# Insights Against "interpretation" - Comments

#### Ian J Miller

If you introduce new premises, the maths are not the same. For my example above, I have introduced the phase velocity of the wave equalling the particle velocity. That does not occur in any book or paper on QM of which I am aware, apart from anything I have written, such as the above. What it does is provide a method for calculating properties that standard theory can not dowiht0put introducing "validation corrections" (See Pople's Noble lecture).

#### PeterDonis

Mentor
If you introduce new premises, the maths are not the same.
True, but the math might also be inconsistent. See below.

For my example above, I have introduced the phase velocity of the wave equalling the particle velocity.
But you have not shown that this leads to a consistent model, or given a reference to one. In the pilot wave version of standard (non-relativistic) QM, you can't arbitrarily set the phase velocity of the pilot wave; it's not a free parameter, it's determined by the Schrodinger Equation.

#### Ian J Miller

True, but the math might also be inconsistent. See below.

But you have not shown that this leads to a consistent model, or given a reference to one. In the pilot wave version of standard (non-relativistic) QM, you can't arbitrarily set the phase velocity of the pilot wave; it's not a free parameter, it's determined by the Schrodinger Equation.
The Schrödinger equation defines the energy of the particle, and it applies even if there is no wave with physical properties. But if the wave is not at the slits, how can it affect what the particle does when it goes through? Accordingly, what I have written above is not the standard pilot wave, nevertheless it gives results in accord with observation for molecules.

#### Dale

Mentor
If you introduce new premises, the maths are not the same.
What matters is whether or not the experimental predictions are the same. Same predictions -> same theory.

#### Pleonasm

If the model makes different predictions for some experiments, then it is a different theory, not an interpretation. But a model that just says "there are hidden variables", but keeps all of the experimental predictions the same, is an interpretation.
I suppose it depends on the context. In a philosophy context, a theory of the world is what one thinks constitutes the world. A world of hidden variables as opposed to no hidden variables would constitute two difference universes cosmetically. I write cosmetically, because they would in this case be operationally identical nevertheless. Perhaps a physics context doesn't give a damn about this, but it would seem overly reductionist.

Definitely not. A prime example is Lorentz aether theory which posits that nature has an additional feature (the aether), but is generally considered an interpretation of S.R. rather than a new theory precisely because it makes no new predictions.
How do you square "definitely not" with "generally concidered". Is statement 1 a personal opinion expressed?

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#### Dale

Mentor
In a philosophy context
This forum is a scientific context.

How do you square "definately not" with "generally concidered". Is statement 1 a personal expression?
Everything I write is a personal expression. I believe that expression to be consistent with the professional scientific literature as referenced earlier in this thread.

Btw, spell check might be helpful, or at least copy and paste. Both of your manual quotes introduced spelling errors that were not in my original. At first I thought you were trying to make fun of me.

#### PeterDonis

Mentor
if the wave is not at the slits, how can it affect what the particle does when it goes through?
Because the pilot wave version of standard non-relativistic QM has an explicitly nonlocal interaction between the pilot wave and the particles. This feature is a key reason why nobody has yet been able to come up with a consistent relativistic version.

what I have written above is not the standard pilot wave
Then your model is under-specified, because you have not given the complete statement of all the entities and dynamics, and therefore we don't know what your model predicts for all experiments that we have predictions from standard QM for. So it's impossible to tell whether it is a different theory from standard QM, or just a different interpretation.

#### PeterDonis

Mentor
I suppose it depends on the context.
Sure, it could, but in this context we care about the physics definition, not about any philosophical definition. This is a physics forum.

#### Pleonasm

This forum is a scientific context.
How one defines "theory" as opposed to "interpretation" is ultimately a philosophical question. It's just semantics at the end of the day.

My point was that your initial statements are contradictions. You wrote "definitely not" to my claim, only to follow it up with a "generally not" example. This is a contradiction.

