# How is entanglement not weird ?

1. Aug 22, 2009

### fereopk

How is entanglement not "weird"?

But explain to me how this is not weird:

So 2 people receive a set of boxes, all the boxes are numbered and the 2 sets have the same numbers, the boxes have 3 doors, opening a door will cause the box to either flash red or blue.

If person A and B open the same numbered box and the same door, it will flash the same color. If the boxes are "programmed" to flash the same color, a program for a box may be some thing like "blue, red, blue (a color for each door)", this may seem like an explanation to why the same boxes flash the same color for A and B.

Here are all the possible combinations of the doors the can be opened by A and B (1 represents top door, 2 represents side door, etc.): (1,1),(1,2),(1,3),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3). 9 combinations

(1,1),(2,2),(3,3),(1,2),(2,1)-5 combinations
These combinations will result in each box having the same color (since at least 2 of the doors have to be the same color, 1 and 2 are the same color)

So if the boxes are "programmed", if randomly chosen, over 50% of the time the boxes will have the same color, because 5/9 is more than 50%.

But that was obviously proven wrong and with experiments, over 50% of the time you did not get the same color.

So if the particles aren't "programmed" or "predetermined", must not that mean there is some connection that allows them to have the same spin on the same axis? How is this connection not weird?

Last edited by a moderator: Apr 24, 2017
2. Aug 22, 2009

### WaveJumper

Re: How is entanglement not "weird"?

Is this the 1st time you see people with the attitude - 'pretend there is no problem and it will go away'? What did you expect, there are probably more than 200 000 physicists on Earth. Did you really expect All of them to accept the possibility that there is a chance that their most cherished assumption about the world might be wrong?

Last edited by a moderator: Apr 24, 2017
3. Aug 22, 2009

### DrChinese

Re: How is entanglement not "weird"?

Entanglement is weird, I think. Trying to have a mental picture is problematic, and leads to a lot of debate.

The thing that is not weird is the part where this is a direct result of any setup where you try to do better than the Heisenberg Uncertainty Principle. EPR spotted this in 1935, leading ultimately to Bell's Theorem in 1965; as well as the many experimental examples we have today.

Are Alice and Bob communicating superluminally? You certainly might think so given how the results correlate. But this is not a strict requirement of Bell's Theorem itself, it is more likely to be something we fill in to provide a convenient mechanism for entanglement. But really, that doesn't answer other key fundamental questions about entanglement. Consider:

a) Why does such communication (if it exists) limit itself to respecting the HUP? You still get no mechanism for beating the HUP, which is weird. So it still appears that there is no more "complete" theory out there, and there is no greater level of realism.

b) Why is it that Alice and Bob can be entangled on multiple levels (hyper-entangled) and yet: it is possible to make measurements on Alice and Bob which leave them still entangled in other bases? I.e. they are still entangled as to time-energy after spin measurements. So there must be multiple channels of communication if there is in fact FTL communication going on.

c) Why have no other FTL influences been found? Why is QM otherwise respectful of c?

4. Aug 22, 2009

### DrChinese

Re: How is entanglement not "weird"?

What would that be? And how does that relate to entanglement?

5. Aug 22, 2009

### WaveJumper

Re: How is entanglement not "weird"?

A challenge to the assumed nature of reality.

Based on the violation of Bell's inequaities, the correlation between entangled particles must be non-local.

Entanglement IMO raises other questions - if the universe was designed or programmed, why is there entanglement? Is it an artifact resulting from a limitation of the underlying system or is the whole universe inter-connected(as has been suggested multiple times)? Or is conscious awareness caused or related in some way to entangled particles in the brain and thus entanglement couldn't be avoided in a universe like ours?

Last edited: Aug 22, 2009
6. Aug 22, 2009

### fereopk

Re: How is entanglement not "weird"?

