Entanglement and Bell's theorem. Is the non-locality real?

mbd

Sylvia, the simulation counts all events that would be counted in an idealized CHSH experiment where only entangled pairs are involved, only one entangled pair is active at a time, and the coincidence window is less than the time-step.

You can change the code in the following way to convince yourself of this: Continue the random-walk on E until both A and B have been detected. Then, write out all detections with the setting, the result, and the timestamp. Later, process the file to find detections that occured at both A and B within your coincidence window. If you choose a coincidence window smaller than the time-step, you will get the same result as the code produces.

I question the assumption inherent to Bell and CHSH that entanglement begins with the emission of two particles and ends with the detection of two particles (assuming perfect detection). It is this flawed assumption that leads to spooky action at a distance, too many worlds, and all that.

Greg-ulate

I dont understand what bells inequality is refuting. Why does local realism predict a different outcome? The probability for a photon to pass through a polarizer is the Cos of the angle between it and the polarizer. So if you put a source of linearly polarized photons through a polarizer oriented at 45° to the axis of polarization and .707 of them go through it.

If you set up bells experiment then you are making a cut on a statistical sample of photons which average out to be polarized in the direction of polarizer A and asking how many identical ones make it through polarizer B and its .707. Why is this surprising? How could it be any different? I feel like I'm taking crazy pills! I really can't see any reason anyone comes to the conclusion that there is something superluminal going on, especially since the correlation between A and B is not known until Alice walks over to where Bob is and they compare notes.

About your paper, it doesn't seem to matter that E is updated in the iteration of the loop that comes before its comparison with A and B. So how does this make a comment on the speed of information travel? The simulation could be interpreted as a model of two detectors, A and B, at the same location as past E.

I recreated your code in LabVIEW and I get .678 for the correlation.

Is this
emmitt += (2 * rand.Next(2) - 1) * Math.PI / 4;
the same as
emmitt += (rand.Next(4) - 1) * Math.PI / 4;
which would tend to increase emmitt instead of maintaining equal probability to be negative?

This seems like its measuring the probability of your random number generator to generate numbers within a certain range.

Edit: Oh I see rand.Next(2) returns an integer, I get .707 now

Sylvia Else

Did you look at this link, posting earlier by bohm2?

http://lanl.arxiv.org/pdf/1212.5214.pdf

In Bell's theorem we're not just concerned with the measurements that are actually made. We're also considering the other measurements that could have been made instead, and how nature balances its books with entangled particles so that the numbers come out right in the end regardless of which measurements we choose to make.

Bell's theorem says in essence that there is no way in which nature can achieve this if the result of a given measurement depends only on that measurement and not on the other measurement. Since measurements can be space-like separated, this means that whatever nature is doing, it cannot be mediated by light-speed influences, and thus that whatever it is must be non-local.

Sylvia.

lugita15

I think this easy-to-understand explanation of Bell's theorem should help:
http://quantumtantra.com/bell2.html

DrChinese

Ah, you are treading into some deep water here!

If you are ready to take the DrChinese challenge, we will find out what your code is made of. To make your claim successfully, you MUST present results at a third angle other than for Alice and Bob. So we will need to see some results for Chris as well. Otherwise you fail the realism requirement.

Let me know if you are ready to go down this road. Else you will be forced to move this line of discussion elsewhere. In fact that may be necessary anyway.

mbd

DrChinese, you are moving the goal line! I have shown that CHSH experiments, as performed thus far, cannot rule out the mechanism I've proposed. And, I have proposed an experimental modification to CHSH to confirm or rule out this mechanism. The mechanism is most certainly local realistic. That said, I am NOT claiming that it is capable of performing everything that nature can.

Further, the reason I have shared it is that I figure others may find it compelling and may want to test it, theoretically, against other phenomena.

Regarding a third angle, note there are four angles in the code. Can you be more specific as to your challenge? Are you asking whether the mechanism honors Malus' Law? (it does)

Lastly, your last paragraph is thoroughy rude and inappropriate.

Perhaps you're reacting to my careless reference to EPR exerpiments when I meant CHSH EPR experiments?

DrChinese

The issue relates to values for other angles than A and B. for example, when A, B ,C are 0, 120, 240 respectively, you cannot have a data set in which the cos^2 relationship is maintained independently of selecting which 2 are being actually observed. That means the outcome is observer dependent, which violates the premise of realism. Try it with about 10 sets of triple values and you will quickly see the problem.

