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Local realism is dead

quamtum mechanics physics

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#1 platypus

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Posted 25 October 2015 - 06:44 PM


RIP

 

http://www.nature.co...ature15759.html

 

Spooky action at a distance rules ok



#2 Turnbuckle

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Posted 25 October 2015 - 08:51 PM

So it might seem. But if you allowed particles to travel back and forth in time, that would explain many things--such as nonlocality and the squared modulus of the wave function that predicts the location of a particle. By traveling back and forth in time, the spookiness goes away. 



#3 nightlight

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Posted 25 October 2015 - 08:56 PM

I happen to be theoretical physicist who had this problem (quantum paradoxes, mainly non-locality) for my master’s thesis. Since mid-1970s these claims would come along periodically every few years, and only when the next group of ‘quantum magicians’ comes along it is suddenly revealed to the gullible reporters and public — ‘oops, the previous experiment had a very subtle yet fatal flaw and only this new one is actually the real thing’.

 

Those who who have seen the routine many times will just roll their eyes. The latest quantum magicians get to bask in their temporary glory for few years, while quietly but quickly snatching the loads of funding, until the next team of magicians decides it’s their turn now.

 

In this case the inevitable fatal flaw is fairly easy to spot. Since the Nature paper is paywalled, use the free arXiv copy here.

You basically have setup with 3 experimental locations which are far apart (see Fig 1, page 2 and its description):

A —— C —— B

The spins to be measured in the final step (and demonstrate the alleged ‘quantum non-locality’) are at the A and B locales. The location C contains the event-ready detectors (photo-detectors). In each test the light photons interact first with spins at A and B, then they are sent from A and B to C where the two photons are measured in order for ‘event-ready’ computer logic at C to decide and signal YES/NO to A and B indicating whether spins at A and B should be tested. Then, on YES, the spins at A and B are measured in one of two ways, and magically they show apparent non-local correlations. On NO, that try is not counted and new try is started. The alleged non-local statistical correlations occur between the results that were not discarded.

 

It is clear though that the measuring procedure itself, with its common ‘event-ready’ detection & decision at common location C, is explicitly non-local, hence the non-locality claim is a kind of 'term or art' but not what one would normally describe as non-local behavior (aka it's bogus).

 

Consider analogy of ‘telepathic’ magician twins at A and B claiming they can ‘randomly’ pick the cards from the far away decks, one twin at A the other at B, and make them match at greater rate than regular chance would allow. But then, their magic procedure consists of each twin picking the card, then each sending their messenger to C, and then the two messengers meet at C to decide whether this test instance is to be counted or discarded.

 

Anyone with few brain cells would tell them, ‘is this a joke? you call that telepathy? get out of here’. Of course, when this same kind of magic procedure is obfuscated in the heavy technical jargon, reporters and public, as well as some investors (lured by the promise of magic ‘quantum computing’ which rests on the existence of the above effect) will get duped.

 


Edited by nightlight, 25 October 2015 - 09:00 PM.


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#4 platypus

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Posted 26 October 2015 - 08:08 AM

Consider analogy of ‘telepathic’ magician twins at A and B claiming they can ‘randomly’ pick the cards from the far away decks, one twin at A the other at B, and make them match at greater rate than regular chance would allow. But then, their magic procedure consists of each twin picking the card, then each sending their messenger to C, and then the two messengers meet at C to decide whether this test instance is to be counted or discarded.

 

I'm not sure if I get your example, if the letter that is carried by the messenger has been written by A/B and the rules for counting and discarding the instances are objective and suitably formed, why could the experiment not show that "telepathy" works?

 

BTW, don't you think it's inevitable that as measurement-techniques improve all the loopholes (except super-determinism which sounds crazy to me) will be closed in not-too-distant future? 


Edited by platypus, 26 October 2015 - 08:11 AM.


#5 nightlight

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Posted 26 October 2015 - 09:44 AM

I'm not sure if I get your example, if the letter that is carried by the messenger has been written by A/B and the rules for counting and discarding the instances are objective and suitably formed, why could the experiment not show that "telepathy" works?

 

BTW, don't you think it's inevitable that as measurement-techniques improve all the loopholes (except super-determinism which sounds crazy to me) will be closed in not-too-distant future? 

 

 

The messengers from A and B are photons, one from A, one from B, which are entangled with the distant spin defects at A and B (those spin defects emit these photons in state ms=0; see page 3, right column). Then the messengers are sent to common point C, measured there and the results of that measurement are used to make YES/NO decision. Hence, in the analogy of magician twins, each messenger talks to the respective twin at A and B, then the messengers meet at common point C and are interrogated by the 'YES/NO decider' at C, which upon checking their message declares YES/NO (so called "entanglement swapping"). Or in your variant of the magician twins analogy with envelopes, the 'YES/NO decider' opens and reads both envelopes before deciding on YES/NO.

