Is Quantum Entanglement Just Correlation or a Real Physical Process?

[zenith8]

I think it's not fair to even dwell on this subject. We must immediately resort to 'Bertlmann's socks' argument whenever we, as the more knowledgeable, need to explain this to somebody.

Even the simplest things caused quite a stir in their times, but this just isn't important.

Sokrates - as has been pointed out to you several times, you're just wrong about this. Here is a summary of the current state of affairs:

We define nonlocality as a direct influence of one object on another, distant object, contrary to our expectation that an object is influenced directly only by its immediate surroundings.

Consider an EPR experiment, measuring spins. With parallel analyzers, we find that measurement of the spin on one side instantly predicts the result on the other. If you do not believe one side can have a causal influence on the other, you require the results on both sides to be determined in advance (the Bertlmann's socks argument). But this has implications for non-parallel settings (e.g. measure spin on axes 45 degrees apart in the two wings) which conflict with quantum mechanics (Bell).

Bell's analysis showed that any account of quantum phenomena needs to be non-local, not just any 'hidden variables' account i.e. nonlocality is implied by the predictions of standard quantum theory itself. Thus, if nature is governed by these predictions (which it is, according to real experiments) then nature is non-local. This is essentially because the many-particle wave function in the Schroedinger equation is defined on the configuration space of the system, an abstraction which combines or binds distant particles into a single irreducible reality.

So nonlocality - spooky action at a distance if you like - sounds strange and yet it is experimentally verifiable. If you want to refuse to believe it, what are your options?

(1) Loopholes: claim that improving detector efficiencies in the EPR-style experiments will invalidate the results. This is now widely understood to be desperate clutching-at-straws.

(2) Deny, in one way or another, that there is a material world - the description of which is the task of physics. Without objective reality, there is nothing to be objectively nonlocal. Despite its manifest ludicrousness, this has actually become a surprisingly fashionable viewpoint.

However, standard QM is not self-consistent due to the measurement problem. This is solvable only by granting real physical existence to theory objects. Standard QM is thus fundamentally an anti-realist stance - the wave function is just about probabilities, but probabilities of what? Something does travel - of course - along different paths in, say, an interference experiment; to refuse to call it 'real' is merely to play with words. Radical anti-realism can pretend to resolve interpretative paradoxes in virtually any context, e.g. Mach's rejection of grounding 'pressure' and 'temperature' in terms of real microscopic entities obviates the need to understand, say, convergence to thermodynamic equilibrium. More broadly, the philosophical doctrine of solipsism can 'solve' every problem in the history of science by just denying that anything but one's own mental experiences exist. This is ludicrously distant from the kind of solution we are interested in as scientists.

Instrumentalist Copenhagen QM is effectively 'an idea for making it easier to evade the implications of quantum theory for the nature of reality' (Deutsch). The positivist belief that empirical adequacy plus a formalized proof procedure is the best any theory can properly aspire to is - when you think about it - bizarre.

(3) Be a many-worlds person, then everything that can possibly happen happens in both branches of the experiment thus there can be no correlations. This makes two problems - nonlocality and macroscopic superpositions in measurement - go away, at the cost of believing in something apparently ludicrous (bazillions of ontologically-real extra universes) on the basis of assigning an entire universe to each term in a mathematical expansion.

(4) Allow time travel into the past (like in Cramer's transactional interpretation). But then we need to abandon the metaphysical picture of the past generating the future, and this is a step too far for most people.

(5) Make claims along the lines that the universe is necessarily Lorentz invariant and Lorentz invariance of a physical theory requires locality. However, this is just wrong as should be clear from the meaning: 'Lorentz invariance' describes the behaviour of a theory under certain transformations of the reference frame. 'Locality' implies there is no action at a distance. (Nonlocal Lorentz-invariant Wheeler-Feynman electrodynamics good counterexample to this).

(6) Claim that, in quantum field theory, the Equal Time Commutation Relations (operators which represent field quantities at space-like separation all commute) show that the theory contains no superluminal action. However, this is an empty claim. What it actually shows is that measurements on one side do not affect the long-term statistics on the other, that is that no signals can be sent from one region to the other by manipulating the apparatus on one side. However, superluminal influences are still required to explain the correlations between the two regions in an individual experiment.