#### Pleonasm

FWI, I know of a working physicist who is of the opinion that the pilot wave model is a theory, not just an interpretation. It doesn't seem to be self-evident to him at least.

#### PeterDonis

Mentor
I know of a working physicist who is of the opinion that the pilot wave model is a theory, not just an interpretation.
Is he claiming that the pilot wave model makes different predictions from standard QM?

If he is, you should ask him to back up that claim (since AFAIK every other physicist agrees that the pilot wave model makes the same predictions as standard QM).

If he is not, then he's just using the words "theory" and "interpretation" differently from how we define them here at PF. That's a matter of choice of words, not physics.

#### Dale

Mentor
How one defines "theory" as opposed to "interpretation" is ultimately a philosophical question
Nonsense. It is a semantic question as are all definitions. Philosophy does not own all definitions. Scientific definitions belong to the scientific community just as financial definitions belong to the financial community.

My point was that your initial statements are contradictions. You wrote "definitely not" to my claim, only to follow it up with a "generally not" example. This is a contradiction.
I said “generally considered” not “generally not”. Please don’t misquote me.

There is no contradiction. A definition is what a word is “generally considered” to mean by the community using the word. “Generally considered” indicates my belief that the terminology I am using is not my personal usage but is the usage by the general scientific community.

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#### Demystifier

2018 Award
Because the pilot wave version of standard non-relativistic QM has an explicitly nonlocal interaction between the pilot wave and the particles.
More precisely nonlocal interaction between the particles, in the same sense in which Newtonian gravity is a nonlocal interaction between particles, not a nonlocal interaction between the gravitational field and particles.

#### Demystifier

2018 Award
This feature is a key reason why nobody has yet been able to come up with a consistent relativistic version.
In the paper linked in my signature below I argue that Bohmian mechanics predicts that the Standard Model is only an effective theory emergent from a more fundamental non-relativistic theory. In this way Bohmian mechanics becomes a "theory" (in the sense of making a new prediction) and the problem of relativistic Bohmian mechanics is avoided.

#### martinbn

More precisely nonlocal interaction between the particles, in the same sense in which Newtonian gravity is a nonlocal interaction between particles, not a nonlocal interaction between the gravitational field and particles.
But to me it doesn't seem to be the same as in the Newtonian case. There, if I move a particle here, it will result in a measurable effect to the particle over there. In the Bohmian case there is nothing you can do to a particle here that will have observational consequence to a particle over there, right?

#### Demystifier

2018 Award
But to me it doesn't seem to be the same as in the Newtonian case. There, if I move a particle here, it will result in a measurable effect to the particle over there. In the Bohmian case there is nothing you can do to a particle here that will have observational consequence to a particle over there, right?
You seem to be speaking as if, in the Newton case, a particle can move by a human will. But this is wrong. In Newtonian mechanics particles move by deterministic forces, not by human will. So one has to use a passive language: If a particle moves here, it will result to a measurable effect over there. When put in this form, the same can be said about Bohmian mechanics.

#### martinbn

You seem to be speaking as if, in the Newton case, a particle can move by a human will. But this is wrong. In Newtonian mechanics particles move by deterministic forces, not by human will. So one has to use a passive language: If a particle moves here, it will result to a measurable effect over there. When put in this form, the same can be said about Bohmian mechanics.
I move one of the particles, you can see that I've done something by measurering the other particle. Just like Alice can choose and measure spin in a direction (or whatever she wants), but here Bob cannot tell just looking at the other particle.

#### Demystifier

2018 Award
I move one of the particles, you can see that I've done something by measurering the other particle. Just like Alice can choose and measure spin in a direction (or whatever she wants), but here Bob cannot tell just looking at the other particle.
You don't seem to understand my objection. I insist on formulation that does not contain athropomorphic notions such as the bolded ones above.