That's an interesting theory. http://en.wikipedia.org/wiki/Quantum_brain" [Broken] But apparently "the structures of the brain are much too large for quantum effects to be important. It is impossible for coherent quantum states to form for very long in the brain and impossible for them to exist at scales on the order of the size of neurons".

Last edited by a moderator: May 4, 2017
7. Aug 22, 2009

### ronridings

Re: How is entanglement not "weird"?

Is there a good beginners book for me to read so I can get a better understanding of this topic?

8. Aug 22, 2009

### ronridings

Re: How is entanglement not "weird"?

what is meant by quantum brain?

9. Aug 22, 2009

### fereopk

Last edited by a moderator: May 4, 2017
10. Aug 23, 2009

### WaveJumper

Re: How is entanglement not "weird"?

I am sure Henry Stapp, Roger Penrose, Stuart Hameroff, just to name a few, would not agree. I am not stating that their approach is correct, but just pointing out that this is a highly contested topic and no opinion could be singled out as 'correct' at this time.

If i was to trust my instincts(which are often unreliable), i would come to the conclusion that entanglement must play a central role in a universe like ours. I view it more like a flaw or limitation of the underlying system, there probably was no other way to construct a universe with conscious life.

Seth Lloyd of MIT raises good points that the universe is a quantum computer(exploiting entanglement) and that everything in the universe is made of bits. This has been a growing trend among physicists to revert to information as the possible underlying source of all reality. (there should be some cheat codes somewhere within the program, maybe those filthy rich guys on 100-metre yachts had found them).

Last edited by a moderator: May 4, 2017
11. Aug 23, 2009

### Descartz2000

Re: How is entanglement not "weird"?

I'm not sure what quantum brains have to do with entanglement. However, the loophole of the experimenter not being able to make a 'free' choice will always be open, that is until free-will is disproven. It seems there is no evidence for FTL communication, just an argument that needed to be made for it, so that we do not have to entertain the notion that there may be a lack of free choices in our experiments.

12. Aug 25, 2009

### Chek

Re: How is entanglement not "weird"?

Perhaps perception is relative to the observer and how we perceive the universe to work and exist does not contain all the information at this time.

In holographic images two lasers are focused at an image and a picture is taken. If you cut a holographic imagine in two you do do not receive 1/2 of all the information about the picture. You receive all the information but in two smaller pictures.

In other words if I cut a holographic picture of a rose in half. I would have 2 pictures of the same rose. Regardless of the distance between the two pictures the total amount of information (all available) would be contained in both parts regardless of the distance apart. This doesn't mean that information was transmitted FTL.

Perhaps entanglement is a process were two particles are given the same information. Perhaps its the information itself that you are manipulating. The entangled state is removed once the particle is measured. If you thought of the universe as a quantum computer itself. Then entangling two protons and separating them by distance doesn't necessarily separate the information about them. If the bit is located at the start of the program or any point after. The information as it changes is reflected everywhere else in the program at quantum computation speed

13. Aug 26, 2009

### Zarqon

Re: How is entanglement not "weird"?

I think your example of holography is not quite right. Holograms are based on interferometry, and if you cut one in two pieces, even though you get two images, the resolution/contrast of each goes down (by a factor of two I would guess), and so the total amount of information should be conserved.

14. Aug 26, 2009

### Chek

Re: How is entanglement not "weird"?

Cut the hologram in half and both halves still regenerate a whole scene. Try quarters, eighths -- and it's the same thing! The reason is that a whole code exists at every point in the medium. The reasons are mathematical. But, basically, the holographic code depends on ratios established within the medium, not absolute values.

At any rate, with very tiny pieces of a diffuse hologram, the regenerated image does blur but the information itself doesn't degenerate. It's in the communication of it; the loss of fidelity is an effect of "noise" on the very weak signal a tiny piece of hologram generates; it's like what static does to a weak radio signal or snow to a dim TV picture.