To summarize finally the connection between non-locality and relativity, remember that although relativity is often taken to imply the existence of some sort of absolute speed limit, this is not actually the case. The fundamental feature of the Lorentz transformations is that they leave the speed of light invariant, not that they render it an insuperable boundary. Note that theories of tachyons and other superluminal transport do exist. We must therefore turn our attention to the question of the compatibility of non-locality with the relativistic picture of space-time. One can say that:

* Violation of Bell's inequality does not require superluminal matter or energy transport

* Violation of Bell's inequality does not entail the possibility of superluminal signalling (unless you believe in Bohm-Valentini style quantum nonequilibrium).

* Violation of Bell's inequality does require superluminal causal connections.

* Violation of Bell's inequality can be accomplished only if there is superluminal information transmission.

An excellent reference is Tim Maudlin's book 'Quantum non-locality and relativity' from where I adapted the previous four starred points.

 

[Ilja]

The situation with entanglement today is similar in that there is no single ontological story that accommodates all theories of physics, and finding one will, it appears, entail sacrifice so as to subsume EPR-Bell phenomena. For example, Bohmian mechanics violates relativity in that it requires a preferred frame and Many Worlds violates parsimony with its indenumerably infinite “universes.”

I disagree. The Bohmian picture can accommodate all theories of physics. It requires a preferred frame, but that means only that it violates relativistic metaphysics, but not relativistic physics.

The problems of BM with spinor fields and BRST quantization seem solvable. For spinor fields, see my approach to spinor quantization in http://ilja-schmelzer.de/papers/clm.pdf" . Spinor fields appear there together with some heavy bosonic partners in a canonically quantized way, which makes the standard BM scheme applicable. Gauge fields and gravity appear there as emergent, non-fundamental fields, thus, they don't need a special Bohmian representation as well as thermodynamic fields need such a representation.

Ilja

 

[Demystifier]

Zenith8, excellent post!

 

[Demystifier]

For example, Bohmian mechanics violates relativity in that it requires a preferred frame

That is not true. There is a version of Bohmian mechanics that does not require a preferred frame:
http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]

 

[DrChinese]

That is not true. There is a version of Bohmian mechanics that does not require a preferred frame:
http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]

Question, Demystifier: As I understood it, some if not most Bohmian versions do require a preferred frame. Is that so?

 

[zenith8]

Question, Demystifier: As I understood it, some if not most Bohmian versions do require a preferred frame. Is that so?

This is true - the standard de Broglie-Bohm pilot-wave theory requires a preferred frame, but so what? As Ilja said this is just a metaphysical question - there is no disagreement with relativistic physics.

The standard 'interpretation' of relativity (all inertial frames are equivalent) is simply a positivistic metaphysical preference. There are other interpretations - such as the Lorentzian one - where there is a preferred frame but nevertheless everything is still entirely observationally equivalent to the standard view. See the recent book 'Einstein, Relativity, and Absolute Simultaneity' edited by William Lane Craig and Quentin Smith which contains a variety of essays by prominent physicists on this topic.

Note that the standard de Broglie-Bohm pilot-wave theory implies a preferred frame essentially because the notion of a configuration, as used in the non-relativistic version, already presupposes simultaneity. Configurations are configurations at some time - they specify where all of the particles in a system are at a given moment. So the very notion of a configuration is not a Lorentz invariant concept.

The reference given by Demystifier is to his own recent paper, which is extremely interesting but not yet incorporated into the Bohmian mainstream (most of them probably haven't read it yet).

 

[DrChinese]

The reference given by Demystifier is to his own recent paper, which is extremely interesting but not yet incorporated into the Bohmian mainstream (most of them probably haven't read it yet).

Yes, not helped by the fact that he is awesomely prolific!

 

[RUTA]

I disagree. The Bohmian picture can accommodate all theories of physics. It requires a preferred frame, but that means only that it violates relativistic metaphysics, but not relativistic physics.

Ilja

The "sacrifice" is the "relativistic metaphysics." Very little interest among relativists (physics) for giving that up.

I suspect no interpretation will win the day unless it yields new physics simply because otherwise it's left to personal preference.

