the underlying assumptions rig the debate

Seems like you are dodging, and the reason is that to state that the past is not affected by future events could be interpreted to mean that once the past is determined, it is not affected by future events.Clearly, these men are stating the past "becomes" real based on present events. So why not make your position clear?Do you believe that, or not?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?So the simple fact is that at that point in time, the photon was acting more particle-like than wave-like and if measured, it would have shown no interference pattern. I assume you agree with that, but claim the path wasn't real or something, and if that is the case, then the fixing of the photon's path you refer to would only occur upon actual measurement, not whether it could be measured, and that is a major contradiction in your stance.Moreover, this sort of reminds me of the superluminal tangent, though more germane to this discussion than that. I quoted Zeilinger along with Mandel, Wheeler and others to show that they all agreed the past takes on definite form as a result of the way we measure it in the present. To this point, you have not really made it clear whether you agree with that or not, imo.Do you agree, or disagree with that?

What do you mean by indeterminate? The interference pattern shows a real interaction of wave-like propogation. It is real, and in our universe, correct? And it has measurable effects, right?Just because it is in superposition as a wave does not mean it isn't within our universe as real.

It's not ambigious at all. The way we measure a photon determines it's path, period, and that includes the path the photon already took.What don't you understand about that?If you want to say, like Wheeler and others, that the photon never took a path in the past until observed in the present, fine, but it still means the past is formed by the present.

Being "smeared" or however you want to describe it across all possible paths or in a wave-like manner is not the same as indeterminate. It's a determined path. It's just not a single path.To be "indeterminate", it would have taken no path at all, but merely exists as a potential to take all paths, and there would be no interference pattern as nothing would have occured.There are those like Wheeler that say the photon's path is indeterminate until observation, but once it is determined by measurement that the photon behaved like a wave, it is determined.I think you confused this a little.

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.

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.

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.

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.

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?

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.

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?

What kind of problems are you having? --AdminEdited by Admin, : Ask question.

[qs] Strictly speaking all we can say from the experiments is that what we see at the far end is what we would see if the photon had taken a single path.

[qs] Strictly speaking all we can say from the experiments is that what we see at the far end is what we would see if the photon had taken a single path.