Not saying quantum entanglement is exactly like a hologram in every way. I do think its interesting that it takes interferometry to make a hologram and quantum particles have a wave function.

I am wondering if something similar is happening on a quantum level. The particles are separated and both particles retain the same information and unlike a hologram they are not reduced in size. I do not claim to understand whats going on. It just seems to be similar to a hologram. Not exactly as you stated but our mind has a hard time grasping the fact that two particles could contain the exact same information regardless of the distance separated.

I think its interesting that the entanglement is broken once a measurement is taken.

15. Aug 27, 2009

### bjacoby

Re: How is entanglement not "weird"?

Actually this is wrong. If you break a hologram in two you actually do receive half the information. It couldn't be any other way in that the film (plate) has a certain information storage capacity and assuming that it's pretty much filled up then cutting the storage space in half cuts the information in half.

You are fooled by the fact that both halves contain pictures of roses. But they are NOT the SAME rose! In truth each image is of the Rose viewed from a slightly different direction.

Yes, you did have a good quantum theory going there for a minute.

16. Aug 27, 2009

### DrChinese

Re: How is entanglement not "weird"?

Interestingly, this is not always the case. A full measurement does NOT break all entanglement in special cases. Specifically, when 2 particles are hyper-entnagled, they are entangled in 4 or more degrees of freedom, i.e. 2 non-commuting pairs of observables. Observing of those ends entanglement along the selected non-commuting observables, but NOT on the other ones. Example would be a spin observation which leaves momentum-position entanglement intact.

See for example:
http://arxiv.org/abs/quant-ph/0406148

17. Aug 27, 2009

### VincentJL

Re: How is entanglement not "weird"?

Typicly when people talk quantum entanglement, they bring up the example of the left and right hand gloves in two closed boxes.
You know, if you open one bos and it contains a left hand glove, "the other instantaniusly becomes a righthand". That's a very force interpretation, since in this particular case, the behaviour at the quantum level is fully explainable by the classical model (at 0 and 90 deg angles between the detectors).
I haven't read much about experiments confirming bells theorem, sadly experiments aren't really coverd much even in advanced quantum mechanics courses, except as short remarks in the lines of "And this has been proven a thousand times over in experiments". However in what I have read, you really only have the quantum mechanical wierdness when you have something like a two state meassurement of a continues variable, for example meassuring the spin of a single particle. And it only seems wierd when the two detectors are at angles different to 0 and 90, in these cases we are back to a fully understandable glove model.

Does anyone have some links to good detalied reports on experiments breaking Bells inequality? Personally I have only come accross experiments that use the fair sampling assumption to break it, which seems like cheating.
Also are there any engtanglement experiments that meassure 100% correlation when the detectors are alligned? If not, what are the best detectors up to?

18. Aug 27, 2009

### Chek

Re: How is entanglement not "weird"?

I'm not trying to say that entangled particles are holographic just saying that there is an underlying principle involved that we haven't figured out as of yet.

The hologram analogy was a way of showing how information can be in two places at once and still convey the same thing and not break the FTL barrier.

This is a quote from wiki concerning cutting a hologram in half. I'm afraid that I am not an expert in the field.

quote: Since each point in the hologram contains light from the whole of the original scene, the whole scene can, in principle, be reconstructed from an arbitrarily small part of the hologram. To demonstrate this concept, the hologram can be broken into small pieces and the entire object can still be seen from each small piece. If one envisions the hologram as a "window" on the object, then each small piece of hologram is just a part of the window from which it can still be viewed, even if the rest of the window is blocked off.

One does, however, lose resolution as the size of the hologram is decreasedâ€”the image becomes "fuzzier." This is a result of diffraction and arises in the same way as the resolution of an imaging system is ultimately limited by diffraction where the resolution becomes coarser as the lens or lens aperture diameter decreases. : unquote

My question would then be whats the difference between an entangled particle and an untangled particle. In the process of entanglement do you spit the particle in half or are you manipulating one particle to contain the information of another?