 

[RUTA]

That is not true. There is a version of Bohmian mechanics that does not require a preferred frame:
http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]

Neither the words "preferred" nor "frame" appear in this paper according to my search engine. Relativistic covariance does not mean "no preferred frame." GR and SR both accommodate a preferred frame, in fact, there are arguments for the CMB rest frame as a preferred frame in the context of GR cosmology. Please explain, say, the Mermin device in terms of BM without a preferred frame.

 

[zenith8]

The "sacrifice" is the "relativistic metaphysics." Very little interest among relativists (physics) for giving that up.

Whole book full of 'em in the reference I gave in my earlier post #41. How many physicists would be enough for you?

"2005 marked the centenary of one of the most remarkable publications in the history of science, Albert Einstein's 'On the Electrodynamics of Moving Bodies' in which he presented a theory that later came to be known as the Special Theory of Relativity. This 1905 paper is widely regarded as having destroyed the classical conceptions of absolute time and space, along with absolute simultaneity and absolute length, which had reigned in physics from the times of Galileo and Newton to the dawn of the twentieth century. As we embark upon a new century, the Special Theory is now 100 years old, and a great deal has transpired in both philosophy and physics since its first publication. This volume is a timely reappraisal of the theory's central claims, especially concerning the elimination of absolute time and absolute simultaneity.''

"This collection draws together essays by both philosophers and physicists and reflects the cutting edge of research and thought on the question of absolute simultaneity. The issues discussed in the book include Aspect's confirmation of Bell's theorem, de Broglie-Bohm's quantum mechanics, the privileged cosmic time series in a Friedman universe, Lorentz's ideas and neo-Lorentzian theory and other relevant issues. Almost all the contributors are convinced that the received view that simultaneity is not an absolute relation is not only unwarranted but false, and it is hoped that this collection will stimulate discussion among both philosophers and physicists concerning the warrant for and problems with assertions of the relativity of simultaneity on the basis of Einstein's theory."

Keep up!

I suspect no interpretation will win the day unless it yields new physics simply because otherwise it's left to personal preference.

Try http://www.sciencemag.org/cgi/content/short/324/5934/1512" .

 

[DrChinese]

Try http://www.sciencemag.org/cgi/content/short/324/5934/1512" .

This is about Antony Valentini, who is a Bohmian. Humorously, he has a Wiki page which may surprise a number of people on this board (including Demystifier) who are Bohmians: "Currently Antony Valentini is the only person in the world doing research into the De Broglie Pilot Wave theory..."

Apparently, hype rules everywhere. As to the reference above, you will need to have a subscription to view. He writes in the arxiv, for instance:

http://arxiv.org/abs/quant-ph/0506115

And perhaps more relevant to this thread:

Hidden Variables and the Large-Scale Structure of Spacetime:

"We discuss how to embed quantum nonlocality in an approximately classical spacetime background, a question which must be answered irrespective of any underlying microscopic theory of spacetime. We argue that, in deterministic hidden-variables theories, the choice of spacetime kinematics should be dictated by the properties of generic non-equilibrium states, which allow nonlocal signalling. Such signalling provides an operational definition of absolute simultaneity, which may naturally be associated with a preferred foliation of classical spacetime. The argument applies to any deterministic hidden-variables theory, and to both flat and curved spacetime backgrounds. We include some critical discussion of Einstein's 1905 'operational' approach to relativity, and compare it with that of Poincare."

 

[zenith8]

This is about Antony Valentini, who is a Bohmian. Humorously, he has a Wiki page which may surprise a number of people on this board (including Demystifier) who are Bohmians: "Currently Antony Valentini is the only person in the world doing research into the De Broglie Pilot Wave theory..."

Well, it's true to a first approximation..

Especially if you consider the de Broglie theory to be different from the Bohm one.

Apparently, hype rules everywhere. As to the reference above, you will need to have a subscription to view.

Well, I'm not saying you should type the title of the paper into Google (that would be against the rules), but..

 

[DrChinese]

Well, it's true to a first approximation..

Especially if you consider the de Broglie theory to be different from the Bohm one.

Ha, I hope there are a few more than that... and yes, there are probably a few who Bohmians who are not dBBers, and vice versa. Apparently Valentini is big on labels, as he references Poincare over Einstein in places. I presume he is one of the group who feel Einstein's legacy unjustly overshadows Poincare in certain respects.

 

[zenith8]

This is about Antony Valentini, who is a Bohmian. Humorously, he has a Wiki page which may surprise a number of people on this board (including Demystifier) who are Bohmians: "Currently Antony Valentini is the only person in the world doing research into the De Broglie Pilot Wave theory..."

