the underlying assumptions rig the debate

You still aren't really understanding quantum mechanics at all. Part of it is wiki's fault I guess, they have oversimplified to the point of inanity. This is one of the dangers of trying to reduce complex math to simple English, the words don't mean what we want them to mean, they become technical terms with a very rigid limited application. But most of it is just wishful thinking on your part.Here's the actual math and technical details for the truly gifted
System Unavailable I'm going to stick with the wiki, because I'm a bit of a dolt myself.First the original experiment, and why you are misunderstanding words like "observe":

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In the double-slit experiment, the common wisdom is that the Heisenberg Uncertainty Principle makes it impossible to determine which slit the photon passes through without at the same time disturbing it enough to destroy the interference pattern. However, in 1982, Scully and Druhl found a way around the position-momentum uncertainty obstacle and proposed a quantum eraser to obtain which-path or particle-like information without introducing large uncontrolled phase factors to disturb the interference.

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Here's more detail about this less-direct method of "observation" that could conceivably not be directly destructive to the waveform

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After the photon goes through slit A or B, a special crystal (one at each slit) uses spontaneous parametric down conversion (SPDC) to convert the photon into two identical entangled photons with 1/2 the frequency of the original photon. One of these photons continues to the target detector, while the other entangled photon is deflected by a prism to bounce off a mirror some distance away.

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Do you get this? In the course of determining the particles behavior, we have split it in two, reflected half of it in the opposite direction, and arranged to measure things in a particular order. Depending on which thing we measure LAST, location (the particle) or speed (the wave), the previous measurement becomes impossible and therefore is said to have been "erased". There is no actual knowledge of the previous "measurement" EVER.This isn't something that happens over a measurable period of time, with results printing out somewhere, and some scientist deciding to read them or burn them and getting different results depending on what he decides. It is all a singular event, the "past" in question is merely the order of measurements, and the "measurements" themselves involve massive amounts of screwing with the little entities involved.This is why we can't use this trick to transmit information faster than light for example, we can't force the entangled photon on our end to be a 1 instead of a 0, and therefore insure that the one on the other end turns out to be a 0 instead of a 1.All we can do is kill him, cut him open, find out what he was, and thereby know what the other one must have turned out to be. And it isn't truly that the "observing" made him that. It is rather more like having twin brothers, one of whom has had his appendix out and the other who hasn't. After the autopsy, you know which brother is still alive even if he isn't there to be x-rayed.All quotes from the same place you got yours, Delayed-choice quantum eraser - Wikipedia

No, you still aren't getting it at all; and yes the reduction of the math to English is partly to blame.You have the idea, from the very simple summary given in your link, that the photon is entering the apparatus, then the experimenter is making a conscious choice in his brain, reaching out and touching some sort of a button which makes the mirror pop up, and thereby changing time backwards so that the photon entered by only one slit instead of two. This simply isn't true, our neurology isn't fast enough to do this kind of thing.The "choice" referred to in the article is the mirror popping up. This is preprogrammed, it has to be. The tricky part is that the order of events is such that the photon is generated BEFORE the mirror is in place. Conventional wisdom says that the photon enters either through one slit, or the other, or perhaps even both. The final measurement then is extrapolated backwards to determine which of these 3 possibilities are true.What the experiment proves is that conventional wisdom is WRONG. The photon is always a wave, it is always a particle, it always enters through both slits, it only proves itself to be a particle AFTER it has demonstrated in one way or another that it is also a wave.All we are doing with these experiments is controlling where the waveform collapses. If we let it hit the wall without screwing with it, it collapses there and provides a measurable interference pattern. If we screw with it before that, it collapses then and is already behaving as a particle when the final measurement takes place.Do the double-slit experiment with sound, sound turns out to have been a wave. Do it with normal light, light turns out to have been a wave. Do it with a single photon, without screwing with it, that single photon turns out to have been a wave! (That was the original really shocking part.) The collapse we cause by interfering with it midway through causes it to "turn out to have been" a particle. All along? No. Only from the point where the interference took place and the waveform collapsed.Come up with a way to stick up two walls, one after the other, the first sees the waveform collapse (the interference pattern) and the second doesn't. This last hasn't been done yet exactly, it's still technically impossible, if someone does manage to do it and the results turn out differently than expected, it is quantum theory that will have to be revised, not our conception of causality.* I'm not saying the past isn't changing all the time, by the way. I'm just saying we will never know it if it is. That's what makes it the past. If we set up an experiment to change the past, and did, it would have always been whatever we changed it to. From our point of view the experiment would fail, because we wouldn't remember what the original past was that we have now changed, we would have all along been trying to change this new past, and it would look like we hadn't.(Oh, and a side note to cavediver: shoe's on the other foot now, huh)

