Question about nonlocality

[uzername]

I'm not a physics student, just a layperson, and I'm wondering if anyone can briefly explain to me the concept of nonlocality in the context of quantum mechanics.

My understanding is that basically it means that an electron at one physical location (or just theoretical?) can instantaneously "know" the behavior of another electron to which it's somehow mysteriously paired (or is that necessary?) and adjust its own behavior accordingly, without there being any physical proximity in a classical sense whatsoever.

Is that essentially accurate? If so, is it still an accepted theory, or is it refuted? I'm also not sure how this supposedly ties in to 'entanglement'. Are they essentially the same concept, or is entanglement more refined somehow, or different in some other way?

[QuantumClue]

I'm not a physics student, just a layperson, and I'm wondering if anyone can briefly explain to me the concept of nonlocality in the context of quantum mechanics.

My understanding is that basically it means that an electron at one physical location (or just theoretical?) can instantaneously "know" the behavior of another electron to which it's somehow mysteriously paired (or is that necessary?) and adjust its own behavior accordingly, without there being any physical proximity in a classical sense whatsoever.

Is that essentially accurate? If so, is it still an accepted theory, or is it refuted? I'm also not sure how this supposedly ties in to 'entanglement'. Are they essentially the same concept, or is entanglement more refined somehow, or different in some other way?

More or less. Basically you need to throw out the idea that in all circumstances electrons do not act locally, meaning sometimes it is best to view the space between particles as not being a limit.

Superdeterminism states that information is already predetermined. I like this idea, and works well with Bohmian Mechanics. Basically superdeterminism acts like a loophole which removes the non-locality spooky action at a distance.

Nevertheless, proving that the universe is predetermined seems to be out of our scopes, atleast for now.

As for being disproven, I doubt it will be disproven any time soon. Non-locality is a well-understood, and apparently, observed phenomenon. Particles simply do not have time for all this space between theories ;)

[QuantumClue]

I also think it is possible that quantum tunnelling could provide an answer to the strange phenomenon. Just like in situations, a particle can come across a potential in the vacuum of space. It's like a hill, and in order for the particle to use as little energy as possible (the principle of least energy, or the ''general action''), it will tunnel very large distances in order to reach point B from point A.

In much the same respect, our classical idea of entanglement would require information to be transferred from particle A to particle B over very large distances. It is possible that perhaps information tunnels the very large distance, just like how a particle will tunnel beneath spacetime very large distances when pressured into making the most efficient trajectory.

This is slightly speculative, but fringe at best.

[uzername]

Okay! Thanks for the responses. I'm glad to see that I'm on the right track, at least.

The direction I'm going in this, and what is confusing to me, is that we - I mean, us as human beings, and specifically thinking about our brains - have electrons in us, too, don't we? I've been reading about how our consciousness, in fact, appears to be working in some respects, maybe even fundamentally, through the actions of "ion channels" - calcium ion channels, potassium ion channels, etc.

Like I said, I'm not a physics guy, but isn't an ion a "charged particle?" Which has electrons, right? So what is confusing to me is that if nonlocality is true, and electrons at great distances can affect the behavior of other electrons even light years away, then wouldn't that tend to imply that our consciousness is in some ways potentially being affected by "nonlocal" phenomena and events?

Or is the idea more that if the two electrons are paired somehow in this hypothetical relationship, that the simultaneous action of both electrons doesn't really mean one is having an "influence" on the other, but just that they are acting in tandem, i.e., which would mean that essentially they are the same phenomenon?

Or again, it gets confusing because I'm not sure if this is all really just theoretical, or if the fact is that nonlocality actually is happening in "reality," like an electron on venus is somehow "communicating" with one somewhere else in the universe, possibly even in our own brains?

Trying not to sound schizo here, just confused about what the implications appear to be if nonlocality is literally true.

[QuantumClue]

An ion \bar{e} is any charged particle, so yes you are right. As for quantum entangled brains, this is something a doctor has already picked up on... Doctor Dean Radin has postulated on this, give him a google and he will show up.

Also a more famous scientist who speculated entangled brains before him was Doctor Jack Sarfatti. Many of his idea's have been ridiculed by science up to date, but do not let this hinder you. He is very intelligent, I have had a few debates with him myself. Even Susskind recognizes him as a brilliant yet adventageous scientist.

More importantly, you seem to be asking how two particles become entangled? It is possible all particles where entangled from the very beginning of time! If two particles are created from the same source, then the two particles will quantum mechanically entangled. This is the same as saying we can get an electron and a positron from a gamma gamma decay, and the two particles will be entangled, or have hidden information which describes them.

If there is a simultaneous action, either some information about them is being taken over very large distances in a very short time (such as tunnelling for instance) or a superluminal transfer of energy (which is forbidden by special relativity) or the final idea is that somehow everything is already determined. You'd be right in saying that there seems to be some indication that it is not a direct influence from particle A to B, and this is where non-locality arises from. However, non-locality could simply be a nice description to a rather incomplete knowledge on the system.

[uzername]

Thanks for the references. I will definitely look those up. I don't know what ideas specifically have been ridiculed, but it seems strange to think any would be in a field that has "many world" hypotheses and things like that. What could be more bizarre and seemingly implausible than that?


More importantly, you seem to be asking how two particles become entangled? It is possible all particles where entangled from the very beginning of time! If two particles are created from the same source, then the two particles will quantum mechanically entangled. This is the same as saying we can get an electron and a positron from a gamma gamma decay, and the two particles will be entangled, or have hidden information which describes them.

This is definitely an aspect I was thinking of. Everything must have come out the Big Bang (it seems to me), meaning essentially that the idea of the individuality of basically anything really would just be a perceptual or definitional quirk. If I move my finger, that's considered part of "me," so if an electron on Mars moves at the same time as one in me (i.e,.because they're somehow linked, not meaning just randomly), then why shouldn't that be considered part of "me," also?