Though having just looked at this - it's clear his Wikipedia page has recently been heavily vandalized by an illiterate moron - presumably since the Science magazine article came out.

 

[zenith8]

Though having just looked at this - it's clear his Wikipedia page has recently been heavily vandalized by an illiterate moron - presumably since the Science magazine article came out.

I mean, come on, let me quote a bit more:

"Currently Antony Valentini is the only person in the world doing research into the De Broglie Pilot Wave theory, although he has attracted the attention of a reading group of Post Doctoral students, Doctoral Students and Honours Students called "The Cowboy Bebop Experience" who despite their irreverant name, comprise some of the brightest emerging minds in physics who are not yet able to admit their interests lest their careers be stunted forever."

Believe it or not - like they don't have enough trouble with every other quantum physicist hating/ignoring them - there are mutually aggressive factions within the de Broglie-Bohm community. To me this sounds like one of the "Bohmian mechanics" crowd throwing his toys out of the pram because Valentini was getting more attention than them.. (I speculate wildly).

Ha ha - this is so funny.

 

[zenith8]

[Valentini] writes in the arxiv, for instance:

http://arxiv.org/abs/quant-ph/0506115

And perhaps more relevant to this thread:

Hidden Variables and the Large-Scale Structure of Spacetime:

Relevant to the thread, yes, but the one I was referring to (in response to RUTA's 'interpretation is only personal preference' remark) and the one the Science magazine article is presumably pumping up is this one:

"Inflationary cosmology as a probe of primordial quantum mechanics"
http://arxiv.org/abs/0805.0163" (in press, Phys. Rev. D).

which seems to be a sequel to

"Astrophysical and cosmological tests of quantum theory"
J. Phys. A 40, 3285 (2007)
http://arxiv.org/abs/hep-th/0610032"

The article also references his forthcoming book with Bacciagaluppi
"Quantum Theory at the Crossroads: Reconsidering the 1927 Solvay Conference"
http://arxiv.org/abs/quant-ph/0609184"

 

[DrChinese]

I mean, come on, let me quote a bit more:

"Currently Antony Valentini is the only person in the world doing research into the De Broglie Pilot Wave theory, although he has attracted the attention of a reading group of Post Doctoral students, Doctoral Students and Honours Students called "The Cowboy Bebop Experience" who despite their irreverant name, comprise some of the brightest emerging minds in physics who are not yet able to admit their interests lest their careers be stunted forever."

Believe it or not - like they don't have enough trouble with every other quantum physicist hating/ignoring them - there are mutually aggressive factions within the de Broglie-Bohm community. To me this sounds like one of the "Bohmian mechanics" crowd throwing his toys out of the pram because Valentini was getting more attention than them.. (I speculate wildly).

Ha ha - this is so funny.

I was laughing... especially at the part about students not wanting to admit their interest in dBB for fear of retribution...

It just goes to show that you have to take Wikpedia with a grain of salt.

 

[zenith8]

I was laughing... especially at the part about students not wanting to admit their interest in dBB for fear of retribution...

This is still pretty much true in most physics departments! De Broglians or should I say Bohmians really have to watch what they say..

When I went to the course I learned this stuff from, the lecturer said he had counted 14 Nobel prize winners he had to disagree with in order to write the lecture notes. You can't normally do that without getting a slap.

 

[zenith8]

Apparently Valentini is big on labels, as he references Poincare over Einstein in places. I presume he is one of the group who feel Einstein's legacy unjustly overshadows Poincare in certain respects.

And this is controversial, you say..?

 

[DrChinese]

And this is controversial, you say..?

I guess it depends on your perspective, as I certainly don't credit Poincare with special relativity. (Not that I want to debate that in this thread.)

And while I have no doubt that going against mainstream is not healthy for a career in physics... I wouldn't say you had to hide your opinions/beliefs in order to pursue your career. There is a big difference in a field of study and an opinion.

If you choose a career path that goes against the grain, you would more or less expect to take heat. (It would be unreasonable for the development of science otherwise.) Then if you come up with an unexpected (to the majority) big discovery, you get to gloat.

 

[RUTA]

Whole book full of 'em in the reference I gave in my earlier post #41. How many physicists would be enough for you?