One small part of the problem is that the word "entanglement" is being used 2 different ways in the array of sources being appealed to. I'm going to try to get around this by using capital-E Entanglement in reference to the new theory that is gently replacing Heisenberg's Uncertainty Principle and lowercase-e entanglement in reference to the phenomenon which is covered by both, but which the experiments are showing is covered best by the new, in that the results seem to reduce the old to nonsense.IF and only if Heisenberg were a complete picture of the phenomenon of entanglement, these experiments could be said to break causality and send information backwards in time. Seeing as how this is manifest nonsense, for the simple reason that we couldn't catch it happening if that was the case, and whatever is happening is in fact observable, the Uncertainty Principle is being supplemented / replaced by what is presently being referred to as Entanglement theory in honor of the phenonomenon that is doing the work of breaking the old paradigm. Yep, that's me carefully selecting which inanities I'm willing to be reduced to in order to cover a specific point. A more accurate analogy would be one guy who can somehow be in two places at once, who is mistakenly believed to be twins, and doctors who are surprised that when one "twin" has his appendix out, the appendix of the "other twin" also seems to have disappeared. (An even more accurate analogy would be if the "twins" or manifestations of the single person were too small to see, too fast to see, seemed to appear and disappear at will, and had to be operated on with scalpels that were already cutting away at them while the operating table was still empty.)Here's the main deal though. The mistaken, bad, wrong assumption playing out here is that entanglement involves two separate entities, thought of as classical particles, which retain a specific causal relationship due to some prior relationship. The reality is that they are not separate entities at all, they are different ends of the same waveform. I'm just saying, if I ever have to teach a class, I'm going to call on the guy who has his shoes on backwards, because it appears to be more educational for the general audience when we correct answers that are dead wrong than when we try to improve on someone who mostly has it right already

No, we have a waveform with some aspects of a particle which can only be trapped once in any given point-event. No, the waveform propagates, collapses, sings hymns to itself, whatever it may be imagined as doing, at exactly C. It always behaves like a wave, it always takes all potential paths, if we make it impossible to measure any path but one then it appears to behave merely like a particle, this appearance was once believed to have some bearing on reality, these experiments prove that it does not. Dead wrong. If this were true, if it could be true, then Entanglement wouldn't be replacing Heisenberg as the cutting edge of QUIP research. The action taken at any single point in the waveform simply makes other previous actions irrelevant and immeasurable. Categorically false. The photon only appears to behave like a particle if we prevent all wavelike aspects of its behavior from being observed. The same is true of sound, it could be (mistakenly) proven to be a particle if we block one of the slits.Let's say you have two speakers on your stereo, and you turn one off. Now you have mono. That's your fault, writing the stereo manufacturer and saying he ripped you off would be fraud.Here's an example of what I mean by fraud. Let's say someone "proves" that the moon is not made of green cheese. They do it by pointing out that cheese ferments and produces noxious chemicals over time, and life on earth would have been destroyed by these chemicals somehow.Capitalizing on the language being used to overthrow Heisenberg to promote false ideas about science and theology is ethically equivalent to selling gas-masks to protect the general populace from deadly moon-fumes.

Thread still exists, you just had trouble measuring it for a minute.I won't be repeating myself though, "categorically false" is where I stop. The answers to your pointy questions are contained in my previous posts and revolve around what an "interference pattern" actually consists of.Good luck with that misrepresentation-by-proxy tic you have developed

I don't believe I have stood on any points which are not fully documented in the reference I provided in my first post. But if there are any aspects of the assertions I have made that do not seem to follow directly from the math, or even from a rational reading of Wiki's attempt to express the math in verbiage, then I will be happy to paraphrase the posts in which I have covered this material in such a way as to make it clearer. Please just let me know, I don't have any intention of undermining the debating system here but I am also not responsive to whining and loophole-surfing.In the meantime, as a gesture of good faith, I will resubstantiate my base argument with a different reference

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III. Misconceptions regarding measurement

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7. "The 'collapse of the wavepacket' involves (or permits) faster-than-light communication."