And so the implications of that seem to be what the Buddhists are talking about when they mention "Emptiness," and so on, meaning a deep kind of interconnection in the underlying energy patterns that appear (because of how our sense apparatuses work) to be solid things when in fact it's really all just aspects of the same energy "field."

Or something like that! :D

[DrChinese]

... This is definitely an aspect I was thinking of. Everything must have come out the Big Bang (it seems to me), meaning essentially that the idea of the individuality of basically anything really would just be a perceptual or definitional quirk. If I move my finger, that's considered part of "me," so if an electron on Mars moves at the same time as one in me (i.e,.because they're somehow linked, not meaning just randomly), then why shouldn't that be considered part of "me," also?

And so the implications of that seem to be what the Buddhists are talking about when they mention "Emptiness," and so on, meaning a deep kind of interconnection in the underlying energy patterns that appear (because of how our sense apparatuses work) to be solid things when in fact it's really all just aspects of the same energy "field."

Or something like that! :D

Welcome to PhysicsForums, uzername!

I would not characterize this description as an accurate rendering of the situation. Moving your finger "here" does not cause something to move "there". Rather: If you observe a particle state "here", you may deduce that an entangled particle will be observed to be in a matching state "there".

There are many reasons to believe that everything is NOT set in stone from the big bang. Nor that entanglement has anything whatsoever to do with the concept of "Superdeterminism". I would strongly recommend that you learn more about quantum physics before trying to tie it to philosophy.

[uzername]

Welcome to PhysicsForums, uzername!

I would not characterize this description as an accurate rendering of the situation.

Okay, thanks. So in your view, which aspects of the description are inaccurate? Everything didn't arise out of the Big Bang? Or there is no underlying connectedness or interrelatedness of phenomena?

[QuantumClue]

Thanks for the references. I will definitely look those up. I don't know what ideas specifically have been ridiculed, but it seems strange to think any would be in a field that has "many world" hypotheses and things like that. What could be more bizarre and seemingly implausible than that?



This is definitely an aspect I was thinking of. Everything must have come out the Big Bang (it seems to me), meaning essentially that the idea of the individuality of basically anything really would just be a perceptual or definitional quirk. If I move my finger, that's considered part of "me," so if an electron on Mars moves at the same time as one in me (i.e,.because they're somehow linked, not meaning just randomly), then why shouldn't that be considered part of "me," also?

And so the implications of that seem to be what the Buddhists are talking about when they mention "Emptiness," and so on, meaning a deep kind of interconnection in the underlying energy patterns that appear (because of how our sense apparatuses work) to be solid things when in fact it's really all just aspects of the same energy "field."

Or something like that! :D

I agree with dr Chinese here. There are many leaps of faith in this post. It starts out ok, but then delves into the realm of psuedoscience. See, Buddhism is a belief system, while quantum mechanics is a physical accuracy of the world. One is structured on only idea's, while the other has evolved from idea's to experimental justification. You are doing what a scientist should not do. That is applying nutty phenomenon to quantum physics. You need to apply first quantum physics to the nutty phenomenon to accurately measure the likelihood of it properly helping to describe what is going on.

[DrChinese]

Okay, thanks. So in your view, which aspects of the description are inaccurate? Everything didn't arise out of the Big Bang? Or there is no underlying connectedness or interrelatedness of phenomena?

Moving your finger "here" does not cause something to move "there". Rather: If you observe a particle state "here", you may deduce that an entangled particle will be observed to be in a matching state "there".

There are many reasons to believe that everything is NOT set in stone from the big bang. Nor that entanglement has anything whatsoever to do with the concept of "Superdeterminism". I would strongly recommend that you learn more about quantum physics before trying to tie it to philosophy.

I would skip the comments by QuantumClue as being misleading as a starting point.

[QuantumClue]

Welcome to PhysicsForums, uzername!

I would not characterize this description as an accurate rendering of the situation. Moving your finger "here" does not cause something to move "there". Rather: If you observe a particle state "here", you may deduce that an entangled particle will be observed to be in a matching state "there".

There are many reasons to believe that everything is NOT set in stone from the big bang. Nor that entanglement has anything whatsoever to do with the concept of "Superdeterminism". I would strongly recommend that you learn more about quantum physics before trying to tie it to philosophy.

This I don't fully agree with dr Chinese.

Superdeterminism showed there was a loophole in the understanding of Bells Inequalities, which was the mathematical formulation that helped quantum physics understand the nature of non-locality. Non-locality of course came from the understanding of entanglement.

[QuantumClue]

I would skip the comments by QuantumClue as being misleading as a starting point.

Please, elaborate on the points of being misleading.... I would love a debate on the subject of any misleading points provided by myself.

[uzername]

There are many reasons to believe that everything is NOT set in stone from the big bang. Nor that entanglement has anything whatsoever to do with the concept of "Superdeterminism". I would strongly recommend that you learn more about quantum physics before trying to tie it to philosophy.

Okay - I see your objection in your edit. I'm not really trying to tie anything to anything else that is not deserving of a tie, just trying to get a grasp on some of these concepts in relation to those that I'm more familiar with and that seem to be similar. I really wish now that I had more of a science and physics background, because all these topics are exceedingly interesting to me. But right now this is all I have to go on, and I'm trying to get an entry point.

Regarding the finger example, I see your point about 'here' and 'there'. I was trying to comment more on our definitional concepts of "us" as beings, as in we consider our finger to be us, and yet, if nonlocality is true and electrons somewhere else are acting in tandem with our own, then strictly speaking, logically, that would have to be considered part of the phenomenon we call 'us', even though definitionally we're typically not thought of as being physically anything beyond our own skins. That latter view doesn't really seem to be accurate, imho. Correct me if I'm wrong on this point also, but I believe I've heard it said that actually we are continually sharing electrons with everything around us - the furniture, the air, the ground we walk on, etc.

[DrChinese]

Please, elaborate on the points of being misleading.... I would love a debate on the subject of any misleading points provided by myself.