Keep up!

Try http://www.sciencemag.org/cgi/content/short/324/5934/1512" .

It's not up to me. I've been to conferences on the ontology of spacetime, I come at this problem with a background in GR, I'm simply reporting on my observations. I could cite a special issue on time-symmetric QM in Studies of History and Phil of Mod Phys. Would that convince you backwards causation QM is winning the interpretations debate? I hope not!

With the extensive evidence on EPR-Bell to date, the Bohmians still don't command a plurality, a fortiori anywhere near a majority, within the foundations community. The only objection to BM I've heard voiced is their need for a preferred frame. Now, if the Bohmians make a new prediction which is experimentally confirmed, that would constitute "new physics" and you'll win many (albeit reluctant) converts. But, the prediction would have to lie outside QM in order to have those in love with relativity of simultaneity give it up. I spoke with Aharonov and he complained that no one would pay attention to his two-vector formalism until he had proposed new experiments. Having since done so, backwards causation (ontological implication of his formalism) is still not as popular as BM and Many Worlds in the foundations community. Why? IMO, because the proposed experiments are not outside of QM so BM and the other interpretations are still on the table, i.e., again, it's left to personal preference.

These are just my impressions from attending foundations and relativity conferences over the past 25 years. My experience could be statistically skewed :-)

 

[zenith8]

It just goes to show that you have to take Wikipedia with a grain of salt.

I know this is somewhat off-topic, but it's fun. I spent ten minutes looking into the vandalism of Valentini's Wikipedia page. Before the 25th June (5 days ago) his currently extensive entry consisted of a single sober relevant paragraph - which is still the first paragraph today. On the 25th June, it was vandalized by someone from the University of Sydney (according to the IP tracker).. He added the paragraph:

"Currently Antony Valentini is the only person in the world doing research into the De Broglie Pilot Wave theory, although he has attracted the attention of a reading group of Post Doctoral students, Doctoral Students and Honours Students called "The Cowboy Bebop Experience" who despite their irreverant name, comprise some of the brightest emerging minds in physics who are not yet able to admit their interests lest their careers be stunted forever."

which is written in good English, has a certain amount of wit about it, and reads like it is written by a published pilot-wave author who is sore about Valentini's good PR in the Science paper. (How many of those work in Sydney? I'll stop my investigation there..) He then followed this edit with a longish summary of pilot-wave theory written in a series of single sentence paragraphs in bad English with spelling mistakes. Don't know what to make of this.

However, and this is the interesting thing, I then noticed that someone thinks this group really exists i.e. the above paragraph appears to be at least partly serious; our Australian subsequently wrote a Wikipedia article about the 'Cowboy Bebop Experience' setting out the manifesto for this group of young genius physicists. This appears to have been swiftly deleted from Wikipedia on the grounds that it refers to a club no-one knows about, but the entry is still available in Google's cache - see for yourself. So - as it is actually rather interesting and it appears to provide some insight into the desperate life of the Bohmian (see in particular the last two paragraphs) - I preserve it here for posterity (at least until this post gets deleted by the PF moderators). See attached.

How exciting - it's like tracking down the Rosicrucians.. Can I join?

 

[sokrates]

Sokrates - as has been pointed out to you several times, you're just wrong about this.

I just read the relevant parts of your humongous reply, and I found it interesting that "trivial details" you are glossing over are actually much more significant than most of what you present (time travel, loopholes in experiments etc...)

As I said: I had the chance of learning this from Murray Gell-Mann, and even though I didn't write any papers on this, I am really confident. I believe that it's very very misleading to immediately label Bertlmann's socks argument as "wrong" based on your personal prejudice on interpretations of Quantum Mechanics.

Let's examine your statements:

Violation of Bell's inequality does require superluminal causal connections.

This is a courageous statement!... Violation of Bell's inequality is the violation of an inequality and what could be extracted from it heavily depends on the choice of your interpretation. It's really strange that you could jump to this conclusion by cleverly arranging my available options and aptly shooting them down. MGM has a chapter in his book I recommend you to read: Quantum Mechanics and Flapdoodle

MGM believes in the Many-Worlds Interpretation school, which has gained huge popularity in the last few decades, and at the present time your only argument against it seems to be this:

[...] nonlocality and macroscopic superpositions in measurement - go away, at the cost of believing in something apparently ludicrous (bazillions of ontologically-real extra universes) on the basis of assigning an entire universe to each term in a mathematical expansion.

