How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics - Comments

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name123 said:
There are multiple guiding waves? I had thought there was one for the universe, and that it appeared random because there was no way to have all the information about all the non-local influences. Are you suggesting each particle has its own guiding wave, and that particle guiding waves can become entangled? If so how do they become entangled and disentangled?
There is only one wave for the whole system, but when the system consists of non-entangled subsystems the wave can be decomposed into separate waves for each subsystem.
name123 said:
On page 7 under the Non-locality section it states:
"Since the wavefunction is defined on the configuration space, the guidance equation of an N-particle system links the motion of every particle to the position of the other particles at the same time". Is this only if the N-particles are entangled?
Yes.

name123 said:
In the same section it goes onto state:
"Finally does the non-locality of the de Broglie-Bohm theory vanishes if the state is not entangled."

Which seems like a question, but perhaps the "does" can be removed and it would be a statement. Is this how you would read it?
Yes.
 
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Demystifier said:
There is only one wave for the whole system, but when the system consists of non-entangled subsystems the wave can be decomposed into separate waves for each subsystem.

If they are entangled how are you suggesting that changes to the wave subsystems influence each other at faster than light speeds, because waves are fields are they not, and you have stated that tachyon fields do not propagate at faster than light speed? Are you suggesting that tachyon particles are involved in the entanglement of the wave subsystems?
 
name123 said:
If they are entangled how are you suggesting that changes to the wave subsystems influence each other at faster than light speeds, because waves are fields are they not, and you have stated that tachyon fields do not propagate at faster than light speed? Are you suggesting that tachyon particles are involved in the entanglement of the wave subsystems?
They are called waves, but the equation is not a wave equation, it isn't hyperbolic to expect finite speed of propagation. In fact, if I am not wrong, it has infinite speed of propagation.
 
martinbn said:
They are called waves, but the equation is not a wave equation, it isn't hyperbolic to expect finite speed of propagation. In fact, if I am not wrong, it has infinite speed of propagation.

Yes, I also understand that, the wave in BM has infinite speed of propagation. But earlier Demystifier had given me a link to a paper in which he had seemed to suggest that QFT did not rule out the type of superluminal influences in BM, and I had asked him about it. He wrote that:

Demystifier said:
@name123 one should distinguish classical tachyon particle from classical tachyon field. It is true that classical tachyon field does not propagate faster than light. Nevertheless, classical tachyon particle does travel faster than light.

But in BM the guiding wave would (I think) be a field (it is not a particle), and so even if imagined to have an imaginary mass (in order to propagate at faster than light speeds and be compatible with relativity), it would be a tachyon field (not a tachyon particle). And, as I understood it, QFT does rule out tachyon fields propagating at faster than light speeds. Which is why I was checking whether it was being suggested that tachyon particles were involved.
 
martinbn said:
They are called waves, but the equation is not a wave equation, it isn't hyperbolic to expect finite speed of propagation. In fact, if I am not wrong, it has infinite speed of propagation.
Which speed are you referring to? Take a free particle. The dispersion relation is
$$\omega=\frac{\vec{p}^2}{2m},$$
and thus the phase velocity is
$$c_{\text{phase}}=\frac{\omega}{|\vec{p}|}=\frac{|\vec{p}|}{2m},$$
and the group velocity is
$$c_{\text{group}}=\partial_{|\vec{p}|} \omega=\frac{|\vec{p}|}{m},$$
neither of which is infinite.
 
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name123 said:
If they are entangled how are you suggesting that changes to the wave subsystems influence each other at faster than light speeds, because waves are fields are they not, and you have stated that tachyon fields do not propagate at faster than light speed? Are you suggesting that tachyon particles are involved in the entanglement of the wave subsystems?
No. The waves do not have superluminal influences on each other. Bohmian particles have.
 
Well, in non-relativistic theory there's no "speed limit", and it's not a contradiction within the non-relativistic theory to have instantaneous interactions (as, e.g., in Newton's model for the gravitational interaction). The only trouble is that it contradicts observations, which clearly prefer relativistic spacetime models over non-relativistic ones.
 
