Aspect's Experiment Was Flawed [Archive]

Maestro

Aug16-04, 10:43 PM

I'm a newbie to theoretical physics and I'm having difficulty accepting quantum mechanics. For starters, it sounds like the validity of quantum mechanics rests solely on the shoulders of Aspect's experiment (which sounds a bit far fetched to me). If I understand correctly, the experiment involves two entangled particles that are being analyzed by two different sensors. The sensors can only detect the spin direction of each particle about a given axis. Since the two particles must have the same spin (because they are entangled particles), simply measuring each particle's spin using each corresponding sensor set to the same axis should reveal identical results for every run. Instead, Aspect chose to measure the rotation about three random but specific axes and then see how many times the rotations were detected as identical. According to Aspect, the rotations of the two particles should be in the same direction more than 50% of the time. Simply put, there are nine possible combinations of clockwise and countercockwise rotations between the two particles. If the particles both have the exact same spins, then they will both have the exact same rotations for each of the three given axes. Regardless of what those rotations are (assuming they are not all identical), the results of the test should reveal that the rotations are in the same direction 5 out of every 9 runs, which is obviously greater than 50%. Here is where the experiment is flawed. Aspect's experiment assumes that every set of particles will have the exact same spin. Otherwise, the rotations about each axis will change for every set of particles. While one set of particles may have a clockwise rotation at a 54-degree axis, another set of particles could easily have a counterclockwise rotation about the same axis. Am I missing something, or are all of the particles used in the experiment virtually identical? If they are not all identical, then I don't see how the experiment is valid. My math says the rotations of each set of particles should be the same exactly 50% of the time (which is exactly what the results of the experiment revealed). It seems impossible that all the great minds in physics could have overlooked such a simple error, so I'm sure I must be missing something.

SOMEONE PLEASE ENLIGHTEN ME!

ahrkron

Aug17-04, 12:41 AM

I don't have too much time right now, but I just wanted to say (for now) that QM rests on much more than Aspect's experiment.

The whole theory started from a detailed description of black-body radiation. Spin (a purely QM property) was discovered using molecular beams and later measured much more accurately. The wave behavior of electron beams was observed using crystals. There are semiconductor devices based on QM. Currently, Atomic Force Microscopes have shown configurations of atoms perfectly in agreement with QM.

I can't promise I'll get back to you on Aspect's experiment soon, but I'll try.

ZapperZ

Aug17-04, 07:20 AM

humanino

Aug17-04, 08:19 AM

BTW, the most convincing evidence that QM works and is valid came from you - you are using your modern electronics.

Zz is in a terrible mood today :mad:

But as usual, Zz is perfectly right :biggrin:

danitaber

Aug17-04, 08:39 AM

ZapperZ

Aug17-04, 08:49 AM

DrChinese

Aug17-04, 08:52 AM

Aspect is not now and has never been considered a test of Quantum Mechanics. QM was established circa 1927 and Aspect was performed circa 1981.

Questions arose early on about whether the Heisenberg Uncertainly relations represented an underlying reality, or whether it simply represented a limit on our ability to gain information about a system. The answer to this question would not affect QM itself directly, but could potentially have pointed the way to an even better theory in the future.

EPR, Bell and Aspect were inquiries along this line of reasoning. There was never really much doubt that the results of the Aspect experiments would obey the Heisenberg relations. But seeing is believing, and the results demonstrate that "reality" is incompatible with "locality". That was the issue with Aspect. It does not prove QM, although technically the results could have disproven QM had they been different.

As already pointed out, there are literally hundreds of specific effects predicted by QM. It is also extraordinarily precise. That places extreme limits on competing theories! And that is why alternative theories rarely get very far - they make predictions which are incompatible with already known phenomena.

So QM takes on all contenders, and remains standing. Aspect simply knocks out a whole class of competing theories, but does not eliminate all such competitors. If you can construct an alternative non-local realistic theory, maybe you will have something.

DrChinese

Aug17-04, 09:06 AM

Instead, Aspect chose to measure the rotation about three random but specific axes and then see how many times the rotations were detected as identical. According to Aspect, the rotations of the two particles should be in the same direction more than 50% of the time. Simply put, there are nine possible combinations of clockwise and countercockwise rotations between the two particles. If the particles both have the exact same spins, then they will both have the exact same rotations for each of the three given axes.

You logic is far off here. You are looking at the problem from a perspective which is inaccurate. You should read the derivation of the Bell Theorem first, which presents the argument in a straightforward fashion. In fact, you should read EPR before that as well. Aspect should be read last. You can read all three from my web site:

EPR, Bell and Aspect (http://www.drchinese.com/David/EPR_Bell_Aspect.htm)

ZapperZ

Aug17-04, 09:40 AM

You logic is far off here. You are looking at the problem from a perspective which is inaccurate. You should read the derivation of the Bell Theorem first, which presents the argument in a straightforward fashion. In fact, you should read EPR before that as well. Aspect should be read last. You can read all three from my web site:

EPR, Bell and Aspect (http://www.drchinese.com/David/EPR_Bell_Aspect.htm)

Hey, I like your website. It looks quite useful in the sense that you have the historical collection of the EPR stuff. I am definitely putting your site as one of the links in the Yahoo e-Group that I run, so thanks for the effort. I have a couple of comments/questions though:

1. Did you realize that you have copyrighted documents on there? :) Not that this would be a problem since it appears that the site is predominantly for educational purposes.

2. You cited a rather dubious source (C.H. Thompson) regarding the validity of the EPR experiment interpretation. Having had an "encounter" with her, I can safely say that she can't work herself out of a paper bag on simple physics problems, much less handling QM and EPR experiments. [Her major objective is to disprove ALL of QM] I know for a fact that her "Chaotic Ball" paper was rejected by Am. J. of Phys. for publication. The only half-way legitimate questions being raised regarding Bell Theorem would be the one by Hess and Phillip on the possible time-loophole. But even that is highly disputed, especially by Mermin.

Zz.

Nereid

Aug17-04, 09:48 AM

Welcome to Physics Forums Maestro!

Your interesting first post brought forth a number of very good responses, particularly the point of clarifying what you are really asking:
a) what are the core set of experimental and observational results which support the major aspects of QM?
b) in what way does the Aspect experiment relate to those major aspects?
c) how does the Aspect experiment support one set of (QM) proposals (details of the experiment, how it tests EPR, etc)?
d) what other tests of the Bell inequality, EPR etc have been proposed? What experiments have been done? what were the results? how did they differ from Aspect's (e.g. greater sensitivity, different domain)?
e) post-Aspect, what are the main areas of QM that physicists are looking into?

Perhaps you could let us know which of these - or others quite different - you are interested in?

DrChinese

Aug17-04, 11:58 AM

Hey, I like your website. It looks quite useful in the sense that you have the historical collection of the EPR stuff. I am definitely putting your site as one of the links in the Yahoo e-Group that I run, so thanks for the effort. I have a couple of comments/questions though:

1. Did you realize that you have copyrighted documents on there? :) Not that this would be a problem since it appears that the site is predominantly for educational purposes.

2. You cited a rather dubious source (C.H. Thompson) regarding the validity of the EPR experiment interpretation. Having had an "encounter" with her, I can safely say that she can't work herself out of a paper bag on simple physics problems, much less handling QM and EPR experiments. [Her major objective is to disprove ALL of QM] I know for a fact that her "Chaotic Ball" paper was rejected by Am. J. of Phys. for publication. The only half-way legitimate questions being raised regarding Bell Theorem would be the one by Hess and Phillip on the possible time-loophole. But even that is highly disputed, especially by Mermin.

Zz.

Thanks, I hope folks can get something out of these!

1. The 3 main docs I am keeping on the site were not provided with their authors' explicit permission. I can only hope that their inclusion here would meet with all of the authors' approval by presenting their wonderful work in its entirety. I cannot imagine an issue with it as they are strictly for educational purposes only. (I do not advertise or otherwise in any way seek revenue from my site.) The Bell paper is actually a reprint as the original is no longer in print (a few are still around though). I have all 3 as "original" paper copies in my own collection, but unfortunately I had marked them up years ago in my excitement!

2. I do not endorse nor do I agree with Ms. Thompson. However, I think she summarizes the best the "opposition" has to offer - and anyone who has encountered her is bound to have noticed her tenacity (as you must know, she denies that photons are particles). You are correct that she has been turned down for publication on the Chaotic Ball concept, and that is why I used a different one of her papers for my site. I did have her permission to include this paper.

The history of the debate (on the completeness of QM) is in many ways contained in these 3 papers. I have not supplied a plethora of links as my site is more of a special interest for those interested in seeing the original papers, and perhaps the occasional first-timer. If you have some links that you think I should include here, please send my way!

By the way, I strongly agree with your statements above about "trivializing" the descriptive power of QM. The difference between "describe" and "explain" when it comes to science is in many ways semantic. Actually, all scientific theories are "descriptive" models of some aspect of reality. Ultimately, their utility is more meaningful than their ability to explain the "true" nature of reality (or claim to explain it, as the case may be). And nowhere is the debate more clearly focused than with the completeness of QM.

danitaber

Aug17-04, 03:12 PM

So let's not pick just on Quantum Mechanics for this reason.
. . .
Being able to say that something works is nothing to sneer at.

Zz.

ZapperZ (you *are* in a fiesty mood) :wink:
A) I'm not the one picking on QM; I would never do such a thing unless I had some ground-breaking alternative. It's just that Joe Public picks on QM constantly, and the thread had been going in that direction.

B)I was not sneering. Any theoretical framework that works is the definition of a scientifically sound theory, and is rare; and finding one that has worked as well as QM has not been done, and it doesn't look like one will come up in the near future.

But, when boiling down to the absolute basics, there it is. Any interpretation of QM (for use as description) is lacking for many reasons.
1) we have no accurate analogies.
2) Any time one answers the question "why", one opens the door to farther- and farther-fetched answers.
3)we can't directly experience what is happening.

Furthermore, the point I was trying to make (but obviously didn't communicate very well), is this: A final descriptive interpretation of QM does not exist. So "acceptance" of QM cannot be based on how it "feels" or "seems". Now, since all of you with letters after your names know the details of the experiments better than this lowly housewife, I leave you to explain all the other things on which QM rests. I am only able to confidently assert that the calculations and predictions of QM --no matter how it seems or how difficult it is to accept --are accurate enough to build an entire society out of them, as ours is. That is no laughing matter, nor is it a matter at which I sneer.

Nereid

Aug17-04, 03:25 PM

Welcome to Physics Forums danitaber!

Great post; I hope you stick around.

meteor

Aug17-04, 05:24 PM

I still have to understand completelly aspect's experiment, but I read somewhere time ago taht a scientist called Franson also denied the validity of Aspect's experiment

DrChinese

Aug17-04, 06:58 PM

I still have to understand completelly aspect's experiment, but I read somewhere time ago taht a scientist called Franson also denied the validity of Aspect's experiment

The Aspect experiment draws out people who don't like QM. They deny Aspect, often holding out hope that a local realistic theory is still possible. But it takes a lot more than denial to make a dent in Aspect's work. It takes solid science, and that is lacking in most critiques.

Maestro: you mention something about 5 of 9 permutations. The Bell Theorem is based around 8 permutations, not 9. And 4 of those 8 are considered "unreal" because their chances of being detected are outside the range of 0% to 100%. This is the science that Aspect tested. In other words, your math is wrong.

Maestro

Aug17-04, 08:39 PM

DrChinese,

You are absolutely correct that my math is wrong. I slept on the idea last night and woke up this morning realizing where I made the mistake. The 5 out of 9 numbers, however, came from the book that got me insterested in the subject, "The Fabric of the Cosmos" by Brian Greene. The book is very well written for the uneducated, but it tends to oversimplify the math and theories at the expense of a complete understanding. Thank you all for the numerous responses.

I have only one question about some of the responses. Several of you have mentioned (in one way or another) that QM is not flawed because of its accuracy in making predictions. I must wholeheartedly disagree. While there should be no question that QM is mathematically sound, its the how and why that I have a problem with. Danitaber may have described it most accurately when he said that "QM is a description, not an explanation". I have a hard time swallowing a theory that seems so far fetched (no offense), without a decent explanation of why. Until I get the answers I'm looking for, I'll just assume that QM is a theory that accurately makes predictions but has not yet been fully explained.

By the way, Danitaber, if that "housewife" comment was directed at me, you should know that a PhD is on the way, but not in physics. I'm engineering a cure for prostate cancer. Physics is just a recent curiosity.

ZapperZ

Aug17-04, 09:23 PM

I have only one question about some of the responses. Several of you have mentioned (in one way or another) that QM is not flawed because of its accuracy in making predictions. I must wholeheartedly disagree. While there should be no question that QM is mathematically sound, its the how and why that I have a problem with. Danitaber may have described it most accurately when he said that "QM is a description, not an explanation". I have a hard time swallowing a theory that seems so far fetched (no offense), without a decent explanation of why. Until I get the answers I'm looking for, I'll just assume that QM is a theory that accurately makes predictions but has not yet been fully explained.

But then, you are admitting that you are questioning QM simply based on a matter of "taste". Physics doesn't work this way. In the history of physics, valid challenges to any ideas have to be based on something more substantial, such a experimental observations. You also should consider the possibility that you may be basing your taste on ignorance of the subject matter. After all, a lot of people found it distasteful and "far fetched" that the earth wasn't at the center of the universe. This isn't a beauty contest. We don't get to pick and choose based on emotional content.

Again, show any part of physics that is an "explanation" and I'll show you someone who hasn't understood physics. QM isn't the exception. Look at classical E&M if you don't believe me. Coulomb's law is purely phenomenological. I don't see you complaining about that.

The most common problem that I have often encounter when someone complains about QM in this manner is (i) a lack of understanding of QM and (ii) the a priori assumption that classical principles MUST be valid. You are locking your understanding of the universe based solely on your prejudices that your classical universe MUST work, that your classical concept of "wave" and "particle" should be applicable, that "position" and "momentum" must have clear definitions, etc, etc. So when QM indicates something entirely different, that these ideas must be redefined, you refuse to let go. Why? Because it feels weird and "far fetched", regardless on how spectacularly the experimental evidence are.

I find such things rather ironic. The most common criticism that quacks always throw at physicists is that they are stuck with the "party line" and that they refuse to have an "open mind" (whatever that is) and be creative to look at new things (such as their pet "theory"). And yet, to be able to understand and realize the validity of QM, one has to finally realize that all of our classical notions, things that we have taken for granted to be valid, must be re-evaluated in ways that can be truly revolutionary and very different than what we have known. This requires more creativity than what most people realize!

Zz.

DrChinese

Aug17-04, 10:06 PM

Several of you have mentioned (in one way or another) that QM is not flawed because of its accuracy in making predictions. I must wholeheartedly disagree. While there should be no question that QM is mathematically sound, its the how and why that I have a problem with. Danitaber may have described it most accurately when he said that "QM is a description, not an explanation". I have a hard time swallowing a theory that seems so far fetched (no offense), without a decent explanation of why. Until I get the answers I'm looking for, I'll just assume that QM is a theory that accurately makes predictions but has not yet been fully explained.

The interesting thing is: you are now on a path to understanding the significance of Aspect, even though your current position is to minimize it.

You see, your words above could verbatim be the words of Albert Einstein. It was certainly the position that drove him to be a part of EPR. He, too, felt that QM was incomplete. It seems so obvious that it must be... at first. After all, there is always the hope for learning more - obtaining an exciting explanation instead of boring descriptions. Why is h significant? There must be a good reason, and perhaps even a way around it.

But then Bell arrived - after Einstein had passed. So Einstein never had the benefit of Bell's work. Bell showed that the counterintuitive position - there is no deeper level of reality - was incompatible with locality. Locality, of course, being a cornerstone of Einstein's relativity. So now you have a choice, one which is yours freely to make:

a) There is a deeper level of reality, just as you suspected; but locality does not hold;
b) Locality rules, as Einstein believed, but there is no deeper level of reality.

Had he lived, I believe that Einstein would have accepted the overwhelming evidence that Aspect and other experiments have provided with regards Bell. He certainly would have accepted Bell itself as a fair test. And I would venture a guess that in the end, he would choose b) over a).

DrChinese

Aug17-04, 10:06 PM

P.S. If you are not familiar with my tag line - "the map is not the territory" (Korzybski) - consider this: all theories are maps, and no map is ever the territory itself. All maps are always useful representations of the territory. All theories are useful models of reality. But no theory is explaining reality itself - always a subset of reality. Example: Do you believe the sun heats the Earth? If so, why does it heat the Earth? Why is there a sun? Why does it emit heat? Where does the heat come from? Why is there fusion? Why do neutrinos come out of the sun? No matter what theory you put forth, a criticism can be made that it is incomplete because it describes and does not explain. I don't see the point of stating the obvious: there is still more for us to learn.

No one thinks our understanding of QM has reached an endpoint. That is NOT a conclusion I would draw from Aspect. But the bar has been raised for competing theories.

Maestro

Aug17-04, 10:24 PM

vanesch

Aug17-04, 11:55 PM

By the way, can you suggest an unbiased resource that might help to speed the understanding of modern physics and Quantum Mechanics? So far I've only encountered those that support it or those that challenge it, but none that offer an open-minded analysis of it.

I don't think you will find an introductory textbook that will at the same time teach you the material and will be "unbiased" (in the sense above) towards it.
You should btw make a distinction between "having a critical attitude" towards a theory, and "learning the machinery" of a theory. You cannot do the former without having done the latter.
From what you wrote I think that your understanding of quantum mechanics is still incomplete, so if you are serious about this, you just take up any introductory text, you put your critical attitude for the moment in the fridge, and you learn first how QM works. It will be any way not a lost effort. Afterwards, once you know what's going on, you can come back to your critics.

cheers,
Patrick.

ZapperZ

Aug18-04, 06:32 AM

ZapperZ,

You misunderstand my questioning. I am not challenging QM. Clearly, I don't have the background in physics to boast that I know better than the other members of this forum. I am merely trying to understand QM from an analytical perspective. If you remember that (at one time) people actually refused to believe that the earth could be spherical, and that people refused to believe that the earth was not the center of the universe, and that people refused to believe that time was not an absolute, then how can you refuse to accept that QM may be inaccurate (not in its ability to predict, but in its ability to explain why)? A good scientist should always partially question the validity of his/her predecesors. Otherwise, without the pioneering scientists who challenged the false notions about the shape of the world, we might still believe that the earth is flat.