 

That kind of grossly non-local setup is a complete disqualifier for any non-locality claim, whether we're dealing with magician twins or physics experiments.



#6 platypus

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Posted 26 October 2015 - 10:30 AM

 

That kind of grossly non-local setup is a complete disqualifier for any non-locality claim, whether we're dealing with magician twins or physics experiments.

Ok I see your point. Do you think all the loopholes can be closed in the coming years as progress is made in preserving the entanglement?



#7 nightlight

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Posted 26 October 2015 - 11:51 AM

 Ok I see your point. Do you think all the loopholes can be closed in the coming years as progress is made in preserving the entanglement?

 

No they won't be closed simultaneously. The reason is that predicted violations are based on particularly strong postulates of quantum "measurement theory" (the strong assumptions about the projection postulate for composite systems). But that interpretation is only one possible version of measurement theory going back to 1920s & 1930s. Many notable physicists (including Einstein, Schrodinger, Planck, de Broglie, Bohm, `t Hooft, Jaynes, Barut, Wolfram,...) don't believe in those strong postulates and some alternatives don't predict any Bell inequality violations. A paper by by a fellow physicist I corresponded with, Emilio Santos, has a paper on arXiv presenting this "heretical" perspective here.

 

Basically, the situation with still unresolved QM "measurement theory" is similar to that of physics before the 1st and 2nd laws of thermodynamics, when numerous perpetuum mobile devices were claimed (see page 25 in Santos' paper for this analogy). All of them were characterized by ever shifting series of loopholes. It was only after the laws of thermodynamics were discovered that it became clear such device cannot work, even in principle. In this thread on PhysicsForums I describe a newer (by Roy Glauber, founder of Quantum Optics, from 1960s) and more rigorous alternative measurement theory that uses weaker assumptions about the projection for composite systems (it derives it from the simple system measurement postulate). In that theory, which is actually the one used in Quantum Optics experiments, there is no prediction of Bell inequality violation. Less mathematical description of this alternative for general reader is given in this post in another forum.


Edited by nightlight, 26 October 2015 - 12:01 PM.


#8 nowayout

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Posted 26 October 2015 - 09:43 PM

I'm also a physicist, and I find the reportage on this in the lay press exasperatingly bad.  Even the New York Times, supposedly a higher quality paper, had an article about this that was a bunch of incoherent nonsense written by someone who has no idea what he was talking about.

 

You cannot use this effect to transmit any information "instantaneously" between spatially separated points, or even at any speed faster than the speed of light.  There is therefore no instantaneous "action at a distance."  The quantum field theories that describe the separated particles, as well as the experimenters and their apparatus, are by construction explicitly local - "no nonlocality" (the lightspeed limit on the propagation of information) is built into the Standard Model of Physics.  (Technically, spacelike separated operators in the Standard Model commute, assuming it is a consistent Quantum Field Theory.)

 

This is not to say that there isn't something mysterious and unresolved about the Measurement Problem in the interpretation of Quantum Mechanics.  But however you cut it, the one particle isn't affecting the other particle instantaneously and no faster than light communication is happening here, so I wish people would stop saying that it is.

 

I hope the scientists themselves here weren't the ones encouraging this misleading New Agey language in their press releases, which I haven't checked, but I wouldn't be surprised if they were, since I have seen this kind of thing many times before. Unfortunately this kind of nonsensey sensationalism is the new normal in university communications.  


Edited by nowayout, 26 October 2015 - 10:19 PM.

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#9 platypus

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Posted 27 October 2015 - 09:21 AM

My understanding is that not being able to transfer information faster than light does not mean that instantaneous "action at a distance" does not happen. Or is this passage from wikipedia incorrect?

 

The seeming paradox here is that a measurement made on either of the particles apparently collapses the state of the entire entangled system—and does so instantaneously, before any information about the measurement could have reached the other particle (assuming that information cannot travel faster than light). In the quantum formalism, the result of a spin measurement on one of the particles is a collapse into a state in which each particle has a definite spin (either up or down) along the axis of measurement. The outcome is taken to be random, with each possibility having a probability of 50%. However, if both spins are measured along the same axis, they are found to be anti-correlated. This means that the random outcome of the measurement made on one particle seems to have been transmitted to the other, so that it can make the "right choice" when it is measured. The distance and timing of the measurements can be chosen so as to make the interval between the two measurements spacelike, i.e. from any of the two measuring events to the other a message would have to travel faster than light. Then, according to the principles of special relativity, it is not in fact possible for any information to travel between two such measuring events—it is not even possible to say which of the measurements came first, as this would depend on the inertial system of the observer. Therefore the correlation between the two measurements cannot appropriately be explained as one measurement determining the other: different observers would disagree about the role of cause and effect.

