the underlying assumptions rig the debate

So Wheeler is an ignoramus as well, eh? Hmmmm....why don't you let me know when your name is in the encyclopedia for your accomplishments in physics. At least I know I am keeping good company.Britannica Does it? Those conducting the experiment disagree with what you claim is causing the interference pattern to appear or disappear. They didn't expect it to appear. They expect it to appear only if there is no way in principle to tell which way the photon went. But let's look at your explanation first. So you admit the delayed-choice works even before the choice is made?So let's hear Mandel's take on what has changed to affect the final result. http://www.fortunecity.com/emachines/e11/86/qphil.html#Zeilinger echoes this same observation: Home – Physics WorldIn other words, if we know, there is no interference pattern and if we do not know, the interference pattern appears. That's what these guys are saying, right?Edited by randman, : No reason given.

Percy, I suggest you read Iblis' last post, not because he agrees with me, but because of his derision of "Wheeler and his friends" who have the same view of what occurs in the 2-slit on his part in attacking their and my view because you guys, as usual, start off arguing no one in science agrees with or comes close to agreeing with the basic views I present, even though it is from these guys that I learned the science does show these things.It's not only arrogant of you and others, but it's wrong and offensive. These could be good discussions, if you treated them with respect and intellectual honesty. Instead you guys resort to things like deriding men like Wheeler as looney, and similar tactics, and yet none of you, not one, can adequately offer any other plausible explanation for what occurs in these experiments.I suggest you reread the quotes I provided from Wheeler, Mandel and Zeilinger and carefully consider what they are saying, not inserting some label of something you don't even understand, but actually consider what their claims are. They all claim that potential present knowledge affects what the past indicates, or put it another way, what occured in the past in our universe of experience. The photon's path is revealed in our universe of experience by what can be said about it.Until you take the time to learn what they are talking about, you are just blowing hot air.Why not take some time to see what they are talking about, and then we can have a much more fruitful discussion?fyi, Wheeler's quote again (hint: he quotes someone else in it) Wheeler takes Bohr's statement and takes it to a new level asserting that "you wouldn't have the stuff out of which to build the universe" without observer participancy. Now that conclusion may or may not be a stretch, but he has a good reason based on these experiments for stating it.The statement "No elementary phenomenon is a phenomenon until it is an observed (or registered) phenomenon," in the context of this entire quote about how the stuff that the universe consists of is made up of observer participancy is that the universe itself takes on real form only when it is an observed or registered phenomenon. I think some others were just saying no phenomenon is real, but Wheeler extends this to the building blocks of the real universe.So what does this mean in respect to the past and why make such outlandish statements? The reason is that
"the central point of the quantum" is that discrete form, physical reality, only occurs after observation, and this does include the past.Wheeler is the one that posed the original delayed-choice experiment as a thought experiment concerning a photon travelling from billions of light-years away. He specifically pointed out the conundrum of how the way we decide to measure the photon determines which path the photon took (in other words what the past was). Wheeler's solution to the causality here is to state the photon didn't exist until observation, and that's one perspective. I think cavediver even said: But he didn't elaborate.Wheeler is relying on the observation that how we observe the photon appears to dictate what path the photon took, and thus the past, indeterminate or determinate or however you want to look at it, is formed in part by the present potential knowledge (in the universe of our experience).Edited by randman, : No reason given.Edited by randman, : No reason given.

What do you mean by information we already have? Did you understand my question and analysis about the path of the photon at any particular stage.All that matters is whether the potential for knowing the photon's path is, right? So if someone can know it's path, it will indicate and have travelled in the universe of our experience on one path, right?But that same photon down the road if someone encounters it, and there is not the ability to determine it's path, then it will indicate in our universe a superposition and wave-like propogation, right?So the same photon can and does probably, along the same path, travel only a single path in our universe, and then later can have travelled all paths, and back again, and so forth, for as long as the potential AT THAT POINT IN TIME to know it's path changes.Do you understand that?