Anything to do with Superdeterminism or Sarfatti does not belong in a discussion with someone who is just beginning to learn about entanglement. Period.

[DrChinese]

Correct me if I'm wrong on this point also, but I believe I've heard it said that actually we are continually sharing electrons with everything around us - the furniture, the air, the ground we walk on, etc.

You could as accurately state that there is a mutual gravitational influence between every electron in your body and those of the moon. That was known a long time ago, and is taught in elementary school.

But I would not say it proves we are all one. For all practical purposes, your statement is not accurate. I.e., it is not a useful statement. As I said earlier, I would strongly recommend you learn some of the basics before going into the philosophical implications. Then you will understand how difficult it is to translate from one arena to the other. Many of the issues start to become semantics, and your definitions dictate your conclusions.

[uzername]

I'm just looking up Superdeterminism, and then apparently that leads to the idea of "local hidden variables," and I can see that these ideas can start snowballing out of control very rapidly. :D

Since this idea of local hidden variables (I'll call it LHV) seems related to my initial question, I guess I'll ask about that. If I'm understanding correctly, there is some conflict or incompatibility between LHV and quantum theory, but I don't understand why something traveling at the speed of light or not has to be the determining factor, i.e., why they need to be mutually exclusive. Why can't events have the possibility of being both instantaneous (or faster than light speed), or not instantaneous, and still be quantum? Couldn't there be some other quantum variable that is 'delaying' the effect, or having some influence on the effect so that it's not instantaneous, but still quantum?

edited: nevermind - I think I get that, as a deterministic approach would negate the need for any kind of entanglement, because everything would "know" in advance what to do and how to behave anyway. Is that accurate?

[QuantumClue]

Anything to do with Superdeterminism or Sarfatti does not belong in a discussion with someone who is just beginning to learn about entanglement. Period.

As I said Superdeterminism showed there was a loophole in the understanding of Bells Inequalities, which was the mathematical formulation that helped quantum physics understand the nature of non-locality. Non-locality of course came from the understanding of entanglement.

So it has everything to do with a possible solution to entanglement itself. Not to mention that the person themselves asked about quantum mind entanglement. I never intruduced Jack Sarfatti into the conversation for the hell of it. He was mentioned because he was the first scientist to talk about the possibility of the phenomenon.

So I don't know what you would have wanted me to tell a layperson??

[DrChinese]

I'm just looking up Superdeterminism, and then apparently that leads to the idea of "local hidden variables," and I can see that these ideas can start snowballing out of control very rapidly. :D

Since this idea of local hidden variables (I'll call it LHV) seems related to my initial question, I guess I'll ask about that. If I'm understanding correctly, there is some conflict or incompatibility between LHV and quantum theory, ...

Yes, this snowballs and you get things out of order. Forget superdeterminism. That is not physics, more like a religious concept.

What IS physics is the idea that local hidden variable (LHV) interpretations of quantum mechanics are NOT viable. That conclusion is due to 3 important papers: EPR (1935), Bell (1965) and Aspect (1982). If you would like to learn a bit about these, check out the link which is part of my signature below.

[DrChinese]

Or read the original papers:

http://www.drchinese.com/David/EPR_Bell_Aspect.htm

[uzername]

Yes, this snowballs and you get things out of order. Forget superdeterminism. That is not physics, more like a religious concept.

What IS physics is the idea that local hidden variable (LHV) interpretations of quantum mechanics are NOT viable. That conclusion is due to 3 important papers: EPR (1935), Bell (1965) and Aspect (1982). If you would like to learn a bit about these, check out the link which is part of my signature below.

Thanks - did you see my earlier edit? I'll repost it here for convenience:

---------------------
edited: nevermind - I think I get that, as a deterministic approach would negate the need for any kind of entanglement, because everything would "know" in advance what to do and how to behave anyway. Is that accurate?
----------------------

[DrChinese]

Thanks - did you see my earlier edit? I'll repost it here for convenience:

---------------------
edited: nevermind - I think I get that, as a deterministic approach would negate the need for any kind of entanglement, because everything would "know" in advance what to do and how to behave anyway. Is that accurate?
----------------------

That is the basic concept, yes, and it is NOT generally accepted as having any scientific basis whatsoever.

[QuantumClue]

Yes, this snowballs and you get things out of order. Forget superdeterminism. That is not physics, more like a religious concept.

What IS physics is the idea that local hidden variable (LHV) interpretations of quantum mechanics are NOT viable. That conclusion is due to 3 important papers: EPR (1935), Bell (1965) and Aspect (1982). If you would like to learn a bit about these, check out the link which is part of my signature below.

Your audacity and ignorance is overwhelming. It is not a religious subject at all.

Superdeterminism has every ingredient as the Bohmian Interpretation has, stating that wave function has a structure made from pilot waves, stating also there is determinism ingrained into reality. There is no destinguishing the two, so unless you are calling superdeterminism a religion, you must also be calling the Bohmain Interpretation word salad.

[DrChinese]

So I don't know what you would have wanted me to tell a layperson??

I would recommend starting with conventional science rather than fringe ideas. Not trying to be mean, but it confuses people when they start at the end rather than the beginning. There is plenty of cool ideas to learn by what I call a more conventional approach... which would be learning about the early quantum ideas (Copenhagen). Followed by EPR perhaps, etc.

[uzername]

That is the basic concept, yes, and it is NOT generally accepted as having any scientific basis whatsoever.

That's too bad, because I have to admit that just on the face of it the idea has a kind of appeal. I don't mean in the sense that I would hope it is that way, but the idea that things have a kind of momentum or inevitable trajectory from an initial starting point just seems to make a lot of sense. Unless something were to interfere with that trajectory - but how can something interfere with itself? But I guess the deeper you go, the more it probably seems like it would have to be a massive oversimplification, with so many other factors involved, like maybe black holes or something? But then that would have to have been determined, too, wouldn't it? Unless the black hole was somehow extra-big bang, ie., before or "outside" or not a part or result of the big bang, only being incorporated into or merging with the results of it later, after the fact?