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This misconception frequently comes up in connection with Bell's theorem [9], and it almost always involves an implicit acceptance of misconception 3. If permitted to grow unchecked, this misconception can do enormous harm. For example, Larry Dossey [12] invokes this misconception to "explain" faith healing at a distance.

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An analogy to electrodynamics helps students here. In the Coulomb gauge, the electric potential at a point in space changes the instant that any source particle moves, regardless of how far away it is. This does not imply that information moves instantly, because electric potential by itself is not measurable. The same applies for wavefunction.

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8. "Measurement disturbs the system."

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In more detail, this misconception holds that each particle really does have definite values for both position and momentum, but these definite values cannot be determined because measurement of, say, a particle's position alters the value of its momentum. (It is related to the idea of a classical picture underlying quantum mechanics mentioned in item 6.) This is a particularly common misconception because some arguments due to Heisenberg ("the gamma ray microscope") and Bohr can be interpreted to support it. It is another attractive idea rendered untenable through tests of Bell's theorem[9].

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(This idea is also shown to be incorrect through "quantum eraser" arguments, as in reference[14].)

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http://www.oberlin.edu/physics/dstyer/TeachQM/misconnzz.pdf

No, not exactly. I'm sorry, I realize some of the language I've used to describe this process could lead to that conclusion. It's not really a bad model, certainly better than this backward-in-time delusion, but it still implies that the photon is sometimes a particle and sometimes a wave, which is basically what the experiments disprove. It gets even worse when you realize that the ALWAYS a particle / ALWAYS a wave language I would be happy to replace it with is still technically false. What it actually is is a waveform, thats a unit of energy which has some of the properties we associate with a standing wave and some of the properties we associate with a solid particle.If you are really trying to follow this argument then I guess the best thing I can do is to delve into what an "interference pattern" actually consists of. Randy is depending on his audience not knowing this part for a bit more than half his points; he's essentially making the argument that because an interference pattern was the original proof that light is a waveform rather than a substance, therefore all waves must produce an interference pattern under all circumstances, and anything that doesn't is de facto not a wave.Let's go to the beach first, and watch ordinary water waves crashing together. When two crests meet, we end up with a single crest quite a bit higher than either original wave. Same with two troughs, we get an even deeper trough. These kinds of combinations are examples of constructive interference. On the other hand, when a crest meets a trough, we get a much smaller crest or a much shallower trough, depending on which wave had the most variance from the median. This is an example of destructive interference. Notice we havent specified any pattern yet?Now let's find some nice still water somewhere and chuck a couple of pine cones in at the same time near one another. We are making our own systems of waves, so that we can watch the troughs and crests meeting one another and engaging in both constructive and destructive interference at once. This produces a particular kind of pattern, consisting of nodes (destructive interference) and anti-nodes (constructive interference), viewed in this case as ovals and lines. Unlike the waves that make them up, the nodes and anti-nodes don't seem to move around much, this is called a standing wave pattern. Notice that the phenomenon is caused by waves meeting one another and ends as soon as we run out of waves to meet and feed the system?Now we are ready for the Young Double-Slit experiment. This is how we prove that light is more like a wave than a stream of particles. If we set up a bulletproof closed box with two slits in the front, and shoot at it with a machine-gun for a while, and then open it up, we find that the bullets that make it through the slits impact the back wall in two places, one behind each slit. On the other hand, if we use a big firehose to spray colored water at it, we find that the waves of water split when they hit the slits but recombine on the other side, and this recombination, consisting as it must of both constructive and destructive interference, leaves a nice pattern of nodes and anti-nodes in the single area affected on the far wall.Now, if instead of all this wacky stuff we just shine light through the two slits, light being a wave, we get not two images on the far wall but one, and that one has lines of light and dark to it representing the constructive and destructive interference caused by the wave, which is split into two by the slits, recombining. This isn't terribly surprising as we already know light is a wave. It doesn't prove that the wave does not consist of particles either, remember we used water waves to set this standard and they do consist of particles. The machine-gun fire is the odd man out here, because the little individual bullets never form a wave.No, the surprising part is if we contrive