Please substantiate that. Where does he say "information is already fixed"? The quantum eraser shows the exact opposite, that information can be erased. Nope, not at all. You exhibit a major misunderstanding of what the quantum eraser experiment shows. It shows that indeed you can see a change in the photon's path back again; that once collapsed, the photon's path can become uncollapsed.And what is the determining factor? Whether we can know or not know it's path.Edit to add. Zeilinger in following the Copenhagen interpretation does indeed think in terms of the elementary particle have a Bit and so once spent, it is fixed. This is, of course, because he believes the there is an interaction somehow with the observer, which is why he makes the comments not just on a mechanical observer but suggests the importance of whoever operates the experiment.However, he does indeed think the past is formed by the present questions; the photon's path is determined by the observer's question, and so implies an actual connection between conscious observation and reality.I don't deny that this could be true and do believe there is a connection between consciousness and physical reality, but I'd have to hear him out on this a little more to agree fully with you.For example, what if the information is lost. Say the initial observers are all dead. Does the photon revert back to wave-like status in it's path?In the quantum eraser experiment, it is clear that if one were to measure the photon at one point, it would have travelled along one path. I think in the context of what I am talking about, you are not seeing the significance of that. Imo, the causal effect of the photon at that point in time, whether observed or not, is likely to be the effect of the photon in a collapsed state, and history at that point in time would reflect that. Now, you can say it is indeterminate, like Wheeler, but if you do, you are also stating that perhaps a great deal of the past is indeterminate.So when the photon enters a zone where at that point in time, it cannot be determined which path it took, the photon then will have taken all possible paths. Imo, the causal effect then is that in the past, it took all possible paths.So we see the photon taking over the same stretch of path different physical manifestations depending on the observer's ability to know the path.Moreover, are there any experiments that show someone measuring a photon without the one measuring the photon being able, even in principle, the photon's path? That would settle this issue between you and I here but may be hard to construct.For example, if your claim is correct, we should see some photons that never exhibit wave-like behaviour at all, and I don't think that is the case.Secondly, I am not sure Zeilinger beleives exactly what you think he does. I think you could be taking some things out of context. I read that paper and did not get that from him. It could, for example, that he beleives elementary particles can take on Bits somehow. So a collapsed photon for one observer could down the road be measured by another who has no way of knowing the photon's path before, and see the photon having taken all possible paths, even for the time period someone else measured it as a single path. If we are going with observer participancy, then this makes sense.Otherwise, why don't we routinely see photons directed at 2-slits pass through only one slit as a particle instead of a wave? The idea that once a particle collapses into one path so to speak, that this path is fixed and the photon thus never acts as a wave is not correct, imo.Edited by randman, : No reason given.Edited by randman, : No reason given.Edited by randman, : No reason given.

Percy, there is a wide variety of interpretations, which is why I tried to stress first what is observed in these experiments. If we can agree on that, and it's not so challenging to do that, then we could agree and disagree on the interpretations, but you guys seemed to refuse to agree on the process as seen from a human perspective, and that's frustrating. I didn't see enough grappling with the actual experiments here, but a lot of bashing me when I was presenting repeatedly what occured in the experiments, regardless of how you wish to interpret it.As far as uncollapsing a wave-function, it's not my claim. It's the claim of Mandel and others that did these experiments, and imo, it is demonstrated fact.

So in your view, if we send a photon towards 2-slits that has been measured before, it will not exhibit wave-like qualities?

It's a bad habit. Right after posting, I have more thoughts and try to do a quick edit before any responses and add more to it. Probably need to cut that out.

Well, let's consider the quantum eraser experiment or one of them. The photon passes through a polarizer and is measured and so takes on one path, but if we put a scrambler, a third polarizer in front of it, it will then revert back and take on the wave pattern.Now, I hear what you are saying. The 2nd run is with different photons and so you are saying if the photons were measured and then moved down and sent through some process so we couldn't determine what path they took from that point on, that they would stay in the single path mode and not show a wave pattern.Personally I disagree, but first let me point out that no experiment I know of has validated your idea here. It shouldn't be too hard to do, but it hasn't been done that I know of (maybe someone else knows of something?).But I want to ask you something. Do you really think the same photon arriving theoritically down the road to a different group of people is not going to show a wave-like pattern unless they too somehow devise a way to determine what path the photon took?Edited by randman, : No reason given.