[DrChinese]

Your audacity and ignorance is overwhelming. It is not a religious subject at all.

Superdeterminism has every ingredient as the Bohmian Interpretation has, stating that wave function has a structure made from pilot waves, stating also there is determinism ingrained into reality. There is no destinguishing the two, so unless you are calling superdeterminism a religion, you must also be calling the Bohmain Interpretation word salad.

LOL.

Superdeterminism is in fact a religious idea because it is a matter of belief and cannot be falsified. There are NO superdeterministic interpretations of physics which have EVER been presented. And I am familiar with the literature on the subject.

[DrChinese]

I have written extensively in other threads about superdeterminism. At least 59 posts in fact. If you want to discuss or debate the subject, start a thread on it!

[QuantumClue]

LOL.

Superdeterminism is in fact a religious idea because it is a matter of belief and cannot be falsified. There are NO superdeterministic interpretations of physics which have EVER been presented. And I am familiar with the literature on the subject.

Bell took the idea seriously.

''John Bell discussed superdeterminism in a BBC interview:[1]

There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be.''

So yes, physics as we know it has adopted the possibility of this as a solution to the problem. So I refute your comments in its entirity.

[QuantumClue]

From wiki, sorry.

http://en.wikipedia.org/wiki/Superdeterminism

[DrChinese]

From wiki, sorry.

http://en.wikipedia.org/wiki/Superdeterminism

LOL, you might want to read the comment at the top about needing the attention of an expert.

I will repeat: superdeterminism is more like religion than science. Else perhaps you would care to present a superdeterministic version of physics that can be experimentally tested. You see, I can also present the GOD theory of QM which says there is a being - God - who decides each random event that is to occur in real time. He is the guy behind that curtain. Now I hope it is clear that theory is not science.

[DrChinese]

Bell took the idea seriously.

''John Bell discussed superdeterminism in a BBC interview:[1]

There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be.''

So yes, physics as we know it has adopted the possibility of this as a solution to the problem. So I refute your comments in its entirity.

You are hijacking a legitimate thread.

[A. Neumaier]

The direction I'm going in this, and what is confusing to me, is that we - I mean, us as human beings, and specifically thinking about our brains - have electrons in us, too, don't we? I've been reading about how our consciousness, in fact, appears to be working in some respects, maybe even fundamentally, through the actions of "ion channels" - calcium ion channels, potassium ion channels, etc.

Like I said, I'm not a physics guy, but isn't an ion a "charged particle?" Which has electrons, right?
Electrons are in every atom, whether it is neutral or an ion. The only exceptions are ions such as H^+ (protons) or He^++ (alpha particles), which are atoms stripped of _all_ their electrons and only consist of a nucleus.

So what is confusing to me is that if nonlocality is true, and electrons at great distances can affect the behavior of other electrons even light years away, then wouldn't that tend to imply that our consciousness is in some ways potentially being affected by "nonlocal" phenomena and events?
Nonlocality is a real effect but not of the form you describe here. An electron here does not the slightest affect a far away electron.

Or is the idea more that if the two electrons are paired somehow in this hypothetical relationship, that the simultaneous action of both electrons doesn't really mean one is having an "influence" on the other, but just that they are acting in tandem, i.e., which would mean that essentially they are the same phenomenon?

What happens is that in _very_ special situations (that take high quality equipment to produce, and that are difficult to maintain over longer distances), pairs of electrons are produced that are ''entangled'' in such a way that the following can be observed:
When the two electrons of such an entangled move in different directions from the source where they were produced, later measurements of the properties of the two (now far away) electrons are correlated statistically in a way not explainable by classical reasoning.

This has no consequences for most real life situations, but optical versions of the same situation have (in the eyes of many) the potential of being used in special high-tech equipment for cryptography or quantum computing.

[uzername]

Electrons are in every atom, whether it is neutral or an ion. The only exceptions are ions such as H^+ (protons) or He^++ (alpha particles), which are atoms stripped of _all_ their electrons and only consist of a nucleus.

Nonlocality is a real effect but not of the form you describe here. An electron here does not the slightest affect a far away electron.


What happens is that in _very_ special situations (that take high quality equipment to produce, and that are difficult to maintain over longer distances), pairs of electrons are produced that are ''entangled'' in such a way that the following can be observed:
When the two electrons of such an entangled move in different directions from the source where they were produced, later measurements of the properties of the two (now far away) electrons are correlated statistically in a way not explainable by classical reasoning.

This has no consequences for most real life situations, but optical versions of the same situation have (in the eyes of many) the potential of being used in special high-tech equipment for cryptography or quantum computing.

Thanks, that is interesting and clarifying information.

From a lay perspective, what is confusing to me is the idea that it's "real," and yet doesn't seem to be the case in most instances. Like for example, if we say a water molecule has a particular characteristic or behavior, then ALL water molecules should have those characteristics or behavior, right?

So if nonlocality is an effect or a phenomenon of particular electrons, I don't understand why it wouldn't apply to all electrons, as just a general principle of how they operate.

Are you saying when talking about high quality equipment (supercolliders, etc. I would guess you mean), that we have to perform some action on electrons to then make them act in a non-local way? So it's not really a characteristic of the electron itself to act 'nonlocally', but it's a principle or an effect of an action you are taking on the particle? Possibly with the idea that that effect or action could have occurred naturally, in the big bang, and caused some electrons to behave nonlocally?

And then I'm back at wondering then why apparently only some, and not all? What I am missing or getting wrong here?

[DrChinese]

...

So if nonlocality is an effect or a phenomenon of particular electrons, I don't understand why it wouldn't apply to all electrons, as just a general principle of how they operate.