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name123 said:
But in BM the guiding wave would (I think) be a field (it is not a particle), and so even if imagined to have an imaginary mass (in order to propagate at faster than light speeds and be compatible with relativity), it would be a tachyon field (not a tachyon particle). And, as I understood it, QFT does rule out tachyon fields propagating at faster than light speeds. Which is why I was checking whether it was being suggested that tachyon particles were involved.
The superluminal influences in Bohmian mechanics are not directly related to tachyons. Tachyons are mentioned only as a well-known counterexample to the frequent claim that superluminal influences contradict relativity.
 
The only trouble is that there's no convincing theory of tachyons, and fortunately so far we don't need any to describe nature (at least after the OPERA collaboration has found their bug leading to the claim that neutrinos might be tachyons :biggrin:).
 
Demystifier said:
The superluminal influences in Bohmian mechanics are not directly related to tachyons. Tachyons are mentioned only as a well-known counterexample to the frequent claim that superluminal influences contradict relativity.

But in BM with the Bell Tests, are the changes to the 2nd particle's position not explained by changes to the guiding wave on measurement of the first particle? The reason I ask is that if they are, and the guiding wave is a field, then the superluminal influence suggested by BM would be ruled out by QFT I think.
 
vanhees71 said:
Which speed are you referring to?
The speed of propagation of the wave function e.i. the solution of the Schrödinger's equation, in the PDE sense. Compactly supported initial data don't remain compactly supported.
 
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name123 said:
But in BM with the Bell Tests, are the changes to the 2nd particle's position not explained by changes to the guiding wave on measurement of the first particle?
No. They are expained by changes of the position of the first particle.
 
Demystifier said:
No. They are expained by changes of the position of the first particle.

So the guiding wave for the second particle is no different from how it would have been if the first particle had not been measured? (sorry if I am being slow here, but just checking that you aren't suggesting that the change in the position of the first particle (rather than its measurement) changes the guiding wave and thereby changes the position of the second particle).
 
vanhees71 said:
Sure, but why should it be in a non-relativistic theory?
Where did I say or implied that it should!
 
name123 said:
So the guiding wave for the second particle is no different from how it would have been if the first particle had not been measured?
That's correct (except for the technical detail that we cannot really talk about the second-particle wave, because there is only a second-particle density matrix).
 
name123 said:
So what is the suggested mechanism for the first particle altering the second particle's position across that distance?
There is no mechanism in the mechanical sense. There is only an equation which describes how it happens.
 
Demystifier said:
There is no mechanism in the mechanical sense. There is only an equation which describes how it happens.

So nothing more than an equation that gives the result, no theoretical explanation of how such "spooky action at a distance" could happen in a physical universe?
 
name123 said:
So nothing more than an equation that gives the result, no theoretical explanation of how such "spooky action at a distance" could happen in a physical universe?
Yep.
 
Demystifier said:
Yep.

Thanks for your help, and clearing up my misconception (of thinking that the guiding wave/field propagating at faster than light speed was the explanation) :)
 
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name123 said:
Thanks for your help, and clearing up my misconception (of thinking that the guiding wave/field propagating at faster than light speed was the explanation) :)
Thank you for asking sharp questions. It's a pleasure to explain things to people who know what confuses them.
 
name123 said:
Thanks for your help, and clearing up my misconception (of thinking that the guiding wave/field propagating at faster than light speed was the explanation) :)

Why didn't you mention about the quantum potential, name123? I heard the quantum potential is non-local in that it can track a particle somewhere in Andromeda galaxy and a particle on Earth especially if they are entangled.. so it's like the quantum potential can track all the particles in the universe at once. What do you think?
 
fanieh said:
Why didn't you mention about the quantum potential, name123? I heard the quantum potential is non-local in that it can track a particle somewhere in Andromeda galaxy and a particle on Earth especially if they are entangled.. so it's like the quantum potential can track all the particles in the universe at once. What do you think?