You are lecturing me about what good science is and so on , but it seems like your ONLY counter argument against many world interpretations is a "personal trouble" related to a mathematical curiosity. It's an effective - but not scientific - way of belittling a scientific theory (the same pattern emerges in attacks to string theory) but all of a sudden, my naive remark on spooky action at a distance TURNED INTO an MWI - Copenhagen war. Hmm... So what you are really attacking is NOT the Bertlmann's socks but it's the MWI as a whole. Good. Then I am not the only person who is "just wrong about this". Now an army of remarkable people joins me, lol.

So as you admit it, there's really a significant possibility of non-locality GOING AWAY, right? So there's a good chance of the old, easy

explanation being true, while the spooky action at a distance being flapdoodle?

I think this ends the discussion for me, because I wasn't fighting for preferring one over the other, I was simply saying that a huge amount of unnecessary concentration goes into selling the "non-locality" idea when we have viable alternative theories that can completely get rid of that!...
------
PS: And my personal choice is to buy into the ideas of MWI rather than some magical superluminal causal connection tale which may not even be wrong.

 

[Demystifier]

Question, Demystifier: As I understood it, some if not most Bohmian versions do require a preferred frame. Is that so?

Yes, that is so.

 

[Demystifier]

Neither the words "preferred" nor "frame" appear in this paper according to my search engine. Relativistic covariance does not mean "no preferred frame." GR and SR both accommodate a preferred frame, in fact, there are arguments for the CMB rest frame as a preferred frame in the context of GR cosmology. Please explain, say, the Mermin device in terms of BM without a preferred frame.

I don't know what the Mermine device is, but let me explain more generally how the approach in this paper avoids a preferred frame. Particles still have instantaneous influences on each other and these influences are still instantaneous with respect to some particular Lorentz frame. Nevertheless, this particular Lorentz frame does not need to be specified in advance. Instead, it is determined by the initial conditions, which, a priori, are arbitrary. In fact, even if there are only two entangled particles, the Lorentz frame with respect to which their influence is instantaneous is not a constant of motion. At the beginning that may interact instantaneously in one Lorentz frame, while later they can interact instantaneously in another Lorentz frame. And all this is a consequence of very simple manifestly covariant and naturally looking equations of motion.

 

[Demystifier]

Ha, I hope there are a few more than that... and yes, there are probably a few who Bohmians who are not dBBers, and vice versa. Apparently Valentini is big on labels, as he references Poincare over Einstein in places. I presume he is one of the group who feel Einstein's legacy unjustly overshadows Poincare in certain respects.

I think it is very important to distinguish few different versions of relativity. My preferred view of relativity, which allows me to construct Bohmian mechanics without preferred frames, is neither the Poincare's nor Einstein's view. Instead, my preferred view is the Minkowski's one. The difference between Einstein and Minkowski view is subtle, but essential. For Einstein, spacetime still consists of two different entities - space AND time. The split of spacetime into space and time depends on the observer, but such a split exists and plays an important role. By contrast, in the Minkowski's view there is ONLY a spacetime, while the split into space and time does not play any fundamental role. Clearly, observers do not play any fundamental role in the Minkowski's view.

If someone is interested, I have also written some papers in that spirit that have nothing to do with Bohmian mechanics:
http://xxx.lanl.gov/abs/gr-qc/0403121 [Found.Phys.Lett. 19 (2006) 259-267]
http://xxx.lanl.gov/abs/0905.0538 [Phys. Lett. B 678 (2009) 218-221]

 

[DrChinese]

Yes, that is so.

Thanks for clarifying that.

I am guessing that you might have seen some of Valentini's papers. Not expecting you to comment on those, but interested in the idea that there might be cosmological implications for one perspective or another. Obviously, you see relativistic possibilities one way and Valentini sees them a certain way; and as mentioned by RUTA and others: a good experiment would do wonders for one interpretation gaining ground over another. Clearly, experiments searching for a preferred frame have not yet uncovered any - and of course that would be expected in a variety of cases.

