and usually, never at all); rather, a computer registers them, calculates frequencies (statistical averages) and displays these to a human observer.

Does it mean, thousand of collapses? No; rather, a single collapse after the whole experiment. No definite values for individual spin projections; only a definite value for the average.

See references I provided including Henry P. Stapp's recent books on the subject. There are many credible quantum physicists in the past and today (not the least, John Von Neumann) who maintained that it is the conscious observer that is the ultimate cause of the wave function collapse. This is not a "fringe" concept (as you and your friend here are trying to make it out to be) and therefore has every right to be included in this article. Jamenta (talk) 09:53, 22 January 2013 (UTC)

• Consequence 2.

Do you believe that human consciousness acts on the microsecond scale? Probably not. Probably, on the scale of seconds. Then, a collapse takes about seconds. Then, entanglement could be relevant to faster-than-light communication only on distances of million kilometers (or so). Definitely irrelevant in all experiments performed for now (on the Earth) or planned in the near future.

Boris Tsirelson (talk) 12:25, 10 January 2013 (UTC)

As Von Neumann clearly established , the entire physical universe can be made subject to Schrodinger's equation. So what then is collapsing the quantum wave function? Certainly you cannot argue that any arbitrary physical device - for that physical measuring device itself is subject to collapse (i.e. Von Neumann chain.) Where then does the chain end? Answer this question FIRST. If not consciousness then what? Are you going to propose that all measuring devices contain fundamental particles not subject to quantum physics? ABSURD. Jamenta (talk) 10:03, 22 January 2013 (UTC)

Sorry, but wave functions do not collapse. Remember that all that stands between your feet and the center of the Earth are a bunch of electron wave functions. Should these collapse, you will fall. Hcobb (talk) 16:01, 10 January 2013 (UTC)

Hope you do not confuse collapse of electron's wave function and "fall" of the electron onto the nucleus. Some interpretations of QM stipulate collapse, some do not; but their predictions are the same (except maybe some exotic situations never observed in reality). Electrons between my feet and the center of the Earth have no reason to collapse as long as they are not "measured". A wide beam of intensive hard gamma radiation could in principle "measure" most of them at once and, well, it would really be the last second of my staying on the Earth. :-) Boris Tsirelson (talk) 16:53, 10 January 2013 (UTC)

Even gamma ray bombardment only "collapses" the electron wave function down to the scale of the wavelength of the photons. (For a tiny instant.) The electron wave packet never becomes a point particle. Hcobb (talk) 19:42, 12 January 2013 (UTC)

I agree. So what? Who told otherwise? Boris Tsirelson (talk) 20:10, 12 January 2013 (UTC)

Collapse does not exist. What does exist are simply wave functions that have quantum interactions. The observer sits on no special pedestal. Hcobb (talk) 00:02, 13 January 2013 (UTC)

You can only make this claim assuming Hidden Variables Theory. Most physicists currently believe there is no compelling proof for Hidden Variables. Jamenta (talk) 00:41, 13 January 2013 (UTC)

No, I'd say, Hcobb prefers the (or rather, a) many-world interpretation. That is legitimate (but not necessary). Boris Tsirelson (talk) 06:56, 13 January 2013 (UTC)

I don't like either hidden variables or many-worlds, just multiply the Probability amplitude by the Cross section (physics) and there's your chance that a given interaction will occur in a given volume of space. There's no need for particles. Hcobb (talk) 21:08, 13 January 2013 (UTC)

So, all you need is this value!

Well, be happy.

But someone (I forgot, who) did an experiment called (by someone else) experiment with the most evident result. His apparatus measured a spin and moved a macroscopic mass accordingly, and then measured the gravitation from that mass. It appears that gravitation is generated only by the mass as we see it, and not by the alternative position of the mass (where it could be in the other case). Yes, it could not be otherwise. The "only" problem is, a formula for the gravitation source: the squared modulus of the probability amplitude times... (you know what). Having no kind of collapse (=reduction) you inevitably have today a giant wave function (of very entangled everything!) with a lot of terms describing a lot of alternatives (generated by numerous "measurements" in the past). And we observe only one. Only one world, that is. But I feel, all that is just boring for you; sorry. Boris Tsirelson (talk) 21:34, 13 January 2013 (UTC)

Single-particle wave functions (of 3 variables) are not problematic, and not related to entanglement. Two-particle wave functions (of 6 variables) are more problematic, and related to entanglement. N-particle wave functions (of 3N variables) are highly problematic for large N, and related to the Problem of Measurement, Collapse and all that. Boris Tsirelson (talk) 07:17, 14 January 2013 (UTC)

BTW, where exactly is the claim that consciousness is deterministic? As long as you acknowledge that the brain is fuzzy, then you knock the Heisenberg cut off its pedestal. Hcobb (talk) 09:04, 14 January 2013 (UTC)