But then you missed completely what I wrote in that last posting. In the examples you just gave, you somehow neglected to notice HOW these scientists challlenged and questioned the status quo at that time! This is a very important point in the evolution of scientific thought! These scientists did NOT challenged conventional understanding based on TASTES! They challenged it based on experimental observations! Galileo did not state the earth is not the center of the universe because the idea that the earth is at the center of the universe just seemed "far fetched" to him. Einstein did not challenge classical mechanics simply because he thought the idea of the ether was "distasteful". That is what I've been trying to convey in that last posting. Reread what you wrote. Nowhere in your argument did you cite where QM has failed. All you indicated was that, according to what you have understood (which you admitted isn't much), it seems incomprehensible and "far fetched". This is not good enough and even you should know this!

The best example I can think of is Newton. His theories explained everything (at least to the sophistication of his day and for two centuries afterward). The mathematical formulas of Newtonian physics could predict with amazing accuracy. However, newton was wrong. When Einstien came along and permanently changed our view of the physical world, he changed the very foundation of physics. Experiment after experiment showed that Newton's calculations were correct. His math wasn't wrong (to a certain extent), but his how's and why's were wrong. It is for this reason that I partially question the validity of QM's assumptions and suggest that another perfectly acceptable explanation could be a possibility. Once again, I am not challenging QM. I am merely trying to keep an open mind (the very thing that you accuse me of not doing).

Sorry, but Newtonian laws are the clearest example of DESCRIPTION and not EXPLANATION. It is purely phenomenological based on the physical properties and observation on how things behave! I mean, try to explain "fields" if you can! Inverse square law gravitational field? Where did THAT come from? If you did deeper, you will notice that classical mechanics is NOTORIOUS for being only descriptive. It only APPEARS to you as if it is an explanation. It is not!

By the way, can you suggest an unbiased resource that might help to speed the understanding of modern physics and Quantum Mechanics? So far I've only encountered those that support it or those that challenge it, but none that offer an open-minded analysis of it.

What about a regular QM textbook? If there is a shortcut to understanding QM, I haven't found it.

Zz.

Nereid

Aug18-04, 07:02 AM

Maestro,

Just to extend what ZapperZ said:They [scientists] challenged it [an established theory] based on experimental observations!There is another route to challenging an established theory - inconsistency with another established theory.

QM and GR (General Relativity) are both modern theories of physics, and both are extraordinarily successful - there are (AFAIK) *NO* good experimental or observational results which are inconsistent with either.

However, if we look to domains far, far beyond what we can test today, we see that QM and GR are inconsistent - they make incompatible predictions. This inconsistency provides fertile ground for both theoreticians - modify or extend either QM or GR (or both) to resolve the inconsistencies; or develop completely new theories - and experimentalists and observers - devise ingenious ways to test possible incompatibilities within the realms of what we can see and do today, find ways to explore energy/mass/size/whatever regions that are beyond what we can observe today.

vanesch

Aug18-04, 07:08 AM

His theories explained everything (at least to the sophistication of his day and for two centuries afterward). The mathematical formulas of Newtonian physics could predict with amazing accuracy. However, newton was wrong. When Einstien came along and permanently changed our view of the physical world, he changed the very foundation of physics. Experiment after experiment showed that Newton's calculations were correct. His math wasn't wrong (to a certain extent), but his how's and why's were wrong.

I think you completely miss what Einstein did. He did not, for the sake of argument, "change the very foundations of physics", just for the fun of it, while Newton's predictions were correct. It is because NEWTON'S PREDICTIONS WERE WRONG, at least some of them, that something new had to be invented.
Newton's predictions were wrong concerning things which had the speed of light (such as light :-) ; Newton's gravity was wrong concerning the orbit of Mercury.
Einstein's stuff predicts OTHER outcomes than Newton's, and experiment decided in favor of Einstein's. Now in many cases, both give approximately the same answer, and that's why in many cases, Newton's theories can still be used.
The story with quantum theory is similar. It is experiment which decides. A says 2.34, B says 2.14, you measure 2.14, B is right and A is wrong.

cheers,
Patrick.

chronon

Aug18-04, 07:28 AM

Nowadays a physical theory means a set of mathematical equations together with a description of how they apply to the real world. You can be a realist and believe that there is some sort of 'stuff' that obeys the equations or not as you feel, it won't make any difference in explaining why the world behaves like that - realism is a purely philosophical issue. I'm not sure why this causes a problem, but clearly it does since people claim that you can have a local non-realist theory of quantum mechanics, whereas from my point of view a non-realist theory is meaningless. Realism applies to the connection between theory and the world, not to the theory itself.

Actually I think the real problem with quantum mechanics is that people keep saying how good it is at making predictions of how the world behaves. Its just not true, since the calculations of quantum mechanics are so hard that only the simplest cases can be worked out. The reason that there is a problem with how quantum mechanics leads to the classical world is that the calculations cannot be done. That is why everyone spends so much time philosophising about it.

Nereid

Aug18-04, 07:30 AM

A says 2.34, B says 2.14, you measure 2.14, B is right and A is wrong.This might seem like nitpicking, but I believe it's quite important in terms of conveying how science is *actually* done.

"A says 2.34, B says 2.14" Yep
"you measure 2.14" actually, you measure 2.1 +/- 0.2 (95% CL); Zapper then measures 2.20 +/- 0.05, Dr Chinese 2.16 +/- 0.06, and so on. Theoreticians tweak A, and find that 2.31 is what it really predicts, and tweak B to find that anything in the range 2.11 to 2.15 will fit. However, re something apparently quite unrelated, A says 19.3456 and B says 1.9876. Experimentally this is really hard to do. Others refine their experiments and after five years, the consensus is 2.14 +/- 0.02. After ten years, an ingenious way of testing "A says 19.3456 and B says 1.9876" is devised, and you find 1.8 +/- 0.7. Case closed.

The classic case of an observation which clearly distinguished between two competing theories but didn't is the Eddington 1919 eclipse expedition, to observe the bending of light by a massive object (the Sun), a prediction of GR. The world was told 'Einstein is right! Newton proven wrong!!', but an objective analysis of the actual photographs shows no such clear-cut result - both theories are consistent with the data.

vanesch

Aug18-04, 07:47 AM

This might seem like nitpicking, but I believe it's quite important in terms of conveying how science is *actually* done.

Don't tell them in all gory detail :rofl:

cheers,
Patrick.

danitaber

Aug18-04, 07:51 AM

Danitaber may have described it most accurately when he said that "QM is a description, not an explanation". I have a hard time swallowing a theory that seems so far fetched (no offense), without a decent explanation of why. Until I get the answers I'm looking for, I'll just assume that QM is a theory that accurately makes predictions but has not yet been fully explained.

By the way, Danitaber, if that "housewife" comment was directed at me, you should know that a PhD is on the way, but not in physics. I'm engineering a cure for prostate cancer. Physics is just a recent curiosity.

No, Maestro, the housewife comment is directly at me. I am a housewife, and just a housewife; no upcoming degrees in the near (10-20 year) future. I just have a passion for mathematics and physics. :eek:

Maestro, you're not alone in finding QM "hard to swallow". QM is hard to accept. Most people who study QM seem to come to a point where they simply admit they can't wrap their brains around it. And I think the theorists have completely given up, except, of course, for the metaphysical nutjobs.

Actually I think the real problem with quantum mechanics is that people keep saying how good it is at making predictions of how the world behaves. Its just not true, since the calculations of quantum mechanics are so hard that only the simplest cases can be worked out. The reason that there is a problem with how quantum mechanics leads to the classical world is that the calculations cannot be done.

Nor with string theory, QFT, EM or even Classical mechanics. We must have perturbative theories simply because there are too any variables. But then we're sacrificing not only accuracy, but understanding. See ZapperZ's reply to my original post, LOL. (We shouldn't just pick on QM for this.)

P.S. If you are not familiar with my tag line - "the map is not the territory" (Korzybski) - consider this: all theories are maps, and no map is ever the territory itself. All maps are always useful representations of the territory. All theories are useful models of reality. But no theory is explaining reality itself - always a subset of reality. Example: Do you believe the sun heats the Earth? If so, why does it heat the Earth? Why is there a sun? Why does it emit heat? Where does the heat come from? Why is there fusion? Why do neutrinos come out of the sun? No matter what theory you put forth, a criticism can be made that it is incomplete because it describes and does not explain. I don't see the point of stating the obvious: there is still more for us to learn.

No one thinks our understanding of QM has reached an endpoint. That is NOT a conclusion I would draw from Aspect. But the bar has been raised for competing theories.
That was worth repeating from Dr Chinese.

vanesch

Aug18-04, 07:52 AM

ZapperZ

Aug18-04, 08:00 AM

Actually I think the real problem with quantum mechanics is that people keep saying how good it is at making predictions of how the world behaves. Its just not true, since the calculations of quantum mechanics are so hard that only the simplest cases can be worked out. The reason that there is a problem with how quantum mechanics leads to the classical world is that the calculations cannot be done. That is why everyone spends so much time philosophising about it.

And I think you have missed the whole point of QM. Our world deals with many particles making a gazillion interactions over long periods of time (using a time scale of a period of Cs atom, for example). While the outcome of ONE single measurement is unpredictable under QM, the outcome of a gazillion measurement is uncannily accurate as predicted by QM. It is why your modern electronics work! Everything that was built using the foundation of QM (refer to solid state physics) deal with LARGE amount of particles and interactions. A whole subfield called condensed matter physics came into existence just to handle such a thing. And it is built with QM as the foundation!

I have mentioned this before in another string, but obviously, it needs to be repeated here. Just because one has a complex system without any analytical solution, doesn't mean one doesn't know about that system. This applies to ALL of physics, not just QM. For example, the 3-body system, in the most general form, has no closed analytic solution. I can write down the differential equation to take into account ALL the interations and dynamics of the system, but I'd be damned if anyone can solve for the most general solution to that differential equation. Want another example? A flat disk with a uniform charge density. In intro physics, you can solve for the E-field along the axis of symmetry of this configuration without batting an eye. But try solving it everywhere! Just going slightly off the axis of symmetry will cause you to end up with an infinite series expansion, no analytical solution! You have to truncate the solution (i.e. make approximation) if you want to use it.

In the above examples, does that mean both classical mechanics and classical E&M have problems?

The "approximations" we make when dealing with QM has nothing to do with its accuracy. If it does, our predictions would be way off in the MAJORITY of the phenomena that we are describing since our everyday world almost never involve just ONE particle or ONE interaction. Phenomena such as superconductivity, magnetism, quantum hall effect, etc, are all many-body phenomena which requires a gazillion interactions. The fact that we have theoretical descriptions for all those phenomena should never be trivialized. In fact, it should be awed that we can even find such descriptions, considering how complex and dauting the amount of interactions that are involved. Statistical mechanics and many-body physics isn't about "approximations", it is about the science of dealing beyond N-body physics. It is why, for example, Landau's Fermi Liquid theory is so powerful and became the fundamental description of the properties of conventional metals and semiconductors - the very same materials that you use in your modern electronics.

Since I'm repeating myself like a broken record, I will say this again: the most CONVINCING evidence that QM is valid does not come from some estoreric experiments in particle physics or nuclear physics or even EPR-type measurements. The most convincing evidence come from experiments on the properties and behavior of materials (condensed matter physics)! This is because such experiments are easily controlled, easily manipulated, and easily reproducible! It is why the values of two fundamental constants - h and e - are obtained from condensed matter experiments. These are the experiments that gave the values of h and e with the highest accuracy and highest reproducibility. Considering that these are "many-body systems", if all QM can do is make "approximations" here, there's no way we can arrive as such consistent conclusions.

Zz.

vanesch

Aug18-04, 08:02 AM

Maestro, you're not alone in finding QM "hard to swallow". QM is hard to accept. Most people who study QM seem to come to a point where they simply admit they can't wrap their brains around it. And I think the theorists have completely given up, except, of course, for the metaphysical nutjobs.

QM is certainly counter intuitive, and there are still open questions left. To me, the most important one is the measurement problem. But the difficulties in QM lead to an understanding of the difficulties in classical mechanics. Do you find that Newton's gravity *explains* things ? Can you say *why* one has to divide the other mass by the distance squared, and this somehow equals the second derivative of the position ?

cheers,
Patrick.

ZapperZ

Aug18-04, 08:18 AM

QM is certainly counter intuitive, and there are still open questions left. To me, the most important one is the measurement problem. But the difficulties in QM lead to an understanding of the difficulties in classical mechanics. Do you find that Newton's gravity *explains* things ? Can you say *why* one has to divide the other mass by the distance squared, and this somehow equals the second derivative of the position ?

cheers,
Patrick.

I can even add to that one. Classical theories are full of "fields". No explanation on what it is, it's just...... THERE! It explains ZERO mechanism on the type of interactions that a charged particle experience in such a field. All it says is "if you put q there in a field of V, then you get so and so....".

People don't find this "mysterious" because we deal with such things often. It is a "common" concept. They don't realize that these too are full of holes. Yet, this is nothing better nor worse than the same method done in QM.

I always tell people that you are NOT born with your current intuition. Your intuition is based on your accumulated knowledge. If you haven't stuidied QM, OF COURSE you find it intuitively difficult. But try doing a number of experiments. Try looking closely at what it is that you are measuring when you try to determine the position of something - what did you take for granted in doing that? You will soon realize that classical physics is more of a facade, the very same way that people think the sky is the blue ceiling when they look up on a clear, sunny day.

I can bring out many examples of simple, everyday observations in which, if I were to describe to you, are not "intuitively" obvious. It is only after I explain to you why such things happen will it become "intuitively obvious". Thus, your intuition changes with knowledge! What you found difficult to accept before, now becomes clearly obvious.

Zz.

Nereid

Aug18-04, 08:27 AM

Don't tell them in all gory detail :rofl:

cheers,
Patrick.Well, at least I didn't start to tell the neutrino story, or tectonic plates, or snowball Earth, or the distance scale of the universe, ... :wink:

In the sense of having a relatively smooth path from theory to good experimental consistency and validation, QM had an easy ride.

Perhaps I should start a thread called 'unfinished symphonies'?

ZapperZ

Aug18-04, 08:36 AM

In the sense of having a relatively smooth path from theory to good experimental consistency and validation, QM had an easy ride.

I'm not so sure about that. Like any new and revolutionary theory, QM had many obstacles to over come, as should anything new. The founding fathers certainly didn't get honored for their work till quite late. See

http://physicsweb.org/article/world/15/8/7/1

Zz.

Nereid

Aug18-04, 09:28 AM

DrChinese

Aug18-04, 09:44 AM

My rule of thumb is it takes at least a decade for something new to get sufficient experimental and theoretical oomph (a point I keep emphasising re dark energy (and other areas in astrophysics and cosmology);

A decade seems about right to me too. Funny that for all the old stuff (SR, QM), a decade is just a blip. For new theory (dark energy, currently inflating universe, or whatever), a decade seems like an eternity and the progress appears negligible.

But it won't in retrospect. Why, even Aspect is old hat now! That was over 2 decades ago...

vanesch

Aug18-04, 10:03 AM

Can we agree that in real science Patrick's summary is perhaps just a tad too high level?

Sure, I was cutting corners !
But I had the idea, maybe wrongly, that Maestro claimed that the predictions of Newton were correct, and that Einstein, just for the sake of it, changed everything to relativity in order to provide deeper understanding , and not for the sake of better experimental succes. I guess he is thinking that both make the same predictions.

And if you want to talk about real, real science, there's a lot of sociological considerations too ! (these were the "gory details" I was referring to).

cheers,
Ptrick.

ZapperZ

Aug18-04, 10:04 AM

To be sure Zapper, new stuff is always a struggle, and something as radical as QM certainly had its challenges! My rule of thumb is it takes at least a decade for something new to get sufficient experimental and theoretical oomph (a point I keep emphasising re dark energy (and other areas in astrophysics and cosmology); to my taste far too many people are rushing off to their PR departments with marketing fluff that glosses over the decade or more of work that has to be done yet before anything halfway decent can be established).

My rule of thumb has been that theory needs a longer "gestation" period than experimental observation. It takes a theory at LEAST 10 years (on par with your decade) of continuous testing and prodding for it to be widely accepted to be valid. This of course, assumes that the theory makes testable predictions, which totally disqualifies String, Superstring, M-Theory. Experimental observations, on the other hand, only require that another independent group reporting a consistent observation. Thus, monumentous discovery such as the high-Tc superconductor, only required a 1-year period between discovery and complete chaos! :)

And I totally agree with you about people rushing to publicize their work, even way before those things appear in a peer-review journal. One would think we would all have learned a lesson from the Fleishmann-Pons debacle.

QM had lots of experimental validation, fairly quickly (measured on timescales of decades), and from many different directions; to be sure many aspects had to wait many decades for experiments to shed light on the theory (so to speak) - e.g. Aspect.

Can we agree that in real science Patrick's summary is perhaps just a tad too high level?

I think both situations are valid, and there are enough examples in each. I can also bring in other types of situations where there are only qualitative, not quantitative, agreements in the beginning. So the path towards acceptance can be many (much like all the possible paths in a Feyman path integral). In the end, a large collection of experimental results are the only means to filter out what theoretical description is valid.

This last point is what I think a lot of people outside of physics do not fully appreciate. A single theory does not make a single, or even a small number of predictions. The BCS theory of superconductivity, for example, make a whole slew of predictions/consequences, ranging from the energy gap in the density of states (tested via tunneling experiments), superfluid density (from optical conductivity experiments), Meissner effect (via magnetic susceptibility measurement), etc, etc... A good theory must be consistent with A LOT of results from various kinds of experiments. This is because physics is inter-related - it isn't just a set of disjointed, unconnected collection of information. You can't pull something out in one corner and not expect something else in a totally different area to be affected. So when people claim to have some wild "theory" of something, they seem to forget about a slew of experimental observations that they need to be consistent with.

