I think that's what it's called. For example if you created two electrons and sent one billions of miles into space, then if you did something to one it'd effect the other instantly.

Is this really true or just a theory? And how do you create two electrons? Why would they be connected to each other but not connected to any other electrons?

This looks like a job for... Wikipedia!

http://en.wikipedia.org/wiki/Quantum...ent#Background
http://en.wikipedia.org/wiki/Quantum...f_entanglement

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

You may have a look at the experiments of Dr. Anton Zeilinger (http://en.wikipedia.org/wiki/Anton_Zeilinger

At the moment he is doing the first test runs for entangled photons in space distances

Here is the link to a site in German:http://derstandard.at/?url=/?id=3274428

As I said it is in German. But googling his name and "quantum entanglement" may lead to some English hits also.

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Andre

"They did not know it was impossible, so they did it!"
Mark Twain

I suggest you purchase yourself a copy of Amir D. Aczel's book 'Entanglement'. That should assist you in understanding this issue.

Its meant to be read by the non scientist, and explains the issue well. I have it in audiobook form from Audible myself.

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http://code.google.com/p/nmod/

Entanglement is a prediction of quantum mechanics, and all experiments on it so far have confirmed quantum mechanical predictions. However, none of them have required something you do somewhere to "affect the other instantly". The two offending words are "affect" and "instantly". An affect implies causation, and causality is limited to the speed of light (no entanglement experiment violates that). Also, "instantly" is a frame-dependent concept (a la relativity), and no entanglement experiment violates that either. What happens is, an experiment you conduct on one electron gives you information about the other-- information that no one else has and no one else needs to successfully use quantum mechanics to make their own predictions. The only way you see this as an "affect" is if you apply philosophical concepts that are outside of science, like if you say that the electron "has a wave function" and changes in the way you would describe its wave function somehow actually affect the electron. The fact is, the only time we ever know "the wave function" of anything is when we prepare a system to have a certain wave function, thereby erasing whatever history it may have had. When we don't do that, as we don't in entanglement experiments, then we only know the wave function that we are using to make our prediction for what will happen-- and someone else with different information will use a different wave function and will find that quantum mechanics works for them too.
When stated in a proper way, entanglement is experimentally verified. Unfortunately, there is a whole lot of baloney written about this effect, ranging from unnecessary philosophy to just plain wrong physical claims.
You don't create them necessarily, it's fine to use pre-existing ones. They can be entangled based on their history. But you are completely right-- it is quite possible, depending on the experiment, that they will also be entangled with other electrons in ways that don't matter to the experiment and we simply choose not to include in their wave function. That's the key point.

If one passes a particle through a grating, and collects/constrains a pair of particles that exit the grating, then moves the first of the constained pair of particles 1 ly away from the second, then forces some characteristic of the "local" member of the pair of particles, say the spin, to a specific state/sense, then (someone) measures the spin of the second (distant) particle of the pair some short period of time later (a period significantly less than 1 year). Will the two spins be found to be of the same sense? What will be found if this experiment is repeated a large number of times, by having passed through the grating, and collected, a large number of particles and particle pairs, in the first place?

Robert

You don't want to "force" the spin to be something, that won't do anything interesting. You want to "measure" the spin. If the two particles are entangled in some particular way (perhaps they must have opposite spin), then your measurement on the one electron will change your quantum-mechanically produced predictions for the results of someone else measuring the spin of that other particle. And when you test your predictions (statistically over a large number of trials as necessary), you will find they are statistically correct. But here's the kicker many overlook: the other person, who does not know of your result, will make their own prediction of their own measurement, will not incorporate your result, and will also conclude that quantum mechanics is working fine for them too! That's why "quantum mechanics is in your head", and there's no paradox about "instantaneous effects" when they occur only in your own thought process. There's an awful lot of hooey written about quantum entanglement! (And I don't mean Bell's theorem, that's all pretty rigorous stuff-- I wouldn't call it hooey, I'd call it over-interpreted.)