Are you saying when talking about high quality equipment (supercolliders, etc. I would guess you mean), that we have to perform some action on electrons to then make them act in a non-local way? So it's not really a characteristic of the electron itself to act 'nonlocally', but it's a principle of an effect or an action you are taking on the particle? Possibly with the idea that that effect or action could have occurred natural, in the big bang, and caused some electrons to behave nonlocally?

And then I'm back at wondering then why apparently only some, and not all? What I am missing or getting wrong here?

Most entanglement setups involve light (photon pairs) and not electrons. Entangled photons are created using a laser which is shined through a nonlinear crystal which results in a small fraction of the photons emerging in the entangled state. These are identified using filters and other techniques.

Entanglement - i.e. an entangled state - normally results from a setup in which there are 2 or more particles in a known state (as above) which is itself a superposition. At that point, there are strict conservation laws which are obeyed. Usually, it is believed that the entangled state essentially dissipates through a process called decoherence. It is not clear completely whether everything may be in some sense entangled but we just don't notice it because the effect is so very very slight.

[uzername]

Most entanglement setups involve light (photon pairs) and not electrons. Entangled photons are created using a laser which is shined through a nonlinear crystal which results in a small fraction of the photons emerging in the entangled state. These are identified using filters and other techniques.

Entanglement - i.e. an entangled state - normally results from a setup in which there are 2 or more particles in a known state (as above) which is itself a superposition. At that point, there are strict conservation laws which are obeyed. Usually, it is believed that the entangled state essentially dissipates through a process called decoherence. It is not clear completely whether everything may be in some sense entangled but we just don't notice it because the effect is so very very slight.

Okay, that post just blew my mind. I sometimes think you guys do that on purpose - provide just enough of a provocative answer to open up 10 more cans of worms. :D

"Everything might in some sense be entangled" -- that in itself is a very cool idea, and kind of where I am aiming, or where my original thoughts were directed, wondering about the extent to which that might be the case, but thinking only in terms of the electrons. Not sure what you mean by it being a "slight" effect - if it's in that state, it's in that state, right? Or you mean it's slight because of decoherence?

But given the answer that A. Neumaier gave that said nonlocality isn't really a real-world or actual thing that's happening on the everyday level, the idea that everything might actually be entangled seems to be in contradiction to that.

Then to confuse things even more, you say that entanglement dissipates, or eventually "wears off." This is all happening like in a micro nano-second, or a super small amount of time that it's in the entangled state, I'm guessing? And then what? Back to being non-entangled again?

So if it's true that everything is 'slightly' entangled, then what in "nature" entangles these particles in the first place? Space, time or gravity acts as some kind of "prism" or crystal like the one you mentioned to entangle them? Do they go in and out of entanglement, even though Neumaier said that in the 'real world' they probably weren't entangled in the first place? I don't get all the seeming contradictions.

And just to clarify, bringing up the fact that photons apparently are what we do entanglement studies on, doesn't necessarily mean to exclude the possibility of electrons being entangled, right? And by saying "everything" might be entangled, by "everything" you mean all particles, like the quarks and other subatomic particles? All that is what is possibly entangled very slightly?

[QuantumClue]

You are hijacking a legitimate thread.

What a load of rubbish. I answered the OP's questions with a legitimate base.

[uzername]

I don't think it was too much of a hijack. Or if it was, it was a useful one, as it's allowed us to have been able to discard Superdeterminism as untestable, which seems to make sense. onward!

[DrChinese]

Okay, that post just blew my mind. I sometimes think you guys do that on purpose - provide just enough of a provocative answer to open up 10 more cans of worms. :D

"Everything might in some sense be entangled" -- that in itself is a very cool idea, and kind of where I am aiming, or where my original thoughts were directed, wondering about the extent to which that might be the case, but thinking only in terms of the electrons. Not sure what you mean by it being a "slight" effect - if it's in that state, it's in that state, right?

:smile:

It takes a little time to decipher a lot of this stuff. That is why I try to aim people in a reasonable direction.

Again, you will see that the words can get in the way. If I have 2 particles in a known superposition, the entanglement effect can be substantial. But if I have 3, it is noticeably less. If I have 10^30 particles... well, I think you can see the effect is very very slight. The same thing is true of gravity. So my point is that with the words "in some sense", you could make almost anything be anything else. We don't actually know, when we look at an individual particle, if it is entangled as part of a system of 2 or more particles somewhere. We could determine such entanglement if we knew *which* other particles to look at. But except in these special setups, we have no idea where to look.

I don't know what others would say, but I would say that the quarks in a proton are in fact entangled. Anyone care to comment on that?

[DrChinese]

... what in "nature" entangles these particles in the first place?

That is a GREAT question.

The (sorta) answer is somewhat strange: a certain kind of ignorance leads to entanglement. If you have 2 electrons in the same ground shell of an atom, I would call these entangled. They are indistinguishable, and yet their spin must net to zero. There are 2 ways for this to occur, leading to a superposition of possible states.

Anyone care to comment? I would guess there are others who could add to this explanation.

[uzername]

:smile:

It takes a little time to decipher a lot of this stuff. That is why I try to aim people in a reasonable direction.

Again, you will see that the words can get in the way. If I have 2 particles in a known superposition, the entanglement effect can be substantial. But if I have 3, it is noticeably less. If I have 10^30 particles... well, I think you can see the effect is very very slight. The same thing is true of gravity. So my point is that with the words "in some sense", you could make almost anything be anything else. We don't actually know, when we look at an individual particle, if it is entangled as part of a system of 2 or more particles somewhere. We could determine such entanglement if we knew *which* other particles to look at. But except in these special setups, we have no idea where to look.

I don't know what others would say, but I would say that the quarks in a proton are in fact entangled. Anyone care to comment on that?

Okay, that's very interesting. I never really thought about it in terms of multiple particles greater than two, to be honest. Only 2 particles.

