the underlying assumptions rig the debate

I think I have been very clear on my position.

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Also, reviewing and thinking about Zeilinger's theory, I think he does believe that once the Bit of information is spent, even if not observed by a conscious observer, that the photon remains in the collapsed state, but I am not sure how he reconciles that with the quantum eraser experiment and think this is a logical error because along it's path in the quantum eraser experiment, the photon though unmeasured by people could have been measured and we know from earlier experiments that it would have showed a collapsed state, right?

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The reconciliation is that the bit is not "spent" until the photon's state is measured. Only when the information becomes available through measurement does the state collapse. I've quoted Zeilinger to that effect more than once in this thread.I suspect that you are wrong about the experiments - but I'll wait for you to produce the actual experiments so we can see if they are inconsistent with Zeilinger's ideas.i

So what percentage of particles do you think have been "measured"?I would think a very tiny percentage such that it is statistically equal to 0, right? So that would mean essentially almost all particles have never been measured, and so nearly all particles have yet to be determined, right?I hope you can see where this is going.....

PaulK, maybe this can help some as far as clarifying Zeilinger's views. You said: But that's not what Zielinger says. This is what he says. So if at any point in time, you could have determined the path of the photon, the interference pattern at that point in time would have disappeared. It doesn't hinge on actual measurement, and it doesn't matter if the technical possibility is there, as far as Zeilinger is concerned. This is the larger quote for your reference. http://www.physik.fu-berlin.de/...ikationen/RevModPhys99.pdfNow you claim Zeilinger says that this collapsed state is fixed once it occurs, right?I am not sure if that is what he believes or not, but let's look at that idea. In the quantum eraser experiment, there is a point in the photon's path where we could determine it's path, and so at that point, it's path was a single path. There is no question on that, as you don't have to actually measure and the previous run of the experiment showed that at this stage a photon will act like a particle.But, if the photons are then sent through a scrambler such that at a later date (the third polarizer being placed AFTER THE INITIAL ones), the experiment shows an interference pattern emerging. This conclusively shows a change in the photon's path as first particle-like and then wave-like.The way some get around this is to claim that the photon didn't take any path until observed. The problem though with removing the conscious observer from the experiment is that the photon was initially "observed" by the equipment and that would have indicated a single path and later observed by equipment to take all paths.This is a fundamental problem and the reason QM is considered strange. You cannot easily dismiss it.Edited by randman, : No reason given.

It could mean: By measuring the photon, we gain knowledge of what the path was in the past.It could also mean: By measuring the photon we cause it to have taken a particular path in the past.Those are two quite different meanings.

No, it cannot mean that. The way the photon is measured dictates the way the photon behaved (note past tense). Yep.There is a question though, but you didn't hit it. Does the measurement change what the photon did (say from wave-like to more particle-like in it's path), or did the photon only exist as a probability for one or the other and so there is no path until measurement.

I hope that we can agree that it is unlikely that Zeilinger is contradicting himself in a single paper, and that we should look for a plausible resolution.I think that the answer is in this piece I quoted earlier Now if the experimental apparatus does not include a detector which could register the path before the quantum eraser removes the information that would let us determine the path, then the path is not available from the experimental apparatus. So I don't think that "in principle" refers to what we could do if we changed the experimental apparatus - because the apparatus affects the results.I do think that the "in principle" refers more to the latter part - to the need to completely destroy the information that would let us perform the measurements - even if it requires an ideal system beyond our current technological capabilities (perhaps beyond any practical capability).So I think that you have miunderstood what Zeilinger means by "in principle""

Well, if we reading this collapse as only occuring when tied to an experiment, then what about the nature of the real world where the vast majority of things have never been subjected to such experiments? Without setting up a detector apparatus, there is no way then to tell what path the photon took, and hence in this view, no observation.Are we to assume that this is all a mirage, an indeterminate state?It seems to me that regardless of how you look at this, it still comes back the OP's point that the past is indeed mutable. Keep in mind some claim that these quantum effects fall away when interacting with other particles, the macro-world, etc,....but an experiment demonstrated that 2 entangled particles stayed entangled even after being shot through a sheet of gold. So clearly entangled particles can retain that entanglement more than people thought in the past. Page has gone | New ScientistEdited by randman, : Made a mistake and also added reference.Edited by randman, : No reason given.

I never said that things collapse "only when tied to an experiment".

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It seems to me that regardless of how you look at this, it still comes back the OP's point that the past is indeed mutable.