Does the mathematics of the prediction (in terms of the joint wave function) give the information, or do you mean the information stems from the measurement at one detector? I can see the joint probabilities for both electrons as being predictive, but when we talk about specific measured states, none of that is predictive is it? I appreciate that the measured state is kind of book keeping, but I still find it difficult to relate this book keeping as being common to two separated locations. I mean I cannot predict from the joint wave function that an entangled particle at source will evolve to have a specific measured up state at detector A and a specific measured down state at detector B can I? All I can say is that there is a 50% chance of it being up or down in either location and that the rules say if it is up in one detector it will be down in the other. Are you saying that the book keeping is just recording the nature of the predictive outcome, it is just the final part of the quantum prediction that gives a chance to tabulate the probability outcomes - the measurement should not be thought of as some kind of deterministic event that kicks in to ensure the other particle follows the rules, but rather the rules are inherent in the wave function which is a product of our experimental set up.

I don't wish go back over ground that was amply covered in the thread ("Spooky Matter at a Distance" - in General Science I think) but it seems like an opportunity to clarify a few points.

If it's just that measuring one particle tells you information about the other, and NOT that doing something to it has the same effect on the other (as it's often said to be), then where's the "action" in Einstein's "spooky action"?

That's an interesting question. I suppose one must distinguish "independent information" from "information transformed via a calculation". The former is the result of something that couples to reality (i.e., a measurement), and the latter is like a function that always gives the same output from the same input (i.e., the information out is just a reprocessed version of the information in, like a coded message). I see the process as gathering actual information from your experiment, then using a calculation to make a prediction about another measurement. That prediction is a form of information too, but it just converts the information you got from your experiment into a prediction. If it sounds like you are ending up with more information than you started with by doing that calculation, then you have overestimated how much information was "really there" in the first place.

We don't get information about that except by doing the measurements. The predictions are only about joint results (which is why the experiments always involve coincidence detectors).

You can get three things from the joint wavefunction of two particles. The first two are a statistical prediction of an observation on one particle, or on the other. Nothing at all strange will happen if you do that.

Or, you can get a prediction about joint probabilities for observations on both particles, and then you will get some results that people concern themselves with, but it will always be what the joint wave function predicted. So the "problem" is already there as soon as you accept a joint wavefunction as your representation-- yet we couldn't get very far in quantum mechanics if we didn't do that.

It's as though people were expecting joint wave functions to successfully predict the Pauli Exclusion Principle in white dwarf stars, and the "exchange energy" correction in two-electron atoms and molecules, all bizarre yet perfectly well documented, but expected them to break down somehow whenever they disagree with our classical intuition in EPR-type experiments. Go figure. One could say that the value of Bell's theorem is simply to elucidate the ramifications of quantum mechanics, but why this somehow is interpreted as throwing quantum mechanics into a tizzy is beyond me because I never attributed that theory with a particular set of philosophical principles based on classical expectations.
Yes, that sounds like what I'm saying indeed.
I don't mind at all, this point comes up a lot and it stands to get it out there. If I'm right, the more places it appears the better, and if someone can refute me, then I want to give them the best possible opportunity (because I'd like to know).

The key to all of this seems to relate to the distinction between two computing methods that can be used when dealing with these entanglement experiments. I mentioned in the other thread that these are described in a book that I am reading by Bernard d'Espagnat ("On Physics and Philosophy").

The one method he describes as being used by those who view the Aspect - type experiments in a "realist" manner - i,e, they imagine that wave functions are "real stuff" - that one wave function of the pair of photons is "reduced" on measurement resulting in the other photon getting its own well specified wave function. The upshot of this of course is that there is real physical influence that travels faster than light. This method he defines as the descriptive method and I think relates to the comment by Delvo regarding the notion of "action".