So I suppose to summarize what you seem to be saying (pls. correct me if I'm wrong) is that, in practical terms, when we entangle our own particles with the laser and the crystal, etc. we know which ones we're looking at, whereas when it's just "out there," in the wide world and universe at large, 1) multiple particles could be entangled together in such great numbers that it would be totally impossible to measure the extent of the entanglement effect, because the effect would be so weak between particles, and 2) even starting with any given particle, we wouldn't know which other particle/s to look at anyway, even if we could look at particles in that "world at large" condition, which I guess is ridiculous to begin with.

So I'm also just now reading your link on Bell and EPR. I think it's making a little more sense, but every time I think I understand something, a monkey wrench seems to get thrown in at the end confusing the issue.

Briefly - again, correct me if mistaken - the general idea is that all the typical things we think of in terms of quantum physics - wave/particle duality, uncertainty principle, collapse of the wave function/schroedinger's cat, etc. -- all that is Copenhagen, and Einstein's ideas of QM are in opposition to Copenhagen?

So EPR was developed to try to refute the idea that we can't know both the speed and location at the same time, but only one or the other, and the way they proposed to do it is through a 'thought experiment' involving entanglement? We entangle some particles and then separate them, and then since they're entangled, when we look at particle 1 we automatically DO know the state of particle 2, and vice versa, so there's really no uncertainty or collapse of the wave function at all? Do I have that much right?

But I don't really understand why we need to know A, B, and C simultaneously. Isn't it enough to just know one? Or are those like the 3 axis that are the minimum required to give us all the info needed to refute the uncertainty principle?

Then finally, Bell is the refutation of EPR, so actually Copenhagen is still considered true, while EPR is therefore discredited? Or... ?

Point #2 in your explanation is what confuses me:

"Specifically, a measurement setting for one member of an entangled particle pair should not affect the results of a measurement on the other member of the pair located at a distance. Otherwise, you would have so-called "spooky action at a distance".


But I thought that *was* the case. I thought that in essence is nonlocality. :confused: I've heard this phrase, "spooky action at a distance" before, I thought it was Einstein's statement. ?

[DrChinese]

Then finally, Bell is the refutation of EPR, so actually Copenhagen is still considered true, while EPR is therefore discredited? Or... ?

Point #2 in your explanation is what confuses me:

"Specifically, a measurement setting for one member of an entangled particle pair should not affect the results of a measurement on the other member of the pair located at a distance. Otherwise, you would have so-called "spooky action at a distance".


But I thought that *was* the case. I thought that in essence is nonlocality. :confused: I've heard this phrase, "spooky action at a distance" before, I thought it was Einstein's statement. ?

I will comment on the rest of your post tomorrow, but wanted to pass this on now.

Yes, I consider EPR's final conclusion (or speculation or whatever you want to call it) incorrect. Bell was the one that showed why it was not correct.

Yes, "spooky action at a distance" is a reference to Einstein's aversion to quantum non-locality. It is also a way of referring to non-locality, whereas locality is an assumption of the local realistic camp (which Einstein was a member of).

:smile:

[QuantumClue]

:smile:

It takes a little time to decipher a lot of this stuff. That is why I try to aim people in a reasonable direction.

Again, you will see that the words can get in the way. If I have 2 particles in a known superposition, the entanglement effect can be substantial. But if I have 3, it is noticeably less. If I have 10^30 particles... well, I think you can see the effect is very very slight. The same thing is true of gravity. So my point is that with the words "in some sense", you could make almost anything be anything else. We don't actually know, when we look at an individual particle, if it is entangled as part of a system of 2 or more particles somewhere. We could determine such entanglement if we knew *which* other particles to look at. But except in these special setups, we have no idea where to look.

I don't know what others would say, but I would say that the quarks in a proton are in fact entangled. Anyone care to comment on that?

Hasn't the LHC just experimentally shown the entanglement of the nucleus of atoms? I don't have the news off-hand. I do remember it being presented.

[QuantumClue]

I don't think it was too much of a hijack. Or if it was, it was a useful one, as it's allowed us to have been able to discard Superdeterminism as untestable, which seems to make sense. onward!

But doctorn Chinese seems to haven a corrupt sense of logic. It is even to the point as resembling the camps that preserve the idea in the Copenhagen Interpretation that if you cannot see it, why worry about it? The core of the interpretation states that a thing does not exist until it is measured.

Superdeterminism is simply a world we cannot directly act on. It is a world beyond our usual four dimensional sphere. Just like dr Chinese, he refutes anything at first glance. Superdeterminism is not in any way, psuedoscientific. Or a religion, as I once recall him saying. It is itself, an interpretation of quantum mechanics, a root not only to a belief system, but also the understanding of a logic driving reality.

I speak to you so freely like this, is because I don't believe that you care much about the finer points of any mathematical theory. I feel that I might be guilty of telling you what you want to hear. I guess it does not matter, so long as I tell you it right.

[A. Neumaier]

Thanks, that is interesting and clarifying information.

From a lay perspective, what is confusing to me is the idea that it's "real," and yet doesn't seem to be the case in most instances. [...]
So if nonlocality is an effect or a phenomenon of particular electrons, I don't understand why it wouldn't apply to all electrons, as just a general principle of how they operate.

Allow me to explain it in terms of a parable: Nonlocality is due to entanglement. But entanglement between two electrons is a very private matter; so they are very shy about it and won't let you observe it easily. Like with shy animals in the woods, you need special preparation to observe them - get up very early in the morning before everyone else, sit silently and with very open eyes in the forest, and interpret correctly every slightest movement....

In the usual terms: There is a very powerful, almost omnipresent process called decoherence that almost instantly destroys entanglement (and hence the nonlocal features) of a system unless you carefully guard your system from interacting with anything else. But the latter is never the case in ordinary life (where interaction in the form of light is everywhere) and quite difficult to achieve in the laboratory.

