Metaphysics and QM

ArjenDijksman

The results of the experiments described at those links simulate quantum tunneling and quantum interference (as well as other features like orbiting particles with discrete orbitals...). They provide a way to investigate pilot-waves at macroscopic level and therefore to test the consistency of different pilot-wave interpretations of QM. As a matter of fact, they teach us that there's a two-way action between the pilot-wave and the particle, which is a feature that one doesn't find in the conventional Bohmian interpretations.

ZapperZ

Er.. this is strange.

These experiments merely MIMIC the QM results. They are not QM experiments!

Furthermore, in those experiments, you can DETECT the associated waves that the "walker" is on. Would you like to guess whether we can detect the analogous "associated waves" in the pilot wave formulation?

Zz.

ArjenDijksman

Yes, exactly. That's what I would require for an interpretation: a formulation that reproduces the results of QM experiments.

One way to detect the associated waves is through investigation of the spots whereto the "walker" is guided. This concurs with the way how de Broglie conceived the pilot wave interpretation.

ZapperZ

So you don't see that the fact that these are not QM experiments make any difference? I can mimic many Standard Model physics using various condensed matter systems. I can even show Higgs-like mechanism! If we use your logic, there is no need to build the LHC to find the Higgs, since we have already seen a resemblance of it elsewhere. Does this makes any sense to you?

No, you missed the point. If we can detect the "associated waves" that came with the pilot wave formulation, we won't be having this conversation. Just looking at where the walker is doesn't tell you anything to distinguish between one interpretation versus another. That's why QM interpretation is still a matter of tastes and personal preference!

Zz.

apeiron

Thanks for pointing to such an interesting analogue.

Do you see this fitting in also with a transactional interpretation where there is a "both ways" action?

The droplet/walker is a resonance effect of a system. Inject energy at a locale and (over sufficient time) you produce a standing wave that reflects the global boundary conditions (the shape of the containing vessel, the "diffraction grating" on the bottom).

In QM, the interpretive mistake seems to be to try to find some way to preserve strict locality of causality. Point A in spacetime must connect to point B as a simple path in spacetime - and that is all there is.

Non-locality is really about the global scale in the droplet experiment. The fact that it takes "time" for global downward constraint to be expressed, for a pilot wave-like situation to develop.

In the classical analogue, it actually does take time for a standing wave resonance to build. A clock ticks off locally. But in QM, the "when" becomes a global issue. The local ticking clock to measure, say, the exchange of a photon across a space, is what emerges.

At the global level, this is why the action seems as much retrocausal as causal. The wholeness of the standing wave has to emerge along with the wobbly path traced by a droplet, in effect.

ArjenDijksman

Oh yes, there is a big difference between QM interpretations (a formulation using math, language, analogues, logic...) and the actual QM behavior. Like you stated it, these walker droplet experiments only mimic some aspects of QM experiments.
I don't understand what you mean by "my logic" because I don't agree with the inferences you make concerning my line of thought. We need the LHC to validate or invalidate our different interpretations. Meanwhile, nothing prevents us from developing these interpretations along different lines.
Yes, I agree. That's why it is also important to discuss interpretations and to approach them in different ways. With regard to pilot wave interpretations, there's a whole aspect that hasn't be discussed in the past 80 what years: their connexion with pilot wave experiments on another scale.

Yes, why not. Any wave interpretation of QM could benefit from our understanding of ordinary wave behavior.
I agree. The global scale of quantum interactions is well illustrated by the extended wave of the droplet analogy.

ZapperZ

And I don't see why you are so gung-ho on these experiments. They are not QM experiments. They are classical experiments that HAPPENED to reproduce some aspect of QM observation. What's the big deal?

First of all, none of these experiments are validating "interpretations", and certainly NOT the LHC!

Secondly, if your experiment is nothing more than something that mimics something else, you can't directly test that "something else". This is because that something else has a bunch of other effects that your first experiment cannot replicate. And in QM, everything is connected to each other - you simply can't turn something off while testing something else. You can't test superposition without acknowledging (and testing) the fact that you can also detect the presence of superposition via measuring a non-commuting observable! Try using these experiments that you are such a fan of and produce something similar to the coherence gap observed in the Delft/Stony Brook SQUID experiments!

These are NOT QM experiments. Period. You have no ability to construct a Hamiltonian that is identical to a QM Hamiltonian. The starting point is all wrong, and one is only deceiving oneself to think that one can test "interpretations" of QM using these experiments.

Zz.

Erwins_mat

Thanks for the input, Zapperz. This makes more sense to me. From my perspective, as a neo-Kantian of sorts, it looks completely obvious that the metaphysical interpretations of QM are not science and never can be. We are stuck making observations of, and predictions about, the phenomenal, material world. The interpretations of QM are an attempt to link that phenomenal, material world with a noumenal world. For me, that's metaphysics. The position you end up defending isn't based on empirical evidence but on the need for consistency with other non-scientific beliefs such as "I am a conscious observer", "I believe I have free will" or with other principles like the need for parsimony or a desire to defend metaphysical naturalism.