The photon's path is a past event. You should reread your quotes of him you provided in context. He referred to the whole apparatus and experimenter, I believe, when he made the comments you referred to.Also, you need to go back and edit in the links. I have given a lot of links and people won't know what you are referring to. My quote of Zeilinger was where he believed as others such as Mandel that the determining factor in whether we observe a wave or particle path is whether we can know what the particle-path was. I think you have been reading him by some of your comments, and glad to see that, but at the same time, I am not necessarily agreeing with all of his ideas. The basic idea of what the criterion is based on experiments that others agreed with as well is my point.Imo, if that criterion is present, the photon's path will appear to take only one path and in our universe, we shall see no interference pattern, and at that point the photon will have an impact as having taken one path. But if that criterion is not present, then the photon will not have taken one path and the interference pattern will be there as a real effect in our universe.Now the question is if down the road someone observes a photon without being able to know even in principle the path, then the photon imo will have taken all possible paths even if someone in the past could and did measure the photon's path. Why do I think this?Because the simple criterion is whatever at any point in time can be known of the path, that will be the way the photon behaves. If at any point in time, it becomes not possible to know the path a photon took even in principle, then the photon will have taken all possible paths even if in the past it took only one path. The criterion changes and so does the path (at least in the universe of our experience).

Wrong. First, Zeilinger, Wheeler and Mandel and others all agree that the criterion for whether the photon behaves as a wave or particle is whether can know the path; what we can know about it. That was my point in quoting Mandel and Zeilinger on this point.Now, do all these men agree on everything? No, they do not, but they agree on that point and it appeared you did as well.The experimental data supports that point, namely that at any point in time that whether the photon behaves as a wave or particle depends on whether in principle we can know it travels in a single path like a particle. If that is not determinable at that point in time, then it travels like a wave taking all paths.So if the same photon, based on this principle, at any point in time can be determined to travel along a single path, it will travel along that path. But if at a later point in time, it cannot be determined what path that same photon took even in principle, then it will have taken all possible paths even if in the past situation it took only one path.That's what these experiments show. Now, if you want to say there is some limiting factor, go ahead, but they are not seen in experiments relating to quantum mechanics. You have to apply classical mechanics, and frankly, you just don't have any evidence or experiments to support your view on the quantum level.Edited by randman, : No reason given.

Note: PaulK, please supply the link for people reading.So in your view, what is the criteria for whether we see the photon travel in superposition, taking all paths, or whether we see the photon travel on only one path?I think before we go any further, we need to establish this first, and then we can assess when such instances occur with that criteria or not. For example, you state: But you offer no reason as to why. What is the criteria here? So then you are admitting that the past path is determined by a present event in some instances? Percy thinks you can't possibly believe that, even though you have stated it repeatedly.One problem with your belief here in indeterminacy of the superposition is that it creates an interference pattern in the here and now. Do you think prior to observation that the photon's path is not real, as some think such as Wheeler, or do you think the photon's path changes as a result of observation?

So PaulK, are you are admitting that the past path is determined by a present event in some instances?Or are you just saying Zeilinger believes that?What is your position here?Edited by randman, : No reason given.

One problem though you keep ignoring is that information can change back again.I think you are also failing to realize that regardless of whether Zeilinger's theory in connecting QM to information theory is correct and regardless of whether your reading of him is correct, he is still stating that the past path of the photon is determined by the present. That is still the past being determined by the present, at least in the universe people live in.Now, you have made the argument, and did so before quoting Zeilinger, that this does not change the past because the past is indeterminate, but the path when in superposition does reveal an interference pattern, right? So it has real world effects.How do you resolve this?I will come back to Zeilinger and information exchanges later, but I think you don't realize that either way, the past path is determined by the present, and so we see the past in some sense being shaped by the present in QM.

Well, I give you Werner Heisenberg, and yes, it is all over the Net. http://www.physicsnow.net/history/heisenberg/p08c.htm Page not found | American Institute of PhysicsThis last quote is sort of interesting from a human perspective as well. Edited by randman, : No reason given.

But is the past path of the photon determined by the present, or not?"Future events", btw, is less clear than talking about the present affecting the past. I think concerning this question, we should be precise.So your answer....?Edited by randman, : No reason given.