The degree of difficulty can be estimated from the fact that the first experiment to convincingly demonstrate the existence of entanglement, done in 1982, earned Alain Aspect in 2010 (together with Anton Zeilinger, whom you might heard of) one of the most prestigious prizes in science, the Wolf prize http://en.wikipedia.org/wiki/Wolf_Prize_in_Physics

[A. Neumaier]

But given the answer that A. Neumaier gave that said nonlocality isn't really a real-world or actual thing that's happening on the everyday level, the idea that everything might actually be entangled seems to be in contradiction to that.

So if it's true that everything is 'slightly' entangled, then what in "nature" entangles these particles in the first place? Space, time or gravity acts as some kind of "prism" or crystal like the one you mentioned to entangle them? Do they go in and out of entanglement, even though Neumaier said that in the 'real world' they probably weren't entangled in the first place? I don't get all the seeming contradictions.


Nonlocality is a real-world effect but observable only under specially prepared circumstances.

Entanglement is created by a number of quantum processes, the simplest being that of light passing through a doubly refracting crystal like calcite http://en.wikipedia.org/wiki/Birefringence or a half-silvered mirror http://en.wikipedia.org/wiki/Half-silvered_mirror
which both entangles momentum and polarization of a single particle. Entanglement between two particles is commonly achieved using a process called parametric down-conversion http://en.wikipedia.org/wiki/Parametric_down-conversion

But it is destroyed by _all_ uncontrolled interactions, and the latter usually dominate.

[A. Neumaier]

I don't know what others would say, but I would say that the quarks in a proton are in fact entangled. Anyone care to comment on that?

Strictly speaking, yes. But due to confinement, this entanglement is both unobservable and stable under decoherence. So it is somewhat inappropriate to use the notion in this context since it only conjures misleading intuitions.

[A. Neumaier]

a certain kind of ignorance leads to entanglement. If you have 2 electrons in the same ground shell of an atom, I would call these entangled.

Ignorance is commonly said to lead to mixtures, not to superpositions.

On the other hand, the electrons you mention might be considered to be entangled.
But again, one wouldn't use the word since one cannot access the electrons singly.

To talk usefully about entanglement , the systems that are considered to be entangled must be distinguishable (usually, by their position or momentum). This is not the case for quarks bound in a proton, or for electrons bound in an atom.

[uzername]

Nonlocality is a real-world effect but observable only under specially prepared circumstances.

Okay, so that's a little bit different than implying that it basically only *happens* in a laboratory setting, and saying, "This has no consequences for most real life situations," isn't it? The mating behavior of a certain species of animal might not *ever* have been observed, but that doesn't mean those animals aren't mating, right?


Entanglement is created by a number of quantum processes, the simplest being that of light passing through a doubly refracting crystal like calcite http://en.wikipedia.org/wiki/Birefringence or a half-silvered mirror http://en.wikipedia.org/wiki/Half-silvered_mirror
which both entangles momentum and polarization of a single particle. Entanglement between two particles is commonly achieved using a process called parametric down-conversion http://en.wikipedia.org/wiki/Parametric_down-conversion

But it is destroyed by _all_ uncontrolled interactions, and the latter usually dominate.

I guess I'm still not clear about whether this a natural process, happening around us all the time, or just something we discovered we can do, which helped disprove a theory? I mean, I look out my window, and there is plenty of light out there. I have to imagine there are crystalline structures or mirror-like surfaces somewhere that could be producing entangled electrons.

I think, however, I am at least seeing that my original conception of it as being almost a given property of all electrons is not 100 percent accurate, like that there are particles "out there" somewhere that this very second are entangled with ones in our bodies, for example. Although Dr.Chinese did say it's theoretically possible that all particles are entangled, even if only perhaps weakly, so there's that.

And the comment that they're entangled through our ignorance is also very interesting. Because it almost seems to be the opposite case, in fact: if hypothetically all particles are entangled, Dr.C said that the effect presumably would be so weak that we wouldn't be able to detect it, and we also wouldn't know which particles to look at (presuming again that we could). So rather it seems to be that ignorance is what is preventing us from seeing entanglement, not producing entanglement. "Ignorance" seems rather to produce the uncertainty principle, and then when we become not "ignorant" anymore about speed or position, the uncertainty vanishes.

[A. Neumaier]

Okay, so that's a little bit different than implying that it basically only *happens* in a laboratory setting, and saying, "This has no consequences for most real life situations," isn't it? The mating behavior of a certain species of animal might not *ever* have been observed, but that doesn't mean those animals aren't mating, right?
I'd consider my first and my second formulation as essentially synonymous. But classical imagination for quantum situations is very limited anyway, so everyone's imagination is a bit different (and unreliable).



I guess I'm still not clear about whether this a natural process, happening around us all the time,
Decoherence happens all the time; it is something very common, leading to observable mixtures. Observable nonlocality - i.e., strange superpositions = entanglement - is something rare: you must create it on purpose, though it happens to a small extent naturally (e.g., light happening to fall through a calcite crystal).


I mean, I look out my window, and there is plenty of light out there. I have to imagine there are crystalline structures or mirror-like surfaces somewhere that could be producing entangled electrons.

No. Imagined mirrors only have an imaginary effect. Normal light is in a mixed state and has no observable entanglement. But if you happen to have a calcite crystal and look through it, some of the strange quantum things happen: We see ''double''. But to find out experimentally that this had lead to entanglement needs already care....



I think, however, I am at least seeing that my original conception of it as being almost a given property of all electrons is not 100 percent accurate, like that there are particles "out there" somewhere that this very second are entangled with ones in our bodies, for example.

All the electrons are in some sense entangled, but to turn this entanglement into measurable effects requires special preparation.


And the comment that they're entangled through our ignorance is also very interesting.

This is a misunderstanding. Ignorance doesn't change the entanglement, only whether it is perceptible. Just as walking inattentively through a forest doesn't change the mating behavior of the animals but you won't notice it.


"Ignorance" seems rather to produce the uncertainty principle, and then when we become not "ignorant" anymore about speed or position, the uncertainty vanishes.
This is another misunderstanding. One cannot become certain about every property of a quantum system.

