Copenhagen interpretation of Quantum Theory

vanesch

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setAI said:
not according to Deutsch- the Copenhage interpretation predicts that in Deutsche's experiment the photons would appear at BOTH detectors at the end- MWI predicts just the right detector- and this was experimentally confirmed-
This is what I don't understand: as I said, if you put the Heisenberg cut in Copenhagen/von Neumann far enough back (say, at the level of the person looking at the result of the quantum computation), then both are equivalent in their predictions, so I don't see how "Copenhagen" can predict anything different from MWI, UNLESS it is a specific version of Copenhagen where certain systems are declared being "classical" which turn out not to be so.

But the point is: MWI cannot be "somewhat" true. If it is "true up to a certain level of macroscopicity" then it is a form of Copenhagen !

Let us not forget that there are as many "Copenhagen" flavors (with DIFFERENT empirical predictions) as there are ways to put the Heisenberg cut (meaning: different ways of defining what are "measurement apparatus").
If you say that photons are "measurement apparatus" then you have a version of Copenhagen that is easily falsified because any interference experiment would do so.
If you say that "atoms" are measurement apparatus, but not photons, then optical interference is predicted, but not, say, Stern-Gerlach experiments.
If you say that not atoms and photons are measurement apparatus, but only buckeyballs, or golf balls, or humans or ... then you make these "Copenhagen" flavors come closer and closer to MWI predictions.

So when you say something about "Copenhagen predicts this, and MWI that", it is necessary to say WHAT FLAVOR of Copenhagen predicts this (in other words, what has been declared "measurement apparatus" in the given flavor). And it is sufficient to remove the culpable object from the list of "measurement apparatus" to find out that we have now a *different* prediction of Copenhagen.

In fact, von Neumann said that we have to put the Heisenberg cut "far enough" so that it doesn't make any difference anymore: if you do so, you will NEVER find a disagreement with MWI's predictions.
 

ZapperZ

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Hey vanesch,

Would you consider the Penrose proposal[1] of superposition using mirrors involving 10^14 atoms as a "macroscopic" interference and thus, extending this cut off? Or is this cut off not defined by the scale of coherence but rather the "interacting" system?

Zz.

[1] W. Marshall et al., PRL 91, 130401 (2003).
 
setAI said:
as the reference to the poll indicates- it is MWI- since this poll the MWI has been experimentally verified http://www.quiprocone.org/Protected/Lecture_2.htm - since around the year 2000 the Everett interpretation has been confirmed as the only EXPERIMENTALLY VALID interpretation of QM- all other [non multiverse[ interpretations no longer fit with observations- as a result we now have the field of quantum computers- which are only predicted and described by the Everettian MWI-
I read this out to my colleague at work and he laughed? Which I'm glad about because frankly, I've always seen MWI as a complete cop out, with no real way of obtaining proof of alternate realities, I find it hard to believe someone has, who knows I may read the link later so I can really giggle myself hoarse.

I'll also have to remember that becasue of MWI the researchers can get to grips with quantum computing, theres me thinking it was because of mainstream physics? I may have a basic understanding of physics and the various interpritations but I certainly favour the two slit proofs over some science fiction novelists wet dream.:biggrin: Tell you what get me to send myself a postcard from the other universes and if I get it I'll believe this hocus pocus.:tongue:
 

vanesch

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ZapperZ said:
Hey vanesch,

Would you consider the Penrose proposal[1] of superposition using mirrors involving 10^14 atoms as a "macroscopic" interference and thus, extending this cut off? Or is this cut off not defined by the scale of coherence but rather the "interacting" system?

Zz.

[1] W. Marshall et al., PRL 91, 130401 (2003).
Didn't read your reference (I'm pretty busy for the moment). I take it you allude to one or other variant of the Felix experiment.

The point Penrose was trying to make was: from the moment that gravity becomes an appreciable interaction (even ever so tiny), "collapse" would occur. Mind you that we don't have any counter example! Even in "macroscopic" quantum phenomena such as superconduction, with a big number of involved degrees of freedom, the gravitational difference between the different terms in the superposition is entirely neglegible.