With this in mind, there is one impressive fact that can never be overemphasized. Considering the unbelievably huge area of application and testability of QM, ranging from particle physics to atomic/nuclear physics, to the very material we all use everyday, there hasn't been even ONE experimental evidence that is inconsistent with QM! ZILCH! I mean, think about it! If this isn't astounding to you, then you haven't learned enough physics. It is not without any weight that during the centenial celebration of QM in 1999, physicists almost unanimously declared that QM is the most successful physical theory so far in the history of human civilization.

Zz.

ZapperZ

Aug18-04, 10:11 AM

And if you want to talk about real, real science, there's a lot of sociological considerations too ! (these were the "gory details" I was referring to).

cheers,
Ptrick.

Of course there are, but only with respect to what areas to pursue and how easy (or difficult) it is to pursue them. Sociological considerations have no bearings on the validity of physics ideas, at least not for long. So this is in contradictions to the post-modernists claim that all of science and scientific ideas are social constructions. No matter how much money is poured into something, or how much social and political pressure there is to accept something, if something is invalid, it remains invalid.

Zz.

Ontoplankton

Aug18-04, 10:24 AM

Speaking of broken records, there exists a fully local, deterministic, and in a sense realistic interpretation of QM that everyone agrees is compatible with Aspect's results (http://www.anthropic-principle.com/preprints/manyworlds.html). Learning of it may reduce your desire to reject quantum mechanics itself (which you shouldn't do; it works perfectly well).

And speaking of sociological considerations, I'm beginning to wonder if there isn't some sort of cognitive dissonance effect at work: if it turns out QM makes good sense after all, then all those six impossible things people forced themselves to believe before breakfast were needless effort. ;)

vanesch

Aug18-04, 10:58 AM

So this is in contradictions to the post-modernists claim that all of science and scientific ideas are social constructions.

Sure, didn't want to indicate this at all, I also have a post-modernist for breakfast each morning :-) I was more thinking of new ideas being favored by big boys to emerge easier than those being not liked. But it is just a matter of, well, a generation at most. A concrete example is probably Chandrasekar and his black hole formation.

cheers,
Patrick.

vanesch

Aug18-04, 11:54 AM

Speaking of broken records, there exists a fully local, deterministic, and in a sense realistic interpretation of QM that everyone agrees is compatible with Aspect's results (http://www.anthropic-principle.com/preprints/manyworlds.html). Learning of it may reduce your desire to reject quantum mechanics itself (which you shouldn't do; it works perfectly well).

Care to discuss a bit Many-worlds ? I know about it, but not in all the details, so questions remain.
I'll start a new thread for it.

cheers,
Patrick.

kurious

Aug19-04, 04:42 AM

I would like to see Aspect's experiment and other entanglement experiments done
in a much weaker gravitational field _perhaps deep inside the Earth or in space -
in order to see if gravity has any effect on the outcome.Physicists will say gravity has nothing to do with it but shouldn't this be tested experimentally.

metacristi

Aug19-04, 05:47 AM

kurious

Aug19-04, 06:19 AM

The enrgy associated with gravitational field is small compared to other fields like EM
but it takes little or no energy to change the polarization of a photon.

ZapperZ

Aug19-04, 06:39 AM

The problem regarding the sensibility of detectors ceased to be considered a serious problem though some doubts still remain.It's interesting to note however that there are other objections which are principially unsolvable,based only on empirical evidence.

The first is that in interpreting the results of Aspect's experiment we have to reside on logic,namely on modus tollens.From the empirical observation that Bell's inequalities are violated we deduce that one of the premises is false.In this case we have two main choices:either deny the principle of realism altoghether (by denying the existence of hidden variables altoghether,meaning also intrinsic indeterminism) as copenhagenists do or deny only the principle of locality (this is the minimal case).There is however another possibility namely denying that logic is a valid way of reasoning about natural facts,in this case at least!Of course there is no good reason to think that the traditional hypothetico-deductive method does not work here (it had a tremendous success before) so no scientist will be too much bothered by this problem.Still this let the door open to skepticism,basically there is no way to refute it in a clear way.We have the right however to prefer rationally the stance that modus tollens is a valid way of reasoning,there are more logical reasons supporting it.

The second,much more serious one,is that Bell's assumes,intrinsically,in the premises the principle of free choice,namely that experiencers have free will,the measuring angles are free variables.As even Bell recognize '...if our measurements are not independently variable as we supposed...even if chosen by apparently free-willed physicists... then Einstein local causality can survive...apparently separate parts of the world become deeply entangled, and our apparent free will is entangled with them.'Thus the meaning of Bell's inequalities violation is not so clear cut in spite of the fact that majority of scientists prefer to consider Aspect's experiment as ruling out at least the principle of locality.

Let's be clear on one thing here: if we have a photon detector with 100% efficiency, we won't be having most these kinds of questions anymore. A lot of issues surrounding the possible loopholes surrounding the interpretations of EPR-type of experiments hinges on the ability to detect the coincidences at both detectors.

Secondly, we seem to be ignoring a stricter, and clearer variation of Bell's theorem. I am pretty sure that the CHSH scheme has address some, if not all, of the issues you have brought up.[1] Practically all of the latter-day EPR-type experiments test for violation of the CHSH scheme. However, at some point, this becomes a question of semantics, and what we mean exactly by "local realism" and "non-local hidden variables", etc. I think that may belong in a separate string by itself (not that we haven't had several already during the previous months).

Zz.

[1] J.F. Clauser et al., Phys. Rev. Lett. v.23, p.880 (1969).

ZapperZ

Aug19-04, 07:35 AM

DrChinese

Aug19-04, 11:33 AM

1. The first is that in interpreting the results of Aspect's experiment we have to reside on logic,namely on modus tollens.From the empirical observation that Bell's inequalities are violated we deduce that one of the premises is false.In this case we have two main choices:either deny the principle of realism altoghether (by denying the existence of hidden variables altoghether,meaning also intrinsic indeterminism) as copenhagenists do or deny only the principle of locality (this is the minimal case).There is however another possibility namely denying that logic is a valid way of reasoning about natural facts,in this case at least!Of course there is no good reason to think that the traditional hypothetico-deductive method does not work here (it had a tremendous success before) so no scientist will be too much bothered by this problem.Still this let the door open to skepticism,basically there is no way to refute it in a clear way.We have the right however to prefer rationally the stance that modus tollens is a valid way of reasoning,there are more logical reasons supporting it.

2. The second,much more serious one,is that Bell's assumes,intrinsically,in the premises the principle of free choice,namely that experiencers have free will,the measuring angles are free variables.As even Bell recognize '...if our measurements are not independently variable as we supposed...even if chosen by apparently free-willed physicists... then Einstein local causality can survive...apparently separate parts of the world become deeply entangled, and our apparent free will is entangled with them.'Thus the meaning of Bell's inequalities violation is not so clear cut in spite of the fact that majority of scientists prefer to consider Aspect's experiment as ruling out at least the principle of locality.

Semantics does figure into the equation here. Accepting Aspect (as I do) implies that either reality or locality must be rejected. Tying to your comments:

1. Reality rejected: I think it would be reasonable to conclude that reality is rejected if logic does not hold. That is certainly in the flavor of what EPR was getting at. Although later writers have tried to split hairs over the words, EPR had simpler roots. I do not think the authors of EPR would have taken refuge in criticisms of EPR experiments by raising the "fair sampling" criticism or by stating that logic might not hold true at the quantum level (even though they could acknowledge such possibility).

2. There is more than one way to violate locality. Exceeding c is not the only way. Another route is that the future can affect the past. c could still be respected and locality violated because the time for a cause/effect to traverse a distance is in effect negative from the reference of an observer moving forward in time, which seems to be faster than c. In such a scenario, the "free choice" you describe is not truly "after the fact" in all reference frames. I would call this a violation of locality, but some might not see it that way.

The Bell Theorem is plenty strong, and certainly accomplishes primary objective #1: to limit competing theories to QM. It sets a major hurdle, although it does not eliminate all future competitors. If anyone proposes a classical local realistic theory, you know without further consideration it is wrong and will not be useful.

metacristi

Aug19-04, 03:09 PM

Let's be clear on one thing here: if we have a photon detector with 100% efficiency, we won't be having most these kinds of questions anymore. A lot of issues surrounding the possible loopholes surrounding the interpretations of EPR-type of experiments hinges on the ability to detect the coincidences at both detectors.

Secondly, we seem to be ignoring a stricter, and clearer variation of Bell's theorem. I am pretty sure that the CHSH scheme has address some, if not all, of the issues you have brought up.[1] Practically all of the latter-day EPR-type experiments test for violation of the CHSH scheme. However, at some point, this becomes a question of semantics, and what we mean exactly by "local realism" and "non-local hidden variables", etc. I think that may belong in a separate string by itself (not that we haven't had several already during the previous months).

Zz.

[1] J.F. Clauser et al., Phys. Rev. Lett. v.23, p.880 (1969).

We haven't escaped of all problems yet,even using observables other than spin.As far as I know the last such experiment,using ions,is not considered as compeling because they were not enough separated in space.So mere skepticism is still rational.Anyway since establishing a standard of knowledge (openly accepted as fallible) does not involve absolute truth I consider the current evidence as representing a sufficient reason to support the rejection of local hidden variables.If some compelling data against will ever appear,way beyond a mere skepticism,counting as sufficient reasons,science will (re)accept the principle of locality.However this does not mean we are deceived now in accepting provisionally the rejection of locality as knowledge.

As regarding the validity of modus ponens,well the problem is much more complicated.We have no proof that logic should apply with necessity to natural facts,even if a conclusion were unique and unavoidable logically,deduced from true premises.Likewise with the modus tollens when applied in this case (the premises are fallible).Even if we had 100% empirical certainty that Bell's inequalities are violated (more generally all such types of equalities,even those involving single detection) we still need to assume the validity of the modus tollens scheme as applying to nature in order to accept that one of the premises is false.For example some might argue that logic does not apply here to nature,that is even if we are compelled to think (as logic indicates) that one premise is false this does not mean also that ontologically this must be the case.Basically there is no way to avoid this on empirical grounds entirely but,as I've pointed before,we have enough reasons to prefer that logic is a valid 'tool' even here.

metacristi

Aug19-04, 03:27 PM

Semantics does figure into the equation here. Accepting Aspect (as I do) implies that either reality or locality must be rejected. Tying to your comments:

1. Reality rejected: I think it would be reasonable to conclude that reality is rejected if logic does not hold. That is certainly in the flavor of what EPR was getting at. Although later writers have tried to split hairs over the words, EPR had simpler roots. I do not think the authors of EPR would have taken refuge in criticisms of EPR experiments by raising the "fair sampling" criticism or by stating that logic might not hold true at the quantum level (even though they could acknowledge such possibility).

2. There is more than one way to violate locality. Exceeding c is not the only way. Another route is that the future can affect the past. c could still be respected and locality violated because the time for a cause/effect to traverse a distance is in effect negative from the reference of an observer moving forward in time, which seems to be faster than c. In such a scenario, the "free choice" you describe is not truly "after the fact" in all reference frames. I would call this a violation of locality, but some might not see it that way.

The Bell Theorem is plenty strong, and certainly accomplishes primary objective #1: to limit competing theories to QM. It sets a major hurdle, although it does not eliminate all future competitors. If anyone proposes a classical local realistic theory, you know without further consideration it is wrong and will not be useful.

Well certainly the Bell's theorem is strong,there is enough evidence for this but skpeticism (without any 'positive' claims) is still rational.Interesting the points you made at 2.I still have to think at all the implications of future affecting the past to the 'free will' assumption (had you in mind the transactional interpretation?) considered by many one of the strongest objection to the rejection of locality (at least).In all case this objection is enough strong to cool down those who claim that we [have] almost certitudes (if not certitudes) that local hidden variables theories are impossible.

Nereid

Aug19-04, 03:32 PM

We haven't escaped of problems yet,even using observables other than spin.As far as I know the last such experiment,using ions,is not considered as compeling because they were not enough separated in space.So mere skepticism is still rational.Anyway since establishing a standard of knowledge (openly accepted as fallible) does not involve absolute truth I consider the current evidence as representing a sufficient reason to support the rejection of local hidden variables.If some compelling data against will ever appear,way beyond a mere skepticism,counting as sufficient reasons,science will (re)accept the principle of locality.However this does not mean we are deceived now in accepting provisionally the rejection of locality as knowledge.

As regarding the validity of modus ponens,well the problem is much more complicated.We have no proof that logic should apply with necessity to natural facts,even if a conclusion were unique and unavoidable logically,deduced from true premises.Likewise with the modus tollens when applied in this case (the premises are fallible).Even if we had 100% empirical certainty that Bell's inequalities are violated (more generally all such types of equalities,even those involving single detection) we still need to assume the validity of the modus tollens scheme as applying to nature in order to accept that one of the premises is false.For example some might argue that logic does not apply here to nature,that is even if we are compelled to think (as logic indicates) that one premise is false this does not mean also that ontologically this must be the case.Basically there is no way to avoid this on empirical grounds entirely but,as I've pointed before,we have enough reasons to prefer that logic is a valid 'tool' even here.One small (:wink:) challenge with re-evaluating logic is the need to construct descriptions/explanations/(whatever they would be called in the 'new logic') for everything that has been shown to be consistent with the current theories (QM, GR, etc). If there were some 'smooth transition at the limit', so outside its main domain of applicability, the new logic worked just like that embedded in QM etc, it may not be so challenging. However, just my personal guess, any 'new logic' would require pretty much a complete re-write of all of physics ... not a job for the faint-hearted! :smile:

metacristi

Aug20-04, 03:47 AM

One small (:wink:) challenge with re-evaluating logic is the need to construct descriptions/explanations/(whatever they would be called in the 'new logic') for everything that has been shown to be consistent with the current theories (QM, GR, etc). If there were some 'smooth transition at the limit', so outside its main domain of applicability, the new logic worked just like that embedded in QM etc, it may not be so challenging. However, just my personal guess, any 'new logic' would require pretty much a complete re-write of all of physics ... not a job for the faint-hearted! :smile:

I tend to agree with you,especially that the new logics would require a broad rethinking of all physics.Anyway,from what I've read,physicists and philosophers of science reduced substantially their initial interest in devising quantum logic(s).Omnes for example say something about the efforts of von Neuman in this direction (some axioms of classical logic are dropped) but underlie further that formal logic is enough for the interpretation of the standard formalism of QM.

vanesch

Aug20-04, 06:56 AM

I tend to agree with you,especially that the new logics would require a broad rethinking of all physics

And all of mathematics ! That's a bigger problem, because then the toolbox for physicists is empty ! You wouldn't even have integers !

cheers,
Patrick.

metacristi

Aug20-04, 11:52 AM

The idea with devising quantum logics appeared as a consequence of the implications of the Copenhagen interpretation of QM.Some logic formulas,valid under formal logic,seemed to be violated when applied to the quantum world so it seemed that we need a new,non boolean logic.Probably from here stemed (also) the Putnam-Quine thesis that mathematics and logic can be revised in the light of new empirical evidence.

The problem with this approach is that it is presupposed too much in the premises,namely the validity only of copenhagen interpretation.Or,it is well known,both 'weak' interpretation of Heisenberg's uncertainty principle and the 'pilot-wave' hypothesis are [also] equally valid,on empirical grounds,thus interpreting observed facts (namely the two slits experiment and so on) do not really require devising new logics with necessity.Anyway today it is much more widespread the approach,even amongst copenhagenists,that we do not need a new quantum logic,algebraic systems are enough to formulate quantum mechanics.From what I've read Omnes is in line with this by requiring that the axioms of any quantum logic be consistent with those of formal logic.

Finally it is interesting to note here that even Quine renounced later at his own thesis by arguing that quantum logics are not replacements of formal logic.

Nereid

Aug20-04, 12:41 PM

danitaber

Aug20-04, 12:42 PM

hi. I posted a new thread about this physics logic thing. sounds interesting. I would like to learn more.

meteor

Aug24-04, 12:07 PM

You DO know that EPR-type experiments have progressed SIGNIFICANTLY beyond the Aspect experiment, and that more accurate tests by Zeilinger & Co. have produced even more accurate confirmation of QM, don't you?

Wineland also violated Bell's inequality. The experiment was reported in an issue of Nature in 2001
Here's the paper, but requires subscription
"Experimental violation of a Bell's inequality with efficient detection"

http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v409/n6822/abs/409791a0_fs.html

DrChinese

Aug24-04, 02:42 PM

Just in time for all the fun and excitement, Travis Norsen posted a paper titled "EPR and Bell Locality" on arXiv appearing today (well, late yesterday evening, to be precise). Have a look at it. At the very least, you will have a good set of references from it.

http://arxiv.org/abs/quant-ph/0408105

Zz.

I have looked over this paper. I think the conclusion is very controversial - that EPR and Bell combine to "prove" that it is the locality condition which must be sacrificed. In fact, I think the author's conclusion is wrong. Has anyone else looked at this in detail?

Specifically, he draws his conclusion (28) from EPR (26) and Bell (27) and I think this was unjustified for several reasons. First, it requires use of boolean logic which may or may not hold. I think I can demonstrate this error in logic.

In addition, his (27) is not a fair synopsis of the Bell formalism. He says that according to Bell: If quantum mechanics is incomplete, then it must be non-local. I think a more accurate formulation is (according to Bell): Any hidden variable theory which agrees with QM must be non-local. To me, those statements are far from equivalent. Comments?

kurious

Aug24-04, 03:24 PM

DrChinese

Aug24-04, 03:46 PM

DR Chinese:
In addition, his (27) is not a fair synopsis of the Bell formalism. He says that according to Bell: If quantum mechanics is incomplete, then it must be non-local. I think a more accurate formulation is (according to Bell): Any hidden variable theory which agrees with QM must be non-local. To me, those statements are far from equivalent. Comments?

Kurious:

Why are hidden variables non-local?

