Understanding Bohmian Mechanics of Instrumentalists

[Lynch101]

Are there any?

Not all interpretations are realist are they?

 

[user30]

Thanks Peter.

Would it then be fair to amend the previous statement and say: interpretations that are truly indeterminate/ stochastic AND not based in realism, would seem to require that the current state of the system be causally disconnected from its antecedent state. This would seem to necessitate the total absence of causality with events occurring without reference to a prior cause?

The Copenhagen interpretation does not think it's meaningful to speak of the antecedent stage since it does not have well defined properties. It simply bows out of the discussion. I suppose a good analogy would be your train of thought prior to wakening up. It's simply not relevant to define and speak of from the Copenhagen interpretations point of view.

 

[PeterDonis]

Not all interpretations are realist are they?

You said not realist and "truly indeterminate/stochastic". Are there any?

My point is that you should not be asking questions about hypothetical interpretations or general categories of interpretations that might or might not exist. You should be asking questions about specific interpretations that actually exist, and your questions should be based on what those actually existing interpretations actually say.

 

[Lynch101]

You said not realist and "truly indeterminate/stochastic". Are there any?

My point is that you should not be asking questions about hypothetical interpretations or general categories of interpretations that might or might not exist. You should be asking questions about specific interpretations that actually exist, and your questions should be based on what those actually existing interpretations actually say.

Ah, I see, my apologies.

It might have been better to ask if there are such non-realist interpretations and which one they are. Are you familiar with any such non-realist interpretations? I thought Copenhagen was an example of a non-realist interpretation, or at least a variation of it and I thought QFT could be interpreted as non-realist.

I know discussing the details of them would be off-topic in this thread. The general question about realist vs non-realist theories is, I would say, relevant to the discussion of Demystifier's paper, but probably at the boundaries. The details of non-realist interpretations might be too far in that direction though.

 

[Lynch101]

@Demystifier

Another idea that caught my attention in your paper was this statement:

What we propose here is that the Earth (and everything else) is made of ether. No experiment so far ruled out that possibility, so such a neo-Lorentzian ether theory is a viable possibility.

It certainly sounds like a very interesting suggestion. I'm not even sure what the right questions to ask are to delve into this further. In a very crude manner I would interpret this as there being a Universal field, of some sort, or that the Universe is a single [to use an even more crude term] "thing" or substance. Would you be able to offer any clarifications on how to think about this.

Apologies, this is a very brute force attempt to delve into this idea. I'm not even sure how to phrase the questions, I'm just hopeful that simply starting a discussion on it will lead somewhere. Even if you might only be able to offer an explanation that would be over my head, it might give me a starting point to look into it further.

 

[PeterDonis]

I thought Copenhagen was an example of a non-realist interpretation

Copenhagen as usually understood does not take the quantum state to be the actual real state of the system, yes.

However, Copenhagen as usually understood also does not take any position on whether the indeterminacy in the math of QM regarding measurement results (i.e., that the math only predicts probabilities) reflects a "true" indeterminacy in reality. So I don't think Copenhagen as usually understood qualifies as "truly indeterminate/stochastic".

I thought QFT could be interpreted as non-realist

AFAIK QFT admits the same interpretations as QM in general, which would include both realist and non-realist ones.

 

[Lynch101]

Copenhagen as usually understood does not take the quantum state to be the actual real state of the system, yes.

However, Copenhagen as usually understood also does not take any position on whether the indeterminacy in the math of QM regarding measurement results (i.e., that the math only predicts probabilities) reflects a "true" indeterminacy in reality. So I don't think Copenhagen as usually understood qualifies as "truly indeterminate/stochastic".

Ah I see, thank you for the explanation. I have read a few things which have gone from Copenhagen to a non-realist interpretation but I guess that should be viewed as appending an interpretation to Copenhagen. Is Copenhagen then synonymous with "Shut up and calcualte"?

AFAIK QFT admits the same interpretations as QM in general, which would include both realist and non-realist ones.

Are there other non-realist interpretations, outside of a non-realist interpretation of QFT?

 

[PeterDonis]

Is Copenhagen then synonymous with "Shut up and calcualte"?

Not quite. As far as I can tell, Copenhagen as it is usually understood adds to "shut up and calculate" the belief that there is in fact (not just as a matter of doing calculations to make predictions) nothing more there: there is no deeper "underlying reality" beneath the QM model.

 

[PeterDonis]

Are there other non-realist interpretations, outside of a non-realist interpretation of QFT?

I'm not sure what you mean. QFT is a quantum theory and, as I said, has the same interpretations as QM in general.