If you split the particle in half are you loosing any aspects of the entire particle. If your manipulating the information of one particle onto another are both particles truly identical?
What tests could be taken or have been taken to determine these questions.

I'm not a physicist and I apologize if my questions are unlearned. I think its an interesting subject and I am trying to read as much as possible in order to fill out my understanding.

19. Aug 27, 2009

### DrChinese

Re: How is entanglement not "weird"?

Unfortunately, the hologram example does not at all account for Bell test results. The results are clearly biased according to measurement angle settings. This cannot be accounted for with local and predetermined settings under any system. You might consider looking at my web page to see why not:

Bell's Theorem with Easy Math

20. Aug 27, 2009

### DrChinese

Re: How is entanglement not "weird"?

Now why would that be cheating? All science is based on sampling. And much particle physics is based on so-called fair sampling. It seems odd that the "undetected" photons just happen to be the ones that wouldn't match to theoretical predictions, but all the others do.

At any rate, no one much takes fair sampling as a serious critique anymore. As Bell test accuracy has improved along with detection efficiency, the violation of Bell's Inequality has increased to over 200 standard deviations from about 5 originally. Further, most feel the detection threshold has already been exceeded at which any "missing" photons could account for any change in the result. (To be fair, there are still some technical debates about what the "correct" threshold is.) But even that debate is made moot by the fact that several experiments have been done in which fair sampling is not an issue. See for example, per Rowe et al (2001):

"Local realism is the idea that objects have definite properties whether or not they are measured, and that measurements of these properties are not affected by events taking place sufficiently far away. Einstein, Podolsky and Rosen used these reasonable assumptions to conclude that quantum mechanics is incomplete. Starting in 1965, Bell and others constructed mathematical inequalities whereby experimental tests could distinguish between quantum mechanics and local realistic theories. Many experiments [1, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15] have since been done that are consistent with quantum mechanics and inconsistent with local realism. But these conclusions remain the subject of considerable interest and debate, and experiments are still being refined to overcome 'loopholes' that might allow a local realistic interpretation. Here we have measured correlations in the classical properties of massive entangled particles (9Be+ ions): these correlations violate a form of Bell's inequality. Our measured value of the appropriate Bell's 'signal' is 2.25 plus/minus 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called 'detection' loophole."

In addition, there are other experiments of a different nature that also support Bell test and show that QM is incompatible with local realism.

21. Aug 27, 2009

### vanesch

Staff Emeritus
Re: How is entanglement not "weird"?

Well, whatever you think about it, don't you think that it *is* surprising that assuming the fair sampling hypothesis, you DO find the exact quantum predictions ? In other words, if QM were totally wrong on this, and the only way to violate Bell's inequalities would be by introducing a mis-understood correction (the fair sampling hypothesis in this case), then it would be quite some luck that all these misunderstandings work together to come out exactly on the quantum result, no ?

I have to say I haven't followed the experimental side of this in any great detail in the last years, so I don't know if there have been any experiments that give you a Bell-like test without any detector correction.

22. Aug 28, 2009

### VincentJL

Re: How is entanglement not "weird"?

DrChinese: You seem to know alot about the subject, so I hope you would answer some more questions.
When it reads "improved along with detection efficiency"? What exactly is the detection efficency, if we set up the best detectors in the world to meassure engangled states (A related question is what states are the easiest meassurable), and have them meassuring at a 0deg relative angle, what is the correlation? Am I correct to assume that quantum mechanics would allow you to have messurements of 100% correlation?

When you say that it would be odd for the undetected photons to be the only ones that didn't obay the theory, I disagreee that this would be a wierd behaviour. As I see it if the world obays local reality, then I personally can think of no classical model where the meassured results would not give a curve with respect to detector angles which would break Bells curve is you assumed fair sampling.

23. Aug 28, 2009

### DrChinese

Re: How is entanglement not "weird"?

