A question regarding the Copenhagen interpretation.

[bohm2]

I think that Bohmian mechanics has some sort of "real explanation" (do you know?), but not in detail how the non-locality is 'implemented', and anyhow, there are serious trouble with RoS as soon as you make "real stuff" being there and influencing other distant "real stuff".

This is one possibility and is sort of based on Couder's experimental stuff:

We refer neither to potentials nor to a "quantum force" or some other dynamics, but show that a "systemic nonlocality" may be obtained as a phenomenon that emerges from an assumed sub-quantum kinematics, which is manipulated only by changing its constraints as determined by the changes of the apparatus.

"Systemic nonlocality" from changing constraints on sub-quantum kinematics
http://iopscience.iop.org/1742-6596/442/1/012012/pdf/1742-6596_442_1_012012.pdf

A Classical Framework for Nonlocality and Entanglement
http://arxiv.org/pdf/1210.4406.pdf

 

[atyy]

I smell a rat.

On PF we've seen numerous cranky attempts with "African Doctors", "French Epidemics" and god knows what, "explaining" EPR-Bell experiments preserving local realism. Everybody has failed, catastrophically, and of course the "Slip/Envelope" case is no different.

The "Slip/Envelope" case is mentioned in the FAQ, explaining how the 1935 EPR paradox gets handled in Consistent Histories. Of course, Bell's 1964 theorem is not mentioned once, since this would ruin the case completely.

In the Brief Introduction to Consistent Histories we are served the same moldy dish:
But what does Griffiths say about this in his book Consistent Quantum Theory?

Well, the "Slip/Envelope" case gets introduced in chapter 23.4 about Stern-Gerlach and Measurements of One Spin, where we have the mutual exclusion outcome of Z⁺ or Z^-, in which the "Slip/Envelope" case naturally fit like a glove. If we combine this with the eccentric methodology of stopping time at 1935, and 'forgetting' everything about Bell's theorem, we're almost there...

Wow, Griffiths is a crackpot??

No, certainly not, because in chapter 24.4 about Bell Inequalities, the "Slip/Envelope" case is not mentioned once (only in 24.1 about the 1935 EPR Paradox). Instead we get this restriction:
The phrase "the “hidden” variable λ can simply be the value of S_aw at some earlier time" is just a circumscription of the "Slip/Envelope" case, where this prerequisite is an absolute necessity, thus the "Slip/Envelope" case only works as long as "only a single choice for w_a is under consideration".

Hence, Griffiths himself, in chapter 24.4 points out that the "Slip/Envelope" case in not compatible with Bell Inequalities, and he sums up the chapter with the following:

[my bolding]Everybody, including Einstein, understands that the "Slip/Envelope" case is a hidden variable theory. End of discussion.

What's the problem?

The problem is when guys like postdoctoral fellow Vlad Gheorghiu packages the whole thing into an unrecognizable quicksand of delusion, capable of making an erudite SA swallow it hook, line, and sinker – into the hole of scientific deception.

Just to make clear, I do agree that one cannot have a local realistic interpretation of quantum mechanics unless one violates the assumptions of the Bell theorem. For example, one can violate the assumptions of the Bell theorem by assuming that a measurement does not yield a unique outcome, but rather all outcomes occur - even then - it is not clear if the interpretation is local - but I'll certainly grant that its nonlocality is not assured by violation of the Bell inequalities. I also agree that it is not enough to say that the measurement results don't exist before measurement in order to violate the assumptions. One has to do something drastic like saying that there are not two observers, but only one.

However, it does seem that Griffiths claims consistent histories to be "realistic" and local. You can find the claim of locality in http://quantum.phys.cmu.edu/CQT/chaps/cqt24.pdf and the claim of "realism" in http://quantum.phys.cmu.edu/CQT/chaps/cqt27.pdf. In fact, both claims are made as points 2 and 3 on p318 of the second link. I don't know enough about consistent histories to comment on the claim, but my impression is that his definition of reality isn't "common sense realism", so if his claim is correct, my bet would be that his definition of reality is actually a form of nonrealism.

 

[bhobba]

my bet would be that his definition of reality is actually a form of nonrealism.

I have studied Consistent Histories and most definitely do NOT agree its a realistic interpretation in any usual sense.

In fact why it is described that way has me beat - but people do:
http://www.siue.edu/~evailat/pdf/qm12.pdf

This semantic nit picking of calling something 'weak property realism' leaves me cold. That's probably because philosophy in general leaves me cold.

Basically the idea seems to be only one history actually exists, and is in that sense real, but we do not know it and can only predict probabilities. Like I said before its MW without the MW's, and wanting that IMHO leads to an unnecessary complication. Still its a nice interpretation - just not my favorite.

Thanks
Bill

 

[bhobba]

I smell a rat.

Well its the other thing I often say about Consistent Histories - its defining your way out of problems.

Want a realistic theory - no problem - simply define realism the way you like.

Its a 'rat' all right - but not one I particularly worry about.

Thanks
Bill

 

[DevilsAvocado]

This is one possibility and is sort of based on Couder's experimental stuff:

Thanks bohm, that's interesting.

 

[DevilsAvocado]

Just to make clear, I do agree that one cannot have a local realistic interpretation of quantum mechanics unless one violates the assumptions of the Bell theorem. For example, one can violate the assumptions of the Bell theorem by assuming that a measurement does not yield a unique outcome, but rather all outcomes occur - even then - it is not clear if the interpretation is local - but I'll certainly grant that its nonlocality is not assured by violation of the Bell inequalities.

Okay, that must be MWI, right?

I also agree that it is not enough to say that the measurement results don't exist before measurement in order to violate the assumptions.

Agreed 100%, it especially goes baloney if the outcome assumption is always [1, 0] or [0, 1] ...

One has to do something drastic like saying that there are not two observers, but only one.

Wow, that's a new one, isn't it?

However, it does seem that Griffiths claims consistent histories to be "realistic" and local. You can find the claim of locality in http://quantum.phys.cmu.edu/CQT/chaps/cqt24.pdf and the claim of "realism" in http://quantum.phys.cmu.edu/CQT/chaps/cqt27.pdf. In fact, both claims are made as points 2 and 3 on p318 of the second link. I don't know enough about consistent histories to comment on the claim, but my impression is that his definition of reality isn't "common sense realism", so if his claim is correct, my bet would be that his definition of reality is actually a form of nonrealism.

Yeah I know... it's quite strange... he writes:

"By contrast, a consistent application of quantum principles provides a positive demonstration of the absence of nonlocal influences, as in the example discussed in Sec. 23.4."​

But chapter 23.4 is about Stern-Gerlach and Measurements of One Spin, not about Bell. And in chapter 24.4 about Bell inequalities, he instead admits that:

"Such a theory must either exhibit peculiar nonlocalities which violate relativity theory, or else incorporate influences which travel backwards in time, in contrast to everyday experience."​

And finish chapter 24.4 with:

"This seems a rather high price to pay just to have a theory which is more “classical” than ordinary quantum mechanics."​

And there it all ends... no explanation, just a 'statement'.

A quite inconsistent story, if you ask me.

 

[DevilsAvocado]

Well its the other thing I often say about Consistent Histories - its defining your way out of problems.

Okay, then there's some serious defining ahead (after post #93).

 

[atyy]

Wow, that's a new one, isn't it?

Old one :) http://arxiv.org/abs/quant-ph/0509061, see the discussion on p9-10, which includes "I suggest that Einstein was quite deliberately not assuming the existence of more than one observer"

 

[Dale]

Closed for moderation