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Author Topic:   Quantum physics: Copenhagen vs decoherence interpretations
randman 
Suspended Member (Idle past 4899 days)
Posts: 6367
Joined: 05-26-2005


Message 1 of 57 (468785)
06-01-2008 4:05 PM


I found an old NYTs article to be interesting on this subject....
To further highlight the weirdness of the Copenhagen view, Einstein and two of his Princeton colleagues constructed the E.P.R. (Einstein-Podolsky-Rosen) thought experiment. Let an atom spit out two particles, which then fly apart for an enormous distance. The physics equations tell us that the two particles must have opposite spin: if one is ''spin up,'' the other must be ''spin down.'' But according to the Copenhagenians, the particles have no spin state at all until observed. So now we observe one particle and find, say, that it is spin up. We have thus ''resolved'' the spin state of a particle that allegedly had no such state until we made the observation. But that means that the other particle, millions of miles away, suddenly ''became'' spin down. How did it know that its state was now supposed to be spin down?
Logic would seem to dictate that the particles actually had spin states all along. Einstein took that position, postulating that some underlying, causal agency must carry the spin. In other words, the spin state is not decided at the moment of observation after all, as Bohr claimed, but was in the particles to start with. But there is no evidence that any such mechanism exists. Theories like Einstein's are therefore known as ''hidden variables'' interpretations, since they propose the existence of something hidden in the quantum systems.
Since the Copenhagen view rejected hidden variables, the question remained at an impasse for decades. Which interpretation a given physicist preferred mainly depended on which seemed less repugnant, the hidden variables theory or spooky action at a distance.
Then the Irish physicist John Stewart Bell thought up an experiment that would decide whether hidden variables exist, as Einstein believed. The experiment, which involved obtaining the statistics of large numbers of photon interactions, was not technologically feasible when he proposed it in 1964. But in the 1970's Bell's experiment was performed, first by John Clauser and Stuart J. Freedman at Berkeley and later by Alain Aspect and his colleagues at the University of Paris. The verdict was clear: there are no hidden variables of the sort Einstein envisioned. Quantum physics really does exhibit nonlocality.
.....
Despite Bohr's posthumous defeat of Einstein, the Copenhagen interpretation is on the wane.
One reason is that theorists have begun to apply quantum physics to the study of the origin and early evolution of the universe -- and unless you believe in some Robert Service-like devil amid the flames, it's very difficult to imagine that observers existed in the fireball of the Big Bang, as the Copenhagen interpretation requires. A popular approach nowadays is to replace the concept of observation with that of ''decoherence,'' an interference among particles that resolves quantum systems into one or the other of their complementary states. The jury is still out on decoherence, but neither its success nor its failure will do much to rescue the Copenhagen interpretation from its wider difficulties.
Scientists, curious souls that they are, are growing tired of being told by the Copenhagenians, Don't ask. ''We've always had people who say you can't ask this or that question,'' remarks Marlan Scully, whose experiments on quantum weirdness at the University of Arizona and Germany's Max Planck Institute have led to prototypes of a new, more efficient form of laser. ''And yet these questions are so natural that we are led to ask them. As Eugene Wigner used to say: Well, why can't I ask? What will happen to me if I do?''
Weirdness Makes Sense - The New York Times
note also....
The distinction is demonstrated by a simple test that the physicist Richard Feynman called ''the experiment with the two holes.'' To run the experiment, punch two small holes in a sheet of steel, fire a stream of photons or other quanta at the sheet and record what comes through, using a detector of some sort on the far side of the steel sheet. (The detector can be something as simple as a sheet of photographic film.) When both holes are open, the detector records an interference pattern -- the signature of interacting waves. Drop two stones in a pond and an interference pattern appears where the waves intersect. Wave peaks reinforce each other where they coincide, as do valleys, and where a wave peak intersects with a valley, the two cancel each other out. In the two-holes experiment, the interference pattern appears even if you send only a single photon through the apparatus: the photon finds its way through both holes and interferes with itself. Close one hole, however, and the photon's wavelike behavior disappears. Now it acts like a bullet: either it emerges from the single open hole to register a point impact on the detector, or it misses the hole and hits the steel sheet, and nothing comes through.
The weird thing is that the photon does this -- responds to whether one or both holes are open -- instantly, even if you wait until the last moment, just before it reaches the steel sheet, before deciding to close one hole or leave both open. It is as if the particle (or wave, whichever you prefer) were everywhere at once, feeling out the entire setup and responding to it instantaneously, everywhere.
Bohr explained the wave-particle duality by declaring that subatomic systems don't have either of their complementary states until they are observed. This view came to be known as the ''Copenhagen'' interpretation of quantum mechanics, named for the city where Bohr and his colleagues set up shop. It might be summarized as ''Don't ask, don't tell.'' Are photons particles or waves? Don't ask! They are neither -- or they are both. Their complementary states are only resolved, one way or the other, by their being observed.
Edited by randman, : No reason given.