 

 ( https://en.wikipedia...pparent_paradox )

 

I have to confess I've always been confused about this "instantaneous action" in QM. For example if I see my friend in front of me I know "instantaneously" that she is not in Betelgeuze, which is ~600 light-years away. However nothing needed to travel 600 light-years instantaneously for me to know that. 

 


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#10 nightlight

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Posted 27 October 2015 - 02:26 PM


 ( https://en.wikipedia...pparent_paradox )

 

I have to confess I've always been confused about this "instantaneous action" in QM. For example if I see my friend in front of me I know "instantaneously" that she is not in Betelgeuze, which is ~600 light-years away. However nothing needed to travel 600 light-years instantaneously for me to know that. 

 

That's the core of the unresolved measurement problem. The dynamical equations describing how quantum system evolves in time (Schrodinger, Dirac, etc) cannot produce the basic empirical fact that measurement yields single result. Instead, these equations, due to their linearity, predict that object and measuring apparatus remain in the superposed state of all possible results, which contradicts the empirical fact of single result. Hence, the linear evolution equations cannot be the whole story.

 

von Neumann suggested state collapse (caused by observers via conscious act of observation) in late 1920s. Since no one knows how to incorporate "consciousness" into a physical theory, others have since proposed dynamical/physical collapse (from 1970s to present), but the question then becomes how and when the two kinds of system evolution in time alternate -- what are the conditions when ordinary linear evolution ceases and collapse method takes over, and then how/when does the ordinary linear evolution resume. No one knows how to scientifically answer that (there only handwaving). There is also no good way to make a coherent theory out of such assumptions since the two ways of system evolving in time (linear and collapse) are mutually contradictory/exclusive. Any logical system containing mutually contradictory assumptions can yield arbitrary false statements and thus it cannot be basis for a logically coherent theory.

 

Another approach, which is my favorite, was proposed in different forms by Einstein, deBroglie, Barut, Jaynes, etc. -- the linear evolution equations (which cannot produce the observed single measurement outcome) are mere linear approximation of the full non-linear equations (such as the coupled Maxwell-Dirac system of equations that Barut developed under name "Self Field Electrodynamics" or SFED).

 

The only requirement for this solution to work is that there is no genuine (loophole free) experimental violation of Bell inequalities. Since that is indeed the case, so far despite the phony claims like the story in this thread, the non-linear evolution remains the simplest and logically the most coherent solution.


Edited by nightlight, 27 October 2015 - 02:28 PM.

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#11 Multivitz

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Posted 24 December 2015 - 10:56 AM

Magnetism has memory in space, space contains potentials, the field of space has logic that these QM show. Electrical theory of Maxwell and the simplification of it others have shown determines hyperspace potentials of electric. Some potentials are so finely balanced that measuring them is very difficult. Experiments in imbalance show up the effects, Quantum theory has many experiments but it's proprietors seem to mix words where conveying thier results of observation. The black box experiment is a crude ussumption at best, lets hope they get it together.
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#12 Multivitz

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Posted 26 December 2015 - 11:43 AM

Throw your clock away, how did time get in to the equation. Things appear instantaneous and are not infinite in value.
Just do yourselves a favour and watch some Thornhill.

Edited by Multivitz, 26 December 2015 - 11:58 AM.

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#13 Multivitz

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Posted 01 January 2016 - 08:09 PM

State collapse is a result of the charge field effect of conscious observation, the photon is lightweight enough to be effected. Because it operates under the effects of it's environment, observation will interfere, be it emotional or potential.

I think that thinking about QM will exercise your brains ready for when you want to start using the whole body for thought.
Linear and none linear equations, will only, work if they are correct theories. I haven't seen any yet, let's hope QM will become the king of flexable theories and be used for some good. At the moment it has a few novel observations for engineering and math about particles that hasn't included field conjugations that include the wave profile. It's instantaneous action of wave interaction, the objects in the field show the delay as their local fields get effected. It's not rocket science, just the heart not being free enough to hold another view comfortably.
Excuse my spelling.

Edited by Multivitz, 01 January 2016 - 08:17 PM.

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