[DrChinese]

Ignorance is commonly said to lead to mixtures, not to superpositions.

On the other hand, the electrons you mention might be considered to be entangled.
But again, one wouldn't use the word since one cannot access the electrons singly.

To talk usefully about entanglement , the systems that are considered to be entangled must be distinguishable (usually, by their position or momentum).

I thought it had to be an INdistinguishable set of states... i.e. HV> + VH> to me is a superposition of states. Whereas if it is either HV> OR VH> AND we simply don't know which... that is a mixed state.

I agree with you that *general* ignorance of the source may be (usually is) a mixed state. But a special kind of ignorance is that we know "something" about the source but not everything. That can lead to an entangled state, and why I qualified with the word "special".

And of course a proton contains bound quarks, so we are not going to be able to test much on those babies as you say.

[DrChinese]

... "Ignorance" seems rather to produce the uncertainty principle, and then when we become not "ignorant" anymore about speed or position, the uncertainty vanishes.

There is always uncertainty with respect to non-commuting observables. That is true even with entangled pairs. There is no "vanishing"!

[A. Neumaier]

To talk usefully about entanglement , the systems that are considered to be entangled must be distinguishable (usually, by their position or momentum). This is not the case for quarks bound in a proton, or for electrons bound in an atom.
I thought it had to be an INdistinguishable set of states... i.e. HV> + VH> to me is a superposition of states. Whereas if it is either HV> OR VH> AND we simply don't know which... that is a mixed state.
I was talking about systems, not about their state.

For example, two electrons are on the fundamental level indistinguishable; their joint wave function is proportional to |12>-|21>; no other superposition is allowed. Similarly, two photons are on the fundamental level indistinguishable; their joint wave function is proportional to |12>+|21>; no other superposition is allowed. On the other hand, a photon and an electron are intrinsically distinguishable (e.g. by their spin), and arbitrary superposition are possible.

But if, on a more practical level, you know already that (by preparation) you have two electrons or two photons, one moving to the left and one moving to the right, you can use this information to distinguish the electrons or photons; and then you can assign
separate state information to each of them, and also construct arbitrary superpositions.

I agree with you that *general* ignorance of the source may be (usually is) a mixed state. But a special kind of ignorance is that we know "something" about the source but not everything. That can lead to an entangled state, and why I qualified with the word "special".
Can you give an example so that I better understand what you mean?

[uzername]

There is always uncertainty with respect to non-commuting observables. That is true even with entangled pairs. There is no "vanishing"!

Doesn't the "wave function" collapse though, once you know? You've reduced the probability to either 1 or 0, right? so how is the uncertainty not vanished?

[DrChinese]

Doesn't the "wave function" collapse though, once you know? You've reduced the probability to either 1 or 0, right? so how is the uncertainty not vanished?

Sure it collapses, and the results give you complete certainty for at least one observable - let's say position. That makes momentum, which is non-commuting with respect to position, completely UNcertain.

:smile:

[DrChinese]

Can you give an example so that I better understand what you mean?

Sure. If I have a system of 2 particles with total spin=0, and I don't know which is which (indistinguishable), those particles are ALWAYS spin entangled. And by the term "don't know" I mean: cannot know, in principle.

[DrChinese]

Sure. If I have a system of 2 particles with total spin=0, and I don't know which is which (indistinguishable), those particles are ALWAYS spin entangled. And by the term "don't know" I mean: cannot know, in principle.

And just to add to that: those 2 particles can be ANY 2 particles, existing anywhere, with any prior history, at any points in spacetime. I believe that is the rule. Strange as it may seem.

[A. Neumaier]

Sure. If I have a system of 2 particles with total spin=0, and I don't know which is which (indistinguishable), those particles are ALWAYS spin entangled.
It is precisely this situation that I had in mind when saying that entanglement is no longer meaningful when particles are indistinguishable. Entanglement requires a tensor product state space, while in this case, you only have the symmetric or antisymmetric part of the tensor product. The state space of indistinguishable particles is very different from that of distinguishable particles. Almost nothing of the usual theory about entanglement survives this change of basic setting.
And by the term "don't know" I mean: cannot know, in principle.
I consider something that cannot be known in principle to be meaningless, not a case for ignorance.

[DrChinese]

It is precisely this situation that I had in mind when saying that entanglement is no longer meaningful when particles are indistinguishable.

So I guess you are saying that 2 particles with total spin 0 are NOT entangled if they are indistinguishable. Or ??? Perhaps my use of terms is different than yours? Because I have never heard it described otherwise.

[A. Neumaier]

So I guess you are saying that 2 particles with total spin 0 are NOT entangled if they are indistinguishable. Or ??? Perhaps my use of terms is different than yours? Because I have never heard it described otherwise.

The common assumption in a formal definition of of entangled systems, here quoted from http://en.wikipedia.org/wiki/Entangled_state , is: ''The Hilbert space of the composite system is the tensor product''.

This is violated for indistinguishable bosons or fermions, where the Hilbert space of the composite system is the symmetrized and antisymmetrized tensor product, respectively.

Of course, many people use the term without referring to a precise definition of the context in which it makes sense. And commonly there is a lot of imprecision in working with indistinguishable particles outside of quantum field theory!

But I like to have precise concepts determined by the usefulness of what is defined.

[uzername]

Sure it collapses, and the results give you complete certainty for at least one observable - let's say position. That makes momentum, which is non-commuting with respect to position, completely UNcertain.

:smile:

Yes - I meant only one observable. If we claimed to know them all, is that the same or related concept as hidden variables?

[DrChinese]

...Of course, many people use the term without referring to a precise definition of the context in which it makes sense. And commonly there is a lot of imprecision in working with indistinguishable particles outside of quantum field theory!

But I like to have precise concepts determined by the usefulness of what is defined.

Me being one of the guilty!

Thanks for clarifying.