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Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 2 of 57 (468795)
06-01-2008 4:31 PM
Reply to: Message 1 by randman
06-01-2008 4:05 PM


Your reason for presenting this information?
I'm not sure if this belongs in the "Coffee House". I'm not even sure this belongs as a topic at at all.
As it currently sits, it seems to be somewhere in the vicinity of being spam.
Why did you post this stuff?
Adminnemooseus

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Replies to this message:
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 Message 5 by randman, posted 06-01-2008 4:56 PM Adminnemooseus has replied
 Message 9 by randman, posted 06-02-2008 1:02 PM Adminnemooseus has not replied

  
Admin
Director
Posts: 12998
From: EvC Forum
Joined: 06-14-2002
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Message 3 of 57 (468800)
06-01-2008 4:45 PM
Reply to: Message 2 by Adminnemooseus
06-01-2008 4:31 PM


Re: Your reason for presenting this information?
I think Randman is trying to resume discussions he's had in the past concerning the views of various physicists like Wheeler, Zeilinger and Feynmann on quantum theory. These kinds of discussions have usually taken place in the [forum=-2] forum in the past, though not exclusively. Maybe move it there?

--Percy
EvC Forum Director

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Adminnemooseus
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Posts: 3974
Joined: 09-26-2002


Message 4 of 57 (468801)
06-01-2008 4:53 PM


Thread moved here from the Coffee House forum.

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


Message 5 of 57 (468803)
06-01-2008 4:56 PM
Reply to: Message 2 by Adminnemooseus
06-01-2008 4:31 PM


Re: Your reason for presenting this information?
Seemed appropiate to the Coffee House as views on quantum non-locality didn't fit any particular forum, though you can tie into the Big Bang stuff (article does that)....but reason for posting it was to discuss non-locality, not the Big Bang per se.

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 Message 2 by Adminnemooseus, posted 06-01-2008 4:31 PM Adminnemooseus has replied

Replies to this message:
 Message 6 by Adminnemooseus, posted 06-01-2008 5:26 PM randman has replied

  
Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 6 of 57 (468813)
06-01-2008 5:26 PM
Reply to: Message 5 by randman
06-01-2008 4:56 PM


Re: Your reason for presenting this information?
The "Coffee House" in generally a place for non-science and non-religious themes. The "Big Bang..." forum seems to be the catch-all for things physics.
Now, your reason for presenting the information in message 1?
Adminnemooseus
Edited by Adminnemooseus, : Change ID.

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 Message 5 by randman, posted 06-01-2008 4:56 PM randman has replied

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 Message 7 by randman, posted 06-01-2008 7:31 PM Adminnemooseus has replied

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


Message 7 of 57 (468827)
06-01-2008 7:31 PM
Reply to: Message 6 by Adminnemooseus
06-01-2008 5:26 PM


Re: Your reason for presenting this information?
Guess you didn't catch it: to discuss non-locality.

This message is a reply to:
 Message 6 by Adminnemooseus, posted 06-01-2008 5:26 PM Adminnemooseus has replied

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Adminnemooseus
Administrator
Posts: 3974
Joined: 09-26-2002


Message 8 of 57 (468922)
06-02-2008 12:43 PM
Reply to: Message 7 by randman
06-01-2008 7:31 PM


Re: Your reason for presenting this information?
In my all powerful opinion, you have not justified the starting of this topic. So far your input is a couple of properly attributed cut and pastes without any real commentary from you, which is not much above the posting of bare links.
Had this been started in the "Proposed New Topics" forum, I would not have promoted it as presented. Unless you contribute some personal input on why this topics theme should be a discussion item in this forum, it is going to be closed down. Maybe your topic starting privileges should also be suspended.
No replies to this message, or you are permanently suspended. Reply to your message 1.
Adminnemooseus

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


Message 9 of 57 (468926)
06-02-2008 1:02 PM
Reply to: Message 2 by Adminnemooseus
06-01-2008 4:31 PM