The other method he describes as the predictive method - those who view the Aspect - type experiments in this manner he describes as seeing physics as describing human experience. I should add that the whole theme of his book very definitely falls into this latter camp.

It is this predictive method that he outlines that is of interest to me in terms of your views, I can't decide if d'Espagnat is saying the same as you, or (given your comments and those of Grey in other threads) that in fact you are going beyond the current physics community consensus which I would imagine would also be going beyond what d'Espagnat is saying. I only say this because d'Espagnat describes these two methods in a very matter of fact way, as if they are accepted alternative ways of looking at the raw experimental data. I thought that if I include his word for word outline of this predictive method, you may be able to give me some clue as to whether or not I am justified in thinking that you are both basically saying the same thing - this will help me in being able to place d'Espagnat's views and yours in some kind of context. I appreciate there may not be enough detail here for you to make a meaningful comment, but the book is an overview of realism in physics in relation to quantum mechanics and so does not go into great depth with regard to the various topics covered.

He says:

"The other method at our disposal consists in not introducing at any stage any wave function other than just the one of the pair. To the mathematical expression of this wave function some calculation rules are directly applied that, according to the formalism, yield the joint probability of observing a given pair of results on the left and right instruments, and this for any pair of orientations of the latter that one may choose. This calculation thus yields correlation predictions and (fortunately!) the latter are identical to those obtained by means of the descriptive method (a confirmation of the fact that quantum mechanics is a consistent theory).

Note, that in this method, no faster than-light influence explicitly appears. But this circumstance is tightly linked with the fact that the method in question is purely predictive and lends itself to no interpretive picture*. As we just saw, it just consists in applying a set of observational predictive rules (the quantum mechanical ones) concerning which it has been found that up to now they correctly predicted what was observed. In other words, it is grounded on just induction, quite apart from any reference (not even implicit) to a realist interpretation liable to support the latter and make it somewhat plausible. At first sight, it may therefore be wondered whether it yields a genuine explanation of the observed correlation. In fact this may be considered a first illustration of the difference, noted in section 2-8, between explanation as understood by the objective realists and explanations as conceived of by upholders of the view that physics merely describes human experience."

"*The fact should be kept in mind that, in quantum mechanics, a statistical ensemble of pairs described by "the pair wave function" cannot be identified with a mixture of pairs whose orientations in space are well defined, differ from one pair to the others, and are statistically distributed. Relative to most correlation measurements these two ensembles lead to quantitatively different outcome predictions." (foot note by d'Espagnat)

I'll step in to point out (as I always do ) that this isn't really accurate. Ken G is correct that there is no way for us to use quantum entanglement to send messages that violate causality, or anything of that sort. However, Bell's theorem demonstrates that, for the results to be consistent with the predictions of quantum mechanics and observation, the whatever underlying mechanism determines the result at A must take into account information about the choice of measurement at B, which can be arbitrarily far away, and can be outside the light cone (past or future) of measurement A. It does not require ascribing any reality at all to the electron's wave function, or treating it as anything more than a bookkeeping technique to come to that conclusion.

Now, it's true that Bell's theorem does rely on a couple basic assumptions; all theorems do. If you're committed to preserving the assumption of locality, you can focus on those other assumptions as well. In some cases, that's hard to do (for example, one assumption is simply that the most basic rules of logic are valid), but others are a little trickier to defend (such as contrafactual definiteness, the assumption that the choice of measurement at B could have been different, and that if it had been, we would have seen definite results which still would have been consistent with the other measurements we made and the predictions of quantum theory). There's been a fair amount of discussion about all of that within the scientific community over the years, but most physicists whose views on the matter I'm aware of, either from direct communication or from reading their work, accept the conclusion of nonlocality.

Ken G seems to accept most of the steps of that argument, but balks toward the end, insisting that the universe is neither local nor nonlocal, preferring to use words like "holistic". Except that the way he uses "holistic" is essentially equivalent to a subset of possible nonlocal universes, as the term is used by everyone else. But for some reason, he doesn't want to use the term.