 

[Demystifier]

Is Brownian motion not attributable to a fundamentally deterministic process though? With the apparent randomness being due to a lack of information on our part, but the underlying particle collisions being, themselves, deterministic?

That's true for the physical Brownian motion, but not for the mathematical Brownian motion. The latter, as a model for the former, is fundamentally non-deterministic.

 

[Demystifier]

Even if you might only be able to offer an explanation that would be over my head, it might give me a starting point to look into it further.

As a first step, look at Ref. [49] in the paper.

 

[Lynch101]

That's true for the physical Brownian motion, but not for the mathematical Brownian motion. The latter, as a model for the former, is fundamentally non-deterministic.

Is the same true for the Nelson interpretation, you mentioned before, where it is the mathematical model that is non-deterministic while the physical system itself is deterministic?

Going on what @PeterDonis has said about the GRW interpretation, would it be fair to say that the GRW interpretation suggests both physical and mathematical non-determinism?

 

[Lynch101]

As a first step, look at Ref. [49] in the paper.

Thanks, I've downloaded a copy of that and will check it out now.

 

[Demystifier]

Is the same true for the Nelson interpretation, you mentioned before, where it is the mathematical model that is non-deterministic while the physical system itself is deterministic?

No. The Nelson interpretation assumes that stochasticity is fundamental.

Going on what @PeterDonis has said about the GRW interpretation, would it be fair to say that the GRW interpretation suggests both physical and mathematical non-determinism?

Yes.

 

[user30]

So how does the probabilistic math of Markov Chain differ from the probabilistic math of partial differential equations in Quantum Mechanics?

The descriptions look very similar yet all partial differential equations are deterministic. What is the fundamental difference between the two?

https://en.m.wikipedia.org/wiki/Markov_chain

 

[user30]

Here's someone asking the same question

https://physics.stackexchange.com/questions/74885/can-i-treat-a-quantum-process-as-a-markov-process

"The Schrodinger equation is deterministic, so the time evolution of its solutions would be a Markov process only in some trivial sense."

 

[PeterDonis]

The Schrodinger equation is deterministic

The math of QM is more than just the Schrodinger Equation.

https://www.physicsforums.com/insights/the-7-basic-rules-of-quantum-mechanics/

 

[Lynch101]

As a first step, look at Ref. [49] in the paper.

Thanks for the direction on this Demystifier. Firstly, apologies if the questions that follow are of the sort that you don't even know where to begin to try and explain. I have been in discussions before where someone poses a question that just doesn't seem to make sense and you can be left scratching your head as to how to even begin addressing it. So, no offence taken if this post falls into that category.

I read the paper but didn't understand most of it. I've started studying some maths again, so far refreshing what I've learned in high-school, so it'll be a long time before I can understand the maths in the paper. Is it possible to get a very rough, general idea of what the paper says, do you think, without the mathematics? In my mind I'm trying to get a rough understanding of the consequences of what the paper says, as opposed to being able to determine the accuracy of what is being said, if that makes sense?

In truth, I probably didn't understand too much after the introduction even (or possibly even in the introduction).

To allow for gravitational Lorentz violation without abandoning the framework of general relativity (GR), the background tensor field(s) breaking the symmetry must be dynamical. Einsteinæther theory is of this type. In addition to the spacetime metric tensor field gab it involves a dynamical, unit timelike vector field u a .

.
I have a very limited understanding of fields, but I tend to think of them as analogous to a sheet of some sort stretched out through space, with a vector field having some sort of directionality to it at a given location - perhaps another analogy here might be like a putting green, the kind you see in golf video games, where arrows show the direction the ball is likely to break.

My understanding of the above would be that there some form of fundamental, deeper lying field - the background tensor field - which might break Lorentz invariance, which appears to be a necessity for Bohmian mechanics.

To say that the Earth and everything else is made of Ether, I am picturing some sort of fundamental field which gives rise to all matter. My intuitive thinking would be that this would be a single universal field, but I think you suggested that this might not be the case.

A separate, but related question: under the Bohmian interpretation, is the Universe continuous?

 

[Elias1960]

Is the same true for the Nelson interpretation, you mentioned before, where it is the mathematical model that is non-deterministic while the physical system itself is deterministic?

In general, every deterministic theory can be obtained from a more fundamental stochastic theory, and every stochastic theory from a more fundamental deterministic one.

 

[Lynch101]

@Demystifier
Another question just occurred to me: is there a "measurement problem" with Bohmian Mechanics?

 

[Demystifier]

@Demystifier
Another question just occurred to me: is there a "measurement problem" with Bohmian Mechanics?