Yes, there should be "perfect" correlation at 0 degrees, and there is (within statistical limits). In the case of the Rowe experiment, the correlation is between pair of Beryllium ions (not photons as per most Bell tests). There is no fair sampling assumption made. The detector doesn't miss any of the pairs, but there is some detection error. The error rate itself is small, about 2%, but this amount is far too small to change the results. Per the paper:

"The result above was obtained using the outcomes of every experiment, so that no fair-sampling hypothesis is required. In this case, the issue of detection efficiency is replaced by detection accuracy. The dominant cause of inaccuracy in our state detection comes from the bright state becoming dark because of optical pumping effects. For example, imperfect circular polarization of the detection light allows an ion in the |down arrowright fence state to be pumped to |up arrowright fence, resulting in fewer collected photons from a bright ion. Because of such errors, a bright ion is misidentified 2% of the time as being dark. This imperfect detection accuracy decreases the magnitude of the measured correlations. We estimate that our Bell's signal would be 2.37 with perfect detection accuracy."

You see, the idea has been to consider alternative explanations all along. So it is not as if scientists don't consider other possibilities - they do! But there is a point at which it becomes impossible to hold onto a hypothesis that has NO experimental support, if you want to continue to call your viewpoint scientific.

It turns out that if you disagree with QM - which I guess you do - then you have a hard time explaining why all the experiments agree with QM. You may as well argue that there is no moon... it is actually an elaborate illusion. There is solid support for QM, it is no illusion.

24. Aug 28, 2009

### VincentJL

Re: How is entanglement not "weird"?

DrChinese
You have much the same attitude that most lectures have towards quantum mechanics. You defend it out side the bounds of experiments. It would not state Quantum mechanics to be false, simply based on my sceptical attitude, however I will not "accept" it simply because of the number of publications that proclaim to prove without doubt that quantum mechanis is definently to within half a degree of certenty most likely correct. I am looking for proof, which does not base itself on making assumptions which I cannot fully agree with, and when reading about polarisations experiments I simply came to the conclusion that I could not agree with the fair sampling assumption.
I have read that some scientists hold the belief that the very nature of quantum theory makes a loophole free violation of the Bells theorem impossible, this would lead one to think that no loophole free experiments have actually been conducted, if so, what would be the closest thing to a loophole free experiment?

I am reading the Rowe article now, and of cause, it isn't without a loophole, it's just not the fair sampling loophole. I would still like to know if the fair sampling loophole can be eliminated in photon polarisation meassurements, or if that is outside the scope of pressent experiments, and I am still curius as to what the actual detection rate at 0 degrees angle is in such experiments.
And when you write
"Yes, there should be "perfect" correlation at 0 degrees, and there is (within statistical limits)."
Within what statistical limits? Do you have a good reference to experiments?

Just for the sake of the discussion, I must add that apparently, I am fellowed by quite some intelligent people in looking for other descriptions of quantum mechanics:
http://www.technologyreview.com/blog/arxiv/24044/
This ofcause does not offer any support of claims, however it does provide for some interessting reads.

Last edited: Aug 28, 2009
25. Aug 29, 2009

### DrChinese

Re: How is entanglement not "weird"?

You are free to doubt QM, that is your right. It doesn't really sound to me that the result of experiments really matters to you, you just want to continue to hold on to a preconceived notion against solid evidence to the contrary. I suggest this reference to answer some of your questions about loopholes:

Towards a loophole-free test of Bell's inequality with entangled pairs of neutral atoms by Wenjamin Rosenfeld, Markus Weber, Juergen Volz, Florian Henkel, Michael Krug, Adan Cabello, Marek Zukowski, Harald Weinfurter (2009).

But if the facts don't matter to you, I won't be able to help you much. You also might consider starting a new thread about "Towards a Loophole Free Bell Test", although I think this has already been discussed in earlier threads.