#### Dale

Mentor
I insist on formulation that does not contain athropomorphic notions such as the bolded ones above.
Why? Science is done by anthropomorphic entities such as Bob and Alice who do have wants. Seems counterproductive to insist otherwise.

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#### martinbn

You don't seem to understand my objection. I insist on formulation that does not contain athropomorphic notions such as the bolded ones above.
That objection doesn't appear anywhere in Newtonian mechanics, why is it so essential in Bohmian mechanics?

Consider two different scenarios for one of the particles. Say it is stationary, or it moves back and forth. The two scenarios have different effect on the other particle. They (the two scenarios) are distinguishable. And that distinction is local for the other particle. In the Bohmian mechanics that is not the case. Same as standard quantum mechanics. Locally the behavior of one particle doesn't distinguish the two different behaviors of the second particle.

#### PeterDonis

Mentor
I move one of the particles
Newtonian mechanics is deterministic, so you can't just arbitrarily choose to move one of the particles. Whatever any particle does is completely determined by the initial conditions of the universe; the same goes for what you do. I think that is the point that @Demystifier is trying to make.

#### A. Neumaier

I move one of the particles, you can see that I've done something by measurering the other particle. Just like Alice can choose and measure spin in a direction (or whatever she wants), but here Bob cannot tell just looking at the other particle.
Newtonian mechanics is deterministic, so you can't just arbitrarily choose to move one of the particles. Whatever any particle does is completely determined by the initial conditions of the universe; the same goes for what you do. I think that is the point that @Demystifier is trying to make.
But @martinbn is making a point different from @Demystifier, namely that in the conventional analysis of long-distance correlation experiments, one has to assume that Alice can make choices. Otherwise everything was determined according to @Demystifier at the big bang, and nothing at all needs to be explained, nothing baffling is left.

To be convincing with his argument, Demystifier has to explain is why the Bohmian universe behaves such that seeming choices can be made by Alice!

[In the original post I had also claimed: ''In a Bohmian universe, one can also consider two universes that are identical except for a difference in the initial conditions of some particle at a particular time. One finds that this difference in initial conditions does not influence the other particles.'' But this is not true; see the next two posts.]

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#### stevendaryl

Staff Emeritus
In a Bohmian universe, one can also consider two universes that are identical except for a difference in the initial conditions of some particle at a particular time. One finds that this difference in initial conditions does not influence the other particles - all beables of the two universes (except for the position of the one particle moved) behave exactly the same!
Maybe I'm misunderstanding something. In one formulation of Bohmian mechanics, the wave function gives rise to a "quantum potential" whose value depends on the locations of every particle in the universe. So changing the location of one particle potentially affects every other particle.

#### A. Neumaier

Maybe I'm misunderstanding something. In one formulation of Bohmian mechanics, the wave function gives rise to a "quantum potential" whose value depends on the locations of every particle in the universe. So changing the location of one particle potentially affects every other particle.
Oh, yes, you are right, sorry. The wave function is unaffected by the particles, but the motion of the other particles depends on its value at the particle whose position changed, thus the latter affects the former.

This answers the concern by @martinbn in a more direct way than the response by @Demystifier had suggested.

#### martinbn

Oh, yes, you are right, sorry. The wave function is unaffected by the particles, but the motion of the other particles depends on its value at the particle whose position changed, thus the latter affects the former.

This answers the concern by @martinbn in a more direct way than the response by @Demystifier had suggested.
Yes, this does answer my concern better. But I still have a question left. My point was that in Newtonian gravity I can by only observing one particle deduce something about the behavior of the other, without the need of me knowing the initial state of the universe, just local observations of one particle. That is not possible in quantum mechanics. Is it possible in Bohmian mechanics? If not, then the claim that the nonlicality of Bohmian mechanics is the same as that in Newton's gravity is simply incorrect. This was the only point that I wanted to make. If on the other hand it is possible, then it seems that Bohmian mechanics is substantially different from QM, not just an interpretation. So different that it is already ruled out.

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