ZapperZ

This is true. However, having said that, we should also learn a little bit from history. This is because human ingenuity can sometime surprise us, and what we think can't be tested, later on proved to be wrong.

For example, after the EPR paradox was formulated, the argument on whether it is true or not dragged on for years. It was considered to simply be a "philosophical argument", where various camps adopt a certain specific view or interpretation based on a matter of "tastes". This was because at that time, it was difficult to imagine the possibility of testing such non-local effect.

That all changed after Bell proposed a way to make such a test. This is now no longer philosophy, but physics. The validity of the effect is no longer a matter of "tastes". The interpretation of the effect may still be up in the air, but the result isn't.

I'm not saying that we can differentiate between all of these interpretations eventually. That would be an a priori assumption that the current, standard interpretation of QM is incorrect or incomplete, and we have seen many instances where philosophical arguments never get resolved by physics. All I'm pointing out is that there have been instances where human ingenuity have managed to test something where it wasn't thought to be possible before.

Still, I don't think these experiments based on the "walkers" are such tests.

Zz.

ArjenDijksman

Hmmm... gung-ho? I merely appreciate those experiments as a physicist because they retrieve some QM results which were regarded impossible to obtain with ordinary macroscopic experiments. They complement our understanding of wave particle duality. What's wrong with mentioning them in a thread about scientifically-acceptable interpretations of QM?

I think we misunderstand each other. There is a century old history in quantum mechanics with endless discussions, hundreds of thousands of publications, leading us on a path that made us think in terms in which quantum behavior appears counter-intuitive. And here we have an ordinary physics experiment, which any low-budget lab can reproduce and investigate (you only need a frequency generator, a loud speaker, and a vessel of silicon oil), that challenges the counter-intuitive aspect of quantum behavior. This experiment is still in its infancy. There are only a handful of publications on this experiment, each of which points towards new similarities with QM. Are you inferring that with those few publications, we can have a definite opinion about its applicability to QM?

apeiron

The argument would seem to be that an interpretation that makes sense in the classical analogue ought to then lend strength to an equivalent interpretation in QM - given nothing better coming along.

Given two intepretations - say decoherence and MWI - I would prefer the one that has the logic shared with some "obvious" classical system over the truly weird one.

Of course, some direct experimental test would be better. But having an accurate classical analogue is not nothing.

ZapperZ

Again, as I've illustrated in my previous post on when something that was a "philosophy" migrates into physics and becomes testable, the only convincing way to settle such an issue is via a very clever methodology of measuring, but on the very same system, not on an "analogous" system that exhibit only SOME of the same effect. One cannot solve the issue of superconductivity by simply studying superfludity, even though a very strong argument can be made that they share many of the same physics. The EPR paradox argument was not solved using an "analogous experiment". It was solved by using the actual, same experiment!

It is a major shortcoming to make a comparison between something when the starting point is all wrong. If you are comfortable in "testing" out some of the interpretation of QM using a classical, non-QM, wrong-Hamiltonian phenomenon, then that's something you have to deal with. I'm surprised we don't just stick to ripple tank. After all, that can "reproduce" QM results too, with so much less cost and so more accessible to grade school students!

Zz.

ArjenDijksman

I agree. Testing analogous systems only helps us to distinguish between general principles that are valid in both systems, and specific ones applicable only to one particular system.

Or as Fritz Zwicky stated it in New Methods of Thought and Procedure (1967):

It helps us to achieve broad vistas and to derive solutions of specific problems more easily by starting from more general ones. What is most important, however, is that bold generalization enormously stimulates the imagination and often yields unexpected results.

This work has not yet fully been achieved for Quantum Mechanics.

ZapperZ

The problem here is that the "generalization" of the two experiments you cited has nothing to do with QM (ref: the Hamiltonian).

If the Hamiltonian of the two system are similar, then I can be persuaded that there's some merit to such study. Again, this is done in condensed matter all the time, where insights into the mathematics used in, say, elementary particles, are actually similar to those used in various condensed matter system. It isn't a coincidence that Peter Higgs got many of his inspiration in arriving at the so-called Higgs mechanism from various broken symmetry principles already established in condensed matter.

So it is not as if I'm not aware of the usefulness of looking at analogous systems. I just don't see these as being the same and how you could do what you wish to accomplish with them.

Zz.

ArjenDijksman

I didn't say that the Hamiltonian can be generalized to the wave + droplet experiment. The generalization with QM seems essentially phenomenological: there are similarities, they apply further than what seemed possible 10 years ago, but it's not yet clear to which extent they apply. There's too little theoretical study on it (unlike for your example of condensed matter physics). However your claim that these experiments have nothing to do with QM sounds to me unconvincing, let alone for the way it is presented in the peer-reviewed papers.

All in all, I think that any scientist who's discussing, advocating or rejecting Bohmian pilot wave interpretations with respect to other interpretations, should know how "real-life" pilot waves behave. That's how I see the way QM interpretation can benefit from the droplet-wave experiments. The same when you use condensed matter analogies for particle physics: you need to know how condensed matter electrons, excitons or plasmons behave in order to draw conclusions for high energy particle physics.

Kind regards,

Arjen