Re: Your reason for presenting this information?
The thread topic relates to varying views of non-locality which is the intent and topic of this thread. The reason for putting it in the Coffee house forum is that quantum non-locality is a physics question which albeit may have applications to the EvC debate or the Big Bang is offered not for those purposes but simply to discuss the varying views of non-locality.....for example, the article discusses the difference between decoherence which does not require a conscious observer with the Copenhagen interpretation. Many others view the Copenhagen view as including both conscious observers and decoherence or non-conscious observers. The article also brings up other ways to discuss QM such as the transactional and Many World hypotheses.
By reviewing such things, it becomes clear that the observance of non-locality in our space-time perspective is indeed real and a fact that must be wrestled with to properly understand the basic laws of the universe.

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 Message 10 by cavediver, posted 06-02-2008 1:59 PM randman has replied

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


Message 10 of 57 (468935)
06-02-2008 1:59 PM
Reply to: Message 9 by randman
06-02-2008 1:02 PM


Re: Your reason for presenting this information?
it becomes clear that the observance of non-locality in our space-time perspective is indeed real
What do you mean by non-locality?

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 Message 9 by randman, posted 06-02-2008 1:02 PM randman has replied

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


Message 11 of 57 (468941)
06-02-2008 2:52 PM
Reply to: Message 10 by cavediver
06-02-2008 1:59 PM


Re: Your reason for presenting this information?
I thought the meaning would be fairly clear. Here is a wiki article's description.
In physics, nonlocality is a direct influence of one object on another, distant object, in violation of principle of locality. In classical physics, nonlocality in the form of action at a distance appeared in corpuscular theories and later disappeared in field theories. Action at a distance is incompatible with relativity. In quantum physics nonlocality re-appeared in the form of entanglement. Physical reality of entanglement has been demonstrated experimentally [1] leading to its application in quantum cryptography and quantum computing.
Nonlocality - Wikipedia
I am specifically referring to the principle of entanglement which by the way is verified by experimental observation and predicted by quantum mechanics.

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 Message 10 by cavediver, posted 06-02-2008 1:59 PM cavediver has replied

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 Message 12 by cavediver, posted 06-02-2008 3:20 PM randman has replied

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


Message 12 of 57 (468949)
06-02-2008 3:20 PM
Reply to: Message 11 by randman
06-02-2008 2:52 PM


Re: Your reason for presenting this information?
I thought the meaning would be fairly clear. Here is a wiki article's description.
That Wiki description is anything but clear, and desperately needs rewriting.
I am specifically referring to the principle of entanglement which by the way is verified by experimental observation and predicted by quantum mechanics.
Yes, as an ex quantum physicist, I am fully aware of entanglement. But you were talking about non-locality. Entanglement and non-locality are not synonymous. And you say earlier that
the observance of non-locality in our space-time perspective is indeed real and a fact that must be wrestled with to properly understand the basic laws of the universe.
Well, entanglement is embedded in our basic laws of the Universe, is well understood, and requires no wrestling. So what is it about 'non-locality' that needs to be wrestled with?

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 Message 11 by randman, posted 06-02-2008 2:52 PM randman has replied

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


Message 13 of 57 (468952)
06-02-2008 3:30 PM
Reply to: Message 12 by cavediver
06-02-2008 3:20 PM