Now, the problem I see is that from the moment we try to put something in a superposition, such that the contributing terms are gravitationally different, we usually have already so many other interactions going on that the different terms decohered, and no quantum interference is possible.

So Penrose wanted to put an object (the mirror) in a quantum-mechanical superposition of positions, such that it would count for a tiny gravitational difference, and in such a way that no decoherence occurs otherwise. Not much of course! Probably not even measurable. A mirror in superposition would reflect a photon differently than a mirror in a mixture, and his experiment is designed in such a way as to find out the difference between the two kinds of reflection, by showing an optical interference pattern or not.

But I'm somewhere affraid that - apart from the difficulty of doing the experiment in such a way that no decoherence happens by "trivial" means, I'm affraid that his setup misses the point. Because if it is true that the two different mirror configurations in the superposition have different gravitational contributions, then THROUGH GRAVITATIONAL INTERACTION, they will get entangled with other stuff (say, some air molecule or something). Now, as one cannot "shield" gravitational interaction, I don't see how one can avoid this entanglement to take place, and hence how decoherence TRHOUGH GRAVITY will be avoided.

Now, Penrose's a much smarter guy than I am, so he must have thought of this. But I never saw an account that dealt with the problem.

It is a bit as if one wanted to show that EM charge destroys superposition, and one wants to put a 1 microCoulomb object in a superposition of two positions at 10 cm apart. It is almost sure that no interference effect will be observed, because I don't know how you can avoid a 1 microcoulomb charge not to interact (and hence entangle) with something else. And there's more hope for the charge, because there's maybe a shielding technique using superconductors or so ; something that is not available for gravitational interaction.
 
2setAI,

just so you know - THERE ARE NO EXPERIMENTS, which confirmed "mutliverse" interpretation.
 

DrChinese

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quddusaliquddus said:
I'm sorry guys. You lost me ages ago. Are there major conclusions about QM that all the interpretations agree on?
I think most of them would match your #2: That no greater description of reality is possible in principle. This covers Copenhagen and MWI, as well as the Relational and Transactional interpretations at this time. There are attempts being made to identify experimental opportunities to distinguish these. You can see from the comments above that there has not been any breakthrough to date that is generally accepted.
 
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ZapperZ said:
1. The VERY FACT that one can conduct A POLL on this means that the acceptance of some form of interpretation of QM means it is still A MATTER OF TASTE! Real physics isn't done this way. You cannot simply adopt something and call it physics when all you can base it on is PREFERENCE! So by the very act that you are citing A POLL of OPINIONS shows CONCLUSIVELY that this is NOT a done deal! Don't you see this?

If you don't believe me, show me any other part of accepted physics that is done via such a popularity contest. Did the acceptance of BCS Theory of Superconductivity done via such a similar poll? Or was it simply based on an astounding body of evidence?

I believe that some part of the physics procedure is governed by preferences. Looking at reality is not an action which has only one way. Reality is constructed by our way of looking at it instead of captured simply.

Some examples may be pointed out as for example, the pseudo vectorial character of some electrical concepts.
 
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vanesch said:
The reason is that in order to get an indication of the validity of MWI, that one needs to put in superposition, and show interference, of VERY MACROSCOPIC systems
Hi vanesh,

I miss your point in this quote. Could you help me with a little precision?

Also, I dont understand some things about the MWI. I'm sure you will easily help me.

First, I'm not sure it is a universe of what that split under a measurement. Is it a universe of matter? Is it a universe of possibility? Is it a universe of experimental prediction, of phenomenon, of events? What is the definition of a universe in the MWI?

Secondly, my understanding of the MWI make me think that a proponent of it has choosen between these two possibilities:
1. We add a universe (of something) in our theory in order to eliminate the measurement problem.
2. We remove a part of the wave function (the collapse) in order to explain the experimental fact.