No, Bohmian mechanics is a solution of the measurement problem.

See also my lecture http://thphys.irb.hr/wiki/main/images/e/e6/QFound4.pdf
especially page 24.

 

[Lynch101]

@Demystifier Sabine Hossenfelder just put out a video about Bohmian Mechanics. Any thoughts?

 

[Demystifier]

Any thoughts?

She should read my http://thphys.irb.hr/wiki/main/images/3/3d/QFound5.pdf

 

[Lynch101]

She should read my http://thphys.irb.hr/wiki/main/images/3/3d/QFound5.pdf

Nice one. I'll have a read it myself.

 

[Lynch101]

How does a measurement occur in Bohmian Mechanics? I was thinking that the pilot wave guided the particle towards the detector and once it comes into contact with the detector a measurement is registered (allowing for the internal processes of the measurement apparatus). Is that accurate, or is it possible that a particle can come into contact with a detector but a measurement fail to be registered?

 

[Demystifier]

How does a measurement occur in Bohmian Mechanics? I was thinking that the pilot wave guided the particle towards the detector and once it comes into contact with the detector a measurement is registered (allowing for the internal processes of the measurement apparatus). Is that accurate, or is it possible that a particle can come into contact with a detector but a measurement fail to be registered?

It's not accurate because it's not clear what do you mean by "comes into contact". Do you mean that particles come into contact, or that wave functions come into contact? Does "coming into contact" mean they arrive at the same place and touch each other, or just that they influence each other? Have in mind that particles interact non-locally in BM, so particles don't need to arrive at the same place to influence each other.

 

[martinbn]

It's not accurate because it's not clear what do you mean by "comes into contact". Do you mean that particles come into contact, or that wave functions come into contact? Does "coming into contact" mean they arrive at the same place and touch each other, or just that they influence each other? Have in mind that particles interact non-locally in BM, so particles don't need to arrive at the same place to influence each other.

Don't want to intrude on your conversation, but what does it mean for the wave functions to come into contact? Also what is meant by the particles influence each other?

 

[Demystifier]

Don't want to intrude on your conversation, but what does it mean for the wave functions to come into contact? Also what is meant by the particles influence each other?

You think that BM is nonsense, so why bother?

 

[martinbn]

You think that BM is nonsense, so why bother?

Can you blame me? Every Bohmian mechanic gives me such answers.

 

[Demystifier]

Can you blame me? Every Bohmian mechanic gives me such answers.

I blame you for asking questions you are not really interested in. What do you mean by "such answers"?

 

[Lynch101]

It's not accurate because it's not clear what do you mean by "comes into contact". Do you mean that particles come into contact, or that wave functions come into contact? Does "coming into contact" mean they arrive at the same place and touch each other, or just that they influence each other? Have in mind that particles interact non-locally in BM, so particles don't need to arrive at the same place to influence each other.

I guess I'm just wondering how a measurement occurs in BM.

I had an intuitive idea as to how a measurement occurs. For example, a ball thrown at a wall collides with the wall and leaves a mark. I thought measurements in BM were analogous. The particle is guided by the pilot wave until it collides with the detector (which gets amplified for the purpose of human observation).

Is it the case that a particle which arrives at position A, on the LHS of the detector, can result in a measurement at a position Z on the RHS? For example, in the picture, is it possible for the particle to arrive at the red position but result in the yellow measurement?

 

[Nugatory]

For example, in the picture, is it possible for the particle to arrive at the red position but result in the yellow measurement?

That depends on the design of the lab equipment that does the amplification. If it could behave as you describe we would not use it for experiments involving interference patterns, although it might be perfectly satisfactory as a particle counting device.
(And note that only the Bohmians do not have to wrap the phrase “particle arrives at…” in interpretational disclaimers before they can use it)

 

[Demystifier]

Is it the case that a particle which arrives at position A, on the LHS of the detector, can result in a measurement at a position Z on the RHS? For example, in the picture, is it possible for the particle to arrive at the red position but result in the yellow measurement?

Under certain conditions, something like that is possible. When it happens, one talks about surrealistic Bohmian trajectories, on which you can find more information by googling.

 

[Demystifier]

The particle is guided by the pilot wave until it collides with the detector

The particle is always guided by the pilot wave. Collision with the detector means that pilot wave of the particle gets entangled with pilot wave of the detector, i.e. they form one big pilot wave for the joint system consisting of the particle and the detector (which itself consists of many particles).

 

[Lynch101]

Does the Legget-Garg inequality tell us anything about Bohmian Mechanics, or does it simply not apply?