to send one single quantum of light at the slits. If it is a particle, it will have to go in one slit or the other. And if it isn't, then what the hell is it? Turns out it too is a wave. We know this because as long as we leave both slits open and allow the recombination to happen naturally, we get an interference pattern on the far wall. This is, kind of novel, in that all the natural waves we can measure at the beach or in our stereo or wherever move through something, little particles wacking into one another and imparting energy which is what is getting passed on in the wave. Light consists of energy doing this same phenomenon without any medium to be passing through. The photon is not, as we might have hoped, the medium by which energy is passed on, it's just the absolute smallest standing waveform that can exist in a universe shaped the way ours is.This really annoyed the quantum physicists. It's like finally cracking open some sort of puzzle box and discovering there is another box inside the same size. First of all, obviously, another box is bad enough. But worse that that, the same size!?! How can it be the same size and still fit inside the other box? The photon is exactly like this. When we split it, we get two photons of the same size but half the frequency (twice the wavelength.) This is how waves behave, not particles. How can the smallest consistent unit of something not be a particle of some kind? What the hell is this stuff made out of, then?So they tried to trick it. The original quantum-tricking double-slit experiment consists of sticking an arrangement of telescopes or cameras or polarizers or detectors of some kind into the box. Note that these are solid objects, the only solid in the path before this was the back wall. Anyway, it tricked them right back! With these additions to the experiment, the photon no longer produces an interference pattern on the back wall. This is said to "prove" that it is only a particle under these circumstances. This is about the point where Wheeler and his buddies get a little paranoid. It appears to know, whether we are looking at it, or not!!!So they tried to trick it again. This is where the delayed-choice comes in. At the point in time where the photon is theoretically either passing through both slits or else just one, the detector array is not yet in place. It snaps into place just before the photon or photons would be arriving at either one or both sides of the detector, well before the back wall where the interference pattern either would or would not be displayed.If we hold on to the classical idea of a particle either splitting in two or not splitting in two, with the additional fetish that it knows we are looking at it when we are looking at it, it should be split at this point, having traveled in through both slits, and we should be able to catch it being in two places at once. But no, it doesn't leave an interference pattern under these circumstances either. It appears to know, that we are going to be looking at it, before we actually do!!! Wheeler basically stops doing useful math at this point and begins building analogies out of party games where his guests conspire together to cheat him into thinking he knows things he doesn't. Very sad, and also super-funny Adding in the "quantum eraser" solves the whole problem quite handily though. If we intentionally split the photon, so that we are quite sure it is going through both slits, and then pop up the detector array, it still doesn't produce an interference pattern on the back wall. It then becomes rather obvious what is happening. The interference pattern only appears as a result of the recombination of the split waveform, this only happens once during the experiment. Without the detector, it happens at the back wall. With the detector, it happens where? At the detector. On one side. Giving the impression that the waveform is sometimes a particle, even though it never is.I'm sure this has been hard to follow, so now I'm going to oversimplify even more. If we block one of the slits, the interference pattern disappears. This does not prove the waveform has become a particle, it just proves it never had to recombine. It doesn't make any difference whether the slit is blocked when we generate the photon, what matters is whether it is blocked when the waveform tries to go through it. Exactly WHEN the blockage occurs doesn't effect the final result. What does effect the final result is exactly WHERE the recombination takes place. Interfering with the process before the wall is equivalent in result, but not in technique, to blocking one slit. Either way, there will be no interference pattern back there.The final proof will be in the pudding though. The next step is to see if we can come up with a way to measure the interference pattern AT the detector. Based on the current logic, it should be there. But we don't know how to see it without stopping the wave. Actually stopping the wave will certainly produce the pattern though, which will tell us nothing. We need to come up with some way to stop it and not stop it at the same time. In order to do this, or at least keep doing stuff like this, we need for the public to invest big gobs of money in particle accelerators and supercomputers and time for us to use them and stipends to buy us whiskey. Seeing as how most of this gibberish isn't really interesting to investors as is, we use catch-phrases like "teleportation" and "quantum computing" and "superluminal" to keep them excited. But we draw the line at bad theology (Yes I know, still reduced to inanities in the end. But at least these don't paint an intentionally false picture of the realities of Quantum Mechanics.)