 

[Demystifier]

Let me comment the ideas of Valentini. His approach does not strictly predict deviations from the standard predictions of QM. Instead, his reasoning can be summarized by this:
1. The Universe today is clearly in the quantum equilibrium (QE), but in the far past it MIGHT not be in QE. His approach does not predict a deviation from QE, but only contains it as a possibility.
2. If the Universe was not in QE, then his approach does not predict what the actual statistical distribution were. He can only argue that some particular distribution could have been "natural" in some sense. If (and only if) the actual distribution was such, then he can make definite measurable predictions. However, there are too many "ifs" in his approach.

 

[RUTA]

I don't know what the Mermine device is, but let me explain more generally how the approach in this paper avoids a preferred frame. Particles still have instantaneous influences on each other and these influences are still instantaneous with respect to some particular Lorentz frame. Nevertheless, this particular Lorentz frame does not need to be specified in advance. Instead, it is determined by the initial conditions, which, a priori, are arbitrary. In fact, even if there are only two entangled particles, the Lorentz frame with respect to which their influence is instantaneous is not a constant of motion. At the beginning that may interact instantaneously in one Lorentz frame, while later they can interact instantaneously in another Lorentz frame. And all this is a consequence of very simple manifestly covariant and naturally looking equations of motion.

Your explanation suffices, so you don't need to apply this to the "Mermin device" :-) However, if you want to look it up, since it is often referenced in EPR-Bell conversations:

N.D. Mermin, Amer. J. Phys. 49, #10, 940-943 (1981).

So, you don't have a SINGLE preferred frame (i.e., preferred spacetime foliation), but rather the preferred frame varies from experiment to experiment (you choose a space-like hypersfc from one foliation in experiment one and you choose a space-like hypersfc from another foliation for experiment two). In otherwords, you still need a preferred frame for EACH experiment, otherwise you'll have to allow for backwards causation. Or, are you going to allow for backwards causation and keep relativity of simultaneity?

Thanks for the clarification.

 

[Demystifier]

However, if you want to look it up, since it is often referenced in EPR-Bell conversations:

N.D. Mermin, Amer. J. Phys. 49, #10, 940-943 (1981).

Thanks, I'll take a look.

So, you don't have a SINGLE preferred frame (i.e., preferred spacetime foliation), but rather the preferred frame varies from experiment to experiment (you choose a space-like hypersfc from one foliation in experiment one and you choose a space-like hypersfc from another foliation for experiment two). In otherwords, you still need a preferred frame for EACH experiment, otherwise you'll have to allow for backwards causation. Or, are you going to allow for backwards causation and keep relativity of simultaneity?

Thanks for the clarification.

First, it is not that an experimentalist chooses particular (I would not say "preferred") Lorentz frames, but rather that particles themselves do that. Or more precisely, the only choice the particles have are the initial conditions, while all these particular Lorentz frames are then determined automatically through the deterministic evolution. Observers play a passive role here. Some observers will see it as instantaneous causation, some will see it as superluminal forward causation, and some will see it as superluminal backwards causation. However, since their role is passive, they cannot use it to send information to the past at will. (So yes, this approach allows for backwards causation and keeps relativity of simultaneity.)

 

[RUTA]

First, it is not that an experimentalist chooses particular (I would not say "preferred") Lorentz frames, but rather that particles themselves do that. Or more precisely, the only choice the particles have are the initial conditions, while all these particular Lorentz frames are then determined automatically through the deterministic evolution. Observers play a passive role here. Some observers will see it as instantaneous causation, some will see it as superluminal forward causation, and some will see it as superluminal backwards causation. However, since their role is passive, they cannot use it to send information to the past at will. (So yes, this approach allows for backwards causation and keeps relativity of simultaneity.)

Welcome to the Dark Side!

 

[Demystifier]

Welcome to the Dark Side!

I don't have problems with backwards causations. Even though it means that the future may influence the past, it is still safe because the future cannot CHANGE the past. Therefore, causal paradoxes (like grandfather paradox) are excluded.

 

[RUTA]

I don't have problems with backwards causations. Even though it means that the future may influence the past, it is still safe because the future cannot CHANGE the past. Therefore, causal paradoxes (like grandfather paradox) are excluded.

I agree, in fact, I have argued that QM supports the blockworld view of reality:
“An Argument for 4D Blockworld from a Geometric Interpretation of Non-relativistic Quantum Mechanics,” Michael Silberstein, W.M. Stuckey & Michael Cifone, Relativity and the Dimensionality of the World, 197 – 216 (Springer-Verlag, Germany, 2007), quant-ph/0605039.