I'm interested, if these two points are not stupid, in an argument that point towards number 1. I dont know why, but at this moment, I prefer to choose to remove the little part instead of adding the gigantic one...



Thank you very much for your help, and the help of anyone else interested,


Tipi
 
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Ok, I have read your (very nice) posts https://www.physicsforums.com/showpost.php?p=1012700&postcount=9".

Some points are clearer, but I still dont get what is a universe. Suppose (like in Bohmian Mechanics) that we have more than one point in the configuration space, each point representing the state of the object under consideration and the state of the observer corresponding. Since we have different point, we have different "observations". These different observations come from different what?

Do I have many body, one corresponding to each point? Do I have only one body and many-minds, one mind for each point? Or do I have only one body and one mind, but many universe, one corresponding to each point?

Are these choices only a matter of taste?

Thanks,

Tipi
 
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I have a question that I'm confused with. It's about the delayed quantum eraser experiment [http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm].

According to Copenhagen interpretation, wouldn't the superposition of the second photon collapse at every interaction it has with the measuring apparatus? That would be, with the PS, BSA, BSB and the "eraser" BS. And yet, if the quantum information of the which path information is lost, it would seem to us that the photon went thru both slits; even tho it had to interact with the beam splitters to get to the eraser.

The result is consistent with the HUP, but for me this seems to be a failure of the copenhagen interpretation... unless I'm confusing something.
 
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setAI said:
the Copenhagen Interpretation hasn't been 'dominant' for many years -

“Political scientist" L David Raub reports a poll of 72 of the "leading
cosmologists and other quantum field theorists" about the "Many-Worlds
Interpretation" and gives the following response breakdown [T].

1) "Yes, I think MWI is true" 58%
2) "No, I don't accept MWI" 18%
3) "Maybe it's true but I'm not yet convinced" 13%
4) "I have no opinion one way or the other" 11%

Amongst the "Yes, I think MWI is true" crowd listed are Stephen Hawking
and Nobel Laureates Murray Gell-Mann and Richard Feynman. Gell-Mann and
Hawking recorded reservations with the name "many-worlds", but not with
the theory's content. Nobel Laureate Steven Weinberg is also mentioned
as a many-worlder, although the suggestion is not when the poll was
conducted, presumably before 1988 (when Feynman died). The only "No,
I don't accept MWI" named is Penrose.

The findings of this poll are in accord with other polls, that many-
worlds is most popular amongst scientists who may rather loosely be
described as string theorists or quantum gravitists/cosmologists. It
is less popular amongst the wider scientific community who mostly remain
in ignorance of it.” http://www.anthropic-principle.com/preprints/manyworlds.html



non-local interpretations of QM have been shown to be unphysical: http://arxiv.org/abs/quant-ph/9906007
It seems a little rich to associate Gell-Mann with Many Worlds, since he helped develop the Consistent Histories formalism.

EDIT: Just noticed how old the poll was. Still, though, it's worth noting that he's evidently changed his views significantly.
 
know this thread is damn old but anyway...
none of you guys remembered to mention 1997 poll where Copenhagen won and minor 2000 one when MWI was last:smile:
 
for everyhting else i do not know but i do know that the part about matter well electrons effecting other across the universe is possible its known as "string theory"
I found a website that says:

"The still-dominant "Copenhagen interpretation" of Quantum Theory developed by Niels Bohr, Werner Heisenberg, Wolfgang Pauli, and others says two basic things:

1. Reality is identical with the totality of observed phenomena (which means reality does not exist in the absence of observation), and
2. Quantum mechanics is a complete description of reality; no deeper understanding is possible."


Is it true that the "Copenhagen interpretation" of Quantum Theory is the dominant theory?

And is number 1 and 2 true?

Is it also true that the 'rules' of the Universe seem to change reflect the 'maths'.

Is it also true that Non-Locality (defined as phenomenon that occurrences on one side of the Universe can instantly effect 'matter' on the other side of the Universe) happens? (Im not sure if 'happens' is the correct word to use here.
 
also i beliave in the many worlds theory but the many minds theory im not sure about its true we all exist on a certain level of consciousnees but could they be altered or many for that matter who knows
 
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Interesting... In MWI, or "pure" QM + decoherence any measurement, in principle, can be "undone" (even it is difficult to do). Hence, it can be experimentally proven that CI is wrong.
 
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I have a question that I'm confused with. It's about the delayed quantum eraser experiment [http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm].

According to Copenhagen interpretation, wouldn't the superposition of the second photon collapse at every interaction it has with the measuring apparatus? That would be, with the PS, BSA, BSB and the "eraser" BS. And yet, if the quantum information of the which path information is lost, it would seem to us that the photon went thru both slits; even tho it had to interact with the beam splitters to get to the eraser.

The result is consistent with the HUP, but for me this seems to be a failure of the copenhagen interpretation... unless I'm confusing something.
Delayed choice experiments are no problem for Copenhagen, because in Copenhagen a measurement is only a measurement after macroscopic amplification. Once the choice is delayed, we conclude that the measurement in the Copenhagen sense is delayed too.

Ilja
 
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Any theory or interpretation can be valid forever, if it is not limited by the number of assumptions.
Ptolemeus geocentryc system can be valid now if we admit ANY number of epycircles and other parameters.
Copenhagen interpretation can be valid forever, if it is not limited by the number of assumptions.
 
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Good point... Copenhagen is a total mess of epycircles :)
Macroscopic systems built from microscopic particles. At the same time properties of these microscopic particles are defined based on the macroscopic measurements. Dead recursion, no hope for any axiomatisation. Fuzzy definitions for 'what is macroscopic'? 'what is a measurement'? what is a 'knowledge?' Epycircles everywhere :)
 
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The Copenhagen Interpretation is a "for-all-practical-purposes" interpretation (and an interpretation nonetheless). It simply takes into account that if we don't have the experiment or other sustainable proof for it, then it is left to interpretation; and for the most part, since the Quantum Theory works out very well, "for-all-practical-purposes" we may leave the question to interpretation for the time being.
 
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As i know there are many other interpretations.
For example Plank - De Broigle interpretation (zpe/zpf: see Google search). Even Shroedinger equation can be deduced from this interpretation (De Broigle wave is Doppler shift of vibrating particle in zpf).

I always interpreted spontaneous emission as induced emission in zpf and it was very useful for quantum calculations :)

And by now Copenhagen and ZPF interpretations give equal numbers :)
 
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SixNein

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the only interpretation of QM that succesfully predicts quantum computing is the MWI- Deutsch has DEFINED quantum computation as computation accross parallel universes-

the experimental evidence of quantum computation- specifically independant CNOT operations carried out in parallel on single photons- physically demonstrates the MWI- and demonstrates that non-multiverse interpretations are unphysical- according to the leaders of the field-

as I have said before- this is all rather recent- but I guarantee you within 5-10 years the physical verification of the MWI will be in all the texbooks- from that point Copenhagen and Hidden Variable interpretations will only be historical footnotes-

Qunatum Mechanics IS the physics of parallel universes
I thought that MWI caused problems with quantum computation because of quantum decoherence?

Doesn't this research show an objective reality? Also doesn't MWI reject an objective reality?
http://www.sciencedaily.com/releases/2009/03/090304091231.htm
 
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On the contrary, MWI is one of few interprettions where wefunction is REAL
Regarding Hardy's experiment there is nothing new except the experimetal part of it
About "I thought that MWI caused problems with quantum computation because of quantum decoherence?" - I dont know what you are talking about, but there is no known way to tell one interpretation from another, so if it would 'cause problems' then there will be a way to do it -> Nobels prize :)
 
I don't accept that the MWI is a necessarily favoured alternative to the Copenhagen interpretation,and I would like to hear how others view Cramer's Transactional interpretation and also the Bohm alternative.
 

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