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Author Topic:   the underlying assumptions rig the debate
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 31 of 246 (322713)
06-17-2006 7:48 PM
Reply to: Message 21 by randman
06-17-2006 6:40 PM


Re: Yes it's possible
Moreover, please don't misrepresent me
Believe me, I'm not. I would never try to. I have nothing to defend other than a true reading of QM because I hate the idea of readers and lurkers getting a false impression of what QM says. There is far too much BS on the web as it is, and if I can clean up one small patch, I will. I may not get paid to teach QM anymore, but old habits die hard.
You know full well I am not arguing causility isn't true
What you are arguing is that QM holds a mechanism where-by causality can be violated - "present events can affect the past" being such a violation.
I am simply pointing out that QM has no such mechanism.

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 Message 21 by randman, posted 06-17-2006 6:40 PM randman has replied

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 32 of 246 (322715)
06-17-2006 8:05 PM
Reply to: Message 30 by randman
06-17-2006 7:48 PM


Re: Yes it's possible
these leading scientists in their field
Are they? Can you provide support?
And shall we talk about misrepresentation and honesty?
which apparently you were attempting to be a part of
Do you understand the concept of "invitation"? And who said anything about these guys? They live in a quantum optics department!!! What the hell has that to do with me? The invite came from the author of reference [18], Professor Chris Isham, one of the foremost quantum gravity guys and also codeveloper of the decoherent histories approach to QM.
Do you want to try again?
And please don't quote New Scientist at me as some sort of recommendation. It's not exactly renowned for getting its facts straight.
The paper was released 28 months ago and how many citations does it have?
You also failed to make any comments on the math
No, and you wouldn't have a clue if I did. No one here (with the posible exception of some lurkers) would. So what's the point? I'm not objecting to their maths anyway, I just have some qualms about their logic and applicability. The fact that THEY HAVE NOT BEEN PUBLISHED tends to give some comfort that I'm not misreading the situation. Why do you think the paper has not been published?
There is no onus on me to spend valuable time explaining dubious papers to you.
There is an onus on me due to integrity and honesty to point out bogus and bullshit claims regarding my sciences.
Edited by cavediver, : No reason given.
Edited by cavediver, : No reason given.

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 33 of 246 (322716)
06-17-2006 8:08 PM
Reply to: Message 22 by randman
06-17-2006 6:50 PM


Re: general reply to all
randman in reply to PaulK writes:
So you are saying that a present can occur which there was no determinate past, but that when the present occurs, the past is then determined.
How is this not a demonstration that a present event can determine and thus have a causal effect on the past?
I may not be following PaulK correctly, but what he should be saying is that it isn't the past that changes, only the present. The collapse of the wave functions to a single possibility for each particle happens in the present, not the past. In the past the particles continue to exist in their superimposed state.
You see, the observation doesn't change the past so that from the outset of the original entanglement one particle had one spin and the other the opposite spin. Quantum theory experiments have established beyond any doubt whatsover that up until the observation both particles existed in a superimposed state.
In other words, the observation isn't revealing to us what state the particles were actually in. And it isn't retroactively changing the state in the past to what was eventually observed. Prior to the observation the particles existed in a superimposed state. This much we know for certain.
There's another perspective on this discussion. If your view were actually a valid conclusion of quantum theory then it would be famous and you would be able to walk into any bookstore and find book after book about it. It would be the basis of thousands of time-travel sci-fi stories.
But this supposed aspect of quantum theory isn't famous, and not even sci-fi writers have latched onto it (well, that would be expecting too much, probably some have). That's because you misunderstand the implications of entanglement.
--Percy

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Admin
Director
Posts: 12998
From: EvC Forum
Joined: 06-14-2002
Member Rating: 2.3


Message 34 of 246 (322717)
06-17-2006 8:11 PM
Reply to: Message 32 by cavediver
06-17-2006 8:05 PM


Re: Yes it's possible
cavediver writes:
And shall we talk about misrepresentation and honesty?
Please, no. I already noted to Randman that he should keep his discussion focused on the topic and not the people he's debating with.