Because Bell's Theorem rules out local hidden variable theories (if the predictions of QM are correct, as they appear to be per Aspect). The "standard" interpretation of this is that either a) locality is violated in nature; or b) there are no hidden variables. Norsen's paper says it is a) specifically.

kurious

Aug24-04, 05:10 PM

Can a signal that travels faster than light in principle explain instantaneous action at a distance.It takes little or no energy to change the polarization of a photon so a signal
would not need much energy and would be hard to detect.When a photon interacts with a detector or polarizer it must transfer some momentum to the detector or polarizer and cause them to accelerate slightly.Electric charges would give off electromagnetic radiation if they were accelerated but is there equivalent gravitational radiation
when a mass such as a detector or polarizer is accelerated?If so, this could be a communicating signal between photons in Aspect's experiment.I know nobody can prove something can travel faster than light, but in principle wouild that be helpful to restoring causality?

selfAdjoint

Aug24-04, 06:49 PM

metacristi

Aug25-04, 06:50 AM

The standard formalism of QM does not give an explanation for quantum entanglement,the interpretations do,via the ontologies proposed.Unfortunately as of now there is no satisfactory answer,[quantum entanglement]is,still,quite a mistery.We have the following options:

1.The observed statistical correlations are 'nonclassical' not 'nonlocal',the wavefunction is only a mathematical tool (the point of view of Bohr and Heisenberg),'c' (the speed of light which may vary,slowly,in time) is the maximum,so that there are no instant connections.This is the main view today among copenhagenists,trying to retain full coherence with SR (it's about the requirement of no preferred frame of reference-NOT about the alleged superluminal transmissions involved,as I've argued before this is a red herring,at least in the case of hidden variables interpretation).The drawback is that it offers no real explanation for the observed correlations (see for example Bohr's answer to EPR paradox,not satisfactory).Everett's many worlds interpretation also qualify here for it does not require nonlocality,c being also a limit (here the assumption of counterfactual definiteness is rejected-this amounts to retaining locality and reality but with the expense of basically rejecting free will).

2.There exist nonlocality,the wavefunction is real,stretched in space,so that the entangled particles still form a single system (superposition of states) even when far apart,allowing instant connections,the 'collapse' of the wavefunction is responsible for the complementary values of spin measured.Thus nature is 'wired' by allowing instant connections but we cannot use this link to send information superluminally.This view is held by a minority of copenhagenists.

3.Superluminal connections exist,nature is somehow 'wired',possible outside our spacetime,though we cannot use those connection to send information superluminally (see Bohm's interpretation of quantum potential,though,strictly speaking,it is rather a philosophical attempt,not part of the interpretation itself).There exist non local hidden variables (it is widely accepted that Aspect's experiment rule out only the premise of locality) or advanced and retarded waves (as implied by the transactional interpretation of QM).In Bohm's interpretation the quantum potential (an effect of a subquantum unified domain) is responsible for the connection at distance observed,causality is retained.

ZOverLord

Dec18-04, 04:06 AM

Doc Al

Dec18-04, 06:10 AM

Here is one interesting solution to particle/wave seperation.

The Theory of Elementary Waves (http://www.yankee.us.com/TEW/TEW96paper.html)
Unfortunately, Lewis Little's "Theory of Elementary Waves", being a local "hidden variable" theory, is unable to explain the double-delayed choice experiments. (That's just one problem with it.)

ZapperZ

Dec18-04, 07:12 AM

Much as in the past Electron flow was thought to flow negative to positive as well as even how lightning begins. Current QM seems to not assume possible reverse flows.

The concept of tracers preceding the actual return bolt of lightning as well as that electrons now have been proven to flow NOT from negative to positive but in fact from positive to negative make it probable at least that maybe waves ALWAYS are present in reverse flow when involved in the standard double-slit experiment behavior of particles/waves.

What nonsense is this? What does this have anything to do with QM? If electrons flow from positive to negative potential, it is CLASSICAL E&M that is in trouble! But then again, you would have known this had you had any formal lessons in E&M.

This would also show how Aspect's experiment had a shortcoming, but which nonetheless does not conflict with Bell's theorem.

Why are people still obsessed with the Aspect experiment done in the early 70's? Have these people been asleep since then and completely overlook a whole zoo of experiments since then that have improved upon that experiment by orders of magnitude, and with different scenarios?

There's nothing worse than a quack, but a quack with out-of-date information.

Zz.

jtbell

Dec18-04, 08:15 AM

Why are people still obsessed with the Aspect experiment done in the early 70's? Have these people been asleep since then and completely overlook a whole zoo of experiments since then that have improved upon that experiment by orders of magnitude, and with different scenarios?

Probably the same reason why some people are obsessed with the Michelson-Morley experiment (1880s), or the Hafele-Keating experiment (1970s). :frown:

Nereid

Dec18-04, 09:46 AM

So, if we apply Zapper's suggested criterion for distinguishing pottery magic (thank you Chronos) from maverick capers (thank you Garth) - i.e. publication in (physics) peer-reviewed journal - would Little's idea stay here, or should it be moved to TD? The link which ZOverLord gave us (and Welcome to Physics Forums ZOverLord!) mentions 'Accepted for publication in Physics Essays' - was it published? Is Physics Essays a peer-reviewed journal?

Doc Al

Dec18-04, 11:28 AM

So, if we apply Zapper's suggested criterion for distinguishing pottery magic (thank you Chronos) from maverick capers (thank you Garth) - i.e. publication in (physics) peer-reviewed journal - would Little's idea stay here, or should it be moved to TD?
Any further discussion of Little's work should probably be moved to TD.

The link which ZOverLord gave us (and Welcome to Physics Forums ZOverLord!) mentions 'Accepted for publication in Physics Essays' - was it published? Is Physics Essays a peer-reviewed journal?
I think it was published in Physics Essays. A glance at the table of contents of past issues would suggest that their peer review policy is quite liberal. :bugeye:
"Articles submitted for publication will be reviewed by scientific peers. Realizing the interchangeable roles of authors and reviewers, the positive aspect of the reviewing process will be retained by providing the authors with the reviewers' comments. Authors should judge which part of the reviewers' suggestions are appropriate to improve the quality of his or her paper. The editor, who is responsible for the Journal, will allow a large degree of freedom to the authors in this process."
(From www.physicsessays.com.)

ZapperZ

Dec18-04, 02:37 PM

Take note that Physics Essays has a history of publishing "fringe" physics. I do not know of anyone who is a referee for this journal - or maybe they are too embarass to admit it. Either way, this doesn't bode very well for that journal.

It is also a journal that isn't easy to find. Most institutions do not subscribe to it, either electronically or hardcopy. This in itself should tell you how "important" it is.

Zz.

gptejms

Dec20-04, 05:38 AM

caribou

Dec20-04, 08:47 AM

Sure, but an FTL signal is nonlocal, that is it violates relativity. Quantum mechanics explains the experimental results without violating relativity, but you have to give up the notion that the particle "really" had a polarization before they were measured. Quantum mechanics says not; it says they were in a superposition of polarization states, which was neither one nor the other nor both, but rather something different made of the two possible states and already correlated at the time the particle pair was created.

Yes, this is how I understand what Gell-Mann calls "the modern interpretation of quantum mechanics" is supposed to work.

Also, in a short overview article Zurek wrote called "Decoherence and the Transition from the Quantum to the Classical", he says:

And the experiments that show that such nonseparable quantum correlations violate Bell’s inequalities (Bell 1964) are demonstrating the following key point: The states of the two spins in a system described by | Φc > are not just unknown, but rather they cannot exist before the “real” measurement (Aspect et al. 1981, 1982). We conclude that when a detector is quantum, a superposition of records exists and is a record of a superposition of outcomes—a very nonclassical state of affairs.

http://arxiv.org/abs/quant-ph/0306072

A superposition of records is an interesting conclusion! I think understanding what superpositions really mean is important in understanding EPR and the like. :smile:

ZapperZ

Dec20-04, 09:17 AM

A superposition of records is an interesting conclusion! I think understanding what superpositions really mean is important in understanding EPR and the like. :smile:

This is the VERY reason why one cannot just learn physics, and especially QM, in bits and pieces. You cannot understand why an EPR-type experiment differs from simple classical conservation of angular momentum if you do not understand quantum superposition/Schrodinger Cat-type experiments. There is an interconnectedness of QM that is essential as a single, coherent picture. It has always been the single most source of frustration (at least on my part) when someone picks on one aspect of QM but did not bother understanding all the connected ideas surrounding it.

You can't understand physics this way, and you certainly as hell cannot understand quantum mechanics this way.

Zz.

Gokul43201

Dec20-04, 10:05 AM

I haven't read through most of this thread, but it reminded me of the experiments done earlier this year, by Shahriar Afshar (sp?), on a slit apparatus, where he detected a photon without collapsing its wavefunction . Another experimenter later came up with a rebuttal, but I think his experiment was intrinsically different in the way he identified the path of the photon.

Haven't really followed up on this though, so does anyone know what the final word on this is ?

ZapperZ

Dec20-04, 11:12 AM

DrChinese

Dec20-04, 03:35 PM

To follow with the "non-classical" points mentioned by ZapperZ and others above...

Bell's Theorem has portions which relate to both locality and reality. Specifically, the likelihood of a correlation X in a "classical" world must be:

0 <= X <= 1

Every time you try to restore classical determinism - in any form - you still run into this point because the empirical evidence does not support the above constraint. In other words, it is not just that the angle between the polarizers determines the results of the experiment. It is "as if" the original photon polarity was exactly matched (or anti-matched) to one or the other of the polarizers, and no other polarizer angle setting.

You don't get these results from the "Theory of Elementary Waves" as I read it. He doesn't really discuss this point while trying to sell his interpretation. Moreover, it no more predicts the observed polarity than the man in the moon in specific cases. So where is his claimed local determinism anyway? (As an aside, Lewis Little also claims that General Relativity does not stem from the curvature of space-time.) Ultimately, this paper goes nowhere when it acknowledges Bell as correct but denies Aspect. This is just another paper doing that same job, and all fall victim to the same reality:

a) Aspect is repeatable;
b) The results are clearly in line with the predictions of QM;
c) The results are outside the predictions of classical locality;
d) The greater the precision of the experiment, the greater the disagreement between classical and quantum worlds.

Hans de Vries

Dec20-04, 03:41 PM

There are no "action on a distance terms" in the Standard Model
It would simply render the path integral mechanism useless by inter-
connecting all points in space-time.

We have to do with an QM interpretation issue here and there is
a certain element of denial of the QM laws which then leads to
these "action on distance" conclusions:

What QM says:

Position and Momentum are not defined arbitrary accurate simultaneously.
The spread in one is reversely proportional to the spread in the other.

What people often think: (the denial in my opinion)

Yes, but somehow the both must be still there accurately. And we've
got the freedom to decide which one we measure accurately. Only if
we measure one accurately then we can not measure the other one
accurately.

So, In this interpretation it becomes a measurement issue. And then
the problem arrises that the measurements do not only exclude each
other locally, but also at any distance.

Heisenberg's position/momentum and time/energy relations are best
handled as a property of the Fourier Transform. There are many
ordinary situations which are governed by the same rule: The spectrum
analyser on your audio set can not determine the audio spectrum in
an infinitesimal small amount of time. There's nothing mysterious here.

If momentum is defined by a Fourier component then Heisenberg's
law follows automatically. If taken literally then there's no way that
"somehow, both must be still there accurately"

If two particles obtain the same spread (during entanglement) in
their spin components, then the outcome of the experiments will
show the correlation we see in today's experiments without the
need for any action on a distance.

Each individual particle must be presumed to have a certain
spread in one physical quantity, and an opposed spread in the
other associated quantity.

The spread in, for instance, position is lost if a particle hits the
wall at an exact x,y position. This doesn't mean that the spread
was not there. It's wrong to say that we have chosen to
"measure the position exact" It could have hit the wall at another
nearby position.

The x,y measurement has an error from the average position and
only repeated measurements will reveal the size of the error and
the spread. There is no way that the experiment can reduce the
spread the particle had during flight. (at the expense of the
spread of the momentum).

Still, it's this interpretation, that we have chosen to measure the
position exact, that leads to the idea that "both quantities must
somehow still be there accurately" and "we can choose which of the
two we measure exact at the expense of the other"

Regards, Hans.

Gokul43201

Dec20-04, 05:14 PM

The damn thing still hasn't appeared in any peer-reviewed journal yet, in spite of all the advanced hype. :)

Zz.

What !! :eek: I looked around and couldn't find it anywhere, but thought I wasn't trying hard enough.

caribou

Dec20-04, 05:41 PM

You mean this?

http://www.irims.org/quant-ph/030503/

Hmmm... Afshar's experiment is a bit like the standard textbook two-slit experiment but with wires in the dark bands, then remove the screen and adding interferometer arms to keep the particle's superposition until a much later detection.

The "detection" of the interference pattern by not interacting with the wires involves... er... no interaction, so it doesn't sounds like a true violation of complementarity to me.

danim

Dec22-04, 01:15 PM

I would like to take a moment to remind everyone of the basic fact that Quantum Mechanics does not explain the world we live in, it just accurately describes it. It is much like an owner's manual or (and this is overused, but I'll use it again) a recipe. The point is, it works. The previous posts do a better job of explaining why and how, so I'll leave that to them.

Maybe I'm wrong but you can see QM is absolutely epistemological just looking at the math. One could think that once the answer you have from asking (measuring) one system (at the quantum level) means nothing. As the answer comes as an eigenvalue of this operator related to the measuring, you just have the same asking in a new form, because an eigenvalue may be pictured as a representation of the operator in the correspondent eigenspace. So you just have the same asking in a new form. But the whole system collapses to the corresponding eigenspace so it's not just a new form of the asking. Otherwise you coldn't have the eigenvalue as the desired answer, once the eigenvalue would not be a representation of the operator. You end this line by thinking that to measure is to shape the system in some eigenspace of the operator that corresponds to the variable you want. Trying to figure out the quantum mechanics is impossible if you take a realistic classical view. To measure is just like to ask somebody. The answer were not previously in his head, but comes as he starts to think about. Now the one has a personal position about the theme of the asking. Nocommuting operators is just like to ask the answer of a paradox. Simply the answers of the paradox are contraditory, what means are based on alternative grounds. It's like to have two operators that don't have the same eigenspaces. I think almost all of the weird things about quantum mechanics can be pictured if you try to use human minds os something like it to explain to the laymen.
I think the final conclusion is: You can't have a reductionist or materialist approach if you want to grasp the fundamental concepts of the contemporary physics.

thank you.

reilly

Dec23-04, 01:12 PM

I'm quite possibly repeating, but the number of experiments and bodies of knowledge supporting QM is legion: chemical bonding, molecular dynamics, theory of mattter -- solid state physics, superconductivity, superfluids, semiconductors; ATOMIC spectra, nuclear composition, the Lamb Shift, Casimir force, and on and on and on.Like it or not, QM will be around forever, modified ? Probably. Any change in the interprretation of QM will have a lot of explaining to do. There is an astonishing stability and solidity to QM, as it has been practiced. It's a great theory, maybe the best ever.
Regards,
Reilly Atkinson

Caroline Thompson

Jan6-05, 04:53 PM

... it is not just that the angle between the polarizers determines the results of the experiment. It is "as if" the original photon polarity was exactly matched (or anti-matched) to one or the other of the polarizers, and no other polarizer angle setting.

This would be true if the experiments really did behave as claimed, but doesn't the title of this thread imply that they don't? In any event, my own studies have confirmed that there are enough loopholes in all the actual experiments to allow for explanations using ordinary ideas about polarisation and the accepted way in which light, as an electromagnetic wave, interacts with polarisers.

You don't get these results from the "Theory of Elementary Waves" as I read it. He doesn't really discuss this point while trying to sell his interpretation. Moreover, it no more predicts the observed polarity than the man in the moon in specific cases. So where is his claimed local determinism anyway?

I agree that Lewis Little's ideas don't help, but why are you assuming that Aspect's experiments really did support quantum mechanics? I had hoped that you had realised that there were serious flaws.

a) Aspect is repeatable;
b) The results are clearly in line with the predictions of QM;
c) The results are outside the predictions of classical locality;
d) The greater the precision of the experiment, the greater the disagreement between classical and quantum worlds.

(a) is true and so, in a sense, is (b), though it might have been interesting to see more results using different settings for parameters such as beam intensities and detector efficiencies. (c), however, is not, since the results analysed were not the raw data but the data after subtraction of "accidentals". There is very good reason (as people in the field now agree) to think that this is not, in the context of Bell tests, a legitimate procedure. It can be shown (see http://arXiv.org/abs/quant-ph/9903066) that the raw results in Aspect's first experiment did not exceed the Bell limits. It is extremely likely that those of the third experiment did not do so either, but the data to check this is not available. The only experiment in which the subtraction played no significant part was the second, and this one, using 2-channel polarisers and the CHSH test, was subject to the "detection loophole". As my work (confirming that of Pearle in 1970) has shown, the use of this test and low efficiency detectors is not valid. See http://arXiv.org/abs/quant-ph/9611037 and other papers on my web site.

The net result is that none of Aspect's three experiments can be said to have truly violated Bell's inequality. None of the tests can be considered to be valid unless one accepts a number of assumptions that are, to a local realist, unacceptable.

I don't know on what grounds you claim (d). Knowing how the detection loophole works, something that does seem clear is that increased detector efficiency will increase the gap between the quantum theory prediction and reality! With 100% efficiency, no Bell inequality will (unless other loopholes are introduced!) be violated.

Caroline

DrChinese

Jan6-05, 05:44 PM

(a) is true and so, in a sense, is (b), though it might have been interesting to see more results using different settings for parameters such as beam intensities and detector efficiencies.

(c), however, is not, since the results analysed were not the raw data but the data after subtraction of "accidentals". There is very good reason (as people in the field now agree) to think that this is not, in the context of Bell tests, a legitimate procedure. It can be shown (see http://arXiv.org/abs/quant-ph/9903066) that the raw results in Aspect's first experiment did not exceed the Bell limits. It is extremely likely that those of the third experiment did not do so either, but the data to check this is not available. The only experiment in which the subtraction played no significant part was the second, and this one, using 2-channel polarisers and the CHSH test, was subject to the "detection loophole". As my work (confirming that of Pearle in 1970) has shown, the use of this test and low efficiency detectors is not valid. See http://arXiv.org/abs/quant-ph/9611037 and other papers on my web site.

The net result is that none of Aspect's three experiments can be said to have truly violated Bell's inequality. None of the tests can be considered to be valid unless one accepts a number of assumptions that are, to a local realist, unacceptable.

I don't know on what grounds you claim (d). Knowing how the detection loophole works, something that does seem clear is that increased detector efficiency will increase the gap between the quantum theory prediction and reality! With 100% efficiency, no Bell inequality will (unless other loopholes are introduced!) be violated.