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At this point I can only note that you hvae tried quite hard to avoid discussing the sort of mutability required by the OP. From the last two posts it appears that the past is mutable only to the extent that the information required to reconstruct it is unavailable even with unlimited technical resources. Zeilinger asserts that the information that we have is immutable. If the past can only be changed in ways that do not affect the observed present then the OP is not correct at all.e

PaulK, you wrote this: So in your view, based on this statement, you believe he is saying the photon does not collapse until the detector is set up.That does not help your point at all because if the collapse only occurs when we can determine what path the photon took by having a detector set up, then almost no photons have ever collapsed at all.If you are saying that if via interaction, the photon does collapse, then the photon would have collapsed in the quantum eraser experiment without the detector being present (especially since at that point there is no way for the photon "to know" the detector would be present). The photon passed through a polarizer and so should be collapsed at that point (if real). But when the scrambler was put in place, the formerly collapsed photon then becomes uncollapsed.Zeilinger does talk about the need to consider the whole phenomena only after the whole experiment is conducted, but you fail to realize the implication of that. What appears to be said then is that the photon doesn't take any path at all, but only becomes IN THE PAST at the end of the experiment, and so the basic conundrum of QM remains. The present measurement affects the past path.Edited by randman, : No reason given.

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So in your view, based on this statement, you believe he is saying the photon does not collapse until the detector is set up.

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I understand him as sayign that the photon will not collapse unless the apparatus is capable of measurign the path or if it leaves the path information determinable in principle after the photon leaves the apparatus.

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That does not help your point at all because if the collapse only occurs when we can determine what path the photon took, then almost no photons have ever collapsed at all.

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The reasoning appears to be absent. If it is true that most photons are in a superimposed state how would it hurt my point ?

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If you are saying that if via interaction, the photon does collapse,then the photon would have collapsed in the quantum eraser experiment without the detector being present

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Not so. If I understand Zeilinger correctly only interactions that would let us determine the path would collapse the state. The eraser prevents such an interaction from happening by destroying the information that would permit such an interaction to happen.t

You earlier defined an uncollapsed state as being indeterminate. Now, I don't happen to agree with you since I think both the wave-like and particle-like paths are determined paths. Indeterminate would be to say no path was taken until observation, and that is what some physicists do say.But let's look at both propositions. First, if the path is indeterminate until someone sets up a detector that can determine a single path, then essentially all of pasy reality is indeterminate, right?If you say the photon took no path until observation, it is still the case that the past is determined by the present, right?

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You earlier defined an uncollapsed state as being indeterminate. Now, I don't happen to agree with you since I think both the wave-like and particle-like paths are determined paths. Indeterminate would be to say no path was taken until observation, and that is whatsome physicists do say.

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To explain again, when I say that the path is indeterminate I mean that the wave-like behaviour is the result of the photon being "smeared" across all possible paths. (i.e. it is in a superposition of states where the states are the possible paths, rather than being in a single determinate state).

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But let's look at both propositions. First, if the path is indeterminate until someone sets up a detector that can determine a single path, then essentially all of pasy reality is indeterminate, right?

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Provided by "most of the past" you mean insignificant details like the exact path followed by individual photons. It doesn't mean that anything important is indeterminate. Remember that according to Zeilinger if the information needed to reconstruct any past event has not been completely eradicated then that event is immutable.So it seems as if there is no real hope for your OP here.The more so since, more than 200 posts later, you haven't dealt with the philosphical and theological issues I raised in my first post to this thread.s

So you believe the photon travels as a wave until there is some means to determine a single path, and then it takes a single path, even if the measurement takes place after the photon has taken the path.How is this not a change in the past? It moves from a superposition state to a single state, right? That is a change, correct? Why? Isn't the world we live in made up of particles? If those particles have never been measured, according to your analysis, they can change in the past still because they are "indeterminate".PaulK, every stance you have taken is inconsistent with observed reality. You err by calling superposition indeterminate first off, but regardless, you admit that the path changes from a superpositional state to a collapsed state and that this is retroactive. Your admission proves my point.Edited by randman, : No reason given.

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So you believe the photon travels as a wave until there is some means to determine a single path, and then it takes a single path, even if the measurement takes place after the photon has taken the path.

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No, I mean that the particle is "smeared" across all possible paths unless there is information that would restrict it to a single path.

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How is this not a change in the past? It moves from a superposition state to a single state, right? That is a change, correct?

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As I keep having to repeat it isn't the sort of change required by the OP.

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PaulK, every stance you have taken is inconsistent with observed reality.

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That certainly isn't true.

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You err by calling superposition indeterminate first off

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To claim that something in a superposition of states is in a single state would be a contradiction. Therefore it is wong to say that I "err" in rejecting such a view. If a particle is in a superposition of states it is because it is not in a single determinate state - it can only be described in terms of the probabilities of the various states in the superposition.

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...but regardless, you admit that the path changes from a superpositional state to a collapsed state and that this is retroactive. Your admission proves my point.

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I woul say that your refusal to defend the claims in the OP, instead settling on this lesser claim which I haven't disputed proves MY point. The claims of the OP lack scientific support. Or more specifically, to go back to the point which started this discussion of QM, it is reasonable to reject your views without rejecting quantum entanglement. Thus your claims of inevitable victory have been shown to be hollow and unfounded.
o

PaulK, you have stated that the particle is in a superposition, smeared as you say, until some observation and then it collapses to a single state. The experiments you have referenced show that even when the means of detection is at the end of the process, the photon before the detection still has collapsed into a single state.You explain what happens then, PaulK. How does a later measurement affect a prior path?