I've given up on convincing Ken G to think other than he does after many long conversations about it; I fear that we just go around in circles, and I don't have the time to devote to it these days. However, I always feel honor bound to follow after him in these discussions, and point out that his views are not mainstream in this matter. In one sense, that's not particularly a problem, he's welcome to hold his own views. But since he's extremely knowledgable about many aspects of physics and astronomy, very skilled at explaining them, and therefore seen as an authority here, it might be easy to assume that his views on this matter do reflect those of the majority of physicists.

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Conserve energy. Commute with the Hamiltonian.

I don't think that many people think that Bell's theorem throws "quantum mechanics into a tizzy". They just think that it shows that quantum mechanics is inconsistent with a local model of reality, and further, that since we now have experimental results in this matter (that unsurprisingly match the predictions of quantum theory), any future theory will also be inconsistent with a local model of reality. That would have really bothered Einstein, who had hoped to use the assumption of locality together with thinking about EPR-type experiments, to show that quantum theory could not be a complete description of reality. Instead, Bell was able to show that the assumption of locality itself was a problem. It was a big shock at the time, but unless you're still committed to a local model of reality, it shouldn't still be a big issue.

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Conserve energy. Commute with the Hamiltonian.

That does seem to be the trouble with this
subject, lots of philosophy but a derth of
clear experiments illustrating very very
clearly the paradoxes. I was chuffed however
to extract an agreement from Dr Chinese some
time ago that Bells inequality was another
manefestation of the curve of polaroid cut off
law known for 200 years. It has a name, sorry
I cannot recall it.

So just to be clear, I take it you are not talking about a faster than light influence here?

But that's not a "method", the method is science: organization and prediction of experimental results using mathematical axioms. No part of this is the "attribution of what is real" step, that part is merely a picture, to accomplish cognitive resonance in the mind of the scientist. That's fine when recognized for what it is, but all too often, it is mistaken for part of the method. Is not the most important aspect of scientific methodology its objective and demonstrable nature?

It is a description, yes, but not a method. The scientific method involves testing-- how does one test a physical influence that travels faster than light? No such test ever succeeds in finding anything real that travels faster than light, this is trying to tell us something.
The key point is that these are not separate approaches-- everyone uses the latter approach, it is a subset of the former. It is the objective subset, in fact-- it is the science part. People are welcome to take that science and build any structures in their minds that generate whatever level of cognitive resonance they like, while others go to church or for a walk in the woods to acheive a similar state of cognitive satisfaction. What is the distinguishing characteristic of science? It is the subset that gives you no choice, that is objective.
My approach is certainly not part of the consensus, but its goal is to notice the lack of consensus and point out that this is a good indicator that science has taken an unnecessary step.
Yes, that does sound like what I'm saying, except I add that the "predictive" piece he describes is in fact what science is, and adding anything to that makes it something less than what it is, not something more. It is a backtrack, a return to when the opinions of science were highly suspect (just ask Galileo). Ironically, you often see it in the very same types who come down most harshly on people who reject science as their paths to all truth, and it is that core hypocrisy that bothers me the most about it.


The key word is "fortunately", but it is not "fortunate" at all-- it is the simple expression of the fact that what is described is the science, there's no way the "other approach" could yield anything different and still be science. The one is a car, and the other is a car with a periscope that thinks it's a car/submarine. "Fortunately" they both drive on roads.
Right, except that it does lead to an interpretive picture-- any interpretive picture you want that is consistent! That's the beauty of interpretive pictures, they are tacked onto science in any way we like, often many in the same situation. That is quite common in science, you see it everywhere. Why did we expect quantum mechanics to be different, because it is a "theory of everything"? Please.
What an "explanation" is is a tricky subject, not really part of science. One can debate it, but one is not debating a scientific result, one is debating what one thinks the goal of science should be. But science is not defined by its goals, it is defined by its methods, and they give what they give.