I am not sure what it is. Is it supposed to be a field or a particle or something else? My physics is pretty poor, so if you think it might be an answer maybe one of the advisers could help. As I understand it tachyon fields are not theorized to travel faster than the speed of light, only tachyon particles. Apart from spacetime, fields, and particles (in some theories) I am not aware of anything else being said to exist in a physical universe.
 
name123 said:
I am not sure what it is. Is it supposed to be a field or a particle or something else? My physics is pretty poor, so if you think it might be an answer maybe one of the advisers could help. As I understand it tachyon fields are not theorized to travel faster than the speed of light, only tachyon particles. Apart from spacetime, fields, and particles (in some theories) I am not aware of anything else being said to exist in a physical universe.

How come tachyon fields are not theorized to travel faster than the speed of light, while tachyon particles can? May I know what is the explanation based on what you learnt?
 
name123 said:
I am not sure what it is. Is it supposed to be a field or a particle or something else? My physics is pretty poor, so if you think it might be an answer maybe one of the advisers could help. As I understand it tachyon fields are not theorized to travel faster than the speed of light, only tachyon particles. Apart from spacetime, fields, and particles (in some theories) I am not aware of anything else being said to exist in a physical universe.

according to wiki: https://en.wikipedia.org/wiki/Quantum_potential

"Bohm and Basil Hiley also called the quantum potential an information potential, given that it influences the form of processes and is itself shaped by the environment.[9] Bohm indicated "The ship or aeroplane (with its automatic Pilot) is a self-active system, i.e. it has its own energy. But the form of its activity is determined by the information content concerning its environment that is carried by the radar waves. This is independent of the intensity of the waves. We can similarly regard the quantum potential as containing active information. It is potentially active everywhere, but actually active only where and when there is a particle." (italics in original).[73]"

But Demystifier and other researchers think de Broglie pilot wave approach without quantum potential is more elegant.. but isn't Bohm Quantum Potential also elegant in that this is directly connected to his idea of the Implicate Order? This is closer to AdS/CFT idea than the approach used by Valentini where the quantum vacuum is some kind of fluid of hydrodynamics? Is it not Demystifier? So does it depend on researchers if quantum potential is elegant or not.. or it's just not or never will be elegant?
 
fanieh said:
How come tachyon fields are not theorized to travel faster than the speed of light, while tachyon particles can? May I know what is the explanation based on what you learnt?

Regarding tachyon fields I had read in wiki
---
The term "tachyon" was coined by Gerald Feinberg in a 1967 paper[7] that studied quantum fields with imaginary mass. Feinberg believed such fields permitted faster than light propagation, but it was soon realized that Feinberg's model in fact did not allow for superluminal speeds.[6] Instead, the imaginary mass creates an instability in the configuration: any configuration in which one or more field excitations are tachyonic will spontaneously decay, and the resulting configuration contains no physical tachyons. This process is known as tachyon condensation. A famous example is the condensation of the Higgs boson in the Standard Model of particle physics.
---

But with tachyon particles I assume they are not theorized to undergo tachyon condensation (something only fields do maybe), and their imaginary mass allows faster than light speed in the relativity equations. As I mentioned though, I was just assuming.
 
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fanieh said:
according to wiki: https://en.wikipedia.org/wiki/Quantum_potential

"Bohm and Basil Hiley also called the quantum potential an information potential, given that it influences the form of processes and is itself shaped by the environment.[9] Bohm indicated "The ship or aeroplane (with its automatic Pilot) is a self-active system, i.e. it has its own energy. But the form of its activity is determined by the information content concerning its environment that is carried by the radar waves. This is independent of the intensity of the waves. We can similarly regard the quantum potential as containing active information. It is potentially active everywhere, but actually active only where and when there is a particle." (italics in original).[73]"

But Demystifier and other researchers think de Broglie pilot wave approach without quantum potential is more elegant.. but isn't Bohm Quantum Potential also elegant in that this is directly connected to his idea of the Implicate Order? This is closer to AdS/CFT idea than the approach used by Valentini where the quantum vacuum is some kind of fluid of hydrodynamics? Is it not Demystifier? So does it depend on researchers if quantum potential is elegant or not.. or it's just not or never will be elegant?