There are those in the GR community who debate causal paradoxes like the grandfather paradox, but I don’t see GR addressing this issue. Instead, I suspect the answer will come from quantum physics. Let me briefly explain.

The paradox: GR allows for vacuum solutions with closed, time-like curves (CTCs). Suppose I introduce an object (ball, say) that is too small to affect this structure, i.e., adding the ball’s correction to the stress-energy tensor (SET) does not (effectively) change the solution (metric). Now I launch the ball along the CTC so that the future version of it collides with itself at point A, i.e., the point where the CTC intersects itself. If the ball is hit at point A, how does it continue around the CTC to get back to point A to collide with itself? Just a simplified grandfather paradox. GR doesn’t have anything to say about this situation because while the small correction to the SET does not significantly affect the spacetime structure, the spacetime structure and the SET must satisfy Einstein’s Eqns (EEs). Can you write down the SET that describes this situation while keeping it, say, divergence free (as required by EEs)? No? Then it’s not a soln of EEs and, therefore, not a solution of GR. So, GR has nothing to say about this paradoxical situation. But, what WILL happen if I’m in a spacetime like this and decide to roll the ball?

Suppose I have someone along the CTC who is told to knock the ball off course after it passes point A, so that it can’t collide with itself at point A and cause a “non-GR” situation. In other words, this additional observer decides whether we have a GR solution with the ball or not. Can the person decide NOT to deflect the ball? What happens?

This strikes me as analogous to decision making in the delayed choice experiments of QM. Consider Aharonov’s “double-slit” experiment (Y. Aharonov & M. S. Zubairy, Science v307, 11 Feb 2005, 875-879). In that experiment, there are beam splitters and mirrors configured to send one photon (A) of a correlated pair to one of four detectors while the correlated sibling (B) goes to another detector. Photons B create an interference (wave) pattern or particle pattern, depending on the outcomes of photons A, but photons B are detected well before photons A. Suppose I send people to act like beam splitters, i.e., they hold mirrors up half the time, and drop them the other half. When the mirrors are up, we get an interference pattern for photons B. When the mirrors are down, we get a particle pattern for photons B. These people (P) depart for their experimental positions agreeing to leave the mirrors down, say. I get a beautiful particle pattern for photons B, rather than the comingled mess of a combined wave/particle outcome, before the photons A have even arrived at the mirrors of P. Can the people P decide to put their mirrors up? Is this situation covered by QM? What happens?

My bet is that in fact WHATEVER we get for photons B ends up agreeing with WHATEVER the people P decide to do with photons A, exactly as described by QM. Reality is, at bottom, a self-consistent (per EEs, QM, etc) blockworld and this may be at odds with what we want to believe is free will. So, anyway, once we can get GR from quantum physics, then we'll have a resolution to the CTC paradox. How's that for "spooky at a distance?"


 

 

[Demystifier]

RUTA, the blockworld view is my preferred view too. However, I do not think that we really need quantum mechanics to resolve the grandfather paradox. Let me explain.

GR is not only the Einstein equation. Instead, GR is a set of coupled equations, one of them being the Einstein equation, while others being equations describing the dynamics of (classical) matter. Everything, including billiard balls and humans is supposed to be described by this set of coupled equations. The actual universe (whatever it is) is one particular solution of this set of equations. This solution must be self-consistent, because otherwise it is not a solution at all. Thus, the ball either hits or does not hit itself.

One often argues: "But what if I decide to do this or that?" The answer is that our decisions are also constrained by the set of equations above. If there is no solution that corresponds to a certain decision, then you will simply NOT decide to do that. Or as someone beautifully said: You can do whatever you decide to do, but you cannot decide to do whatever you want to do. (For example, you cannot decide to levitate, to create matter from nothing, ...)

 

[Demystifier]

Your explanation suffices, so you don't need to apply this to the "Mermin device" :-) However, if you want to look it up, since it is often referenced in EPR-Bell conversations:

N.D. Mermin, Amer. J. Phys. 49, #10, 940-943 (1981).

Now I see that I knew about that paper. I even cited it ones. However, I didn't know that it is called "Mermin device". :tongue2: