Quantum Entanglement: EPR Paradox

Bill592
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A Very interesting article !

Bill

http://awildduck.com/?p=3308

Mike Hewson
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Quantum Entanglement: EPR Paradox

The thing about the paradoxes is that they aren't really. Each measurement system ( typically known as an 'observer' ) yields self-consistent results. It's when comparisons are made across observers, typically while holding with some underlying 'common sense' assumptions, is where the trouble lies.

The key for EPR is that Einstein, Podolski and Rosen correctly deduced that QM formalism implied certain correlations of results obtained by different observers with respect to the 'axes' of their measurement devices. But the devices are in separate frames of reference or in generality can be thought of as so. EP&R took that to be unreasonable in a classical sense. Experiment subsequently confirmed that certain quantum states do have an 'extended' nature to them ie. the idea of distinct independent particles breaks down.

For me at least the short answer is that reality must lead our thinking, expectations be damned. Experiment does give us these measurement correlations in certain circumstances and our error is in applying a traditional particle model to interpret the change in energy states of our devices. The cognitive difficulty is that we don't normally experience this, presumably because of a blizzard of environmental interactions that usually blur the effect. Note that entangled pairs take a good deal of upkeep to maintain them that way.

One side issue is the choice of language for description. In strict parlance an 'observer' is simply shorthand for a specified type of event recording system. It doesn't need to be a human, or even living, and so cognition, choice etc are unnecessary layers upon the discussion.

More or less the same arises with Schrodinger's Cat. The cat is either alive or dead and you don't know until you open the box. Whoopty do ! Tonite we might belatedly discover that Alpha Centauri A went supernova a few years ago. Naturally today if I am modelling all possibilities I will include an a priori expectation for that to happen later this evening. All separated observers need a mechanism of disclosure ( look at the sky, open the box*, get Bob to fax his particle counts to Carol ) if we seek to reconcile viewpoints.

You must look to nature for the correct manner of reconciliation. If that breaks some assumption(s) then so be it. If one doesn't like that, well, it sucks for sure ! Good science is full of experiments correcting our thinking. In that regard I follow Mr Feynman ! :-)

Cheers, Mike.

Addendum : One fair point is that often matters of interpretation are scale dependent ie. within some range of size/speed/energy/whatever one can apply a model with certain axioms. The curious thing is that a scale change can morph the axioms to a different looking form. A neat trick is to recognise that one axiom is merely a disguised form of another, with some scale number like Planck's constant or light speed or field strength factored in.

A good example is Heisenberg's Uncertainty Principle which in it's simplest mathematical form relates to the difference b/w operations applied in one order vs. operations in the reverse order. There is a number that expresses that difference in outcomes ( the 'commutator' ) and that is proportional to Planck's Constant. In every day terms that's a tiny number. So if the typical energies of a problem are at everyday level then that commutator is as good as zero and classical rules apply no problem ie. you will never measure any different. If the problem is of an energy level that makes Planck's constant significant then the order of operations does matter and we go down the quantum rabbit hole ... :-)

But you can still think of all scenarios as related upon a spectrum. Just imagine a slider that adjusts the scale and thus the problem transforms from one type to gradually become another. If you look, for instance, at carbon buckyballs they exhibit a mix of quantum and classical features. Why ? Because it is at intermediate scale ....

* You could do a Schrodinger's Cat setup with me on a dunking stool & tank setup in a suitably isolated room. The atom decays, emits a particle which hits the detector that triggers the stool drop. When you open the door you will find out if I am wet or not. The two observers here are me in the room and you outside, but we don't have to be anthropocentric. The formal point to discuss about The Cat is how do quantum level events emerge to be perceived at larger scales, the keyword here being decoherence.

[ That's not the same as incoherence which of course you will all recognise as applying to my explanations of quantum mechanics. NB I could be wet simply by sweating in anticipation of the atom decaying .... :-) ]

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Jim1348
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It is remarkable that the

It is remarkable that the human mind, which evolved over a couple of million years in hunters on the plains of Africa, can grasp such intricate and non-obvious truths about the world. The brain has not changed in the last 100 thousand years, and therefore that ability must have been inherent all along, even though it does not appear to be necessary for its original function. I wonder how many other species in the universe can make that leap in intelligence?

Thanks for the very lucid explanations.

Bill592
Bill592
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Mike. Thanks for that

Mike.
Thanks for that response.
Didn't Feynman say - "If you don't like the way
the universe works, move to a new one ! "

or something like that }

Bill

Mike Hewson
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You're welcome gentleman.

You're welcome gentleman. :-)

Much of science, quantum mechanics included, I feel is unnecessarily obfuscated by the media and publishing concerns. For the sake of pure profit. The 'faux science'/'synthetic news' crowds especially eg. New Scientist buff up straightforward concepts and morph them into rather obtuse constructs. Currently I rank NS only slightly above Wikipaedia for accuracy. So yes, the repeated use of the phrase wrt EPR : 'spooky action at a distance' is at Cliche Richter level 7 now. It really ought not be a surprise that lumbering clouts like us have trouble with descriptions of things some one billion times below our physical scale.

Schrodinger proposed the Cat scenario as a jibe at his contemporaries - an 'in' joke as it were - to prompt them to reflect carefully upon scale issues and interpretations thereof. So that context of the discussion was well known at the time, but alas conveniently forgotten ( or not researched at all ! ) by those that followed. So the whole cat thing has resonated well beyond the initial case, been amplified and modified and analysed and suborned etc .... so much so that The Cat In The Box ( Seuss ought to have done a book on that ) is now typically a sociology event quite devoid of science merit.

Hence an important query is some discussions is akin to "Is this actually Schrodinger's Cat we are talking about, or some other version of your own making for which you would like to implicitly subvert the use of his good name to label ?"*

The key trick is to go to source. It's a real modern marvel that for a modest fee one can get primary statements from the originators of science trends. I urge people to have a go at that. Even the great Einstein wrote several treatises intended for those without prior training. Stephen Hawking has lent his name, forewords and commentaries to many great earlier works too eg. On The Shoulders Of Giants, God Created The Integers. I mean if you are going to be derivative then at least go top quality ! So don't be shy ! :-0

Cheers, Mike.

* Correct. I don't often get re-invited to dinner parties .... :-)

( edit ) This does not mean that I am expert and get it right, it means I reduces my chances of being wrong ! :-)

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

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