A. B. c.
Y n y
Y n n
N y n
Etc

Then compare ab, bc and ac. You want each to match 25% of the time as cos^2(120 degrees) is .25.

DrChinese

Rude, not I my friend. Forum rules are at issue, just trying to point that out. I am not an admin, so I am not the decision maker on this point. Posting unpublished assertions going against the mainstream can bring a thread to a halt. So please be careful how you say it. There are no accepted local realistic explanation for observed results of experiments. Yours does not qualify as such. And I am not the one moving the goal posts, you are. Realism implies observer independence, a key element of the Bell proof.

mbd

DrChinese, the model I've proposed is local realistic. It only involves speed-of-light interaction, albeit direct particle-to-particle. Physics already accepts that particles are affecting each other through fields at the speed of light.

Regarding appropriateness, two participants in this thread have already run the simulation code I provided, one of them being the person who asked the original question, "is the non-locality real?", and both achieved the same results. So, I think this thread is proving to be well within the spirit of the forum.

If nothing else, it serves as an illumination of the significant potential of one of the loopholes to Bell's Theorem. That alone goes well toward answering the question.

StevieTNZ

You might find this paper interesting: http://www.gap-optique.unige.ch/wiki...nal_signalling

Cthugha

I do not see any good proof that the model is indeed realistic. The method DrChinese proposed is the standard way of checking whether it is. This is not moving the goal line by any means. We have seen like 50 to 60 proposals for local realistic models in these forums over the past few years which could reproduce Bell experiments or CHSH experiments for two angles. Some of these proposals contained simple errors in the code, but most of them indeed could not give results when picking three different angles and turned out to be not realistic. So unless you can indeed show that your code works for three arbitrary angles, you have not shown anything interesting so far. It is just a fact that many models, which seem realistic, are in fact not. So you need to rule that out.

Even so, these forums are not the right place for pushing personal theories.

DrChinese

It is local, not realistic.

So: Loophole in Bell's Theorem is what you just said. Please indicate a suitable place your theory has been published or some other indication your ideas are generally accepted. Barring that, your ideas are inappropriate here.

mbd

DrChinese, I will stipulate to the fact that there may have been a slight breach of forum rules if you will accept that the consequence has been a lively discussion from which we all, including myself, have learned something?

That said, it is patently unfair to single out my postings when this forum is chock full of posts with links to unreviewed, unpublished, articles on arxiv. In fact, another active thread today has multiple instances of that. Will you please inform the participants in that thread too of your objections to their behavior?

http://www.physicsforums.com/showthread.php?t=482657

StevieTNZ

I must state that I was surprised that I was given infraction points for asking questions pertinent to an article on arxiv, to which ZapperZ and I exchanged private messages on whether peer-review is more superior to unpublished articles.

mbd

According to definitions in Zeilinger (2010), http://www.pnas.org/content/107/46/19708.full.pdf, the mechanism I described is local and realistic:

The mechanism I proposed, however, is not "local realistic" as defined in the same paper. But, "local and realistic" is not the same as "local realistic", hence the confusion here.

Zeilinger is a good example to use too because the mechanism I described can operate through the experiment - it is NOT ruled out by Zeilinger - because, in Zeilinger, the optical pathways are open, albeit changing, for the duration of the experiment.

The Zeilinger paper also contains an excellent explanation of conditional probability and bayes rule and how it leads to the necessity of closing the "freedom of choice" loophole.

DrChinese

No, the issue is whether the concepts are consistent with generally accepted science. I am an advisor here, not a mentor or admin. You are discussing an issue that I follow closely, and frequently debate with folks who are still learning the the nuances of the area. For those who are asking, there is rarely an issue. For those who are telling others, you should follow established protocol.

If you will simply stop pushing your theory, defending it, explaining it, etc, all is fine. Otherwise I will report it. I, unlike you, bear no burden of proof. As I have already told you, your idea is not realistic. I have also defined, for your example, what realism would require. And you have already been told by a second advisor who is knowledgeable that this is standard science.

The OP asked is nonlocality real. It may be. Otherwise, locality is not realistic. This is Bell.

mbd

The December issue of Physics Today demonstrates that there is no prevailing view on many of these issues. In particular, see the responses to Mermin's excellent commentary on conditional probability that appeared in the July issue.

In any case, it is most definitely NOT a consensus viewpoint to say that a realistic system is one in which outcomes of a measurement are observer-independent. To say so conflates the measurement problem with realism. A system can be realistic whether or not you are able to glean perfect, or no, information from it, and whether or not doing so impacts or does not impact the system.