Caroline

Hi Caroline!

a) & b) we are in sufficient agreement on.

c) The results of the experiments are clearly outside the predictions of local reality. That is why the Aspect experiment is important and why you look for loopholes. Your argument is that a closer look at the evidence might indicate that the raw material might somehow show a different story, if you were allowed to exclude some of the runs. But the papers stand, and as such, you really can't argue that evidence has not been presented.

d) With the recent Innsbruck experiments showing greater precision and showing greater disagreement with your predictions, you really have to ask yourself how the greater disagreement is occurring if you are right all along. In other words, a reasonable person would have a hard time justifying a contrary position as the margin of error gets smaller but the differences get bigger. If your position is valid, greater counting efficiency should return us to the zone in which there is no violation of the Bell Inequality. That clearly isn't happening. Funny: the bias you allege in the experiments just happens to take us to the QM predictions, even though there is no obvious connection.

I freely acknowledge that there are tacit assumptions in the Bell Tests. Perhaps this should have been e). These may turn out to be loopholes, maybe not.

In other words: you could be right about Bell test loopholes. Perhaps future evidence will indicate that fair sampling is not happening. Or that the accidentals make the difference. Further, it possible that once the hypothesized loopholes are plugged, local reality will emerge as a valid possibility again. But I think that my a) b) c) d) are a fair and accurate summary of where things are today, and you clearly have a big hurdle to overcome.

Caroline Thompson

Jan7-05, 04:08 AM

You DO know that EPR-type experiments have progressed SIGNIFICANTLY beyond the Aspect experiment, and that more accurate tests by Zeilinger & Co. have produced even more accurate confirmation of QM, don't you?

Yes, I most certainly do know about recent experiments. I also know that the search for truly valid one (euphamistically termed a "loophole-free" one) is continuing, and have just finished a paper based on:

R. García-Patrón Sánchez, J. Fiurácek , N. J. Cerf , J. Wenger , R. Tualle-Brouri , and Ph. Grangier, “Proposal for a Loophole-Free Bell Test Using Homodyne Detection”, Phys. Rev. Lett. 93, 130409 (2004)
http://arxiv.org/abs/quant-ph/0403191

This experiment (in marked contrast any other recent one) does really look at if it would be loophole-free. Unfortunately, though, the argument they use to suggest that the light is going to be "non-classical" has serious flaws. I can show that the symptom they are going to use as an indicator of non-classicality is a natural consequence of the way homodyne detection works. The experiment will not, therefore, settle the matter one way or the other, as both quantum theorists and local realists will agree (once they've understood my paper!) that the whole thing is classical. Neither side will be surprised to find that the Bell test is not violated.

I'll be posting the paper soon on my web site, when the experts concerned have had a chance to review it.

Caroline

Caroline Thompson

Jan7-05, 04:38 AM

Hi Caroline!

a) & b) we are in sufficient agreement on.

c) The results of the experiments are clearly outside the predictions of local reality.

[Correction: "The published results are clearly outside the predictions of local realism." But more of this later.]

That is why the Aspect experiment is important and why you look for loopholes. Your argument is that a closer look at the evidence might indicate that the raw material might somehow show a different story, if you were allowed to exclude some of the runs.

Hmmm ... But you've got this the wrong way around! It is Aspect who, by subtracting accidentals, is effectively trying to exclude some of the runs. As my paper (http://arXiv.org/abs/quant-ph/9903066) explains, the raw data available (from his first experiment, though the same applies logically to his third) was well within the region expected under local realism. The same can be said of the first experiment published by the Geneva group showing long-distance correlations. They did not analyse the raw data, which did not infringe the Bell inequality. In later papers they published both raw and adjusted results, in recognition of the fact that I was right: the adjustment was suspect.

As far as I know, no recent experiment has used adjusted data, but what they have done instead is use tests that rely on the fair sampling assumption.

d) With the recent Innsbruck experiments showing greater precision and showing greater disagreement with your predictions, you really have to ask yourself how the greater disagreement is occurring if you are right all along. In other words, a reasonable person would have a hard time justifying a contrary position as the margin of error gets smaller but the differences get bigger. If your position is valid, greater counting efficiency should return us to the zone in which there is no violation of the Bell Inequality. That clearly isn't happening. Funny: the bias you allege in the experiments just happens to take us to the QM predictions, even though there is no obvious connection.

Greater counting efficiency would help in some experiments, and, by counting something completely different but to which (if my analysis is correct) Bell's argument still applies, the latest proposed loophole-free tests (http://arxiv.org/abs/quant-ph/0403191 -- see other message) manages to achieve 100% efficiency in that every pair that is analysed produces a +1 or -1 result. They apply a "belt and braces" approach, having "event-ready" detectors as well as effectively 100% efficiency.

However, in most actual experiments there are other possible loopholes. How can you claim a "Bell test has been violated" when the assumptions on which that test is based are either clearly (in the view of realists) not valid or, at least, recognised as suspect?

In other words: you could be right about Bell test loopholes. Perhaps future evidence will indicate that fair sampling is not happening.

This is a matter of logic rather than the need for more experimental evidence, though the latter does come into the story. There are tests relating to "fairness" that could be done but are, in my opinion, either not being done at all or not being done appropriately. It is no use testing for constancy of the sample using only the angles used for the Bell tests, since everyone agrees that these are likely to be constant. They need to look at the total counts for the intermediate angles.

Or that the accidentals make the difference. Further, it possible that once the hypothesized loopholes are plugged, local reality will emerge as a valid possibility again. But I think that my a) b) c) d) are a fair and accurate summary of where things are today, and you clearly have a big hurdle to overcome.

OK! I've devoted over 10 years of my life to it so far and am prepared to continue until death or glory!

Caroline

caribou

Jan7-05, 07:00 AM

I think the viewpoint of Zurek and Omnes and quite possibly others like Gell-Mann and Hartle is that in EPR and similar experiments, there is a superposition of measurement outcomes in the measuring devices. This superposition then decoheres and one measurement result occurs. Or both occur if you like your many-worlds real. A lot like Schrodinger's Cat.

But that's really just my impression at the moment. :smile:

I'm wondering if a ideal von Neumann experiment could recreate a superposition in EPR and what this would mean. Something for me to think about, I guess.

vanesch

Jan7-05, 08:49 AM

I think the viewpoint of Zurek and Omnes and quite possibly others like Gell-Mann and Hartle is that in EPR and similar experiments, there is a superposition of measurement outcomes in the measuring devices. This superposition then decoheres and one measurement result occurs. Or both occur if you like your many-worlds real.

That's close to my opinion on the issue, in that the von Neumann measurement occurs when the final observation of correlation is executed (the transported distant "measurement results" remain in superposition). I've discussed this a few times here before some months ago...

cheers,
Patrick.

DrChinese

Jan7-05, 09:33 AM

OK! I've devoted over 10 years of my life to it so far and am prepared to continue until death or glory!

Caroline

Caroline,

I think what you are trying to do with the Bell tests is very noble, and certainly not a waste of your time. I don't always agree with your characterization of the state of the debate, though.

In medicine, experiments are routinely done on groups of people that are not randomly selected in the purest sense of the term "random". The question always arises, is it a fair sample? Because it is nearly impossible to get a true random sample, experimentalists do their best and are always looking to improve their sampling methods. Even without a true random sample, and without a rigorous proof theirs is a fair sample, the results are considered useful. It is still good science. That does not mean it can't be improved upon, and it does not mean some incorrect results may later be laid at the feet of a biased sample.

The same applies with the Bell tests. You can say all day long that the sample is biased, but you actually have shown nothing more that the results COULD POSSIBLY be biased enough to render an erroneous conclusion. But you really aren't showing any actual bias in the results.

OK, I think everyone recognizes this.

But the march of science in this area is moving away from your personal position of local realism - for which you lack even a shred of actual evidence of equal stature to the Aspect or Innsbruck tests. After all, if you are right, why do 100% of test results of local realism point AWAY from it? In other words, you cling to a position for which there are NO supporting tests and argue against a position for which there is at least SOME strong evidence. Who is really biased here?

I think your assessment of the state of Bell tests misses the mark by a wide margin, even though you make some valid points.

-DrC

Caroline Thompson

Jan7-05, 12:11 PM

Caroline,
In medicine, experiments are routinely done on groups of people that are not randomly selected in the purest sense of the term "random". The question always arises, is it a fair sample? Because it is nearly impossible to get a true random sample, experimentalists do their best and are always looking to improve their sampling methods. Even without a true random sample, and without a rigorous proof theirs is a fair sample, the results are considered useful. It is still good science. That does not mean it can't be improved upon, and it does not mean some incorrect results may later be laid at the feet of a biased sample.

Have you read my Chaotic Ball paper? A recent version can be found at http://arxiv.org/abs/quant-ph/0210150 .

We are not talking about the ordinary kind of sampling bias here, where the experimenter is free to choose his sampling method. The sample is effectively chosen for him, and, if something like the assumption I make in my model is anywhere near correct, it is always going to be biased and will inevitably cause an increase in the Bell test statistic. If the detection loophole is simply assumed away (as is the general practice) then this means that the interpretation is being biased in favour of quantum theory.

This is absurd! Until Aspect inaugurated use of the CHSH test in 1982, it was generally understood that this bias was unacceptable. Other versions of the Bell test were used. Though the experiments all had loopholes, this obvious source of bias was avoided.

But the march of science in this area is moving away from your personal position of local realism - for which you lack even a shred of actual evidence of equal stature to the Aspect or Innsbruck tests. After all, if you are right, why do 100% of test results of local realism point AWAY from it? In other words, you cling to a position for which there are NO supporting tests and argue against a position for which there is at least SOME strong evidence. Who is really biased here?

I think you know my answer! Agreed, there is no hard evidence for my case, other than all the phenomena we have ever encountered in other contexts. All our everyday experience tells us that everything is local and real. Quantum theorists seem to be like man in the middle ages, prepared to believe that something over which he does not yet have full experimental control must work by magic. There must be dragons out there, where he has not yet explored.

But to get back to reality, there could be supporting tests. For the past 10 years I have been trying to tell experimenters what needs to be done in order to prove that the loopholes really are there and that alternative local realist explanations really do exist.

Proving the detection loophole open is easy -- as could have been known since 1970. All you need do is repeat the experiment with different detector efficiencies and see whether the Bell test statistic increases, stays the same, or decreases as efficiency increases. Quantum theory predicts that it stays still. Local realism predicts that, other things being equal, it will decrease.

Testing for other loopholes is equally straightforward. The reason the tests have not been conducted is, I think, that most of the people who have contributed to the literature on the subject have been theorists. They have not felt qualified to comment on the experimental details. Most have never even heard of the "subtraction of accidentals" loophole, or stopped to think whether or not the system for deciding whether or not we have a "coincidence" might be introducing bias.

I think your assessment of the state of Bell tests misses the mark by a wide margin, even though you make some valid points.
Time will tell!

Incidentally, if you want to know just a little more on the experimental side, you could do worse than consult wikipedia. Last summer I contributed a few pages, the key one being http://en.wikipedia.org/wiki/Bell%27s_Theorem . From here links cover the main variations on the Bell test, actual experiments and, last but not least, the various loopholes.

Caroline

DrChinese

Jan7-05, 01:41 PM

1. We are not talking about the ordinary kind of sampling bias here, where the experimenter is free to choose his sampling method. The sample is effectively chosen for him, and, if something like the assumption I make in my model is anywhere near correct, it is always going to be biased and will inevitably cause an increase in the Bell test statistic. If the detection loophole is simply assumed away (as is the general practice) then this means that the interpretation is being biased in favour of quantum theory.

2. Incidentally, if you want to know just a little more on the experimental side, you could do worse than consult wikipedia. Last summer I contributed a few pages, the key one being http://en.wikipedia.org/wiki/Bell%27s_Theorem . From here links cover the main variations on the Bell test, actual experiments and, last but not least, the various loopholes.

Caroline

1. Your model is pure speculation (I don't mean that as an insult). As such it is not proof and it is certainly not a counter-example to Aspect's actual experimental evidence. You have to admit that there may in fact be no significant bias against local realism in Aspect's samples or methods - you just think there could be.

2. I want to talk to you about that. I looked at what you have done in Wikipedia to the Bell's Theorem page and was quite disappointed. In my opinion, you have essentially hijacked what should be a non-controversial page and used it to further your own non-mainstream ideas. Bell's Theorem is barely mentioned or discussed!

I fully support the spreading of your message - even though I personally disagree with its content - because I think that it helps to keep everyone on their toes. As you know, I even link to your site from my own page EPR, Bell & Aspect: The Original References (http://drchinese.com/David/EPR_Bell_Aspect.htm). But I think Wikipedia's Bell Theorem slot is the wrong place for it and your content there probably violates the POV neutrality policy. I hope you will voluntarily shift your contributions on the subject there to a more suitable slot and return Bell's Theorem back to how it was.

Caroline Thompson

Jan7-05, 06:07 PM

I looked at what you have done in Wikipedia to the Bell's Theorem page and was quite disappointed. In my opinion, you have essentially hijacked what should be a non-controversial page and used it to further your own non-mainstream ideas. Bell's Theorem is barely mentioned or discussed!

I fully support the spreading of your message - even though I personally disagree with its content - because I think that it helps to keep everyone on their toes. As you know, I even link to your site from my own page EPR, Bell & Aspect: The Original References (http://drchinese.com/David/EPR_Bell_Aspect.htm). But I think Wikipedia's Bell Theorem slot is the wrong place for it and your content there probably violates the POV neutrality policy. I hope you will voluntarily shift your contributions on the subject there to a more suitable slot and return Bell's Theorem back to how it was.

I strongly disagree, and if the above is what you feel the place to say it is in the wikipedia "talk" pages. The theorem is and ought to remain controversial, since it marks a point of bifurcation in the development of theoretical physics -- the point at which theory went wrong because people did not work hard enough at searching for local realist models. It was local realism that Bell himself expected to win. I don't know why he decided (reluctantly) to accept the general opinion that it had failed.

He once wrote that

“[The] entirely unauthorised `Bell's limit' sometimes plotted along with experimental points more or less ad hoc extrapolation [of the theory]”. [I]Bell, John A, The Speakable and Unspeakable in Quantum Mechanics, Cambridge University Press 1987, P60

Caroline

DrChinese

Jan8-05, 11:03 PM

I strongly disagree, and if the above is what you feel the place to say it is in the wikipedia "talk" pages. The theorem is and ought to remain controversial, since it marks a point of bifurcation in the development of theoretical physics -- the point at which theory went wrong because people did not work hard enough at searching for local realist models.

As far as I can tell, it is the policy of both PhysicsForums and Wikipedia that non-mainstream positions be placed in suitable context so as to identify that they are not mainstream.

I would not have noticed your contributions to Wikipedia had you not mentioned it above. It is my intention to determine if other members of PhysicsForums might desire to work with me to bring back a mainstream version of Bell's Theorem. However, I plan to do this outside of this thread.

It is my recommendation to you that you label your positions as non-mainstream when you present them in places in which others might be otherwise misled. I encourage you to continue presenting your ideas both here and elsewhere but you should respect the intent of the rules.

For anyone wondering what non-mainstream position of Caroline's I am referring to: She is a local realist who denies the existence of photons. ('Nuff said.)

JesseM

Jan8-05, 11:16 PM

As far as I can tell, it is the policy of both PhysicsForums and Wikipedia that non-mainstream positions be placed in suitable context so as to identify that they are not mainstream. Yes, this is definitely the policy at Wikipedia--see the section on how entries should express a "neutral point of view" below:

http://en.wikipedia.org/wiki/Wikipedia:Neutral_point_of_view

Here's one relevant part:

What is the neutral point of view?

What we mean isn't obvious, and is easily misunderstood.

There are many other possible valid understandings of what "unbiased," "neutral," etc. mean. The notion of "unbiased writing" that informs Wikipedia's policy is "presenting conflicting views without asserting them." This needs further clarification, as follows.

First, and most importantly, consider what it means to say that unbiased writing presents conflicting views without asserting them. Unbiased writing does not present only the most popular view; it does not assert the most popular view as being correct after presenting all views; it does not assert that some sort of intermediate view among the different views is the correct one. Presenting all points of view says, more or less, that p-ists believe that p, and q-ists believe that q, and that's where the debate stands at present. Ideally, presenting all points of view also gives a great deal of background on who believes that p and q and why, and which view is more popular (being careful not to associate popularity with correctness). Detailed articles might also contain the mutual evaluations of the p-ists and the q-ists, allowing each side to give its "best shot" at the other, but studiously refraining from saying who won the exchange. So, if Caroline Thompson presents any non mainstream-views, she should label them very clearly as non-mainstream views (presumably this would include views about how strongly different experiments demonstrate a violation of Bell's Inequality). I haven't looked at the Wikipedia article on Bell's Theorem very carefully, so I don't know if she does this or not.

Anyway, the discussion of "neutrality" is worth reading in full, because it goes into a lot more detail.

Caroline Thompson

Jan9-05, 03:45 AM

[QUOTE=JesseM]Yes, this is definitely the policy at Wikipedia--see the section on how entries should express a "neutral point of view" below:
http://en.wikipedia.org/wiki/Wikipedia:Neutral_point_of_view
[QUOTE]

Yes, I'm well aware of this, and there has been some discussion in wikipedia on the "neutrality" of my contributions. I'm happy to admit that my views are not "mainstream", but where would I state this? The entries are usually (almost) anonymous, though one can generally find out who is mainly responsible by looking at the "history" page.

But, perhaps more importantly, my "views" are merely "little known facts". Almost all these facts are already known, some having been known since 1970 or ealier. Are not "facts" in themselves neutral? I can't help it if they happen to be little known! Hasn't the public the right to be told facts in preference to opinion? Before I came on the scene the Bell test pages in wikipedia were strongly biased in favour of the quantum-mechanical point of view and riddled with factual inaccuracies.

Caroline
http://freespace.virgin.net/ch.thompson1/

DrChinese

Jan9-05, 07:17 PM

Before I came on the scene the Bell test pages in wikipedia were strongly biased in favour of the quantum-mechanical point of view ...

I think that sums it up, LOL!