--Percy
EvC Forum Director

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 35 of 246 (322756)
06-17-2006 10:45 PM
Reply to: Message 33 by Percy
06-17-2006 8:08 PM


Re: general reply to all
I may not be following PaulK correctly, but what he should be saying is that it isn't the past that changes, only the present. The collapse of the wave functions to a single possibility for each particle happens in the present, not the past. In the past the particles continue to exist in their superimposed state.
I think you are not fully appreciating what is occuring. PaulK referenced the delayed-choice experiments because they actually do demonstrate the exact opposite of your claim. They show that the inteference causing a collapse via their delayed-choice apparatus actually causes the particle to collapse prior to the measurement that causes the collapse.
Think of it this way. A particle is in superposition travelling for a thousand light-years, did it travel as a wave or particle? It actually travels as neither but as a possibility of either one state or another, as more wave-like or particle-like, but when it is observed, then it has travelled as one or the other.
And it isn't retroactively changing the state in the past to what was eventually observed. Prior to the observation the particles existed in a superimposed state. This much we know for certain.
Percy, you've got it wrong. Delayed-choice experiments show that, in fact, the observation or measurement affects the state the light travels in prior to the measurement.

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 36 of 246 (322757)
06-17-2006 10:49 PM
Reply to: Message 32 by cavediver
06-17-2006 8:05 PM


Re: Yes it's possible
Just hot air? I understand QM from experiments, and in that regard, working with quantum level optics is a good way to come up with hard data and experiments and so is nothing to be scoffed at by theorists.
The reason I asked you about the math was that they present their ideas from the math in that paper and thought you might can comment on it, but I think once you understand the concepts of entanglement, it is not so difficult to grasp the concept that entanglement can work over segments of time. You being so knowledgeable of GR ought to appreciate that if entanglement can work over vast spans of space instantly, that working over segments of time is not at all surprising.

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 37 of 246 (322758)
06-17-2006 10:50 PM
Reply to: Message 31 by cavediver
06-17-2006 7:48 PM


Really?
I am simply pointing out that QM has no such mechanism.
Really, what is the mechanism for entanglement then?

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Jazzns
Member (Idle past 3912 days)
Posts: 2657
From: A Better America
Joined: 07-23-2004


Message 38 of 246 (322760)
06-17-2006 10:54 PM
Reply to: Message 27 by randman
06-17-2006 7:23 PM


Re: QM
If it is determined then it is still linear. You only get only get another dimension of time if it is variable with respect to more than one parameter.
Also, if the past has or has not been determined is also an untestable phenomenon given our current understanding of the universe. Such a test as I said before would require an observation of time outside of time. Linear or not, the test for determination is currently impossible.

Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 39 of 246 (322761)
06-17-2006 10:58 PM
Reply to: Message 33 by Percy
06-17-2006 8:08 PM


some links
percy, here are some basic wika links related to the ideas here.
Wheeler's delayed-choice experiment - Wikipedia
In the double slit experiment, a photon passes through a double slit apparatus, in which the photon must pass either through one or the other of two slits, and then registers on a detector, which can determine where the photon reaches the detector, like an image projected on a screen. If one allows many photons to individually pass through either slit A or slit B and doesn't know which slit they passed through, an interference pattern emerges on the detector. The interference pattern indicates that the light beam is in fact made up of waves. However, if one somehow observes which of the two slits each photon actually passes through, a different result will be obtained. In this case, each photon hits the detector after going through only one slit and a single concentration of hits in the middle of the detection field. This result is consistent with light behaving as individual particles, like tiny bullets. The very odd thing about this is that a different outcome results based on whether or not the photon is observed after it goes through the slit but before it hits the detector.
In a quantum eraser experiment, one arranges to detect which one of the slits the photon passes through, but also construct the experiment in such a way that this information can be "erased" after the fact. It turns out that if one observes which slit the photon passes through, the "no interference" or particle behavior will result, which is what quantum mechanics predicts, but if the quantum information is "erased" regarding which slit the photon passed through, the photons revert to behaving like waves.
However, Kim, et al. have shown that it is possible to delay the choice to erase the quantum information until after the photon has actually hit the target. But, again, if the information is "erased," the photons revert to behaving like waves, EVEN IF THE INFORMATION IS ERASED AFTER THE PHOTONS HAVE HIT THE DETECTOR [all caps added in lieu of italics in original article].
....
How can this be? It would seem that the "choice" to observe or erase the which-path information can change the position where the photon is recorded on the detector, even after it should have already been recorded.
One explanation of this paradox would be that this is a kind of time travel. In other words, the delayed "choice" to "erase" or "observe" the which-path information of the original photon can change the outcome of an event in the past.
Delayed-choice quantum eraser - Wikipedia
Please note the reference to "the delayed "choice" to "erase" or "observe" the which-path information of the original photon can change the outcome of an event in the past."
An alternative is the many-worlds interpretation, of course, but even there, I think there are other experiments that show regardless of potentials for alternative, parallel universes, that the past is indeed affected by the present (such as just looking at more basic delayed-choice experiments or the thought experiments with entanglement and polarization).
Edited by randman, : No reason given.

