End of Realism? Experiments Test Quantum Mechanics

[Demystifier]

But what is the meaning and significance of measurement in Bohmian mechanics? I thought that Bohmians downplay the measurement problem, either through superdeterminism where you say that the observer had no free will in making the particular measurement he did at the time and place he did it, or through decoherence where you say that the measuring device with its large number of particles smears out the wave function (or pilot wave) of the system and makes it look collapsed. Or some combination of the two. Either way, contextuality doesn't seem that important to Bohmian thought. Am I wrong?

BM is deterministic, but not superdeterministic. Both contextuality and decoherence play important roles in BM.

 

[Demystifier]

OK, I understand and that seems very self-consistent. All the same, the empiricist in me is dubious of any concept of "realness" that is independent of (and strongly changed by) measurement. But I recognize that a more rationalistic interpretation of what "real" means in physics does not need to be bothered by that, I'm just more on Bohr's side that understanding physical reality involves connecting with our experience, not about some reality that gets changed by how we experience it. That's not really an objection to the Bohmian interpretation, because I think any interpretation is just an interpretation.

Yes, I can understand such a view as well, especially after my recent development of an interpretation that interpolates between Bohm and Bohr [1], suggesting that these two interpretations are not so different as people usually think.

[1] http://xxx.lanl.gov/abs/1112.2034

 

[Ken G]

Yes, I can understand such a view as well, especially after my recent development of an interpretation that interpolates between Bohm and Bohr [1], suggesting that these two interpretations are not so different as people usually think.

[1] http://xxx.lanl.gov/abs/1112.2034

And it is arguable that unifying interpretations is of greater value than coming up with yet new ones! Interpolations move us toward a kind of "continuity of interpretation" of quantum mechanics.

 

[lugita15]

BM is deterministic, but not superdeterministic. Both contextuality and decoherence play important roles in BM.

Perhaps superdeterministic is a bit too strong, but do you at least agree that Bohmians generally do not believe in the free will of the experimenter, even if that is not the reason why Bell's inequality is violated? So in that sense, a measurement was a totally predetermined even in the history of the universe, and thus there's nothing special about contextuality: just like any interaction between particles can can change the states of the particles involved, a measurement of a particle can change its state.

As for decoherence, if you truly don't believe in wavefunction collapse, then how is measurement philosophically important? It just so happens that under certain circumstances the wave function gets so smeared out by a large number of particle interactions that it becomes difficult to detect wave properties; who cares?

 

[akhmeteli]

BM is deterministic, but not superdeterministic.

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will).

Is this apparent contradiction caused by different definitions?

 

[Demystifier]

Perhaps superdeterministic is a bit too strong, but do you at least agree that Bohmians generally do not believe in the free will of the experimenter, even if that is not the reason why Bell's inequality is violated? So in that sense, a measurement was a totally predetermined even in the history of the universe, and thus there's nothing special about contextuality: just like any interaction between particles can can change the states of the particles involved, a measurement of a particle can change its state.

I agree.

As for decoherence, if you truly don't believe in wavefunction collapse, then how is measurement philosophically important? It just so happens that under certain circumstances the wave function gets so smeared out by a large number of particle interactions that it becomes difficult to detect wave properties; who cares?

I care and think it is important philosophically because otherwise you cannot understand why collapse is still a useful concept for all practical purposes, even when it doesn't really exist. (I am not saying that decoherence alone is enough to understand it, but it definitely plays an important role in understanding it.)

 

[Demystifier]

Is this apparent contradiction caused by different definitions?

Even worst, the contradiction is caused by different levels of understanding at different times. When I was writing the older post you quoted, the difference between determinism and superdeterminism was not completely clear to me. In the meanwhile, the difference became much more clear to me:
superdeterminism = determinism + fine tuned initial conditions

 

[_PJ_]

I still firmly beliewve that there is some underlying principle or 'mechanism'involved, some form of 'Hidden Variable', perhaps operating on a higher dimension spatially, where entangled prticles share a spatial coordinate despite spearation on any or all the others. We just lack the means to understand/measure such things at this time.

 

[akhmeteli]

Even worst, the contradiction is caused by different levels of understanding at different times. When I was writing the older post you quoted, the difference between determinism and superdeterminism was not completely clear to me. In the meanwhile, the difference became much more clear to me:
superdeterminism = determinism + fine tuned initial conditions

Thank you