JesseM

Jan9-05, 11:01 PM

Yes, I'm well aware of this, and there has been some discussion in wikipedia on the "neutrality" of my contributions. I'm happy to admit that my views are not "mainstream", but where would I state this? The entries are usually (almost) anonymous, though one can generally find out who is mainly responsible by looking at the "history" page. Well, the guidelines suggest that any non-mainstream views should be clearly flagged as such--you don't have to say "I, Caroline Thompson, believe X", but you should indicate something like "some dissenters to the mainstream opinion on the Aspect experiment believe X". But, perhaps more importantly, my "views" are merely "little known facts". Almost all these facts are already known, some having been known since 1970 or ealier. Are not "facts" in themselves neutral? I can't help it if they happen to be little known! Hasn't the public the right to be told facts in preference to opinion? Before I came on the scene the Bell test pages in wikipedia were strongly biased in favour of the quantum-mechanical point of view and riddled with factual inaccuracies. If the facts are agreed upon by everyone then sure, they're neutral, but the implications of some facts are still a matter of opinion. For example, perhaps mainstream physicists would agree that there are small loopholes in existing tests, but think that there is very little reason to think these loopholes cast significant doubt on the results, perhaps because you'd need a very contrived set of local laws in order to take advantage of these loopholes, or because successive tests keep on narrowing the loopholes and confirming the violation of Bell's Inequality to greater and greater accuracy. If this is the case, it should be explained along with the loopholes themselves, in order to present the mainstream view fairly.

Again, I haven't gone over the wikipedia entry or the arguments about loopholes very carefully myself, so I don't know to what extent you have or haven't done this.

DrChinese

Jan10-05, 10:51 AM

2. You cited a rather dubious source (C.H. Thompson) regarding the validity of the EPR experiment interpretation. Having had an "encounter" with her, ...

Zz.

ZapperZ,

It hurts me to say this: a) YOU were RIGHT about Caroline; and b) I'm throwing in the towel on her. I naively thought she would have enough professionalism to know where the line is with her opinions. She doesn't, and I have decided to remove that link as a result. Thanks for your input.

-DrC

Caroline Thompson

Jan10-05, 12:27 PM

Well, the guidelines suggest that any non-mainstream views should be clearly flagged as such--you don't have to say "I, Caroline Thompson, believe X", but you should indicate something like "some dissenters to the mainstream opinion on the Aspect experiment believe X". If the facts are agreed upon by everyone then sure, they're neutral, but the implications of some facts are still a matter of opinion. For example, perhaps mainstream physicists would agree that there are small loopholes in existing tests, but think that there is very little reason to think these loopholes cast significant doubt on the results, perhaps because you'd need a very contrived set of local laws in order to take advantage of these loopholes ...
What I try and emphasise is the fact that you do not need any "contrived" set of local laws to explain the violation of those Bell tests for which the detection loophole is open. Not many people know this! Surely it is only right that more people should have access to this information, and, equally, no real justification for prejudicing readers against the idea? "Accepted" opinion has been formed in ignorance of some of the facts. An empirically important loophole -- that concerning the subtraction of accidentals -- was first mentioned with hardly any publicity back in 1985 but seems not to have come to the attention of the community.

Should science progress on the basis of belief and ignorance, or on the basis of as full a version of the facts as possible?

... or because successive tests keep on narrowing the loopholes and confirming the violation of Bell's Inequality to greater and greater accuracy. If this is the case, it should be explained along with the loopholes themselves, in order to present the mainstream view fairly.

I think if you read my wikipedia pages carefully you will see that claims of greater and greater "accuracy" are not true. What we have is observation of violations of the CHSH test by ever greater margins relative to the standard error, but if the detectors are not 100% efficient the violation has no significance due to the need for the fair sampling assumption. If you read my Chaotic Ball papers you will see why this assumption is just not reasonable.

Again, I haven't gone over the wikipedia entry or the arguments about loopholes very carefully myself, so I don't know to what extent you have or haven't done this.

I hope you will now remedy this situation!

Caroline
http://freespace.virgin.net/ch.thompson1/

DrChinese

Jan10-05, 02:21 PM

Should science progress on the basis of belief and ignorance, or on the basis of as full a version of the facts as possible?

There are those of us that think YOU are the one espousing belief and ignorance, and it is you who is trying to present a highly edited version of the "facts" instead a more complete one. :rofl:

Caroline Thompson

Jan10-05, 04:48 PM

There are those of us that think YOU are the one espousing belief and ignorance, and it is you who is trying to present a highly edited version of the "facts" instead a more complete one. :rofl:

DrChinese, as you know, I've devoted over 10 years now to the study of the actual Bell test experiments. I have looked up and found out one way or another enough about optics and how the various pieces of apparatus work to feel that I am on a par with most physicists working in the area. If you doubt this claim, please write privately and I can tell you some of the experts with whom I have had contact. I cannot off hand think of any who have not shown me respect, treating me almost as an equal. I think it likely that I know more facts in the area than you do. I am not ignorant, and what I know has never conflicted with what was, before the modern tendency to mystification of physics took root, generally considered a feature the real world and hence a necessary feature of any fundamental theory: local realism.

Please specify the facts that you think I have misrepresented.

Caroline

DrChinese

Jan10-05, 05:37 PM

DrChinese, as you know, I've devoted over 10 years now to the study of the actual Bell test experiments. I have looked up and found out one way or another enough about optics and how the various pieces of apparatus work to feel that I am on a par with most physicists working in the area. If you doubt this claim, please write privately and I can tell you some of the experts with whom I have had contact. I cannot off hand think of any who have not shown me respect, treating me almost as an equal. I think it likely that I know more facts in the area than you do. I am not ignorant, and what I know has never conflicted with what was, before the modern tendency to mystification of physics took root, generally considered a feature the real world and hence a necessary feature of any fundamental theory: local realism.

Please specify the facts that you think I have misrepresented.

Caroline

What is a fact? What is evidence? Your definitions exclude evidence accepted by the physics community. Specifically, evidence in favor of Bell Inequality violation by Aspect and others.

Even in a court of law, flawed evidence is considered evidence. For example, eyewitness testimony is often unreliable - yet it may be the best evidence available. If I testify I saw a man commit a crime, you may try to cast doubt by saying it was not him - it was an imposter made up to look like the defendant. A jury listens and decides. A verdict is rendered and life goes on. There is a right to appeal, but until it is overturned the man is guilty.

Same in science.

I will start a new thread tomorrow to discuss the local realistic view of Bell tests. I have some questions of substance I wish to pose to you on the matter.

vanesch

Jan11-05, 03:35 AM

Even in a court of law, flawed evidence is considered evidence. For example, eyewitness testimony is often unreliable - yet it may be the best evidence available. If I testify I saw a man commit a crime, you may try to cast doubt by saying it was not him - it was an imposter made up to look like the defendant. A jury listens and decides. A verdict is rendered and life goes on. There is a right to appeal, but until it is overturned the man is guilty.

Same in science.

If I may inject my 2 cents: a few months ago, I spend (way too) much time discussing with another anti-EPR fan here on this board. The problem seems to be not so much in the loopholes in the Aspect-like experiments but in what I would qualify as "the united view of physics".
One shouldn't deny that there are "loopholes" in the Aspect like experiments. But as Dr. Chinese points out, experiments are "evidence" and not "mathematical proof" for scientific theories. It is the entire body of "evidence" that makes theories stand out or not, and not one single type of experiment It now happens that the way people correct for detection efficiencies (the major source of loopholes) is what has always been considered as acceptable ; only NOW it seems to be inacceptable, in order to show that EPR-like results are not violating any Bell equations. Of course, the point can be made, but a reasonable explanation *within the frame of the rest of physics* should be given why suddenly this accepted correction becomes unacceptable.

In that long discussion I had, it turned out that the main discordance with anti-EPR proponents, is not about Bell's inequality. It is about the existance of photons as particles or not. They usually work with classical EM waves, and it is true that in that case, the efficiency corrections seem much more dubious. However, once photons are recognised as particles, it is much harder to find arguments against the fair sampling hypothesis that underlies the efficiency corrections in EPR experiments.

And the existance of photons, as correlated clicks, is very difficult to deny, not only from a theoretical point of view, but there are also very recent experiments that indicate very strongly the particle-like nature of light:

Am. J. Phys. Vol 72, No 9, September 2004.

The point of the experiment is the following:
A PDC (Parametric Down converting xtal) generates an "entangled pair of photons" also called a 2-photon state. One detector (the "trigger") detects one of the photons of the pair, and the other photon is sent onto a beam splitter.
The point is that in the case of a hit of the trigger, there is one photon in the other beamline (the one with the splitter) and as such, a double hit is essentially impossible (except by Poisson coincidence which is a known function of the incident beam intensity) if the photon is a particle, and statistically possible if it are continuous waves, the essence of a particle being that it can be only detected once. The article points out the very low double coincidence rate, which is further exactly explained by Poisson coincidence.
The nice thing about it is that no corrections by efficiencies are needed: raw data are presented, and they are clean enough to prove the point. Of course, this is not an EPR experiment. It is just an experiment that makes it extremely difficult to deny the existence of photons as particles. Indeed, in the classical wave picture, the energy in the second beam is split evenly by the beam splitter, and there's no real reason why there shouldn't be cases of triggering of both detectors, which independently see an incident radiation flux. The fact that there is a strong anti-coincidence indicates that a choice was made at the beamsplitter, and the choice is the path the photon took (naively ; more professionally, it is the detection of the one-photon state which is a non-classical state: it isn't a coherent state).

The first step in the discussion with an anti-EPR supporter should be about the existence of photons. Photons exist or not, and if they exist in one place, they exist everywhere, also in EPR experiments.

I think that people who deny the existence of photons will have a very hard time having a reasonable discussion here. I still have to encounter people who are anti-EPR fans but who accept the existance of photons.

Caroline Thompson

Jan11-05, 04:03 AM

I will start a new thread tomorrow to discuss the local realistic view of Bell tests. I have some questions of substance I wish to pose to you on the matter.

Good!

Caroline

Caroline Thompson

Jan11-05, 04:45 AM

... as Dr. Chinese points out, experiments are "evidence" and not "mathematical proof" for scientific theories. It is the entire body of "evidence" that makes theories stand out or not, and not one single type of experiment It now happens that the way people correct for detection efficiencies (the major source of loopholes) is what has always been considered as acceptable ; only NOW it seems to be inacceptable, in order to show that EPR-like results are not violating any Bell equations. Of course, the point can be made, but a reasonable explanation *within the frame of the rest of physics* should be given why suddenly this accepted correction becomes unacceptable.

I think the reason you have not previously heard much about the objections is partly historical accident, partly the great difficulty that people with views similar to mine have had in getting these published. Objections to the assumption of fair sampling (needed to get around the detection loophole) have been known since 1970 and are, I presume, the main reason that tests in which this loophole was open were not used for the first 10 years of the Bell test experiments (1972-1981). It was only in 1982 that Aspect started using the CHSH test and the trouble became serious. The reasons for this change I have not managed to ascertain, despite correspondence with several of the people concerned.

Local realists at the time seem to have been represented by Marshall, Santos and Selleri. Unfortunately, their seminal article objecting to the QM interpretation of Aspect's experiments did not directly explain why fair sampling could not be assumed and went off at a tangent, concentrating on the idea that the assumption of "no enhancement" was flawed. It is only recently, on re-reading their paper, that I discovered the reaon for this: they had tried to analyse the published results, which were based on adjusted data. Though they did (iirc) register their objected to this adjustment, they don't appear to have realised how serious it was.

Their paper was:
T W Marshall, E Santos and F Selleri, F, “Local Realism has not been Refuted by Atomic-Cascade Experiments”, Physics Letters A, 98, 5-9 (1983)

... the main discordance with anti-EPR proponents, is not about Bell's inequality. It is about the existance of photons as particles or not. They usually work with classical EM waves, and it is true that in that case, the efficiency corrections seem much more dubious. However, once photons are recognised as particles, it is much harder to find arguments against the fair sampling hypothesis that underlies the efficiency corrections in EPR experiments.

Very true!

... the existance of photons, as correlated clicks, is very difficult to deny, not only from a theoretical point of view, but there are also very recent experiments that indicate very strongly the particle-like nature of light:

Am. J. Phys. Vol 72, No 9, September 2004.

I should be most grateful if you could tell me the author, or where I can find this online? I lost my rights to access such journals a year ago, but perhaps there is a copy in http://arxiv.org?

I am familiar with this kind of experiment and with the usual arguments re coincidence rates after beamsplitters. I am not entirely sure of the true explanation for the low observed rates -- it may not always be the same. Marshall et al, with their Stochastic Electrodynamics theory, put it all down to the effect of superposition of the test beams with components of the zero point field. I favour at present an idea that may be mathematically equivalent: that the proportions in which the intensity is divided depends partly on the state of the beamsplitter.

Incidentally, it may be well worthwhile to make a study of how those beamsplitters actually work. They are not just half-silvered plates. If "polarising cubes" are used, there are many layers of dielectric and/or metal on the diagonal interface between the two prisms, with thicknesses carefully engineered so as to be exact half or quater wavelengths. Clearly the idea is to selectively encourage constructive or destructive interference of the partially-reflected or transmitted waves at each surface. This is a purely wave effect, yet is used to make the system "simulate" quantum theory! Which component (reflected or transmitted) is likely to dominate might depend on the exact wavelength. Perhaps careful analysis would reveal that the spectra of the two output beams are slightly different? [This last idea is a new one I had just now! I've had others at various times, but all depend on this kind of factor.]

Caroline

vanesch

Jan11-05, 06:11 AM

Their paper was:
T W Marshall, E Santos and F Selleri, F, “Local Realism has not been Refuted by Atomic-Cascade Experiments”, Physics Letters A, 98, 5-9 (1983)

Yes, I'm aware of these papers. I'm also aware (although not an expert) of stochastic electrodynamics and things like that. But you agree with me that this is NOT classical optics. New ideas ARE introduced - such as the fact that we are exposed to background radiation, with an intensity comparable to the intensity of sunlight, but apparently, we calbrated this away in all our sensors, thermometers and so on so as not to notice it ; a lot of physics is to be rewritten that way: suddenly we don't understand statistical physics, atomic physics, solid state physics anymore. These new ideas should be backed up by specific predictions, and you cannot deny that you're left with the impression that the ONLY reason for doing so is to find a way to explain away the behaviour of light without photons in certain circumstances. And THAT is done because, as you point out, denying photons is the only hope to get around EPR. I'm sorry, it all gives too much the impression that this is to cling onto a religiously held belief in what you call "local realism".
As I explained during that long discussion (which I'm not going to repeat here), second quantization of fields is very difficult to avoid. You can do so for specific situations, but you wipe away too much verified physics in trying to cling to a classical field description of the world. Second quantization explains a lot of things extremely well and I truely have difficulties imagining how you can find tricks to go back to classical fields. How do you rewrite particle physics without second quantization ? What happens to the standard model ? Do you see the mindboggling scale of the attempt you propose ?

I should be most grateful if you could tell me the author, or where I can find this online? I lost my rights to access such journals a year ago, but perhaps there is a copy in http://arxiv.org?

here's the abstract, but I don't have the right to give you the article, unfortunately:

Observing the quantum behavior of light in an undergraduate laboratory

J. J. Thorn, M. S. Neel, V. W. Donato, G. S. Bergreen, R. E. Davies, and M. Beck
Department of Physics, Whitman College, Walla Walla, Washington 99362

(Received 4 December 2003; accepted 15 March 2004)

While the classical, wavelike behavior of light (interference and diffraction) has been easily observed in undergraduate laboratories for many years, explicit observation of the quantum nature of light (i.e., photons) is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light. Spontaneously downconverted light is incident on a beamsplitter and the outputs are monitored with single-photon counting detectors. We observe a near absence of coincidence counts between the two detectors—a result inconsistent with a classical wave model of light, but consistent with a quantum description in which individual photons are incident on the beamsplitter. More explicitly, we measured the degree of second-order coherence between the outputs to be g(2)(0) = 0.0177±0.0026, which violates the classical inequality g(2)(0)>=1 by 377 standard deviations. ©2004 American Association of Physics Teachers.

I am familiar with this kind of experiment and with the usual arguments re coincidence rates after beamsplitters. I am not entirely sure of the true explanation for the low observed rates -- it may not always be the same. Marshall et al, with their Stochastic Electrodynamics theory, put it all down to the effect of superposition of the test beams with components of the zero point field. I favour at present an idea that may be mathematically equivalent: that the proportions in which the intensity is divided depends partly on the state of the beamsplitter.

Incidentally, it may be well worthwhile to make a study of how those beamsplitters actually work. They are not just half-silvered plates. If "polarising cubes" are used, there are many layers of dielectric and/or metal on the diagonal interface between the two prisms, with thicknesses carefully engineered so as to be exact half or quater wavelengths. Clearly the idea is to selectively encourage constructive or destructive interference of the partially-reflected or transmitted waves at each surface. This is a purely wave effect, yet is used to make the system "simulate" quantum theory! Which component (reflected or transmitted) is likely to dominate might depend on the exact wavelength. Perhaps careful analysis would reveal that the spectra of the two output beams are slightly different? [This last idea is a new one I had just now! I've had others at various times, but all depend on this kind of factor.]

Do you realise the twistedness of that explanation ?

Now tell me, how does it occur that when a wave that is generated from a PDC spits "left-right" according to a feature of the beamsplitter, but when you shine a "classical" beam on that beamsplitter, it doesn't (in the sense that you can produce interference effects with the split beams, so you cannot send you bullet left or right at the beamsplitter)...
Also, don't you think that if beamsplitters were also spectral filters, that would have been noticed already a few times in undergraduate labs ?

That's what I mean with "the united view of physics". You cannot invent, at hoc, an explanation for what annoys you in one particular case, without having to consider it in all generality, and apply it systematically to all of physics. If it helps you to explain 2 experiments, but is screws up 70% of the rest of physics, the idea goes into the dust bin. Thinking that you'll fix up that 70% is heroic, but close to hopeless. Most physicists think that when you have to do that 2 or 3 times in a row, you're simply on the wrong track.
I'm one of them :tongue:

Nereid

Jan11-05, 08:34 AM

As I explained during that long discussion (which I'm not going to repeat here), [...]It would be helpful to other readers - such as myself - if we could find this earlier discussion. Do you have a link? If not, maybe approx when the discussion was, or the name of the thread? I'd be happy to search in the PF archives to find it, if you could give me some pointers.

vanesch

Jan11-05, 10:21 AM

It would be helpful to other readers - such as myself - if we could find this earlier discussion. Do you have a link? If not, maybe approx when the discussion was, or the name of the thread? I'd be happy to search in the PF archives to find it, if you could give me some pointers.

The name of the thread was "Young's experiment" or something close, and the discussion was with someone with the nickname "nightlight"

cheers,
Patrick.

DrChinese

Jan11-05, 10:21 AM

One shouldn't deny that there are "loopholes" in the Aspect like experiments. But as Dr. Chinese points out, experiments are "evidence" and not "mathematical proof" for scientific theories. It is the entire body of "evidence" that makes theories stand out or not, and not one single type of experiment It now happens that the way people correct for detection efficiencies (the major source of loopholes) is what has always been considered as acceptable ; only NOW it seems to be inacceptable, in order to show that EPR-like results are not violating any Bell equations. Of course, the point can be made, but a reasonable explanation *within the frame of the rest of physics* should be given why suddenly this accepted correction becomes unacceptable.

Exactly, well said. This is what I was trying to point out, that there is a double standard by the anti-Aspect group when it comes to evidence.

(By the way, Vanesch, I found some interesting discussions including you on some of these matters while Googling around last night - they were in the PhysicsForums archives (http://www.physicsforums.com/archive).)

Let's review the situation so we can see it in a little perspective. All angles below are at 22.5 degrees where 0 degrees means perfect correlation.

a. The QM prediction for EPR correlations at 22.5 degrees is cos^2, or .8536.
b. The local realistic prediction would need to be .7500 to satisfy Bell's Theorem. (I plan to start another thread to discuss this in more detail)
c. Classical optics, as best as I can see it applies, would predict exactly the same as a., or .8536
d. The "flawed, loophole laden" actual experimental value for correlations is .85 with margin of error of about 2%.

To my thinking, it is good evidence when a theory makes a prediction that is closely matched by experiment (a. and d.) and also matches classical formulas (c.) known for over a hundred years. It is a bad theory that makes a prediction that cannot be confirmed by experiment (b. and d.).

Yet the local realitists - including Caroline - argue that the .85 result measured is actually proof of the .75 result. Somehow, her "chaotic ball" model ALWAYS causes all local realistic results to be restated to arrive at exactly the QM predicted value - even though the QM theory itself is actually wrong.

Does this about sum it up? It defies my common sense that: of all of the possible biased values you could measure if Caroline's chaotic ball model is correct - and the QM value is just one of many that could result - the one we actually measure is... the QM value. I mean, we could have seen results of .8 or .9 or .7 or .6 (since we never measure the local realistic predicted value of .75 anyway) with the chaotic ball or its sister models. But no, the one value we consistently get is the QM expectation value. Hmmm.

DrChinese

Jan11-05, 10:30 AM

The name of the thread was "Young's experiment" or something close, and the discussion was with someone with the nickname "nightlight"

cheers,
Patrick.

http://www.physicsforums.com/archive/topic/t-44964_Young's_experiment.html

Yes, that was the same discussion I saw last night - a lot of work went into that by you! By the way, if I recall, nightlight also holds a similar diehard anti-Aspect position as Caroline.

Vanesch, I was researching that thread for another reason. I could use your and some of the others assistance on a minor question I have - but I will place that in a new thread as it is unconnected to this one. If you have time to look at it, it will be titled "Question about Other Tests of EPR Paradox". Thanks!

-DrC

Caroline Thompson

Jan11-05, 12:10 PM

... there is a double standard by the anti-Aspect group when it comes to evidence.

(By the way, Vanesch, I found some interesting discussions including you on some of these matters while Googling around last night - they were in the PhysicsForums archives (http://www.physicsforums.com/archive).)

Let's review the situation so we can see it in a little perspective. All angles below are at 22.5 degrees where 0 degrees means perfect correlation.

a. The QM prediction for EPR correlations at 22.5 degrees is cos^2, or .8536.
b. The local realistic prediction would need to be .7500 to satisfy Bell's Theorem. (I plan to start another thread to discuss this in more detail)
c. Classical optics, as best as I can see it applies, would predict exactly the same as a., or .8536
d. The "flawed, loophole laden" actual experimental value for correlations is .85 with margin of error of about 2%.

I'm afraid the above figures merely confuse the issue, since you can't base a Bell test on just one correlation value. You need at least three, and in practice four.

The simplest way of comparing predictions is to look at the "visibility" of the coincidence curve, i.e. (max - min)/(max + min), as you vary the angle between detector settings. Under the conditions generally assumed, QM predicts a visibility of 1.0 whilst classical optics, using local realist logic, predicts 0.5. [I don't know how you are managing to obtain a different classical optics figure from the local realist one.]

Anyway, we have essentially two different loopholes that can explain why the observed visibility is nearer to 1.0 than 0.5.

Subtraction of accidentals
In certain experiments there were large numbers of "accidentals" and these were adjusted for by assuming them to have the same effect for all time intervals between detections. [It must be remembered that in practice the supposedly synchronous detections are actually separated in time by a random amount, with a limit whose interpretation depends on what theory you are going by.] This constant number of accidentals per sec was subtracted from the counts before calculation of the Bell test statistic, increasing the calculated value. If we're looking at visibility instead of an actual Bell test, it is clear that what we're doing is shifting the whole graph downwards till it almost hits the x axis. The process increases the visibility. It can easily be shown (as in quant-ph/9903066) that the raw data curve has visibility almost exactly 0.5 in the experiments for which this data is available, vis Aspect's 1981 one and Tittel's 1997 one(http://arxiv.org/abs/quant-ph/9707042). After subtraction the visibility increases to over the local realist limit, which is, iirc, 0.71 for this statistic.

Detection loophole
It is not so easy to prove from published results that this loophole is the true cause of the high visibilities in most of the remaining experiments, for which either accidental rates were low or not subtracted. Here there is an urgent need for more information. We need to know just how the total of the four coincidence rates -- the figure used as denominator when estimating the quantum correlation -- varied with difference between detector settings. When this has been tested, what angles have been looked at? I suspect that most experimenters have not fully understood why the test for constancy was needed and have restricted themselves to looking at just the four Bell test angles. Aspect reported in this PhD thesis that the total was not quite constant, but the variations were within one standard deviation so could, he thought, be ignored. He did not state what angles he had looked at, though, nor whether or not there was any hint of a consistent pattern between different repeats of the experiment. If only he'd decided to do sufficient repeats to reduce the SD of the mean to less than the observed discrepancy!

If only, too, all Bell test experiments had been repeated using a range of different settings for the detector efficiencies! If the results from these were available, whether or not the loophole is in operation might have become clear. QM predicts no change in either Bell test statistic or visibility as you change the efficiency. Local realism predicts that as you increase the detector efficiency you decrease both.

... the local realitists - including Caroline - argue that the .85 result measured is actually proof of the .75 result. Somehow, her "chaotic ball" model ALWAYS causes all local realistic results to be restated to arrive at exactly the QM predicted value - even though the QM theory itself is actually wrong.

I don't in general give any quantatitive predictions. All I say is that the loopholes mean that local realist models for the observed values exist. The exact predictions depend on the exact conditions of each experiment.

Caroline

Caroline Thompson

Jan11-05, 12:36 PM

Yes, I'm aware of these papers. I'm also aware (although not an expert) of stochastic electrodynamics and things like that. But you agree with me that this is NOT classical optics ...

Yes, but I think it best not to discuss SED here. It's best not to have any preconceived theory other than a general framework of local causality and a wave model of light. Both are, after all, supported by vast amounts of evidence.

New ideas ARE introduced - such as the fact that we are exposed to background radiation, with an intensity comparable to the intensity of sunlight, but apparently, we calbrated this away in all our sensors, thermometers and so on so as not to notice it ; a lot of physics is to be rewritten that way: suddenly we don't understand statistical physics, atomic physics, solid state physics anymore. These new ideas should be backed up by specific predictions, and you cannot deny that you're left with the impression that the ONLY reason for doing so is to find a way to explain away the behaviour of light without photons in certain circumstances.

Yes, any challenge to QM means re-writing a great deal of physics, but I think it needs to be done. In optical areas I don't see it presenting any problem. Clearly when it comes to modelling actual particles there are going to be difficulties. I don't think they are insuperable, but, be this as it may, I think QM makes a big mistake in trying to apply the same theory to optics as it does to particles. Why not, as a start, just hive off optics from QM and return it to classical physics?

And THAT is done because, as you point out, denying photons is the only hope to get around EPR. I'm sorry, it all gives too much the impression that this is to cling onto a religiously held belief in what you call "local realism".
The main reason for denying the photon is that I have never seen any evidence that it exists! [See my web site, especially http://freespace.virgin.net/ch.thompson1/History/forgotten.htm]

... How do you rewrite particle physics without second quantization ? What happens to the standard model ? Do you see the mindboggling scale of the attempt you propose ?

I've no idea! This is not my area.

Re
J. J. Thorn, M. S. Neel, V. W. Donato, G. S. Bergreen, R. E. Davies, and M. Beck, Observing the quantum behavior of light in an undergraduate laboratory, Am. J. Phys. Vol 72, No 9, September 2004,I can't find any mention of these authors in arxiv.org so can't get hold of the paper without considerable effort. From what you say, though, it sounds as if it is no different from a number of other experiments, and I should dearly like to know just what beamsplitter they used.

Now tell me, how does it occur that when a wave that is generated from a PDC spits "left-right" according to a feature of the beamsplitter, but when you shine a "classical" beam on that beamsplitter, it doesn't (in the sense that you can produce interference effects with the split beams, so you cannot send you bullet left or right at the beamsplitter)...
I don't know quite what you mean here. There is not supposed to be any essential difference in the nature of light output by PDC from light produced by, say, a laser, if you look at just one or other of the output beams.

Also, don't you think that if beamsplitters were also spectral filters, that would have been noticed already a few times in undergraduate labs ?
Yes indeed, though what I had in mind might be too subtle for easy detection. I won't try and explain, partly because I havent' tried to work out the details.

Caroline
http://freespace.virgin.net/ch.thompson1/

DrChinese

Jan11-05, 02:16 PM

I'm afraid the above figures merely confuse the issue, since you can't base a Bell test on just one correlation value. You need at least three, and in practice four.

Despite what you (and others) might think, you don't need to change polarizer settings in flight or otherwise vary the angles to test Bell's Theorem. You only need to calculate the correlation percentages at three particular angle settings (these can be done fully independently). Then combine a la Bell.

Varying is only necessary if you are asserting that the measurement devices are (or might be) communicating with each other so as to affect the outcome of the correlation tests. We already know from Aspect that doesn't happen, because he did the experiments both ways and there was no difference in the outcomes! Even that should be a definitive conclusion of Aspect. Further regarding the varying issue:

a. If you are a local realist, I would assume that wouldn't be much of an issue to you since you think there are classical, intuitive explanations for everything anyway - strange new types of communication between measuring devices should not be an issue.
b. If, on the other hand, you follow the Copenhagen interpretation, varying also shouldn't matter as you don't isolate out communication with other parts of the measurement apparatus for any other type of experiment (such as double slit) either.
c. Also, if you believe the correlation is non-local then the varying analyzers are superfluous.
d. And finally, if you are a local non-realist like me :) then you already believe that the only "real" component being measured is the angle between the remote polarizers anyway i.e. the measurement is fundamental to the process.

So yes, we can meaningfully talk about a single correlation value, and the one I choose is to discuss 22.5 degrees because that (along with its sister 67.5 degrees) is the angle where the differences between the realistic expectation value, the QM expectation value, and the actual experimental values will be most highlighted. To be specific, where A is a detection at one polarizer setting and C is the other one:

[X1] A+ C+
[X2] A+ C-
[X3] A- C+
[X4] A- C-

That would be (X1+X4)/(X1+X2+X3+X4). Please note that we don't care at all about loopholes or other practical issues, just the LR and QM expectation values and whatever it is that Aspect is giving us a measurement of.

QM gives an expectation value of .8536, and Aspect measured a value very close to this. By my calculation, one should assert a LR expectation value of the correlation at that angle of .7500 if you want to be within the Bell Inequality range.

For Caroline: I will explain how I get this in a separate thread. I wonder if you will agree with .7500.

Caroline Thompson

Jan11-05, 04:25 PM

Despite what you (and others) might think, you don't need to change polarizer settings in flight or otherwise vary the angles to test Bell's Theorem. [I never suggested that changing during flight mattered, since your point (a) applies.]

... d. And finally, if you are a local non-realist like me :) then you already believe that the only "real" component being measured is the angle between the remote polarizers anyway i.e. the measurement is fundamental to the process. What a curious belief! The detector angles are set by the experimenter so are of very little interest indeed to me.

I have met in wikipedia one other person (Frank Wappler) who seems to have thought like you, though, so I have learned to follow the idea. Somehow you use the QM prediction in reverse, deducing the angle from the coincidence rates, but what is the point? And how can you modify the idea to cover the case where you do not have rotational invariance, so that the coincidence rate is not a function of the difference in angles?

... Please note that we don't care at all about loopholes or other practical issues, just the LR and QM expectation values and whatever it is that Aspect is giving us a measurement of.
But if you want to talk about what Aspect measured you cannot avoid the matter of accidentals! He measured one set of counts then subtracted a substantial count and then calculated his Bell test statistic.

QM gives an expectation value of .8536, and Aspect measured a value very close to this. I would advise turning to my paper http://arxiv.org/abs/quant-ph/9903066 if you want the true figures.

For Caroline: I will explain how I get this in a separate thread. I wonder if you will agree with .7500.You have succeeded for now in confusing me! However, I trust my papers and look forward to your new thread.

Caroline
http://freespace.virgin.net/ch.thompson1/

DrChinese

Jan11-05, 04:46 PM

But if you want to talk about what Aspect measured you cannot avoid the matter of accidentals! He measured one set of counts then subtracted a substantial count and then calculated his Bell test statistic.

It matters to you, but doesn't matter quite so much to the rest of us. Why?

Because as I and others said above, it is the totality of the evidence that matters and Aspect's results are just one part of it. It is in context of the totality where your arguments fall on their face. When the arguments for both sides are viewed in this context, LR fails.

More importantly: After Bell, I would not accept local realism even if an experiment were never performed! What else is Bell but this point? So after Bell sunk in, the debate about LR was over for most scientists anyway. That is why Aspect was the nail in the coffin. If you totally unwound Aspect, it still would not change most scientists minds in favor of LR. That is why your "loopholes" are off base.

You need an experiment in favor of a different value for the observed correlations to convince anyone at this point. There is obviously an observed pattern: predict it and measure it! That is what Aspect did.

Hans de Vries

Jan11-05, 06:10 PM

For Caroline: I will explain how I get this in a separate thread. I wonder if you will agree with .7500.

(After looking at Caroline's:
appendix C: "Integration of the standard realist formula" in:
http://arxiv.org/PS_cache/quant-ph/pdf/9903/9903066.pdf
which uses the optical approach )

She will probably agree to (depending on the situation)

A) 0.8536 (!)

In the situation you seem to sketch were the photon source is
linear polarized at 0 degrees. In this case Malus law will give
\cos^2(0) \cos^2(22.5) where the two normalized intensities (= photon
rates) after the polarizers are multiplied with each other to give
the detect incident rate.

B) 0.67677

In the situation handled in appendix C: The polarization of the
photons is random. (but equal for the two entangled photons)
In this case one must apply Malus law for all angles \lambda and then
integrate over them:

A+B+ \ \ = \ \ \frac{1}{2\pi} \int \cos^2(\lambda-0) \cos^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} + \frac{1}{8} \cos(45) \ \ = \ \ 0.338388
A+B- \ \ = \ \ \frac{1}{2\pi} \int \cos^2(\lambda-0) \sin^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} - \frac{1}{8} \cos(45) \ \ = \ \ 0.161611
A-B+ \ \ = \ \ \frac{1}{2\pi} \int \sin^2(\lambda-0) \cos^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} - \frac{1}{8} \cos(45) \ \ = \ \ 0.161611
A-B- \ \ = \ \ \frac{1}{2\pi} \int \sin^2(\lambda-0) \sin^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} + \frac{1}{8} \cos(45) \ \ = \ \ 0.338388

Adding A+B+ and A-B- then gives 0.67677

Regards, Hans

P.S. The setup in (B) is also the one I presumed in the 3 photon
experiment with three instead of two polarizers. This is basically
the optical approach for the calculation of the intensities and
then presuming that the photon rate = intensity.

P.P.S: Tip: use http://integrals.wolfram.com/ to get the integrals.

DrChinese

Jan11-05, 08:09 PM

She will probably agree to (depending on the situation)

A) 0.8536 (!)

B) 0.67677

In the situation handled in appendix C: The polarization of the
photons is random. (but equal for the two entangled photons)
In this case one must apply Malus law for all angles \lambda and then
integrate over them:

A+B+ \ \ = \ \ \frac{1}{2\pi} \int \cos^2(\lambda-0) \cos^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} + \frac{1}{8} \cos(45) \ \ = \ \ 0.338388
A+B- \ \ = \ \ \frac{1}{2\pi} \int \cos^2(\lambda-0) \sin^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} - \frac{1}{8} \cos(45) \ \ = \ \ 0.161611
A-B+ \ \ = \ \ \frac{1}{2\pi} \int \sin^2(\lambda-0) \cos^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} - \frac{1}{8} \cos(45) \ \ = \ \ 0.161611
A-B- \ \ = \ \ \frac{1}{2\pi} \int \sin^2(\lambda-0) \sin^2(\lambda-22.5) d\lambda \ \ = \ \ \frac{1}{4} + \frac{1}{8} \cos(45) \ \ = \ \ 0.338388

Adding A+B+ and A-B- then gives 0.67677

Regards, Hans

P.S. The setup in (B) is also the one I presumed in the 3 photon
experiment with three instead of two polarizers. This is basically
the optical approach for the calculation of the intensities and
then presuming that the photon rate = intensity.

P.P.S: Tip: use http://integrals.wolfram.com/ to get the integrals.

Way to go, Hans! That is what I am talking about. A specific value pulled from the opposition that is within the Bell Inequality range. I don't think I made it clear above, but the .7500 value I mentioned was the top value (by my estimate) this could be and still satisfy Bell's Theorem. The .6767 value is a great start. I am sure you can see that sets up a great reference point - there is naturally a huge difference between that and the QM and experimental values! After all of Caroline's moaning about the errancy of QM, and why Aspect's results are no good even though the results are to the penny... she now has to explain why experiments do not support her predictions. Of course, I have a feeling we will see a bit of waffling on this point. She is quick to talk down Aspect, let's see her come forth with something positive to the debate rather than negative. Perhaps some experimental results?

Hans de Vries

Jan11-05, 09:08 PM

Caroline Thompson

Jan12-05, 03:38 AM

There's much more information on Aspect's experimental setup here:
http://chaos.swarthmore.edu/courses/phys6_2004/QM/17_EPR_Bell_Details.pdf

It shows that the experiment uses Wollaston Prisms instead of the
usual polarizers (page 310) and the total setup has 2x4 detectors
instead of 2x2. (page 316)

From what you say it appears that the paper covers only one of Aspect's experiments, or, possibly, confuses them all.

His first, Physical Review 47,460 (1981), used parallel plate polarisers, with only the '+' results counted. It used the CH74 Bell inequality (see http://en.wikipedia.org/wiki/Clauser_and_Horne%27s_1974_Bell_test)

The second, Physical Review Letters 49, 91-94 (1982) used Wollaston Prisms (though he did not call them by that name. They were "polarising cubes"). These have two outputs and both '+' and '-' outcomes are counted. It used the CHSH test (see http://en.wikipedia.org/wiki/CHSH_inequality).

The third, PRL 49, 1804 (1982), used parallel plates again. This was the one with time switching, with two possible routes for the beam on each side, leading to detectors set at two different angles. The path was switched effectively randomly between the two paths so that for each experimental run there were four counts to be analysed, but logically the setup is (from a local realist point of view) just the same as his first. Only '+' results are counted. It again used the CH74 test.

It is the first that I have analysed (in http://arXiv.org/abs/quant-ph/9903066) with and without subtraction of accidentals, this being the only one for which sufficient data is available (from Aspect's PhD thesis).

Incidentally, Aspect presents a pretty comprehensive description of his experiments at:
A. Aspect, “Bell’s theorem: the naïve view of an experimentalist”, Text prepared for a talk at a conference in memory of John Bell, held in Vienna in December 2000. Published in Quantum [Un]speakables – From Bell to Quantum information, R. A. Bertlmann and A. Zeilinger (eds.), (Springer, 2002); http://arxiv.org/abs/quant-ph/0402001

As far as I remember, though, his coverage of the subtraction of accidentals leaves much to be desired (if, indeed, it is mentioned at all?) but, more interestingly from my point of view, it is clear from his description of the different Bell inequalities that he has, by using for the CH74 inequality the derivation given in the 1969 paper instead of the simpler one of 1974, persuaded himself that the CH74 test is at least as bad the CHSH one when it comes to the detection loophole. As far as the logic covered by my Chaotic Ball model is concerned, this is not true.

I discuss the matter in:
http://freespace.virgin.net/ch.thompson1/Papers/TheRec/TheRecord.htm/and
http://freespace.virgin.net/ch.thompson1/Papers/CH74/CH74assumptions.htm

((Like you suggested: let's forget the
in-flight switching)

It also seems (on this page 310) that the Wollaston Prisms don't have
an angle dependent intensity loss like polarizers have.

What's the difference supposed to be between Wollaston Prisms (which were used, incidentally, by Weihs et al in their experiment with a more genuinely random switching system) and a polarising cube?

By a "polariser", do you mean something such as a polarising filter that you can use on sunglasses?

Caroline

Caroline Thompson

Jan12-05, 04:06 AM

Way to go, Hans! That is what I am talking about. A specific value pulled from the opposition that is within the Bell Inequality range. I don't think I made it clear above, but the .7500 value I mentioned was the top value (by my estimate) this could be and still satisfy Bell's Theorem. The .6767 value is a great start. I am sure you can see that sets up a great reference point - there is naturally a huge difference between that and the QM and experimental values! After all of Caroline's moaning about the errancy of QM, and why Aspect's results are no good even though the results are to the penny... she now has to explain why experiments do not support her predictions. Of course, I have a feeling we will see a bit of waffling on this point. She is quick to talk down Aspect, let's see her come forth with something positive to the debate rather than negative. Perhaps some experimental results?

You're quite right, and this is all covered in my various papers. The calculated classical prediction is for the "perfect" case, with the detectors such that the probability of detection is exactly proportional to the input intensity and the input from the polarisers emerges with intensity exactly complying with Malus' Law. In the situations in which the detection loophole pushes the local realist value up above the Bell limit, what must be happening is that either Malus' Law is not quite appropriate and/or the detector response is not quite proportional to the input intensity. The discrepancies, between them, cause the effective law to be not exactly Malus' Law, which depends on cos^2, but a slightly different one, in which the troughs of the cosine^2 curve are relatively wide. The same mathematics (Appendix C of http://arXiv.org/abs/quant-ph/9903066) then leads to higher visibilities for the coincidence curves.

You need, incidentally, to be very careful when interpreting the published figures. All will have been "normalised" in some manner,and some will in addition have had accidentals subtracted.

Anyway, if you read my various papers you will find that here and there I suggest how the experiments could be extended so as to give local realism a chance of showing its colours. It will make different predictions from QM if, for example, you vary the beam intensity and/or the kind of detector used. Before any actual figures can be predicted, the local realist model needs to be completed by inserting (empirically-determined?) functions to replace the assumed cos^2 terms. Even without any quantatitive predictions, though, we can make the qualitative one that the CHSH statistic will (other things being equal) increase as you decrease detector efficiency, decrease as you increase it.

Caroline
http://freespace.virgin.net/ch.thompson1/

vanesch

Jan12-05, 08:11 AM

Yes, but I think it best not to discuss SED here. It's best not to have any preconceived theory other than a general framework of local causality and a wave model of light. Both are, after all, supported by vast amounts of evidence.

Well, my viewpoint is exactly the opposite! If your aim is to show that, for specific setups, other explanations than the one given by QM is possible, I won't argue with this ; the scientific method doesn't, in any way, allow to say the opposite. Even if your claim is that experiments didn't rule out LR, I will agree with you, and even say that I don't care too much.
The scientific method requires you to have a theory that can spit out numerical predictions of measured quantities in experiments, and we have 1 such theory, namely quantum theory. If you want to propose something else, you must come up with a specific theory, and then we'll compare. First we'll compare with all established results where QM gave the right result, and see if your theory does the same. And, as I pointed out, there's a huge amount of data to be explained: spectroscopy of atoms and molecules, quantum chemistry, solid state physics (semiconductors, phonons...), optics, particle physics... Remember that ALL of this forms, within the framework of quantum theory, one single machinery. You should come up with a viable alternative, from which we can calculate predictions in all the above mentioned cases.

Yes, any challenge to QM means re-writing a great deal of physics, but I think it needs to be done. In optical areas I don't see it presenting any problem. Clearly when it comes to modelling actual particles there are going to be difficulties. I don't think they are insuperable, but, be this as it may, I think QM makes a big mistake in trying to apply the same theory to optics as it does to particles. Why not, as a start, just hive off optics from QM and return it to classical physics?

What do you win ? First of all, I'd say that the more you have a united view of the physical world, the better. But ok, let's go for it.

So you want to save local realism. You know that if you keep the superposition principle of quantum mechanics, you are going to have at least a theoretical problem (cfr Bell's inequalities and the quantum predictions, which are not limited to optics, or even to spin). So taking out electromagnetism still leaves you with exactly the same conceptual problem, with,say, electrons (which is, however, much harder to test experimentally).

There's no discussion about the wavelike nature of "particles" (electrons, ...)
I'm into thermal neutron stuff right now, and what we do all day is diffraction of neutrons on matter (crystals, soft matter etc...). So you will have to accept some wavy matter stuff a la Schroedinger. But single-particle waves will do fine for you. However, multiparticle superpositions are going to be inacceptable for you (they automatically lead to entanglement).
This gives you already a serious problem in the prediction of, say, the Helium spectrum, where there is a significant difference between the prediction of the lines with and without the so-called "cross terms". You'll have to find a way to find the results of QM, without using it, but using single-particle matter waves or something of the kind. In a similar way, the quantum prediction of binding and anti-binding orbitals in molecules (which works out very well in quantum chemistry) is entirely based upon entangled electrons.

You will object that this is microscopic, and that there, you can use QM. But then you have to explain me why you can use multiparticle superpositions there, and not when it menaces local realism?
Worse: if you go to solid state physics, you get massive entanglement of electrons, giving rise to most of semiconductor behaviour. So again, why can we use it there, but not when it doesn't suit you?

You are going to have one hell of a difficult task, and it is not sufficient to demonstrate that certain properties you don't like in QM might not be absolutely essential: you will have to put a hard alternative on the table and do the calculations. Personally, I'm so much convinced that it won't work that I cannot spend much time on that. But your mindset is different, so why don't you go ahead ? After all, if you find ways to do so, maybe they lead to calculations which are much easier than in QM, and maybe that opens up methods and techniques to tackle problems that are, today, too hard to solve through the QM way. So you would not only be famous, but you'd be also very rich: think of all the chemical and pharmaceutical companies that would like to use your faster molecular modelling !

Next step: electron-positron annihilation.
The only way people have found to reconcile:
wavelike behaviour of matter/lumpedness of matter (energy-momentum relationship)/pair creation-annihilation is a quantum field. Feel free to think up another technique. This is a honest challenge. People don't know - in the sense of being completely ignorant - of how to describe the behaviour of electrons in another way than with a quantum field. Maybe there are other ways, good luck.
Also, people have only found one way in which they can make interact a quantum field with EM, that is by considering EM also as a quantum field. If you do that, you describe very well e+/e- annihilation and all other particle interactions.

The problem is, that if you accept special relativity, that there is no difference between the gamma pulse that comes out of this annihilation and a light pulse in an optics system (doppler effect). So the description should be the same. But the description that works very well in the case of the e+e- annihilation, is quantum field theory so it is a logical inconsistency to set optics apart. IT IS NOT POSSIBLE TO SET OPTICS APART FROM THE REST OF PHYSICS.

Or you rewrite all of it, or you rewrite none of it.

This is science, so nobody stops you from doing so. Nothing is graved in stone. But you should realize the scope of the undertaking. I wouldn't bet on it, honestly.

The main reason for denying the photon is that I have never seen any evidence that it exists!

No, the main reason why you deny it is that it takes away all the amunition you can shoot on the loopholes of Aspectlike experiments, and you want to cling onto LR at all cost. You don't seem to have similar conceptual difficulties with, say, the chemical bond, or the quantum hall effect.
The evidence for the photon is that it is part of a theory which turns out to be successful in atomic and molecular physics, solid state, elementary particle physics, nuclear physics, and we haven't got the slightest bit of a clue how we could achieve a similar success without it. I repeat myself: nobody stops you from trying, as long as you realize on what adventure you embark yourself :smile:

I can't find any mention of these authors in arxiv.org so can't get hold of the paper without considerable effort. From what you say, though, it sounds as if it is no different from a number of other experiments, and I should dearly like to know just what beamsplitter they used.

You're right, it is such a cube. Have a look at their website
http://people.whitman.edu/~beckmk/QM/

Maybe you can propose them to change it for a half-silvered mirror.

I don't know quite what you mean here. There is not supposed to be any essential difference in the nature of light output by PDC from light produced by, say, a laser, if you look at just one or other of the output beams.

What I meant was the following:
the classical picture of the two photons coming out of a PDC is just a correlated pulse in intensity, and in fact, the only reason for using the PDC is to have a time correlation of the intensity peaks in both beams.
If photodetectors are just producing clicks with a probability given by the incoming intensity - socalled square-law detectors (the only way to match the photon count rate, and the classical intensity), and we consider classical waves, there can be two things that happen at the beam splitter:

or it splits the intensity in 2 halves (that's the classical description of a beam splitter), but that would mean that both photodectectors see the same intensity. Given a finite efficiency, none can click, one can click or both can click, and given the square law, the number of cases when both click is a function of the number of cases when one clicks. THIS IS NOT OBSERVED EXPERIMENTALLY.

or something funny happens, and sometimes the whole intensity is sent left, and sometimes sent right. So only one can click at a time. THIS IS OBSERVED. However, if the beamsplitter sends intensity pulses once to the right, and once to the left, then the same beamsplitter cannot give rise to any (classical) interference !! Nevertheless, interference has been demonstrated for these beamsplitters by every first-year student.

You cannot at the same time have an equal-intensity split that gives rise to interference, without, using square law detectors, also generating a very predictable number of double clicks. The very fact that this double click is absent illustrates that what is observed is a one-photon state that has no classical description.

Hans de Vries

Jan12-05, 09:54 AM

W Have a look at their website
http://people.whitman.edu/~beckmk/QM/

Experiments like the Quantum Eraser may turn out to be much
more effective in convincing people:

http://people.whitman.edu/~beckmk/QM/qe/qe.pdf

Switching an Interference Pattern on and off at one place
by manipulating a \lambda/2 Half-Wave plate at another place,
in another beam, that went the other way, to never to
go back to the place were the interference happens.......

Regards, Hans

Nereid

Jan12-05, 10:20 AM

To add one small comment to vanesch's post (and thanks to Dr Chinese for finding those 'old' threads): fortunately, eating an elephant is easier if you take it one bite at a time.

If Caroline (or anyone else) wants to develop an alternative, it may be sensible to start with something 'easy', and just do an OOM (a.k.a. back of the envelope) calculation. It's highly likely that if your favourite alternative doesn't come within an OOM or two, it won't work out when you do the detailed calculations ... best to avoid wasting more time on that; put it to one side, and try another. The good thing about OOMs is that they can often (usually?) be done in a day or two.

vanesch

Jan13-05, 03:05 AM

If Caroline (or anyone else) wants to develop an alternative, it may be sensible to start with something 'easy', and just do an OOM (a.k.a. back of the envelope) calculation. It's highly likely that if your favourite alternative doesn't come within an OOM or two, it won't work out when you do the detailed calculations ... best to avoid wasting more time on that; put it to one side, and try another. The good thing about OOMs is that they can often (usually?) be done in a day or two.

I am indeed absolutely in favour of that - it would be extremely exciting to see a working alternative. My personal problem with it is a problem of motivation: I'm so convinced that it won't work out that I cannot spend much effort on it. But people like Caroline, who are convinced that 99% of all physicists are deluding themselves since about 80 years now, should jump on the enormous occasion that presents itself to them. I tried to point that out. My intuition would be that any local realist theory would be computationally simpler than quantum theory, and if that is the case, it would be a revolution in computational chemistry, solid state physics and so on. Their methods would be monstruously more efficient. Think of the power of it, to model, say, macromolecules and their interactions!

However, they concentrate themselves just on arguing that "there might STILL be possibilities to develop alternatives" without presenting any. The only one I've seen is Stochastic Electrodynamics. This is essentially Maxwell's electrodynamics, together with the postulate that we are exposed to radiation which comes down to half a photon in each mode, and the argument that photodetectors are calibrated to "observe" what goes beyond this intensity. I know a bit about it, but before it can convince me, it should indeed first predict "basic" stuff where intuition says they will have difficulties, like with thermodynamics (given the huge flux of energy, how come that we don't boil off any glass of water in no time - probably naive, but these things should be addressed). I'm not very impressed with its success of demonstrating the ability to explore the efficiency loopholes in the Aspect like experiments, because _it has been invented for that purpose_. I would be more impressed if it shows that it fits in with the rest of physics.
Stochastic Electrodynamics, together with a classical Dirac field is supposed to supplant QED, and seems to make a correct prediction of the Lamb shift (Barut) (I didn't verify it) if you leave out the stochastic part :smile: ; however it doesn't even arrive at predicting the existence of the electron, and I challenged them to come up with the correct spectrum for Helium.

So we get a lot of blahblah on how there are still possibilities for local realist theories etc... but we don't get to see any that work! It is not even a matter of OOM calculations, there simply ISN'T any proposition of an alternative. Just an argument that its potential existance is not yet 100% ruled out yet. Big deal.

cheers,
Patrick.

Caroline Thompson

Jan13-05, 03:44 AM

I am indeed absolutely in favour of that - it would be extremely exciting to see a working alternative. My personal problem with it is a problem of motivation: I'm so convinced that it won't work out that I cannot spend much effort on it. But people like Caroline, who are convinced that 99% of all physicists are deluding themselves since about 80 years now, should jump on the enormous occasion that presents itself to them.

The classical explanation of actual "quantum eraser" experiments does not require any new model, once you've allowed for the properties of outputs from PDC sources. I have no theory of the physics of what goes on in a nonlinear crystal, but have reason to think that nobody else has either! I disagree with the Stochastic Electrodynamics explanation as well as with quantum theory. Can't we go back to the situation that existed 200 years ago when they first started trying to explain the polarisation properties of "iceland spar"? Various people had various ideas, which were discussed and tested. It was admitted that we did not know the truth!

Anyway, the absence of a satisfactory theory of the physics of the interaction of light with nonlinear crystals does not prevent us using them for interesting experiments. Instead of theory, though, we have to rely on the observed behaviour to find the empirical laws governing the output.

Unfortunately the quantum theorists have, it seems, from an early stage decided on their model and insisted on interpreting all that they see within this narrow framwork! This has led them into all sorts of apparent paradoxes, quantum erasers being just one of them.

My understanding of the properties of a particular class of PDC output -- that produced in the "degenerate case", when the frequencies of both "photons" are the same -- was initially a logical deduction from experiments on "induced coherence". The key properties are covered in:
Thompson, C H, “Rotational invariance, phase relationships and the quantum entanglement illusion”, http://arxiv.org/abs/quant-ph/9912082
and a paper I'm on the point of putting on my web site.

I think I'd better break off from PhysicsForum to do this! The paper is:
Homodyne detection and parametric down-conversion: a classical approach applied to proposed “loophole-free” Bell tests

Don't worry too much if you've never met "homodyne detection" before. If you haven't met parametric down-conversion, though, perhaps now is the time to remedy the situation!

Caroline
http://freespace.virgin.net/ch.thompson1/