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 40 of 246 (322763)
06-17-2006 11:03 PM
Reply to: Message 38 by Jazzns
06-17-2006 10:54 PM


Re: QM
You fail to consider the implications that in all likelihood, some aspects of the past and perhaps most of the past has been "determined" but if just small areas have not, introducing one or the other event in the past, changes the past and over time adds up.

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Iblis
Member (Idle past 3896 days)
Posts: 663
Joined: 11-17-2005


Message 41 of 246 (322774)
06-18-2006 12:08 AM
Reply to: Message 39 by randman
06-17-2006 10:58 PM


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

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 42 of 246 (322775)
06-18-2006 12:14 AM


the importance of entanglement
Just as a reference, for awhile here I have emphasized entanglement as a principle dealing with the 2-slit experiment and other experiments and at times have been derided for stating that, and specifically derided for saying the principle of entanglement has overshadowed the Uncertainty principle and to prevent those sorts of arguments in this discussion, I note the following, taken from a good historical overview of QM in some respects.
Leaving aside questions of non-local action for now, the fact remains that the phenomenon known as entanglement is a real feature of our world, whatever its exact nature. For some time entanglement was thought to be important only in very special circumstances, but in the last decade or so it has been shown to be much more important than was thought - it is in fact ubiquitous in quantum mechanics, the rule rather than the exception. It turns out, for instance, that entanglement seems to be necessary to explain the results of the classic Young’s Two-Slit Experiment17, which have traditionally (but erroneously) been explained in terms of Heisenberg Uncertainty.
http://fergusmurray.members.beeb.net/Causality.html

  
randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 43 of 246 (322778)
06-18-2006 12:19 AM
Reply to: Message 41 by Iblis
06-18-2006 12:08 AM


not misunderstanding "observe" here
I didn't get this from Wiki articles, but point these things out from those articles for the benefit of evos here.
Furthermore, I think you are focussing on the technical difficulties with building quantum computers to somehow reject 80 plus years of development of quantum theory and hard experiments. It is to be expected to be a challenge to build quantum computers, but one of the reasons they are trying is that current quantum theory suggests it is indeed possible. The very act of trying to do this, based on theory, shows indeed that you are wrong about what previous data from experiments have shown.
Moreover, it is simply too early in the process to claim technical difficulties with developing quantum computers are due to faults within the theory......in fact, it is way too early for that conclusion to even be mildly credible, and yet you present it as fact.
Edit to add you also make a common fallacy of claiming that somehow there is a misunderstanding of actual experiments with photons as wave or particle-like due to not "really knowing" the math. That's hogwash and shows a major misunderstanding of the real-world nature of these experiments. The experiments are not about math. math may be used to describe the experiments and make predictions, but they are an actual, real-world process, and to suggest otherwise is a stupendous error.
Edited by randman, : No reason given.
Edited by randman, : No reason given.
Edited by randman, : No reason given.

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randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 44 of 246 (322781)
06-18-2006 12:45 AM
Reply to: Message 41 by Iblis
06-18-2006 12:08 AM


more on delayed-choice experiments
At least three "delayed choice" experiments, which test what happens if the experimenter does not choose until the light is moving through the apparatus, have been done. Alley reported on one conducted with his student Oleg G. Jakubowicz. A group from the University of Munich and the Max Planck Institute for Quantum Optics in Garching, West Germany -- T. Hellmuth, Arthur G. Zajonc and Herbert Walter--did the other two.
....
So far, all three of these experiments support the conventional quantum wisdom that whether you make the choice before or after the event occurs, the effect of the choice is the same.
Questia
These experiments can be understood with or without the math.
Edited by randman, : fix quotation

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Iblis
Member (Idle past 3896 days)
Posts: 663
Joined: 11-17-2005


Message 45 of 246 (322789)
06-18-2006 2:24 AM
Reply to: Message 44 by randman
06-18-2006 12:45 AM


Re: more on delayed-choice experiments
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)

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