My mathematical knowledge is poor and so is my understanding of physics described mathematically rather than conceptually. From what I read in that wiki link I thought the quantum potential was being described as a feature of the guiding wave. So I am not sure how it can be done away (it seems to be part of the equation). Perhaps reply to a Demystifier post directly, and he can explain his position concerning it.
 
name123 said:
My mathematical knowledge is poor and so is my understanding of physics described mathematically rather than conceptually. From what I read in that wiki link I thought the quantum potential was being described as a feature of the guiding wave. So I am not sure how it can be done away (it seems to be part of the equation). Perhaps reply to a Demystifier post directly, and he can explain his position concerning it.

Are you saying the quantum potential is like the guiding wave where the guiding wave can't affect the quiding wave of different particles? But it seems the quantum potential can affect quantum potential of different particles.. wiki mentioned "David Bohm and Basil Hiley in 1975 presented how the concept of a quantum potential leads to the notion of an "unbroken wholeness of the entire universe", proposing that the fundamental new quality introduced by quantum physics is nonlocality"

So I'm thinking the quantum potential is the cause of your "theoretical explanation of how such "spooky action at a distance" could happen in a physical universe".. but Demystifier seems to say no. So I'm now kinda confused. I'll think about it more. You research it too. Thanks.
 
I just found this site:

Problems with Bohmian mechanics <mod: approved link>

While this website is (like any web site) not peer reviewed, it contains numerous references to peer-reviewed work substantiating that the claims made there are not those of a crank but have a significant support in the scientific community. In fact, much of the contents of the site may be viewed as a review of critiques of Bohmian mechanics. Some references to web sites supporting Bohmian mechanics are also given.

Enjoy!
 
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A. Neumaier said:
I just found this site:

Problems with Bohmian mechanics <mod: approved link>

While this website is (like any web site) not peer reviewed, it contains numerous references to peer-reviewed work substantiating that the claims made there are not those of a crank but have a significant support in the scientific community. In fact, much of the contents of the site may be viewed as a review of critiques of Bohmian mechanics. Some references to web sites supporting Bohmian mechanics are also given.

Enjoy!

BM is good to differentiate between the wave function and the object.. the so called trajectories.. if I have to buy just one book.. which of the following is good:

https://www.amazon.com/dp/3642179738/?tag=pfamazon01-20
https://www.amazon.com/dp/3642180914/?tag=pfamazon01-20
https://www.amazon.com/dp/0387229647/?tag=pfamazon01-20

BM can be saved if the original idea of this thread which is about quasiparticles and fundamental particles in condense matter analogy is correct (which Neumaier shared site doesn't mention).

But if BM is just wrong and can be proven to be wrong. Then we either have MWI and Copenhagen as the remaining viable candidates. I prefer Copenhagen.
Sabine is writing a book about the whole thing. She removed the following illustration because she explained her book not funny:

Vj7pWp.jpg


Sabine explains in: http://backreaction.blogspot.com/ (September 6, 2017 entry)
"Why did I remove it? To begin with it was pretty pointless. Also, style doesn't fit with the rest of the book. It's not a funny book really. Then I removed the whole explanation in the text about consistent histories because I found it to be unnecessary and more confusing than enlightening, and somehow I felt with only 5 items the list wouldn't really be a list.

I think in the end I just got fed up with it and that was that."

Bhobba favorite is consistent histories.. so other physicists don't like it.
My question is about Copenhagen. Is Sabine right that it is about "I don't care if the cat is dead"?

It seems our discussions are more advanced that I wonder if the new books coming out would be more complete or breathtaking that shared in PF.
 
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