Re: Your reason for presenting this information?
Did you read the article? Apparently, a great many quantum phycists "wrestle" with this. This is another article saying the same thing in Science magazine.
The early quantum physicists dealt with this unreality by saying that the "is"--the fundamental objects handled by the equations of quantum theory--were not actually particles that had an extrinsic reality but "probability waves" that merely had the capability of becoming "real" when an observer makes a measurement. This so-called Copenhagen Interpretation makes sense, if you're willing to accept that reality is probability waves and not solid objects. Even so, it still doesn't sufficiently explain another weirdness of quantum theory: nonlocality.
In 1935, Einstein came up with a scenario that still defies common sense. In his thought experiment, two particles fly away from each other and wind up at opposite ends of the galaxy. But the two particles happen to be "entangled"--linked in a quantum-mechanical sense--so that one particle instantly "feels" what happens to its twin. Measure one, and the other is instantly transformed by that measurement as well; it's as if the twins mystically communicate, instantly, over vast regions of space. This "nonlocality" is a mathematical consequence of quantum theory and has been measured in the lab. The spooky action apparently ignores distance and the flow of time; in theory, particles can be entangled after their entanglement has already been measured.
On one level, the weirdness of quantum theory isn't a problem at all. The mathematical framework is sound and describes all these bizarre phenomena well. If we humans can't imagine a physical reality that corresponds to our equations, so what? That attitude has been called the "shut up and calculate" interpretation of quantum mechanics. But to others, our difficulties in wrapping our heads around quantum theory hint at greater truths yet to be understood.
Some physicists in the second group are busy trying to design experiments that can get to the heart of the weirdness of quantum theory. They are slowly testing what causes quantum superpositions to "collapse"--research that may gain insight into the role of measurement in quantum theory as well as into why big objects behave so differently from small ones. Others are looking for ways to test various explanations for the weirdnesses of quantum theory, such as the "many worlds" interpretation, which explains superposition, entanglement, and other quantum phenomena by positing the existence of parallel universes. Through such efforts, scientists might hope to get beyond the discomfort that led Einstein to declare that "[God] does not play dice."
Just a moment...
On your beef with non-locality, it is a standard term in the literature when discussing entanglement which is a form of non-locality. I would have thought you were aware of that. Just googling with no particular paper in mind, this came up. There are numerous other papers that reference non-locality in respects to entanglement.
Are you claiming they are incorrect to do so?
Experimental test of quantum nonlocality in three-photon Greenberger-Horne-Zeilinger entanglement
Experimental test of quantum nonlocality in three-photon Greenberger—Horne—Zeilinger entanglement | Nature
Edited by randman, : No reason given.

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


Message 14 of 57 (468958)
06-02-2008 4:23 PM
Reply to: Message 13 by randman
06-02-2008 3:30 PM


Re: Your reason for presenting this information?
Did you read the article?
Not to be flippant, but my knowledge of what quantum physicists think of non-locality and entanglement comes from having been one and having spent numerous years amongst others, many with far more knowledge and talent than I possess... I don't need to read popular press articles to understand my own world, thank you.
On your beef with non-locality
I'm sorry, what beef would that be? My concern is that you do not understand the terms you are using, as evidenced by your swapping and changing from non-locality to entanglement, and back again. And evidenced further by your choice of topic title...
it is a standard term in the literature when discussing entanglement which is a form of non-locality
Of course it can be mentioned, but that does not make the terms interchangable...
Experimental test of quantum nonlocality in three-photon Greenberger-Horne-Zeilinger entanglement
Yep, another 'ta-da' experiment showing that experimental quantum mechanics does indeed behave just like us theorists say it should. Great. Next?
Cutting to the chase, the simple fact is that no form of 'non-locality ' exhibited by quantum mechanics allows for superluminal transfer of information, leaving causality intact. Or from your layman's position, are you suggesting otherwise?

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 Message 13 by randman, posted 06-02-2008 3:30 PM randman has replied

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


Message 15 of 57 (468961)
06-02-2008 4:32 PM
Reply to: Message 14 by cavediver
06-02-2008 4:23 PM


Re: Your reason for presenting this information?
If you are interested in discussing the topic, please do so. Merely repeating your resume is not discussion, nor are baseless insinuations somehow I am ignorant of non-locality.
In fact, it seems you are the one with some beef using that term in discussing entanglement, which is standard within the literature. You also falsely accuse me of saying non-locality is the same as entanglement whereas I specifically stated it is a subset of that. Be that is may, in the peer-reviewed literature, not simply popular press, entanglement is specifically referred to as quantum non-locality.
Perhaps you have a beef with quantum physicists? If so, take it up with them. I am advancing the topic in the language that is acceptable and used by science in this area.
Yep, another 'ta-da' experiment showing that experimental quantum mechanics does indeed behave just like us theorists say it should. Great. Next?
Cutting to the chase, the simple fact is that no form of 'non-locality ' exhibited by quantum mechanics allows for superluminal transfer of information, leaving causality intact. Or from your layman's position, are you suggesting otherwise?
You seemed to have missed the thread topic entirely. Perhaps you should read the OP again so we can discuss the topic instead of "cutting to" a chase which isn't on the table. Not to say a different thread might be worth entertaining, but suffice to say here, we are discussing the varying interpretations of quantum mechanics in respect to non-locality....such as whether observation is mere decoherence, the Many Worlds hypothesis and the transactional hypothesis, and exactly what the Copenhagen interpretation is.
On causality, it's clear that causality or local realism are violated by QM or perhaps both. On being able to use QM for superluminal communication, however, that is another topic or a subject to come up much further down the road in the discussion.

This message is a reply to:
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